E ‘ ‘12 o F E s s I o N AL The Acootink Schist, Lake Barcroft Metasandstone, and Popes Head Formation— Keys to an Understanding of the Tectonic Evolution of the Northern Virginia Piedmont By AVERY ALA DRAKE, JR, and PETER T. LYTTLE GEOLOGICAL SURVEY PROFESSIONAL PAPER 1205 A stratigraphic, sea’imentotogic, and tectonic study of a crystalline terrane in the northern Virginia Piedmont UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1981 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES C. WATT, Secretary GEOLOGICAL SURVEY Doyle G. Frederick, Acting Director Library of Congress Cataloging in Publication Data Drake, Avery Ala, 1927— The Accotink Schist, Lake Barcroft Metasandstone, and Popes Head Formation-Keys to an understanding of the tectonic evolution of the northern Virginia Piedmont. (Geological Survey Professional Paper 1205) Bibliography: p. 15 Supt. of Docs. no.: I 19.1621205 1. Geology, Stratigraphic—Cambrian. 2. Schist—Virginia—Fairfax Co. 3. Sandstone—Virginia~Fairt'ax Co. 4. Geology—Virginia—Fairfax Co. I. Lyttle, Peter T., joint author. II. Title. [11. Series: United States Geological Survey Professional Paper 1205. QE656.D7 551.7'23’09755291 80-607934 For sale by the Branch of Distribution, US. Geological Survey Washington, DC. 20404 CONTENTS Page Page Abstract --------------------------------------------------- 1 Popes Head Formation .................................... 10 Introduction ----------------------------------------------- 2 Old Mill Branch Metasiltstone Member ...... , ........... 10 Acknowledgments -------------------------------------- 3 Felsic metatuff .................................... 11 Eastern Fairfax sequence ----------------------------------- 3 Mafic metatuff .................................... 11 Accotink Schist ---------------------------------------- 3 Contact relations ---------------------------------- 12 Lake Barcroft Metasandstone --------------------------- 5 Station Hills Phyllite Member ......................... 13 Type I meta-arenite ------------------------------- 6 Environment of deposition ............................. 13 Type 11 metagraywacke ------------------------------ 6 Age and correlation .................................... 14 Environment of deposition - -. ---------------------------- 8 Results and conclusions .................................... 15 Age and correlation ------------------------------------- 8 References cited ........................................... 15 ILLUSTRATIONS Page PLATE 1. Generalized geologic map of part of Fairfax County, Va. ---------------------------------------------------------- In pocket FIGURE 1. Diagram showing ideal sequence (the Bouma sequence) of structures in a turbidite bed --------------------------- 2 2—8. Photographs showing: 2. Accotink Schist from Accotink Creek about 800 m northwest of New Hope, Annandale quadrangle ---------- 4 3. Peters Creek schist, from Potomac River gorge about opposite the center of Bear Island, Falls Church quad- rangle, showing segregation of quartz and mica-rich layers, probably a result of both original compositional layering and later metamorphic differentiation -------------------------------------------------------- 4 4. Accotink Schist from west bank of Accotink Creek about 500 m northwest of the intersection of the Capital Beltway (1—495) and the Little River Turnpike, Annandale quadrangle ---------------------------------- 5 5. Accotink Schist from Accotink Creek at New Hope, Annandale quadrangle, showing steep-plunging folds in first schistosity ------------------------------------------------------------------------------------- 5 6. Accotink Schist, from Accotink Creek about 800 m northwest of New Hope, Annandale quadrangle, showing rotation of mica flakes that define early recrystallization schistosity and incipient later spaced strain-slip cleavage -------------------------------------------------------------------------------------------- 6 7. Type I meta-arenite of the Lake Barcroft Metasandstone from Indian Run about 900 m southeast of Little River Turnpike, Annandale quadrangle --------------------------------------------------------------- 6 8. Type II metagraywacke of the Lake Barcroft Metasandstone from Holmes Run about 200 m northwest of Annan- dale Road, Annandale quadrangle, showing an early isoclinal fold and garnet porphyroblasts that have chlorite l‘lmS ----------------------------------------------------------------------------------------------- 7 9. Stereographic projections comparing structural elements in rocks of the Eastern Fairfax sequence with those in rocks of tonalite plutons and the northern part of the Occoquan Granite batholith ----------------------------------- 9 10-12. Photographs showing: 10. Typical Old Mill Branch Metasiltstone Member of the Popes Head Formation from east bank of Bull Run about 150 m south of north border of Independent Hill quadrangle -------------------------------------------- 10 11. Felsic metatuff from the Old Mill Branch Metasiltstone Member of the Popes Head Formation from a small stream tributary to Bull Run about 1,900 m west of Bull Run Marina, Independent Hill quadrangle ------- 11 12. Mafic crystal metatuff from old Mill Branch Metasiltstone Member of the Popes Head Formation from out- crop on Popes Head Creek about 400 m northwest of Clifton, Manassas quadrangle, showing high ratio of 12 euhedral igneous phenocrysts of amphibole, plagioclase, and sphene to mature clastic matrix -------------- 1H 1133i 1" CONTENTS TABLE Page TABLE 1. Classification of turbidite and other resedimented facies ............................................................. 3 THE ACCOTINK SCHIST, LAKE BARCROFT METASANDSTONE, AND POPES HEAD FORMATION—KEYS TO AN UNDERSTANDING OF THE TECTONIC EVOLUTION OF THE NORTHERN VIRGINIA PIEDMONT By AVERY ALA DRAKE, JR, and PETER T. LYTTLE ABSTRACT The newly named Accotink Schist and Lake Barcroft Metasand- stone of the Eastern Fairfax sequence are the structurally lowest metamorphic rocks in the northernmost Piedmont of Virginia. The Ac- cotink consists of beds of pelitic schist that have thin basal intervals containing graded, very fine grained metasiltstone, as well as interbeds of metasandstone like that in the overlying Lake Barcroft Metasand- stone. The unit is characterized by the Bouma turbidite sequences Te and Tde and can be assigned to turbidite facies D and E. The thickness of the Accotink is not known because its base is not exposed. The Accotink Schist grades up into the Lake Barcroft Metasand- stone, which consists of two types of metasandstone. Type I meta- arenite is quartzofeldspathic granofels which forms thick sequences of amalgamated beds that can best be described as belonging to the Bouma turbidite sequence Ta and to turbidite facies B2. Type II metagraywacke of the Lake Barcroft Metasandstone consists of micaceous metagraywacke in thin to medium beds, which can be described as belonging to the Buoma turbidite sequences Tabe and (or) Tae and to turbidite facies C. The Lake Barcroft Metasandstone ap— pears to be about 400 m thick. It and the Accotink Schist are thought to represent a coarsening-upward sequence of an outer submarine—fan association of rocks. The Eastern Fairfax sequence is overlain by the Sykesville Forma- tion. We believe that this contact is a movement surface upon which the Sykesville was emplaced by subaqueous sliding. The Sykesville contains isoclinally folded fragments, thought to be rip-ups, of Ac- cotink and Lake Barcroft rocks. The Eastern Fairfax sequence is in- truded by rocks of the Occoquan Granite batholith, which contains pendants of isoclinally folded schist and metagraywacke. After intru- sion, the metasedimentary and plutonic rocks were folded together. Garnet and chlorite porphyroblasts Within the Eastern Fairfax se- quence appear to be related to the emplacement of the batholith. The minimum age of the Eastern Fairfax sequence is that of the Occoquan Granite batholith, currently thought to be about 560 my. The se- quence, then, is considered to be of Early Cambrian age or older. The Accotink Schist and Lake Barcroft Metasandstone have some lithic similarity to the Loch Raven Schist and Oella Formation of Crowley (1976) of the Baltimore area, but a correlation is very uncertain at this time. The newly named Popes Head Formation overlies all other metasedimentary and transported meta-igneous rocks in northernmost Virginia west of the Occoquan Granite batholith and is intruded by the batholith. The Popes Head consists of a lower Old Mill Branch Metasiltstone Member and an upper Station Hills Phyllite Member. The Old Mill Branch consists largely of alternating coarser and finer grained strata that are mostly fine- to very fine grained, mineralogically quite mature graded metasiltstone, which can be described as belonging to Bouma turbidite sequence dee and (or) Tde, more rarely Tcde. The metasiltstone contains interbedded inter- vals in which both felsic and mafic metatuff contain pristine euhedral crystals of igneous minerals. We believe that the metatuff represents ash-fall deposits. The Old Mill Branch appears to be about 730 m thick. The Old Mill Branch grades up into the Station Hills Phyllite Member, which consists of thin- to medium-bedded pelitic phyllite and smaller amounts of very fine grained metasiltstone. The metasilt- stone beds are graded, and many phyllite beds appear to have basal in- tervals containing graded, very fine grained metasiltstone. These beds can be described as belonging to Bouma turbidite sequence Tde. The Station Hills has intervals containing chlorite-rich phyllite, which probably represents mafic metatuff. No felsic metatuff has been recognized. The top of the Station Hills is not known, neither therefore, is its thickness. This unit appears to have a maximum thickness of about 300 m in northernmost Virginia. The metasedimentary rocks of the Popes Head Formation probably belong to turbidite facies D and were probably deposited by weak tur- bidity flows. The interbedded volcanic material suggests that the Popes Head was deposited by the bilateral filling of a basin, perhaps a back—arc basin. The minimum age of the Popes Head depends on the age of the Oc- coquan Granite batholith. The unit, therefore, is considered to be of Proterozoic Z and (or) Early Cambrian age. The unit has some similarity to the Chopawamsic Formation of the Quantico fold se- quence south and east of the Occoquan Granite batholith, but that unit is thought to be older than the Sykesville Formation; whereas the Popes Head is younger. Metasiltstone like that of the Popes Head For- mation is interbedded with purple and green pelitic phyllite characteristic of the Ijamsville Phyllite in southern Frederick County, Md. These two units may have a lateral facies relationship. 2 ACCOTINK SCHIST, LAKE BARCROFT METASANDSTONE, POPES HEAD FORMATION, VIRGINIA PIEDMONT INTRODUCTION The names Accotink Schist and Lake Barcroft Metasandstone, which refer to rocks constituting the Eastern Fairfax sequence, and Popes Head Formation are introduced here for two sequences of metamorphic rocks in the Piedmont of northern Virginia. These se- quences are part of a terrane of matamorphosed sedimentary and less common volcaniclastic rocks, now pelitic phyllite and schist, metasiltstone, metagray- wacke, and psammitic-matrix sedimentary mélange that crops out between the Culpeper Triassic and J uras- sic basin and the Atlantic Coastal Plain. At the turn of the century, all the rocks of this terrane were mapped as Carolina Gneiss (Darton and Keith, 1901). Since that time, most geologists (Fisher, 1970; Hopson, 1964; Johnston 1962, 1964); Mixon and others, 1972; Reed and Jolly, 1963; Seiders and Mixon, in press; Seiders and others, 1975; Southwick and others, 1971; and Stose, 1928) have mapped these rocks as Wissahickon Forma- tion, although some have considered the complicated psammitic-matrix sedimentary mélange to be a separate Sykesville Formation. This stratigraphic assignment is not surprising, as the rocks are on strike With a metamorphic terrane in the Maryland Piedmont that has largely been called Wissahickon and, in fact, is con- sidered one giant formation by Higgins and Fisher (1971). More recently, Drake and Morgan (in press) have suggested that the Wissahickon Formation could better be visualized as a Wissahickon terrane because of severe stratigraphic uncertainties and the presence of al- lochthonous rocks. Bennison and Milton (unpub. data, 1950), in their mapping of the Fairfax and Seneca 15—minute quadrangles, did not follow the conventional Wis- sahickon terminology. They recognized a sequence of flyschoid schist and metagraywacke that they correlated with the Peters Creek Schist (Stose and Jonas, 1939) of Maryland and Pennsylvania and they thought that the psammitic-matrix sedimentary mélange was granitized schist. More important, they mapped a separate se- quence of metasiltstone and phyllite that they named the Clifton Phyllite. This unit is renamed Popes Head Formation in this paper because the stratigraphic name Clifton is pre-empted. More recent detailed mapping in Fairfax County (U.S. Geol. Survey, 1977, p. 54-55; Drake and Froelich, 1977; Drake and others, 1979) has shown that there are five se- quences of metamorphic rocks in northernmost Virginia: (1) A flyschoid sequence of pelitic schist or phyllite and metagraywacke; (2) psammitic-matrix sedimentary mélange; (3) a sequence of metasiltstone and phyllite named herein the Popes Head Formation; (4) a previously unrecognized sequence of schist and metasandstone in the eastern part of the county named herein the Accotink Schist and Lake Barcroft Metasand- stone; and (5) allochthons consisting of the Piney Branch Complex, a mixture of about subequal parts of ultramafic and mafic rocks, and its discontinuous sole of mélange, the Yorkshire Formation (Drake and Morgan, in press). Drake and others (1979) and Drake and Morgan (in press) recognize the psammitic-matrix sedimentary mélange as the Sykesville Formation and agree with Bennison and Milton (unpub. data, 1950) that the flyschoid sequence of rocks that crops out west of the Sykesville Formation along the Potomac River can best be correlated with the Peters Creek Schist. As the northern Virginia exposures of these last two units have recently been described by Drake and Morgan (in press), they will be discussed further herein only as they relate to other rocks. Since the pioneering work of Hopson (1964), most of the rocks called Wissahickon have been recognized as turbidites that were deposited in a deep marine basin. The new stratigraphic units defined in this paper are also turbidites and are described using Bouma’s (1962) concept of an ideal sequence of structures (fig. 1). This ideal sequence is rare, if present, in the rocks described herein. Hence, they are described on the basis of the Grain Bouma (1962) size divisions u Interturbidite g 6 (generally shale) ’ Upper parallel d laminae Ripples, wavy c or convoluted laminae Sand-Silt b Plane parallel laminae Sand Massive, graded Sand (to granule at base) 0: FIGURE 1.—~—Ideal sequence (the Bouma sequence) of structures in a turbidite bed modified (from Middleton and Hampton, 1973). EASTERN FAIRFAX SEQUENCE 3 Bouma divisions recognized in a sedimentation se- quence. A sequence beginning with massive graded rock passing up into pelite is described as a Tae turbidite, whereas one beginning with an interval containing rip- pled, cross-laminated rock that passes up into an inter— val containing parallel laminated rock and finally into pelite is described as a Tcde turbidite. This shorthand notation is convenient and is common usage in the modern literature. In recent work, particularly in Italy, concepts to analyze and subdivide turbidite facies have been devised (see particularly Walker and Mutti, 1973; Mutti and Ricci Lucchi, 1978). These concepts are purely descrip— tive and are used to indicate the primary characteristics of a body of rock that differentiate it from adjacent rock bodies, both laterally and vertically. The most impor- tant criteria used in facies subdivision are: grain size, bed thickness and sand/shale ratios, bed regularity, sole mark assemblages, and internal structures and textures such as presence or absence of grading, massive bedding in sandstones, and variations in the Bouma sequence. The concept of facies subdivision is of utmost impor- tance in determining sedimentary environments, and we have attempted to apply that concept to the poorly ex- posed metamorphosed turbidites of Fairfax County. Table 1 presents the classification used for the rocks described herein. ACKNOWLEDGMENT S We are indebted to our colleagues A. E. Nelson for some of the geologic mapping that went into this study and for many hours of discussion of the complex geology of northern Virginia; J. M. Aaron for early guidance in interpreting the sedimentology of the Popes Head For- mation; and Louis Pavlides for many hours of discussion of the Virginia Piedmont, which has been of utmost im- portance to our understanding of the stratigraphy of the northern part of this enigmatic terrane. EASTERN FAIRFAX SEQUENCE Rocks here called the Eastern Fairfax sequence crop out in the eastern part of Fairfax County in the Fairfax, Annandale, and Falls Church 71/2—minute quadrangles (pl. 1). These rocks are not known north of this outcrop area, but south of the area they form inclusions and medium- to large-sized roof pendants in tonalite plutons and the Occoquan Granite batholith (pl. 1). In addition, we have seen identical rocks within the terrane mapped as Wissahickon Formation by Seiders and Mixon (in press) in the southwestern part of the Occoquan 71/2- minute quadrangle. The Eastern Fairfax sequence appears to be beneath TABLE l.—Classification of turbidite and other resedimented facies [Modified from Walker and Mutti, 1973] Facies Description A __________ A, ...... A2 ______ A, ______ A, ______ B ......... Coarse-grained sandstones and conglomerates. Disorganized conglomerates. Organized conglomerates. Disorganized pebbly sandstones Organized pebbly sandstones. Medium-fine- to coarse-grained sandstones. Massive sandstones having “dish" structure. Massive sandstones not having “dish" structure. Most beds lack alternating parallel lamination but may contain crude, sub- parallel, faint stratification. Beds have a very high (>10:1) sand/shale ratio, indicating that sandstone are amalgamated; that is, beds are welded together without interbedded shales. Beds range from tens of centimeters to about 2 m thick, have scoured bases, and most are lenticular. C --------- Medium» to fineegrained sandstoneSe-classic “proximal” turbidites beginning with Bouma division a. Strata typically are sharp, flat based, regularly bedded, and have good lateral continuity. Sandstones range from about 10 cm to 1 m in thickness and have sand/shale ratios ofabout 5:1. Amalgamation is uncommon, and most sandstone beds grade up into shale (Bouma division e). Most beds in a sequence begin with Bouma division a. Parallel (Bouma divisions b and d) and ripple cross-lamination (Bouma division c) is uncommon, and rock can typically be described as a Tae turbidite, Facies C is not sharply separated from Facies Bi, and there is a spectrum of beds between B2 and C. D --------- Fine- to very fine grained sandstones and siltslones—classic “distal" turbidites beginning with Bouma division b or c. Sandstone beds have sharp flat bases, are prominently graded, and are about 1710 cm thick. The sand/shale ratio is low, 1:1 or less. Most sequences start with the Bouma division b or c and can be described as Tbcde, dee, or Tcde turbidites, the Tcde being the model sequence. There is a gradation between turbidites ofFacies C and D. E --------- Similar to Facies D, but has higher sand/shale ratios, thinner. more irregular beds, and more discontinuous beds in wedges and lenses. The tops of most sandstone beds are not graded but are in sharp contact with overlying shales. Facies is characterized by Tae turbidites. Chaotic deposits formed by downslope mass movements. Hemipelagic and pelagic shales and marl—silty or calcareous deposits having indistinct and poorly developed lamination or distinct parallel bedding and resulting from very dilute suspensions. the Sykesville Formation. It consists of a lower Accotink Schist and an upper Lake Barcroft Metasandstone. Both units in the sequence contain beds of the other rock type. ACCOTINK SCHI ST The Accotink Schist is herein named for exposures at its type locality along Accotink Creek west of the Capital Beltway (Interstate Route 495), just north of the Little River Turnpike exchange in the Annandale 71/2-minute quadrangle, Fairfax County, Va. (pl. 1). Other exposures in this general area are in the small streams tributary to 4 ACCOTINK SCHIST, LAKE BARCROFI‘ METASANDSTONE, POPES HEAD FORMATION, VIRGINIA PIEDMONT Accotink Creek. Good outcrops are sparse in this deeply weathered, highly urbanized area, but the unit is well ex— posed along the upper reaches of Accotink creek at New Hope and in a small stream tributary to Lake Barcroft south of J EB. Stuart High school in the Annandale 71/2 - minute quadrangle. Many of the exposures of the unit are saprolite. If fresh, the Accotink Schist is light gray, but in most exposures the rock is weathered to yellowish gray, moderate brown, or very pale orange. In outcrop it can be characterized as a quartz-muscovite-biotite—chlorite- plagioclase schist. The total mineral assemblage seen in thin section for the Accotink Schist is quartz-musco- vite-biotite-chlorite-plagiolase (garnet-magnetite- epidote-apatite-zircon-pyrite). Here, and throughout this paper, hyphenated mineral-assemblage lists are ar- ranged in order of decreasing modal percentages. Acces- sory minerals that are not present in all specimens are listed in parentheses. A typical texture consists of an in- terlocking network of angular, recrystallized, more rarely subrounded and equigranular quartz and subordinate plagioclase and laths of muscovite, biotite, and chlorite. Quartz is more abundant than the phyllosilicates and the relative proportions of the phyllosilicates stay fairly constant throughout a given specimen. In a few samples, phyllosilicates are more abundant than quartz. In no sample are the quartz and phyllosilicates segregated into rhythmic sedimentation units, a feature so typical of the Peters Creek Schist of the Potomac River gorge (Drake and others, 1979; Drake and Morgan, in press; compare fig. 2 with fig. 3). FIGURE 2.—-Accotink Schist from Accotink Creek about 800 m northwest of New Hope, Annandale quadrangle. Texture to be noted is the intimate intergrowth of quartz, micas, and chlorite. This contrasts sharply with cleanly segregated layers of micas and quartz in the Peters Creek Schist (fig. 3). Mineralogy in order of decreasing abundance is muscovite, quartz, chlorite, garnet, magnetite, and minor plagioclase. Plain light; 1 cm in photo equals 0.5 cm. FIGURE 3.—Peters Creek Schist, from Potomac River gorge about opposite the center of Bear Island, Falls Church quadrangle, show- ing segregation of quartz and mica-rich layers, probably a result of both original compositional layering and later metamorphic dif- ferentiation. Early cleavage is tightly folded. Quartz layers show recrystallization and shearing that produce long, very thin at- tenuated lenses. Incipient formation of late-spaced cleavage also evident. Crossed polarizers; 1 cm on photo equals 0.5 cm. The schist is interbedded with two types of metasand- stone that are characteristic of the overlying Lake Barcroft Metasandstone (see below). Most of the in- terbedded metasandstones are well-foliated, regularly bedded, micaceous metagraywacke. Where present, this metagraywacke appears to be a more quartzofeldspathic element of a pelitic sedimentary sequence. The other type of metasandstone is a poorly foliated, quartzofeld- spathic granofels that typically forms randomly scat- tered, discontinuous beds. Some of these beds form lenses having a maximum thickness of about 2 m in a stream exposure. Both types of metasandstone are dis- cussed in the section on the Lake Barcroft Metasand- stone. Muscovite, biotite, and tiny chlorite laths have grown in the first cleavage. These phyllosilicates are transposed into the second cleavage, and it looks as if a second generation of muscovite also crystallized in the second cleavage. Large porphyroblasts of chlorite and garnet, which contain numerous inclusions, grow at nearly any angle to the second cleavage and in outcrop appear to have grown under static conditions. Thin-section study, however, shows that some of the garnet porphyroblasts have been slightly rotated and that the second cleavage bends around the ends of some of the seemingly random- oriented chlorite porphyroblasts suggesting that the chlorites have also been rotated to varying degrees (fig. 4). The ends of a few large chlorites are splayed and rotated approximately parallel to the second schistosity. These relations suggest that porphyroblast growth was, in part, syntectonic with the second-cleavage formation. EASTERN FAIRFAX SEQUENCE 5 FIGURE 4.——Accotink Schist from west bank of Accotink Creek about 500 m northwest of the intersection of the Capital Beltway (I—495) and the Little River Turnpike, Annandale quadrangle. Well- developed late second cleavage (roughly horizontal in photograph) has almost totally transposed early cleavage. Large poikioblastic chlorites (c) containing numerous quartz inclusions and small euhedral pseudomorphs after garnet formed after development of early schistosity were rotated to varying degrees during develop- ment of late transposition cleavage, and probably formed during an intervening contact metamorphism related to the intrusion of the Occoquan Granite batholith. Relict cores of garnet (G) rimmed by chlorite and (or) biotite (center of photograph) are occasionally seen. Plain light; 1 cm on photo equals 0.5 cm. A poorly developed third cleavage transposes the second cleavage, but there is no evidence of new mineral growth. In most exposures, bedding is transposed, and cleavage is the dominant planar element. This cleavage is folded (fig. 5), and a later strain-slip cleavage formed axial planar to these folds as shown by mica alignment (fig. 4). In a few exposures, a third cleavage can be seen, but its common manifestation is a crenulation of the se- cond cleavage (fig. 6). Bedding characteristics are difficult to determine because of the extreme deformation and poor exposure, but within the unit most intervals that contain pelitic rocks are 20—210 cm thick. These intervals do not contain single beds but are the intervals between metagraywacke layers. Determination of the number of sedimentation units within such an interval is very difficult, but in one well-exposed fold hinge, we can see that individual sedimentation units have a maximum postdefor- mational thickness of about 1.5 cm and average about 1 cm. In this good exposure, the pelite has a few intervals less than 0.5 cm thick that contain very fine grained, graded silt. This suggests that these intervals of the Ac— cotink contain turbidites belonging to the Tde sequence of Bouma (1962). The intervals containing fine pelite are probably Te sequences. The Accotink then, can be FIGURE 5.—Accotink Schist, from Accotink Creek at New Hope, Annandale quadrangle, showing steep-plunging folds (to the left of knife) in first schistosity. Outcrop face is about vertical. assigned to turbidite facies D and E of Mutti and Ricci Lucchi (1978) and Walker and Mutti (1973). The thickness of the Accotink Schist is unknown because the base is not exposed in Fairfax County, nor is it known elsewhere. The schist appears to grade up into the Lake Barcroft Metasandstone. In mapping, the con- tact is arbitrarily placed stratigraphically below out- crops Where the eastern Fairfax sequence consists of as much as 50 percent metasandstone. LAKE BARCROFT METASANDSTONE The Lake Barcroft Metasandstone is herein named for exposures at its type locality at the confluence of and along the Holmes Run and Tripps Run arms of Lake Barcroft, Annandale 71/2-minute quadrangle, Fairfax County (pl. 1). The unit is-also well exposed in a large 6 ACCOTINK SCHIST, LAKE BARCROFT METASANDSTONE, POPES HEAD FORMATION, VIRGINIA PIEDMONT FIGURE 6.—Accotink Schist, from Accotink Creek about 800 m northwest of New Hope, Annandale quadrangle, showing rotation of mica flakes that define early recrystallization schistosity and in- cipient later spaced strain-slip cleavage (roughly horizontal in photograph). Minerals in order of decreasing abundance are muscovite, quartz, chlorite, minor biotite, pyrite, and magnetite. Plain light; 1 cm on photo equals 0.2 cm. pendant in the Occoquan Granite batholith along a 1,200-m reach of Pohick Creek from a point about 400 m south of Old Keene Mill Road and along Accotink Creek and its tributaries between Old Keene Mill and Hooes Roads, Annandale 71/2—minute quadrangle, Fairfax County (pl. 1). The unit consists of two types of metasandstone. Type I meta-arenite is thick-bedded quartzofeldspathic granofels, without interbedded pelite; whereas, Type II is thin- to medium-bedded micaceous metagraywacke containing pelitic layers. TY PE I M ETA-ARENITE Type I meta-arenite of the Lake Barcroft Metasand- stone is typically a light-greenish-gray to light-gray to bluish-white granofels that weathers grayish orange pink or yellowish gray. Some of the rock can properly be cal- led metagraywacke, although most exposures are meta- arenite. In fresh outcrop, the rock seems much more quartzose than it is, but abundant chalky—weathering feldspar is apparent in saprolite. _ The typical mineral assemblage of Type I meta- arenite. is quartz-epidote-plagioclase—chlorite (-musco- Vite-magnetite). Thin—section study shows that the rock consists of an equigranular mass of very closely packed and interlocking recrystallized quartz, plagioclase, and clumps of epidote, sericite, and chlorite after plagioclase (fig. 7). Muscovite, where present, generally forms small laths, but some are larger and contain quartz inclusions. Muscovite orientation suggests that some rocks have-a second cleavage, but this could not be measured in the field. Individual beds are as much as 2 m thick, but the mas- sive nature of much of the rock probably results from the sedimentary amalgamation of beds; that is, successive sand beds are welded together without interbedded ‘ shales. The continuity of individual beds of Type I meta- arenite cannot be determined within the Lake Barcroft terrane, but beds of this type of rock within the Accotink 'Schist ar'e lenticular. A vague distribution grading was noticed in a few exposures as was a faint lamination in others. Cross-lamination was not seen. Only a very few bed bottoms were seen; these are marked by what appear to be deep bulbous flute casts. No other sedimentary structures were seen. The massive granofels shows a faint foliation marked by flattened quartz and, in ex- posures that contain it, orientated muscovite. The thick sands, no intervening pelite, high sand/ shale ratio, and few internal structures of the Type I meta-arenite suggest that it is probably a sequence of Ta turbidites as defined by Bouma (1962). These features also suggest that this rock type can be assigned to tur- bidite facies B2 of Walker and Mutti (1973). TYPE I] METAGRAYWACKE Type II metagraywacke of the Lake Barcroft Metasandstone is typically a very light gray to light- gray, yellowish-gray-weathering, fine- to medium- FIGURE 7.—'I‘ype I meta-arenite of the Lake Barcroft Metasandstone from Indian Run about 900 in southeast of Little River Turnpike, Annandale quadrangle. Quartz-rich meta-arenite containing minor amounts of fresh plagioclase and clumps of intergrown sericite, epidote, and chlorite. These clumps probably represent bothaltera- tion products of plagioclase and an original minor clay component. crossed nicols; 1 cm on photo equals 0.5 cm. EASTERN FAIRFAX SEQUENCE 7 grained rock. Much of it can be characterized as a graywacke that has well-developed cleavage but little segregation of individual minerals into metamorphically differentiated layers. Isoclinal folds having long limbs and tight hinges are common (fig. 8). The typical mineral assemblage of Type II meta- graywacke of the Lake Barcroft Metasandstone is quartz-biotite-muscovite-plagioclase (-garnet-epidote- magnetite). Biotite and muscovite parallel the first cleavage and have been partly transposed into a later strain-slip cleavage. Garnet porphyroblasts have grown across the first schistosity and typically are partly altered to chlorite on crystal margins (fig. 8). The general presence of garnet in the Type II metagraywacke suggests that it is fairly aluminous and points up the dif- ference in composition between these rocks and the metagraywackes of the Peters Creek Schist, which are not known to contain garnet at the same grade of metamorphism. Epidote forms well-developed euhedral grains and is never seen as an obvious alteration product of plagioclase. The amount of calcium in both the plagioclase and epidote suggests that the original sedi- ment was fairly rich in calcium and perhaps contained carbonate. Beds are generally regular, sharp, flat based, and 10- 15 cm thick, although in some exposures they reach a maximum thickness of about 30 cm. In many exposures, individual sedimentation sequences begin with a graded interval and terminate with pelitic material. Some beds appear to have parallel laminations, but this is not cer- tain because of the well-developed schistosity that generally parallels bedding on the limbs of early isoclinal FIGURE 8.—Type II metagraywacke of the Lake Barcroft Metasand- stone from Holmes Run about 200 m northwest of Annandale road (TI on pl. 1), Annandale quadrangle, showing an early isoclinal fold (above and to the right of the hand lens) and garnet porphyroblasts that have chlorite rims. folds. In other exposures, no sedimentary structures other than bedding can be seen, but sedimentation sequences begin with graywacke and grade up into pelite. We have not seen cross-lamination in the metagraywacke. Classically, a sequence consisting of Type II metagraywacke of the Lake Barcroft would be con- sidered a distal turbidite unit (facies D of Walker and Mutti, 1973) because of the relatively fine grain size of sediments and the thin bedding. However, the unit should probably be assigned to turbidite facies C (Mutti and Ricci Lucchi, 1978, Walker and Mutti, 1973), as many beds appear to have the Bouma (1962) sequence Tabe or perhaps sequence TE,1e in which there is little bed amalgamation. The apparent large number of beds starting with Bouma (1962) division a and the apparent lack of division c seems particularly important. The tur- bidite facies C interpretation is strengthened by the fact that the Type II metagraywacke is found in the same sedimentation package as the turbidite facies B2 rocks of the Type I metaarenite. Some exposures of the Lake Barcroft, in fact, contain beds that appear to be tran- sitional between Types I and II metasandstones. The Lake Barcroft Type II metagraywacke is physically overlain by the Sykesville Formation. Most authors have made the interpretation that the Sykesville has a gradational relation to both underlying and overly- ing rocks Hopson, 1964, Fisher, 1970, Crowley, 1976). In eastern Fairfax County, however, no evidence existsfor a gradational boundary between the Lake Barcroft Metasandstone and Sykesville Formation. In fact, if a modification of the terminology of Hsfi (1968) is used, there are chips (15 cm), fragments (15 cm to 1.5 In), small blocks (1.5-15 In), large blocks (15-150 m), and small slabs (150-1,500 m) of rocks identical with Lake Barcroft metagraywacke as well as Accotink Schist within the Sykesville. These exotic clasts were foliated and some were isoclinically folded before they were in- corporated into the Sykesville. Exotic Lake Barcroft Metasandstone and Accotink Schist, and also ultramafic, mafic, and other strange rocks, can best be seen along Indian Run in the Annandale 71/2-minute quadrangle (pl. 1). The contact between the Lake Barcroft and the Sykesville has been interpreted as the movement surface upon which the Sykesville was emplaced by subaqueous sliding (US. Geological Survey, 1977, p. 54—55.) This interpretation was made because the Sykesville everywhere appears to be physically above the Lake Barcroft, and there is no direct evidence that the units grade into one another. All modern authors have believed that the Sykesville was emplaced by subaqueous sliding. For this to be true, it had to slide on something. We believe that in Fairfax 8 ACCOTINK SCHIST, LAKE BARCROFI‘ METASANDSTONE, POPES HEAD FORMATION, VIRGINIA PIEDMONT County, the surface of movement is the top of the Lake Barcroft Metasandstone. If the above interpretation is correct, the exotic Lake Barcroft Metasandstone and Ac- cotink Schist are small to very large rip-ups related to the sliding of the Sykesville. However, we cannot com- pletely rule out the possibility that the entire Eastern Fairfax sequence constitutes a large slab within the Sykesville. The thickness of the Lake Barcroft Metasandstone cannot really be determined because of the relations described above. Where the most data are available, just northwest of Annandale and along the east part of Lake Barcroft (pl. 1), the unit appears to be about 400 m thick. ENVIRONMENT OF DEPOSITION The poorly exposed, strongly deformed Eastern Fair- fax sequence yields too few data to allow a detailed dis- cussion of its depositional environment. Some generalizations, however, can be made from the observa- tions cited above. The very fine grained, graded silt tur- bidite facies D (Mutti and Ricci Lucchi, 1978, Walker and Mutti, 1973) and pelite turbidite facies G (Mutti and Ricci Lucchi, 1978, Walker and Mutti, 1973) rocks of the Accotink Schist suggest low-density turbidity- current deposition combined with normal pelagic “rain”. These fine-grained rocks are overlain by the coarser Types I and II Lake Barcroft Metasandstone. Type I meta-arenite has been assigned to turbidite facies B2 (Walker and Mutti, 197 3) and probably was deposited from dense rapid currents that were in disequilibrium with the bottom. The possible deep bulbous flute casts described above suggest that current flow was turbulent and capable of minor erosion and that deposition had to follow erosion rapidly to ensure preservation. The tur- bidite facies C beds (Mutti and Ricci Lucchi, 1978, Walker and Mutti, 1973) of the type II metagraywacke are quite typical of classical proximal turbidites, though they lack the abundant sedimentary structures of the metagraywackes of the Peter Creek Schist. The Types I and II metasandstones can be linked by rocks tran- sitional between turbidite facies B2 and C. The Eastern Fairfax sequence, then, appears to be a coarsening-upward sequence, which we suggest belongs to the outer submarine-fan association of Walker and Mutti (1973). The facies G beds of the Accotink grade up into progressively thicker facies D beds. These rocks in turn grade up into Type II metagraywacke of the Lake Barcroft which would herald the progradation of the suprafan represented by the B2 facies rocks of Type I meta-arenite. The lenticular beds of Type I meta-arenite within the Accotink Schist probably represent channels filled when the suprafan was at a different position. AGE AND CORRELATION The age of the Eastern Fairfax sequence cannot be determined directly. It is clearly older than the Sykesville Formation, which contains large and small clasts of rock identical with both Accotink Schist and Lake Barcroft Metasandstone. The sequence is also older than the Occoquan Granite batholith and the several tonalite plutons in eastern Fairfax County, as proved by direct outcrop observations. Particularly good intrusive relations with tonalite can be seen in the Annandale 7 1/2- minute quadrangle along Holmes Run about 300 m northwest of Annandale Road (11 on pl. 1) and good in- trusive relations with rocks of the Occoquan can be seen on the west bank of Holmes Run about on the Fairfax County—Alexandria City line, about 650 in north of Beauregard Street (01 on pl. 1). The minimum age of the Eastern Fairfax sequence, then, ultimately depends on the age of the rocks of the Occoquan. Seiders and others (1975) obtained both concordant and discordant U—Th—Pb ages of about 560 my. from zircon from this granite. Higgins and others (1977) have questioned these dates and have suggested that the zircons may have in- herited a component of older radiogenic lead in seed crystals derived from Proterozoic basement rocks. The age of the Occoquan is a significant problem for which a final resolution has not been reached. However, we know of no direct geologic evidence that prevents the Occo- quan from being as old as Early Cambrian. We have shown that rocks of the Eastern Fairfax se- quence were isoclinally folded before the intrusion of the tonalite plutons and the Occoquan Granite batholith. Actually, the isoclinal fold shown in figure 8 is in a pen- dant. Textural evidence described above and shown in figure 6 shows that garnet and large chlorite porphroblasts had largely grown before the formation of the second cleavage. Possibly the heat necessary for porphyroblast growth was supplied by the plutonic rocks. The Occoquan and smaller satellite bodies crop out over a much larger area than the entire Eastern Fair— fax sequence and are commonly in contact with these rocks. What appears to be regional metamorphism could be, and most likely is, a large-scale contact metamor- phism. That the Eastern Fairfax sequence and the plutonic rocks were deformed together after pluton emplacement is clearly shown by a comparison of the at- titudes of axes of folds in schistosity and joints in the schist and metagraywacke with the attitudes of linea- tions and joints in the plutonic rocks (fig. 9). Until ad— ditional isotopic work is completed and proves the con- trary, we are forced to conclude that the Eastern Fairfax sequence has a minimum age of Early Cambrian and may actually be Proterozoic Z. We, therefore, consider the Eastern Fairfax sequence to be Proterozoic Z and (or) Early Cambrian in age. EASTERN FAIRFAX SEQUENCE 9 N 75 70 O 15 5 70 70 \Q (‘3 B D FIGURE 9.—Stereographic projections comparing structural elements in rocks of the Eastern Fairfax sequence with those in rocks of tonalite plutons and the northern part of the Occoquan Granite batholithi A. Equal-area plot (lower hemisphere) of 50 axes of small folds in schistosity in rocks of Eastern Fairfax sequence. Contours at 15,10, and 5 percent per 1—percent area. B. Equal-area plot (upper hemisphere) of 100 poles to joints in rocks of Eastern Fairfax sequence. C. Equal-area plot (lower hemisphere) of 40 mineral and rodding lineations in rocks of tonalite plutons and northern part of Occoquan Granite batholith. D. Equal-area plot (upper hemisphere) of 160 poles to joints in rocks of tonalite plutons and northern part of Occoquan Granite batholith. 10 ACCOTINK SCHIST, LAKE BARCROFI‘ METASANDSTONE, POPES HEAD FORMATION, VIRGINIA PIEDMONT Correlation of the Eastern Fairfax sequence with other rocks in the central Appalachian Piedmont is difficult, if not impossible. The position of the sequence beneath. the Sykesville Formation suggests that the sequence may possibly correlate with rocks called Wissahickon Forma- tion, eastern sequence, by Hopson (1964) or Loch Raven Schist and Oella Formation by Crowley (1976). Hopson (1964) considered these rocks to be Proterozoic Z, an interpretation that would fit the tentative age of the Eastern Fairfax sequence, but most recent authors ( for example, Crowley, 1976) have considered them to be the upper part of a sequence of probable Cambrian and Or- dovician age. Crowley (1979) stated that his Loch Raven Schist and Oella Formation near Baltimore are al- lochthonous and therefore could be older than was previously thought. If so, they could correlate with the Eastern Fairfax sequence. POPES HEAD FORMATION The Popes Head Formation is herein named for ex- posures at its type locality along Popes Head Creek and the adjacent tracks of the Southern Railroad between Station Hills, Fairfax 71/2-minute quadrangle, and the confluence of the creek with Bull Run, Manassas 71/2- minute quadrangle, Fairfax County (pl. 1). The unit can be seen in many exposures in streams tributary to Bull Run and Popes Head Creek in the Manassas and Fairfax 71/2-minute quadrangles in saprolite exposures in streams, and in road, railroad, and construction-site cuts in the Fairfax, Annandale, Vienna, and Falls Church 71/2-minute quadrangles. The unit is not known north of the outlying Coastal Plain deposits near Tysons Corner (pl. 1), but it continues to the southern limit of our map- ping in the Independent Hill quadrangle, Prince William County. The Popes Head Formation is divided into a lower Old Mill Branch Metasiltstone Member and an upper Sta- tion Hills Phyllite Member. The lower member is com- posed largely of metasiltstone but contains subordinate phyllite, felsic metatuff, and mafic metatuff. The upper member is composed largely of pelitic phyllite and con- tains subordinate very fine-grained metasiltstone and only minor amounts of mafic metatuff. The bulk of the Popes Head is within a complexly refolded synform above various rocks of the Wissahickon terrane, Peters Creek Schist of our usage (pl. 1). The unit also is found in two small subsidiary synforms west of this major structure (pl. 1). In the southern part of the map area, the formation is intruded by the Occoquan Granite batholith. OLD MILL BRANCH METASILTSTONE MEMBER The Old Mill Branch Metasiltstone Member is herein named for exposures at its type locality along Old Mill Branch between Clifton Road and the Occoquan Reser- voir, Manassas 71/2-minute quadrangle, Fairfax County, Va. (pl. 1). Other good exposures are along the two un- named streams between Old Mill Branch and Bull Run in the Manassas 7 1/2-minute quadrangle; in the type sec- tion of the formation, along Piney Branch between Robeys Mill and its confluence with Popes Head Creek, Fairfax 7 1/2-minute quadrangle; along Popes Head Road between Popes Head Creek and Ox Road, Fairfax 71/2- minute quadrangle; and along Long Branch north of Arlington Boulevard in the Falls Church and Annandale 71/2-minute quadrangles (pl. 1). Where fresh, the Old Mill Branch Metasiltstone Member is light greenish gray, but in most exposures it weathers to pale greenish yellow or yellowish gray. Saprolite exposures are typically dusky yellow. The unit consists of alternating coarser and finer grained strata. Most of the coarser grained beds are medium- to fine- grained micaceous metasiltstone, but a few are fine- grained micaceous metasandstone. Some of the coarser beds, however, are extremely rich in quartz and have only wispy seams of phyllosilicates (fig. 10). The finer grained beds are metapelite and extremely fine-grained micaceous metasiltstone. The unit is isoclinally folded, and in most exposures, phyllitic cleavage is subparallel to bedding. Both bedding and cleavage have been a . v, \ - -, .-~ . J" g M . V, l \ ‘ . , 5i“ _ -7 » "r ’ "7 «r . . ' ‘ i' L A Xmfii" . ‘3: W i , . 193:.‘533’5353 i"? 3" “1‘5 ' FIGURE 10.—Typical Old Mill Branch Metasiltstone Member of the Popes Head Formation from east bank of Bull Run about 150 m south of north border of Independent Hill quadrangle. Quartz-rich metasiltstone containing plagioclase, wispy seams of biotite (sometimes chlorite) parallel to a faint foliation, and scattered magnetite. Plain light; 1 cm on photo equals 0.5 cm. POPES HEAD FORMATION 11 deformed by a later fold phase, but a second cleavage is seen in only a few exposures. In spite of this deformation, certain sedimentologic observations can be made. The beds are 2—24 cm thick, averaging about 15 cm. They have sharp bases, appear to be regular, and show no evidence of wedging or lensing. In many exposures, metasiltstone clearly grades up into metapelite. Other beds, however, appear to be laminated, and the grading is obscure. Penetrative phyllitic cleavage makes such observations difficult. We have searched for but have found only a few cross-laminated sedimentation inter- vals and no sole marks. Thesedata suggest that the Old Mill Branch consists of turbidites that can be described by the Bouma (1962) sequence dee and (or) Tde, and, more rarely, Tcde . The typical mineral assemblage of the metasiltstone is quartz-muscovite-biotite-plagioclase (-chlorite— magnetite-epidote). Mineral assemblages in the metapelite are the same except that they contain more total phyllosilicates than quartz. Thin-section study shows that the long dimensions of all minerals, including flattened quartz, parallel the phyllitic cleavage. Bedding is largely obscured by transposition in the more pelitic rocks, but remnants suggest that the outcrop determina- tion of lamination is correct. FELSIC METATUFF The Old Mill Branch Metasiltstone Member contains fairly abundant felsic metatuff. To determine the amount is impossible because of poor exposure and deep weathering and because the saprolite formed from metasiltstone closely resembles that formed from felsic metatuff. Where fresh, the metatuff is greenish gray. It weathers light gray to yellowish gray. The rock is fine grained, but euhedral plagioclase can easily be seen with a hand lens. The metatuff forms beds as thick as 60 cm within normal sedimentary sequences of Old Mill Branch rocks. Strata both above and below metatuff beds seem to contain about subequal parts of terrigenous and volcanigenic material. Thin-section study shows that the metatuff consists of quartz, plagioclase, epidote (probably after plagioclase), muscovite, biotite (altering to, and interleaved with chlorite), chlorite, tiny green pleochroic amphibole, and magnetite. The plagioclase forms large euhedral zoned crystals in which the more calcic interiors are altered to epidote (fig. 11). The biotite and chlorite form wispy seams parallel to the phyllitic cleavage. Thin-section study of rocks thought to have both ter- rigenous and volcanigenic components shows the typical well-foliated quartz-muscovite-biotite-magnetite meta- FIGURE 11.—Felsic metatuff from the Old Mill Branch Metasiltstone Member of the Popes Head Formation from a small stream tributary to Bull Run about 1,900 m west of Bull Run Marina, Independent Hill quadrangle. Large euhedral plagioclase crystals (p, near center of photograph) have more calcic cores that have altered to epidote in a fine-grained matrix of quartz, chlorite, epidote, biotite, muscovite and opaque minerals. Biotite and chlorite form wispy seams parallel to foliation. Crossed nicols; 1 cm on photo equals 0.2 cm. siltstone that also contains tiny epidote grains and tiny needles of green pleochroic hornblende. There is no recognizable zoned or twinned plagioclase, but the rock most probably contained some, because epidote, a com- mon alteration product of plagioclase in these rocks, is abundant. The textures suggest that this rock contains a volcanigenic component. The felsic metatuff must have resulted from an ash fall. The perfectly preserved zoned euhedral plagioclase crystals would never have survived the abrasion and dis- integration accompanying a normal sedimentation process. MAFIC M ETATUFF Mafic metatuff does not appear to be as abundant in the Old Mill Branch Metasiltstone Member as felsic metatuff. Where best exposed, the mafic metatuff is fairly crystalline; probably a fair amount of more finely crystalline tuff was not recognized because of its similarity to greenish-gray, very fine grained metasilt- stone or phyllite. The mafic metatuff weathers grayish olive green, and many outcrops are characterized by abundant oxidized pyrite. The metatuff forms layers as thick as about 60 cm and series of layers as much as 180 cm interbedded with the metasiltstone and phyllite of the Old Mill Branch. Euhedral grains of amphibole and plagioclase can be seen with a hand lens in most ex- posures. 12 Thin-section study shows that the rock has a high ratio of euhedral well—preserved blue-green amphibole, zoned plagioclase, and sphene, to mature granular ter- rigenous quartz and minor fine-grained plagioclase. Most rocks are extremely altered, but some retain remarkably pristine igneous textures (fig. 12). The euhedral nature of these igneous minerals suggests that the mafic metatuff layers, like the felsic metatuff, resulted from ash falls. If the original igneous protolith had been a flow or hypabyssal rock, it is unlikely that in— dividual euhedral minerals could have been incor- porated in the fine-grained matrix without greater destruction. CONTACT R ELATIO N S The Old Mill Branch Metasiltstone Member physically overlies all the other rocks of the Wissahickon terrane in Fairfax County (Drake and others, 1979). On the east, it is strongly discordant on rocks of the Peters Creek Schist, Sykesville Formation, Lake Barcroft Metasandstone, and Accotink Schist which are more deformed and at a higher metamorphic grade (pl. 1; Drake and others, 1979). On the west, it is discordant on rocks of the Peters Creek Schist, Sykesville Formation, Yorkshire Formation, and Piney Branch Complex (pl. 1; Drake and others, 1979). All these rocks are FIGURE 12,—Mafic crystal metatuff from Old Mill Branch Metasilt- stone Member of the Popes Head Formation from outcrop on Popes Head Creek about 400 m northwest of Clifton, Manassas quadrangle, showing high ratio of euhedral igneous phenocrysts of amphibole (A), plagioclase (B), and sphene (C), to mature clastic matrix. The large calcic plagisclase phenocrysts (B) are altered to epidote and chlorite. They make up most of photomicrograph. The sericite in the elastic matrix is an alteration product of a less calcic plagioclase. Crossed nicols; 1 cm on photomicrograph equals‘0.5 cm. ACCOTINK SCHIST, LAKE BARCROFT METASANDSTONE, POPES HEAD FORMATION, VIRGINIA PIEDMONT polydeformed and polymetamorphosed, and much of the Peters Creek Schist constitutes a zone of severely retrograded phyllonites and other pervasively sheared rocks. These sheared rocks had been at high metamorphic grade, and many are sheared migmatites. The contact of the Old Mill Branch is particularly dif- ficult to map where it overlies the zone of phyllonized and pervasively sheared Peters Creek Schist (Drake and others, 1979; Drake and Morgan, in press). Both rocks are similar in fine-grain size, closely spaced foliation, and color, although the zone of mylonites and phyl- lonites has been multiply deformed and metamorphosed; whereas the Old Mill Branch is much less deformed and metamorphosed. Detailed mapping shows that the metasiltstone is in a large synform over- turned toward the east and two much smaller outlying synforms. Both sides of the outcrop belt show abundant POPES HEAD FORMATION 13 younging directions, on the basis of primary sedimentary structures, which indicate that these folds are synclines. The Old Mill Branch then is less deformed, is at a lower metamorphic grade, and is stratigraphically above the older rocks. In addition, bedding in the Old Mill Branch parallels the contact that cuts across structural markers in the older rocks. All the available‘evidence, therefore, strongly suggests that the contact with the older rocks is an unconformity. The contact theoretically might be a décollement, but no direct data support such an in- terpretation. On the basis of map width and constructed geologic cross sections, the Old Mill Branch is about 730 m thick in southern Fairfax County. This figure is almost cer- tainly a maximum because of the problems of mapping in poorly exposed terrane and probably unrecognized deformation. STATION HILLS PHYLLITE MEMBER The Station Hills Phyllite Member is herein named for typical exposures at its type locality along the tracks of the Southern Railroad from a point about 350 111 west of Station Hills, Fairfax 71/2-minute quadrangle, Fairfax COunty, to a point about 900 m east of that village (pl. 1). The unit crops out in the core of the 'synform defined by the Popes Head Formation and can be traced from the northern exposure of that unit south of the Tysons Corner Coastal Plain outlier to the southwestern corner of the Fairfax 71/2-minute quadrangle where it plunges out (pl. 1). The phyllite is not nearly as well exposed as the metasiltstone of the Old Mill Branch , because most of its outcrop belt is on a drainage divide in an urbanized area. The unit is relatively well exposed, chiefly as saprolite, in and around the village of Fairfax Station, Fairfax 71/2 -minute quadrangle, in the type section of the formation, along Braddock Road between Ox and Roberts Roads, Fairfax 71/2-minute quadrangle, and in an unnamed tributary to Accotink Creek north of Arlington Boulevard in the extreme northeast corner of the Fairfax 71/2-minute quadrangle (pl. 1). The unit consists of light-greenish-gray, dusky-yellow- weathering phyllite and lesser very fine grained metasilt- stone. Locally, it is interbedded with fine‘grained metasiltstone. Some chlorite-rich phyllite within the unit is possibly highly altered mafic metatuff. No felsic metatuff was recognized. The member is isoclinally folded and has a strong penetrative phyllitic cleavage subparallel to bedding. Both bedding and cleavage have been deformed by a later fold phase, but a second cleavage is seen only in a few exposures. This deforma- tion makes the recognition of sedimentary features in this incompetent unit difficult. Pelitic beds are 2-12 cm thick. Many beds appear to have thin basal intervals that contain vaguely graded, very fine grained metasilt- stone. There is some suggestion that the basal metasilt- stone beds are laminated, but the strong subparallel ~ cleavage makes this determination difficult. On the basis of these rather tenuous data, the Station Hills may be described as a turbidite showing the Bouma (1962) se- quence Tde' The typical mineral assemblage for the phyllite is muscovite-quartz-biotite-chlorite (-plagioc1ase-magne- tite-epidote). Metasiltstone beds are identical with the underlying Old Mill Branch. Thin-section study shows that the long dimensions of all minerals, including recrystallized quartz, parallel the phyllitic cleavage. The Station Hills Phyllite Member conformably overlies the Old Mill Branch Metasiltstone Member. The contact is gradational and is arbitrarily placed where more than 75 percent of the beds are pelitic phyl- lite. The top of the Station Hills is not exposed in Fairfax County; therefore, the unit’s thickness is unknown. The unit appears to have a maximum thickness of about 300 m in Fairfax County. ENVIRONMENT OF DEPOSITION In a terrane like this, interpretation of a depositional environment for the Popes Head Formation is difficult. Some generalizations, however, can be made. The metasiltstone and phyllite are turbidites composed of mostly fine- to very fine grained quartz, a very mature terrigenous sediment, and appear to have been deposited in a large-scale fining-upward sequence. The Bouma (1962) sequences dee and Tde and very rare Tcde sug- gest that these rocks can be assigned to turbidite facies D (Mutti and Ricci Lucchi, 1978; Walker and Mutti, 1973) and that they are quite distal. The rocks were probably deposited from weak turbidity flows as evidenced by lack of current-produced flow marks, the apparent absence of Bouma a divisions and sparsity of Bouma c divisions, and the fine grain size. Interbedded with these distal turbidites are felsic and mafic metatuff, both of which contain pristine euhedral igneous minerals that show no evidence of being water worn. These metatuffs probably are ash-fall deposits. The Popes Head, then, results from simultaneous sedimentation from two sources areas. The quartzose beds probably result from a longitudinal fill from a cratonal source, although our only direct evidence is the maturity and composition of the sediment. The metatuff probably was supplied by volcanoes, and this long, fairly narrow strike belt of rocks containing the volcanigenic material suggests the possibility of an island arc. We would like to suggest, then, that the Popes Head Forma- tion resulted from the bilateral filling of a back-arc 14 ACCOTINK SCHIST, LAKE BARCROFT METASANDSTONE, POPES HEAD FORMATION, VIRGINIA PIEDMONT basin, as it seems to fulfill the criteria of Winn and Dott (1978). Petrochemistry has not been completed, so that aspect of the problem must be held in abeyance. AGE AND COR RELATION Like the Eastern Fairfax sequence, the age of the Popes Head Formation cannot be directly determined. It is younger than all the rock units in Fairfax County north and west of the Occoquan Granite batholith and is intruded by rocks of that batholith. The best and most easily reached exposure where the intrusive relations may be seen is on the north bank of a small stream tributary to Bull Run about 275 m north of Bull Run marina, Independent Hill 71/2-minute quadrangle, Fair- fax County (BR on pl. 1). The phyllitic cleavage in the Popes Head in this and other exposures is roughly paral- lel to foliation in the batholithic rocks, suggesting that they were deformed together, a suggestion supported by the map pattern of the contact (pl. 1). The minimum age of the Popes Head, then, is the age of the Occoquan Granite batholith, which has been determined radio- metrically as Early Cambrian. The controversy as to the correctness of this age has been discussed in the treat- ment of the Eastern Fairfax sequence. Like that se- quence of rocks, we will consider the Popes Head Forma- tion to be Proterozoic Z and (or) Early Cambrian until such time that additional isotopic work proves otherwise. It is as difficult to find correlatives of the Popes Head Formation as it is for the Eastern Fairfax sequence. One possible correlative is the Chopawamsic Formation, which crops out south and east of the Occoquan Granite batholith in the Quantico fold sequence (Drake and others, 1979). The Chopawamsic consists mainly of volcanic and volcaniclastic rocks but contains admixed and interbedded quartzose rocks of terrigenous origin and is, therefore, more or less an analogue of the Popes Head. Seiders and others (1975) consider it to be of Early Cambrian or Proterozoic Z age. Perhaps these two units have a lateral equivalency. One problem with this speculation is that the Popes Head appears to be younger than the Sykesville Forma- tion in field relations. Another problem is that we have never recognized an exotic fragment of Popes Head within the Sykesville. We have seen abundant exotic fragments identical with rocks of the Chopawamsic For- mation within the Sykesville; therefore, the Chopawam- sic must be older than at least part of the Sykesville. Southwick and others (1971) consider that the Sykesville and Chopawamsic are partial equivalents and grade laterally into one another, and Seiders and others (1975) have described Sykesville-like material interbedded with the Chopawamsic. Both are interpretations made to explain the distribution of rock types in a poorly exposed terrane. We believe that the data presented by the earlier workers can be explained as well, if not better, as a result of the presence of fragments, blocks, and slabs of Chopawamsic within Sykesville matrix. This interpreta- tion is supported by the direct observation of Chopawamsic-like clasts in other outcrops. The relation of the Popes Head to the Chopawamsic awaits direct study somewhere in the area south of the Occoquan Granite batholith. North of the Potomac River in Maryland, the Wissa- ‘ hickon terrane (Peters Creek Schist of our usage, Wissa- hickon Formation, or western sequence of Hopson (1964), is bounded on the west by the Ijamsville Phyllite (Hopson, 1964, Cleaves and others, 1968). The Ijamsville is an alumina-soda-iron-rich rock characterized by pur- ple and green muscovite-paragonite-chloritoid phyllite. It closely resembles many of the rocks of the Taconic se- quence of New York and New England (Zen, 1967) and probably results from starved sedimentation on the abyssal plain. The Ijamsville is succeeded on the west by a sequence of lightly metamorphosed, immature sandstone, silt- stone, quartzite, impure marble, and basalt. These rocks, the Urbana Phyllite of Cleaves and others (1968) or Harpers Phyllite of Hopson (1964) have all the features of shallow—water deposits and are thought, by Hopson (1964) at least, to be related to the Chilhowee Group of the Blue Ridge anticlinorium. While doing a hurried reconnaissance in Montgomery and southern Frederick Counties, Md., to prepare a tec- tonic lithofacies map of the central Appalachians published in Williams (1978), we found rocks that closely resemble the Popes Head in the Urbana 71/2- minute quadrangle along Interstate Route 270 about 2.9 km south of its intersection with Maryland Route 80. These outcrops are found within a terrane compiled as Urbana by Cleaves and others (1968), but the rocks do not resemble other exposures of Urbana that we have seen, nor do they resemble Hopson’s (1964) description of this unit (his Harpers). About 1,600 m N. 35° E. from these exposures, in outcrops along Maryland Route 355, similar metasiltstone is interbedded with purple and green phyllite typical of the Ijamsville. Hopson (1964) mentioned laminated, even—bedded metasiltstone within the terrane he considers Ijamsville but did not describe them as turbidites. If we might speculate on these sparse data, we would like to suggest that the Ijamsville and Popes Head are related. If this speculation is correct, the interbedded Popes Head-like siltstone and Ijamsville Phyllite would have been deposited at the margin of the longitudinally RESULTS AND CONCLUSIONS 15 filled turbidite basin where mature quartzose sediment became intermingled with the starved sedimentary se- quence of the abyssal plain.1 This discussion shows that the far western Piedmont of Montgomery and im— mediately adjacent Frederick Counties is the critical area in which to determine the relation of these rocks. RESULTS AND CONCLUSIONS In this paper we have named and described three new stratigraphic units in the enigmatic Wissahickon terrane of the central Appalachian Piedmont and have speculated on their possible environments of deposition. Even if we are completely wrong in our speculations, we present data that clearly show that rocks of the Eastern Fairfax sequence differ greatly from those of the Popes Head Formation and that both units differ from the Peters Creek Schist in sedimentologic as well as in struc- tural and metamorphic character (Drake and others, 1979; Drake and Morgan, in press). For these reasons, we believe that it is folly to continue using the concept of a Wissahickon Formation. In discussions of a regional nature, however, the term Wissahickon is useful because of its historical usage. We strongly suggest that the name Wissahickon be used to define a terrane rather than a stratigraphic unit except in the Philadelphia area. One other important result has come from this work. The Popes Head Formation is unconformable above a terrane of polydeformed and polymetamorphosed rocks that includes a stack of at least three allochthons: the Sykesville Formation (if one considers, as we do, that a rock body emplaced by subaqueous sliding is an al- lochthon), the Potomac River allochthon (pl. 1; Drake and others, 1979; Drake and Morgan, in press), and the metamorphosed ophiolite fragment called the Piney Branch allochthon (Drake and others 1979; Drake and Morgan, in press). If the Popes Head is of Proterozoic Z and (or) Early Cambrian age, then a great deal of Proterozoic deformation and metamorphism probably took place before the formation of the turbidite basin in which it was deposited. Even if the Popes Head is younger and the pre-Popes Head deformation and metamorphism can be ascribed to an early Paleozoic orogeny, the rocks beneath the Popes Head had a com- plex and varied structural and metamorphic history before its deposition. This history suggests that the model for the tectonic development of the central Ap- palachian Piedmont as first cast by Hopson (1964) and refined by Fisher (1976) is greatly oversimplified. ‘Since this was written, the Maryland outcrops described in the paragraph above were restudied. This restudy casts some doubt on the correlation of the metasiltstones in Maryland with the Popes Head Formation and, thereby, on this sedimentalogic interpretation. REFERENCES CITED Bouma, A. H., 1962, Sedimentology of some flysch deposits: New York, Elsevier, 168 p. Cleaves, E. T., Edwards, Jonathan, Jr., and Glaser, J. D., compilers and editors, 1968, Geologic map of Maryland: Baltimore, Maryland Geological Survey, scale 1:250,000. Crowley, W. P., 1976, The geology of the crystalline rocks near Baltimore and its bearing on the evolution of the eastern Maryland Piedmont: Maryland Geological Survey Report of Investigation 27, 40 p. Crowley, W. P., 1979, The Appalachian Piedmont: A cross section near Baltimore [abs]: Geological Society of America Abstracts with Programs, v. 11, no. 1, p. 9. Darton, N. H., and Keith, Arthur, 1901, Description of the Washington quadrangle [D.C.-Md.-Va.]: U.S. Geological Survey Geologic Atlas, Folio 70. Drake, A. A., Jr., and Froelich, A. J., 1977, Bedrock map of Fairfax County, Virginia: U.S. Geological Survey open-file map 77—523. Drake, A. A., Jr., and Morgan, B. A., in press, The Piney Branch Complex—a metamorphosed fragment of the central Ap- palachian ophiolite in northern Virginia: American Journal of Science, in press. Drake, A. A., Jr., Nelson, A. E., Force, L. M., Froelich, A. J., and Lyttle, P. T., 1979, Preliminary geologic map of Fairfax County, Virginia: U.S. Geological Survey open-file report 79—398. Fisher, G. W., 1970, The Piedmont; the metamorphosed sedimentary rocks along the Potomac River near Washington, D. C., in Fisher, G. W., and others, eds.: Studies of Appalachian geology—central and southern: New York, Interscience, p. 299—315. Fisher, G. W., 1976, The geologic evolution of the northeastern Pied- mont of the Appalachians [abs]: Geological Society of America Abstracts with Programs, v. 8, no. 2, p. 172—173. Higgins, M. W., and Fisher, G. W., 1971, A further revision of the stratigraphic nomenclature of the Wissahickon formation in Maryland: Geological Society of America Bulletin, v. 82, no. 3, p. 769—774. Higgins, M. W. Sinha, A. K., Zartman, R. E., and Kirk, W. S., 1977, U—Pb zircon dates from the central Appalachian Piedmont; a pos- sible case of inherited radiogenic lead: Geological Society of America Bulletin, v. 88, no. 1, p. 125—132. Hopson, C. A., 1964, The crystalline rocks of Howard and Montgomery Counties, in The geology of Howard and Montgomery Counties: Baltimore, Maryland Geological Survey, p. 27—215. Hsii, K. J ., 1968, Principles of mélanges and their bearing on the Fran- ciscan—Knoxville paradox: Geological Society of America Bul- letin, v. 79, no. 8, p. 1063—1074. Johnston, P. M., 1962, Geology and ground-water resources of the Fair- fax quadrangle, Virginia: U. S. Geological Survey Water-Supply Paper 1539—L, 61 p. Johnston, P. M., 1964, Geology and groundwater resources of Washington, D. C., and vicinity: U.S. Geological Survey Water- Supply Paper 1776, 97 p. Middleton, G. V., and Hampton, M. A., 1973, Sediment gravity flows; mechanics of flow and deposition, in Middleton, G. V., and Bouma, A. H., co-chairmen, Turbidites and deep-water sedimen- tation: Los Angeles, Society of Economic Paleontologists and Mineralogists, Pacific Section, p. 1—38. Mixon, R. B., Southwick, D. L., and Reed, J. C., Jr., 1972, Geologic map of the Quantico quadrangle, Prince William and Stafford Counties, Virginia, and Charles County, Maryland: U.S. Geological Survey Geologic Quadrangle Map GQ—1044. 16 ACCOTINK SCHIST, LAKE BARCROFT METASANDSTONE, POPES HEAD FORMATION, VIRGINIA PIEDMONT Mutti, Emiliano and Ricci Lucchi, F. R., 1978, Turbidites of the northern Apennines; introduction to facies analysis: American Geological Institute Reprint Series no. 3, 166 p. Reed, J.4C., Jr., and Jolly, Janice, 1963, Crystalline rocks of the Potomac River gorge near Washington, D. C.: U.S. Geological Survey Professional Paper 414—H, 16 p. Seiders, V. M., and Mixon, R. B., in press, Geologic map of the Occo- quan quadrangle and part of the Fort Belvoir quadrangle, Prince William and Fairfax Counties, Virginia: U.S. Geological Survey Miscellaneous Investigations Map. Seiders, V. M., Mixon, R. B., Stern, T. W., Newell, M. F., and Thomas, C. B., Jr., 1975, Age of plutonism and tectonism and a new minimum age limit on the Glenarm Series in the northeast Virginia Piedmont near Occoquan: American Journal of Science, v. 275, no. 5, p. '481—511. Southwick, D. L., Reed, J. C., Jr., and Mixon, R. B., 1971, The Chopawamsic Formation—a new stratigraphic unit in the Pied- mont of northeastern Virginia: U.S. Geological Survey Bulletin 1324—D, 11 p. Stose, G. W., and Jonas, A. I., 1939, Geology and mineral resources of York County, Pennsylvania: Pennsylvania Geological Survey, 4th Series, Bulletin C—67, 199 p. Stose, G. W., compiler, 1928, Geologic map of Virginia: Charlottesville, Virginia Geological Survey, scale 1:500,000. U.S. Geological Survey, 1977, Geological Survey research 1977: U.S. Geological Survey Professional Paper 1050, 411 p. Walker, R. G., and Mutti, Emiliano, 1973, Turbidite facies and facies associations, in Middleton, G. V., and Bouma, A. H., co- chairman, Turbidites and deep water sedimentation: Los Angeles Society'of Economic Paleontologists and Mineralogists, Pacific Section, p. 118—157. Williams, Harold, compiler, 1978, Tectonic lithofacies map of the Ap- palachian orogen: St. Johns, Memorial University of New- foundland, scale 1:1,000,000. a U.S. GOVERNMENT PRINTING OFFICE': 1931~777.034/102 as 7; F b v. i 20 5’ p101 UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 1205 GEOLOGICAL SURVEY PLATE 1 I ' mg) 770mm" Cchp 38' 3 , fil 0P9], _ _ l e r FAIRFAX :5 ( ANNANDAit 3B"45’ 1 ' 7 j . DCCOQUANV , IIIIII BIIVUII‘I I o, 6“; a” INDEX MAP SHOWING AREA OF THIS REPORT ’1 0‘6" x 0/99" MONTGOMERY Alexandria PRINCE 77°22'30” 77‘xi5' 77‘07’30” Base from US. Geological Survey,1980 SCALE 11100 000 GGOIOQY by A3 A- Drake, Jr., 1 1/2 O 1 2 3 4 SMILES A. E Nelson and P. T. Lyttle, 1974—75 l—l I————I I———I l—l 1 .5 O 1 2 3 4 5 KILOMETERS I—I I I I I I I NATIONAL GEODETlC VERTICAL DATUM OF 1929 AEEEBZ'ETSENEQI" EXPLANATION The rocks beneath the Popes Head Formation and above the Eastern Fairfax sequence constitute a stack of allochthons. The stacking sequence is listed below Popes Head Formation Unconformity Piney Branch allochthon _A_—A—A__ Potomac River allochthon _A_._L—A_ Sykesville Formation _A__A—A_ Eastern Fairfax sequtence INTRUSIVE ROCIKS C C Lower Cambrian 9° ° CAMBRIAN Granitoid complex Tonalite Occoquan Granite METASEDIMENTARY, METAVOLCANIC, AND TFRANSPORTED INTRUSIVE ROCKS Popes Head Formation CZps, Station Hills Phyllite Member CZpo, Old Mill Branch Metasiltstone Member Unconformity Proterozoic Z PROTEROZOIC and (or) 4 PINEY BRANCH ALLOCHTHON POTOMAC RIVER ALLOCHTHON EASTERN FAIRFAX SEQUENCE * AND (OR) Lower Cambrian CAMBRIAN I J? Piney Branch Complex ‘ . , Lake Barcroft Metasandstone Peters Creek Schist , , Sykesvxlle Formation —A——A——A— Cchp, pelitic schist Ophlolite blocks and slabs Within melange Cchg, metagraywacke CZum, serpentinite, soapstone, or actinolite schist 623 . CZab, metagabbro ‘ CZmum, undivided ultramafic and mafic rocks Accotink Schist t Yorkshire Formation 4 Contact Thrust fault Sawteeth on upper plate; where overturned, sawteeth in direction of dip ____H— Overturned syncline Showing trace of axial surface and direction of dip of limbs Places mentioned in text: TI, intrusive contact of tonalite with type II metagraywacke of Lack Barcroft Meta— sandstone Ol, intrusive contact of rocks of Occoquan Granite batholith with type II metagraywacke of Lake Barcroft Metasandstone BR, intrusive contact of rocks of Occoquan Granite batholith with Old Mill Branch Metasiltstone Member of Popes Head Formation GENERALIZED GEOLOGIC MAP OF PART OF FAIRFAX COUNTY, VIRGINIA a U5. 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Effects of Flooding Upon Woody Vegetation along Parts of the Potomac River Flood Plain By THOMAS M. YANOSKY GEOLOGICAL SURVEY PROFESSIONAL PAPER 1206 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON11982 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES C. WATT, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging in Publication Data Yanosky, Thomas M Effects of flooding upon woody vegetation along parts of the Potomac River flood plain. (Geological Survey professional paper ; 1206) Bibliography: p. 1. Floodplain flora—Potomac Valley. 2. Plants Effect of floods on—Potomac Valley. 3. Forest ecology—Potomac Valley. 4. Potomac River—Floods. 5. Flood damage—Potomac Valley. I. Title. II. Series: United States. Geological Survey. ‘ Professional paper ; 1206. QK191.Y36 581.5’26325 80—607999 For sale by the Distribution Branch, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 CONTENTS Page Conversion factors ................................................................... vi Abstract ............................................................................ 1 Introduction ........................................................................ 1 Acknowledgments ................................................................... 1 Literature review .................................................................... 1 Flooding on the Potomac River near Washington, DC ................................... 2 The monumented plot study .......................................................... 3 Methods ........................................................................ 3 The study areas ................................................................. 4 Chain Bridge. . .‘ ............................................................. 4 Spalding farm flood plain .................................................... 5 Uplands .................................................................... 5 Changes in woody vegetation ..................................................... 5 Basal area .................................................................. 5 Survival .................................................................... 7 The eflects of the Hurricane Agnes flood along the Potomac River downstream from Great Falls ............................................................ Effects of local site characteristics ................................................ 8 Species survival ................................................................. 13 Summary and conclusions ............................................................ 16 References cited ..................................................................... 19 ILLUSTRATIONS Page FRONTISPIECE. Potomac River at Great Falls Park, Va., June 22, 1972. FIGURE 1. Map of Potomac River near Washington, D.C., showing study areas at Chain Bridge and Spalding farm ................ 3 2. Map of study site below Great Falls ............................................................................... 9 3, 4. Photographs showing 3. Potomac River Gorge below Great Falls .................................................................... 9 4. High water near Difficult Run ............................................................................. 9 5. Line drawing showing representation of sheltering during floods along inner and outer channel bends .................. 10 6—18. Photographs showing 6. Yellow Pond flood plain in March 1967 ..................................................................... 10 7. Lower tract of Yellow Pond flood plain in 1975 .............................................................. 11 8. Upper tract of Yellow Pond flood plain in 1975 .............................................................. 12 9. Rock outcrop adjacent to Yellow Pond and alluvial tract just downstream .................................... 14 10. Upper part of Old Angler flood plain during flood of February 1966 ........................................... 16 11. Old Angler flood plain during low flow, 1975 ................................................................ 17 12. Downstream view from protective wall at head of Old Angler flood plain, 1975 ................................ 17 13. View of the lower part of Old Angler flood plain ............................................................ 18 14. Madeira flood plain ....................................................................................... 18 15. Silver maple forest on Madeira flood plain .................................................................. 19 16. Sheltered sycamore below Great Falls ..................................................................... 19 17. Flood-damaged sycamores below Great Falls ............................................................... 20 18. Downstream view from Rocky Islands in 1968 .............................................................. 21 CONTENTS TABLES Page TABLE 1. Summary of flooding at seven monumented plots during water years 1963-1972 .......................................... 4 2. Basal area of woody vegetation at seven monumented plots ............................................................ 6 3. Survival of plants at seven monumented plots ........................................................................ 7 4. Survival of single—stemmed and clumped plants at seven monumented plots ............................................. 8 5. Summary of condition of trees still standing in July 1973 on a 20-m by 10-m plot on the Yellow Pond flood plain just downstream from the protective wall ................................................................... 13 6. Summary of condition of trees still standing in July 1973 on alluvial plot just downstream from the rock outcrop adjacent to Yellow Pond ................................................................................. 15 7. Summary of selected core data from Old angler flood plain (upstream tract) and Madeira flood plain along the Potomac River .............................................................................................. 17 GLOSSARY Adventitious growth. Stems or roots that arise from parts of the plant where they would not arise under ordinary conditions. Ad- ventitious growth often occurs following injury from flooding. Alluvium. Sediment deposited by moving water. Basal area. Cross-sectional area of a stem or trunk at breast height. Botanical evidence. Evidence from vegetation for the past or pres- ent occurrence of geomorphic processes or land use. Crest. The highest altitude of a flood. Discharge. The rate of flow in a river or stream. Flood. Any flow that rises above the banks and spreads across the flood plain. Flood damage. In this report, the killing or injury of plants by flooding. Flood plain. An area adjacent to a stream or river formed of deposi- tion and erosion during floods. Frequency. The average number of times per year that a given dis- charge is equaled or exceeded. Monumented plot. In this report, study areas marked by concrete monuments that act as permanent reference points. Peak discharge. The maximum discharge attained by a flood. Recurrence interval. The average interval in years between flows that equal or exceed a given discharge. Stage. The water-surface altitude of a stream. Water year. The 12-month period, October 1-September 30. Woody vegetation. In this report, trees and shrubs. CONVERSION FACTORS Units of measure used in this report are International System of Units (SI). The following factors can be used to convert SI units to US. customary units. To convert from centimeter (cm) meter (m) kilometer (km) meter2 (m2) hectometer2 (hmz) meter3 per second (ma/s) To Multiply by inch (in) 2.54 foot (ft) 3.281 yard (yd) 1.094 mile (mi) 0.6214 foot2 (ftz) 10.76 acre 2.471 foot3 per second (ft3/s) 35.31 EFFECTS OF FLOODING UPON WOODY VEGETATION ALONG PARTS OF THE POTOMAC RIVER FLOOD PLAIN By THOMAS M. YANOSKY ABSTRACT A two-part study along the Potomac River flood plain near Wash- ington, D.C., was undertaken to investigate the effects of flooding upon woody vegetation. Floods abrade bark, damage branches and can- opies, and often uproot trees. The first study was of vegetation in five monumented flood-plain plots, which differed in the frequency and severity of flood flow over a 10—year period. Basal area and survival of trees appear to be related to velocity of flood flow, which in turn is related to flood magnitude and channel shape. However, the effects of flooding also depend on the nature of the flood-plain surface and size and growth habit of vegetation. In the second study, a catastrophic flood following Hurricane Agnes in June 1972 was found to cause large-scale changes in the age, form, and species composition of flood-plain forests below Great Falls, Va. The impact of the flood depended primarily on the flow regime of the river; destruction was greatest in areas exposed to the maximum flood force, and minimal at sheltered locations. Age determinations from dead trunks and surviving trees suggest that most trees in severely damaged areas started to grow after the last great flood, which oc- curred in 1942. Trees along sheltered reaches survived several pre- vious catastrophic floods. In addition, species varied in their ability to withstand damage from the Hurricane Agnes flood. The least likely to recover were species growing on infrequently flooded surfaces, which may explain, in part, their absence at lower flood-plain altitudes. INTRODUCTION Flood-plain forests are generally different from those on adjacent terraces and uplands. These differences in part are related to the local frequency, duration, and velocity of floodflow and are important in gaining an understanding of the hydrologic environment. In this study, woody vegetation along a part of the Potomac River between Washington, DC, and Great Falls, Va., was investigated to determine the effects of flooding on plant growth and survival. In the first part of the in- vestigation, vegetation was studied on two reaches of flood plain which differ in flood frequency and severity of flow velocities during high water. Another study area was in an upland forest which is never flooded. Woody stems were initially mapped and measured by personnel of the U.S. Geological Survey in a series of monumented plots in 1962 (flood plain) and 1965 (upland). Stems were remapped and remeasured after the 1972 growing sea- son, and data from the two mappings were compared. The second part of the study concerns specific effects of the catastrophic flood following Hurricane Agnes in June 1972. The age, form, and survival of flood-plain trees were studied where destruction was locally vari- able. Areas exposed to the maximum current velocities of the flood were compared to nearby reaches where vegetation was sheltered from severe floodflows. ACKNOWLEDGMENTS The author wishes to thank Richard L. Phipps and Jane F. Hill for reviewing the manuscript and making helpful suggestions and Mrs. Esther R. Flint for her assistance with much of the typing. Thanks are ex- tended to S. P. Spalding and the Madeira School for permission to conduct field studies on their properties. Thanks are also extended to Kenneth J. Fassler and John W. Zuke but most of all to Dr. Robert S. Sigafoos, who kindly provided much of the data in this report and greatly encouraged the author’s interests in riparian vegetation and hydrology. LITERATURE REVIEW McGee (1891) defined a flood plain as land “Within reach of the river and suffering overflows by freshets, or at least by great floods.” More modern definitions em- phasize dynamic associations between the stream and flood-plain formation (Kilpatrick and Barnes, 1964). During high flows, sediment may be deposited on flood plains, or previously deposited materials may be eroded away. The establishment of woody vegetation on flood plains is related to these processes in ways that are not completely understood. Seeds of some species germinate on thick alluvial deposits only after leaf litter and other organic debris have been removed by spring floods. Oth- ers are able to grow on thinly scattered alluvium over- lying bedrock. Seedlings are often uprooted or buried by sediments due to flooding in late spring or early sum- mer, suggesting that successful growth may coincide with periods of low flow (Sigafoos, 1964). Once established, flood-plain forests may be inun- dated periodically for extended periods. Trees are often damaged by supernormal velocity and by debris trans- ported at or near the water surface. Vegetation is most likely to be damaged or removed when velocity and quantity of debris are extreme, particularly when chan- nels are choked with ice. Floods abrade bark, break branches and canopies, and often partially uproot trees. Although aerial parts may be lost, the roots are often not killed; stumps subsequently send out a profusion of adventitious sprouts and the tree survives. Although literature on the ecology of flood-plain veg- etation is abundant, most studies are primarily descrip- tions of bottomland communities and successional stages in their development. The most significant works 1 2 EFFECTS OF FLOODING UPON WOODY VEGETATION, POTOMAC RIVER FLOOD PLAIN are the vegetation studies along the Lower Illinois River (Turner, 1936), on flood plains of the Wabash and Tip- pecanoe Rivers, Ind. (Lindsey and others, 1961), and along the Raritan River, NJ. (Buell and Wistendahl, 1955; Wistendahl, 1958). Succession on an island in the Mississippi River was investigated by Schull (1944) and on levees along the Illinois River by Turner (1931). These and other studies confirm differences in climate, soils, and species composition between upland and flood-plain forests. Most workers believed that vegeta- tional zones along flood plains represent normal succes- sional stages that in time will be replaced by adjoining upland species. Sigafoos (1961) offered the alternative hypothesis that flood-plain vegetation is related to the frequency and magnitude of looding. In a study along the White River, Ark., Bedinger (1971) found four distinct vegeta- tion zones related to the frequency and duration of yearly flooding. Although he did not conclude that this was necessarily cause and effect, he found strong evi- dence for it. It seems unlikely, however, that flood fre- quency and duration alone control the distribution of vegetation along many eastern rivers and streams. Un- like the White River flood plain, eastern flood plains are often highly variable in width and topography, and the generally steeper stream gradients result in greater ve- locities. Trees in some areas are continually damaged or killed by floods. Factors such as flood magnitude and site characteristics explain the more variable nature of vegetation. Other investigations have concentrated on the effects of partial or complete inundation on flood-plain vegeta- tion. Hosner (1958) found that first-year seedlings of six flood-plain species died within 32 days after complete submergence and that different species died at different rates. In more extensive studies, Hosner (1960) found that seedlings survived for longer periods when only the roots were flooded because the crowns retained the ca- pacity for gas exchange. Turner (1930) found that few trees along the Illinois River were killed when flooded for long durations during the fall and early winter of 1926 but suffered high mortality when inundated from April to mid-June in 1927. In a bottomland timber area permanently flooded by impoundment near the junction of the Illinois and Mississippi Rivers, Yeager (1949) found that standing water to a depth of 50 cm resulted in almost complete mortality of all trees within 8 years. Furthermore, mortality by species was highly variable, with white ash (Francinus amem'ccma L.) most resistant (8 years) and pin oak (Quercus palustm's Muenchh.) most susceptible (3 years). Broadfoot and Williston (1973) state that chemical properties of soil determine many of the effects of in- undation upon roots. Toxic reactions may occur in soils with high sodium content, or in those which are highly acid. Harper (1938) attributed root mortality along the Canadian River, Okla., to oxygen deprivation after de- position of clay. Species vary in their abilities to develop adventitious roots and withstand leaf moisture deficits caused by the oxygen deficiency of saturated soils (Hos- ner and Boyce, 1962). Other flood-plain studies have used botanical evi- dence to reconstruct the recent history of floods and flood-related phenomena. Sigafoos (1964) found that trees growing along the Potomac River near Washing- ton, D.C., showed damage from numerous floods. By dat- ing sprouts from inclined or broken trunks, flood dates could be determined. Sigafoos was also able to deter- mine the year of burial of aerial shoots from changes in wood anatomy during subsequent growth. Similarly, Everitt (1968) used cottonwood (Populus sargentii Dode) as an indicator of channel movement and flood-plain development along the Little Missouri River, N. Dak. Botanical evidence may be valuable where stream-flow records are lacking or short (Sigafoos, 1964). Harrison and Reid (1967) tested this hypothesis by constructing a flood-frequency graph based on scarred trees along the Turtle River, N. Dak. Their graph approximated fre- quencies recorded in 25 years of hydrologic data. Helley and LaMarche (1973) determined radiocarbon dates for trees buried in ancient flood deposits to extend the record of known catastrophic floods of northern Califor- nia streams. FLOODING ON THE POTOMAC RIVER NEAR WASHINGTON, D.C. A stream floods when the volume of flow is so great that stream stages overtop the banks and spread across the flood plain. Flow discharge is measured at stream- gaging stations and is expressed in cubic meters per second (m3/s). Once recorded, the annual peak dis- charges at a site can be used to define a flood-frequency curve, which relates discharge to recurrence interval (Patterson, 1964). For example, a flood with a recur- rence interval of 2 years is equaled or exceeded on an average of once every 2 years or has a 50 percent proba- bility of being equaled or exceeded in any 1 year. Dis- charges for the Potomac River near Washington, D.C., were continuously measured from 1930 to 1964 by a water-stage recorder 1.6 km upstream from Brookmont, Md., and from January 1965 to the present by a water- stage recorder with concrete control located at Brook- mont. Datum, or zero of the gage, is 11.57 m, National Geodetic Vertical Datum of 1929. Between 1930 and 1971, the flood of March 19, 1936 (13,707 m3/s), was the maximum recorded on the Poto- mac River near Washington, D.C. Large floods also THE MONUMENTED PLOT STUDY 3 occurred in October 1942 (12,649 m3/s) and April 1937 (9,827 m3/s). Prior to 1930, a flood in May 1924 was probably about 8,500 m3/s, and a flood on June 2, 1889, was approximately as great as that of 1936. These and all other streamflow data cited in this report were ob- tained from surface-water records of the US. Geologi- cal Survey. The flood in the wake of Hurricane Agnes crested near Washington, D.C., at 10,167 m3/s on June 24, 1972 (Bailey and others, 1975). This is the third highest dis- charge of the century, exceeded only in 1936 and 1942. The river rose to flood stage early on the morning of June 22 and remained above that level through June 25. Floods of this magnitude can be expected approxi- mately once every 30 years (Darling, 1959). The impact of floods in the Potomac River basin may be determined by factors other than magnitude of flow. Although floods at the same site are considered identi- cal if they have the same peak discharge, no two floods have the same flow characteristics and hence the same potential for damaging vegetation. The duration of flood- flow and the amount and type of debris may differ greatly. Most physical damage to trees appears to result from floating debris, particularly large logs or blocks of ice. Small winter floods preceded by unusually cold weather may culminate in destructive ice jams, such as those which occurred near Chain Bridge in 1948 and 1968. Winter floods are generally of greater duration than summer freshets, exposing trees to longer periods of damaging flows. Similarly, destruction along the river is often highly variable due to differences in gradient, channel sinu- osity, width and depth, and obstructions in the bed. Maximum damage is most probable along steam sec- tions where flood velocities are high, especially during debris-choked events of long duration. Damage is less likely along the higher altitudes of flood channels be- cause roughness near shore reduces flow velocities. Even here, however, smaller plants may be buried under sediment or blocks of ice and larger trees may be damaged. Most flooding along the Potomac River near Wash- ington, D.C., takes place during winter or early spring, when vegetation is dormant. As was mentioned earlier, even prolonged inundation does not usually kill flood- plain vegetation at this time, although continued submergence during the growing season may cause mortality to some species. However, flood durations sel- dom exceed a few days; even the greatest flows on record remained above flood stage for less than 5 days, and thus inundation alone probably kills only a small num- ber of trees and shrubs. THE MONUMENTED PLOT STUDY METHODS A series of seven monumented study plots was estab- lished in 1962 by R. S. Sigafoos along the Potomac River flood plain near Chain Bridge and on the upland near Washington, DC. Three are on the flood plain in Wash- ington, D.C., two are on the flood plain of the S. P. Spalding “Potowmack farm” in northern Fairfax County, and two are in an oak-hickory upland on the Spalding farm (fig. 1). Each monumented flood-plain plot is a 0.04 hm2 circle with a radius of 11.3 m. A concrete post marks the center and acts as a reference point. All trees and shrubs 0.8 cm or greater in diameter were identified and measured by Sigafoos following the 1962 growing sea- son. Diameter measurements were at breast height (dbh), except for saplings less than 2.5 cm in diameter, which were measured near the base. The location of each plant was mapped by use of a plane table. No herbaceous vegetation was recorded. After 10 growing seasons, plants were remeasured and remapped by Sig- afoos and the author. Many flood-damaged species bear multiple stems, often arising from a buried trunk. The normal growth habit of some flood-plain species, such as spicebush (Linden; Benzoin (L.) Blume) and red osier dogwood (Camus Amomum Mill.), is almost invariably a shrub- like clump of stems. Each clump was considered an indi- vidual plant, although the number of aggregated stems was recorded. The stem size assigned to each clump, thus to an individual plant, was that of the largest stem. MARYLAND / / / WASHINGTON D. C. Brookmont gaging station VIRGINIA Chain Bridge 0 5 MILES 0 5 KILDMETERS 77° FIGURE 1.—Potomac River near Washington, D.C., showing study areas at Chain Bridge and Spalding farm. Base is fromWashington and Baltimore quadrangle, 1:250,000. 4 EFFECTS OF FLOODING UPON WOODY VEGETATION, POTOMAC RIVER FLOOD PLAIN From the 1962 and 1972 maps and data, the following computations were made for each plot: (1) total number of woody plants, (2) basal area (cross-sectional area at the point of measurement) of each species, (3) total basal area, which gives a measurement of standing crop per unit area, and (4) number of plants less than 2.5 cm in diameter and number greater than 2.5 cm. In addi- tion, data were analyzed by species and size classes to determine which plants mapped in 1962 were still living in 1972. Surviving plants usually increased in basal ar- ea, although in some instances, as when large trunks were broken off and replaced by a mass of young sprouts, basal area was less. The minimum discharge required to inundate each study plot was estimated from floodmarks and obser- vations during high flows. Because the plots are nearly level, the discharge that inundates the fringes of the plot differs little from that which covers the entire area. The number of days that each plot was inundated is summarized in table 1. The two upland study plots were originally mapped by Sigafoos and Phipps in 1965 (oral communication) and are contiguous 0.04—hm2 rectangles. THE STUDY AREAS CHAIN BRIDGE The Potomac River near Chain Bridge flows in a narrow channel bordered on the Virginia shore by steep palisades and on the Maryland-Washington, D.C. side by a broad, bedrock flood plain extending to the Chesa- peake and Ohio (C & 0) Canal. Channel width at this point increases dramatically from approximately 35 m at low flow to more than 335 m at flood stage (2,945 m3/s). Bedrock increases gradually in altitude to the east and is covered at higher altitudes by alluvial deposits of variable thickness. The straight channel, heavy flow volumes, and steep river bed descent of 11.6 m in 2.4 km between Brook- mont, Md., and Chain Bridge result in high current velocities during floods. Leopold (1953) reports a max- imum point velocity of 6.7 m/s at Chain Bridge during a minor flood on May 14, 1932. I estimated a surface velocity in the mainstream of at least 9 m/s during the flood of June 24, 1972, which had a peak discharge 10,167 m3/s.1 Sigafoos (1961) lists 24 tree species common on the Chain Bridge flood plain. Predominant among these are sycamore (Platanus occidentalis L.), ash (Fraxinus L.), boxelder (Ace’r negundo L.), cottonwood (Populus del- to'ides Bartr.), river birch (Betula m'g'ra L.), silver maple (Ace'r saccharinum L.), elm (Ulmus L.), and swamp white oak (Quercus bicolor Willd.). Most vegetation on the low bedrock flood plain is small and shrubby and shows damage from numerous floods and ice jams. Larger trees grow near the C & O canal, where floods are less frequent and flow velocities are lower. Alluvium overlies the bedrock. In spring, much of this area is a series of shallow swamps amid luxuriant masses of en- tangled vegetation. The first permanent plot is about 60 m downstream from Chain Bridge and 35 m from the canal. This area is inundated by about 2,820 m3/s, although it is not unusual for several years to elapse between floods of this magnitude. Leaf litter and other organic debris accumulate over the alluvium, and growth conditions for established trees are good. The largest trees in 1962 included an elm 43 cm and sycamores 69 and 104 cm dbh. Most trees mapped in 1972 showed some flood dam- age. Few vertical trunks were observed, and many were deeply abraded on the upstream side. Most of this dam- age resulted from the June 1972 flood, which inundated the plot for about 4 days to a depth of 4 m at the crest. Despite this, the three largest trees survived. Permanent plot 2 is about 600 m upstream from Chain Bridge and 150 m from the canal. Just upstream ‘Estimations of surface velocities in this report were made by the surface—float method. TABLE 1.——Summary of flooding at seven monumented plots during 1963—72 water years Discharge inundating Number of Number of floods Number of floods Total Location Plot plot1 (cubic meters floods during expected in period in period days of per second) 1930—61 water years 1963—722 1963—72 inundation Chain Bridge ___ 1 2,830 29 9 5 10 flood plain____ 2 2,270 42 13 16 27 ____ 3 1,420 105 33 34 3 83 Spalding farm _1 4 2,550 37 12 10 17 flood plain____ 5 2,830 29 9 5 10 Spalding farm __ 6 Never flooded — — — — upland ______ 7 Never flooded — —— — — ‘ Based on observation of stage at plot and simultaneous gage height for the Potomac River near Washington, DC. Discharge at plot is believed to approximate discharge at gaging station. ‘1 Calculated to compare flood frequencies during the study interval with the earlier period of 32 years. 3 Includes 4 days representing peaks dependent on prior flows above 1,416 ma/s (see Dalrymple, 1960, p. 12, para. 4.) THE MONUMENTED PLOT STUDY 5 from the plot is a man-made tailrace running diago- nally from the canal to the river. Parallel to the down- stream edge of the tailrace is a ridge, about 3 m high, that acts as a levee for much of the area immediately below. Hence the plot is initially inundated at about 2,270 m3/s by slow-moving backwaters that deposit allu- vium over the bedrock. High velocities are reached only during floods exceeding about 2,900 m3/s, when the tail- race levee is overtopped. Alluvial deposits and lower frequencies of damaging floods in the plot have favored growth of larger trees than on bedrock areas of comparable elevation. Box- elder and ash exceeding 20 cm dbh were measured in 1962. The Hurricane Agnes flood (June 1972) damaged or destroyed all woody vegetation, completely removing most large trees and leaving others horizontal. Permanent plot 3 is just upstream from the tailrace and at about the same altitutde as plot 2. Flooding at plot 3 occurs at about 1,420 m3/s, and swift currents scour the bedrock. Alluvial deposits are confined to shallow depressions and other surface irregularities, and it is there that plants are growing. Most trees are shrubby and seldom exceed 8 cm dbh. This is probably due in part to the open environment and to the contin- ual breakage of aerial parts and subsequent resprouting. SPALDING FARM FLOOD PLAIN Two flood-plain plots are located about 27 km up- stream from Chain Bridge on the S. P. Spalding “Pa- towmack farm”, in northern Fairfax County, Va. The channel here is about 730 m wide and the river flows slowly over a gradient averaging only about 1 m/km between Seneca, Md., and Aqueduct Dam (just above Great Falls). The river is shallow and dotted with is- lands and occasional rifiles. Much of the flood plain in the Spalding farm study area is bordered along the channel by steep banks and hence not flooded until bankfull stage is exceeded. Alluvial soils are at least 4 m deep in some locations (Sigafoos, oral communication, 1975), and bedrock is exposed only along the edges of the main channel. I estimated crest velocity of the June 1972 flood to be about 2—3 m/s in the main channel and at lower rates at increasing distance from the low-water channel. The main-channel velocity of smaller floods, such as those cresting March 22, 1963, and March 9, 1967, was esti- mated at approximately half that of the June 1972 flood. Most woody species noted at Chain Bridge are also on the Spalding farm flood plain. Ash, boxelder, hackberry (Celtis occidentalis L.), sycamore, and elm are predom- inant, some exceeding 1 m in diamter. Less common are black walnut (Juglans m'gra L.), basswood (Tilia ame’r— icana L.), swamp white oak, swamp chestnut oak (Quercus michauxz'z' Nutt.), and Shumard oak (Quercus shumardii Buckl.). Shrubs and small trees such as spicebush and pawpaw (Asimina tm'loba (1.) Dunal) abound in the understory. The flood-plain forest borders an oak-hickory upland or ends abruptly in cultivated fields. Permanent plot 4 is on Patowmack Island, a small alluvial island near the Virginia shore about 2.3 km down- stream from the mouth of Seneca Creek. The plot and most of the island are inundated by about 2,550 m3/s. Six trees greater than 25 cm dbh were mapped in 1962, the largest a basswood 55 cm dbh. Spicebush was abun- dant in the understory. Permanent plot 5 is on the Virginia shore, opposite plot 4 and about 100 m from the channel. It is inundated at about 2,830 m3/s. Eleven trees exceeded 25 cm dbh in 1962, with a swamp white oak and a Shumard oak meas- uring 66 cm and 67 cm dbh, respectively. The understory was primarily spicebush and boxelder. Vegetation on the Spalding farm flood plain shows damage from the Hurricane Agnes flood but not to the extent noted at Chain Bridge and at many other down- stream areas. Some canopy and subcanopy sized trees were scarred or partly uprooted, although nothing com- parable to the destruction of entire flood-plain forests was observed. Some small members of the understory were damaged or killed following burial by flood debris. UPLANDS Plots 6 and 7 are in an upland forest on the Spalding farm tract and have never been flooded. Most of this forest was selectively cut-over about the time of World War I (Sigafoos, oral communication, 1975) and is pres- ently a privately owned wildlife refuge. Dominant can- opy species include white oak (Quercus alba L.), scarlet oak (Quercus coccinea Muenchh.), red oak (Quercus mbra L.), black oak (Quercus velutina Lam.), mockernut hick- ory (Cam/a, tome’ntosa Nutt.), pignut hickory (Carya glaz- bra, (Mill.) Sweet), and sour gum (Nyssa sylvatica Marsh.) Beech (Fagus grandifolia Ehrh.), tulip tree (Lim'odendmn tulipzfem L.), cherry (P'runus L.), sassa- fras (Sassqfras albidum (Nutt.) Nees), and flowering dogwood (Camus florida L.) abound in the understory. CHANGES IN WOODY VEGETATION BASAL AREA Numerous factors affect the growth and mortality of trees, and it is difficult to correlate changes in basal area solely with flooding. This study indicates that changes in basal area are most striking on frequently flooded surfaces at sites where flow velocities are high. Changes become less apparent on ground that is seldom flooded, and at sites where slower currents during high water are less likely to damage vegetation. 6 EFFECTS OF FLOODING UPON WOODY VEGETATION, POTOMAC RIVER FLOOD PLAIN Basal area measurements at upland and flood-plain locations are shown in table 2. If flood plain plots are ordered by the minimum discharge inundating their surfaces, basal area cannot be related solely to flood frequency because of differences in the channels at the two locations. As was mentioned previously, flow veloc- ities are higher at Chain Bridge than at the Spalding farm. However, basal areas at Chain Bridge increased as inundation discharge increased. For example, the 1962 basal area of plot 3 was 5.4 percent that of plot 2 and 2.8 percent that of plot 1. In 1972, the percentages were 38.6 and 3.3, respectively. This agrees with most field observations that trees at Chain Bridge are largest on infrequently flooded surfaces and progressively smaller nearer the river. Sigafoos (1961) related flood frequency to three general vegetation zones based on tree size and form near Chain Bridge. Near the Spalding plots, woody vegetation is scarce along the steep banks that separate the low-water chan- nel from the flood plain. Trees along the low-water channel are generally smaller than trees on the flood plain. However, unlike at Chain Bridge, the average size of trees of the same species seemingly does not increase on less frequently flooded portions of the flood plain. The basal area of plot 5 was nearly twice that of plot 4 after both mappings, even though both plots are in- undated during great floods for approximately the same time interval (table 1). Plot 4, located more toward mainstream, may be exposed to greater flood velocities than is plot 5. Furthermore, near plot 5 are frequently flooded stretches with less sloping banks, commonly with large trees growing near the edge of the low-water channel. In some places, large trees grow on surfaces flooded by less than 550 m3/s. These frequently flooded surfaces are exposed during floods to low velocities that deposit alluvium and rarely inflict serious damage to vegetation. Differences between 1962 and 1972 basal area meas- urements were greatest at Chain Bridge, especially in the two most frequently flooded plots. Plot 2 decreased in basal area by 80 percent, while plots 1 and 3 increased by 23 percent and 44 percent, respectively. At the Spal- ding farm, where flood velocities are not as great, plot 4 decreased by 4 percent and plot 5 increased by 14 per- cent. The basal area of the two upland plots decreased by 7 percent and 1 percent in a somewhat shorter period. Because large trees make up a greater percentage of total basal area in most of the plots, their fate has the greater influence on changes in basal area. In plot 1, for example, three large trees accounted for nearly 85 per- cent of the total 1962 basal area. Had one or more been killed between mappings, the 1972 figure would have been far less. However, each survived, and the addi- tional 10 years of radial growth accounted for an in- crease in basal area despite high mortality among many smaller trees from the Hurricane Agnes flood. Basal area will continue to depend on these three trees, and since they survived a major flood equaled or exceeded on the average once in 30 years, they are unlikely to be killed or uprooted by more common floods. Mortality is more likely from other agents, such as windthrow, dis- ease, insects, lightning, or senescence. Large fluctuations in basal area within this plot may thus be independent of flooding. On frequently flooded surfaces, however, the range in size is generally less than on infrequently flooded sur- faces, and basal area does not depend on a few large trees. Changes in stem number result in high per- centage changes in total basal area. Basal area declines when flooding destroys many stems or increases when there is a profusion of new growth. For example, all stems measured in plot 3 in 1962 had diameters less than 8 cm; thus basal areas of largest and smallest stems differed only slightly. Frequent floods and ex- treme velocities during high water have prevented the growth of large trees. Germination of seedlings and continued production of sprouts from established roots cause large percent increases in plot basal area. On in- frequently flooded surfaces, such growth has a negli- gible percent effect on total basal area. On the other hand, because stems in plot 3 are repeatedly broken off during high water, there are also large percent TABLE 2.—Basal area of woody vegetation at seven monumental plots . . Basal area Inundatlon (cubic Basal area . (square meters) Location Plot meters per second) change (percent) 1962 1972 Chain Bridge ,,,,,,,,,,,,,,,,,,, 1 2,830 1.618 1.992 +23.1 flood plain ____________________ 2 2,270 0.841 0.169 —79.9 ____________________ 3 1,420 0.045 0.065 +44.4 Spalding farm __________________ 4 2,550 1.087 1.040 —4.3 flood plain ____________________ 5 2,830 2.123 2.414 +13.7 Spalding farm __________________ 6 Never flooded 1.234 1.149 —6.9 upland1 1111111111111111111111 7 Never flooded 0.942 0.931 —1.2 ‘Upland plots were mapped in 1965. THE MONUMENTED PLOT STUDY 7 decreases. Basal area probably fluctuates significantly, being greatest after the growing season and smallest after winter or early spring floods. It thus seems probable that fluctuations in basal area at Chain Bridge are greatest on frequently flooded sur- faces and become less pronounced at higher altitutdes. Further supporting evidence is that all other study plots, including those on the Spalding farm flood plain and on the uplands, derived more than 99 percent of 1972 basal areas from continued growth of stems mapped in 1962; less than 1 percent resulted from stems which became measurable after that date. In plot 3, however, only 78.5 percent of the 1972 basal area re- sulted from originally mapped stems. The 80 percent decline in basal area at plot 2 resulted primarily from the Hurricane Agnes flood. Perturba- tion on this scale had not occurred since 1948, when most vegetation was destroyed by an ice jam (Sigafoos, 1964). The presence of trees up to 20 cm dbh and a total basal area of 0.84 m2 in 1962 suggest that even the Au- gust 1955 flood, 6,117 m3/s, did not damage vegetation as severely as did the Hurricane Agnes flood. Minor floods during 1963—1971 water years, the largest being 4,163 m3/s in March 1967, probably removed only a small number of trees; hence, just prior to the Hurricane Agnes flood, basal area was probably at least as great as at the 1962 mapping. SURVIVAL The survival and, continued growth of originally mapped plants are primarily responsible for changes in basal area. It has already been noted that survival de- pends to a great extent on the channel characteristics at a particular location and not on flood frequency and duration alone. In addition to these factors, the size and growth habits of vegetation are important. In none of the flood-plain plots, for example, did survival of plants less than 2.5 cm exceed that of larger plants; on the uplands, however, survival for both size classes was about the same. At all sites, plants with multiple stems (clumps) survived at higher rates than did single- stemmed plants. Numbers and survival percentages of plants at seven monumented plots are shown in table 3. On the uplands, 90 percent of the originally mapped plants survived in comparison with 40 percent on the five flood-plain plots. Differences in age and species composition only partly explain the lower survival at flood-plain sites. Survival of flood-plain plants ranged from 7 percent at plot 2 to 66 percent at plot 3; at plots 1, 4, and 5, which are inundated by flows exceeding 2,550 m3/s, survival was approximately half that of the uplands. Flood-plain plants with stem diameters exceeding 2.5 cm consistently survived at rates higher than did smaller plants. In plots 4 and 5, survival of plants greater than 2.5 cm compares favorably with that on the uplands; at plot 1, however, survival was about 25 per- cent lower, probably as a result of greater flow velocities at Chain Bridge. A similar trend was observed for plants less than 2.5 cm in diameter; survival on the Spalding farm flood plain exceeded that at plot 1 by about 50 percent, and on the uplands nearly 91 percent of the plants survived. Better established root systems may account for the increased survival of larger plants, while smaller plants may be more easily uprooted or buried by debris. Plots 2 and 3 represent the extremes of flood-plain survival. Vegetation at plot 2, normally sheltered by the tailrace levee just upstream, was nearly all destroyed. At plot 3 there is no sheltering effect, and flooding is even more frequent; yet this plot had the highest sur- vival percentage of any flood-plain tract. Part of the explanation may be that because frequent flooding has kept the vegetation small, trees were not battered by surface debris during the higher stages of the Hurri- cane Agnes flood. The larger trees in plot 2 were de- stroyed during higher flood stages when velocities and amounts of surface debris appeared greater. Debris TABLE 3.—Survival of plants at seven monumented plots Total number of plants Total plants Total plants <2.5 cm 22.5 cm Inundation Proportion Proportion Proportion Location Plot (cubic meters 1962 1972 surviving 1962 1972 surviving 1962 1972 surviving per second) (percent) (percent) (percent) Chain Bridge -_ 1 2,830 142 66 46.5 66 18 27.3 76 48 63.8 flood plain___ 2 2,270 226 16 7.1 90 5 5.6 136 11 8.1 ___ 3 1,420 47 31 66.0 23 13 56.5 24 18 75.0 Spalding farm _ 4 2,550 204 106 52.0 160 68 42.5 44 38 86.4 flood plain___ 5 2,830 765 336 43.9 690 275 39.9 75 61 81.3 Spalding farm _ 6 Never flooded 183 164 89.6 129 121 93.8 54 43 79.6 uplandl _____ 7 Never flooded 161 144 89.4 120 105 87.5 41 37 90.2 ' Upland plots were mapped in 1965. 8 EFFECTS OF FLOODING UPON WOODY VEGETATION, POTOMAC RIVER FLOOD PLAIN carried by flows of about 1—2 m above the surface of plot 3 possibly causes the greatest amount of stem breakage. However, velocities at such discharges were estimated at about 1.5 m/s and are unlikely to uproot plants. There were small trees at plot 2, and nearly all Were destroyed. A second factor may be the bedrock charac- ter of the flood plain above the tailrace. Because bedrock is resistant to erosion over short intervals of time, the surface probably remained essentially unchanged by flooding over the 10-year period. Due to frequent flood- ing, only those plants most firmly anchored in the bed- rock have survived. Great floods may have no greater impact on this area than more frequent floods. In plot 2, however, alluvium was severely eroded by the Hurri- cane Agnes flood, in places stripping it to the bedrock and washing away much of the vegetation. It seems likely, therefore, that the flood-plain surfaces also influence survival of vegetation. Many plants tallied in both 1962 and 1972 consisted of multiple stems. For example, of the 101 stems mapped in plot 3 in 1962, only 31 were single-stemmed plants; the remaining 70 stems comprised 16 plants. It is un- known how and to what extent this growth habit affected survival of 1962 plants. In all seven plots, how- ever, plants with multiple stems survived at higher rates than those with, single stems (table 4). THE EFFECTS OF THE HURRICANE AGNES FLOOD ALONG THE POTOMAC RIVER DOWNSTREAM FROM GREAT FALLS The effects of the Hurricane Agnes flood upon woody vegetation were observed in 1973 alonga 4- km reach of the Potomac River downstream from Great Falls(fig.2). Below the steep cataracts of the Falls, the river enters a deep and narrow gorge along a fault (US. Department of the Interior, 1970) where extremely high flow levels and velocities are reached during floods (figs. 3 and 4). Vegetation growing along the exposed rock walls of the gorge is flooded several times each year and is generally shrubby and of poor form. Sycamore, willow (Salim L.), elm, and ash are abundant. 0n higher, infrequently flooded terraces, red oak, chestnut oak (Quercus minus L.), post oak (Quercus stellata Wangenh.), mockernut hickory, pignut hickory, and Virginia pine (Pinus vir- giniana Mill.) predominate. In the lower part of the 4-km reach below Great Falls, the channel widens near Difficult Run and turns sharply to the northeast, followed closely by a sharp southeast- ern turn. Alluvium overlies the bedrock in numerous localities, supporting mixed flood-plain forests of syca- more, willow, boxelder, silver maple, river birch, and cottonwood. The four latter species are rare in the upper gorge. Specific sites in the gorge and near Difficult Run were arbitrarily chosen where damage was greatest, and in other tracts where damage was minimal. At each site, the condition of flood-plain forests was related to the flow regime during floods. At some places, ages of sur- vivors were determined. Also investigated was the abil- ity of various flood-plain and upland-terrace species to recover from damage incurred during Hurricane Agnes. Tallies of species were taken in transects of arbitrary length and in several 10-m by 10-m plots. Species that are rare on the steep bedrock in the gorge were studied on broad alluvial flood plains near Difficult Run. EFFECTS OF LOCAL SITE CHARACTERISTICS This study indicates that maximum damage to vege- tation occurred on flood plains adjoining outside bends of the main channel, where floodflow velocities appeared greatest. In these areas, large tracts of flood-plain forest were destroyed. Along the inside of channel bends, where trees were sheltered from high floodfiow velocities, damage was minor (fig. 5). This “sheltering effect” was also observed on a local scale where destruc- tion otherwise was greatest; some trees immediately downstream from rock outcrops suffered little damage even though other trees in the general vicinity were TABLE 4.—Sumival of single-stemmed and clumped plants at seven monumental plots Single-stemmed plants Clumped plants Location plot Number Number Proportion Number Number Proportion 1962 surviving, survivmg 1962 survwlng, survivmg 1972 (percent) 1972 (percent) Chain Bridge ____________ 1 139 64 46.0 3 2 66.7 flood plain _____________ 2 223 15 6.7 3 1 33.3 _____________ 3 31 20 64.5 16 11 68.8 Spalding farm ___________ 4 153 69 45.1 51 36 70.6 flood plain _____________ 5 664 270 40.7 100 66 66.0 Spalding farm ___________ 6 175 156 89.1 8 8 100 upland1 _______________ 7 153 136 88.9 8 8 100 lUpland plots were mapped in 1965. THE EFFECTS OF THE HURRICANE AGNES FLOOD DOWNSTREAM FROM GREAT FALLS 9 (—to Great Falls MARYLAND 1000 0 500 1000 METEHSV/ Contour |mervalz100 Feet APPROXIMATE SCALE g” :5 77°18 FIGURE 2.—Potomac River downstream from Great Falls showing study area. Map is enlarged from Falls Church, Va., quadrangle, 124,000. FIGURE 3.—Downstream View of the Potomac River along the upper gorge below Great Falls in November 1968. Discharge is approxi- mately 85 ma/s. Floods such as those occurring in 1936, 1937, 1942, and 1972 covered the tops of the gorge. destroyed. These findings suggest that characteristics of the main channel and flood plain, in addition to flood frequency and duration, determine many differences in composition, age, and form of flood-plain forests. Many trees were killed on a 100-m by 30-m alluvial tract (“Yellow Pond flood plain”) about 600 m east of FIGURE 4.——High water (about 4,250 ma/s) in lower study area just upstream from Diflicult Run. The water is about 6 m above summer levels. Difficult Run. The location of this area and others is shown in figure 2. Prior to Hurricane Agnes, a silver maple-ash-cottonwood forest grew on this tract just downstream from a series of high rock walls. Even dur- ing the 4,163 m3/s flood peak of March 9, 1967, inundated trees were Sheltered from main-channel velocities, and 10 EFFECTS OF FLOODING UPON WOODY VEGETATION, POTOMAC RIVER FLOOD PLAIN EXPLANATION little damage was observed (fig. 6). The Hurricane Low water channel Agnes flood, however, roared through a large gap in the rocks and swept across the downstream half of the tract, destroying all vegetation (fig. 7). In July 1973 a l::l She'le’ing 20-m by 10-m plot on this lower part supported no trees, ___ and in some areas the alluvium had been stripped to ”— ‘ F \ ~bedrock. A plot of identical size on the upstream half of the flood plain supported 20 trees. Tops of the rock walls sheltering this plot remained above the Hurricane Agnes flood, and 8 of 11 trees directly below were still living (fig. 8). Four showed little or no damage. Trees in the remainder of the upstream plot, however, grew just below a smaller wall inundated by about 5,000 m3/s, and only 3 of 9 trees survived (table 5). At the age of the main channel and adjacent to Yellow Pond flood plain is a large rock outcrop. The upstream face forms a vertical clifl' about 10 m above the river at low flow, with the downstream wall sloping steeply to an alluvial flat at its base. In 1973, this flat measured 35 m by 20 m and was inundated by approximately 1,130 m3/s. Prior to Hurricane Agnes, willow and silver ______ Flood plain limits FIGURE 5.—Representation of sheltering during floods along inner and outer channel bends. r -' , ass» «*I '3' _ ,1! ., ,. , 7 3 FIGURE 6.—The lower tract of the Yellow Pond flood plain along the Potomac River during the flood of March 9, 1967, peak flow 4,163 ma/s. Trees are sheltered from flood currents by a rock wall just upstream. View is from the Virginia shore toward the main channel, which flows from left to right. . I THE EFFECTS OF THE HURRICANE AGNES FLOOD DOWNSTREAM FROM GREAT FALLS . 11 FIGURE 7.—The lower tract of the Yellow Pond flood plain in 1975. View is from the main channel looking toward the Virginia shore. maple grew on the lower alluvium, with cottonwood, ash, and bitternut hickory (Carya cordifo’rmis (Wan- genh.) Koc) predominating on the higher alluvial sur- faces. Red oak, chestunut oak, and black locust (Robim'a pseudoacacz'a L.) grew along the downstream rock wall. Vegetation is sheltered from high velocities, pre- sumably until the entire outcrop is inundated at about 8,500 m3/s. Even at about 5,700 m3/s, when water is within about 4 m of the top of the rock, a large eddy extends immediately downstream; minor abrasion and breakage of stems may be caused by large pieces of de- bris floating in the backwash, but large trees are rarely destroyed. The Hurricane Agnes flood completely in- undated the outcrop and eroded away part of the allu- vium below (fig. 9), battering vegetation with currents estimated to exceed 9 m/s. Although the number of uprooted trees is unknown, all willows and most small trees were removed. Of those remaining, most were damaged, some so severely that they could be identified only by wood characteristics. Of 14 trees still standing in July 1973 on the downstream half of the tract, 10 were dead; 16 of 24 trees on the upstream half of the island were also dead (table 6). Of four trees directly below the highest part of the rock wall, however, a red oak and two bitternut hick- ories showed no signs of damage. A third bitternut had a broken canopy. These four trees were cored with an increment borer to determine the years of germination. Unfortunately, all trees had rotten centers and exact ages could not be obtained. The partial core showed that the largest hickory started to grow before 1890. The crown-damaged hickory could be less precisely dated because a larger part of heartwood had rotted. The hickory was at least 38 years old at the time of the 12 EFFECTS OF FLOODING UPON WOODY VEGETATION, POTOMAC RIVER FLOOD PLAIN FIGURE 8.—View of the upper tract of the Yellow Pond flood plain in 1975 and part of the rock walls just upstream. A small pond may be seen in the background at left. Note the striking difference between the upper and lower tracts of the flood plain. (See fig. 7.) hurricane Agnes flood. Three cores from different sides of the red oak trunk averaged 24 years in 70 mm. Be- cause this is only about one fourth of the total radius, the tree is probably considerably older. At least three of these sheltered trees survived great floods in 1924, 1936, 1937, and 1942 that approximated or exceeded the discharge of the Hurricane Agnes flood. The oldest hickory (and perhaps the red oak) was alive during the flood of June 2, 1889, which was approxi- mately the same magnitude as the March 1936 flood. Downstream from the Yellow Pond flood plain, the river turns sharply to the southeast. Damage was min- imal to trees on the Virginia shore (‘Madeira flood plain’) downstream from the inner bend. The gently sloping, alluvial flood plain supports a silver maple-ash- cottonwood forest; some trees reach 1 m dbh, and many grow on surfaces flooded by less than 700 m3/s. Few trees were uprooted during the Hurricane Agnes flood, and most damage was confined to minor bark abrasions and shearing of low limbs. On a GOO-m reach of Maryland shore (‘Old Angler flood plain’) along and downstream from the outer bend most trees received the major force of the flood and were partly uprooted or destroyed (figs. 10, 11, and 12). This was most striking on a 100-m reach along the up- stream part of the Old Angler flood plain. During floods of less than about 4,250 m3/s, this area is sheltered by a rock outcrop just upstream, and a silver maple- sycamore-cottonwood forest developed. Downstream from this forest the sheltering effect is gradually lost, resulting in thin alluvial deposits or exposed bedrock at most locations. In contrast to the denser forest of larger THE EFFECTS OF THE HURRICANE AGNES FLOOD DOWNSTREAM FROM GREAT FALLS 13 TABLE 5.—Summary of condition of trees still standing in July 1978 on a 20-m by 10-m plot on the Yellow Pond flood plain just downstream from the protective wall Diameter at breast height Status1 (centimeters) Species Condition2 Behind rock shelter covered by the Hurricane Agnes flood Ash 3 ___________ 15/13 S/ S 4/4 Ash ____________ 8 D Boxelder ________ . 8 D Boxelder ________ 8 S 4 Birch, river ______ — D Diameter unknown. Blue beech _______ 10 D Elm 3 ___________ 51/ 56 D/ D Possiblydead prior to Hurricane Agnes. Hickory, bitternut- _ 8 D Maple, silver ______ 31 S 1 Behind rock shelter not covered by the Hurricane Agnes flood Ash ____________ 31 S 2 Ash ____________ 20 S 1 Birch, river ______ 10 D Black locust ______ 10 S 1 Blue beech _______ 13 S 2 Blue beech _______ 8 D Blue beech _______ 5 D Tulip trees _______ 51/10 S/ S 1/1 Basswood ________ 13 S 3 Hickory, bitternut- _ 38 S 1 Oak, red _________ 10 S Cut by beavers in 1973. ‘ Status: D=Dead; S=survived. 2 Condition: 1=no or little flood damage; 2=partially uprooted; 3=horizontal; and 4=broken or heavily damaged crown. “Diameter, status, and condition for two-trunked tree. trees along the upstream reach, most vegetation on bed- rock was small and shrubby prior to Hurricane Agnes, consisting primarily of sycamore, elm, ash, and willow. Several sycamore and cottonwood reaching 60 cm dbh grew on localized stretches of thick alluvium, particu- larly near the low-water channel. The Hurricane Agnes flood heavily damaged most vegetation on bedrock and uprooted many of the larger trees; some parts overlain with thin alluvium were eroded to bedrock (fig. 13). All flood-plain trees along the upstream tract were destroyed or heavily damaged. Survival was greatest just downstream from the protective wall, but even there, trees were partly uprooted or broken along the trunk. Age determinations indicated that none of the trees were growing prior to 1944 (table 7), which strongly suggests that the forest had grown up since the last major flood (1942). On the Madeira flood plain (figs. 14 and 15), however, trees were found that had germinated prior to floods, in 1924, 1936, 1937, and 1942. Large-scale destruction apparently did not occur. As a result of the sheltering effect below the inner bend, trees have a greater range in size and age. In addition, silver maple is dominant on the alluvium laid down by reduced cur- rent flow and rare on thinner alluvium and bedrock along lower parts of Old Angler flood plain. In addition to the sheltering of large stretches of flood-plain forest, similar sheltering of smaller tracts was observed along the walls and rims of the gorge. Due to the velocity and flow levels attained by the Hurricane Agnes flood, destruction along this section was severe. In the midst of widespread damage, however, individual trees or small groups of trees immediately downstream from rock outcrops were often undamaged, particularly when the entire tree (or group) was sheltered (fig. 16). However, trees with canopies above the level of the shel- ter often were broken at some point along the trunk, commonly at altitudes approximating the top of the shelter (fig. 17). While many examples of small-tract sheltering were observed, numerous other trees growing in apparently sheltered areas were destroyed. This suggests that shel- tering decreases the probability of damage rather than entirely precludes it, although it is sometimes difficult to predict which areas will indeed provide shelter dur- ing high flows. Some flood plains just downstream from outcrops are inundated by severe backwash flows, re- sulting in destroyed or partly uprooted trees leaning heavily upstream. In some cases, deposition over roots kills trees that are undamaged by floating debris. SPECIES SURVIVAL A final consideration of the study below Great Falls concerns the survival of different species following the Hurricane Agnes flood. The poor form and sprout origin of many flood-plain trees are evidence of continued growth after numerous floods. However, observations in the summer of 1973 revealed that many damaged trees still standing after this flood died soon after the flood or within the following year. Furthermore, as the greater mortality of certain species indicates, differential sur- vival is a factor in the distribution of flood-plain species. Tallies of surviving trees do not completely describe the impact of the Hurricane Agnes flood, because the numbers and kinds of trees uprooted are unknown. Even frequently flooded trees, many of which previously had recovered from severe damage, were destroyed in great numbers as sandbars and gravel bars were com- pletely eroded by the flood. Willow and sycamore are the dominant trees on fre- quently flooded bedrock near Rocky Islands (fig. 2). Willow is most abundant along the lowest altitudes of the flood plain, often forming dense clumps, and is rare on surfaces flooded by more than about 570 m3/s. Syca- more is also common, but also grows on less frequently flooded surfaces. Transects were established at eleva- tions flooded by less than 850 m3/s along bedrock chan- nels at Rocky Islands and along the lower walls of the 14 EFFECTS OF FLOODING UPON WOODY VEGETATION, POTOMAC RIVER FLOOD PLAIN FIGURE 9.—The large rock outcrop adjacent to Yellow Pond as seen from near the Maryland shore in 1975. Note living trees just downstream (to the left) from the rock wall. Several large cottonwood trees damaged by the Hurricane Agnes flood can be seen near the middle of the alluvial island; these trees were living in 1973, but most were dead at the time of the photograph. The alluvial island stretched at least 20 m farther downstream prior to the flood. gorge just downstream. A tally of 148 willow and 236 sycamore was recorded. Of these, only 9 willow and 32 sycamore were dead, some of which may have died prior to Hurricane Agnes or succumbed to agents unrelated to flooding. Similarly, Schull (1944) found that black willow (Salim m’gra Marsh) along the Mississippi River withstood great floods that often damaged aerial parts but seldom killed roots. Other common species included in these transects were elm, ash, red osier dogwood, and black haw (Vi- burnum mnifolium L.). Most trees were small and shrubby, and nearly all showed damage from the Hurri- cane Agnes flood. In addition, mortality was greater among ash and elm than among willow and sycamore; 13 of 30 ash and 11 of 20 elm were dead. Two 100-m transects at Rocky Islands along surfaces flooded by less than 2,800 m3/s showed that despite severe damage most trees survived. An exception was one 10-m by 10-m tract where extreme deposition of unknown thickness had occurred. Seven trees still standing were dead. These included elm measuring 13, 18, and 18 cm and ash measuring 10, 20, 23, and 23 cm at dbh. Trees were partially uprooted and girdled at points along the trunk, but no sprouting was observed. Because river birch and cottonwood are rare on bed- rock, these species were investigated downstream near the Yellow Pond flood plain and on transects along nearby reaches where both species are common. It was found that trees growing in areas sheltered from high velocities during the Hurricane Agnes flood generally THE EFFECTS OF THE HURRICANE AGNES FLOOD DOWNSTREAM FROM GREAT FALLS 15 TABLE 6.——Smnmary of condition of trees still standing in July 1973 on the alluvial flat just downstream from the rock outcrop adjacent to Yellow Pond Diameter at Species breast height Status‘ Condition2 (centimeters) Downstream half of flat Maple, silver ______ 25 S 2,4 Maple, silver ______ 51 D Maple, silver ______ 25 D Maple, silver ______ 10 D Maple, silver ______ 25 D Maple, silver ______ 8 D Maple, silver3 _____ 31/10 S/ S 2,4/2,4 Cottonwood ...... 41 D Cottonwood ______ 61 S Dead at start of 1974 growing season Boxelder ________ 10 D Boxeldera ________ 5/8 D/ D Persimmon _______ 15 D Elm ____________ 15/15 S/ D 2,4 Elm3 ___________ D Diameter unknown Upstream half of flat Maple, silver3 _____ 15/25 D/ D Maple, silver ______ 20 S 2 Maple, silver ______ 51 S 2 Maple, silver ______ 13 S 2 Maple, silver3 _____ 15/20 S/ S 2/4 Cottonwood3 ______ 61/20 S/ S 1/4 Cottonwood ______ 61 S 2 Cottonwood ______ 51 S 2 Boxelder ________ 5 S 3 Elm ____________ 10 D Elm 3 ___________ 15/15 D/ D Ash ____________ 18 D Ash ____________ 10 S 2 Ash ____________ 51 S 3 Ash ____________ 13 S 4 Ash ____________ 10 S Cut by beavers in 1973 Ash ____________ 5 D Ash ____________ 5 D Ash ____________ 5 D Ash ____________ 5 D Birch, river ______ 18 D Oak, red“ ________ 61 S 1 Hickory, bitternut‘ _ 18 S 4 Hickory, bitternut“ _ 31 S 1 Hickory, bitternut“ _ 33 S 1 ‘ Status: D=dead; S=survived. 2Condition: l=no or little flood damage; 2=partially uprooted; 3=horizontal; and 4= broken or heavily damaged crown. 3 Diameter, status, and condition for two-trunked tree. ‘ Grows directly below the highest part of the rock wall. survived. For example, transects along the Madeira flood plain and parts of the Virginia shore downstream tallied 58 cottonwoods and 69 river birch. Of these, only 6 cottonwood and 12 river birch were dead. However, along reaches where many other flood-plain species sur- vived severe damage, 20 of 34 cottonwood and 18 of 23 river birch were killed. In addition, several large cotton- wood trees surviving the flood died during the 1973 or 1974 growing season. Turner (1930) similarly observed high mortality of cottonwood along the Illinois River after the 1927 flood. Trees were also tallied on surfaces that are inundated only by great floods. These high terraces were sampled on Rocky Islands at altitudes above the 6,117 m3/s flood of August 1955 and have been flooded in this century in 1924, 1936, 1937, 1942, and 1972 (fig. 18). Species greater than 2.5 cm dbh were counted on three main terraces. In addition, a 25-m transect and two plots measuring 10-m by 10-m were made at similar altitudes along parts of the Maryland shore just down- stream from Rockey Islands. Dominant species are Vir- ginia pine, post oak, and red oak; mockernut hickory, pignut hickory, black locust, and shadbush (Amelan- chier Med.) are less common. Virginia pine grows mainly on shallow alluvium flooded by more than 5,750 m3/s and was the most abun- dant species tallied. Of 218 individuals, 129 were dead and many were partly uprooted (often nearly horizon- tal) or broken off along the trunk or canopy. Most sur- vivors had minor damage, such as shearing of small stems or bark abrasions along upstream-facing trunks, and none showed adventitious sprouting. Most adjacent hardwoods, however, survived despite often severe dam- age to aerial parts and, in addition, rarely were partly uprooted. The greater proportion of uprooted pines may be due to their establishment in marginal sites where roots do not firmly anchor to underlying bedrock or to the generally shallow root systems. It thus appears that the survival of Virginia pine is precluded by damage often well tolerated by hardwood species. Post oak is rare on surfaces flooded by less than about 4,250 m3/s and, like Virginia pine, is confined to allu- vium on terraces underlain by bedrock. It is rare on surfaces that are never flooded. Red oak grows at all elevations along the Potomac River but is most abun- dant on infrequently flooded surfaces. Both species near Rocky Islands were tallied less often than was Virginia pine, and most individuals were heavily damaged. Sprouting along basal parts was common, however, and 28 of 46 post oak and 24 of 29 red oak were still living. Other species in these infrequently flooded areas in- cluded mockernut and pignut hickory, although only 18 trees were tallied. Ten were living. Black locust, shad- bush, chestnut oak, red cedar (Juniperus virginiana L.), and persimmon (Diospyros virginiana Mill.) were less common. These results are preliminary and are not an attempt to rank species by differential mortality due to flood damage. The high survival rates of bedrock flood- plain species, particularly those at frequently flooded 16 EFFECTS OF FLOODING UPON WOODY VEGETATION, POTOMAC RIVER FLOOD PLAIN ‘ 1 . 5‘: .r i! 3| H. 351 was ‘~ - .mmth .1.- FIGURE 10.—View of the flood plain forest on the upper part of Old Angler flood plain along the Potomac River during the flood of February 15, 1966, peak flow 2,512 m3/s. Trees are sheltered from main-channel velocities by a rock wall just upstream. elevations, suggest that even a great flood does not significantly alter species composition. Form of trees, however, may be highly altered by growth of new sprouts from broken trunks, resulting in aerial shoots much younger than roots. Vegetative reproduction ap- pears to be the primary manner by which new aerial stems are produced. Seedlings are locally rare on fre- quently flooded bedrock, probably due to the lack of seeds or available sites for their establishment or to mortality from flooding. On infrequently flooded surfaces, great floods may decrease numbers of individuals and alter species com- position due to site factors or different genetic toler- ances to inundation and damage. The time of year at which flooding occurs may also be important, with toler- ance probably being lowest during the growing season. The absence at lower altitudes of Virginia pine, post oak, and mockernut and pignut hickory is likely due in part to these species’ intolerance of continued flooding. The recovery of severely damaged trees in the subcan- opy may also depend on the fate of larger trees within the stand, for not only are genetic considerations im- portant in recovery but also the amount of light is often critical in sprouting of adventitious stems. SUMMARY AND CONCLUSIONS Flooding is the dominant environmental influence upon flood-plain forests of the Potomac River near Washington, DC. Because catastrophic floods are par- ticularly destructive to vegetation, such floods deter- mine the age, form, and composition of many flood-plain forests. Trees are uprooted or severely damaged during smaller floods, but the simultaneous destruction of great numbers of trees is unlikely. The variability in destruction by the Hurricane Agnes flood indicates that damage is mainly due to fac- tors other than flood discharge. Characteristics of the flood channel determine where flood velocities are greatest. Destruction was most evident near Chain Bridge and the reach below Great Falls, where maxi- mum velocities during the Hurricane Agnes flood were observed; conversely, the slower-flowing currents above SUMMARY AND CONCLUSIONS FIGURE 11—View from the middle of Old Angler flood plain looking toward main channel during low flow in 1975. Note sprouts from inclined boxelder (right) that survived the Hurricane Agnes flood. Much of the flood debris was cleared to make way for a canoe launching site. Great Falls caused relatively little damage to trees on the Spalding farm flood plain. Even below Great Falls, however, destruction was highly variable. Many forests normally sheltered during smaller floods were totally destroyed when sheltering was lost during the Hurri- cane Agnes flood. Other areas are sheltered even during the greatest. recorded floods, and widespread damage has apparently never occurred. As a result, trees in close proximity may differ strikingly in size and age depending on the shelter afforded. Similarly, the com- position of flood-plain forests may be controlled by the different abilities of species to become established on highly altered surfaces and subsequently to withstand severe mechanical damage. Flood-plain forests at many sites are destroyed by catastrophic floods, grow again, and are uprooted or killed during subsequent great floods. Understanding the rate of recurrence of these events is important in applying botanical evidence to determining past hydro- 17 FIGURE 12.—A downstream view in 1975 from the protective wall at the head of Old Angler flood plain. Survival was greatest just below the wall (foreground), where numerous sprouts have grown from buried or severely damaged trunks. logic events. Evidence may extend records of great floods or indicate recent occurrence on streams where data are unavailable. Evidence of catastrophic floods is most probably in areas where streamflow velocities are greatest and vegetation is not sheltered by obstructions or the channel geometry. TABLE 7 .—Summary of selected core data from Old Angler flood plain (upstream tract) and the Madeira flood plain along the Potmmw River Core height Tree diameter Age at onset 0f Specres (centimeters) (centimeters) 1972 growmg season (years) Old Angler’s flood plain (upstream tract) Cottonwood ______ 25 38 18 (partial core) Boxelder ________ 20 36 18 (partial core) Sycamore ________ 15 23 25 Sycamore ________ 10 23 25 Sycamore ________ stump 25 Sycamore ________ stump 25 i 1 Silver maple ______ stump 25 i 1 Silver maple ______ stump 24 Willow __________ 25 31 28 FIGURE 13.—The lower part of Old Angler flood plain 3 years after the Hurricane Agnes flood. Note the contrasting state of the Madeira flood plain on the opposite shore. TABLE 7 .—Summary of selected core data from Old Angler flood plain (upstream tract) and the Madeira flood plain along the Potomac River— Continued Core height Tree diameter Age at onset of Spec1es (centimeters) (centimeters) 1972 growmg season (years) Madeira flood plain Ash ____________ 31 56 29 Ash ____________ 46 41 92 (partial core) Ash ____________ 20 23 33 Ash ____________ 91 43 78 (partial core) Silver maple ______ 71 61 48 (partial core) Silver maple ______ 38 89 4O (partial core) FIGURE 14.—View of the Madeira (Virginia) flood plain opposite the lower portion of Old Angler flood plain. Photograph was taken in 1975 from midstream. REFERENCES CITED 19 Flooding directly or indirectly influences the distribu- tion of vegetation on flood plains. Just as upland and flood-plain forests are composed of different species, there appear to be vegetation zones on the flood plain based on some of the factors considered in this report. These zones do not represent successional stages in which flood-plain species are eventually replaced by up- land species. Zonation is undoubtedly further compli- cated by vast differences in the topography and lateral size of flood-plain surfaces. Studies are needed that re- late flooding to the distribution of flood-plain species, possibly leading to a botanical delineation of flood-plain boundaries. REFERENCES CITED Bailey, J. F., Patterson, J. L., and Paulhus, J. L. H., 1975, Hurricane Agnes Rainfall and Flood, June-July 1972; US. Geological Survey Professional Paper 924, 403 p. Bedinger, M. S., 1971, Forest species as indicators of flooding in the Lower White River Valley, Arkansas, in Geological Survey Re- search 1971: U.S. Geological Survey Professional Paper 750-C, p. C248—C253. Broadfoot, W. M., and Williston, H. L., 1973, Flooding effects on south- ern forests: Journal of Forestry, v. 71, p. 584—587. Buell, _M. F., and Wistendahl, W. A., 1955, Flood plain forests of the Raritan River: Torrey Botanical Club Bulletin, v. 82, p. 463—472. Dalrymple, T., 1960, Flood frequency, Manual of hydrology: Part III. Floodflow techniques: US. Geological Survey Water-Supply Paper 1543 A, 104 p. Darling, J. M., 1959, Floods in Maryland, magnitude and frequency: U.S. Gelogical Survey Open-File Report, 9 p. Everitt, B. L., 1968, Use of the cottonwood in an investigation of the recent history of a flood plain: American Journal of Science, v. 266, p. 417—439. Harper, H. J ., 1938, Effect of silting on tree development in the flood plain of Deep Fork of the North Canadian River in Creek 00.: Oklahoma Academy of Science Proceedings, v. 18, p. 46—49. Harrison, S. S., and Reid, J. R., 1967, A flood frequency graph based on treescar data: North Dakota Academy of Science, Proceedings, v. 21, p. 23-33. Helley, E. J ., and LaMarche, V. C., J r., 1973, Historic flood information for Northern California streams from geological and botanical evidence: US. Geological Survey Professional Paper 485-3, 16 p. Hosner, J. F., 1958, The effects of complete inundation upon seedlings of six bottomland tree species: Ecology, v. 39, p. 371-373. 1960, Relative tolerance to complete inundation of fourteen bottomland tree species: Forest Science, v. 6, p. 246-251. Hosner, J. F., and Boyce, S. G., 1962, Tolerance to water saturated soil of various bottomland hardwoods: Forest Science, v. 8, p. 180—186. Kilpatrick, F. A., and Barnes, H. H., Jr., 1964, Channel geometry of Piedmont streams as related to frequency of floods: U.S. Geolog- ical Survey Professional Paper 422-E, 10 p. Leopold, L. B., 1953, Downstream change in velocity of rivers: Ameri- can Journal of Science, v. 251, p. 606-624. Lindsey, A. A., Petty, R. 0., Sterling, D. K., and Van Asdall, W., 1961, Vegetation and the environment along the Wabash and Tip— pecanoe Rivers: Ecological Monographs, v. 31, p. 105—156. McGee, W. J ., 1891, The flood plains of rivers: Forum, v. 11, p. 221—234. Patterson, J. L., 1964, Magnitude and frequency of floods in the United States, Part VII. Lower Mississippi River basin: US. Geological Survey Water-Supply Paper 1681, 636 p. FIGURE 15.—Silver maple forest on Madeira flood plain in 1975. Many ' trees grow on surfaces flooded by less than 700 ms/s. FIGURE 16.—Sycamore growing in a shelter behind a rock wall down- stream from Great Falls in 1975. This tree is larger and of different form than trees growing in more exposed locations. Direction of current is from left to right. Discharge is about 255 ma/s. 20 EFFECTS OF F‘LOODING UPON WOODY VEGETATION, POTOMAC RIVER FLOOD PLAIN FIGURE l7.—View of several sycamore broken along the trunk during the Hurricane Agnes flood at altitudes corresponding to shelter height. Photograph was taken in 1975 and looks directly upstream from a small cove in the lower study area. REFERENCES CITED 21 Schull, C. A., 1944, Observations of general vegetational changes on a river island in the Mississippi River: American Midland Natural- ist, v. 32, p. 771—776. Sigafoos, R. S., 1961, Vegetation in relation to flood frequency and magnitude near Washington, D. C., in Geological Survey Re- search 1961: U.S. Geological Survey Professional Paper 424-C, p. 0248—250. 1964, Botanical evidence of floods and flood-plain deposition: U.S. Geological Survey Professional Paper 485-A, 35 p. Turner, L. M., 1930, The 1926-27 floods and the Illinois River Valley vegetation: Illinois State Academy of Science, Transactions, v. 22, p. 95-97. 1931, Plant succession on levees in the Illinois River Valley: Illinois State Academy of Science, Transactions, v. 24, p. 94—102. 1936, Ecological studies in the lower Illinois River Valley: Botanical Gazette, v. 97, p. 689-727. U.S. Department of the Interior, 1970, The river and the rocks: 46 p. Wistendahl, W. A., 1958, The flood plain of the Raritan River, New Jersey: Ecological Monographs, v. 28, p. 129-153. Yeager, L. E., 1949, Eflect of permanent flooding in a river-bottom timber area: Illinois Natural History Survey, Bulletin, v. 25, p. 33—65. FIGURE 18.—View from Rocky Islands looking downstream along the Potomac River in 1968. Discharge is about 850 ms/s. The main river is in the background. Upland species were tallied on high pinnacles that are rarely flooded. fl U.S. GOVERNMENT PRINTING OFFICE: I982-361-594/II3 Middle Triassic Molluscan Fossils of Biostratigraphic Significance from the Humboldt Range, Northwestern Nevada By N. J. SILBERLING and K. M. NICHOLS GEOLOGICAL SURVEY PROFESSIONAL PAPER 1207 Taxonomic and superpositional documentation of an unusually complete fauna] succession UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1982 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES G. WATT, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Co gress Cataloging in Publication Data Silberling, No an John, 1928— Middle Triass' molluscan fossils of biostratigraphic significance from the Humboldt Range, northwestern Nevada. (Geological S rvey Professional Paper 1207) Bibliography: p. 71 Supt. of Docs. No; l 19.16: 1207 l. Mollusks, Fossil. 2. Paleontology—Triassic 3. Geology, Stratigraphic—Triassic. 4. Geology—Nevada—Humboldt Range. 1. Nichols, athryn Marion, 1946— joint author. 11. Title. Ill. Series: United States. Geological Survey. Professional Paper 1207. Q8801 .564 564 80—607925 ‘ For sale by the Distribution Branch, U.S. Geological Survey i 604 South Pickett Street, Alexandria, VA 22304 CONTENTS Page Abstract ------------------------------------------------- 1 Paleontology — Continued Introduction --------------------------------------------- 1 Systematic descriptions — Continued History ---------------------------------------------- 1 Class Cephalapoda —— Continued Description of study and acknowledgments ------------- 3 Subclass Ammonoidea — Continued Stratigraphic occurrence and composition of faunas --------- 3 Genus Japonites ......................... General statement ------------------------------------ 3 Genus Gymnites ......................... Lower Anisian --------------------------------------- 4 Genus Epigymnites ----------------------- Middle Anisian -------------------------------------- 5 Genus Sturia ............................ UpperAnisian -------- 5 Genus Discoptychites ..................... Lower Ladinian -------------------------------------- 7 Genus [sculites ........................... Upper Ladinian -------------------------------------- 10 Genus Czekanowskites .................... Age and correlation --------------------------------------- 11 Genus Pseudodanubites ................... Genus Unionvillites ----------------------- Genus Lenotropites ----------------------- Genus Intomites ------------------------- Paleontology ............................................. 11 Genus Longobardites --------------------- Procedures and conventions --------------------------- 11 Genus Metadinarites --------------------- Systematic descriptions ------------------------------- 14 Genus Aplococeras ----------------------- Class Cephalopoda ------------------------------- 14 Genus Tropigastrites --------------------- Subclass Ammonoidea ------------------------ 14 Genus Tozerites .......................... Genus Sageceras ------------------------- 14 Genus Thamzmites ....................... Genus Koipatoceras ---------------------- 18 Genus Proarcestes ........................ Genus Alanites --------------------------- 19 Genus Protrachyceras ..................... Genus Ismidites -------------------------- 20 Genus Sirenites -------------------------- Genus Amphipopanoceras ----------------- 20 Genus Ussurites -------------------------- Genus Humboldtites ---------------------- 21 Genus Monophyllites --------------------- Genus Paracrochordiceras ----------------- 21 SubClass Nautiloidea ------------------------- Genus Cuccoceras ------------------------ 23 Genus Aulametacoceras ------------------- Genus Nicomedites ----------------------- 24 Genus Germanonautilus ------------------ Genus Hollandites ------------------------ 24 Genus Grypoceras ------------------------ Genus Anagymnotoceras ------------------ 25 Genus Paranautilus ---------------------- Genus Gymnotoceras --------------------- 25 Genus Michelinoceras -------------------- Genus Parafrechites ---------------------- 27 Subclass Coleoidea --------------------------- Genus Frechites -------------------------- 29 Genus Atractites ------------------------- Genus Paraceratites ---------------------- 31 Class Bivalvia ----------------------------------- Genus Eutomoceras ---------------------- 34 Genus Pteria --------------------------------- Genus Nevadites ------------------------- 36 Genus Daonella ------------------------------ Genus Hungarites ------------------------ 38 References cited ------------------------------------------ Genus Tropigymnites --------------------- 39 Index --------------------------------------------------- ILLUSTRATIONS [Plates 1—3 in pocket, 4—38 follow “Index”] PLATE 1. Geologic map of part of the Humboldt Range, Nev., showing collecting-sites A, B, and C. 2. Locality map of collecting-site A on the south side of Fossil Hill, Humboldt Range, showing fossil localities. 3. Locality map of collecting~site C on the south spur of Saurian Hill, Humboldt Range, showing fossil localities. 4. Sageceras, Koipatoceras, and Acrochordiceras. 5. Acrochordiceras and Sageceras. 6. Hollandites, ?Anagymnotoceras, Nicomedites, Thanamites?, Amphipopanoceras, and Unionvillites. 7. Gymnotoceras. 8. Gymnotoceras. 9. Gymnotoceras and Frechites. 10. Frechites. 11. Frechites and Parafrechites. III Page CONTENTS . Parafrechites. . Para/rechites. . Frechites. . Frechites and Paraceratites. . Paraceratites. . Paraceratites. Eutomoceras. . Eutomoceras, Pseudodanubites, and Czekanowskites. . Cuccoceras, Hungarites, and Intomites. . Intornites, Longobarbites, Metadinarites, and Aplococeras. . Aplococeras and Nevadites. . Nevadites. Neuadites and Protrachyceras. . Protrachyceras and Sirenites. . Tropigymnites and Tropigastrites. . Tozerites and Proarcestes. . Proarcestes, Humboldtites, Isculites, Ismidites, and Alanites. . Paracrochordiceras, Isculites, Lenotropites, and Alanites. . Isculites, Gymnites, and Sturia. . Gymnites, Aulametacoceras‘? and Epigymnites. . Monophyllites, Ussurites, Germanonautilus, Paranautilus, and Grypoceras. . Michelinoceras? and Atractites. . Atractites. . Daonella. . Daonella. . Daonella. . Daonella and Pteria? Page 1. Index map showing the Humboldt Range ....................................................................... 2 2. Photograph showing View south across South American Canyon towards Fossil Hill -------------------------------- 2 3. Photograph showing view northwest towards collecting-site A on the south side of Fossil Hill ----------------------- 6 4. Photograph showing view southeast across collecting-site C on the south spur of Saurian Hill ---------------------- 6 5. Correlation chart showing the stage and substage assignments of Middle Triassic biostratigraphic units -------------- 12 6. Frequency distributions of morphologically different variants within single species of ammonites ———————————————————— 14 7—18. Drawings of suture lines of: 7. Koipatoceras discoideus .............................................................................. 18 8. Alanites mulleri ...................................................................................... 19 9. Alanites obesus ...................................................................................... 20 10. Ismidites aff. I. marmarensis .......................................................................... 20 11. Amphipopanoceras cf. A. selwyni ...................................................................... 21 12. Humboldtites septentrionalis .......................................................................... 21 13. Acrochordiceras hyatti ................................................................................ 23 14. Acrochordiceras of. A. carolinae ....................................................................... 23 15. Cuccoceras bonaevistae ............................................................................... 24 16. Nicomedites sp. ...................................................................................... 24 17. Hollandites aff. H. voiti .............................................................................. 25 18. Frechites johnstoni ................................................................................... 31 19. Scatter diagram comparing width between ventral spines to whorl height in population samples of Nevadites ------- 37 20—23. Drawings of suture lines of: 20. Gymnites tregorum ................................................................................... 40 21. Gymnites perplanus .................................................................................. 40 22. Gymnites cf. G. humboldti ........................................................................... 40 23. Discoptychites sp. .................................................................................... 42 24. Diagrammatic cross section of Discoptychites sp. ............................................................... 42 25—26. Drawings of suture lines of: 25. Isculites meeki ....................................................................................... 43 26. Isculites tozeri ....................................................................................... 43 27. Scatter diagram comparing Isculites tozeri with I. meeki ........................................................ 44 28—43. Drawings of suture lines of: 28. Pseudodanubites halli ................................................................................ 45 29. Uniorwillites asseretoi ................................................................................ 46 30. Lenotropites caurus .................................................................................. 46 31. Intomites mctaggarti ................................................................................. 48 32. Intornites nevadanus ................................................................................. 49 33. Longobardites paruus ................................................................................. 50 TABLE CONTENTS 34. Longobardites zsigmondyi ............................................................................. 35. ?Metadinarites desertorus ............................................................................. 36. Aplococeras smithi ................................................................................... 37. Aplococeras vogdesi .................................................................................. 38. Aplococeras parvus ................................................................................... 39. Tropigastrites louderbacki ............................................................................ 40. Tozerites gemmellaroi ................................................................................ 41. Tozerites humboldtensis .............................................................................. 42. Proarcestes cf. P. balfouri ............................................................................. 43. Proarcestes gabbi .................................................................................... 44. Scatter diagram comparing shell width to diameter for Proarcestes gabbi ......................................... 45—47. Drawings of suture lines of: 45. Sirenites homfrayi ................................................................................... 46. Ussurites of. U. arthaberi ............................................................................. 47. Monophyllites cf. M. agenor .......................................................................... 48. Siphuncular structure of Atractites ............................................................................ 49. Diagrammatic sketch of the right valve of a Daonella ........................................................... TABLES 1. Stratigraphic distribution of upper Anisian ammonoids, coleoids, and Daonellas at Fossil Hill and vicinity - - - - 2. Correlation of upper Anisian and lower Ladinian localities at collecting-sites A, B, and C in the vicinity of Fossil Hill and Saurian Hill ------------------------------------------------------------------------------- 3. Triassic fossil localities in the Humboldt Range and vicinity ------------------------------------------------- 4. Morphologic comparison of longobarditinids from Nevada --------------------------------------------------- Page 10 15 47 MIDDLE TRIASSIC MOLLUSCAN FOSSILS OF BIOSTRATIGRAPHIC SIGNIFICANCE FROM THE HUMBOLDT RANGE, NORTHWESTERN NEVADA By N. J. SILBERLlNG and K. M. NICHOLS ABSTRACT Cephalopods and bivalves of the genus Daonella occur at certain levels throughout the Middle Triassic section in the Humboldt Range, northwestern Nevada. These fossiliferous strata are assigned to the Fossil Hill Member and upper member of the Prida Formation, which here forms the oldest part of the Star Peak Group. The distribution and abundance of fossils within the section is uneven, partly because of original depositional patterns within the dominantly calcareous suc- cession and partly because of diagenetic secondary dolomitization and hydrothermal metamorphism in parts of the range. Lower and middle Anisian fossil localities are restricted to the northern part of the range and are scattered, so that only three demonstrably distinct stratigraphic levels are represented. Cephalopods from these localities are characteristic of the Caurus Zone and typify the lower and upper parts of the Hyatti Zone, a new zonal unit whose faunas have affinity with those from the older parts of the Varium Zone in Canada. The upper Anisian and lowermost Ladinian, as exposed in the vicinity of Fossil Hill in the southern part of the range, are extremely fossiliferous. Cephalopod and Daonella shells form a major component of many of the limestone interbeds in the calcareous fine-grained clastic section here. Stratigraphically controlled bedrock collections representing at least 20 successive levels have been made from the Fos- sil Hill area, which is the type locality for the Rotelliformis, Meeki, and Occidentalis Zones of the upper Anisian and the Subasperum Zone of the lower Ladinian. Above the Subasperum Zone fossils are again scarce; upper Ladinian faunas representing the Daonella lommeli beds occur at only a few places in the upper member of the Prida Formation. Although unevenly fossiliferous, the succession of Middle Triassic cephalopod and Daonella faunas in the Humboldt Range is one of the most complete of any known in the world. Newly collected faunas from this succession provide the basis for revising the classic monograph on Middle Triassic marine invertebrates of North America published in 1914 by J. P. Smith and based largely on stratigraphically uncontrolled collections from the Humboldt Range. Taxonomic treatment of these collections, old and new, from the Humboldt Range provides the documentation necessary to establish this Middle Triassic succession as a biostratigraphic standard of reference. Of the 68 species of ammonites described or discussed, 4 are from the lower Anisian, 20 from the middle Anisian, 39 from the upper Anisian, 4 from the lower Ladinian, and 1 from the upper Ladinian. A few ad- ditional ammonite species from other localities in Nevada are also treated in order to clarify their morphologic characteristics and stratigraphic occurrence. Other elements in the Middle Triassic mol- luscan faunas of the Humboldt Range comprise five species of nautiloids and three of coleoids from the middle and upper Anisian parts of the section. Eight more or less stratigraphically restricted species of Daonella occur in the upper Anisian and Ladinian. INTRODUCTION HISTORY The Humboldt Range in northwestern Nevada (fig. 1) has become a classic locality for Middle Triassic paleon- tology, partly because fossils of this age are locally abun- dant and partly because the area was favored by early collectors. By good fortune the most richly fossiliferous Middle Triassic beds in the northern part of the range are closely associated with silver deposits that in 1860 caused one of the many flurries of mining excitement in western Nevada after the discovery of the Comstock Lode. Fossils found in the Humboldt Range by mining men near the boom towns of Unionville and Star City (of which little remains in Star Creek canyon) were acquired by the Geological Survey of California and described by W. M. Gabb in 1864. They were thus among the first marine invertebrates from the New World to be described from rocks of recognized Triassic age. Additional collections of Middle Triassic fossils from the Humboldt Range were made during the years 1867—69 by members of Clarence King’s US. Geological Exploration of the Fortieth Parallel. These were described by Meek (1887) in collaboration with Alpheus Hyatt who subsequently visited and collected from the Humboldt Range in 1888 in company with I. C. Russell. Middle Triassic cephalopods from the Humboldt Range were included in an intended comprehensive study of the marine invertebrate faunas of the North American Triassic by Hyatt of Harvard University and James Perrin Smith of Stanford University. This study was brought to a preliminary conclusion by Smith after Hyatt’s death and was published under the title of “Triassic cephalopod genera of America” by Hyatt and Smith in 1905. As part of this study, Smith first visited the Humboldt Range in 1902 and 1903, and he credited L. F. Dunn of Winnemucca, Nev., for directing him to the extremely rich Middle Triassic locality in the southwestern part of the range that came to be known as 1 2 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA 118°15’ 118° HUMBOLDT RANGE NORTHERN EAST RANGE x SOUTHERN (roam RANGE §KFAVRET MOUNTAINS NEw PASS RANGE 4/ 04 Canyon a5- Bloody g Canyon ifs oote and " (II/w“ "(pH/“u 6! 40° 30’ n Brown canyons i" Big Canyon 3? :— Buena Vista Unio nville Creek and Congress Canyons ottonwood Canyon Area of plate 1 9‘“ a: E fififis'L \\ 4/0wa? o 5 MILES I—fi—J 5 KILOMETERS £2 4% %° ‘II'HMJ' ""3 ’4, =\\\\\ \\\\“‘l \\\\\\\\\\|“ o “Hun/0’ 15’_ ._ ’3 5 2 QbFisher ‘\\\\«' “st g 0 i: anyon \\II—Tt "I P‘: 9% 3 s s!” T“ E S ilk“ J ‘\\\ = 1 _ 0/, Loveiock 5. § 3“»! ¢ w 3 740 WNW“ 3&1} 4’“ ”'1‘"; ’3 1‘ I)“ "I. n &”m: ’ I \\\‘ fi 4 2/ u“ *4- Q‘ t 0/ ’"1/0 In». ':. g s a, a, 0‘ ¢ 5 awe. 4. fi‘ ’Z‘J'M“: FIGURE 1.—Index map showing the location of Fossil Hill and other pertinent place names within the Humboldt Range, Nev. “Fossil Hill” (Merriam, 1908, pl. 1, fig. 1; Smith, 1914) (fig. 2). Collections from the Humboldt Range were basis for the monographic treatment of the “Middle Triassic marine invertebrate fauna of North America” published by Smith in 1914. In this publication 128 species of marine invertebrates, including 110 species of ammonites, are described or listed from Fossil Hill alone. Shortly after Smith drew attention to the richly fos- siliferous Middle Triassic localities in the Humboldt Range, large collections were made from Fossil Hill by Percy Train, a professional collector. Although, ac- cording to his associates, Smith was quite dismayed at this commercial enterprise, Train was responsible for ob— taining much of the Humboldt Range material studied by L. F. Spath (1934; 1951) at the British Museum of National History as well as the collections from the Humboldt Range to be found at many other institutions around the world. FIGURE 2.—View south across South American Canyon, Humboldt Range, towards Fossil Hill (left foreground). Saurian Hill is in right background. While extensive collections of Middle Triassic fossils were being made from the Humboldt Range, study of the geologic and stratigraphic setting of this fauna was generally neglected. Until the studies were made by Cameron (1939) in the northern part of the Humboldt Range and by Ferguson, Muller, and Roberts (1951) in the East Range, the next range east of the Humboldt Range, knowledge of the Triassic section in this part of Nevada advanced little beyond the original survey made by the geologists of the Fortieth Parallel expedition (King, 1878). As the richly fossiliferous Middle Triassic beds in the Humboldt Range are rarely more than a few tens of meters thick at any one place, and as they are part of a Triassic section obviously more than a thou- sand meters thick, it is not surprising that the early col- lectors, including Smith, tended to regard all of the fos- sils from these beds throughout the range as part of a single fauna, and little or no effort was made to segregate collections made from different stratigraphic levels. Most of the Middle Triassic fossils described by Smith (1914) from the Humboldt Range were regarded by him as representative of the “Daonella dubia zone.” He was aware of some difference in age among the faunas of this zone as shown by statements such as “the upper Anisic stage is certainly represented . . . , and the higher beds of the Daonella dubia shaly limestone may represent the lower Ladinic” (Smith, 1914, p. 7). But the faunal as- sociations listed by Smith commonly include species now known to be restricted to the middle Anisian or even in the lower Ladinian. Thus the nature of the faunal suc- cession was largely obscured, which is unfortunate because the paleontologic significance of the Middle Triassic of the Humboldt Range lies not only in its highly fossiliferous nature but in the unusually complete stratigraphic sequence of its different faunas. The succession of Anisian and lower Ladinian am- monite faunas in the Humboldt Range is, in fact, one of the most complete of any known in the world, and it STRATIGRAPHIC OCCURRENCE AND COMPOSITION OF FAUNAS 3 provides an important biostratigraphic standard of reference for rocks of this age. Moreover, the almost con- tinuously fossiliferous upper Anisian beds afford a unique opportunity for detailed study of the changes in ammonite populations through time and give con- siderable insight into the evolution and taxonomy of these fossils. DESCRIPTION OF STUDY AND ACKNOWLEDGMENTS The present study was commenced by Silberling in 1956 and carried out at various times during the late 1950’s and early 1960’s as part of a more general geologic investigation of the Humboldt Range during which the entire range was mapped in some detail by R. E. Wal- lace, E. B. Tatlock, and N. J. Silberling (Wallace, Tatlock, Silberling, and Irwin, 1969; Wallace, Silberling, Irwin, and Tatlock, 1969; Silberling and Wallace, 1967). The location and geologic setting of paleontologically significant outcrops has thus been fairly well es- tablished, but the potential of the area for further paleontologic studies is by no means exhausted. Although about two man-months of pick-and-shovel work were devoted to obtaining bedrock collections from the upper Anisian in the vicinity of Fossil Hill in the southern part of the range, still larger stratigraphically controlled population samples of some taxa would be desirable and would be essential for meaningful statistical study. In the northern part of the range the faunal record of the Middle Triassic is obscured by poor fossil preservation, and discovery of even a single favorably fossiliferous block could add importantly to the known fauna. During the course of this study much useful informa- tion and material on the Middle Triassic paleontology and stratigraphy of Canada, and on the Triassic in general, were received from E. T. Tozer and the late F. H. McLearn of the Geological Survey of Canada. Tozer visited various Triassic exposures in Nevada, including those in the Humboldt Range, in 1964 and has provided encouragement and criticism during the following years. By the mid-1960’s Silberling had organized much of the Middle Triassic material from the Humboldt Range, prepared synonymies of Smith’s numerous species, and written some taxonomic description. Nichols completed the study in 1976 while a National Research Council post-doctoral fellow at the U.S. Geological Survey. Bernhard Kummel of Harvard University aided the present study by providing helpful discussion at various times and by lending the Middle Triassic types from the Whitney collection at the Museum of Comparative Zoology. After a search for Gabb’s missing 1864 types at Harvard proved fruitless, some of them were discovered at the Academy of Natural Science of Philadelphia by Ellen J. Moore during a visit by her to that institution. To Horace G. Richards of the Philadelphia academy we are indebted for providing access to these collections and lending those of Gabb’s types that were recovered. Most of the photographic illustrations were prepared by Kenji Sakamoto of the U.S. Geological Survey. STRATIGRAPHIC OCCURRENCE AND COMPOSITION OF FAUNAS GENERAL STATEMENT Cephalopods of early Anisian, middle Anisian, late Anisian, early Ladinian, and late Ladinian age are represented in the Middle Triassic of the Humboldt Range, and bivalves of the genus Daonella are locally abundant in rocks of late Anisian and Ladinian age. However, the stratigraphic occurrence of these fossils is quite uneven. Parts of the section are much more fos- siliferous than others, and only some of the Middle Triassic faunas are found in sequence in any one part of the range. The fossiliferous Middle Triassic rocks belong to the Prida Formation, the lowest of the formations that locally constitute the Star Peak Group (Nichols and Silberling, 1977). The description of these strata in the Humboldt Range and interpretation of their paleogeo- graphic relationships by Silberling and Wallace (1969) was emended and amplified by Nichols and Silberling (1977) and needs only to be summarized here.1 Three members of the Prida Formation are recognized: a lower member that includes a basal conglomerate or sandstone overlain by a variety of impure calcareous and dolomitic rocks; a middle member, the Fossil Hill Member, which is dark-gray, commonly fossiliferous, lenticular limestone interbedded with calcareous mudstone, silt- stone, and shale; and an upper member of evenly parted, dark-gray or black, laminated, cherty limestone. Within the 5-km (kilometer) length of the Humboldt Range the relative thickness of these three members, and the total thickness of the Prida Formation, undergo pronounced changes owing partly to local relative uplift and erosion during early Anisian time and partly to a southward facies transition of the basinal carbonate rocks of the Prida with carbonate platform rocks of the largely cor- relative Augusta Mountain Formation. In total thickness the Prida Formation ranges from as little as 60 m (meters) at its southernmost exposures in the range to more than 600 m in the northern part of the range. Where the Prida was continuously deposited in the 1The stratigraphic nomenclature used for the Star Peak Group by Nichols and Silberling (1977 ) has been adopted by the Geologic Names Committee for use by the U.S. Geological Survey. 4 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA northern part of the range, the lower member is as much as 140 m thick and includes in its middle part a unit of carbonate rocks that locally is 60 m thick. At least two completely distinct ammonite faunas of Spathian (late Early Triassic) age occur at different stratigraphic levels in this carbonate unit. The higher of these faunas, which is characteristic of the Neopopanoceras haugi Zone, has sometimes been regarded as the basal zone of the Middle Triassic but is correlated by Silberling and Tozer (1968) with the uppermost Lower Triassic Keyserlingites sub- robustus Zone of Canada and Siberia. A description of this fauna is therefore not included here. The Fossil Hill Member also attains its greatest thickness of approximately 120 m in the northern part of the Humboldt Range. Here it includes beds older than those at the base of the member farther south and con— tains ammonite faunas of early, middle, and late Anisian age. Farther south in the range, south of Buena Vista Creek canyon and Unionville, the Fossil Hill Member is less than 60 m thick and contains faunas of late Anisian age only. The type section of the member is on the south side of Fossil Hill within collecting-site A (pl. 1). Here the member is about 60 m thick, but closely spaced minor faults prohibit measurement of its thickness along any single line of section. It rests with sharp contact on quartz-silty, finely crystalline, sugary dolomite at the top of the lower member, and it grades upward through 3—6 m of section into the upper member of the Prida For- mation. At site A the stratigraphically lowest molluscan fossils occur about 30 m above the base of the Fossil Hill Member. However, where intra-Prida Formation erosion was greatest in the central part of the range, as in the vicinity of the Arizona Mine about two kilometers southwest of Unionville, these same upper Anisian faunas occur within about 10 m of the base of the member. Throughout the Humboldt Range the transitional Fos- sil Hill Member—upper member contact roughly coin- cides with the Anisian-Ladinian Stage boundary. In its southernmost exposures in the range the upper member is only about 30 m thick and is of earliest Ladinian age. Farther north in the range it thickens to more than 600 m at the expense of overlying rock units of the Star Peak Group, and in its upper part it locally contains faunas of both late Ladinian (latest Middle Triassic) and probable early Kamian (earliest Late Triassic) age. Although the Panther Canyon Member of the Augusta Mountain For- mation, the Congress Canyon Formation and some of the Smelser Pass Member of the Augusta Mountain Forma- tion, in the southern part of the range are lateral facies equivalent to the upper member of the Prida Formation in the northern part of the range (Nichols and Silberling, 1977), and hence are of Middle Triassic age, no iden- tifiable ammonites or halobiid pelecypods have been found in these platform carbonate rocks. All of the Middle Triassic fossils described herein from the Humboldt Range are thus from the Fossil Hill Member and the upper member of the Prida Formation. The successive biostratigraphic units in these rocks and their age assignments, modified from the classification of the North American marine Triassic by Tozer (1967), Silberling and Tozer (1968), and Tozer (1974) are: Daonella lommeli beds --------------- late Ladinian Protrachyceras subasperum Zone --- -early Ladinian Frechites occidentalis Zone ------------ late Anisian Parafrechites meeki Zone ------------- late Anisian Gymnotoceras rotelliformis Zone ------- late Anisian Acrochordiceras hyatti Zone -------- middle Anisian Lenotropites caurus Zone ------------ early Anisian Following the convention used by most Mesozoic am- monite biostratigraphers, the names of ammonite zones, such as those listed above under the full name of their nominal index species, are generally referred to henceforth in this paper only by the trivial name of their index species. For example, where the context is clear, the name Lenotropites caurus Zone is shortened to Caurus Zone. Some of these biostratigraphic units are much better developed than others, and only the three upper Anisian zones and the lowermost Ladinian zone, as developed at localities near Fossil Hill in the southern part of the range, are stratigraphically contiguous. The others are separated by unfossiliferous beds, leaving room in the section for a number of additional biostratigraphic units of comparable scope. For example, the Balatonites shoshonensis Zone, which occurs in the Favret Forma- tion at localities farther east in northwestern Nevada, is not represented in the Humboldt Range. However, in the southern Tobin Range, about 50 km east of Fossil Hill, it has been found stratigraphically bracketed between the Hyatti and Rotelliformis Zones (Burke, 1973, p. 52) as anticipated by Silberling and Tozer (1968). LOWER ANISIAN In the Humboldt Range the oldest age-diagnostic Middle Triassic ammonites are indicative of the Caurus Zone, which has its typical development in northeastern British Columbia (Tozer, 1967; Silberling and Tozer, 1968). Listed in the order of decreasing abundance, these ammonites in the Humboldt Range are: Gymnites tregorum n. sp. Isculites meeki (Hyatt and Smith) Lenotropites caurus (McLearn) Paracrochordiceras aff. P. americanum McLearn This fauna is restricted to about a meter of beds that crop out at US. Geological Survey Mesozoic localities M2358, M2367, and M2828 along strike between Star Creek canyon and Bloody Canyon (fig. 1) where the Fos- sil Hill Member of the Prida Formation attains its STRATIGRAPHIC OCCURRENCE AND COMPOSITION OF FAUNAS 5 greatest thickness in the Humboldt Range. The part of the Fossil Hill Member beneath these fossiliferous beds varies from about 30—45 m thick. Ammonites identified as Eophyllites sp. and brachiopods assigned to “Spirigera” cf. “S.” stoliczkai Bittner occur near its base, but the few other ammonites found in this basal part of the member are not well enough preserved to be identified. Above the fossiliferous beds of the Caurus Zone, no fossils have been found in the 30—40 m of sec— tion up to the stratigraphically lowest occurrences of Hyatti Zone fossils. MIDDLE ANISIAN The name Acrochordiceras hyatti Zone is introduced here for the strata in Nevada referred to by Tozer (1974) as the “A. hyatti beds.” These strata were originally as— signed by Silberling and Tozer (1968; Silberling and Wallace, 1969) to the Varium Zone whose typical occur— rence is in northeastern British Columbia. Subse- quently, this zone in Canada was recognized as including correlatives in Nevada of both what is now termed the Hyatti Zone and the succeeding Shoshonensis Zone. In the Humboldt Range both the Hyatti Zone and the older Caurus Zone are represented only north of Buena Vista canyon. Farther south in the range, marine strata cor- responding in age to these zones are absent. A complete list of the cephalopods identified from the Hyatti Zone in the Humboldt Range includes: Koipatoceras discoideus n. sp. Alanites mulleri n. sp. A. obesus n. sp. Ismidites aff. I. marmarensis Arthaber Amphipopanoceras cf. A. selwyni (McLearn) Acrochordiceras hyatti Meek Cuccoceras bonaevistae (Hyatt and Smith) Nicomedites sp. Hollandites voiti (Oppel) ?Anagymnotoceras moderatum (McLearn) Japonites cf. J. sugriva Diener Gymnites perplanus (Meek) Isculites tozeri n. sp. Czekanowskites hayesi (McLearn) Pseudodanubites halli (Mojsisovics) Unionvillites hadleyi (Smith) U. asseretoi n. sp. Intornites mctaggarti (McLearn) 1. cf. I. nevadanus (Hyatt and Smith) Ussurites cf. U. arthaberi (Welter) Aulametacoceras? humboldtensis n. sp. Grypoceras whitneyi (Gabb) In addition, orthoconic nautiloids are common. Among the ammonites only Alanites mulleri and the species of Acrochordiceras, Cuccoceras, Gymnites, Isculites, and Intornites are fairly well represented in the available col- lections. Some of the other species listed are represented by only a single specimen. The only other shelly fossils found in the Hyatti Zone are two kinds of bivalves: “Sphaera” whitneyi Gabb and a Posidonia—like form having coarsely rugate ornamentation. Although the Hyatti Zone is the most fossiliferous part of the Triassic section in the northern part of the range, preservation of fossils is generally poor because of in- cipient metamorphism. At most places identifiable cephalopods were collected as float or else they could be obtained from only a single bed within the zone, which has a total thickness of at least 45 m. The typical expression of the Hyatti Zone is designated here as the section that includes USGS Mesozoic localities M2829 and M2830 (Silberling and Wallace, 1967; 1969, pl. 1) in the Fossil Hill Member of the Prida Formation on the east slope of Star Peak. Locality M2830 is about 60 m above the base of the Fos- sil Hill Member and about 30 In higher in the section than USGS Mesozoic locality M2828, which contains ammonites of the Caurus Zone. Compared with other more or less correlative localities in the lower part of the Hyatti Zone, locality M2830 is represented by only a few ammonites, including Alanites cf. A. mulleri, Acrochor- diceras hyatti, Cuccoceras bonaevistae, and Intornites mctaggarti. The last two species listed are especially characteristic of the lower part of the Hyatti Zone. Locality M2829 is approximately 40 In higher in the sec- tion and has yielded the following ammonites: Alanites cf. A. obesus n. sp. Acrochordiceras hyatti Meek Gymnites cf. G. perplanus (Meek) Pseudodanubites halli (Mojsisovics) Unionuillites hadleyi (Smith) U. asseretoi n. sp. Intornites cf. I. nevadanus (Hyatt and Smith) Of these, the last three listed are characteristic of the up- per part of the Hyatti Zone. In the northern Humboldt Range, where the Hyatti Zone occurs, the next higher molluscan faunas are at least 45 km stratigraphically above the Hyatti Zone within the Fossil Hill Member and are poorly represented. If any ammonites are found at all here, they are poorly preserved and generally repre- sent the Frechites neuadanus beds of the upper Anisian Meeki Zone. UPPER ANISIAN Upper Anisian cephalopod and halobiid bivalve faunas are well represented in the southern part of the Humboldt Range, where they are the oldest Middle Triassic larger invertebrate faunas found. Unlike the scattered occurrences of Anisian molluscan fossils 6 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA farther north in the Humboldt Range, at favorable localities, such as those in the vicinity of Fossil Hill and Saurian Hill (pl. 1 and fig. 2), large upper Anisian collec- tions can be obtained from bedrock at fairly closely spaced stratigraphic intervals. Large collections, mostly obtained from stratigraph- ically mixed, weathered surface debris, were made by J. P. Smith from Fossil Hill and vicinity in the early 1900’s and formed the basis for his monograph (Smith, 1914) on Middle Triassic faunas. Using stratigraphically con- trolled bedrock collections from the same area, Silber- ling (1962)‘pub1ished a preliminary taxonomic revision of the many species of ammonoids described by Smith from the upper Anisian and a tabular summary of their stratigraphic distribution. With only minor further tax- onomic revision, this succession formed the basis for the definition of the Rotelliformis, Meeki, and Occidentalis Zones by Silberling and Tozer (1968), who regarded these zones as a complete representation of the upper Anisian in North America. In the vicinity of Fossil and Saurian Hills, cephalopod and Daonella shells, more or less broken but readily identifiable, are important constituents of lenticular, thin to medium-thick, micritic limestone beds within the Fossil Hill Member of the Prida Formation. These limestone beds are irregularly interstratified with calcareous siltstone, mudstone, and shale and generally occur at 1—2 m intervals. Upper Anisian collections have been obtained from at least 20 different stratigraphic levels within a total thickness of about 25—30 m of strata. To achieve this density of stratigraphically successive samples, a total of 55 bedrock collections were made within collecting-sites A, B, and C, the locations of which are shown on plate 1. Because the fossiliferous limestone beds are laterally discontinuous, collecting from single measured sections, as at site B, proved unrewarding. At sites A and C (figs. 3 and 4) collections were randomly made across and along strike wherever fossiliferous bedrock could be found at or near the surface of the gullied, thinly soil-covered hill- sides. Stratigraphic relations between collections at each site were determined, insofar as possible, by laterally trenching certain beds from which vertical stratigraphic measurements could be made. Plates 2 and 3 are detailed plane-table maps of these sites. Stratigraphic superposition at these sites can only be directly observed for several collections at a time, owing to lateral lithologic variation and, at site A, small-scale normal faulting. Thus the overall stratigraphic distribu- tion must be obtained by correlating and combining the superpositional data that can be observed within about a dozen different groups of bedrock collections. Some ad- ditional stratigraphically restricted collections were made from isolated bedrock exposures and from single loose weathered blocks. To correlate these various collec— tions, the faunal sequence observed within the upper Anisian has been used as a local standard (Silberling, 1962). Twelve successive informal biostratigraphic units, termed “beds,” are recognized on the basis of one or more index species of ammonites. The grouping of these informally named beds within the upper Anisian zones is shown on table 1. For all of the collections made near Fossil and Saurian Hills, the superpositional relation- ships, correlations, and assignments to the biostrati- graphic units are given in table 2. The stratigraphic distribution of the upper Anisian species of ammonites, coleoids, and Daonella represented in stratigraphically controlled collections from the Fossil Hill and Saurian Hill area is plotted on table 1. Because successive population samples of some FIGURE 3.—View northwest towards collecting-site A on the south side of Fossil Hill, Humboldt Range (pl. 1). Fossil localities at this site are on the gullied slope in the center of the view. A . . ‘ l B ’ , 1.5"” i).- ' 2 é?‘.~r"f.’.m ‘~ .1 w FIGURE 4.——View southeast across collecting-site C on the south spur of Saurian Hill, Humboldt Range (pl. 1). The cluster of trees in the center of the view is within site C. STRATIGRAPHIC OCCURRENCE AND COMPOSITION OF FAUNAS 7 genera tend to show progressive changes in morphology, in some cases suggesting transitions between arbitrarily defined species, the stratigraphic ranges are plotted in the same manner used by Silberling (1962, table 1). To accommodate gradation between species, where such might exist, “the stratigraphic range of those popula- tions in which the majority of specimens fall within the arbitrarily defined morphologic limits of one species is indicated by a row of X’s. This range is then extended by plus signs to show the occurrence of specimens that typologically would belong to the same species, but are end-member variants of populations that as a whole have the morphology of a different species of the same genus.” The rationale for this procedure is discussed further in Silberling (1962, p. 158—159). Although it can be described as progressive through time, morphologic change, or the replacement of one species by another in successive stratigraphic levels, within several of the better represented families of upper Anisian ammonites from the vicinity of Fossil Hill can- not be demonstrated to be gradual, as pointed out by Silberling and Nichols (1980). This limitation applies even though population samples were obtained from stratigraphic levels as closely spaced as the occurrence and preservation of the ammonites in the section would permit. Thus the data on table 1 permissibly fit the evolutionary pattern termed “punctuated equilibrium” by Eldredge and Gould (1972) and do not necessarily demonstrate “phyletic gradualism.” The 37 species of upper Anisian ammonites listed in table 1 represent a considerable taxonomic revision of the many species described from the Fossil Hill area by Smith (1914). Of the 110 species of ammonites described or listed by Smith from this locality, 14 either are known to be other than late Anisian in age or are based on ap— parently pathologic specimens, as explained by Silber- ling (1962, p. 157—158). Of the remainder, only 5 of the species reported by Smith are not represented in the col- lections on which the present study is based. These are: Gymnites calli Smith, 1914 Ptychites evansi Smith, 1914 [probably best re- garded as a nomen dubium] Trachyceras (Anolcites) barberi Smith, 1914 Ceratites weaveri Smith, 1914 [holotype from New Pass Range, Nev.] Ceratites (Paraceratites) gabbi (Meek) of Smith [= Eudiscoceras gabbi Meek, 1877; holotype from Cottonwood Canyon, Humboldt Range] Although not found by us in the Humboldt Range, the morphologically distinctive Eudiscoceras gabbi was col- lected by the late S. W. Muller in the southern Tobin Range (at Stanford University 100. 2766) in association with ammonites of the upper Rotelliformis Zone or lower Meeki Zone. Only two or three’ kinds of ammonoids different from those described by Smith were collected during the pres- ent investigation from the upper Anisian of the Hum- boldt Range. These additional occurrences, which are not listed on table 1, include: Sturia cf. S. sansovinii Mojsisovics, 1882 [a float specimen from the Frechites nevadanus beds of the Meeki Zone or stratigraphically higher] Ptychites? sp. indet. [an immature specimen from the Parafrechites meeki beds] Discoptychites sp. [a single fragmentary specimen from the Paraceratites clarkei beds of the Rotel- liformis Zone. Possibly the same as “Ptychites” evansi Smith] In addition to the biostratigraphically useful am- monoids, coleoids, and Daonellas listed on table 1 and discussed above, four different nautiloids, Micheline- ceras? cf. M.? campanile (Mojsisovics), Germanonauti- lus furlongi Smith, Grypoceras whitneyi (Gabb), and Paranautilus smithi Kummel, and the bivalve Pteria obesus (Gabb) are described herein as part of the upper Anisian fauna of the Humboldt Range. Considering the very large amount—probably at least several tons—of paleontological material collected from the Fossil Hill area, the approximately 40 species of am- monites accounted for above most likely represent the total number of taxa of late Anisian age present at this locality. This figure, of course, is dependent on the scope of intraspecific variation accepted by us. Of this total of 40 species, as shown on table 1, the Rotelliformis, Meeki, and Occidentalis Zones have yielded, respectively, a total of 16, 15, and 14 species of ammonites, and each zone is characterized by about 10 uniquely occurring species or species having uniquely overlapping ranges. Some species of coleoids and Daonellas are also restricted in their stratigraphic ranges within the upper Anisian. The greatest diversity of ammonites collected from a single limestone layer is 9 species from USGS locality M144, which is representative of the Nevadites humboldtensis beds of the Occidentallis Zone. The average diversity of ammonite species for the 12 biostratigraphic subdivisions or “beds” of the upper Ani— sian zones is 6.8. LOWER LADINIAN The Anisian-Ladinian Stage boundary, as recognized herein, roughly coincides with the lithologic transition from the Fossil Hill Member upward into the upper' member of the Prida Formation. Compared with the Fossil Hill, which consists of calcareous siltstone, mud- stone, and shale with lenticular fossiliferous limestone interbeds, the upper member of the Prida is lithlogically more uniform. It consists mostly of laminated, regularly parted, cherty micritic limestone in which the small MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA x x n x X Wu H mama :vggfibfi mmtggwouguk X X x x x n m n X n u m £53 .5323» mmtuuxmougam x x u u WM H + X X n u n n mvon 33%: mmtggmoagak caoN X X X X WM m + n WM mmztobzmuog muxmucgofiEaO X + n n + n n mum: 38.8 33585an + X x X WM x m + u n X + x x x + x was .3933 maxmqu‘ofiEac n m + n m + m x x X X x m n m + m + m n $5: «32338: @33th X x x X x x + + X X m + m n n n X m n x x mag 33:: 3:53?qu BEN n x + m m m X x X X X X EmmE mngomkEam X X + X WM X m n + n X m x + X X X m m :53 .8: 8x Ea X + X X . B . m X X + WM X + n u .6 .c n WM H. X X X x + X x + x X x .6 m m + m m m 2.85 .EQE 833382 X X X m X m + X m .a mug matwicaEsc 3:33st ocoN X n X + X X WM .0 + n m .o mtg Qtotsx 8:?“32 335398 93.23ng x m + m .o mum: Beam mmtfigmz v .v w )MM .7 mm N N N 3N .3 .3 gsw a a a mum a u a w .9 mm wow d n 07 SJ n1 0 an I: a ,I P D. J o a o a J on Moog”mwoummwMmmmnmwmmmmmwmmmmmgmm mwmmwmwlmmmmmfimmmmmwwwwmumemwmmflm ) 3 (#0 z w. ) 1 w s 1 s a s m‘ 1. mi w L a H a H n msmm m3 m mm was mm m m. w. m my mmm w m m a. m m1 mvm 1mmmealwmwmwmqwmm.mmwmwmeummmm 1v .1. 1‘ 1, fl! ) a mmmmmwmm m lo, M a S d s . S q u.. Pa W J s 3 m . a m I\ u U,“ m‘ b. w m V fl. W M 10. SH. m. m. m. A m ( m m m u. m m w m. w Hm m. m. a s H8 9 G W .mmoqwhzooo 2:28.533 .«0 @6— uEaEmcabm 2: i2: 512.3 .55» 9:3 2: .«o 362$ 3235“ a «o $20.35.: 2: RE: 223 a mm 3.: 2852293 we 35:: Eafiwfifino Pa S: 638% 2:3 2: 8 ”:23 2:03 £133.33 35 mcwEBoam an 85:38 23 $505 mzmi min \3 mmmcfi 035 we Goa—mamm— 36315552? 3%: ammo—csficfi EabEE 9: 55:» Ga 23.50on .8 btoflufi Ba. :92? E gown—anon we await oEaEumaabm cannon @385 «o 953: mmiamw “Sunfish 8&393 “Eu 2.“: 336% 48 «622*ch ES 5383» 63398.53 23.33% Emu: \c :Egafléfin oEQEMQEumlA mqur TABLE 1.—Stratigraphic distribution of upper Anisian ammonoids, coleoids, and Daonellas at Fossil Hill and vicinity, Humboldt Range—Continued STRATIGRAPHIC OCCURRENCE AND COMPOSITION OF FAUNA (W199) WWW '0 (uapaw) guessnow 'g ‘p 'a sangsysfow 1710511013 'g ’30 '0 (331931138) yms 'a 'p 'a qnms mvayawn mzauonq EIVCHINOGISOd VGOdAOH'IEId (fiat-1w) sgsuapnaau 'V WWIS WP?!“ 'V Lupus snlmnnvp saagzamzv v 115‘ $311331;sz EIVCIIGIHLIIEILOHJIX VHGIOEI'IOO (lupus) amp'unxajn saagumfifigdg somosysfow zJMqumt '9 3° saazuwm HVGILINWAD qqyuls smamwoa gsaqguummu EWCILLIWVNVHL (was) syvuqmuaadas s31]; ploqmn H avcmnundvoaw xaew W195 3 (laddo) 111101101; '11 '30 33133::wa CEIVGLLSHOHV (was) Wmm'lod 1 (WilmS) SJW33P10‘1WW 1L (Jeqaqcuv) 10101311111133 334113201 (‘IH‘HS F'“3 3395B) gyavqxap'no] 1L Lupus smwzuoqv] sazmsnfigdou EIVCILLI Sf] ELOHcI (IanBH) squounld ‘.L '30 gsaaguwflfigdo.” ‘EIVGLLINOJVP xxxx xxxx [J Z; xxxx XXXX xxxx xxxx g, (’g’ x X XLXXXXX X X XXXX XXXXXX XXXXX XXX xx xxxx xxxxxxxxxx XXXXXXX XX XX x xxxx xxxx XXXX xxxx XXXXXX x x XXX XXX xxxx xxxx xxxx XXXX xx [J L xxx xxxxxxx XXXX xxxxxx xxxxx xxx XXX XXXX x xxx XXXX xxxxxxxx xxxxxxx xxx ++ + xxxxxxx XXXX m "6 1-: m o —D m U) .-Q m fl .3 '8 '5 g .8 0 '8 'B '13 § a.) to ‘D .Q q, .9 .G k m o 53 .3 .o .9 "E: 3 ,o '3, ._, g '8 73 E v ‘E '5 3 42 '5 0 2g 42 4-" c "3 2 m 2 .2 9 R k " ~~ $0 .9 ":3 3 w a Q ... 0 g 3 >0 0 u '3 E '3 3 '0 Q T; S a 3 v; 3 o a a = a z: a a E a :3 ‘53 a no \ -= -2 i: Q 3 3 5° 3‘ *3 Q to v; :0 a; - -... ~13 3 K.) .3 a 3 s, 2 to E s E E a =3 a -... N .... -. m a: Q Q s. k L "B "a "g ”G x g u.» 2 8 Q: w c» B G a K K .: B u o u a :3 a :3 E E 9 E L E E E m a: w a) a a 93 >1 6 U 3 a Z Z Z 2 an m in C: a. A m m Frechites occidentalis Zone Parafrechites meeki Zone Gymnotoceras rotelliformis Zone 10 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA TABLE 2.—Correlation of upper Anisian and lower Ladinian bedrock and single float-block localities at collecting-sites A, B, and C in the vicinity of Fossil Hill and Saurian Hill, Humboldt Range [ Within each vertical column of numbers, superposition of localities has been objectively determined, and stratigraphic distances in meters between localities are given where known. Vertical scale is not proportional to true stratigraphic thicknesses. Localities are described in table 3] Zone Zonal subdivision Site A Site B Site C E E % M147 M628 3 M627 : m 3.0 m Nevadites gabbi beds M146 M626 M624 i 4.0 m M623 .E .L E Nevadites furlangi beds M145 2.4 m M/Fi25 : 1 :E 4 0er 2.1 m M622 08 Neuadiles humboldtensis beds M962A M961 M144 M620 MT621 1 1‘81"] 3.7 m 5.2 m Nevadites hyalti beds M962 M14445 ft (1.8 m) I f w w 6.4 m Mp1s) Mle Pmafrechites dunni beds M968' i M167 4“? m ‘ i ' 1 M260 5.5 m 1‘ 5.5 m '3 1.2 m 1 l ‘ 8 Pamfrechites meeki beds M143 ‘ M616 M617 2 M140 1 ‘ M615 2.4 m Frechiles neuadanus beds M138 M963 M142 4.0 m M166 M612 4.3 m M614 T 18} m l 2111 m 1 l l i l l l M137 M141 M964 Ngll l, ‘ Gymnolocems blakei beds 1 1. m M610 M608 M613 1 l M 7+2 a (0.6m) i l M609 0. m Paracemtites cricki beds 1 M967 6.0 m M605+10 ft (3.0 m) M607 ‘3 7,3 m T '1 l 4.6 m ‘E 2'71 m 1 M606 g Paracemtltes uogdesi beds M136 ‘ M9676 a (2.7 m) M165 M163 3.6 m E 1 4.5; m 1,2, m l g 115'm 9 M967-15ft (4.5m) M162 M605 M136»5ft(1.5m) M139 0.6m Paraceratites clarkei beds .1 m ' Ml36-7ft(211m) M966 M965+3fl(0.9m) 0.9 m Paracerutites burckhardli beds M965 M164 'Collected as float and placed in sequence by fuunal content amount of quartz silt is evenly distributed as scattered grains or concentrated in laminae. Subordinate in- terstratified thick-bedded units of course-grained bioclastic limestone and carbonate slide breccias are the only other primary rock types in the member and are most important in the higher parts of the section (Silberling and Wallace, 1969). Locally, as in the vicinity of Fossil Hill, much of the upper member is secondarily dolomitized where it stratigraphically underlies the primary dolomite forming the Panther Canyon Member of the Augusta Mountain Formation (Nichols and Silberling, 1977). Deposition of the distinctive basinal limestone of the upper member was interpreted by Nichols and Silberling (1977) to have been relatively rapid and to reflect the development of a carbonate plat- form farther east in north-central Nevada. Along with the lithologic change from the Fossil Hill Member to the upper member of the Prida Formation, the cephalopods and Daonella shells that are so abun- dant in the Fossil Hill become scarce and then all but disappear. Only in the lowermost 10 m or so of the upper member are fossils locally well represented, and these beds that are directly above the Occidental Zone in the vicinity of Fossil Hill constitute the type Subasperum Zone of Silberling and Tozer (1968). Impressions of Daonella rieberi are locally abundant in the Subasperum Zone, but cephalopods are scarce. Stratigraphically restricted population samples that would permit tax- onomic revision and partial synonymy of the primitive species of Protrachyceras described from these rocks in the Humboldt Range could not be obtained. The species that occur together in collections made by us from the Subasperum Zone are: Protrachyceras subasperum (Meek) [along with the possibly synonymous species P. americanum (Mojsisovics) and P. lahontanum Smith] Frechites johnstoni n. sp. Epigymnites alexandrae (Smith) Daonella rieberi n. sp. Protrachyceras meeki occurs low in the upper Prida and therefore may also represent the Subasperum Zone. UPPER LADINIAN Above the Subasperum Zone the upper member of the Prida Formation is mostly unfossiliferous. Identifiable fossils, found at only a few places, usually consist of a AGE AND CORRELATION 11 single species of Daonella similar to or identical with the characteristic Alpine upper Ladinian species D. lommeli (Wissman). The most diverse upper Ladinian fauna was collected in float from the upper member in the upper part of Congress Canyon, Where the specimens of Daonella cf. D. lommeli described herein were found associated with Protrachyceras?, Proarcestes, and Hungarites. Of these ammonites, only the specimen of the Hungarites is described in order to document the occurrence of this genus in North America. It has also been reported from rocks of about the same age in the New Pass Range, Nev. (Silberling and Tozer, 1968, p. 36). From the same general locality in Congress Canyon, collections made previously by F. N. Johnston include, in addition to Daonella cf. D. lommeli, the ammonites Meginoceras cf. M. meginae McLearn, Protrachyceras cf. P. sikanianum McLearn, and Thanamites schoolerensis (McLeam), which are indicative of the Meginae Zone. Another upper Ladinian species of Daonella, D. n. sp. ex aff. D. indica Bittner, is described from Fisher Can- yon in the southern part of the Humboldt Range where it is associated with probable specimens of D. lommeli. AGE AND CORRELATION Figure 5 shows the stage and substage assignments adopted herein for the Middle Triassic biostratigraphic units recognized in Nevada and the correlation of these biostratigraphic units with those recognized in Canada. The application of stage and substage terms to the faunal succession in North America follows the clas— sification proposed by Tozer (1967) and Silberling and Tozer (1968). During the early 1960’s, when the North American classification was being formulated, little modern data were at hand to indicate how the classical Alpine stages and their subdivisions should be applied; the faunal succession in North America was known in much more detail than that in Alpine Europe where the stage names were originally defined. In recent years a rekindling of interest in Triassic biostratigraphy of the Alpine-Mediterranean region has greatly improved knowledge of the classical Middle Triassic sections. Some of the more important studies are: the age of the Avisianus Zone in the Italian Alps (Assereto, 1969), the identity of the Binodosus Zone in the northern and southern Alps (Assereto, 1971), the Anisian biostratigraphy of the island of Chios and nearby northwestern Turkey (Assereto, 1972, 1974),. the Hallstatt facies of Middle Triassic in Greece (Krystyn and Mariolakos, 1975), conodont biostratigraphy (Kozur, 1974, 1975), the unique ammonite and Daonella succession of the Grenzbitumenzone of southern Switzerland in a series of papers by Rieber (culminating in Rieber, 1973), and the type section of the Anisian in Upper Austria (Summesberger and Wagner, 1972). As a consequence of these and other studies, the faunal suc- cession of the Alpine-Mediterranean Anisian is es- pecially well established, as shown by the representative columns included in figure 5. For the most part, agree- ment exists in the correlation of ammonite faunas between North America and Alpine Europe. The place- ment of the Anisian-Ladinian Stage boundary and the choice of substage units, however, is unsettled, and typological arguments can be made for several different points of view. Presumably convention will ultimately rule among the various usages that now exist. To reiterate the argument given by Silberling and Tozer (1968, p. 12), the Anisian-Ladinian boundary in Nevada is placed below the first occurrence of primitive Protrachyceras that are characterized by having a dis- crete ventral furrow and ceratitic saddles. These fossils are known from the southern Alps low in the Buchens- tein beds, the lithologic unit associated with the first use of the stage-name Ladinian by Bittner (1892). However, at a time when the youngest faunas of the Anisian were generally regarded as those of the Trinodosus Zone, the Avisianus Zone in the southern Alps was long regarded as Ladinian in age and mistakenly placed in the zonal succession above the position of the earliest species of Protrachyceras such as P. reitzi. Consequently, even after correction of its superpositional relationships (As- sereto, 1969), an argument can still be marshalled for retaining the Avisianus Zone in the Ladinian, as ad- vocated by Kozur (1974, 1975). PALEONTOLOGY PROCEDURES AND CONVENTIONS Many of the following descriptions involve species or genera that were previously described from the Hum- boldt Range by Smith (1914). For these, complete descriptions are provided here only when the concept of Smith’s taxa has been considerably altered. Thus the present report is intended to be used in conjunction with the original monograph by Smith. In addition to primary types, Smith commonly il- lustrated several or more examples of the species he recognized. Stratigraphically controlled population sam- ples indicate that some of the paratypes or plesiotypes figured by Smith were misidentified. Each specimen figured by Smith must therefore be cited individually in the synonymies. This citation is done by linking together different figure numbers referring to the same specimen by a hyphen and separating the figure numbers of dif~ ferent specimens, where they are written in a series, by a comma. Suture lines for which the illustrations by Smith 12 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA NORTH AMERICA ALPINE EUROPE Biostrahgraphrc units Humb{oldt Range), Nev. Tobin Range, Nev. Northeastern British Columbia European Tethys this a r. k , , . 52 K . , Stages and substagas D De (Bur e 1973 p ) (Tozer,1974) ( on" 1974 1975 ) ('Silberling and Toter, 1968) Zone Substage Stage Sutherlandi Zone upper Maclearni Zone 3 Danna/la lemme/i beds Archelaus Longobard g Meginae Zone < "I __ __ E . D Poseidon Zone < _1 lower Subasperum Zone Subasperum Zone Curionii Occidentalis Zone Reitzi Chischa Zone Fassan upper . Meek: Zone Avisianus Deleeni Zone Rotolliformis zone Hotelliformis Zone Trinodosus lllyr z 5 (I) . g Shoshonensrs Zone upper Balatonicus P350" _ . ‘L’ middle upper Hyam Zone Varium Zone middle Ismidicus 2 (upper part) <2 Hyatti Zone Bithynian lower lower . Osman: lower Caurus Zone Caurus Zone Anodosum Aegean FIGURE5 (above and facing page).—Corre1ation chart showing the stage and substage assignments of Middle Triassic biostratigraphic units in the Humboldt Range and elsewhere in North America compared with biostratigraphic successions, stages, and substages re- cognized in Alpine Europe. Dashed lines indicate approximate boundaries. (1914) are adequate are not illustrated again in the pres- ent report. The terminology used herein for sutural elements of ammonites is purely descriptive and is based on the posi- tion of different elements on the mature phragmocone; it does not necessarily derive from the ontogenetic develop- ment of the elements. The abbreviations Sl, 82, and S3 refer to the first, second, and third principal saddles beginning with the most ventral one. L1, L2, and L3 refer to the principal lobes in the same fashion. Minor sutural elements located dorsally of the principal elements are termed auxiliary elements. The ventral lobe is ab- breviated VL, and the external saddle, which divides the ventral lobe in some ammonites, is abbreviated ES. Reference marks on all of the ammonite suture-line drawings are those conventionally used: the arrow points in the orad direction and marks the midline of the venter; straight lines mark the umbilical shoulder, ventro-lateral shoulder, or both; and an arcuate line marks the umbilical seam where it can be located. Ratios used to express the proportions of coiled cephalopod shells are: greatest width to diameter (W/D), width of umbilicus to diameter (U/D), and greatest width to maximum height (W/H). In reference to the proportions of a single specimen, all of the measure- ments that enter into these ratios are taken in the same plane that includes the axis of coiling. Repositories of figured specimens are abbreviated as follows: PALEONTOLOGY—PROCEDURES AND CONVENTION 13 ALPINE EUROPE Kokaeli Peninsula, Greece Grenzbitumenzone, Turkey and Chios (Krystyn and Switzerland (Assereto, 1972, 1974) Mariolakos, 1975) (Rleber, 1973) Biostratigraphic unit Substage Stage Biostrst‘igrapmc Sabotage Stage Fauna Zone Substage Stage Longobard E D < -‘ z E <( .l Protracycer- atids with F3553" ceramic Curionii Zone sutures Reitzi Zone ”Pratracyceras" Reitzi Zone Fassan . . |||vr . , Avuslanus Zone Sroppamceras w Flexoptychltes beds Danna/la elongate Polymorphus Zone "M E — — _. —— — — — —l "I" TIC/mtes < Parake/lnerites Paracerarites beds g 1: z 3 < 0, Balatonites beds Pelson Pelson 2 <2 lsmidicus Zone Bithynian Bithynian 5 . 3 Osman: Zone 3 Paracrochordiceras- A Japonires beds egean USNM—National Museum of Natural History, Washington, DC. AN SP—Academy of Natural Sciences of Philadelphia M CZ—Museum of Comparative Zoology, Harvard University Data on the occurrence of each of the species collected during the present investigation include the number of specimens obtained from each locality. For example, the entry reading “USGS Mesozoic localities M1181 (25+) and M2829 (4)” means that 4 recognizable specimens of the species were collected from locality M2829, and 25 identifiable specimens, plus additional immature or broken specimens, were obtained from locality M1181. The greatest amount of synonymizing of Smith’s species involves those from the upper Anisian of the Fos- sil Hill area where population samples illustrating the range in intraspecific morphologic variation have been obtained from stratigraphically controlled bedrock col- lections. Actual or potential intergrading variants that occur together at the same stratigraphic level are regarded here as belonging to the same species. Where stratigraphically successive population samples show a progressive shift in morphology, the cutoff between con- tiguous species is essentially arbitrary. The population sample from any particular level is assigned to that species whose arbitrarily defined morphologic scope in- cludes the mean morphologic variants of the sample (Silberling, 1962, p. 158). For some of the better represented single-bed popula- tion samples, a roughly normal frequency distribution of morphologic variants can be demonstrated simply by sorting out all of the specimens in the sample into morphotypes that range spectrally from one extreme to the other with respect to one or more characters. Figure 6 illustrates two examples of this kind of distribution. For most species, however, the number of representatives NUMBER OF SPECIMENS NUMBER OF SPECIMENS 14 40 fi 30— 20 ‘ 10 ‘— 0 MORPHOTYPES 10 B 5 O o l l l l l l r l ' A B C D E F G H | MORPHOTYPES FIGURE 6.—Frequency distributions of morphologically different variants within single species of ammonites from USGS locality M136. A, 99 specimens of Gymnotoceras rotelliformis divided among morphotypes A—G that range progressively from most compressed, delicately ornamented variants (morphotype A) to most robust, coarsely or- namented variants (morphotype G). B, 47 specimens of Paraceratites vogdesi divided among the same kind of morphotypes lettered A—I. from one stratigraphic level is inadequate to demon- strate complete intergradation, and a normal distribu- tion of morphologic variations and a reasonable range in variation within species must be assumed. Regrouping of the narrowly defined species described by Smith (1914) on the basis of stratigraphically con- trolled bedrock samples from the same general locality involves little guesswork. Problems arise where the morphology of previously named species, typologically defined from other parts of the world, is represented within the range of morphologic variation of single population-based species. In these cases, the older typological names are ignored on the basis that they represent populations of unknown morphologic range. They are names for concepts that are intrinsically dif- ferent from the species recognized here. This problem is discussed further in the description of Paraceratites MOLLUSCAN FOSSES, HUMBOLDT RANGE, NEVADA vogdesi, which as revised almost certainly includes variants having the morphology of specimens that typify species named in the last century from the Alpine Trias- s1c. All of the US. Geological Survey fossil-locality numbers to which reference is made in this report are described in table 3. The prefix “M” in these numbers denotes that they are recorded in fossil-locality registers maintained at the Menlo Park, Calif, laboratory of the US. Geological Survey. Numbers less than M1,000 are recorded in an all-purpose register; those greater than M1,000 are recorded in Mesozoic megafossil registers and these localities are properly referred to as “USGS Mesozoic localities.” SYSTEMATIC DESCRIPTIONS Class CEPHALOPODA Subclass AMMONOIDEA Order CERATITIDA Super-family HEDENSTROEMIACEAE (Waagen) Family SAGECERATIDAE Hyatt, 1900 Genus SAGECERAS Mojsisovics, 1873 Sageceras gabbi Mojsisovics, nomen dubium Plate 4, figures 1, 2 Ceratites haidingeri (Hauer) [in part]. Gabb, 1864, p. 22, pl. 5, figs. 8, 10 [not pl. 4, fig. 9 = Longobardites sp.]. Sageceras gabbi Mojsisovics, 1873, p. 71 [new name for Ceratites haidingeri (Hauer) of Gabb, 1864, pl. 5, figs. 8, 10] Hyatt and Smith, 1905, p. 97, pl. 25, figs. 1—3 [= copy of Gabb, 1864]. Smith, 1914, p. 49, pl. 6, figs. 1-3 [ = copy of Gabb, 1864]. The specimen illustrated (ANSP 30783) is thought to be the original of Gabb’s (1864) figures 8 and 10 on his plate 5. In addition to Gabb’s label, a note reading “this may be the type figured on pl. 5, f. 10 & 8” was found as- sociated with this specimen in the collections of the Academy of Natural Sciences of Philadelphia. The note is unsigned but is like others that were written by Alpheus Hyatt and accompany Gabb’s Triassic fossils at the Philadelphia Academy. The specimen, a complete phragmocone showing the final septum and beginning of the body chamber, is sheared parallel to the plane of symmetry, partly crushed, and badly eroded; it lacks the orad part of the venter, but the estimated maximum diameter of the phragmocone was about 110 mm or roughly the size indicated by Gabb for his figure 10. On Gabb’s label the locality is given simply as “Humboldt, Nev.” which agrees with the locality given by him (1864, p. 23) in his description of Goniatites haidingeri. Like other fossils described by Gabb from the Humboldt Range, this specimen is probably from the Middle Trias— sic in the vicinity of Buena Vista or Star Canyons. This specimen is specifically unrecognizable owing to its poor preservation. PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 15 TABLE 3.—Triassic fossil localities in the Humboldt Range and vicinity, north-central Nevada [Unless otherwise noted, all localities are in the Fossil Hill Member of the Prida Formation, and collections were made by N. J. Silberling, 1956—65] USGS locality Field locality Description and collector(s) M136—M146 - - - M147 ......... M162 --------- M163 ......... M164 --------- M165 ......... M166 ......... M 167 --------- M533 --------- M605—M626 - - - M627—M628 - - - M635 --------- M636 ......... M905 --------- M907 ......... M908 --------- 57—66—1 through 11 57—66—12 57—51—B102 57—51—3108 through B110 57—51—F130 57—51—B143 57—51—B163 57—51—B180 through B182 58—3 58—30—1 through 21 58—30—22, —23 None None 59—W—815 58—7 59—3 Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Stratigraphically controlled bedrock collections from collecting-site A (pl. 1) on south side of Fossil Hill between South American and Troy Canyons. Approximately 2,000 feet (600 m) NW from SE comer of sec. 19, T. 28 N., R. 35 E. Localities plotted on plate 2. Rotelliformis, Meeki, and Occidentalis Zones. Same locality as M136—M146 except from upper member of Prida Formation and Subasperum Zone. Union Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from collecting-site B (pl. 1) on west side of low hill capping first small spur south of Fossil Hill between South American and Troy Canyons. Approximately 1,200 ft (370 m) N. 80° W. from SE corner of sec. 19, T. 28 N., R. 35 E., 102 ft (31 m) stratigraphically above base of Fossil Hill Member of Prida Formation. Section complicated by faulting. Rotelliformis Zone. Same as M162 except 108—110 ft (33—33.5 m) above base of section. Rotelliformis Zone. Same as M162 except collected from a single float block at least 130 ft (40 m) above base of sec- tion. Rotelliformis Zone. Same as M162 except 143 ft (43.5 m) above base of section. Rotelliformis Zone. Same as M162 except 163 ft (50 m) above base of section. Meeki Zone. Same as M162 except 180 ft (55 m) above base of section. Meeki Zone. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from north wall of Big Canyon, 11,500 ft (350 m) N. 25° W. from BM 4964. Center of W1/2 NW 1A: sec. 14, T. 30 N., R. 34 E. Locality plotted on Wallace and others (1969). Hyatti Zone. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Stratigraphically controlled bedrock collections from collecting-site C (pl. 1) west side of south spur of Saurian Hill, north side of Troy Canyon. Approximately 4,500 ftzt200 ft (1220160 m) S. 50—55° W. from SE corner of sec. 19, T. 28 N., R. 35 E. Localities plotted on pl. 3. Rotelliformis, Meeki, and Occidentalis Zones. Same as M605—M626 except from upper member of Prida Formation. Subasperum Zone. Gilbert Creek SW Quadrangle, Augusta Mountains, Lander County, Nev. Wildhorse quicksilver district. Float collections 3,000 ft (915 m) NW of Wildhorse Mine on north side of Wildhorse Mine road and then north along strike about 1,000 ft (300 m). Shoshonensis Zone. Cain Mountain Quadrangle, Augusta Mountains, Pershing County, Nev. Float collections from high on north wall of Favret Canyon just below Tertiary volcanic rocks and about 2 mi (miles) (3.2 km) from mouth of canyon. NEW sec. 12, T. 25 N., R. 39E. Fossil Hill Member of Favret Formation. Upper Anisian beds. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection 0.75 mi (1.2 km) south of Indian Creek in gulch bottom, 600 ft (185 m) SE of center sec. 24, T. 29 N., R. 34 E. Upper member of Prida Formation. Subasperum Zone. Collected by R. E. Wallace and D. B. Tatlock, 1959. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from drainage bed of northwest tributary to Congress Canyon. Approximately 700 ft (210 In) due west of center sec. 16, T. 30 N., R. 34 E., and along strike at elevation 7,000 ft (2140 m). Upper member of Prida Formation. Locality plotted on Wallace and others (1969). Daonella lommeli beds. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from divide between heads of Peru and Jackson Canyons. Approximately 10,200 ft (3100 m) N. 71° E. from VABM 8882 in center of 81/2 sec. 34, T. 30 N., R. 34 E. Upper member of Prida Forma- tion. Locality plotted on Wallace and others (1969). Subasperum Zone. 16 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA TABLE 3.—Triassic fossil localities in the Humboldt Range and vicinity, north-central N evada—Continued Description and collector(s) USGS locality Field locality M909 ......... 59—7 M911 ......... 5435 M957 --------- 60—1 M958 --------- 60—1+3 ft M959 --------- 60—1+12 ft M960—M967 - — > 57—66—13 through 20 M968 ......... 57—66 M969 --------- None M970 --------- None M1124 ———————— 58—2 M1180 ........ 58—8 M 1 181 -------- 57—71 M 1182 -------- 61-2 1A M1183 -------- 61—21 B M 1 184 -------- 61— 21 C M1185 -------- 57—5 M 2358 -------- 648—41 1 M2359 -------- 648-412 Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from Jackson Canyon, along road to Wheeler and Cottonwood Mines, approximately 400 ft (125 m) north of Wheeler Mine. South center sec. 34, T. 30 N., R. 34 E. Locality plotted on Wallace and others (1969). Occidentalis Zone. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from north wall of American Canyon. Approximately 11,350 ft (3450 m) N. 13° W. from Saurian Hill (elevation-point 5852). Locality plotted on Wallace and others (1969). Subasperum Zone. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from west side of south spur of Saurian Hill. Immediately north of collecting-site C (pl. 3). Meeki Zone. Same as M957 except 3 ft (0.9 m) stratigraphically higher. Same as M957 except 12 ft (3.7 m) stratigraphically higher. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Stratigraphically controlled bedrock collections from collecting-site A (pl. 1) on south side of Fossil Hill between South American and Troy Canyons. Approximately 2,000 ft (600 m) NW from SE corner sec. 19, T. 28 N., R. 35 E. Localities plotted on pl. 2. Rotelliformis, Meeki, and Occidentalis Zones. Same locality as M960—M967 except single float-block collection. Meeki Zone. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Float collection from north side of Congress Canyon, approximately 30 ft (9 m) above canyon bottom and 70 ft (22 m) above base of Fossil Hill Member of Prida Formation. NW ‘4 SE 14 sec. 16, T. 30 N., R. 34 E. Locality plotted on Wallace and others (1969). Hyatti Zone. Float collection from same locality as M969 except approximately 140 ft (43 In) above base of Fossil Hill Member of Prida Formation. Hyatti Zone. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Float collection from divide between Big and Coyote Canyons. SEWSElANWMl sec. 14, T. 30 N., R. 34 E. Hyatti Zone. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from crest of divide between Congress and Big Canyons. Center N1/2SW ‘4 sec. 15, T. 30 N., R. 34 E. Locality plotted on Wallace and others (1969). Hyatti Zone. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from north side of John Brown Canyon. NW%SE%SE% sec. 16, T. 30 N., R. 34 E. Locality plotted on Wallace and others (1969). Hyatti Zone. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Single float-block collection from crest of divide between main forks of Congress Canyon. South-central WVzSEW SW14 sec. 16, T. 30 N., R. 34 E. Hyatti Zone. Same locality as M1182. Single float-block collection. Hyatti Zone. Same locality as M1182. Single float-block collection. Hyatti Zone. Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Float collection from Congress Canyon. Center SE14 sec. 16, T. 30 N., R. 34 E. Hyatti Zone. Imlay Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from crest of intermediate spur between Star and Bloody Canyons, near range front. Approximately 150 ft (45 m) stratigraphically above base of Fossil Hill Member of Prida Formation. Center E1/2 NWIA sec. 26, T. 31 N., R. 34 E., 11,900 ft (3,620 In) N. 70.5° E. from VABM 9834 (Star Peak). Locality plotted on Silberling and Wallace (1967). Caurus Zone. Imlay Quadrangle, Humboldt Range, Pershing County, Nev. Single float-block collection from crest of intermediate spur between Star and Bloody Canyons. Center W1/2E1/2NW% sec. 26, T. 31 N., R. 34 E., at approximately 11,750 ft (3,580 m) N. 70° E. from VABM 9834 (Star Peak) and 95 ft (29 m) above M2358. Hyatti Zone. PALEONTOLO GY—SYSTEMATIC DESCRIPTIONS 17 TABLE 3.—Triassic fossil localities in the Humboldt Range and vicinity, north-central Nevada—Continued USGS locality Field locality Description and collector(s) M2362 -------- 64S—422 Imlay Quadrangle, Humboldt Range, Pershing County, Nev. Float collection from crest of divide north of Coyote Canyon near range front. SE1/4NE1/4NW1A sec. 2, T. 30 N., R. 34 E. Caurus Zone. M2367 -------- 648—434 Imlay Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collect/on from crest of divide south of Star Canyon. Same as bed M2358 except approximately 1,000 ft (300 m) farther north along strike. Caurus Zone. M2369 -------- 648—436 Imlay Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from crest of divide south to Star Canyon. Approximately 130—135 ft (395—41 In) stratigraphically above M2367. NWIA sec. 26, T. 31 N., R. 34 E. Locality plotted on Silberling and Wallace (1967). Hyatti Zone. M2819 -------- 658—412 Imlay Quadrangle, Humboldt Range, Pershing County, Nev. Float collection from Star Can- yon, approximately 0.4 mi (0.65 km) south of Sheba Mine. Center W1/28E%SW 1/4 sec. 22, T. 31 N., R. 34, E. Locality plotted on Silberling and Wallace (1967). Hyatti Zone. M2821 -------- 65S—423 Imlay Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from crest of spur north of Star Canyon, 245 ft (75 m) above base of Fossil Hill Member of Prida Formation. Center of south boundary of sec. 14, T. 31 N., R. 34 E. Hyatti Zone. M2826 -------- 658—461 Imlay Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from crest of spur on south side of divide between Coyote and Bloody Canyons. Center S WSE‘ASEIA sec. 34, T. 31 N. R. 34 E. Locality plotted on Silberling and Wallace (1967). Hyatti Zone. M2828 -------- 658—463 Imlay Quadrangle, Humboldt Range, Pershing County, Nev. Float collection from Bloody Canyon approximately 0.25 mi (0.4 km) west of Bloody Canyon Mine and 100 ft (30 m) above base of Fossil Hill Member of Prida Formation. Center N1/2SE‘ANE14 sec. 34, T. 31N., R. 34 E. Caurus Zone. M2829 -------- 65S—464 Imlay Quadrangle, Humboldt Range, Pershing County, Nev. Float collection from crest of divide between Coyote and Bloody Canyons approximately 0.3 mi (0.5 km) SW of Bloody Can- yon Mine. Center NVzNE‘ASE‘A, sec. 34, T. 31 N., R. 34 E. Hyatti Zone. M2830 -------- 658—465 Imlay Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from crest of divide between Coyote and Bloody Canyons approximately 0.3 mi (0.5 km) SW of Bloody Can- yon Mine. NEWNEl/i SE%, sec. 34, T. 31 N., R. 34 E. Locality plotted on Silberling and Wal- lace (1967). Hyatti Zone. M2836 -------- 658—484 Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from crest of spur SE of John Brown Canyon approximately 0.5 mi (0.8 km) south of its mouth. SWWSW‘ANEIASW‘A sec. 11, T. 30 N., R. 34 E. Locality plotted on Wallace and others (1969). Hyatti Zone. M3093 -------- 58—30A Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Float block from near M627 on west side of ridge south of peak of Saurian Hill. Upper member of Prida Formation. Subasperum Zone. M3094 -------- 57—32 Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection approx- imately 0.5 mi (0.8 km) east of Fossil Hill. Center E1/2SE1A sec. 19, T. 28 N., R. 35 E. Upper member of Prida Formation. Locality plotted on Wallace and others (1969). Subasperum Zone. M3095 -------- 56—90X Buffalo Mountain Quadrangle, Humboldt Range, Pershing County, Nev. Float from upper- most part of upper member of Prida Formation from south wall of Fisher Canyon approx- imately 80 ft (24 m) stratigraphically below base of Augusta Mountain Formation. 1,000 ft (300 m) south of NE corner sec. 12, T. 27 N., R. 34 E. M5481 -------- None Unionville Quadrangle, Humboldt Range, Pershing County, Nev. Bedrock collection from “1,000 ft [300 m] west of Arizona Mine, Unionville district.” Upper member of Prida Forma- tion. Subasperum Zone. Collected by F. N. Johnson, 1932. 18 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA Sageceras walteri Mojsisovics Plate 5, figures 10—12 Sageceras walteri Mojsisovics, 1882, p. 187, pl. 53, figs. 9a—9c [holotype], 11a—11b?, 12a—12b?, 13? Spath, 1934, p. 56, 58—59. Sageceras gabbi Mojsisovics. Hyatt and Smith, 1905, pl. 74, figs. 8—9; pl. 75, figs. 14—15. Smith, 1914, pl. 11, figs. 8—9; pl. 12, figs. 14—15; pl. 21, figs. 18—20. Silberling, 1962, p. 156. This species occurs sporadically through most or all of the upper Anisian in the vicinity of Fossil Hill. The stratigraphically lowest specimen collected from bedrock is from the Paraceratites vogdesi beds of the Rotel- liformis Zone, and the highest specimen was found as float derived from the Occidentalis Zone or higher. The better preserved specimens from the upper Ani— sian of Fossil Hill described and illustrated as S. gabbi Mojsisovics by Hyatt and Smith (1905) and Smith (1914) are from the same general locality and perhaps from the same part of the stratigraphic section as the specimens on which Gabb based the concept that Mojsisovics named S. gab bi. S. gab bi is suppressed here as a nomen dubium and the specimens of Sageceras from the Middle Triassic of the Humboldt Range are assigned to the Alpine Middle Triassic species S. walteri Mojsisovics. Some Nevada specimens were assigned to S. walteri by Spath (1934, p. 56, 59) despite the priority of the name S. gabbi. The separation of Middle Triassic forms assigned here to S. walteri from the typically Upper Triassic S. haidingerii (Hauer, 1847) is a further problem. As pointed out by Spath (1934, p. 58—60), the latter species seems to be distinguished by a wider umbilicus with an abrupt umbilical rim bordered by a spiral depression, but these differences have not been positively demonstrated. Figured specimen.—Plesiotype, USNM 248641. 0ccurrence.——USGS localities M965 (1), Paraceratites burckhardti beds; M139 (1), Paraceratites clarkei beds; M607 (3), Paraceratites cricki beds, Rotelliformis Zone; M963 (1), Parafrechites meeki beds; M618 (1) Para- frechites dunni beds, Meeki Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Super-family DINARITACEAE (Mojsisovics, 1882) Family DINARITIDAE Subfal'nily DINARITINAE Genus KOIPATOCERAS, n. gen. Type species.—Koipatoceras discoideus n. sp. Definition—Typically small shells; evolute, com- pressed discoidal in shape with narrow, sharply truncate venter. Smooth or with traces of falcoid ribbing on flanks and at ventral-lateral shoulder. Suture subammonitic; VL shallow, L1 pronounced; only two lateral lobes. Discussion.-—Though only three specimens from the Hyatti Zone serve as the basis for this new genus and species, they embody a unique combination of shell characters that sets them apart from any other known Middle Triassic ammonites. The discoidal shape, trun- cate venter, and simple suture pattern of Koipatoceras suggests relationship with the Spathian genus Stacheites Kittl, which is included in the subfamily Dinaritinae by Tozer (1971). As compared with the type species of S tachei tes from Yugoslavia and with Stacheites from the Prohungarites and Subcolumbites beds of Nevada, Koipatoceras, as presently known, is more evolute, more ornate, and has a more coarsely subdivided suture. The name of this new genus is derived from “Koipato,” a transliteration of the Piute Indian name for the Humboldt Range (King, 1878, p. 269). Koipatoceras discoideus n. sp. Plate 4, figures 3—10; text-figure 7 The general characters of this species are those that define the genus. Only three specimens were collected, probably all from the same bed, but these illustrate dif- ferent stages of variation in strength of ornamentation, which is inversely proportional to the whorl compression. The holotype, the largest of the specimens and having a greatest diameter of 24 mm, is the most compressed (W/D about 0.20) and is ornamented only by weak radial folds on the flanks. Its truncate venter is slightly concave between sharp, ridgelike ventral-lateral margins. On the two paratypes, ribbing is marked by sinuous swellings or bullae on the lower flank and by serrations of the ventral lateral shoulder, which have the form of alternating clavi on the more coarsely ornamented of the two. FIGURE 7.—Suture line (X 5) of Koipatoceras discoideus n. sp. Holotype, USNM 248631. The abbreviated external suture line of this species, which has only two lateral lobes and saddles, may be a consequence of the evolute coiling (U/D of holotype 0.31) and whorl height, which is relatively low considering the compressed shape of the shell. Both lateral saddles are PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 19 weakly crenulate with a few pronounced crenulations on the ventrad side of S1; the lobes are coarsely digitate, and the depth of L1 is about twice that of L2. The broad, shallow ventral lobe is only about one-fourth the depth of L1 and is divided into two points by a low ventral saddle. Figured specimens.—Holotype, USNM 248631; paratypes, USNM 248629 and 248630. Occurrence.—USGS Mesozoic localities M1180 (1) and M1184 (2); Hyatti Zone on ridge between Congress and Big Canyons, Humboldt Range, Nev. Subfamily KHVALYNITINAE Shevyrev, 1968 Genus ALANITES Shevyrev, 1968 Alanites mulleri n. sp. Plate 29, figures 31—35; text-figure 8 Dagnoceratid, n. gen., n. sp. A. Silberling and Wallace, 1969, p. 17, table 1. Description—Compressed (W/D 0.30—0.35 at D > 15 mm); moderately involute (U/D 0.16—0.18). Maximum size exceeding 70 mm. Flanks flattened; parallel on inner whorls; convergent ventrally from abrupt, narrowly rounded umbilical shoulders on outer whorls. Umbilical margin slightly flaring on body chamber. Venter broadly rounded, delimited from flanks by narrowly rounded ventro- lateral shoulders. Width of venter about 0.15 of shell diameter. Umbilical wall roughly perpendicular to flanks. Ornamentation varies from falcoid growth striae of ir- regular strength to blunt, foldlike falcoid ribs that are most prominent on lower flanks. Closely spaced (about 3/mm) fine strigae on outer shell surface of mature shell. Suture as for the genus; details of secondary subdivi- sion variable; 81 and S2 of about equal size, asym- metrically triangular in gross shape on inner whorls, becoming rounded and elongate (about twice as long as wide) on outer whorls (fig. 8). Discussion.—The holotype, having a maximum preserved diameter of about 70 mm, is the largest specimen and is septate to an estimated diameter of about 40 mm. This species differs from A. obesus primarily in its much less robust whorl proportions. From the same loose block from which the type specimens of this species were collected, one small specimen having the same external form and ornamentation has a much more advanced suture as illustrated in figure 8D and in this way resem- bles typical Ismidites rather than Alanites. Alanites mulleri is named in honor of the late Prof. Siemon W. Muller of Stanford University. Figured specimens.—Holotype, USNM 248903; paratypes, USNM 248901 and 248902. Occurrence.—USGS localities M533 (3?), M969 (1); Mesozoic localities M1181 (1?), M2359 (50+; mostly small specimens), M2830 (1?), Hyatti Zone, north- eastern part of Humboldt Range, Nev. an NW9) FIGURE 8.—-Sutures lines (X 3) of Alanites mulleri n. sp. A, paratype, USNM 248902. B, paratype, USNM 248901. C, holotype, USNM 248903, dotted where inferred. D, paratype, USNM 248963, specimen not figured. Alanites obesus n. sp. Plate 28, figures 21—25; text-figure 9 Description—Thick discoidal (W/D 0.5—0.6); moderately evolute (U/D about 0.2). Maximum size ex- ceeding 100 mm. Inner whorls subquadrate; outer whorls compressed subtrapezoidal. Flanks flattened, becoming concave near raised, narrowly rounded umbilical margin. Um- bilical wall approximately perpendicular to adjacent part of flank. Venter broadly rounded, about equal in 20 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA width to whorl height on inner whorls, becoming relatively narrow (about 0.5 of whorl height at a diameter of 100 mm) with increasing shell size. Ventro- lateral shoulders on inner whorls abrupt, with low, rounded carina; on outer whorls narrowly rounded. Weak foldlike ribs, swollen on lower flanks and at ventro-lateral shoulders at diameters of 25~30 mm on holotype. Traces of strigation impressed on internal mold. Suture as for the genus; at a height of 10 mm on the holotype S1 and S2 bluntly rounded in general shape; subammonitic with relatively large-scale subdivisions on the ventral side of S1. Discussion—The above description is based on only two specimens, both internal molds, whose maximum diameters are about 30 and 100 mm. Though similar in most respects to A. mulleri, the much broader whorls of these specimens justify establishing a separate species for them. The larger specimen is septate to an estimated diameter of about 50 mm; its suture (not illustrated) could be only partly exposed, but, in agreement with that of the smaller holotype, the width of its lanceolate lateral lobe is about 0.4 of the whorl height. Another specimen, 22 mm in diameter, from USGS Mesozoic locality M2829 in the upper part of the Hyatti Zone near Bloody Canyon (Silberling and Wallace, 1969) may belong to this species with which it agrees closely in shape and proportions but from which it differs in having much stronger ornamentation consisting of regular falcoid ribs that are swollen on the lower flanks and enlarged into blunt tubercles on the ventro-lateral shoulders. Figured specimens.—Holotype, paratype, USNM 248886. 0ccurrence.—USGS locality M533 (2); USGS Mesozoic locality M2829 (1); Hyatti Zone, Humboldt Range, Nev. USNM 248885; FIGURE 9.—Suture line (X 3) of Alanites obesus n. sp. Holotype, USNM 248885. Genus ISMIDITES Arthaber, 1915 Ismidites aft. I. marmarensis Arthaber Plate 28, figures 19—20; text—figure 10 aff. Ismidites marmarensis Arthaber, 1915, p. 185, pl. 15, figs. loa—c. The whorl shape and suture of a somewhat eroded specimen having a maximum preserved diameter of 49 mm, from the upper part of the Hyatti Zone at USGS locality M970 is more likely that of Ismidites mar- marensis as described and illustrated by Arthaber than that of the apparently closely related new species of Alanites described here. Like I. marmarensis, the rounded venter of this specimen grades evenly into the flanks without abrupt change in curvature, and its um- bilicus, which is sharply set off from the flanks, is relatively narrow (U/D 0.12). Its suture (fig. 10), though similar to that of A. mulleri, differs in having the tip of its first lateral saddle drawn out into an elongated pro- jection which is one-half or less the width of the second saddle. Perhaps owing to the eroded nature of the shell, the peculiar proportions of its first lateral saddles are not, however, as extreme as those typical of I. mar- marensis. Figured specimen—Plesiotype, USNM 248884. Occurrence—USGS locality M970 (1), upper Hyatti Zone, northwestern part of the Humboldt Range, Nev. ' W FIGURE 10.—Suture line (X 3) of Ismidites aff. I. marmarensis Arthaber. Plesiotype, USNM 248884. Super-family MEGAPHYLLITACEAE (Mojslsovics, 1896) Family PARAPOPANOCERATIDAE Tozer, 1971 Genus AMPHIPOPANOCERAS Voinova, 1947 Amphipopanoceras selwyni (McLearn) Parapopanoceras selwyni McLearn, 1948, p. 1, pl. 9, figs. 7—9. Parapopanoceras testa McLearn. McLearn, 1969, p. 46, pl. 9, figs. 1, 2 (only). Amphipopanoceras cf. A. selwyni (McLearn) Plate 6, figures 15, 16; text-figure 11 Only one specimen of a parapopanoceratid has been discovered in the Middle Triassic of the Humboldt Range. The recognition of the species A. selwyni, the species to which this specimen is compared, and its in- clusion in the genus Amphipopanoceras follows E. T. Tozer (written commun. 1974). Figured specimen—Plesiotype, USNM 248648. Occurrence—USGS Mesozoic locality M2829 (1); up- PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 21 ”mm ( FIGURE 11.—Suture line (X 4) of Amphipopanoceras cf. A. selwyni (McLearn). Plesiotype, USNM 248648. per part of Hyatti Zone on the divide between Coyote and Bloody Canyons, Humboldt Range, Nev. Family MEGAPHYLLITIDAE Mojsisovics, 1896 Genus HUMBOLDTITE S, n. gen. Type species.——Megaphyllites septentrionalis Smith, 1914. Diagnosis.—Involute; inner whorls robust, sub- quadrate in outline; outer whorls thick discoidal with flattened parallel flanks and arched venter. Inner whorls smooth except for delicate radial striae; outer whorl or- namented by radial constrictions and ridges of uneven spacing and strength. Suture ammonitic with six or more lateral lobes forming a slightly retracted series; saddles progressively decrease in height inwards; principal sad- dles elongate, tend to be constricted at their bases, crenulate or digitate throughout with no second and third order subdivisions. Discussion.——The single species for which this genus is established was originally included in Megaphyllites, but, as noted by Spath (1951, p. 139), it differs from typical members of that genus in having a more am- monitic suture with crenulate rather than monophylletic terminations of the saddles. The suture of Hum boldtites also differs from that of the other genera included in the Megaphyllitacea like Parapopanoceras and Neopopano- ceras, which are characterized by simple phylloid sad- dles. Nevertheless, in the general shape of its saddles and pattern of its suture, H umboldtites is more like the megaphyllitids than any of the arcestacids, and it is therefore included in the Megaphyllitidae. Humboldtltes septentrionalis (Smith) Plate 28, figures 3—9; text-figure 12 Megaphyllites septentrionalis Smith, 1914, p. 42, pl. 21, figs. 4—5 [holotype], 6, 7—9, 10—12. “Megaphyllites” septentrionalis Smith. Silberling, 1962, p. 157. To the general generic diagnosis several morphologic details can be added for this species, which was found only in the Nevadites beds. The whorls of some of the robust (W/D 0.55-0.65) young shells having diameters less than 15 mm increase regularly in size whereas others have approximately three contractions and bulbous expansions of the shell during each volution. All gradations in the intensity of this irregular growth seem to exist. Larger shells more than 25 mm in diameter have a more strongly arched venter in comparison with the subquadrate inner whorls and are more compressed (W/D about 0.45). The largest specimen collected has part of the body chamber and is 36 mm in diameter. On the venter of this specimen near the broken orad end of its final whorl there is irregular closely spaced strigation in addition to the radial orna- ment, which is slightly convex on the flanks and most pronounced on the venter. Figured specimens.—Plesiotypes, USNM 248879 to 248881. Occurrence.—USGS localities M144 (1), M620 (3), and M962 (9), lower part of Occidentalis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. WW lr B ) FIGURE 12.—Suture lines of Humboldtites septentrionalis (Smith). A, plesiotype (X 4), USNM 248880. B, plesiotype (X 6.6), USNM 248881. Superfamlly CERATITACEAE (Mojsisovics, 1879) Family ACROCHORDICERATIDAE Arthaber, 1911 Genus PARACROCHORDICERAS Spath, 1934 Paracrochordiceras americanun McLearn Plate 29, figures 1-9 Acrochordiceras (Paracrochordiceras) americanum McLearn, 1946b, p. 3, pl. 5, fig. 1. McLearn, 1969, p. 12, pl. 1, figs. 1—3. Figured specimens.—-Plesiotypes, USNM 248887 to 248890. Occurrence.—USGS Mesozoic localities M2358 (9), M2362 (1?), M2367 (3), M2828 (1?); Caurus Zone between Coyote and Star Canyons, Humboldt Range, Nev. Acrochordlceras hyatti Meek, 1877 Plate 4, figures 11—28; Plate 5, figures 1—7; text-figure 13 Acrochordiceras hyatti Meek [in part], 1877, p. 124, pl. 11, fig. 5a [herein selected as lectotype] [not fig. 5]. Hyatt and Smith, 1905, 22 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA p. 178 [not pl. 23, figs. 8—11]. Smith, 1914, p. 39, pl. 15, fig. 5a [not pl. 4, figs. 8—11, pl. 15, fig. 5]. Haydenites hatschekii Diener, Smith, 1914, p. 114, pl. 33, figs. 1—3. [?] Haydenites hatschekii Diener, 1907, p. 72, pl. 6, figs. la—lb. [not] Acrochordiceras hyatti Meek. Spath, 1934, p. 394, text-figure 137a—c. [not] Acrochordiceras sp. aff. A. hyatti Meek. Tozer, 1972, p. 32, pl. 10, figs. 11-13. Description.—Thick discoidal; inner whorls moderately evolute (U/D 0.30—0.40), outer whorls more involute (U/D about 0.25). Whorl shape and proportions widely variable, changing with increasing shell diameter. Cross section of inner whorls circular, at larger diameters ranging from compressed to depressed with gently to sharply rounded ventral and umbilical shoulders. Final whorl subquadrate with flattened, nearly parallel flanks and broadly rounded venter. Max- imum diameter exceeding 150 mm. Omamentation modified with growth, varying in strength and ontogenetic development. On inner whorls ribs regularly spaced, nearly straight on flanks, swing slightly forward and pass over venter with or without in- terruption. Ribbing on phragmocone generally passes through distinct ontogenetic stages: first, ribs decrease in strength on venter, tend to alternate in position across venter, and may even crisscross on venter; next, ribbing becomes strong on venter passing straight across; finally, ribs fade on venter and again tend to alternate on either side. Duration and shell diameter of each ontogenetic stage widely variable. Y On body chamber lateral ribs terminate in slightly projected ventral-lateral swellings proportional in size to strength of early ornamentation. Widely spaced tuber- cles or bullae develop at small diameter at or just below midline of flank, form point of origin for two or three ribs, and are separated by two to five intercalated ribs depending on strength of ribbing. Persistence of tuber- cles with growth widely variable: tubercles on some variants weakly developed and absent at shell diameters exceeding 20 mm; on more coarsely ornamented variants lateral tubercles may persist to beginning of body chamber at large diameter. Strength and persistence of tubercles proportional to persistence of rounded shape of inner whorls with increasing shell diameter. Suture ceratitic, nearly subammonitic; principal ele- ments elongate. S1 and S2 of equal height with club- shaped rounded crests but with weak crenulations ex- tending high on sides. L1 coarsely digitate. VL about two-thirds depth of L1; prongs on either side of ES sub- divided. One auxiliary saddle external to umbilical shoulder. Discussion.—The two syntypes of Acrochordiceras hyatti illustrated by Meek (1877, pl. 11, figs. 5 and 5a) differ from one another, and specimens of these two kinds do not occur in the same populations in Nevada. The morphologic characters of the syntype illustrated by Meek’s figure 5 are known only in specimens from the Hyatti Zone, whereas those of the other syntype, Meek’s figure 5, distinguish the kind of Acrochordiceras found in the Shoshonensis Zone near the base of the Fossil Hill Member of the Favret Formation several tens of kilometers southeast and east of the Humboldt Range in the New Pass Range, Augusta Mountains, and southern Tobin Range (Nichols and Silberling, 1977). Population samples of Acrochordiceras from each of these two zones show a wide range of variation, but little, if any, morphologic overlap exists between them. In comparison with those from the Shoshonensis Zone, those from the Hyatti Zone include specimens having more loosely coiled whorls, which tend to be rounded in cross section rather than thickest near the umbilicus, tubercles that are located laterally or well up on the lower flank rather than near the umbilical shoulder, and a less subdivided suture pattern. Meek’s original description of A. hyatti clearly refers to the kind of Acrochordiceras that occurs in the Hyatti Zone, as he describes the lateral tubercles as being “near or within the middle of each side” and attributes the umbilical position of the tubercles on the specimen illustrated by his figure 5 as probably being due to distortion (Meek, 1877, p. 124). Consequently, the syntype (Meek, 1877, pl. 11, fig. 5a) most closely agreeing with Meek’s characterization of the species is selected here as the lec- totype of A. hyatti, and this specific name is applied to the specimens described here from the Hyatti Zone of the Humboldt Range. Because of the wide morphologic variation shown by population samples of Acrochordiceras from the Shoshonensis Zone, the other syntype of A. hyatti (Meek, 1877, pl. 11, fig. 5) can be compared with several previously described European species. Acrochordiceras damesi Noetling (1880) is the oldest name for specimens having this kind of ornamentation and whorl shape, but as originally drawn, the suture of this species differs from that of other Acrochordiceras in having a broad, shallow, first lateral lobe and slender saddles whose sides converge toward their crests (Diener, 1907, p. 100). Though these differences may simply be due to a faulty restoration, until more information is available, the specimens from the Shoshonensis Zone in Nevada are provisionally referred to A. carolinae Mojsisovics, 1882, the next most prior name. A partial list of possibly synonymous names, judging from the wide variation shown by Acrochordiceras cf. A. carolinae from Nevada, would include Acrochordiceras fischeri Mojsisovics, A. haueri Arthaber, A. pustericum Mojsisovics, and A. undatum Arthaber. The syntype of A. hyatti (Meek, 1877, pl. 11, fig. 5), here assigned to A. cf. A. carolinae, is illustrated by figures 8 and 9, on plate 5. The suture of A. cf. A. PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 23 carolinae, text-figure 14, is subammonitic with incipient crenulation of the crests of the principal saddles and some second-order subdivision of the first lateral lobe. The specimen from the Whitney Collection in the Museum of Comparative Zoology, Harvard University, on which Hyatt and Smith (1905), Smith (1914), and Spath (1934) based their concept of A. hyatti is of the kind assigned here to A. cf. A. carolinae. The locality of this and some other specimens from the Whitney Collec- tion is given as “the Shoshone Mountains, Nevada,” which may refer to the New Pass Range as suggested by Smith (1914, p. 239). The only locality given by Meek (1887, p. 126) for A. hyatti is “New Pass, Desatoya Mountains [New Pass Range], Nevada.” In the New Pass Range, specimens like Meek’s syntype that is assigned here to A. cf. A. carolinae occur, along with an abundance of other am- monites characteristic of the Shoshonensis Zone, in float collections made near the base of the fossiliferous Middle Triassic section. However, ammonites like those from the upper part of the Hyatti Zone in the Humboldt Range are also represented in some collections, and thus the lectotype of A. hyatti, which is like specimens elsewhere restricted to the Hyatti Zone, could have been obtained from this level in the New Pass Range, although the stratigraphic relations are unclear. As the 40th Parallel exploration (King, 1878) collections studied by Meek include specimens from both the New Pass and Humboldt Ranges, it is also possible that Meek’s locality is in error and that the lectotype of A. hyatti was actually collected in the Humboldt Range. The character of the body chamber of Acrochordiceras was evidently unknown at the time that Diener (1907) established the genus Haydenites. The large specimen il- lustrated by Diener as the type species, H. hatschekii, appears to be nothing more than a fully developed Acrochordiceras showing the peculiar modification of the body chamber. Haydenites hatschekii, as originally described from the Middle Triassic of India, generally agrees with Acrochoridiceras hyatti in ornamentation, suture, whorl shape, and modification of the shell with growth, and the two species are at least congeneric. The lectotype of A. hyatti is nearly identical with the cor- responding part of the larger of the two specimens from the Humboldt Range figured by Smith (1914, pl. 33, figs. 1—2) as Haydenites hatschekii. Two other species of Acrochordiceras, A. foltsense and A. alternans, were described by Smith (1914, p. 38—39) from the Humboldt Range. The former species is based on a single specimen from the Upper Anisian at Fossil Hill and may be a pathologic Gymnotoceras as suggested by Spath (1934, p. 393). Acrochordiceras alternans, on the other hand, appears to be an Acrochordiceras and resembles A. hyatti in having a growth stage marked by weakening and alternation of the ribs on the venter. However, the two specimens assigned to A. alternans by Smith are more involute than any of the Acrochordiceras from the Hyatti Zone, and they might represent a stratigraphically distinct population, possibly tran- sitional between A. hyatti and A. cf. A. carolinae. Figured specimens.—Lectotype, USNM 12514 (originally figured by Meek, 1877, pl. 11, fig. 5a); plesiotypes, USNM 248632 to 248640. 0ccurrence.—USGS localities M533 (20+), M970 (3); USGS Mesozoic localities M1124 (2), M1180 (12+), M1181 (5), M1184 (3), M2819 (10), and M2829 (12+); Hyatti Zone between Buena Vista and Star Canyons on east side of Humboldt Range, Nev. FIGURE 13.—Suture lines (X 2) of Acrochordiceras hyatti Meek. A, plesiotype, USNM 248983, specimen not figured. B, plesiotype, USNM 248638. J / FIGURE 14.—-Suture line (X 2) of Acrochordiceras cf. A. carolinae Mojsisovics. Plesiotype, USNM 248984. Family BALATONITIDAE Spath, 1951 Genus CUCCOCERAS Diener, 1905 Cuccoceras bonaevistae (Hyatt and Smith) Plate 20, figures 1-12; text-figure 15 Dinarites bonae-vistae Hyatt and Smith, 1905, p. 162, pl. 60, figs. 1—4 [holotype], 6—7. Cuccoceras bonae-Uistae (Hyatt and Smith). Smith, 1914, p. 71, pl. 10, figs. 1—4, 6-7. This species is well represented in the Hyatti Zone of the Humboldt Range. Allowing for some variation in the strength and density of the ribbing and in the spacing of the periodic constrictions, the inner whorls are ade- quately characterized in Hyatt and Smith’s original 24 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA description. Attention is drawn, however, to the peculiar modification of the ornamentation on the outer whorl. As the shell increases in diameter beyond about 25 mm, the ribs bordering the apicad side of each constric- tion become enlarged and develop a slight forward- directed bend at or above the midflank. With further in- crease in shell size, generally at diameters exceeding 40 mm, tubercles develop at the point of bending and ultimately extend forward across the constriction, join- ing with the next orad rib. Thus, on the body chamber of the adult shell, the ribs bordering the pronounced con- strictions pass more or less straight across the venter and then coalesce in tubercles, which interrupt the constric- tions on the upper flank. On the flanks below the tuber- cles the constrictions are less conspicuous and continue to the umbilical margin following a prosiradiate course. Accompanying this change in ornament, the whorls become thicker and the venter more broadly rounded. Figured specimens.—Holotype, USNM 74383 (originally figured by Hyatt and Smith, 1905, pl. 60, figs. 1—4); plesiotypes, USNM 248786 to 248789. Occurrence.—USGS localities M533 (25+), M969 (4); USGS Mesozoic localities M1124 (10+), M1181 (5), M1182 (3), M1184 (2), M2359 (50+), M2821 (5), M2829 (2), M2830 (5), and M2836 (5); Hyatti Zone, northeastern Humboldt Range, Nev. L/l FIGURE 15.-—Suture line (X 3) of Cuccoceras bonaevistae (Hyatt and Smith). Plesiotype, USNM 248786. Family CERATITIDAE Mojsisovics, 1879 Suhfamily BEYRICHITINAE (Bpath, 1934) Genus NICOMEDITES Toula, 1896 Nicomedites sp. Plate 6, figures 9—11; text-figure 16 One specimen of a beyrichitid, whose distinction lies in its rather featureless character, was collected from the Hyatti Zone. The incomplete shell has a maximum diameter of 36 mm, is involute (U/D about 0.14) and compressed discoidal (W/D about 0.35) in shape, and has flattened flanks that converge to an evenly rounded, blunt venter. Only weak falcoid folds are visible on the flanks of the otherwise smooth shell. The suture is ceratitic, nearly subammonitic, with incipient crenula- tions high on the sides of the somewhat asymmetric sad- dles and with coarsely digitate lobes. The suture line of this specimen is generally like that of Hollandites aff. H. voiti collected from approximately the same stratigraphic level, but its tight coiling and weak ornamentation differ from those characteristic of Hollandites. Beyrichites has been applied in a broad sense to various similar unspecialized beyrichitids but it typically has a subtrigonal whorl cross section with a narrowly arched venter and has a rather advanced suture line. Of the recognized genera of beyrichitids, Nicomedites seems most applicable to involute shells that have an unmodified whorl shape and a relatively simple suture pattern like that of the present specimen. Figured specimen.—USNM 248646. Occurrence.——USGS locality M533 (1); Hyatti Zone, between Big and Coyote Canyons, Humboldt Range, Nev. l . FIGURE 16.—Suture line (X 3) of Nicomedites sp. Figured specimen, USNM 248646. Genus HOLLANDITES Diener, 1905 Hollandites voiti (Oppel) Ammonites voiti Oppel, 1863, p. 276, pl. 77, fig. 1. Ceratites voiti (Oppel). Diener, 1895, p. 8, pl. 2, figs. 1a—1b, 2a—2b [holotype]. Ceratites (Hollandites) uoiti (Oppel). Diener, 1907, p. 60, pl. 7, figs. 3a—3b, 4. Hollandltes 311‘. H. voiti (Oppel) Plate 6, figures 1-6; text-figure 17 Hollandites sp. Silberling and Wallace, 1969, p. 17, table 1. Hollandites is represented from the Hyatti Zone by about 20 specimens, most of which are immature. The ontogenetic variation and ontogenetic development is not adequately shown by these specimens; though they differ in some details of their suture and ornamentation from previously described species of Hollandites, they are generally similar to the type species, H. voiti (Op- pel). The largest unbroken specimen (pl. 6, figs. 3—5), hav- ing a greatest diameter of 71 mm, shows the compressed discoidal shape (W/D about 0.25), excentrumbilicate (U/D of outer whorl 0.31) high whorls, and smooth, rounded venter characteristic of Hollandites. About one- half of the outer whorl of this specimen represents the body chamber. The ceratitic suture, with slender, PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 25 somewhat asymmetric saddles, agrees in plan and degree of complexity with that of Hollandites. The broad, deep first lateral lobe is much larger than the second lateral lobe, the second lateral saddle is slightly higher than the first lateral saddle, and of the three auxiliary saddles only the outermost is prominent. Inner whorls, like the specimen illustrated by figures 1 and 2 on plate 6, are ornamented by regular, nontuber- cular, somewhat sigmoidal ribs that arise at the um- bilical shoulder or by intercalation, cross the flanks with uniform strength, and then fade where they are projected strongly forward on the ventral-lateral shoulder. Some more strongly ornamented small specimens develop weak umbilical bullae on the primary ribs. With increasing shell size, the ribbing is reduced to slightly convex folds, which are restricted to the middle part of the flanks and fade ventrally by branching into striae that swing sharply forward onto the venter. This style of ornamentation differs somewhat from that of typical Indian representatives of Hollandites whose ribs on the outer whorls tend to develop umbilical or lateral tubercles and to extend to the ventral-lateral shoulders where they are commonly emphasized as projected swel- lings. However, the large whorl fragment illustrated by figure 6 on plate 6 has coarse simple ribs that are most pronounced near the middle of the flank and at the ventral-lateral shoulder. The ribbing of this fragment, from the same block of matrix as the other two specimens of Hollandites illustrated on plate 6, is like that characteristic of the final whorl of typical Hollan- dites. The specimens from the upper Anisian of the Hum- boldt Range assigned by Smith (1914) to Hollandites, i.e., those he included in “Ceratites (Hollandites)” montis-bovis and “C. (H)” organi Smith, possess the subammonitic suture, whorl shape, ornamentation, and keeled venter of younger genera of beyrichitids and are regarded here as variants of Parafrechites meeki, revised, and Frechites occidentalis, revised. Figured specimens.—Plesiotypes USNM 248642 to 248644. Occurrence—USGS localities M969 (5), M533 (6+); USGS Mesozoic localities M1180 (5), M1181 (2), and M2836 (1); Hyatti Zone, vicinity of Congress Canyon, Humboldt Range, Nev. FIGURE 17.—Suture line (X 3) of Hollandites aff. H. voiti (Oppel). Plesiotype, USNM 248643. Genus ANAGYMNOTOCERAS McLearn ?Ana.gymnotoceras moderatum (McLearn) Plate 6, figures 7—8 Gymnotoceras moderatum McLearn, 1948, p. 3, pl. 10, fig. 10. Anagymnotoceras moderatum (McLearn). McLearn, 1966, pl. 1, fig. 8. Anagymnotoceras aff. A. moderatum (McLearn). Silberling and Wal- lace, 1969, table 1, p. 17. Figured specimen.—Plesiotype USNM 248645. Occurrence—USGS Mesozoic locality M2822 (2); Hyatti Zone, northern Humboldt Range, Nev. Genus GYMNOTOCERAS Hyatt, 1877 Gymnotoceras Hyatt in Meek, 1877, p. 110 [type species Ammonites blakei Gabb, 1864, by original designation]. Revised description.—Discoidal, compressed; moderately involute. Cross-sectional shape of phragmacone whorls subtrigonal with acutely rounded periphery. On body chamber periphery becomes broadly rounded to subtabulate near the aperture. Ribbing nearly absent to strong, decreasing in strength on outer whorl. Ribs falcoid or projected, may branch or intercalate on lower flanks or have weak lateral bullae and faint marginal swellings. Bluntly rounded keel on strongly ornamented inner whorls. Suture typically subammonitic with rounded crenulate saddles. First lateral lobe broad, deeper than ventral lobe, roughly twice as deep as second lateral lobe. Ventral lobe divided by low, generally triangular, ventral saddle. First lateral saddle broader and as high as or higher than second lateral saddle. One or two aux- iliary saddles external to umbilical shoulder. Discussion.—Ammonites of the genera Gymnotoceras, Parafrechites, and Frechites are among the best represented in collections from the Fossil Hill area. Stratigraphically controlled samples totalling nearly 2,000 specimens were collected either from bedrock or from single loose weathered blocks and represent dif- ferent levels throughout the upper Anisian. Only two intergrading stratigraphically restricted species of Gymnotoceras occur in the Fossil Hill area as the scope of Gymnotoceras is herein changed from former usage by Silberling (1962), Silberling and Tozer (1968), and Silberling and Wallace (1969). Allowing for a certain amount of variation in ornamentation, whorl shape, and degree of compression, Gymnotoceras is dis- tinguished from other ceratitacids by its narrowly rounded phragmocone periphery. The generic names Philippites and Beyrichites have also been applied to ammonites from Fossil Hill here included in Gym- notoceras, but for the typical examples of neither of 26 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA these genera, which might be junior synonyms of Gym- notoceras, is the shape and ornament of the inner whorls sufficiently well known. Gymnotoceras rotelliformis Meek Plate 7, figures 1—27; plate 8, figures 1—5 Gymnotoceras rotelliforme Meek, 1877, p. 111, pl. 10, figs. 9—9a. Beyrichites rotelliformis (Meek). Hyatt and Smith, 1905, p. 155, pl. 23, figs. 1—2, 3—5, 6—7a; pl. 58, figs. 1—4?, 5—6, 7-97, 10—12?, 13—157. Smith, 1914, p. 118, pl. 4, figs. 1—2, 3—5, 6—7a; pl. 8, figs. 1—4?, 5—6, 7—9?, 10—12?, 13—15?; pl. 14, figs. 9—93; pl. 31, figs. 1~2?, 3—4, 5—67; pl. 91, figs. 1—2, 3—4?, 5—7, 8?, 9—10?. Spath, 1934, p. 422. Ceratites (Philippites) argentarius Smith, 1914, p. 107, pl. 63, figs. 1—3 [holotype], 4—6, 7—8, 9—11, 12—14?. Beyrichites tenuis Smith, 1914, p. 119, pl. 32, figs 1—2 [holotype], 3-4, 5—67; pl. 89, figs. 15—17, 18—20. Philippites? argentarius Smith. Spath, 1934, p. 419. Gymnotoceras argentarius (Smith). Silberling, 1962, p. 156. [not] Beyrichites rotelliformis (Meek). Smith, 1904, p. 379, pl. 43, figs. 13—14; pl. 45, fig. 5 [= Gymnotoceras blakei (Gabb), revised]. Revised description.—Discoidal, compressed (im- mature W/D 0.30—0.40, mature 0.30—0.50); moderately involute (immature U/D 0.15—0.30, mature 0.12—0.25). Transition from immature to mature morphology at diameter 30—40 mm; maximum diameter exceeding 85 mm. Venter acutely rounded, without ventral shoul- ders, on phragmocone, becoming broadly rounded with growth in some forms. Ribbing on immature shell widely variable in strength from weak to strong, fading with growth. Ribs falcoid, commonly branching from swollen primary ribs on lower flanks and weakening on upper flanks; ventral tips of ribs slightly enlarged. N0 tubercles on ribs. Blunt ventral keel distinct only on more strongly ornamented immature shells; fades with growth. Suture simple, subammonitic with four rounded finely crenulate external saddles decreasing progressively in height inwards. Discussion.—This species, as revised, shows a wide range of morphologic variation and complete intergrada- tion with Gymnotoceras blakei, which characterizes the beds immediately overlying those with G. rotelliformis. Immature specimens of both G. rotelliformis and G. blakei are distinctive in having high whorls whose flanks taper to a narrowly rounded acute venter, but G. rotel- liformis lacks the regular falcoid ribs which cross the flanks with uniform strength in G. blakei. In some variants of G. rotelliformis the outer whorl thickens rapidly and the acute venter of the inner whorls becomes bluntly rounded. The average morphology of G. rotelliformis, as revised, is closest to that of specimens included in G. argentarius by Smith (1914) but with less inflated whorls. Meek’s type specimen of G. rotelliformis agrees with weakly or- namented variants of populations that include forms with the average morphology, but its ornament ap- proaches that of G. blakei in which it was included by Silberling (1962, p. 156). Figured specimens.—Holotype, USNM 12526, originally figured by Meek, 1877, pl. 10, figs. 9—9a; plesiotypes, USNM 248654 to 248665. Occurrence. —Paraceratites burckhardti, P. clarkei, and P. vogdesi beds, grading into Gymnotoceras blakei in the Paraceratites cricki and Gymnotoceras blakei beds. USGS localities M136 (100+), M136 —5 ft (1.5 m) (12), M139 (22), M163 (14), M164 (30+), M165 (20), M605 (38), M606 (14), M607 (3), M608 —8ft (2.5 m) (6), M965 (100+), M965 +3 ft (0.9 m) (18), M966 (40), M967 (3), and M967 -9 ft (2.7 m) (7); Rotelliformis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Gymnotoceras blakei (Gabb) Plate 8, figures 6—19; plate 9, figures 1—18 Ammonites blakei Gabb, 1864, p. 24, pl. 4, figs. 14—15. Ceratites (Gymnotoceras) blakei (Gabb) [in part]. Hyatt and Smith, 1905, p. 173, pl. 22, figs. 10—11, 12—14?, 15—17?, 18—20?, 21-23? [not figs. 1—3, 4—5, 7—9 = Parafrechites meeki (Mojsisovics), revised]. Smith, 1914, p. 109, pl. 3, figs. 10—11, 12—14?, 15—17?, 18—20?, 21—23?, pl. 16, figs. 8—10, 17-19; pl. 66, figs. 1—2, 3—4?, 5—6?, 7—8? [not pl. 14, fig. 10b; pl. 65, figs. 14—16? = Parafrechites meeki (Mojsisovics), revised]. Beyrichites falciformis Smith, 1914, p. 116, pl. 91, figs. 11—13 [holotype]; pl. 92, figs. 1—2, 3—5, 6—8. Spath, 1934, p. 423. Gymnotoceras blakei (Gabb). Spath, 1934, p. 427, text-figure 145? Silberling, 1962, p. 156. [not] Gymnotoceras blakei (Gabb). Meek, 1877, p. 113, pl. 10, figs. 10—10a, 10b [=Parafrechites meeki (Mojsisovics), revised], pl. 11, figs. 6—63 [=Frechites nevadanus (Mojsisovics), revised]. Spath, 1934, p. 427, text-figure 145? [=?Parafrechites meeki (Mo- jsisovics), revised]. Kummel in Arkell and others, 1957, fig. 182, no. 1a—lc? [=?P. meeki (Mojsisovics), revised]. [not] Ceratites (Gymnotoceras) blakei (Gabb). Smith, 1904, p. 386, pl. 43, figs. 9-10; pl. 44, figs. 2, 3 [=Parafrechites meeki (Mojsisovics), revised]. Revised description.—Discoidal, compressed (im- mature W/D about 0.32—0.40, mature about 0.30); in- volute (immature U/D 0.15—C.25, mature about 0.15). Transition from immature to mature morphology at diameter 30—40 mm; maximum diameter more than 80 mm. Venter of immature shell acute, narrowly rounded, without ventral shoulders; with maturity venter becomes bluntly rounded, but whorls remain narrow. Closely spaced falcoid dichotomous nontubercular ribs extend with uniform strength from umbilicus to venter on immature whorls. With growth, ribs fade beginning on lower flanks, leaving faint projected swellings on outer flanks of mature shell. Blunt ventral keel on ribbed immature whorls; fades with growth. External suture simple, subammonitic with rounded crenulate first and second lateral saddles and two auxiliary saddles. Discussion.—The average morphology of Gym- PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 27 notoceras blakei differs from that of G. rotelliformis, which occurs stratigraphically lower, in having regular falcoid ribbing and narrower whorls, but the two species intergrade, and transitional populations include in- dividuals with the average morphology of both. At the upper limit of its stratigraphic range, G. blakei coexists without morphologic intergradation with Frechites nevadanus. Parafrechites meeki, which ranges from the Frechites nevadanus beds upwards, differs from G. blakei mainly in having relatively low whorls with a broadly rounded or subtabulate venter. Of seven numbered specimens (ANSP 1227—1233) at the Academy of Natural Sciences of Philadelphia labeled as the type lot of Ammonites blakei Gabb, the lectotype (ANSP 1227) selected here, though secondarily deformed, is the only one that resembles Gabb’s original illustration (1864, pl. 4, figs. 14-15) in the degree of com- pression and shape of the whorls. Accompanying this specimen is a note reading “this is obviously same species as Gabb’s type of Blakei, pl. 4, f. 14, and may be the type, A.H.” This note was evidently written by Alpheus Hyatt who based the genus Gymnotoceras on this species. Among the other specimens in the type lot that were not illustrated by Gabb, AN SP 1228 belongs to Frechites nevadanus, ANSP 1229 agrees with either Parafrechites dunni or P. meeki, and ANSP 1230 to 1233 belong to P. meeki. The lectotype has thicker whorls and is less regularly ribbed than average specimens in pop- ulations of G. blakei, as revised; it is in closest agree- ment with forms found in the lower part of the G. blakei beds. The large specimen figured as Ceratites (Gym- notoceras) blakei by Smith (1914, pl. 65, figs. 14—16) and refigured by Spath (1934, p. 428, text-fig. 145) and by Kummel (in Arkell and others, 1957, fig. 182, la—lc) is more robust than any specimens found in the G. blakei beds. This specimen is too large to positively identify but probably should be assigned to Parafrechites meeki (Silberling, 1962, p. 156). Figured specimens.—Lectotype, ANSP 1227 (probably the specimen on which Gabb’s figures, 1864, pl. 4, figs. 14—15, were based); plesiotypes, USNM 248666 to 248678. Occurrence—Gymnotoceras blakei beds, strati- graphically above the occurrence of G. rotelliformis and below that of Parafrechites meeki. USGS localities M137 (24), M141 (19), M142 (23), M607 +2 ft (0.6 m) (16), M608 (32), M609 (7), M610 (7), M611 (40), M613 (13), and M964 (35); Rotelliformis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Genus PARAFRECHITES n. gen. Type species.—Parafrechites meeki (Mojsisovics). Definition.—Thickly discoidal to moderately com- pressed, moderately involute. Venter broadly and evenly rounded or with subtle ventral shoulders. Bluntly rounded keel on inner whorls. Mature venter smooth. Strong, regular falcoid ribbing on inner whorls fading adorally. Ribs rarely have weak umbilical bullae or faint ventro-lateral swellings. Suture simple, subammonitic with rounded crenulate first and second lateral saddles; L1 relatively prominent, as many as two auxiliary saddles external to the um- bilical seam. Discussion. ——A new generic name for these relatively nondescript beyrichitids is desirable so that the other upper Anisian genera Gymnotoceras and Frechites can be recognized as morphologically distinctive entities. Parafrechites is easily distinguished from Gymnotoceras by its broadly rounded venter and from Frechites by the absence of tubercles and distinct ventral-lateral shoulders. Parafrechites meeki (Mojsisovics) Plate 11, figures 7—23; plate 12, figures 1—29; plate 13, figures 1—5 Gymnotoceras blakei (Gabb), Meek, 1877, p. 113, pl. 10, figs. 10—10b. Ceratites meeki Mojsisovics, 1888, p. 168 [new name for Gymnotoceras blakei (Gabb) of Meek, 1877, pl. 10, figs. 10—10b]. Ceratites (Gymnotoceras) blakei (Gabb). Smith, 1904, p. 386, pl. 43, figs. 9—10; pl. 44, figs. 2, 3. Hyatt and Smith, 1905, p. 173, pl. 22, figs. 1—3, 4—5, 7—9. Smith, 1914, p. 109, pl. 14, fig. 10b; pl. 65, figs. 14—16? Ceratites (Gymnotoceras) meeki Mojsisovics. Smith, 1914, p. 111, pl. 14, figs. 10—108; pl. 69, figs. 1—2, 3—4, 5-6, 7—9, 10—13, 14—16, 17—19. Ceratites tenuispiralis Smith, 1914, pl. 46, figs. 17—19 [holotype], 20—22, 23?, 24—25?. Ceratites washbumei Smith, 1914, p. 103, pl. 92, figs. 9—11 [holotype], 12—14, 15—17. Ceratites (Hollandites) montis-bouis Smith, 1914, p. 105, pl. 58, figs. 1—4 [holotype], e7, e11, 12—14, 1am, 17—20?. Ceratites (Hollandites) organi Smith [in part], 1914, p. 105, pl. 55, figs. 1—2, 3—47, 5—7, 8—10 [not pl. 54, figs. 1—9; ?pl. 55, figs. 11—30 = Frechites occidentalis (Smith), revised]. Ceratites (Gymnotoceras) beckeri Smith, 1914, p. 109, pl. 3, figs. 4—5, 7—9; pl. 66, figs. 10—13 [holotype], 14—15, 16—19, 20—22, 23, 24—26, 27—297. Ceratites (Gymnotoceras) russelli Smith, 1914, p. 111, pl. 3, figs. 1—3 [holotype], 6; pl. 67, figs. 1—3, 4—7, 8—9, 10—12, 13—15. Ceratites (Gymnotoceras) wemplei Smith, 1914, p. 113, pl. 68, figs. 1—3 [holotype], 4—6, 7—9. Gymnotoceras meeki (Mojsisovics). Spath, 1934, p. 430. Silberling, 1962, p. 156. Frechites tenuispiralis (Smith). Spath, 1934, p. 453. Gymnotoceras russelli Smith. Spath, 1934, p. 429. Gymnotoceras wemplei Smith. Spath, 1934, p. 431. Gymnotoceras washburnei (Smith) [in part]. Silberling, 1962, p. 156. Revised description—Thick discoidal (immature W/D 0.40—0.45, mature 0.35—0.40, W/D of bullate variants in lower part of stratigraphic range may exceed 0.5); moderately involute (immature and mature U/D 0.20—0.30). Transition to mature morphology not 28 marked; loss of ornament begins at diameter 40—50 mm. Maximum diameter exceeds 80 mm. Venter broadly rounded to subtabulate at all growth stages. Ribbing strong and regular, projected or slightly falcoid across flanks. Primary ribs enlarged or slightly bullate on lower flanks below bifurcation point on more coarsely ribbed variants. Ventral tips of ribs slightly enlarged on forms tending to develop ventral-lateral shoulders. Strong umbilical bullae and distinct pro— jected ventral-lateral tubercles only on some variants in lower part of stratigraphic range. Blunt ventral keel per- sistent to diameters exceeding 40 mm. Suture simple, subammonitic with rounded crenulate first and second lateral saddles and usually only one dis- crete auxiliary saddle external to the umbilical shoulder. Discussion.—-Parafrechites meeki, as revised, is dis- tinguished by its broadly rounded or subtabular venter, by the strong, regular ribbing, by the generally‘poor development of tubercles or bullae on the ribs, and by the persistence of the immature ornamentation to relatively large shell diameters. The principal variations in populations from the mid- dle part of the P. meeki beds are in the density of the rib- bing and the degree of angularity at the ventral-lateral shoulders. The average morphology of these populations is close to that of forms included by Smith in “Ceratites (Gymnotoceras) russelli.” Although Smith (1914, p. 110- 112) contended that intergradation did not occur among the various species he included in “Gymnotoceras,” Spath (1934, p. 428—429) pointed out the close alliance of “G.” meeki, “G. ”russelli, “G. ” beckeri, and “G. blakei” (of Smith) and the existence of many “passage forms” between them among the stratigraphically random col- lections from Fossil Hill at the British Museum. Intergradation is well shown in the population samples on which the present revision is based. Populations from the lower part of the Parafrechites meeki beds show a greater amount of variation and range in morphology from relatively robust end members with umbilical bullae and coarse ribs terminating in ventral- lateral swellings or tubercles to regularly ribbed, non— tuberculate, compressed, high-whorled end members. The lectotype (Meek, 1877, pl. 10, figs. 10—10a) of P. meeki, selected here, is in closest agreement with forms from the lower part of the stratigraphic range of P. meeki, as revised. The holotype of Ceratites (Hollandites) montis-bovis, included in Gymnotoceras by Spath (1934, p. 427) and in P. meeki here, is more involute and more delicately ribbed than the characteristic form of P. meeki as revised, and may be transitional to P. dunni, which characterizes the beds stratigraphically above those with P. meeki. However, a morphologic intergradation MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA between P. meeki and P. dunni is not demonstrated by the available stratigraphically controlled collections, perhaps because the number of specimens represented is too small. Figured specimens.——Lectotype, USNM 12512 (originally figured by Meek, 1877, pl. 10, figs. 10—10a); plesiotypes, USNM 74301 (holotype of Gymnotoceras russelli Smith, 1914, pl. 3, figs. 1—3), USNM 74391 (holotype of G. beckeri Smith, 1914, pl. 66, figs. 10—13), and USNM 248694 to 248710. 0ccurrence.——Parafrechites meeki beds; strati- graphically above F rechites nevadanus beds and ranging stratigraphically upwards into the P. dunni beds. USGS localities M138 (9), M140 (60+), M143 (21), M612 (17); M616 (9), M617 (15), M958 (100+), M960 (150+), and M963 (60+); Meeki Zone, vicinity of Fossil Hill, Hum- boldt Range, Nev. Parakechites dunni (Smith) Plate 13, figures 6—30 Beyrichites dunni Smith, 1914, p. 116, pl. 32, figs. 7—8 [holotype], 9—10, 11—12?. Spath, 1934, p. 423. Beyrichites osmonti Smith, 1914, p. 117, pl. 31, figs. 7—8 [holotype], 9—10, 11—12, 1am; pl. 89, fig. 14?. Gymrwtoceras dunni (Smith). Silberling, 1962, p. 156. ['2] Ceratites williamsi Smith, 1914, p. 82, pl. 47, figs. 11—14 [holotype], 15—16, 17—187. [?] Ceratites (Philippites) ransomei Smith, 1914, p. 108, pl. 99, figs. 1—3 [holotype], 4. Revised description.—Discoidal, moderately com- pressed (W/D 0.33—0.40); involute (U/D 0.15—0.20). Whorl shape and proportions constant with growth. Maximum diameter more than 65 mm. Venter broadly rounded, grading imperceptibly into flanks or delimited by poorly developed ventral-lateral shoulders. Ornamentation generally restricted to inner whorls and variable in strength, nearly absent on some forms and commonly lost at shell diameters of more than 30 mm. Ribbing, when developed on immature shell, dense and regular; ribs projected or slightly falcoid, branching on lower flanks. Weak umbilical bullae and ventral swel- lings on ribs only on inner whorls of coarsely ornamented variants. Outer whorls smooth except for falcoid growth lines projected across venter. Blunt ventral keel developed in proportion to strength of ribbing, usually weakly developed for at least part of one volution even on smoothest variants. Suture subammonitic with rounded, weakly crenu- lated first and second lateral saddles and two auxiliary saddles external to the umbilical seam. Discussion.—This species is distinguished by a poor development or early loss of ornamentation and by its thick discoidal whorls having a broad, rounded, or PALEONTOLO GY—SYSTEMATIC DESCRIPTIONS 29 slightly tabular venter. Some specimens, like those in- cluded by Smith in ”Beyrichites” osmonti, are nearly devoid of ornamentation, and for this reason they were assigned to Beyrichites by Smith who derived this genus directly from Gymnotoceras by a progressive loss of sculpture. These smooth forms are included here in Parafrechites because they are like end-member variants of population in which more average forms possess the characteristic ribbing and ventral keel of Parafrechites on their inner whorls. Most of the species of beyrichitids from Fossil Hill tend to become less ornamented with growth and show some individual variation in the strength of sculpture. Consequently, specific assignment of an isolated specimen may be difficult; for example, the paratype of ”Beyrichites” osmonti Smith (1914, pl. 89, fig. 14) might belong to the present species, as revised, or be a smooth and perhaps premature variant of Gymnotoceras rotelliformis, revised. Some large, strongly sculptured specimens with the characteristic ornament and whorl shape of P. meeki oc- cur with populations of P. dunni in collections from a single bed. Forms transitional between the two species appear to be lacking in these collections, perhaps because of the relatively small size of these samples. The lithologic character of the beds characterized by P. dunni differs from that of the beds stratigraphically above and below in being more sandy and pervasively stained with ferric oxides. Matrix material like that of the P. dunni beds can be recognized on one of the paratypes of “Beyrichites” osmonti Smith (1914, pl. 31, figs. 9—10), on a paratype of “B.” dunni Smith (1914, pl. 32, figs. 9—10), and possibly on the holotype of “B.” dunni. The holotype of “Ceratites” williamsi Smith, questionably included in Parafrechites dunni, as revised, bears a shell fragment probably referable to Daonella dubia, a species occurring stratigraphically above the P. dunni beds; ”C.” williamsi may be a smooth variant closely related to forms like “C.” rotuloides Smith as suggested by Smith (1914, p. 83), and hence it might belong with the group of Smith’s species included here in Frechites occidentalis. The suture line of “Ceratites (Philippites)” ransomei as illustrated by Smith (1914, pl. 99, fig. 4) is over- simplified; the saddles on the suture of this specimen are slightly crenulate rather than being smoothly rounded. Figured specimens.—Plesiotypes, USNM 248712 to 248721. Occurrence—Restricted to the Parafrechites dunni beds, stratigraphically above the P. meeki beds and below the Frechites occidentalis beds. USGS localities M167 (20+), M618 (24), M619 (40+), M959 (20+), and M968 (60+); Meeki Zone, vicinity of Fossil Hill, Hum- boldt Range, Nev. Genus FRECHITES Smith, 1932 Frechites Smith [type species Ceratites humboldtensis Hyatt and Smith, 1905, by original designation]. Revised description.—Thickly discoidal to moderately compressed; moderately involute. Whorl section on in- ner whorls has broadly rounded venter, changing on outer phragmacone and body chamber to subtrapezoidal with flattened venter and distinct rounded ventral- lateral shoulders. Venter on inner whorls has bluntly rounded keel, on outer whorls is smooth. Falcoid simple, branching or intercalating ribs having ventral swellings or distinct blunt tubercles at ventral-lateral shoulders and on some having bullae or spines on lower flanks. Suture subammonitic, L1 relatively prominent; one or two auxilliary saddles beyond 82. Frechites nevadanus (Mojsisovics) Plate 9, figures 19—25; plate 10, figures 1—24; plate 11, figures 1—6 Gymnotoceras blakei (Gabb). Meek, 1877, pl. 11, figs. 6—6a. Ceratites nevadanus Mojsisovics, 1888, p. 168 [new name for Gym— notoceras blakei (Gabb) of Meek, 1877, pl. 11, figs. 6—63]. Smith [in part], 1914, p. 101, pl. 15, figs. 6—6a, pl. 64, figs. 1—2?, 8—9? [not? figs. 3—7, 10—12, 13—14 = ?Frechites occidentalis (Smith), revised], pl. 65, figs. 1—4?, 5—7?, 8—9?, 10—11?, 12—13?. Ceratites humboldtensis Hyatt and Smith, 1905, p. 170, pl. 57, figs. 1—3 [lectotype selected by Spath (1934, p. 447)], 4—5, 6—7, 8—11, 12—13?, 14—16?, 17—187, 19—21?, 22—237. Smith, 1914, pl. 7, figs. 1—3, 4—5, 6—7, 8-11, 12—13?, 14—16?, 17—18?, 19—21?, 22-237; pl. 61, figs. 1—3, 4—5, 6—7, 8—12, 13—15. Arthaber, 1915, p. 120, text-fig. 7e—7f. Ceratites cornutus Smith, 1914, p. 98, pl. 62, figs. 1—4 [holotype], 5—7, 8—9, 10—12, 13—15, 16—17?. Ceratites emmonsi Smith [in part], 1914, p. 98, pl. 60, figs. 13—15 [holotype], 19—21; [not figs. 16—18 = Frechites occidentalis (Smith), revised]. Ceratites spinifer Smith [in part], 1914, p. 103, pl. 59, figs. 1—3 [holotype], 9-10 [not figs. 4—7 = Paraceratites cricki Smith, revised]; pl. 60, figs. 1—3, 4—6, 7—97, 10—12. Ceratites (Gymnotoceras) hersheyi Smith, 1914, p. 110, pl. 93, figs. 1—3 [holotype], 4—6?, 7—87, 9—10?, 11-12?, 13—147. Frechites humboldtensis (Hyatt and Smith). Smith, 1932, p. 32. Spath, 1934, p. 447. Frechites cornutus (Smith). Spath, 1934, p. 449. Frechites emmonsi (Smith). Spath, 1934, p. 449. Frechites spinifer (Smith). Spath, 1934, p. 448. Gymnotoceras (Frechites) nevadanus (Mojsisovics). Silberling, 1962, p. 156. [not] Frechites nevadanus (Mojsisovics). Spath, 1934, p. 450 [=Frechites occidentalis (Smith), revised]. Revised description—Thick discoidal (immature W/D about 0.40, mature 0.45—0.60); moderately involute (U/D about 0.25). Transition from immature to mature sculpture beginning at diameter of 25—35 mm; maximum diameter more than 85 mm. Immature whorl cross sec- tion subquadrate with venter broadly arched; mature 30 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA cross section trapezoidal owing to pronounced tubercles on lower flanks and broad flattened venter. Ribs on immature shell coarse and regular, running from umbilical shoulders onto venter and branching on lower flanks. Transition to mature ornamentation by enlargement of ribs into tubercles at ventral-lateral shoulders and then by development on lower flanks of coarse umbilical tubercles from which two or three ribs diverge. Decrease in strength of ribs on outer whorl ac- companied by elongation of ventral-lateral tubercles into low clavi. Umbilical tubercles on mature shell spinose, rising from broad swellings, or elongated radially with their tips sometimes curved adapically. Blunt ventral keel conspicuous on immature whorls, gradually diminishing in strength. Broad venter of mature shell smooth, gently arched, flat, or even slightly biconcave bordered by rows of ventral-lateral tubercles or clavi. Suture subammonitic with crenulate saddles. First lateral saddle and lobe prominent; one or two discrete auxiliary saddles beyond second lateral saddle. Discussion.—-Young stages of F. nevadanus are in- distinguishable from those of Parafrechites meeki, but mature shells of the latter species, even from possibly transitional populations in the lower part of its stratigraphic range, failed to develop the broad flattened venter and pronounced umbilical tubercles of the former species. Robust tubercular variants of F. occidentalis closely resemble the mature form of the present species. They differ from F. nevadanus by the early loss or poor development of the ventral keel, the higher and more rectangular cross section of their early whorls, the more bullate character of the umbilical tubercles on the mature shell, and the shape of their ventral-lateral tubercles, which are more in the form of projected swell- ings than discrete tubercles or clavi. On Meek’s holotype of F. nevadanus the part of the shell bearing the ventral keel is not well preserved, but the presence of a keel is strongly suggested. The nature of the tubercles and venter also indicate that this name is properly applied to the present group. From his study of stratigraphically random specimens, Smith had no way of knowing that populations like those included here in F. nevadanus do not include forms like the robust tuberculate variants of F. occidentalis, and several of the specimens figured by him as belonging to the former species evidently belong to the latter. This incorrect as- signment, in addition to an erroneous conception of Meek’s type specimen, led Smith (1914, p. 101) and Spath (1934, p. 450) to characterize F. nevadanus as dif— fering from the other species of Smith’s “group of ‘Ceratites’ humboldtensis” (= Frechites) by lacking a ventral keel. Figured specimens.—Holotype, USNM 12512 (originally figured by Meek, 1877, pl. 11, figs. 6—6a); plesiotypes, USNM 248679 to 248693. Occurrence—Restricted to Frechites nevadanus beds, stratigraphically above Gymnotoceras blakei beds and below Parafrechites meeki beds. USGS localities M142 (4), M166 (100+), M614 (120+), M615 (35+), and M957 (35+); Meeki Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Frechites occidentalis (Smith) Plate 13, figures 31-34; plate 14, figures 1—33 Ceratites occidentalis Smith, 1914, p. 84, pl. 44, figs. 21—23 [holotype], 24—25, 26—28; pl. 45, figs. 1—2, 3—4, 5—77, 8—9?, 10-11?, 12—13?. Ceratites applanatus Smith, 1914, p. 80, pl. 53, figs. 9—11 [holotype], 12—147. Ceratites rotuloides Smith, 1914, p. 80, pl. 47, figs. 1—3 [holotype], 4—5, 6—7, 8—10'?. Ceratites altilis Smith, 1914, p. 83, pl. 45, figs. 14—16, 17—18, 19—20, 21—22?; pl. 67, figs. 19—21 [holotype]. Ceratites gilberti Smith, 1914, p. 84, pl. 98, figs. 1—3 [holotype]. Ceratites karpinskyi Smith, 1914, p. 100, pl. 44, figs. 4—6 [holotype], 7—8, 9—10, 11—12?, 13—15?, 16—18?, 19—20?. Ceratites nevadanus (Mojsisovics) [in part]. Smith, 1914, pl. 64, figs. 3-7, 10—12, 13-14. Spath, 1934, p. 450. Ceratites pilatus Smith, 1914, p. 102, pl. 46, figs. 1—4, 5—6, 7—8, 9—10, 11—12?, 13-14?, 15—16?; pl. 89, figs. 10—13 [holotype]. Ceratites (Hollandites) organi Smith, 1914, p. 105, pl. 54, figs. 1—4 [holotype], 5—6, 7—9; pl. 55, figs. 11—12?, 13—15?, 16—18?, 19—20?, 21-237, 24—26?, 27—307. Frechites occidentalis (Smith). Spath, 1934, p. 452. Frechites rotuloides (Smith). Spath, 1934, p. 454. Frechites altilis (Smith). Spath, 1934, p. 453. Frechites karpinskyi (Smith). Spath, 1934, p. 451. Frechites pilatus (Smith). Spath, 1934, p. 451. Gymnotoceras occidentalis (Smith). Silberling, 1962, p. 156. Gymnotoceras washburnei (Smith) [in part]. Silberling, 1962, p. 156. [?]Ceratites (Philippites) lawsoni Smith, 1914, p. 108, pl. 56, figs. 1—5 [holotype], 6—8, 9—11, 12—13; pl. 57, figs. 1—3, 4—6, 7—9?, 10—13?, 14—17?. [?]Ceratites (Gymnotoceras) spurri Smith, 1914, p. 112, pl. 67, figs. 16—18 [holotype]. Revised description. —Discoidal, moderately com- pressed (W/D 0.33—0.40, W/D of bullate variants may ex- ceed 0.45); moderately involute (immature U/D 0.25—0.32, mature 0.18—0.30, mainly 0.20—0.25). Loss of ventral keel and development of distinct ventral-lateral shoulders usually occurs at diameters less than 25 mm; ornamentation fades on outer whorl. Maximum diameter about 80 mm; some fully mature shells may not exceed 60 mm diameter. Venter subtabulate, broadly arched between rounded, but distinct, ventral- lateral shoulders, which are commonly emphasized by tubercles at ventral ends of ribs. Ribbing coarse but widely variable in strength. Primary ribs give rise to two or three branches on lower flanks. On some robust variants primary ribs bullate or represented by large umbilical tubercles below bifurca- tion point. Other forms coarsely ribbed without um— PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 31 bilical tubercles or bullae; some variants nearly smooth with faint wide ribs. Ventral ends of ribs enlarged into projected swellings or tubercles at ventral-lateral shoulders. Blunt ventral keel only on inner whorls. Suture simple, subammonitic with rounded crenulate first and second lateral saddles and one or two auxiliary saddles external to the umbilical shoulder. Larger stratigraphically controlled collections might demonstrate that populations in the lower part of the stratigraphic range of F. occidentalis bear a stronger resemblance to Parafrechites meeki, a possible ancestor, than do those that occur higher. These possibly tran- sitional populations were grouped into a distinct species, ”Gymnotoceras” washburnei, by Silberling (1962, p. 156), but their range of morphologic variation is here regarded as too similar to that of Frechites occidentalis for specific separation. The various “species” described by Smith that were included in “G. ” washburnei (Smith) by Silberling are therefore included in either Parafrechites meeki or Frechites occidentalis, as revised. “Ceratites (Philippites)” lawsoni Smith was referred to Frechites by Spath (1934, p. 418—419) and is provisionally included here in F. occidentalis, although no specimens with the exaggerated curved bullae of Smith’s holotype are present in the stratigraphically controlled collections. Some coarsely ribbed variants of Parafrechites dunni, as revised here, resemble the paratypes of ”C. (P. )” lawsoni Smith and suggest a pos- sible transition from P. dunni to F. occidentalis. The inclusion of ”Ceratites” altilis Smith and ”C. (Hollandites)” organi Smith in F. occidentalis is sub- stantiated by shell fragments of Daonella dubia and D. moussoni adhering to the holotypes of these species. These bivalves are indicative of the Occidentalis Zone. Figured specimens.—Plesiotypes, USNM 248722 to 248739. Occurrence.—From the Parafrechites dunni beds stratigraphically upwards into the Nevadites gabbi beds. USGS localities M144—6 ft (1.8 m) (10), M144 (6+), M145 (50+), M622 (7), M623 (10), M624 (35+), M625 (24+), M626 (50+), M961 (11), M962 (10), and M962A (6). Upper part of Meeki Zone and Occidentalis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Frechites johnstoni n. sp. Plate 15, figures 1—5; text-figure 18 Gymnotoceras n. sp. Silberling, 1962, p. 158. Description.—Discoidal, compressed (W/D about 0.33) shell becoming increasingly involute as size in- creases (U/D immature 0.20—0.24, mature 0.15). Flanks flattened, converging to narrow, broadly arched venter. Ventral-lateral shoulders distinct. Ribs falcoid, simple or bifurcating, densely and regularly spaced (about 40 per volution on outer flank), persistent to relatively large shell diameter (more than 60 mm) but fading on orad part of body chamber. Bullae and tubercles lacking, but ventral tips of ribs enlarged, tending to increase angula- tion of ventral-lateral shoulders. Blunt low ventral keel on inner whorls fades with increasing shell size, not dis- cernible beyond diameters of about 30 mm. Suture simple, subammonitic; L1 relatively promi- nent; two auxiliary saddles and lobes. Discussion.—This new species of beyrichitid is placed in F rechites because of its subtabulate venter, and it dif- fers from other species of this genus in having higher, more compressed whorls and in lacking tuberculation. This species is named in honor of Francis Newlands Johnston, who, in addition to his important study of Up- per Triassic ammonites from the New Pass Range, Nev., also collected Triassic ammonites from the Humboldt Range, including the type lot of this species. Figured specimens.—Holotype, USNM 248740; paratype, USNM 248741. Occurrence—Subasperum Zone. USGS locality M627 (2) and USGS Mesozoic locality M3093 (1), vicinity of Fossil Hill; USGS locality M905 (1) associated with Protrachyeras of P. americanum (Mojsisovics) between Cottonwood Canyon and Fitting; and USGS Mesozoic locality M5481 (4), the type lot from a single limestone block associated with Protrachyceras cf. P. subasperum (Meek), Arizona Mine area near Unionville, Humboldt Range. Nev. 1T FIGURE 18.—Suture line (X 4) of Frechites johnstoni n. sp. Holotype, USNM 248740. / Subfamfly PARACERATITINAE Silberling, 1962 Genus PARACERATITES Hyatt, 1900 Paraoeratites burckhardti Smith Plate 15, figures 6—18 Ceratites (Paraceratites) burckhurdti Smith, 1914, p. 90, pl. 52, figs. 19—21 [holotype]. Revised description.—Discoidal, compressed (W/D mainly about 0.30 measured between lateral nodes, max- imum W/D of robust variants including nodes more than 0.45); moderately involute (U/D 0.20—0.25). Maximum diameter exceeding 100 mm. Flanks broadly rounded, 32 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA subparallel; ventral-lateral shoulders marked by tuber- cles but not sharply rounded. Venter high and narrow, extending well above ventral-lateral tubercles as a blunt keel that persists to shell diameters of more than 70 mm. Ribs on inner whorls at diameters less than 30 mm regular, projected or slightly falcoid, branching from umbilical swellings and terminating in projected ventral swellings. With increasing shell growth ribs bifurcate at lateral tubercles developed below midline of flanks on most primary ribs. On outer whorls ribs become weak and irregular, whereas lateral tubercles, numbering about 10 per whorl, develop into pronounced widely spaced nodes at or below midline of flank. Ventral- lateral tubercles persist as projected swellings cor- responding to ventral tips of ribs, outnumber lateral nodes 3: 1 to 35:1, become weak coalescing clavae on out- ermost whorl. Suture ceratitic. SI and S2 high and entire; only one discrete auxiliary saddle. L2 and divided VL about equal in depth and two-thirds that of L1. Lobes coarsely digitate. Discussion. —This species occurs in the strati- graphically lowest collections obtained from the vicinity of Fossil Hill. The pronounced development of widely spaced lateral nodes and the high, bluntly carinate venter, extending well above the ventral-lateral tuber- cles, distinguish P. burckhardti from the strati- graphically succeeding species P. clarkei and P. vogdesi, as revised. By these same characters P. burckhardti closely resembles P. cricki, the stratigraphically highest species of Paraceratites in the Rotelliformis Zone. Though their stratigraphic ranges are not contiguous and those of other species intervene, P. burckhardti and P. cricki are readily separated only by the lower propor- tion (2:1) of ventral-lateral to lateral tubercles and the more regular ribbing of the latter. Some compressed variants of P. burckhardti, es- pecially from USGS locality M164, which may be the stratigraphically lowest ammonite collection from the Rotelliformis Zone, have poorly defined ventral-lateral shoulders and lateral tubercles that arise low on the flanks from umbilical bullae. Figured specimens.—Plesiotypes, USNM 248742 to 248747. Occurrence.—Paraceratites burckhardti beds, strati- graphically below the occurrence of P. clarkei. USGS localities M164 (6) and M965 (40+); Rotelliformis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Paraceratites clarkei Smith Plate 16, figures 1—12 Ceratites‘ (Paraceratites) clarkei Smith, 1914, p. 91, pl. 40, figs. 15—17 [holotype], 18—20, 21—23; pl. 52, figs. 1—3, 4—6, 7—8, 9—11. Ceratites (Paraceratites) newberryi Smith [in part], 1914, p. 92, pl. 40, figs. 6—8, 9—11 [not figs. 1—3, 4—5, 13—14?= Paraceratites vogdesi (Smith), revised]. Ceratites (Paraceratites) trinodosus Mojsisovics [in part]. Smith, 1914, p. 92, pl. 39, fig. 6; pl. 52, figs. 15—18 [not pl. 39, figs. 1—2, 3—5, 7—87, 9-10, 11—137, 14—167, 17—197; pl. 52, figs. 12—14 = Paraceratites vogdesi (Smith), revised]. Ceratites beecheri Smith [in part], 1914, p. 94, pl. 43, figs. 18—20 [not figs. 15—17, 21—22, 23—24?, 25—26? = Nevadites humboldtensis Smith, revised]. Nevadites fontainei Smith [in part], 1914, p. 122, pl. 41, figs 16—17, 18—19, 20—22; pl. 51, figs 5—9 [ not pl. 41, figs. 23?, 24—25?, 26—277; pl. 51, figs. 1—4 = Nevadites humboldtensis Smith, revised]. Paraceratites clarkei Smith. Spath, 1934, p. 445. Silberling, 1962, p. 156 [in part]. [?]Ceratites rectangularis Smith, 1914, p. 85, pl. 41, figs. 14—15 [holotype]. [?]Ceratites (Pamceratites) wardi Smith, 1914, p. 94, pl. 53, figs. 4—6 [holotype], 7—8. Revised description.——Compressed discoidal to thick discoidal (W/D 0.30—0.50); width of umbilicus propor- tional to whorl thickness (U/D 0.25—0.35). Maximum diameter exceeding 70 mm. Ventral-lateral shoulders abrupt, emphasized by tubercles; venter broadly rounded with low, blunt ventral keel of variable strength on inner whorls. Cross section of whorls subrectangular. Ribbing and tuberculation variable in strength proportional to whorl thickness. On inner whorls of com- pressed forms, ribs delicate and falcoid, originate singly or in pairs from indistinct umbilical tubercles, terminate at sharp ventral-lateral tubercles elongated parallel to projected ventral tips of ribs; lateral tubercles developed last, spaced irregularly on consecutive or alternate ribs below midline of flanks. On more robust shells coarse primary ribs join umbilical with lateral tubercles on lower flanks. Most primary ribs bifurcate at lateral tubercles, some rejoin at ventral-lateral tubercles; ratio of ventral-lateral to lateral tubercles less than 2:1. On outer Whorls ribbing becomes weak and irregular, lateral and ventral-lateral tubercles dominate ornamentation. Strength of ventral-lateral tubercles equals or exceeds that of lateral tubercles. Suture ceratitic, like that of P. burckhardti. Discussion.—This species occupies a stratigraphic position intermediate between that of P. burckhardti and P. vogdesi and in some respects combines the morphologic characters of these species, although com- plete intergradation with them is not exhibited. The position of the lateral tubercles low on the flanks is like that of P. burckhardti, whereas the comparable or greater strength of the ventral-lateral compared with the lateral tubercles and the wide, broadly rounded venter are in agreement with P. vogdesi. The young stages of compressed strongly keeled variants of P. clarkei are in- distinguishable from specimens of P. burckhardti of comparable size and proportions on which the lateral tubercles are not yet fully developed. PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 33 Paraceratites clarkei was recognized as a distinct species by Silberling (1962, p. 156), but due to insuf- ficient stratigraphic control its occurrence was mis- placed between that of P. vogdesi and of P. cricki. Though few in number, subsequent stratigraphically controlled collections amply verify the correct stratigraphic position of P. clarkei. Figured specimens.—Plesiotypes, USNM 248748 to 248753. Occurrence—Paraceratites clarkei beds, stratigraph- ically between the occurrence of P. burckhardti and P. vogdesi. USGS localities M136 —7 ft (2.1 m) (1), M606 —8 ft (2.5 m) (4), M966 (30+), and M967 —15 ft (4.5 m) (2); Rotelliformis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Pumaratltes vogdesi (Smith) Plate 16, figures 13—28; plate 17, figures 1-5 Ceratites uogdesi Smith, 1904, p. 384, pl. 43, figs. 7 [holotype], 8; pl. 44, fig. 1 [holotype]. Ceratites (Paraceratites) vogdesi Smith. Smith, 1914, p. 89, pl. 35, figs. 4—6 [holotype], 7—9?. Ceratites (Paraceratites) newberryi Smith [in part], 1914, p. 92, pl. 40, figs. 1—3 [holotype], 4—5, 13—14? [not figs. 6—8, 9—11 = Paraceratites clarkei Smith, revised]. Ceratites (Paraceratites) trinodosus Mojsisovics [in part]. Smith, 1914, p. 92, pl. 39, figs. 1—2, 3—5, 7—87, 9—10, 11—137, 14—16?, 17—197; pl. 52, figs. 12—14 [not pl. 39, fig. 6, pl. 52, figs. 15—18 = Paraceratites clarkei Smith, revised]. Ceratites fissicostatus Hauer. Smith, 1914, p. 96, pl. 53, figs. 1—3. Ceratites haguei Smith, 1914, p. 97, pl. 42, figs. 1—2 [holotype], 3—5; pl. 43, figs. l—2a, 3—57, 6—77, 8—10'?. Paraceratites uogdesi (Smith). Spath, 1934, p. 444. Silberling, 1962, p. 156 [in part]. [?] Ceratites kingi Smith, 1914, p. 85, pl. 41, figs. 1—3a [holotype], 4, 5—6, 7-8?, 9?, 10—11?, 12—137. [?] Ceratites (Paraceratites) trojanus Smith, 1914, p. 88, pl. 36, figs. 1—3 [holotype], 4—5; pl. 37, figs. 1—3, 4—5. [?] Ceratites crassicornu Smith, 1914, p. 95, pl. 43, figs. 11—12 [holotype], 13—14?. [?] Ceratites ecarinatus Hauer. Smith, 1914, p. 96, pl. 44, figs. 1—3. [?] Paraceratites trojanus Smith. Spath, 1934, p. 443. Revised description.—Discoidal, moderately com- pressed (W/D 0.30—0.35 between lateral tubercles or spines); width of umbilicus widely variable proportional to whorl width and strength of ornamentation (U/D 0.22-0.32). Maximum diameter exceeding 95 mm. Ventral-lateral shoulders abrupt, emphasized by tuber- cles; venter broadly rounded with indistinct low keel on inner whorls. Whorl cross section subrectangular in com- pressed, weakly ornamented forms, hexagonal in robust forms with coarse lateral spines. Ribbing and tuberculation widely variable in strength proportional to width of whorls and umbilicus. On inner whorls ribs weakly falcoid, branch from umbilical shoulder or at midflank, terminate in projected tuber- cles. Lateral tubercles above midline of flanks, first ap- pear at about 25-mm diameter on average forms, at less than 20 mm on coarsely ornamented robust variants, may be absent on extremely compressed variants. On average outer whorls, lateral tubercles develop into forward-curving hornlike spines whose length amounts to half the maximum whorl width. Umbilical tubercles develop parallel with lateral tubercles on more coarsely ornamented variants, fade on outer whorl. Ventral- lateral tubercles develop into pronounced clavi on outer whorl, alternate in position on either side of low, broadly rounded venter, extend above height of midline of venter. On outer whorl ribbing weak and irregular, or- ‘ namentation dominated by lateral spines and ventral- lateral clavi. Suture ceratitic, like that of P. burckhardti with high entire principal saddles, deep L1, coarsely digitate lobes, and only one auxiliary saddle. Discussion.—Paraceratites vogdesi shows perhaps the greatest range in morphologic variation of any ammonite species in the Fossil Hill fauna. Nevertheless, it is readily separated from the stratigraphically subjacent and also variable P. clarkei by the position of the lateral tubercles or spines which are above the midline of the flanks in the former and on the lower flanks of the latter. The broad, low venter of P. vogdesi and the relative prominence of the ventral-lateral clavi compared with the lateral spines distinguish this species from P. cricki and P. burckhardti which occur respectively higher and lower in the section. Paraceratztes Clarke; was erroneously conSIdered morphologically and stratigraphically transitional from P. vogdesi to P. cricki by Silberling (1962, p. 156). Further collecting proved this interpretation incorrect, and no clearly transitional forms were found between the stratigraphic occurrence of these two species. Possible intergradation between P. vogdesi and P. cricki might be represented by the specimens described by Smith as Ceratites (Paraceratites) trojanus and questionably in- cluded here in the revised P. vogdesi. The lateral spines of these forms are borne high on the flanks as in P. vogdesi but, like those of P. cricki, are much more pronounced than the weak ventral- lateral tubercles. As pointed out by Spath (1934, p. 436), the specimens from fossil Hill assigned by Smith to Paraceratites trinodosus Mojsisovics, which are included here partly in P. vogdesi and partly in P. clarkei, developed coarser sculpture than the Alpine types of this species. Nevertheless, among the wide range of morphologic variants assigned here to P. clarkei, individuals closely similar to the types of P. trinodosus are expectable, and among the variants of P. vogdesi some specimens are very close to the typical specimens of the Alpine species Ceratites fissicostatus Hauer and C. ecarinatus Hauer. Despite their priority, application of any of these Alpine 34 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA specific names to the species of Paraceratites recognized herein from Nevada seems unwise because the morphologic range of the populations represented by these European names is unknown, and on a population basis the European species may differ considerably. These European specific names represent a different kind of concept than the specific entities recognized here and the two are not strictly comparable. Until the Euro- pean and Nevadan species can be compared on a popula- tion basis it seems preferable for the purpose of tax- onomy to regard Smith’s usage of these European names as misidentifications. Figured specimens.—-Plesiotypes, USNM 248754 to 248763. Occurrence.—Paraceratites vogdesi beds, strati- graphically between the occurrence of P. clarkei and P. cricki. USGS localities M136 (50+), M136 —5 ft (1.5 m) (4), M163 (9), M165 (8), M605 (20+), M606 (24), and M967 -9 ft (2.7 m) (3); Rotelliformis zone, vicinity of Fossil Hill, Humboldt Range, Nev. Paraceratites cricki Smith Plate 17, figures 6—20 Ceratites (Paraceratites) cricki Smith, 1914, p. 87, pl. 37, figs. 6—9 [holotype], 10—11, 12—13; pl 38, figs. 1—2, 3-4, 5—6, 7—8, 9—10?, 11—127; pl. 47, figs. 19-21, 22—247. Ceratites (Paraceratites) taurus Smith, 1914, p. 88, pl. 35, figs. 1—2 [holotype], 3. Paraceratites cricki Smith. Spath, 1934, p. 443. Silberling, 1962, p. 156 [in part]. Revised description.—Inner whorls discoidal, com- pressed (W/D 0.25—0.30); outer whorl more robust (W/D between lateral nodes of outer whorl 0.30—0.42). Moderately involute (U/D 0.20—0.25), outer whorl somewhat more evolute (U/D of robust outer whorls as much as 0.30). Maximum diameter exceeds 90 mm; compressed forms attain larger diameter than robust variants. Ventral-lateral shoulders abrupt, emphasized by tubercles on inner whorls. Venter widely variable in width proportional to thickness of whorls, raised into blunt keel extending well above ventral-lateral tuber- cles, bluntly fastigate on robust outer whorls. Ribbing on inner whorls strong and regular. Primary ribs branch on lower flank; ribs terminate in projected ventral-lateral swellings or tubercles. At about 20-mm diameter lateral tubercles develop at bifurcation point of primary ribs; weak nonpersistent umbilical tubercles may also develop. With increasing shell growth lateral tubercles increase rapidly in strength. On outer whorl 8 to 10 pronounced spinose lateral nodes dominate or— namentation. Ventral-lateral tubercles spaced in regular 2:1 ratio to lateral nodes or tubercles, with increasing shell diameter become clavate and finally coalesce into ventral-lateral ridge on orad part of outer whorl. Suture ceratitic; L1 wide, twice depth of L2 and divided VL; upper half of SI and S2 entire; only one dis- crete auxiliary saddle. Discussion.——This is the stratigraphically highest species of Paraceratites occurring at Fossil Hill. Its high, keeled or fastigate venter and pronounced lateral nodes are in strong contrast with the morphology of P. vogdesi and P. clarkei, the species occurring successively lower in the section. It is therefore surprising that P. cricki closely resembles P. burckhardti, the stratigraphically lowest paraceratite whose occurrence is separated from that of P. cricki by about 6 In of section. The shape of the venter and development of tuberculation is the same in both species; the principal distinctions between them are the more abrupt and angular ventral-lateral shoulders of P. cricki and the ratio of ventral-lateral to lateral tubercles, which is regularly 2:1 in P. cricki but 3:1 or more in P. burckhardti. Unfortunately, the available stratigraphically controlled collections are in- sufficient to show whether P. cricki is j homeomorph of P. burckhardti derived through transitions with the stratigraphically intervening P. clarkei and P. vogdesi, or whether it represents a morphologic stock that sud- denly reappears in the section, presumably by migration from some other area. The holotype of P. cricki is from the New Pass Range, about 100 km southeast of the Humboldt Range, where it has been collected subsequently from beds now assigned to the Favret Formation. Specimens from the Favret Formation in the Augusta Mountains, about 55 km east- southeast of Fossil Hill, were found in association with Gymnotoceras blakei and Tropigymnites sp. and are thus from a stratigraphic level comparable to that at which P. cricki occurs at Fossil Hill. Figured specimens.——Plesiotypes, USNM 248764 to 248770 from the Vicinity of Fossil Hill in the Humboldt Range. Occurrence.—Paraceratites cricki beds, above the oc- currence of P. vogdesi, and with populations transitional between Gymnotoceras rotelliformis and G. blakei. USGS localities M605 +10 ft (3 m) (1), M607 (40+), and M967 (10+); Rotelliformis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Genus EUTOMOCERAS Hyatt, 1877 Eutomoceras cf. E. lahontanum Smith Plate 18, figure 1 cf. Eutomoceras lahontanum Smith, 1914, p. 63, pl. 28, figs. 8—11 [holotype]. This species was placed in synonomy with Eutomoceras dalli Smith in the preliminary summary of the Fossil Hill fauna by Silberling (1962, p. 156). It is provisionally regarded here as a distinct species because its peculiar morphology is not duplicated in the PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 35 available but admittedly small samples of E. dalli, and a single specimen that may agree with Smith’s holotype of E. lahontanum was collected about a meter strati- graphically below the occurrence of E. dalli. This specimen, illustrated here, is mainly part of an outer whorl on which the ornamentation is reduced, but strong bullae, like those of E. lahontanum, can be seen on the umbilical part of the penultimate whorl. Also, the width of the venter is proportional to that of E. lahontanum and greater than that of E. dalli. Eutomoceras lahontanum may be a connecting link between Paraceratites cricki and Eutomoceras dalli; the single specimen assigned to E. lahontanum is from a stratigraphic position intermediate between those of these two species. On E. lahontanum the strong um- bilical bullae and distinct ventral-lateral shoulders, which on the holotype are ornamented by widely spaced paired tubercles, suggest affinity to Paraceratites cricki. But the discrete high keel, the origin of the bullae at the umbilical shoulder, and the bifurcating falcoid ribs of E. lahontanum are more in agreement with Eutomoceras. Figured specimen.—Plesiotype, USNM 248771. 0ccurrence.—USGS locality M610 (1), lower part of Gymnotoceras blakei beds, Rotelliformis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Eutomoceras dalli Smith Plate 18, figures 2—7 Eutomoceras (Halilucites) dalli Smith, 1914, p. 65, pl. 29, figs. 1—4 [holotype], 5, 6—8, 9—10?. Hungarites fittingensis Smith [in part], 1914, p. 58, pl. 90, figs. 5-7 [holotype] [not? pl. 29, figs. 12—14 = ?Eutomoceras dunni Smith] Eutomoceras dalli Smith [in part]. Silberling, 1962, p. 156. [not] Hungarites aff. H. fittingensis Smith. Kiparisova, 1961, p. 164—165, pl. 32, figs. 3a—3c. Eutomoceras dalli is the stratigraphically lowest of an evidently intergraditional succession of species that in- cludes E. dalli, E. dunni, and E. laubei. Compared with younger species of this series, E. dalli has a wider um- bilicus (U/D about 0.25), thicker whorls, a wider venter, and coarser ribbing that commonly branches from enlarged primary ribs on the lower flanks. The develop- ment of irregularly spaced papillae on the ribs, a feature characteristic of Eutomoceras, is widely variable among individuals of a single population. Papillation is generally absent at shell diameters of less than 30 mm; on the outer whorl the strong ornamentation is reduced to discontinuous smooth weak ribs. As suggested by Spath (1951, p. 11), the holotype of “Hungarites” fittingensis Smith is a fragment of the outer whorl of a Eutomoceras; the remainder of this specimen is restored with plaster. Traces of coarse papil- lae are visible on the apicad part of this fragment, and its whorl shape and proportions are like those of E. dalli. Smith’s paratype of ”Hungarites” fittingensis, also part of an outer whorl, is more like E. dunni in shape. The assignment by Smith of E. dalli to Halilucites, which he treated as a subgenus of Eutomoceras, seems incorrect in view of the nonpapillate ribbing of the typical European representatives of Halilucites. Spath (1951, p. 11) was probably correct that Eutomoceras and Halilucites are distinct, perhaps geographically isolated, derivatives from Paraceratites. Figured specimens.—Plesiotypes, USNM 248772 to 248775. Occurrence.—USGS localities M137 (4), M141 (4), M611 (11), M613 (7), and M964 (1); Gymnotoceras blakei beds, Rotelliformis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Eutomoceras dunni Smith Plate 18, figures 8—15 Eutomoceras dunni Smith, 1904, p. 381, pl. 43, fig. 11 [holotype]; pl. 44, fig. 4 [holotype]. Smith, 1914, p. 62, pl. 27, figs. 14—16, 17, 18—19, 20—21, 22—237, 24—257. Silberling, 1962, p. 156. Eutomoceras brewen' Smith, 1914, p. 61, pl. 28, figs. 1-4 [holotype], 5, 6—7a. _ Eutomoceras laubei Meek [in part]. Smith, 1914, p. 63, pl. 26, figs. 7—8, 9, [not E. laubei on pls. 10, 24, 27, and 90 = Eutomoceras laubei Meek]. [7] Hungarites fittingensis Smith, 1914 [in part], p. 58, pl. 29, figs. 12—14 [not pl. 90, figs. 5—7 = Eutomoceras dalli Smith]. Eutomoceras dunni is intermediate between E. dalli and E. laubei in the width of its umbilicus (U/D about 0.20), its whorl thickness, and the strength of its ribbing and papillation. As with E. dalli, the development of papillation varies among individuals and with the stage of growth. Hence, the separation by Smith of E. breweri Smith from E. dunni, from which it differs only in the weaker development of papillae on the ribs, is imprac- tical. Figured specimens.—Plesiotypes, USNM 248776 to 248779. Occurrence.—Frechites nevadanus beds at USGS localities M137+4 ft (1.2 m) (2), M142 (6), and M614 (4); Parafrechites meeki beds at USGS localities M166 (3), M612 (1), M616 (2), M958 (3), and M960 (1); Meeki Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Eutomoceras laubei Meek Plate 19, figures 1—6 Eutomoceras laubei Meek, 1877, p. 126, pl. 10, figs. 8—8a [holotype]. Hyatt and Smith, 1905, p. 131, pl. 60, figs. 7—10, 11. Smith, 1914, [in part], p. 63, pl. 10, figs. 7—10, 11; pl. 14, figs. 8—8a; pl. 27, figs. 1—2, 3—4, 5—7?, mm, 11—13?; pl. 90, figs. 1—4 [not pl. 26, figs. 7—8, 9 = Eutomoceras dunni Smith]. Silberling, 1962, p. 156. Among the known species of Eutomoceras, E. laubei is the stratigraphically highest. Although the available 36 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA samples are relatively small, complete morphologic tran- sition evidently exists between this species and E. dunni, which is characteristic of the beds immediately underly- ing those with E. laubei. Compared with E. dunni, E. laubei is more finely sculptured, lacks enlarged primary ribs on the lower flanks, is more involute (U/D about 0.10 to 0.15), and has thinner whorls whose flanks converge towards a narrow venter. Following Spath’s suggestion, two of the specimens in- cluded by Smith (1914) in E. laubei are transferred here to E. dunni, with which their relatively evolute coiling is in better agreement. In stating that E. laubei was first discovered by geologists of the 40th Parallel Survey in the New Pass Range in association with “Acrochordiceras hyatti,” Smith (1914, p. 64) introduced an unwarranted strati- graphic assumption. In the original description of these two species, Meek (1877, p. 128) did indicate that the “locality and position” of E. laubei is the same as that of “Acrochordiceras hyatti,” but for the latter his entry (p. 126) is simply: “New Pass, Desatoya Mountains [New Pass Range], Nevada; Trias.” The Triassic section of the New Pass Range, about 100 km southeast of the Hum- boldt Range, includes ammonite-bearing beds of both the Hyatti and Meeki Zones, and there is therefore no reason to believe that Eutomoceras laubei, which is restricted to the upper part of the Meeki Zone in the Humboldt Range, occurs in the Hyatti Zone of the New Pass Range. Figured specimens.—Holotype, USNM 12528 (originally figured by Meek, 1877, pl. 10, figs. 8—8a), plesiotypes, USNM 248780 and 248781. Occurrence.—Parafrechites dunni beds, Meeki Zone, at USGS localities M618 (7), M619 (6), M959 (1 +), and M968 (4); lower Occidentalis Zone at USGS localities M144 (1), M144 —6 ft (1.8 m) (4), M620 (2), and M962 (10+); vicinity of Fossil Hill, Humboldt Range, Nev. Genus NEVADITES Smith Nevadites Smith, 1914, p. 121 [type species N. merriami Smith, 1914, a subjective synonym of Nevadites hyatti (Smith, 1904), by original designation]. Stratigraphically restricted collections of Nevadites show a wide range in morphologic variation. Because of the relatively large size and ornate character of these ammonites, bedrock collections sufficiently large and well preserved to completely demonstrate a normal fre- quency distribution and complete morphologic in- tergradation of variants could not be obtained. Nevertheless, the mutual occurrence in a single bed of morphologically distinct but closely related forms evidences their specific identity. All of the ammonites referred by Smith (1914) to Anolcites are regarded here as belonging to Nevadites, thereby enlarging the original concept of the genus. Even in the stratigraphically highest species, however, in which the two rows of ventral spines are closest together, no trace of a ventral furrow, the distinguishing feature of Protrachyceras, is present. Otherwise, the youngest Nevadites, as revised here, are in all respects similar to Protrachyceras and are logical direct ancestors of this and all other clydonitacids. Nevadites hyatti (Smith) Plate 22, figures 24—29; plate 23, figures 1—7 Trachyceras (Anolcites) hyatti Smith, 1904, p. 389, pl. 43, fig. 12 [holotype]; pl. 45, figs. 1 [holotype], 2. Nevadites hyatti (Smith). Smith, 1914, p. 124, pl. 77, figs. 1—3, 4—5, 6—8, 9—11?, 12—13?. Silberling, 1962, p. 157. Nevadites merriami Smith, 1914, p. 125, pl. 75, figs. 1—3 [holotype], 4—6, 7—8, 9-11, 12—14; pl. 76, figs. 1—2?, 3—6?, 7—10?, 11—13?, 14—16. Inner whorls at diameters of about 20 mm have regular ribbing with umbilical and ventral tubercles and a sub- rectangular cross section with the width nearly equal to the height. With increasing shell diameter the whorl out- line becomes hexagonal as lateral spines develop and become increasingly pronounced slightly above the midline of the flanks. Accompanying increase in relative size of the lateral and ventral tubercles, the ribs become increasingly coarse, irregular, and interrupted. On large shells the whorl width measured at the interspaces is about the same as or a little greater than the height; the maximum width measured to the tips of the lateral spines may be as much as twice the corresponding whorl height. Except for weak extensions of the ribs, the venter is smooth, and flattened at all growth stages. The ratio of ventral width between the tips of the ventral spines to the whorl height averages about 0.60 for small shells and about 0.70 for the largest specimens; the range in this ratio for outer whorls is 0.55—0.75. Populations of Nevadites hyatti, as revised, in com- parison with the stratigraphically higher populations of N. hum boldtensis, as revised, include specimens that on the average have thicker whorls, broader venters, fewer but stronger ribs, and more pronounced tuberculation. These distinctions are apparent only in comparing pop- ulations from different stratigraphic levels; the morphologic variation of the two species overlaps and complete transition between them could take place within stratigraphically intermediate samples. The basis for separating the six species that Smith as- signed to Nevadites into these two morphologically more encompassing species is illustrated by the scatter diagram (fig. 19) on which the width of the venter PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 37 measured between the tips of the ventral spines is plot- ted against the corresponding whorl height for two sets of specimens, one set representing a stratigraphic level 2—2.5 m higher than the other. A similar diagram, in which the scattering of points representing specimens from different levels would fall into two distinct but overlapping areas, could be obtained by plotting whorl width against whorl height. Figure 19 shows that Smith’s “species” conform to one or the other cluster of points that are regarded here as characterizing the revised species N. hyatti and N. humboldtensis. 'Younger species referred here toilNZvdcf'tES, but originally included by Smith (1914) in Anolcites, differ fr 1 I r X 18— — U) 0: Lu ,_ W Lu E :16” 2 Z _ a 214— E m .— _l < I 512- LU > LL _ 0 $10— I.— z w LU XX Lu E.— m E ex 9 XX 361.. I l l 1 I | I l | 10 14 1s 22 26 30 WHORL HEIGHT BETWEEN TUBERCLES, IN MILLIMETERS FIGURE 19.—Scatter diagram comparing the width across the venter between the tips of the ventral spines to the corresponding whorl height measured between the tubercles for specimens in population samples of Neuadites from different stratigraphic levels. Dots are specimens of N. hyatti, revised, from USGS localities M144 -6 ft and M962; crosses are specimens of N. humboldtensis, revised, from the stratigraphically higher USGS localities M144 and M962A. For comparison, the trend of width between the ventral spines with increasing whorl height is plotted as a dashed line for each holotype of five of the so-called “species” of Nevadites recognized by Smith (1914). Comparable lines for the specimens as- signed to N. whitneyi (Gabb) by Smith (1914) would be close to those representing the type specimens of Smit ’s “species” here in- cluded in N. humboldtensis. from both N. hyatti and N. hum boldtensis in having four or more rows of tubercles in addition to being generally more discoidal and involute and in having a narrower venter between the rows of ventral spines. Figured specimens.——Holotype, USNM 74268 (originally illustrated by Smith, 1904, pl. 43, fig. 12 and pl. 45, fig. 1), plesiotypes, USNM 248827 to 248831. Occurrence.—USGS localities M144 —6 ft (1.8 m) (11), M621 (11), and M962 (21); lower part of Nevadites beds, Occidentalis Zone, vicinity of Fossil Hill, Hum- boldt Range, Nev. Nevadltes humboldtensls Smith Plate 23, figures 8—19; plate 24, figures 1—4 Nevadites humboldtensis Smith, 1914, p. 123, pl. 78, figs. 1—3 [holotype]; pl. 79, figs. 1—3, 4—6, 7—8, 9—10. Silberling, 1962, p. 157. Nevadites fontainei Smith [in part], 1914, p. 122, pl. 41, figs. 23?, 24—25?, 26—277; pl. 51, figs. 1—4 [holotype]. [Not pl. 41, figs. 16—17, 18—19, 20—22, pl. 51, figs 5—9 = Paraceratites clarkei Smith, revised]. Nevadites sinclairi Smith, 1914, p. 126, pl. 81, figs. 17—19 [holotype]; pl. 82, figs. 1—3. Nevadites whitneyi (Gabb) [in part]. Smith, 1914, p. 126, pl. 80, figs. 1—3, 4—5, 6—8; pl. 81, figs. 1—3, 4—5, 6—7, 8—9, 10—13, 14—16? [not? pl. 48, figs. 4-5 copied from Gabb (1864), genus and species un- recognizable]. Ceratites beecheri Smith [in part], 1914, p. 94, pl. 43, figs. 15—17 [holotype], 21-22, 23—24?, 25-26? [not figs 18-20 = Paraceratites clarkei]. [?] Trachyceras (Anolcites) gracile Smith, 1914, p. 132, pl. 82, figs. 4—5 [holotype], 6—77, 8—9?. The morphologic variation within populations in- cluded in Nevadites humboldtensis overlaps that of N. hyatti, but as a whole specimens of the former have nar- rower whorls (W/H about 0.90 measured at the inter- spaces), denser and more regular ribbing, and relatively weaker tuberculation than those of the latter. Lateral tubercles appear early in the ontogeny of N. humboldtensis and are commonly well developed at diameters less than 15 mm. On the outer whorls the lateral tubercles of densely ribbed, relatively high- whorled variants are relatively small and are located just below the midflanks, whereas on coarsely ornamented variants they are on the upper flanks. As with N. hyatti, the venter of N. humboldtensis is smooth and flattened at all growth stages; a low keel like those on the Paraceratites described by Smith as paratypes of N. fontainei is never present. The ratio of ventral width between the tips of the ventral spines to whorl height averages about 0.50 for whorls of more than 15 mm in height; the extremes for outer whorls range from 0.40 to 0.63 and thus overlap the range of ratios for N. hyatti (fig. 19). Ornamentation of the holotype of N. humboldtensis is coarser than that of average specimens in populations in- . cluded under this name and is more like that of N. 38 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA hyatti. However, none of the populations to which the latter name is applied include specimens with such a narrow ventral width or with whorls as high in propor- tion to their width. One of the two specimens of Ceratites whitneyi Gabb originally illustrated by Gabb (1864) was selected as the type of “Trachyceras” americanum by Mojsisovics (1886, p. 149), leaving the specimen portrayed by Gabb’s plate 4, figures 11 and 11a as the implicit type of C. whitneyi. This specimen, for which no locality is given in the original description, was considered a Nevadites by Smith, and if this were so, N. whitneyi (Gabb) would be the prior name for the specimens included here in N. humboldtensis. Part of the type lot of Ceratites whitneyi, including three small unfigured specimens (ANSP 1222—1224) of Nevadites and the holotype of “Trachyceras” americanum Mojsisovics (ANSP 1220—1221, different numbers for two parts of the same specimen), were located at the Academy of Natural Sciences of Philadelphia with Gabb’s original label. The specimen corresponding to Gabb’s figures 11 and 11a on plate 4 could not be found, and a note written by Alpheus Hyatt and found with the type lot indicates that this specimen has been missing since before 1900. The small, numbered specimens of Nevadites in the type lot were contained in a pillbox from a drug store in Palo Alto, Calif, suggesting that J. P. Smith of Stanford University may have borrowed this collection at some time during his study of the Middle Triassic fauna and perhaps based his concept of C. whitneyi upon them. Because the figured type is missing and Gabb’s illustra- tions of it (pl. 4, figs. 11, 113) are unrecognizable, C. whitneyi is considered here a nomen dubium. The dis- tance between the ventral spines shown on Gabb’s diagrammatic whorl outline (fig. 11a) is considerably less than that of Nevadites humboldtensis, and the specimen portrayed might be a younger Nevadites or even a Protrachyceras, assuming that it came from the Middle Triassic of the Humboldt Range. Figured specimens.—Plesiotypes, USNM 248832 to 248839. Occurrence.—USGS localities M144 (25+), M620 (18+), M622 (15+), M961 (25+), and M962A (20+); Nevadites humboldtensis beds, Occidentalis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Nevadites furlongi (Smith) Plate 24, figures 5—7 Trachyceras (Anolcites) furlongi Smith, 1914, p. 130, pl. 83, figs. 1—4 [holotype], 5—7; pl. 84, figs. 1—2, 3—5, 6—8, 9—11?, 12—13?. [?] Trachyceras (Anolcites) meeki Mojsisovics [in part], Smith, 1904, pl. 45, fig. 3. Compared with Nevadites gab bi, which occurs 5 to 10 ft higher in the section, N. furlongi has more robust whorls, a Wider umbilicus, coarser ribs, and stronger tubercles. From older species of the genus, N. furlongi differs in having besides the umbilical and ventral rows of tubercles both a ventral-lateral and a lateral row of tubercles. The ribs bifurcate at the lateral row, which migrates to the upper flank and becomes exaggerated in size on the outer whorl. Figured specimens.—Plesiotypes, USNM 248840 and 248841. Occurrence.—USGS localities M145 (3), M623 (8), and M625 (3); Nevadites furlongi beds, Occidentalis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Nevadites gabbi (Smith) Plate 24, figures 8—11 Trachyceras (Anolcites) gab bi Smith, 1914, p. 132, pl. 9, figs. 3-6, 7—9?, 10—12?, 13-15?, 16—177; pl. 11, figs. 4—5, 6—77; pl. 85, figs. 11—12 [holotype]; pl. 86, figs. 1—3, 4—6, 7—9‘?, 10—11?. Trachyceras (Anolcites) meeki Mojsisovics. Hyatt and Smith, 1905 [in part], pl. 59, figs. 3—6, 7—9?, 10-12?, 13—15?, 16—177; pl. 74, figs. 4—5, 6—77. [?]Trachyceras (Anolcites) meeki Mojsisovics. Smith, 1904 [in part], pl. 45, fig. 4. Nevadites from the stratigraphically highest of the beds characterized by this genus agree with Smith’s con- cept of ”Anolcites” gabbi but are difficult to compare with the poorly preserved type specimens of this species. Compared with N. furlongi, the whorls of N. gab bi are higher and narrower, and the ribbing and tuberculation are more delicate. The inner whorls have four rows of tubercles as with N. furlongi, but with growth two ad- ditional lateral rows commonly developed. In his original description, Smith mentioned only four rows, and his statement (Smith, 1914, p. 131) that the spines of “Anolcites” gabbi are more numerous than those of “A. ” furlongi may be in reference to the number of spines per spiral rather than the number of rows of spirals. Nevertheless, some specimens with the delicate or- namentation of N. gabbi develop as many as six rows. Unfortunately, the number of spine spirals on the holotype is indefinite owing to its poor preservation. Figured specimens.—Plesiotypes, USNM 248842 and 248843. Occurrence.—USGS localities M146 (6), M624 (8), and ?M626 (1); Nevadites gabbi beds, Occidentalis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Family HUNGARITIDAE Waagen, 1895 Genus HUNGARITES Mojsisovics, 1879 Hungarites sp. Plate 20, figures 13—14 A single poorly preserved specimen of this genus was collected from the upper member of the Prida Formation at Congress Canyon, associated with Daonella lommeli, PALEONTOLO GY—SYSTEMATIC DESCRIPTIONS 39 Proarcestes, and shell fragments of Protrachyceras? of late Ladinian age. Though not adequate for specific as- signment, the specimen is illustrated here as the only true Hungarites yet found in the Middle Triassic of the Humboldt Range. The suture could not be exposed, but the nearly smooth flanks, proportions of the fastigate venter, and degree of involution closely resemble those of the septate inner whorls of Hungarites pradoi illustrated by Mojsisovics (1882, pl. 32, figs. 7, 8) from the Ladinian of Spain and of the specimen assigned to the same species by Diener (1908, p. 18, pl. 4, fig. 11) from the Ladinian Daonella shales of Spiti. Figured specimen.—Plesiotype, USNM 248790. Occurrence—USGS locality M907; upper part of the upper member of the Prida Formation, Congress Can- yon, Humboldt Range, Nev. Superfamily PINACOCERATACEAE (Mojsisovics, 1879) Family JAPONITIDAE Tozer, 1971 Genus TROPIGYMNITES Spath, 1951 Tropig'ymnites planorbis (Hauer) Sibyllites planorbis Hauer, 1896, p. 271, pl. 12, figs. 1—8. Tropigymnites planorbis (Hauer). Spath, 1951, p. 102. Tropig'ymnites? cf. '1‘. Planorbis (Hauer) Plate 26, figures 1—4 Gymnites (Anagymnites) acutus Hauer. Smith, 1914, p. 54, pl. 97, figs. 13—14. Tropigymnites planorbis (Hauer). Silberling, 1962, p. 157. Following the suggestion by Spath (1951, p. 100), specimens like that assigned to the gymnitid species Anagymnites acutus (Hauer) by Smith (1914) are questionably placed in the genus Tropigymnites. Unfor— tunately, the suture could not be exposed on any of the specimens from the Humboldt Range. Because the whorl shape and shell proportions of Tropigymnites and Anagymnites are similar, Smith’s generic assignment re- mains a possibility. Assignment of the present species to Tropigymnites is favored because it occurs strati- graphically below any of the species of Tropigastrites, and it may therefore be the earliest representative of the succession of celtitid species, each of which characterizes a different level of the upper Anisian. Moreover, exter- nally similar specimens found in the Paraceratites cricki beds of the Favret Formation in the Augusta Mountains have a simple suture pattern like that of Tropigymnites with three subammonitic saddles. These specimens from Augusta Mountain, which occupy a stratigraphic posi- tion intermediate between that of the present species and that of Tropigastrites gemmellaroi, differ from the present species only in having a narrower umbilicus and higher whorls. At comparable shell diameters the specimens provisionally assigned here to Tropigymnites planorbis have somewhat higher and more compressed whorls than the typical specimens from the Dinaric Alps as il- lustrated by Hauer (1896). Figured specimens.-—Plesiotypes USNM 248844 and 248845. Occurrence. —USGS localities M136 (4) and M605 (1), Paraceratites vogdesi beds, Rotelliformis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Genus JAPONITES Mojsisovics, 1893 Japonites cf. J. sugrlva Diener cf. Japonites sugriva Diener, 1895, p. 32, pl. 7, figs. la—lc. A single specimen collected in the Humboldt Range by I. C. Russell and Alpheus Hyatt in 1888 is the only known representative of Japonites found thus far in North America. The maximum preserved diameter of about 135 mm of this specimen approximately corresponds to the end of its phragmocone. Its evolute coiling, robust subtrigonal whorl shape, and ornamentation of radial umbilical folds are comparable to those of Japonites sugriva Diener. The suture could not be prepared in detail, but its general plan is like that characteristic of Japonites, having three prominent lateral saddles followed by a series of low aux- iliary elements that are directed radially and do not form a retracted suspensive lobe like that distinctive of Gym- nites. Russell and Hyatt’s locality description reads simply “Star Peak Triassic—Unionville, Nevada,” which might suggest that the specimen came from the Hyatti Zone, the most fossiliferous part of the section in the im- mediate vicinity of Unionville. This source is confirmed by a small ammonite embedded in the matrix that fills the small part of the body chamber preserved on the specimen. This small ammonite is like those from USGS Mesozoic locality M2829, and elsewhere in the Hum- boldt Range, that may be finely ornamented variants of Unionvillites hadleyi Smith and that have been found only in the upper part of the Hyatti Zone. Family GYMNITITIDAE (Waagen, 1895) Genus GYMNITES Mojsisovics, 1882 Gymnites tregorum n. sp. Plate 31, figures 6—12, text-figure 20 Leiophyllites? sp. A. Silberling and Wallace, 1969, p. 17, table 1. Description—Discoidal, compressed (W/D 0.20—0.25); evolute (U/D 0.35—0.40). Flanks flattened and venter evenly rounded. Umbilical wall low and steep. Shell surface smooth except for weak, irregular, slightly falcoid radial folds that cross the venter. 40 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA Suture ammonitic. On one poorly preserved specimen three principal elements are recognized. First saddle is coarsely crenulate. Discussion.—Compared with the specimens assigned here to Gymnites perplanus from the Hyatti Zone in the Humboldt Range, G. tregorum has lower whorls, stronger surficial ornamentation, and a less subdivided S1. G. tregorum also does not attain the large size of G. perplanus. This species is named in honor of Mr. and Mrs. R. H. Trego of Unionville, Nev. Figured specimens.—Holotype USNM 248915; para- types USNM 248914, 248916, and 248917. Occurrence—USGS Mesozoic localities M2358 (30+) and M2367 (14+); Caurus Zone, northern Humboldt Z M FIGURE 20.—Suture line (X 4) of Gymnites tregorum n. sp. Paratype, USNM 248917. Gymnites perplanus (Meek) Plate 30, figures 11—16; text-figure 21 Arcestes? perplanus Meek, 1877, p. 120, pl. 11, figs. 7—7a. Gymnites perplanus (Meek). Smith, 1914, p. 54, pl. 15, figs. 7—7a. This species is characteristic of the Hyatti Zone in the northern part of the Humboldt Range. The original two specimens on which the species is based were collected by the 40th Parallel Survey in the Vicinity of Buena Vista Creek canyon where this zone is the most fos- siliferous part of the section. Smith (1914, p. 54) recorded Gymnites perp lanus from the upper Anisian at Fossil Hill in the southern part of the Humboldt Range, but this occurrence is not documented. The suture of G. perplanus, illustrated here for the first time, is like that characteristic of the genus and has two complexly subdivided principal lobes and a retracted suspensive lobe that is subdivided into aux- iliary elements. As in other species of the genus, L1 is much larger than L2, and S2 is somewhat larger than 81. The suture of G. perplanus, as observed in several specimens, differs from that of species occurring at higher levels in the Anisian of the Humboldt Range chiefly in the number of auxiliary elements on the suspensive lobe. External of the umbilical seam are only three individualized, trifid auxiliary lobes, whereas younger species that are no more involute than G. perplanus are characterized by five or more such lobes. A relatively small number of discrete auxiliary elements may also be characteristic of other species like G. sankara Diener from India and G. volzi Welter from Timor that are from deposits of probable mid-Anisian age and hence of about the same age as G. perplanus. Figured specimens.—Holotype, USNM 12531 (originally figured by Meek, 1877, pl. 11, figs. 7—7a); plesiotypes, USNM 248908 and 248909. 0ccurrence.—USGS localities M533 (8), M970 (1); USGS Mesozoic localities M1180 (2), M1181 (3), M1184 (2), M2826 (1), and M2829 (5); Hyatti Zone in northern part of the Humboldt Range, Nev. FIGURE 21.—Suture line (X 1.75) of Gymnites perplanus (Meek). Plesiotype, USNM 248909. Gymnltes at. G. humboldti Mojsisovlcs Plate 31, figure 1; text-figure 22 cf. Gymnites humboldti Mojsisovics, 1882, p. 235, pl. 55, figs. 1—3. Gymnites of. G. incultus (Beyrich, 1867). Silberling, 1962, p. 158. A single phragmocone of a relatively involute (U/D 0.28), compressed Gymnites having a maximum preserved diameter of about 100 mm was collected in place from the Gymnotoceras blakei beds of the Rotel- liformis Zone in the vicinity of Fossil Hill. Except for conspicuous falcoid growth striae of irregular strength, the shell is smooth and lacks the spiral row of tubercles characteristic of Epigymnites alexandrae Smith, which occurs stratigraphically higher. The suspensive lobe of the suture (fig. 22) is subdivided by six or possibly seven discrete auxiliary lobes, which is twice the number found in G. perplanus (Meek) from the Hyatti Zone. The suture pattern, lack of ornamentation, and degree of in- WW9?“ FIGURE 22.—Suture line (X 1.75) of Gymnites cf. G. humboldti Mojsisovics. Plesiotype, USNM 248911. Some fine detail lost in preparation. PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 41 volution of this specimen are comparable to those of G. humboldti Mojsisovics, which was originally described from the upper Anisian of the Hallstatt Limestone in Austria. Figured specimen.—Plesiotype, USNM 248911. Occurrence—USGS locality M609, Gymnotoceras blakei beds, Rotelliformis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. Gymnltss? calli Smith Gymnites calli Smith, 1914, p. 53, pl. 26, figs. 1—1a. The only known specimen of this species is the holotype that was collected near Fossil Hill in the southern part of the Humboldt Range. The shell is con- siderably less evolute (U/D about 0.14) than other species of Gymnites from the Humboldt Range and is perhaps too tightly coiled for inclusion in this genus as presently delimited (Arkell and others, 1957, p. L184). The suture pattern, however, is that typical of Gym- nites. Although no additional specimens were found during the present study, shell fragments of Nevadites and Daonella dubia in the matrix of the type specimen in- dicate that it was derived from the upper part of the Oc- cidentalis Zone. Genus EPIGYMNITES Diener, 1916 Epigymnites alexandrae (Smith) Plate 31, figure 13 Gymnites alexandrae Smith, 1914, p. 52, pl. 23, fig. 1; pl. 24, figs. 1—2, 3?, 4—487, 5—67, 7—97, %-12?; pl. 25, fig. 1?. Silberling, 1962, p. 156. Several incomplete specimens from different localities in the vicinity of Fossil Hill are ornamented by a single spiral row of tubercles on the middle of the flank and otherwise agree in whorl shape and suture pattern with this species. The stratigraphically lowest of these specimens is from the Parafrechites dunni beds at the top of the Meeki Zone and the highest is from the Subasperum Zone. Epigymnites alexandrae thus ranges through the upper part of the upper Anisian and at least the lower part of the lower Ladinian. An imprint of Daonella cf. D. moussoni on the type specimen of G. alexandrae (Smith, 1914, pl. 23, fig. 1) in- dicates that it was derived from the upper part of the Oc- cidentalis Zone. The ratio U/D for this specimen is 0.365. The “cotype” (Smith, 1914, pl. 25, fig. 1; Stanford University type colln. no. 5429) is appreciably more in- volute (U/D 0.305) and generally resembles G. ecki Mojsisovics, which was originally described from the calcare di Clapsavon of northeastern Italy and is sup- posedly of late Ladinian age. Figured specimen.—Plesiotype, USNM 248918. Occurrence—USGS localities M619 (1), Parafrechites dunni beds, upper part of Meeki Zone; M624 (2) and M625 (1), upper part of Occidentalis Zone; one float specimen from the Occidentalis Zone of collecting-site C; USGS Mesozoic locality M 3094 (1), Subasperum Zone; vicinity of Fossil Hill, Humboldt Range, Nev. Family STURIIDAE (Kiparisova, 1958) Genus STUEIA Mojsisovics, 1882 Sturia cf. 8. japonica Diener, 1915 Plate 30, figures 17—18 cf. Sturia japonica Diener, 1915b, p. 18, pl. 6, figs. 1—2. Part of a large septate whorl of Sturia, having a max- imum whorl height of about 150 mm, was found in the Fossil Hill area as float derived from the Meeki Zone or stratigraphically higher. The suture of this specimen cannot be traced in detail, but it is illustrated photographically to show its general pattern and the degree of complexity of its subdivision. According to Kiparisova (1961, p. 180), Sturia japonica differs from the type species, S. sansovinii (Mojsisovics), mainly in having the spiral furrows on the umbilical part of the flanks more widely spaced, but the validity of this specific distinction has perhaps not been adequately tested as implied by Onuki and Bando (1959, p. 101) who placed the two species in synonymy. Figured specimen.———USNM 248910. Occurrence—Float at USGS locality M614, Meeki Zone (?), vicinity of Fossil Hill, Humboldt Range, Nev. Genus DISCOPTYCHITES Diener, 1916 Discoptychltes sp. Text-figures 23 and 24 ?Discoptychites evansi (Smith). Silberling, 1962, p. 157. [7] Ptychites euansi Smith, 1914, p. 47, pl. 21, figs. 3—3a. A septate fragment of the ventral part of a large am- monite having the compressed, subtrigonal whorl shape and suture pattern of Discoptychites was collected in place from the Paraceratites clarkei beds of the Rotel- liformis Zone at Fossil Hill. This fragment could belong to the same species as the specimen named Ptychites evansi by Smith (1914) though this specific name should probably be regarded as a nomen dubium. Smith’s specimen lacks outer whorls comparable in size to the present specimen, but its whorl shape is similar, and fragments of Daonella americana in its matrix indicate that it came from either the Rotelliformis or Meeki Zones. Other than the Sturia previously described, the only other ptychitid found thus far in the Humboldt Range is 42 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA an indeterminate immature specimen of Ptychites? from the Meeki Zone at USGS Mesozoic locality M960. Figured specimen.—USNM 248985. Occurrence.—USGS locality M139, Paraceratites clarkei beds, Rotelliformis Zone, vicinity of Fossil Hill, Humboldt Range, Nev. FIGURE 23.—Suture line (X 1.5) of Discoptychites sp. Figured specimen, USNM 248985. TIP OF FIRST LATERAL SADDLE FIGURE 24.—Diagrammatic cross section (natural size) of the outer part of an incomplete whorl of Discoptychites sp.; dotted where in- ferred. Figured specimen, USNM 248985. Family ISCULITIDAE Spath, 1951 Genus ISCULITES Mojsisovics, 1886 Isculites Mojsisovics, 1886, p. 154 [type species I. hauerinus (Stolicska) by monotypy]. Smithoceras Diener, 1907, p. 97 [type species S. drummondi Diener by monotypy]. Spitisculites Diener, 1916, p. 101 [type species Isculites hauerinus (Stolicska) by original designation]. Alloptychites Spath, 1951, p. 151 [type species Ptychites meeki Hyatt and Smith by original designation]. Isculites meeki (Hyatt and Smith) Plate 28, figures 10-18; plate 29, figures 10—13; text-figure 25 Ptychites meeki Hyatt and Smith, 1905, p. 87, pl. 25, figs. 6—8 [holotype], 8—10, 11—12. Smith, 1914, p. 47, pl. 6, figs. 6—8, 8—10, 11-12. Alloptychites meeki (Hyatt and Smith). Spath, 1951, p. 151. Isculites meeki (Hyatt and Smith). Silberling and Wallace, 1969, table 1, p. 17. Revised description—Inner whorls moderately in- volute and subglobose with evenly rounded venter and flanks; at diameters of 20—30 mm W/D = 0.50—0.75 and mean U/D = 0.22 for nine specimens; umbilical shoulder narrowly rounded, umbilical wall steep, nearly perpen- dicular. Outer whorls slightly uncoiled and more com- pressed, generally with flattened, subparallel flanks; at diameters > 40 mm W/D is mostly 0.40—0.50 and mean U/D = 0.254 for 13 specimens; umbilical wall shallower and more sloping as a function of egression. Maximum diameter exceeds 75 mm, but specimens having diameter > 50 mm uncommon. Surface smooth except for growth striae of irregular strength. One or more constrictions and flares near aper- ture. Suture only known from holotype; weakly subam- monitic; 81, S2, and SB of equal height, 81 and S2 broadly rounded in shape; L1 and L2 of equal depth and width, equal to VL in depth. Discussion.—The type lot of this species is from the Whitney collection in the Museum of Comparative Zoology, Harvard University, and was originally col- lected at Star Creek canyon in the Humboldt Range. Hyatt and Smith (1905, p. 87; Smith, 1914, p. 47), for reasons not stated, gave the stratigraphic horizon as lower Ladinian, but during the present study I. meeki has only been found in the lower Anisian Caurus Zone in the vicinity of Star Creek canyon. None of the many specimens from the two localities from which the present collections were made show the details of the suture, but its general plan and the propor- tions of its major elements are like that of the suture on the holotype. Compared with other species of the genus, when fully grown I. meeki is more compressed and its venter re- mains broadly rounded rather than becoming more nar- rowly arched as in I. hauerinus. Although the shell proportions and rate of maturity are evidently widely variable, egression of the outer whorls is definitely shown. The relative increase in the size of the umbilicus with growth as indicated by the means of the U/D ratios for shells smaller in diameter than 30 mm and those larger than 40 mm is significant at a probability level of 0.01. Figured specimens.—Holotype, MCZ 3998 (originally figured by Hyatt and Smith, 1905, p. 25, figs. 6—8); PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 43 paratype, MCZ 3900 (originally figured by Hyatt and Smith, 1905, pl. 25, figs. 9—10); plesiotypes, USNM 248882 and 248883; USNM 248891 and 248892. Occurrence.—USGS Mesozoic localities M2358 (75+) and M2367 (35+), Caurus Zone between Bloody Canyon and Star Creek canyon, Humboldt Range, Nev. Mlv FIGURE 25.—Suture line (X 3) of Isculites meeki (Hyatt and Smith). Holotype, MCZ 3998. Isculites tozeri n. sp. Plate 30, figures 1—10; text-figure 26 I. n. sp. ex aff. I. drummondi (Diener). Silberling and Tozer, 1968, p. 38. Isculites n. sp. Silberling and Wallace, 1969, table 1, p. 17. Description—Inner whorls moderately involute and globose; at diameters of 15—25 mm W/D = 0.65—1.00 and the mean U/D = 0.18 for seven specimens; umbilical shoulder narrowly rounded, umbilical wall steeply slop- ing or perpendicular. Outer whorls more compressed (W/D = 0.50—0.90 at D > 35 mm) with marked egression of umbilical margin (mean U/D = 0.23 for 19 specimens of D > 35 mm). Body chamber modified to arched or bluntly subtrigonal cross-sectional shape, reverting to parabolic cross section at apertural margin. Diameter of complete shells mostly 40—50 mm; estimated diameter of largest available specimen 50—55 mm. Surface smooth except for nearly straight growth striae of irregular strength. Projected constriction and flare just apicad of aperture. Suture known only from one specimen; subam- monitic; S1, S2, and S3 broadly rounded in shape and of about equal height and proportions. Discussion—This species is characteristic of the Hyatti Zone, and compared with Isculites meeki from the stratigraphically lower Caurus Zone, it has on the average a more robust shell. On a scatter diagram (fig. 27) comparing width and diameter of specimens of Isculites tozeri from USGS locality M533 and USGS Mesozoic locality M2359 and of I. meeki from localities M2358 and M2367 the shell proportions of the two species plot in two generally distinct but overlapping fields. Both samples of I. meeki plotted on figure 27 show about the same variation in shell proportions, as might be expected because they were collected only about 0.5 km apart probably from within the same few meters of section. The two plotted samples of I. tozeri, however, are from localities several kilometers apart and may represent different levels within the Hyatti Zone. They differ in their average proportions at diameters greater than 35 mm, the sample from locality M533 retaining a more globose shape of the body chamber. Although W/D ratios of the larger specimens of I. tozeri from locality M2358 overlap with those of I. meeki, shells of the two species are still readily distinguished by their different whorl shape, I. meeki having flattened, subparallel flanks and I. tozeri having a parabolic or subtrigonal out- line widest at the umbilical shoulder. The only suture line that could be prepared from the present samples of I. tozeri is more ammonitically crenulated than that of the holotype of I. meeki, but the general applicability of this distinction is uncertain. Of the Indian species herein regarded as belonging to Isculites, Smithoceras drummondi Diener (1907, p. 98, pl. 12, figs. 3a—3c) is like I. tozeri in its shell proportions, shape, and suture line, but the illustrated specimen of this species is still septate at a diameter greater than 60 mm, and it is thus much larger than any of the specimens of I. tozeri from Nevada. As S. drummondi is known from only two specimens, further comparison with I. tozeri is not possible. Isculites tozeri is named for E. T. Tozer of the Geological Survey of Canada. Figured specimens.—Holotype, USNM 248905; paratypes, USNM 248904, 248906, and 248907. Occurrence.—USGS locality M533 (40+) and USGS Mesozoic locality M2359 (50+), Hyatti Zone, northern part of Humboldt Range, Nev. Also represented from the Hyatti Zone of the Humboldt Range at USGS Mesozoic localities M1181 (2), M1182 (2), ?M1183 (5+), ?M2819 (3), M2821 (6), and ?M2829 (1). | FIGURE 26.—Suture line (X 3) of Isculites tozeri n. sp. Holotype, USNM 248905. Super-family DANUBITACEAE (Spath, 1951) Family DANUBITIDAE Genus CZEKANOWSKITES Diener, 1915 Czekanowskites hayesi (McLear-n) Plate 19, figures 16—19 “Ceratites” hayesi McLearn, 1946a, sheet 2, pl. 1, fig. 2. Czekanowskites hayesi (McLearn). McLearn, 1969, p. 43—44, pl. 1, figs. 4—8. The specimen illustrated is one of the only two found of this species and was collected from the Hyatti Zone of the Humboldt Range. The suture cannot be observed, but externally these specimens are nearly identical with 44 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA 55 | | l O X 50 _ // X _ 45 _ X _ // X’ HOIOWDG. ‘g I. tozeri / {1‘ 40 _ / _ ”J / g X j / g / z 35 _ / — E / t: / 2 30 — / EXPLANATION — S / lscu/ites mes/(i D / 0 Type lot 25 _ A Loc. M2367 _ 0 Loc. M2358 lscu/ites tozeri x Loc. M533 20 — # + Loc. M2359 15 I l 10 15 20 25 30 35 40 WIDTH, IN MILLIMETERS FIGURE 27 .—Scatter diagram comparing width and diameter of specimens of Isculites tozeri n. sp. from USGS locality M533 and USGS Mesozoic locality M2359 with Isculites meeki (Hyatt and Smith) from USGS Mesozoic localities M2358 and M23679 Solid lines enclose all points for I. meeki; dashed lines all points for I. tozeri. the holotype of Czekanowskites hayesi , a cast of which was provided us through the courtesy of the late F. H. McLeam along with casts of several variants. Figured specimen.—Plesiotype, USNM 248785. Occurrence—USGS locality M970 (1) and USGS Mesozoic locality M2359 (1), upper Hyatti Zone, Hum- boldt Range, Nev. Genus PBEUDODANUBITES Hyatt, 1900 Pseudodanuhites halli (Mojsisovics) Plate 19, figures 7—15; text-figure 28 Clydonites laevidorsatus (Hauer). Meek, 1877, p. 109, pl. 10, figs. 7 [herein selected as lectotype of Danubites halli Mojsisovics], 7a. Danubites halli Mojsisovics, 1896, p. 696 [new name for “Clydonites laeuidorsatus (Hauer)” of Meek, 1877]. Tropigastrites halli (Mojsisovics) [in part]. Smith, 1914, pl. 14, figs. 7, 7a [not figs. of “T. halli”on pls. 6, 12, 18, and 88 = Tropigastrites gemmellami Arthaber]. Pseudodanubites? halli (Mojsisovics). Silberling and Wallace, 1969, table 1, p. 17. [not] Celtites halli Mojsisovics. Hyatt and Smith, 1905, p. 125, pl. 25, figs. 4—4a, 5, 5a—5b; pl. 75, figs. 1—1a, 2—3, 4—5 [= ?Tropigastrites gemmellaroi Arthaber]. This specific name was applied by Hyatt and Smith (1905) and Smith (1914) to specimens of Tropigastrites from the Rotelliformis Zone, but specimens like those figured by Meek and for which Mojsisovics proposed the name Danubites halli differ from Tropigastrites in whorl shape and ornamentation and occur in the Hyatti Zone. The serpenticone inner whorls of Pseudodanubites halli are roughly quadrate in cross section with gently rounded umbilical and ventral-lateral shoulders and a broadly arched venter. The flanks are ornamented by blunt straight ribs and the venter is smooth. A gradual change in the shape of the outer whorls is produced by further arching of the venter into a bluntly fastigate shape. Although the periphery becomes narrowly rounded, it is not sharp as in Tropigastrites. Accom- panying this change in whorl shape, the ribs first tend to become bulbous and enlarged at the ventral-lateral shoulder and then on the outer whorl project forward onto the venter. The correspondence of ribs on either side of the outer whorl is irregular; where they coincide in position, they pass over the narrowly rounded ventral margin only slightly diminished in strength. Some variation in whorl compression and strength of ribbing occurs among individuals from the same bed. Compressed variants tend to have less bulbous ribs, which extend onto the venter at a smaller diameter, as on the specimen illustrated by figures 7—9, plate 19. This particular specimen may be from a somewhat higher level than others in the Hyatti Zone but is generally the same as some variants found in association with specimens like the lectotype. The suture is simple in plan with three broad, subam- monitically crenulate external saddles of about equal height. L1 is about twice the depth of L2 and slightly deeper than VL which is divided by an elongate triangular ES. This species differs from typical Danubites in the modified fastigate shape and ornamentation of its outer whorl, the absence of any kind of a ventral keel, and its subammonitic suture with relatively low and broad sad- dles. It is assigned to Pseudodanubites, although its typical species, P. dritarashtra (Diener, 1895), differs from the present species in two important respects: the suture, though described as being more advanced than that of Danubites, is still ceratitic, and the venter bears a “thread-like keel” (Diener, 1895, p. 30). Otherwise, P. dritarashtra as described by Diener is in close agreement with P. halli in whorl shape and ornamentation. The relationship of P. halli to some species of Tropigastrites that have similar ornament and equally evolute coiling, is evidently close. Although the ribs of PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 45 Tropigastrites are restricted to the lower flanks and the venter has a sharp fastigate margin, the suture is generally the same in plan and degree of complexity. Thus P. halli is in some respects intermediate between Pseudodanubites and Tropigastrites. This poses a problem in familial assignment because these genera are currently placed (Tozer, 1971) in different superfamilies: respectively the Danubitacea and Nathorstitacea. Figured specimens.—Lectotype, USNM 12522 (originally figured by Meek, 1877, pl. 10, fig. 7); plesiotypes, USNM 248782 to 248784. Occurrence—USGS Mesozoic localities M1124 (1), M1180 (7), M1181 (2), M1184 (1), and M1185 (1), and M2829 (10+), Humboldt Range, Nev. VTWW " M "*7 FIGURE 28.—-Suture lines (X 4) of Pseudodanubites halli (Mojsisovics), dashed where approximate. A, plesiotype, USNM 248986, specimen not figured. B, plesiotype, USNM 248784, suture line reversed. Genus UNIONVILLITES n. gen. Type species.-—Unionvillites hadleyi (Smith). Definition.—Discoidal, strongly evolute; typically with low subquadrate to broadly arched whorls. Well- developed rounded ventral keel. Regularly spaced, typically tuberculate, projected radial ribs. Suture in- completely known but simple and short, having subam- monitic saddles, L1 much deeper than L2 or VL. Discussion.—Specimens of species included in this genus are neither well represented nor completely known morphologically. Nevertheless, among mid-Anisian am- monites they embody a unique combination of characters quite unlike that of any previously described genus. Because they are easily recognized and serve as markers for the upper part of the Hyatti Zone, introduc- ing a new genus for them, even though incompletely characterized, is useful. No other middle Anisian am- monites, except the inner whorls of longobarditinids, possess tuberculate ribbing and a strong persistent ventral keel. The outer margin of Balatonites, in which Unionvillites hadleyi was originally placed, is quite dif- ferent in having ventral spines on ribs that cross the venter rather than being ventrally carinate. Unlonv‘lllites hadleyi (Smith) Plate 6, figures 17—23 Balatonites hadleyi Smith, 1914, p. 119, pl. 90, figs. 8—10. The following description is based largely on Smith’s holotype plus a few other well-preserved specimens from the Tobin Range and Augusta Mountains. The shell is thickly discoidal (W/D about 0.40 at D less than 30 mm), but widely umbilicate (U/D 050—055). In addition to the well-developed, persistent ventral keel, ornamentation consists of regularly but widely spaced projected primary ribs, each of which bears a bullate spine on the flanks and then projects sharply forward, fading toward the keel. On the venter between each primary rib, an additional rib is inserted and the projec- tion of both primary and secondary ribs tends to serrate the keel. The holotype has 16 primary ribs per volution. The suture, as partly seen on a specimen from the Augusta Mountains, is simple in form, having three principal lateral elements and apparently slightly crenulate subammonitic saddles. It is mainly dis- tinguished by having VL much shallower than L1. Figured specimens.—Holotype, USNM 74432; paratypes, USNM 248649 and 248650. Occurrence.—USGS Mesozoic localities M1181 (1), M2829 (1), upper Hyatti Zone, northern Humboldt Range, Nev. Better represented in the upper Hyatti Zone at the southern tip of the Tobin Range and in the Augusta Mountains several tens of kilometers east and southeast of the Humboldt Range. Unionvillites asseretoi n. sp. Plate 6, figures 24—28; text-figure 29 Description.—Evolute and compressed, at diameter of 30 mm, W/D = 0.32 and U/D = 0.50. Low subquadrate whorls with well-developed, persistent ventral keel. Um- bilical wall gently sloping, umbilical shoulder absent. Ornamentation consists of regularly spaced projected ribs with strong ventral swellings. The holotype has 37 ribs per volution. Suture known only from one specimen; subammonitic, three principal elements; VL much shal- lower than L1. This species is named in honor of the late Riccardo Assereto. Discussion.—This species is characteristic of the Hyatti Zone, and compared with Unionvillites hadleyi from the same stratigraphic level, it has a more discoidal shell, more ribs per volution and lacks bullate spines. The suture of Unionvillites asseretoi is about the same as Unionvillites hadleyi. Figured specimens.—Holotype, USNM 248653; paratypes, USNM 248651 and 248652. 46 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA 0ccurrence.—USGS Mesozoic locality M2829 (6), up- per Hyatti Zone, northern Humboldt Range, Nev. . if FIGURE 29.—Suture line (X 4) of Unionvillites asseretoi n. sp. Paratype, USNM 248652. Family LONGOBARDITIDAE (Spath, 1951) Subfamlly GROENLANDITINAE Asserto. 1966 Genus LENOTROPITES Popov, 1961 Lenotropites caurus (McLearn) Plate 29, figures 14—30; text-figure 30 “Hungarites” caurus McLearn, 1948, p. 1, pl. 11, figs. 1, 2. Lenotropites caurus (McLearn). Tozer, 1967, p. 69, 71, pl. 7, figs. 1a, b. Figured specimens.—Plesiotypes, USNM 248893 to 248900. 0ccurrence.—USGS Mesozoic localities M2358 (8), M2367 (4), M2828 (8+), M2362 (20+); Caurus Zone, northern Humboldt Range, Nev. l ham“; I l FIGURE 30.—Suture line (X 3) of Lenotropites caurus (McLearn), dashed where approximate. Plesiotype, USNM 248896. Subfamlly LONGOBARDITINAE The species of Longobardites recognized from the Humboldt Range are, in stratigraphically ascending order: Intornites mctaggarti (McLearn) from the lower part of the Hyatti Zone; Longobardites parvus (Smith) from the Rotelliformis and Meeki Zones; and L. cf. L. zsigmondyi (Bockh) from the Occidentalis Zone. A fourth species, I. nevadanus Hyatt and Smith, which is typical of the Shoshonensis Zone in other parts of northwestern Nevada, may also occur in the Humboldt Range in the upper part of the Hyatti Zone. Intornites nevadanus thus occurs in Nevada at a level intermediate between that of I. mctaggarti and that of L. parvus and is described here on the basis of specimens from the Shoshonensis Zone of the New Pass Range in order to clarify the correct usage of this name. Mature shells of all four species of longobarditinids from Nevada are smooth, compressed, acutely ter- minated oxycones and have the same distinctive pseudoadventitious suture pattern in which the height of S2 exceeds that of SI and the depth of L2 exceeds that of L1. The term “pseudoadventitious” was introduced by McLearn (1951) because these unusual proportions of the principal suture elements result from differential development during ontogeny from a normal pattern of saddles and lobes that progressively decrease in size dor- sally, and this pattern is not a true adventitious arrange- ment in which the ventral elements are developed by subdivision of VL. Compared with the outer whorls of Intomites mctag- garti and I. nevadanus, those of L. parvus and L. cf. L. zsigmondyi have a different configuration of the growth lines and are on the average more compressed. The inner whorls, however, provide the principal means of separating the different species and determining their generic assignment. Intornites mctaggarti, the oldest species recognized in Nevada, has robust, evolute, keeled, ornate inner whorls that pass by gradual transi- tion into the involute, compressed oxyconic mature whorls. The distinctive shape and ornament of the inner whorls may persist to diameters exceeding 25 mm, and the pseudoadventitious suture characteristic of the outer whorls is not developed until the whorls are more than 15 mm high. Successively younger species have young stages less divergent from the mature morphology and develop the mature oxyconic shape and pseudoadven- titious suture line at progressively smaller shell diameters. The inner whorls of L. cf. L. zsigmondyi, the youngest species, have essentially the same shape as the outer whorls at diameters of less than 10 mm. Although the morphology of the inner whorls and rate at which they mature is widely variable among individuals from the same stratigraphic level, little overlap exists between the combined characters of different species. The distinguishing features of the different species are given on table 4. The morphologic differences between successive species of longobarditinids in Nevada suggests a biogenetic pattern whereby recapitulation of an evolute, thick-whorled, costate, carinate, ceratitically septate ancestor recedes farther and farther back into the on- togeny of successive species until it is no longer recognizable in the youngest of the species. Such an evolutionary relationship appears to exist between Intor- nites mctaggarti and I. nevadanus, which in Nevada may be connected by stratigraphically intermediate, morphologically transitional populations, and also between L. parvus and L. cf. L. zsigmondyi. The phyletic relationship between I. nevadanus and L. parvus is obscure, but even so, the implication is strong 47 PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 838:? @2853 .83“. 8 83.58 .88: Edam .888 #833 8.5:? 68:30: .mNdA 8 35a 832 :o 68.8%“. a 53 338:: 4:93:83 28N £3858 wfibg :o 8:58.: 3:895 B. .35:de malbd 3% e Z 3 A 8 EEvo—Zv Ntummfius 383E .8 3: 3:8: 833m “8893 33:53 .8=o< :8th 8358:: 98: .8304 .833“ .83: 8.5:? 8658: .3 .ov .mdv .832 :0 mar :58: 388E: €853 388:: 382: #25803 .Efifim 8:8 £83.: 88:5: 8 82.5w .8 3:3 488:3 .deImod .5546 B 3:388: 28N 8:8: 59a 9:33, 38:53 .3:o< mlv ma Begum 8:585 88:88:80.5 888: .832 8 888888: v5 m8:oN E82 mE£ 8:8: «80me 68.893 833 E8 3833 8 885m 33:53 .853: 3.0V Relic film. NH 8380 3:89 @5qu .4 mmE8fi=3Qm 8:83 Sea w:Tm8> 4.8.833 .28me 38.8838 :N 8.8N .38 83:8 Emvum 338.8: .8:o< modv vdImmd 31m 5 8>:oO .wo mmfifixaoomgu $338380 55.2 3:5 5% Q\D 53 m 8 6 we :3»: 83385850 80:3, 85335 8388:: MO 838:: .813 8 878:3 1855 8:83 Emma: :33 8.80 38:88 82552 3:888 we 8:852 :0 885m. 538» .8 88588 SE 3 D «a 28:3 85: mo 888.8:0 23:6 :omaaamago $8QO uEQEmEmh—w .785 mama .V ”:85 .532» hA ”533 :3? <5 353—55: 90 533 .D 8:: 8.53m .8 2338 1:3“: uuouom .Nm ”8:: 95:8 .8 $53 1:32 «8:83 ~28. gnaw s1— :1— ”Emma: 18:3 .: ”.8853“. =98 N: 38an Eat mEEEESQQM§~ 8 288.2388 £m£238§~|€ BEBE 48 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA that progressive development of the oxyconic shape and distinctive suture pattern of Longobardites from a non- oxyconic ceratitic ancestor may have taken place during one or more relatively brief parts of Anisian time. Genus INTORNITES Assereto, 1966 Intornites mctaggarti (McLeam) Plate 20, figures 15—35; text-figure 31 Longobardites mctaggarti McLearn, 1946a, p. 2, pl. 2, fig. 5. Longobardites larvalis McLearn, 1948, p. 20, pl. 9, figs. 3—4; Silberling and Tozer, 1968, p. 38. Longobardites cf. L. larvalis McLearn. Silberling and Wallace, 1969, table 1, p. 17. Intomites mctaggarti (McLearn). Tozer, 1971, p. 1017. Description.——Mature shell oxyconic, compressed (W/D about 0.25); venter narrowly tapered, acutely ter- minated; umbilicus nearly closed. Diameter of phragmocone exceeds 60 mm. Surface smooth except for growth lines that describe pronounced convex curve on lower flank, recurve about two-thirds of distance across flank, and form a smaller convex curve on outer flank. Inner whorls at diameters less than 10 mm evolute, round or depressed oval in cross section, ornamented by distinct rounded ventral keel and short, coarse, concave radial ribs on lateral margins. Indistinct furrows border keel and strigae cross ribs on more depressed, coarsely ornamented variants. Whorl shape, strength of orna~ ment, and rate of maturing of inner whorls widely variable; at diameter of 15 mm whorl proportions (W/H) varies from 0.7 to 1.5, width of umbilicus (U/D) varies from 0.15 to 0.40, mostly exceeds 0.25. Transition to oxyconic mature morphology gradual, from 10 to 30 mm. During transition lower flanks or- namented by irregular ribs that commonly bear bullae at position corresponding to original lateral ribs of earlier whorls. Suture ceratitic; principal lobes coarsely crenulate; principal saddles high and narrow; ES about two-thirds height of 81. Sutures closely spaced with sides of succes- sive saddles touching or nearly so. At diameters less than 15 mm proportions of principal elements normal: in height 81 equal or greater than S2, S2>SB; in depth L1>L2, L2>>L3. Two or three auxiliary saddles follow S3 whose apex is inside midline of flank. Pseudoadven- titious pattern develops by transitions at diameters more than 15 mm. On outer phragmocone height and breadth of SlL1 in depth and breadth) not developed below whorl heights less than 15 mm; generally 82>Sl by whorl height of 10 mm. Discussion—The range in variation among young stages of Intornites nevadanus may overlap that of I. mc- taggarti, but at a given diameter the inner whorls of I. PALEONTOLOGY—SYSTEMATIC DESCRIPTIONS 49 ”WW \ FIGURE 32.—-Suture lines (X 5) of Intamites nevadanus (Hyatt and Smith). A, plesiotype, USNM 248803. B, plesiotype, USNM 248988, specimen not figured. C, holotype, MCZ 3902. D, plesiotype, USNM 248803. nevadanus are on the average much more compressed and involute. From those of Longobardites parvus they differ in having regular ribbing and in most cases a dis- crete ventral keel. Growth striae on smooth mature whorls of I. nevadanus are unevenly biconvex in contrast with those of L. parvus, which describe a single asymmetric convex curve. In fact, among longobarditinids from Nevada the nature of the growth striae serves to distinguish all mature shells of Intornites from those of the stratigraphically higher genus Longobardites. This is not a generic distinction generally, however, because the lec- totype selected by Assereto (1966) for the type species of Longobardites, L. breguzzanus Mojsisovics, has biconvex growth striae in addition to other Intomites- like characteristics such as distinct ventral shoulders and a sutural development essentially like that of I. nevadanus. In all respects it is closest to nonkeeled, relatively smooth variants of I. nevadanus, so that the only generally applicable distinction between Longo bar- dites, as typified by its type-species lectotype, and Intor- nites is the absence of a distinct ventral keel on the inner whorls of the former, and this derives from the nature of a type specimen rather than a population sample. Thus, in View of the real differences between the various mid- dle and upper Anisian species of longobarditinids, their separation into genera is unfortunately artificial. Confusion regarding the characteristics of I. nevadanus has resulted from the original description by Hyatt and Smith (1905), which was based partly on the small, poorly preserved type specimens, presumably all from the Shoshonensis Zone of the New Pass Range, about 100 km southeast of the Humboldt Range, and partly on younger specimens from the upper Anisian at Fossil Hill. The greatest diameter of the holotype is 20 mm and that of the paratype figured by Hyatt and Smith is 10 mm. Both are somewhat eroded internal molds on which a ventral keel, if present, is obscure and the surface sculpture not preserved. Although they cor- respond with relatively compressed, involute, smooth variants among the inner whorls of populations included here in I. neuadanus, by themselves they are not ade- quate to separate I. nevadanus from other younger species of longobarditinids. Fortunately, one previously unfigured paratype (MCZ 3903a) shows the keeled venter and biconvex growth striae of the inner whorl that distinguishes populations from the Shoshonensis Zone from those that occur in higher zones of the Nevada Mid- dle Triassic. The population sample upon which the pre- sent description is based is from the type locality of the Shoshonensis Zone (at USGS locality M635) in the Wildhorse mining district in the low hills north of the New Pass Range, whereas the type specimens were probably collected farther south in the New Pass Range. Equivalence of the stratigraphic level represented by this population sample with that represented by the type lot is evidenced by a shell fragment on one of the un- figured paratypes (MCZ 3903b) of a distinctive pelecypod referred to Enteropleura cf. E. bittneri Kittl, which is characteristic of the Shoshonensis Zone in the Wildhorse district and elsewhere. Several collections from relatively high in the Hyatti Zone of the Humboldt Range include immature specimens of Intomites whose shell proportions and strength of ornamentation are intermediate between those of the average young stages of I. mctaggarti and I. nevadanus. These may be compared with I. intornatus, which characterizes the middle part of the Varium Zone in Canada (Tozer, 1971, p. 1017). Figured specimens.——Holotype, MCZ 3902 (originally figured by Hyatt and Smith, 1905, pl. 25, figs. 13—16); paratypes, MCZ 3904 (originally figured by Hyatt and Smith, 1905, pl. 25, figs. 17—18), and MCZ 3903a (previously unfigured); plesiotypes, USNM 248800 to 248804. Occurrence.——USGS locality M635 (60+); Sho- shonensis Zone in the lower part of the Fossil Hill Member of the Favret Formation, Wildhorse mining dis- trict, hills north of New Pass Range, Nev. Localities from which I. nevadanus is questionably represented relatively high in the Hyatti Zone in the northern Hum- boldt Range are USGS Mesozoic localities M1181 (25+) and M2829 (4). 50 MOLLUSCAN FOSSILS, HUMBOLDT RANGE, NEVADA Genus LONGOBARDITES Mojsisovics, 1882 Longobardites parvus (Smith) Plate 21, figures 19—25; text-figure 33 Longobardites nevadanus Hyatt and Smith, 1905, p. 132, pls. 58 and 75 [in part]. Smith, 1914, p. 50, pls. 8, 12, and 30 [in part]. Dalmatites parvus Smith, 1914, p. 60, pl. 30, figs. 1—2 [holotype], 3—4, 5—7, 8—97, 10—12?. Dalmatites minutus Smith, 1914, p. 59, pl. 29, figs. 15—16 [holotype], 17—19, 20—21. [not “Neodalmatites minutus (Smith)” of Popov, 1961, p. 64]. Neodalmatites parvus (Smith). Spath, 1951, p. 24. Longobardites hyatti Shevyrev, 1961, p. 74 [holotype = L. nevadanus Hyatt and Smith, 1905, pl. 58, fig. 16 (and 17—18)]. Longobardites parvus (Smith). Silberling, 1962, p. 157. Description—Mature shell compressed (W/D about 0.20), oxyconic; flanks broadly convex, converge to nar- row, acutely terminated venter; umbilicus closed. Max- imum diameter exceeds 60 mm. Surface smooth except for asymmetric convex growth striae, the most orad point of which is above midline of flank. Inner whorls at diameters of 10 to 15 mm involute (U/D less than 0.10) with acute, unkeeled, bluntly tapered venter; strength of ornamentation proportional to variable whorl thickness (W/H 0.4—0.7). Ornamenta- tion varies from convex striae on compressed variants to widely spaced radial folds and depressions on lower flank of robust variants. Immature ornament, even on most coarsely sculptured variants, not persistent beyond diameter of 25 mm. Mature suture with characterisitc pseudoadventitious Longobardites pattern (Sl FIGURE 34.—Suture lines (X 5) of Longobardites zsigmondyi (Bockh), all reversed. A, B, and C, all of plesiotype, USNM 248809, at dif- ferent whorl heights. diameter of the present species, which is nearly restricted to the lower part of the Occidentalis Zone, may be transitional with the somewhat slower rate characteristic of L. paruus, which occurs strati- graphically lower. Gradation, if it exists, between the two species is obscured by the scarcity of Longobardites in the higher parts of the Meeki Zone. Three small specimens of Longobardites from separate localities in the upper part of the Occidentalis Zone of the Fossil Hill area, above the occurrence of L. cf. L. .zsigmondyi, have relatively robust, bluntly terminated whorls, weak ribs on the lower flanks, and discrete ventral keels. On the larger two of these specimens the suture is pseudoadventitious (L1\ A Fr: Tiwfl D1 % \,, $1 >_ E (I) '7 g 'ch1 O E 3 ’4 I— 'wa1, lower felsite unit 'fiwc1, lower clastic unit Koipato Group A 'fiwr \ Porphyritic rhyolite FAULT CONTACT T. 28 N5 .5 I \ Rochester Rhyolite J ‘ Contact Dashed where approximately located _.__I.._ Fault Dashed where approximately located, dotted where concealed; bar and ball on downthrown side ’ 35 ’l )\ : fip' : Cblldcting , site \ me 40 ._L_ Strike and dip of beds 4:5 40‘76' I Strike and dip of flow banding ’ / 15ch l / /“\ \\ , " ./4 ‘ \: /\'—\. 7 -“\ : I, , ‘ X , , i _. \ \\ A : /_\ ll / \- K 3 / iawn //— '- // 5 \lvir ,__T/\<:M¢ /; \ (lggw / A\ I g / x / 5, _/ w I t X "785mm? ‘ _ , \‘fiwfi? " nfixx \ *«._.\\ x/ - y / 7- I wa2; \l -_ l ~ __ I \g 5 118%, R. 34 E R. 35 E. IIETTIG’ Base modified from ”-3- Geological SUWBV "3?: SCALE 1:12 000 Geology by N. J. Silberling, 1955 Unionville, Nev., 1954 0 1000 METERS I j E . I E 0 1000 2000 3000 FEET E S CONTOUR INTERVAL 100 FEET APPROXIMATF MEAN NATIONAL GEODETIC VERTICAL DATUM 0F IQZQ DECLINATION 1981 GEOLOGIC MAP OF PART OF THE HUMBOLDT RANGE, NEVADA, SHOWING COLLECTING SITES A, B, AND C UNITED STATES DEPAKI'MENT OF THE INTERIOR PROFESSIONAL PAPER 1207 GEOLOGICAL SURVEY PLATE 2 3/ /,5.;__,‘___\ // fl ’ ‘ 25 . W, / - (9‘3 M136 : u‘b / '- ‘ ,./ ,/ " ' / A Estimated elevation 4976 ft j 0 15 30 METERS Base and geology by 0 50 100 FEET N. J. Sllbemng, 1950 CONTOUR INTERVAL 10 FEET NAT|0NAL GEUDETIC VERTICAL DATUM OF 1929 EXPLANATION Brown-weathering sandy —I—— Fault—Bar and ball on mmmm Mm ' limestone beds downthrown side DECLINATION, 1981 IlIlIIIIIIIIIIIIIIIII Traces of bedding M141 X USGS fossil localities Boundary between Quaternary A Triangulation station alluvual deposits (Cal) and ’5 Strike and dip of beds bedrock LOCALITY MAP OF COLLECTING- SITE A ON THE SOUTH SIDE OF FOSSIL HILL, HUMBOLDT RANGE, NEVADA did SL 20 LOZI 'A w. UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 1207 GEOLOGICAL SURVEY PLATE 2 0 15 30 METERS "lg: I———Lr——'JW Base at“! 990le by 50 100 FEET N J. SllberIIng, 1950 CONTOUR INTERVAL 10 FEET NATIONAL GEooErIc VERTICAL DATUM OF 1929 TRUE NORTH EXPLANATION g Brown—weathering sandy —J—— Fault—Bar and ball on APPROXIMATE MEAN “mGStone beds downthrown side DECLINATION, I981 IIIIIlIIIIIIIIlIIIlIl Traces of bedding M141 X USGS fOssil localities Boundary between Quaternary A Triangulation station . . 5 alluvual deposns (Cal) and I Strike and dip of beds bedrock '7 MAR 1 I 1983 F08 a ,\ 44’ \8‘ 7” SCIENCE “93‘ IL LOCALITY MAP OF COLLECTING-SITE A ON THE SOUTH SIDE OF FOSSIL HILL, HUMBOLDT RANGE, NEVADA 9d 91. 367 .< I3 O N UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 1207 PLATE 3 Estimated elevat;l7n A 5576 ft ./ EXPLANATION III|IIIllIllllllllllllllmmlll Traces of bedding I ‘1 Juniper trees M616x uses fossil locality A Triangulation station 35. Strike and dip of beds /.,’- APPROXIMATE MEAN DECLINATION‘ 1931 0 IO 20 METH‘IS 0 2 5 50 FEET CONTOUR INTERVAL 10 FEET NATIONAL GEODETIC VERTICAL DATUM OF 1929 Base and geology by N. J. Silberling, R. E. Wallace, and D. B. Tatlock, 1959 LQZI 'A SL 30 :EZA {H .1, .. .‘ Geomorphology of New England By CHARLES S. DENNY GEOLOGICAL SURVEY PROFESSIONAL PAPER 1208 Topography of crystalline rocks, lithology of Coastal Plain sediments, and comparisons with adjacent areas suggest late Cenozoic uplift UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON21982 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES G. WATT, Secretary GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress catalog-card No. 80-607778 For sale by the Distribution Branch, U.S. Geological Survey, 604 South Pickett Street, Alemdria, VA 22304 CONTENTS Page Abstract 1 Topographic and geologic framework-Continued Introduction 1 Gulf of Maine basins Method of study 2 Newport-Concord-Boston line _______________________ Acknowledgments 2 Drainage Topographic and geologic framework _____________________ 2 Divides and basins Hudson-Champlain-St. Lawrence lowlands _____________ 2 Streams, divides, and areas of calc-alkalic plutonic rocks __ Taconic highlands 3 Connecticut River Vermont Valley _ 3 Hudson River Hudson-Green-Notre Dame highlands """""""""" 3 Stream gradients, the subenvelope _______________________ Connecticut Valley 4 Central highlands 4 Age °f the landscape Upper St. John River lowlands _______________________ 5 Relation of Coastal Plain and Gulf of Maine basms to the Coastal lowlands _ 5 emerged Coastal Plain of the Middle Atlantic States _______ New Brunswick Highlands __________________________ 6 Landscape “01‘“th Maritime Plain 6 Tectonism Coastal Plain 6 References cited ILLUSTRATIONS [All figures are on plate 1, in pocket] FIGURE 1. Map of New England and adjacent areas, showing political divisions and geographic features. . Generalized topographic map of the New England region. . Physiographic map of the New England region. Generalized lithologic map of the New England region. Cross sections of the New England region. Map of the New England region showing areas underlain by metamorphic rocks. . Generalized lithologic map of the Hudson Highlands. Generalized geologic map of the Jurassic and Triassic rocks in the Connecticut Valley. . Subenvelope map of the Connecticut Valley in New Hampshire and Vermont. . Relief map of the New England region. . Subenvelope map of the New England region, showing the general altitude of the drainage network. . Map showing the principal streams of the New England region, their drainage basins, and the major drainage divide. . Drainage map of New England region showing areas underlain by platonic rocks of Mesozoic to Proterozoic age and by rocks of Proterozoic age. . Subenvelope map of the New England region showing areas underlain by differing rock types. . Cross section showing topographic relief and rates of erosion. III Page anaconda) 10 11 12 14 15 16 GEOMORPHOLOGY OF NEW ENGLAND By CHARLES S. DENNY ABSTRACT Widely scattered terrestrial deposits of Cretaceous or Tertiary age and extensive nearshore and fluvial Coastal Plain deposits now largely beneath the sea indicate that the New England region has been above sea level during and since the Late Cretaceous. Estimates of rates of erosion based on sediment load in rivers and on volume of sediments in the Coastal Plain suggest that if the New England highlands had not been uplifted in the Miocene, the area would now be largely a lowland. If the estimated rates of erosion and uplift are of the right order of magnitude, then it is extremely unlikely that any part of the present landscape dates back before Miocene time. The only exception would be lowlands eroded in the early Mesozoic, later buried beneath Mesozoic and Cenozoic deposits, and exhumed by stream and glacial erosion during the later Cenozoic. Many of the rocks in the New England highlands are similar to those that underlie the Piedmont province in the central and southern Ap- palachians, where the relief over large areas is much less than in the highlands of New England. These comparisons suggest that the New England highlands have been upwarped in late Cenozoic time. The uplift took place in the Miocene and may have continued into the Quaternary. The New England landscape is primarily controlled by the underly- ing bedrock. Erosion and deposition during the Quaternary, related in large part to glaciation, have produced only minor changes in drainage and in topography. Shale and graywacke of Ordovician, Cambrian, and Proterozoic age forming the Taconic highlands, and akalic plutonic rocks of Mesozoic age are all highland makers. Sandstone and shale of Jurassic and Triassic age, similar rocks of Carboniferous age, and dolomite, limestone, and shale of Ordovician and Cambrian age com- monly underlie lowlands. High-grade metapelites are more resistant than similar schists of low metamorphic grade and form the highest mountains in New England. Feldspathic rocks tend to form lowlands. Alkalic plutonic rocks of Mesozoic age underlie a large area in the White Mountains of New Hampshire and doubtless are a factor in their location and relief. Where the major streams flow across the regional structure of the bedrock, the location of the crossings probably is related to some other characteristic of the bedrock, such as joints or cross faults. The course of the Connecticut River is the result of the adjustment of the drainage to the bedrock geology during a long period of time. There is no ready explanation why many of the large rivers do not cross areas of calc- alkalic plutonic rock, but rather ‘take a longer course around such areas, which tend to include segments of the divide between the streams. The presence of coarse clastic materials in Miocene rocks of the emerged Coastal Plain of the Middle Atlantic States suggests uplift of the adjacent Piedmont and of the Adirondack Mountains at that time. The Miocene rocks of the submerged Coastal Plain in the Gulf of Maine and south of New England ar fine grained and contain only small amounts of fluvial gravel. Perhzfps the coarse clastic materials shed by the New England highlands in ate Cenozoic time are buried by or in- corporated in the Pleistocene glacial deposits. INTRODUCTION The landscape of New England and the surface of the adjacent Continental Shelf in large part reflect the rocks that underlie them. The character and distribution of the bedrock control the form and location of the highlands and lowlands. The adjacent Continental Shelf is underlain in part by Cretaceous and younger rocks that contain a record of the erosional history of the adjacent landmass. The boundary of the New England States does not coincide with that of any physiographic subdivision. The study area, the New England region, includes the New England States and adjacent parts of New York and the Canadian Provinces of Quebec and New Brunswick. The Hudson-Champlain-St. Lawrence lowlands constitute the west and northwest border of the region (fig. 1). Northeast of Maine, no natural physiographic boundary exists, and the limit of the study area may be conve- niently placed along the east border of the St. John River basin in New Brunswick. The New England region excluding the adjacent Continental Shelf com- prises nearly 260,000 kmz; of this, the New England States make up about 173,500 ka, Maine accounting for about half this area. The study includes an analysis of the topography of the New England region in relation to rock types and structural fabrics. The relationships documented here reflect a long history of erosion and adjustment of sur- face form to bedrock character. The Coastal Plain sediments that have been derived from the New England region record times and places of intense ero- sional activity and suggest tectonic events not otherwise determinable. Erosion and deposition during the Quaternary, related in large part to glaciation, have produced many changes in drainage and in topography. Hills have been formed or reshaped, valleys have been deepened, lowlands have been buried, and streams have been diverted. Examples of such changes are legion. Nevertheless, the major elements of the topography and drainage of the New England region can be explained as a response to the character and distribution of the bedrock, even where the bedrock is concealed beneath Quaternary deposits. 1 2 GEOMORPHOLOGY OF NEW ENGLAND METHOD OF STUDY The topographic data used in this study were derived from maps at a scale of 1:250,000, contour interval 100 ft (30.48 m), published by the US. Geological Survey and the Canada Department of Mines and Technical Surveys. The geographic names follow the usage of the 1:250,000-scale maps. The submarine topography of the Continental Shelf is from the map by Uchupi (1965). The topographic data for land areas were analyzed using three derivative maps at scale 121,000,000. The maps portray relief, summit altitudes, and stream gradients. The map of summit altitudes shows what Stearns (1967, p. 1117; Hack, 1973) has called the envelope; the map of stream gradients depicts the general altitude of the drainage network, the subenvelope of Stearns. Longitudinal profiles were drawn for many of the larger streams at scale 121,000,000. Only the derivative maps showing relief and stream gradients are reproduced here. The three basic derivative maps were constructed as follows. A 1:250,000-scale sheet was overlain by a rec- tangular grid 6.4 km on a side. In each square was recorded the altitude of the lowest contour line minus one and of the highest contour line. For example, if in a 6.4-km square the lowest contour line is 200 ft (60.96 m) and the highest contour line is 600 ft (182.88 m), the two altitudes recorded in the square are 100 ft (30.48 m) and 600 ft (182.88 m). The data derived for the square are as follows: summit altitude, the larger number; altitude of the drainage network, the smaller number; and relief, the difference between the two numbers. The derivative maps were constructed in the following manner: The values obtained from the topographic maps were recorded in the center of each 6.4-km square and contoured using a 200-ft (60.96-m) interval. The maps were then reduced to scale 121,000,000. For the maps reproduced in this paper (figs. 9, 10, 11), the contours have been redrawn using a metric interval. The map showing bedrock lithology of land areas (fig. 4) was compiled from geologic maps of the States of New York, Vermont, New Hampshire, Maine, and Rhode Island (New York State Museum and Science Service, Geological Survey, 1962; D011 and others, 1961; Billings, 1955; Hussey and others, 1967; and Quinn, 1971), of the Provinces of Quebec and New Brunswick (Quebec Department of Natural Resources, 1969; Potter and others, 1968), and regional compilations by Dixon and Lundgren (1968), Hatch and Stanley (1973), Goldsmith (1964), Morgan (1972), White (1968), and Zen (1967, 1972). The pre-Pleistocene geology of the Con- tinental Shelf is from maps compiled by Weed and others (1974), King and MacLean (1974), and Ballard and Uchupi (1975). The approximate offshore limit of glaciation is from Pratt and Schlee (1969). ACKNOWLEDGMENTS It is a pleasure to acknowledge the assistance of Richard Goldsmith. I have drawn freely on his knowledge of New England geology and have benefited from his criticism. I am also indebted to J. T. Hack, W. L. Newell, R. N. Oldale, J. P. Owens, and B. D. Stone for assistance during the course of the study. TOPOGRAPHIC AND GEOLOGIC FRAMEWORK New England is largely an area of hills and mountains. The term commonly used in the past, “The New England Upland,” was based in part on the belief that the area was an elevated and dissected peneplain surmounted by monadnocks. Much of the region is at altitudes of more than 200 In (fig. 2), and large areas in the central part are at altitudes of more than 500 m. Small areas in the Green Mountains of northern Vermont and in the White Mountains of northern New Hampshire, as well as Mount Katahdin in Maine and a few other isolated peaks, have altitudes of more than 1,000 m. Altitudes on the floors of the major lowlands are generally not more than 200 m, except in parts of the St. John River valley in Maine, where the altitude ranges from about 200-400 m. The valleys between the highlands are commonly narrow, except for the broad lowlands of the Hudson, Champlain, and St. Lawrence Valleys and those border- ing the west and northwest shore of the Gulf of Maine. Depths on the Continental Shelf are not more than 100 m on the largely submerged Coastal Plain south of New England and east of the Massachusetts coast. In the Gulf of Maine, a belt 20—40 km wide, where depths are less than 100 m, follows the coast from Cape Ann north- east to the Bay of Fundy. The rest of the floor of the gulf ranges in depth from 100 to 200 m, except for many large and small basins whose bottom contours are closed at depths of about 200—300 m. To describe the landscape of the New England region and to attempt to explain its origin, it is convenient to divide both the emerged and submerged parts of the region into several physiographic units (fig. 3). The units are basically topographic and reflect differences in ma- jor bedrock units. However, some of the units are of necessity so broad and varied in character that the distinction between one unit and another is in some areas arbitrary. HUDSON-CHAMPLAIN-ST. LAWRENCE LOWLANDS The lowlands along the Hudson and St. Lawrence Rivers and surrounding Lake Champlain range from about 15 km to nearly 130 km in width and extend for about 700 km from Newburgh, N.Y., to Quebec City (fig. 3). Tidewater extends about as far north as Albany on TOPOGRAPHIC AND GEOLOGIC FRAMEWORK 3 the Hudson River and as far southwest as Trois Rivieres on the St. Lawrence River. The lowlands are underlain largely by shale, dolomite, and limestone (fig. 4) of Or- dovician and Cambrian age. The altitudes of the valley floors range from sea level to about 100 m above sea level. In the St. Lawrence Valley between Montreal and Quebec, more than three-quarters of the area has a relief of less than 60 m, in part the result of deposition on the floor of the Champlain Sea that occupied the valley at the end of the Wisconsinan glacial stade (Gadd, 1971; Elson, 1969). Downstream from Quebec City, the St. Lawrence River estuary follows a major thrust fault, Logan’s Line, between the, Proterozoic rocks of the Laurentian Highlands to the northwest and the Paleozoic rocks of the Notre Dame Mountains to the southeast. In the Champlain and the Hudson Valleys, the bedrock in- cludes sandstone that forms low hills, and the relief ranges from about 60 m to as much as 300 m. The bound- ary of the lowlands is in most areas easily defined on the basis of both bedrock character and topographic form (fig. 5). The Hudson-Champlain-St. Lawrence lowlands are part of a great valley system that extends the length of the Appalachian Highlands and is underlain largely by carbonate rocks of early Paleozoic age (Hack, 1980; Fen- neman, 1938, p. 200). TACONIC HIGHLANDS The Taconic highlands, an area of low mountains and hills east of the Hudson River valley, includes the Taconic Mountains in New York (New York State Museum and Science Service, Geological Survey, 1962, text-fig. 19) and adjacent peaks in Massachusetts and southwestern Vermont (fig. 3). On the west side, the highlands gradually descend to the floor of the Hudson Valley; in many places, no sharp boundary exists be— tween highland and lowland. To the east, however, the highlands are bordered by steep-sided narrow valleys (the Vermont Valley). In Massachusetts and New York, several peaks are more than 760 m in altitude. The highlands extend north into the southwest corner of Vermont, where several peaks rise more than 1,070 m above sea level. The highlands coincide roughly with the Taconic allochthon (Zen, 1967), which has a maximum length of about 210 km and ranges in width from about 25 to 40 km. The rocks of the allochthon are largely shale and graywacke and commonly overlie carbonate rocks of early Paleozoic age. The weathering and removal of the carbonate rocks beneath the overlying sediments of the allochthon has produced the steep- sided mountains and narrow valleys in this part of New England. For example, Dorset Mountain, south of Rutland, Vt., rises steeply almost 915 m above the adja- cent flat-floored valley of Otter Creek. VERMONT VALLEY The lowlands east of the Taconic highlands are a long chain of narrow valleys that extend from north of Rutland south for about 200 km. Near Rutland, the lowlands are called the Vermont Valley (Stewart and MacClintock, 1969, fig. 3); the name is here used for the entire chain that includes Otter Creek, the upper reaches of Batten Kill and the Hoosic River, largely in Vermont, and the broad valley of the Housatonic River in Massachusetts (fig. 3). The valleys range in width from about 1.5 to 4.5 km, too narrow to show on the relief map (fig. 10). Altitudes on the valley floors com- monly range from about 60 to 180 m. The lowlands are in a belt of rocks, largely dolomite and limestone of Or- dovician and Cambrian age, that are separated by the Taconic allochthon from similar rocks in the Hudson- Champlain lowlands to the west. The lowlands are bordered by steep-sided mountains that rise 600-900 m above the valley floors. The highlands to the east include large areas of massive rocks of Proterozoic age. HUDSON-GREEN-NOTRE DAME HIGHLANDS The Hudson-Green-Notre Dame highlands extend across the New England region from the southwest cor- ner to the northern border, a distance of more than 850 km (fig. 3). The west border of the highlands is in many places a sharp break between highland and lowland, whereas the east border is in many places not a con- spicious topographic or lithologic break. The highlands include the Hudson Highlands in New York, the Berkshire Hills in Massachusetts, the Green Mountains in Vermont, and the Sutton and Notre Dame Mountains in Quebec. The Notre Dame Mountains continue to the northeast outside the study area to the Gaspé Peninsula. The highlands range in altitude from about 400 to 1,200 m. The highest peaks are in northern Vermont, where Mount Mansfield northwest of Montpelier has an altitude of about 1,340 m. Rocks of Proterozoic age underlie the Hudson Highlands and much of the higher parts of the Berkshire Hills and the Green Mountains in southern Vermont. Metasedimentary and metavolcanic rocks of Paleozoic age underlie most of the rest of the Hudson-Green—Notre Dame highlands. Discontinuous belts of calc-silicate rocks are found in Massachusetts and in Vermont near the Connecticut Valley. There are only a few small areas of calc-alkalic intrusive rocks. In Connecticut, Massachusetts, and southern Vermont, the metasedimentary rocks of the highlands are largely am- phibolite facies (fig. 6). In the western half of the highlands in central and northern Vermont, the metasedimentary rocks are largely greenschist facies, except in the higher parts of the Green Mountains. 4 GEOMORPHOLOGY OF NEW ENGLAND The Hudson Highlands are a belt of Proterozoic rocks, which is about 20 km wide where crossed by the Hudson River estuary and which extends northeast from New York State into western Connecticut. A hornblende granite and granite gneiss form much of the highlands west of the river, including Storm King Mountain (altitude about 425 m), and are absent on the east side, except near the entrance to the gorge south of Newburgh, NY. (fig. 7). The dominant rock type east of the river is biotite granite gneiss (Hall and others, 1975). The rest of the highlands near the river are underlain largely by gneiss and amphibolite. Some quartz plagioclase gneiss forms ridges, which are slightly lower than adjacent ridges composed of granitic gneiss. A possible connection between the bedrock of the highlands and the course of the Hudson River will be discussed later. The Berkshire Hills in Massachusetts and northern Connecticut are composed of Proterozoic rocks (Berkshire Massif, White, 1968) and are about 90 km long and 5—10 km wide. The Green Mountains in southern Vermont (south of lat 44° N.) are also Pro- terozoic rocks (Green Mountain Massif, White, 1968) and are about 150 km long and 10-20 km Wide. Altitudes in the Berkshire Hills range from about 400 to 800 m, those in the Green Mountains of southern Vermont, from about 600 to 1,100 m. The Proterozoic rocks in- clude large bodies of massive gneiss and subordinate quartzite. In northern Vermont, the higher peaks of the Green Mountains are largely schistose metasedimentary rocks of amphibolite facies (fig. 6); the most extensive rock types are quartz-mica-schist containing abundant quartz segregations, quartzite, and amphibolite (Underhill and Hazens Notch Formations, Doll and others, 1961). The east limit of the highlands is drawn near Montpelier and separates the Green Mountains from the lower moun- tains and hills of northeastern Vermont (Vermont Pied— mont, Stewart and MacClintock, 1969, fig. 3). Most of the calc—alkalic plutonic rocks that form low mountains in northeastern Vermont are included in the Central highlands (fig. 5). The Sutton Mountains just north of the international boundary reach altitudes of about 750—950 m and are underlain in large part by graywacke, slate, quartzite, and volcanic rocks of Ordovician and Cambrian age (Poole and others, 1970). From the Vermont-Quebec border to the Notre Dame Mountains southeast of Quebec City, the northwest border of the highlands is a prominent topographic break. On the other hand, southeast of the highlands are hills, low mountains, and some broad valleys. The southeast border of the Hudson-Green-Notre Dame highlands is drawn along the headwater tributaries of the St. Francois roughly from Newport, Vt., to Thetford Mines, Quebec (fig. 5). The Notre Dame Mountains south of Riviere-du—Loup range in altitude from about 600 to 700 m and are com- posed largely of quartzite, sandstone, graywacke, slate, and volcanic rocks (Poole and others, 1970; Hussey and others, 1967). CONNECTICUT VALLEY The Connecticut Valley in Connecticut and Massachusetts ranges from about 8 to 32 km in width. The altitude of the valley floor ranges from sea level to about 100 m, except for the long narrow ridges of volcanic rock largely on the west side of the valley (fig. 8), which rise to altitudes of about 180—300 m. The relief is less than 60 m on the valley floor between Hartford, Conn., and Springfield, Mass. The bedrock is largely sandstone, shale, conglomerate, and volcanic rocks of Jurassic and Triassic age. In Connecticut and Massachusetts, the borders of the Connecticut Valley are easily defined on the basis of bedrock lithology and topographic form. In New Hampshire and Vermont, the valley is narrow and bordered by hills that rise gradually east and west to the White and Green Mountains. As far north as the mouth of the Passumpsic River, the valley runs more or less parallel to the trend of the bedrock units, largely metasedimentary and metavolcanic rocks of Paleozoic age. The central segment of the valley, roughly from Claremont to Littleton, N.H. (fig. 9), parallels the Am- monoosuc thrust. The rocks east and west of the river differ, but the Connecticut Valley as a physiographic unit is defined solely on the basis of topography. North of the mouth of the Passumpsic River, the Connecticut Valley is slightly wider than it is to the south. Areas underlain by'calc-alkalic plutonic rocks lie both east and west of the axis of the valley. CENTRAL HIGHLANDS The central highlands extend from eastern Connec- ticut to the northern limit of the study area, a distance of about 750 km (fig. 3.). The geology and topography of this unit are varied; the area includes the highest peaks in New England, as well as low mountains, hills, and some broad valleys (fig. 5). From an altitude of about 200 m at their southern end, the highlands gradually rise north to the White Mountains, where many peaks reach altitudes of more than 1,200 m; Mount Washington has an altitude of 1,886 m. The White Mountains and the ad- jacent peaks to the northeast, as far as Mount Katahdin, are the highest segment of the central highlands. North and northwest of the White Mountains, altitude and relief decrease; the area is one of low mountains and hills generally not more than 500 m in altitude, except TOPOGRAPHIC AND GEOLOGIC FRAMEWORK 5 near the international boundary. Several broad valleys have floors as low as 200 m, and the boundary between the central highlands and the Hudson-Green-Notre Dame highlands is arbitrary. In New Brunswick, the central highlands are the Chaleur Uplands of Bostock (1970). Along the eastern border of the central highlands, the topographic break between the highlands and the coastal lowlands is sharp, except north of Con- cord, N.H., where several isolated peaks (Belknap Mountains, Ossipee Mountains) rise steeply above the adjacent lowlands. Except near its southern end, the border is drawn more or less between the 100- and 200-m contour. The central highlands are underlain largely by metasedimentary and metavolcanic rocks of Paleozoic age (fig. 4). In the White Mountains and the highlands to the south, the metamorphic rocks are largely am- phibolite and granulite facies (fig. 6); they rise above areas underlain in part by calc-alkalic plutonic rocks. The medium- to high-grade metasedimentary rocks underlie Mount Washington and adjacent peaks of the Presidential Range and many of the higher peaks to the south, such as Moosilaukee, Kearsage, and Monadnock. Mount Washington is bordered to the south and southwest by resistant alkalic plutonic rocks (fig. 9). To the northeast in Maine, the mountains decrease in altitude, and the metamorphic rocks are largely greenschist and subgreenschist facies (fig. 6). The ease of splitting, the fissility, of the low-grade metamorphic rocks makes them more susceptible to weathering and to erosion than are those of higher metamorphic grade. The next most abundant rock type in the central highlands is calc-alkalic plutonic rocks. Such rocks underlie both mountains and valleys. At Mount Katahdin, for example, calc-alkalic plutonic rocks rise to an altitude of about 1,580 m above sea level. The rocks underlie an area roughly 50 by 30 km. In about half the area, the relief is less than 300 m; in the other half, it is more than 600 m (fig. 5). Metavolcanic rocks form lower mountains just north of Mount Katahdin. Why the plutonic rocks near Mount Katahdin have such a wide range in altitude and in relief is not clear. Perhaps the answer lies in the presence of fine-grained granitic rocks at the summit of Mount Katahdin, rocks that are more resistant to weathering than is the coarse-grained granitic rock at lower altitudes. In northeastern Ver- mont, on the other hand, plutonic rocks form both broad swampy valleys having a relief of only about 180 m and low mountains having a relief of as much as 670 m. From Mount Katahdin southwest to the New Hamp- shire border, oval calc-alkalic intrusive bodies range from about 1 to 8 km in width and from about 15 to 65 km in length. The relief is at least 600 m, except near the State line, where several areas of plutonic rock abOut 16 km in diameter have a relief of less than 300 m. In the highlands from MOunt Katahdin west to the longitude of Rumford, Me., some of the mountains are underlain by metamorphic rocks that form a belt surrounding the plutonic rocks and that appear to be more resistant than those of the central core. In places, a massive hornfels forms steep-sided mountains, such as Big Squaw and Prong Pound Mountains near Greenville, Me., which rise as much as 600 m above Moosehead Lake. In Connecticut and Massachusetts, the relief on plutonic rocks is commonly less than 300 m. To the north in New Hampshire, some areas of plutonic rock are broad valleys having a relief of about 180 m; elsewhere, commonly in areas of very coarse grained plutonic rocks (Kinsman Quartz Monzonite, Billings, 1955), hills or low mountains have a relief of as much as 540 In. From the Massachusetts line north to the White Mountains (fig. 9), many of the calc-alkalic intrusive rocks are separated from the Connecticut River by a narrow belt of resistant rocks, the massive Clough Quartzite and the Ammonoosuc Volcanics (Billings, 1955), which form a belt of hills and low mountains generally on the west side of the intrusive rocks. UPPER ST. JOHN RIVER LOWLANDS The upper part of the St. John River drainage basin, roughly above Grand Falls, New Brunswick, includes some broad lowlands where the relief is low. The river commonly flows in a narrow inner valley below the general level of adjacent lowlands. The bedrock is large— ly metasedimentary rocks of low metamorphic grade (greenschist and subgreenschist faciesXfig. 6). COASTAL LOWLANDS The coastal lowlands, including parts of the adjacent Continental Shelf, form a broad northeast-trending belt from south of the Rhode Island coast north and north- east to Augusta, Me., a total length of about 200 km and a width of about 60-100 km. Altitudes range from more than 100 m below sea level to about 120 m above sea level. Northeast of Augusta, the lowlands continue up the Penobscot River valley for about 240 km to the vicinity of Houlton, Me. The bedrock of the coastal lowlands includes a wide variety of lithologic types. In eastern Massachusetts and Rhode Island are calc-alkalic plutonic rocks and volcanic rocks of Proterozoic age and sedimentary rocks largely of Carboniferous age (fig. 4). The Proterozoic rocks have a relief of less than 60 m and are cut by many faults that have a general northeast trend (Cameron and Naylor, 1976). In New Hampshire and in Maine are extensive areas of calc-alkalic plutonic rocks, the largest being northwest of Portland, where the relief ranges from 60 6 GEOMORPHOLOGY OF NEW ENGLAND to 180 m. Cale-silicate rocks are found in areas from eastern Connecticut to Bangor, Me. From Portsmouth, NH, northeastward, the submerged part of the coastal lowlands is underlain largely by rocks of pre-Triassic age (Ballard and Uchupi, 1975, fig. 3). The coastal lowlands extend from Rhode Island west to the Hudson River (fig. 3); their southern boundary is the submerged northern edge of the Coastal Plain. However, except in the area near New Haven, Conn., which is underlain by rocks of Jurassic and Triassic age, there are no extensive lowlands in the narrow belt from Rhode Island to the Hudson. The altitude of the in- terfluves rises north from the shore of Long Island Sound at a constant rate, as Flint (1963) has clearly shown (fig. 15). In southern Connecticut, the bedrock in- cludes both stratified and plutonic rocks. East of New Haven, the bedrock units run more or less parallel to the shoreline; west of New Haven they are more or less at an angle to the shoreline. The coastal lowlands end abruptly against the central highlands (fig. 5). Altitudes rise from about 100 m in the lowlands to more than 300 m near the edge of the highlands. The relief increases from less than 120 m to more than 375 m, and stream gradients increase as one goes from the coastal lowlands into the adjacent highlands. In places, the lowlands-highlands boundary is a gently sloping escarpment, perhaps as much as 100 m high, cut by many valleys running at right angles to it. In Massachusetts, such an east-facing scarp extends from near Worcester (fig. 5) north to the New Hamp- shire border (west side of the Nashua River valley). In Maine, the coastal lowlands-central highlands boundary follows the belt in which altitude, relief, and stream gra- dients increase. Near Lake Winnipesaukee, south of the highest part of the central highlands, are several isolated mountains, and no sharp boundary exists be- tween highland and lowland. NEW BRUNSWICK HIGHLANDS In Canada (fig. 3), the New Brunswick Highlands of Bostock (1970) are a belt of hills that surround the western part of a broad loWland, the Maritime Plain. The highlands rise to altitudes of more than 200 m and form a U-shaped belt about 60 km wide. The highlands extend into northeastern Maine, where, for the pur- poses of this paper, the boundary of the New Brunswick Highlands is drawn to include an extensive area of low mountains and broad lowlands southeast of the inland extension of the coastal lowlands (Augusta to Houlton, Me.). Some of the peaks near the shore are separated by fiords or narrow bays. Many low mountains reach altitudes of more than 300 m. The dominant bedrock type in the New Brunswick Highlands is calc-alkalic plutonic rock of Paleozoic age. Some of the peaks are in areas of contact metamorphism adjacent to the plutonic rocks. Some metavolcanic rocks are also present, ex- pecially in areas near the coast. The division includes Mount Desert Island and extends south for about 20 kn) beneath the Gulf of Maine, where the bedrock is believed to be similar to that in the adjacent land areas (Ballard and Uchupi, 1975, fig. 3). MARITIME PLAIN Near Fredericton, New Brunswick, the St. John River crosses the western end of a broad plain of low relief— the Maritime Plain of Bostock (1970)— that slopes east, outside the study area, to the coast. Altitudes near Fredericton range from sea level to about 100 m. The bedrock is largely sandstone, siltstone, and conglomerate of Pennsylvanian and Mississippian age. COASTAL PLAIN The Continental Shelf off the coast of southern New England and Nova Scotia is largely submerged Coastal Plain (fig. 3), which includes Georges Bank south of the Gulf of Maine and Browns Bank south of Cape Sable (fig. 2). Georges Bank is a remnant of an extensive wedge of Coastal Plain sediments that formerly covered much of the floor of the Gulf of Maine. The landward edge of the Coastal Plain between Cape Cod and Cape Sable is a north-facing cuesta that includes the north side of Long, Island and Martha’s Vineyard. South of New England, water depths over the submerged Coastal Plain range from about 40 to 80 m, in a few‘ places less than 20 m. On the west end of the Scotian Shelf, depths range from about 90 to 180 m. Browns Bank reaches a depth of only about 29 m below sea level. From Cape Cod northeast into the Gulf of Maine are many remnants of Coastal Plain sediments; only the larger ones are shown diagrammatically on figure 4. The sediments are generally not more than about 100 m thick. (For details, see Ballard and Uchupi, 1975, figs. 3, g 5, 6.) The pre-Quaternary deposits of the Coastal Plain south of New England (Folger and others, 1978; Weed and others, 1974) are elastic sediments, in large part sand, silt, and clay of Late Cretaceous age. The deposits thicken rapidly to the south, reaching about 350 m under Nantucket Island and more than 400 m beneath the southern shore of Long Island (Folger and others, 1978). Sediments of Tertiary age are scattered and thin, in- cluding a little fluvial gravel. Beneath the northern slope of Georges Bank, the sedimentary rocks thicken rapidly to a maximum of perhaps 7.5 km, including rocks of presumed Early Cretaceous, Jurassic, and Triassic age in the Georges Bank trough (Ballard and Uchupi, 1975). l At the north end of the Baltimore Canyon trough, about TOPOGRAPHIC AND GEOLOGIC FRAMEWORK 7 150 km south of Long Island, is a thick section of upper Cenozoic clastic rocks (Scholle, 1977). The Scotian Shelf is underlain by more than 4,250 m of Cenozoic and Mesozoic sedimentary rocks (Jansa and Wade, 1975), which overlie a basement of metamor- phosed rocks of Ordovician and Cambrian age. The lower Tertiary and Cretaceous section, as much as 2,450 m thick, includes continental, deltaic, and marginal marine deposits overlain first by sand and then by shale of a transgressive sequence. The outer part of the shelf is a thick wedge of mudstone of Quaternary and later Tertiary age, thin or absent nearshore but thickening to about 1,200 m near the shelf edge. Georges Bank forms most of the divide at the mouth of the Gulf of Maine. It has been interpreted as a remnant of the Coastal Plain dissected by two streams, one in the Northeast Channel and the other in the now-filled Great South Channel. These streams drained the interior lowland of the Gulf of Maine north of Georges Bank (Oldale and others, 1974). Northeast Channel is about 100 km long and 32 km wide, and the walls are 90—150 m high. Great South Channel is about 90 km long, 25—40 km wide, and only about 20 m deep. Work in 1975 (Lewis and Sylwester, 1976), however, suggests that the history of the bank is more complex than the earlier in- terpretation indicates. After Tertiary erosion of the Coastal Plain sediments by streams flowing in the two gaps, extensive Pleistocene deposition took place on and against the bank, followed by marine planation and subsequent deposition of drift of late Pleistocene age. GULF OF MAINE BASINS The floor of the Gulf of Maine, excluding the sub- merged part of the Coastal Plain and of the coastal lowlands, is about 400 km long, about 200 km Wide, and has an average depth of about 150 m (Oldale and Uchupi, 1970). Numerous depressions separated by narrow ridges characterize the floor and extend to depths of about 300 m. Some are closed, the closure ranging from a few meters to about 100 m. The lithologic map (fig. 4) shows only a few of the larger remnants of Coastal Plain sediments and areas of Jurassic and Triassic rocks deposited in fault basins. Carboniferous sedimentary rocks, a northeast extension of those near Boston, may be present in the central part of the gulf. (For details, see Ballard and Uchupi, 197 5, figs. 3, 5, 6.) The Jurassic and Triassic rocks are presumably similar to those in the Connecticut Valley or in Nova Scotia and New Brunswick around the Bay of Fundy (fig. 4). Pre- Triassic rocks form a high extending from Cashes Ledge east to Yarmouth, Nova Scotia. Jordan Basin is north of this high, and Crowell, Rodgers, and Wilkinson Basins are to the south. The areas of several of the basins at the sill (Emery and Uchupi, 1972) are as follows: Murray- Wilkinson Basins, 10,400 kmz; Jordan Basin, 8,070 ka; and Georges Basin, 5,200 kmz. The floor of the Bay of Fundy rises rapidly east from Grand Manan Island. NEWPORT—CONCORD-BOSTON LINE A major change in topographic grain and to some ex- tent in pattern takes place more or less along a line run- ning from Newport, Vt., south through Concord, NH, and Boston, Mass. (fig. 3). West of the line, the major topographic units trend slightly west of south; to the east, the trend is more nearly southwest. The change is apparent on both the topographic and lithologic maps (figs. 2, 4) and on the derivative maps, such as the relief map (fig. 10) and the subenvelope map (fig. 11). The line runs more or less along the west side of the belt of alkalic intrusive rocks. The largest area of the alkalic rocks is in the White Mountains southwest of Mount Washington (figs. 9, 13), where intrusive rocks of Mesozoic age underlie an area about 50 km long from east to west and about 30 km wide. Over most of the area, the relief ranges from about 600 to 1,000 m. The White Mountains probably owe their altitude in part to the presence of these alkalic plutonic rocks. Similar rocks form the Ossipee and Belknap Mountains that rise about 600 m above Lake Winnipesaukee. The lowlands adjacent to the lake are underlain by calc-alkalic plutonic rocks, and the relief ranges from about 60 to 300 m. Small alkalic intrusive bodies occur in southeastern New Hampshire and adja- cent Maine. Cape Ann 0n the coast north of Boston is underlain by alkalic plutonic rocks of Ordovician age. The cape projects east about 16 km into the Gulf of Maine. The relief is more than 60 m, and the sea bottom deepens to more than 60 m within 10 km of the shore. Another area of similar rocks is just south of Boston (Blue Hill), where the relief is more than 180 m. The Monteregian Hills are a belt of small alkalic in- trusive bodies extending from Montreal eastward toward Newport, Vt. The hills are close to the place where the north-trending Champlain Valley meets the northeast—trending St. Lawrence Valley. It is tempting to extend the Newport-Boston line to Montreal. South of Boston, a continuation of the line enters the Coastal Plain near Martha’s Vineyard. The Newport-Boston line and the adjacent belt of alkalic intrusive rocks mark the approximate western limit of the Gulf of Maine. West of the line, the inner edge of the Coastal Plain trends more or less west, whereas east of the line, the inner edge of the Coastal Plain trends north for nearly 200 km. 8 GEOMORPHOLOGY OF NEW ENGLAND DRAINAGE DIVIDES AND BASINS The rivers of the New England region flow either to the Hudson-Champlain-St.- Lawrence lowlands or to the Atlantic Ocean. The major drainage divide runs from New York City on the Atlantic Coast northeast to within about 20 km of the St. Lawrence River near Riviere-du- Loup, Quebec (fig. 12). About one-third of the New England region is north- west of the divide and about two-thirds is to the southeast. The northern and southern segments of the major drainage divide follow the Hudson-Green-Notre Dame highlands, including the Taconic Mountains, Hoosac Range, and southern Green Mountains to the south and the Notre Dame Mountains to the north. In central Vermont (about lat 44° N.), the drainage divide leaves the Green Mountains and trends east for about 50 km, where it turns north and northeast through north- east Vermont to the Boundary Mountains of Maine and the Megantic Hills of Quebec. The central segment of the major divide in northeast Vermont and along the Quebec-Maine border is about equidistant from the St. Lawrence River to the northwest and the shore of the Gulf of Maine to the southeast. The central segment is in an area of hills and low mountains. The highest part of the central highlands, including the White Mountains and Mount Katahdin, is 50—100 km southeast of the cen- tral segment of the major drainage divide. The largest rivers in the New England region, the St. Francois, Chaudiere, St. John, Penobscot, Kennebec, Androscoggin, and Connecticut have their headwaters in the central segment of the major drainage divide. The largest of the seven rivers, the St. John, flows southeast for perhaps half its course more or less across the north and northeast trend of the major bedrock units. From Grand Falls south to the vicinity of Houlton, Me., the river follows a belt of Carboniferous sedimentary rocks, largely unmetamorphosed. The second largest river, the Connecticut, flows parallel to the trend of the bedrock. The remaining five rivers have courses that are roughly half across the bedrock structures and half parallel with them. The St. John River is about 725 km long and has a drainage basin of about 54,900 kmz. The northwest border of the drainage basin in the Notre Dame Moun- tains is only about 20—40 km southeast of the St. Lawrence River. The drainage basin of the St. John is about three-quarters the size of that of the Susquehanna River and nearly twice that of the Hudson River, as shown in the following table: River Length Drainage area (km) (kmz) Tributary to Hudson-Champlain-St. Lawrence lowlands Richelieu ________________ 370 23,600 St. Francois ______________ 300 9,970 La Chaudiere _____________ 240 6,600 Becancour _______________ 190 2,720 Yamaska ___ __ 180 4,660 du-Loup ____ 50 960 Otter Creek _ 160 2,410 Missisquoi _ 135 2,100 Winooski _ 135 2,770 Lamoille __ 130 1,815 Hoosic ___ 105 1,740 Batten Kill ________ 95 1,140 Kinderhook Creek _________ 70 1,375 Wappinger Creek _________ 55 490 Tributary to Atlantic Ocean St. John _________________ 725 54,900 Connecticut ______________ 625 29,000 Kennebec ________________ 410 25,600 Penobscot ________________ 370 21,000 Androscoggin ____________ 355 8,800 Merrimack _______________ 290 12,700 Housatonic _______________ 225 4,900 Saco _______ __ 185 4,560 Quinebaug __ 135 3,650 Presumpscot 115 1,605 Charles ____ 105 775 Machias -_ 95 1,320 Taunton ___ 80 1,370 Tributary to Connecticut River Farmington ______________ 130 1,580 Deerfield ________________ 120 1,605 Chicopee _________________ 105 1,320 Westfield ________________ 95 1,320 White ___________________ 95 1,710 Ashuelot _________________ 95 985 Ammonoosuc _____________ 90 1,035 West ____________________ 80 1,190 Millers __________________ 80 985 Passumpsic ______________ 65 1,190 Sugar ___________________ 50 490 Other major rivers of northeastern North America Hudson __________________ 490 34,700 Delaware ________________ 625 29,800 Susquehanna _____________ 715 71,500 St. Lawrence1 ____________ 1,183,500 2828,800 d 1 IAbove mouth of Riviere Saguenay, about 30 km north of Riviere- uZ 13211136 Niagara Falls, from headwaters of Ottawa River. The second largest river in the New England region is the Connecticut, which flows south from the Boundary Mountains on the Maine-Quebec border for a total length of about 625 km, only about 100 km less than that of the St. John River. The Connecticut River drainage basin is long and narrow. The drainage area of 29,000 km2 is about half that of the St. John River. The basins of these two rivers more or less enclose those of the four other large rivers that drain to the Atlantic— the Ken- nebec, Penobscot, Androscoggin, and Merrimack. DRAINAGE 9 The rivers that flow northwest from the central seg- ment of the major drainage divide cross the adjacent mountains—in northern Vermont, the higher parts of the Green Mountains, and in Quebec, the Sutton Moun- tains and the southern end of the Notre Dame Moun- tains. The longest of the northwest-flowing rivers is the St. Francois, which is about 300 km long and has a drainage basin of about 9,970 kmz. Below Sherbrooke, Quebec, the drainage basin is long and narrow where the river crosses the Hudson-Green-Notre Dame highlands and the St. Lawrence lowlands. Above Sherbrooke in the central highlands, a large headwater basin extends northeast, parallel to the bedrock structure from the vicinity of Newport, Vt., to Thetford Mines, Quebec, a distance of nearly 200 km (fig. 11). The headwater basin is underlain in part by calc-silicate metasedimentary rocks (fig. 5). The west-flowing rivers in Vermont are smaller than those in Quebec. The Winooski River, about 135 km long, heads in the central highlands and crosses the Green Mountains between Camels Hump and Mount Mansfield in a narrow valley about 700 m deep. The west-flowing tributaries of the Hudson River are short; the largest, the Hoosic River, is 105 km long and has a drainage basin of about 1,740 kmz. STREAMS, DIVIDES, AND AREAS OF CALC-ALKALIC PLUTONIC ROCKS The longer streams of the New England region are largely in areas underlain by sedimentary or metasedimentary rocks. Areas of calc-alkalic plutonic rocks are drained by shorter streams and, in some places, form divides (fig. 13). Why the large rivers ap- pear to avoid granitic plutons has no ready explanation. Several possibilities are discussed in later paragraphs. Fredericton, New‘Brunswick, is on a segment of the St. John River that runs eastward for about 100 km and crosses a northeast-trending belt of calc-alkalic plutonic rocks. The drainage basin narrows toward the area where it is crossed by the belt of plutonic rocks, and the river’s course is close to the narrowest part of the belt. Although the drainage basins of both the Kennebec and the Penobscot Rivers include large areas of calc— alkalic granitic rocks, the main channels of the rivers are largely in metamorphic rocks. The divide on the east side of the Penobscot basin is in or near areas of plutonic rocks. The Androscoggin River, about 355 km long, flows east from Berlin, N.H., for about 80 km around the north side of a large granite pluton that is drained largely by the Presumpscot River, which is only abOut 115 km long. The Merrimack River at Concord, N.H., turns slightly east to skirt a small area of plutonic rock. To the SOuth, the river crosses a northeast-trending belt of plutonic rock that is about 13 km wide and a second narrow belt about 1.5 km wide. Near the Massachusetts State line, however, the river turns northeast and flows for about 50 km close to the north edge of a body of plutonic rock. The north edge of the granite pluton is the Clinton- Newbury fault (Cameron and Naylor, 1976). The Taun- ton River in southeastern Massachusetts heads in areas of plutonic rock, but most of its drainage basin is underlain largely by sandStone, graywacke, and shale of Carboniferous age. CONNECTICUT RIVER The Connecticut River in New Hampshire and Ver- mont runs more or less parallel to the trend of the bedrock units as far north as the mouth of the Passump- sic River. North of the Passumpsic, the trend of the river is northeast across the bedrock structure. The up- per Connecticut River traverses calc-alkalic plutonic rocks for about 30 km. South of the mouth of the Passumpsic, the river avoids areas of calc-alkalic plutonic rocks. Two exceptions are in the highlands east of Middletown, Conn. (fig. 8), and just south of Brat- tleboro, Vt. (fig. 9). From Littleton, N.H., south to Claremont, the Connecticut River follows closely the trace of the Ammonoosuc thrust (fig. 9). In New Hamp- shire, the divide east of the river follows a wide belt of plutonic rock for about 160 km. However, the actual divide for more than half its length is in or close to nar- row belts of metasedimentary rock between larger areas of plutonic rock. In northeast Vermont, the divide on the west side of the Connecticut River is also in or adjacent to areas of plutonic rock. In southern New England, the Connecticut Valley follows a belt of sandstone, shale, and conglomerate of Jurassic and Triassic age. From Springfield to Middle- town (fig. 8), the Connecticut River flows east of long narrow outcrop belts of mafic volcanic rocks that form ridges. SOuth of Middletown, the volcanic rocks extend southeast across the area of Jurassic and Triassic rocks to abut against the older Paleozoic rocks. The river turns east at Middletown and enters the pre-Triassic rocks. It appears that the river’s southerly course is blocked by the volcanic rocks and that the river enters the older rocks of the central highlands where there is a break in a belt of felsic gneiss that is close to or that forms the east border of the Jurassic and Triassic rocks. The river flows around the south end of the Great Hill syncline, where the ridge-forming Silurian quartzite plunges out (loo. 1, fig. 8). Near Long Island Sound, the Connecticut River flows across the northeast trend of the bedrock. 10 GEOMORPHOLOGY OF NEW ENGLAND HUDSON RIVER Throughout most of its course, the Hudson River follows a lowland underlain largely by dolomite, lime- stone, and shale of Ordovician and Cambrian age. However, the course of the river through the highlands south of Newburgh, N.Y., is not easy to explain in terms of the bedrock geology (fig. 7). South of the highlands, on the other hand, the Hudson River estuary, 15—20 km wide, follows the contact between rocks of Late Triassic age to the west and those of Paleozoic and Proterozoic age to the east. The estuary skirts the east side of a ridge of diabase (the Palisades) and, at the north end, the west side of an area of mafic and ultramafic rocks of Late Ordovician age (norite and pyroxenite of the Cort- land Complex). South of Newburgh, the Hudson River leaves the broad lowlands underlain by shale, dolomite, and limestone and traverses a deep narrow gorge for about 100 km through the Proterozoic rocks of the Hudson Highlands. Except near the northwest side of the highlands, the river follows a break in lithology. West of the river, the bedrock is chiefly hornblende granite and granite gneiss; to the east, the dominant bedrock is biotite granite gneiss. The river also tends to follow faults, both the major northeast-trending structures and shorter cross faults. Only in the first 25 km of the gorge south of Newburgh does the river flow southeast at right angles to the northeast trend of the faults and of the ma- jor lithologic units. Perhaps the course of the river in the first 25 km is related to cross joints in the hornblende granite. STREAM GRADIENTS, THE SUBENVELOPE The derivative map portraying the general altitude of the drainage network, the subenvelope (fig. 11) shows how stream gradients differ from one drainage basin to another or from one physiographic unit to another. The map also shows at a glance how the gradient of a river changes where the nature of the adjacent bedrock changes. The Connecticut River, for example, from its mouth north for about 400 km (junction with Passumpsic River) rises less than 90 m. The average gradient is about 0.2 m per km. Between the mouth of the Passumpsic and Lit- tleton, N.H., the Connecticut River turns northeast and crosses belts of metavolcanic rocks (Ammonoosuc Volcanics, Billings, 1955), where the bed rises about 90 m in a distance of about 24 km (fig. 9). The rise, formerly known as Fifteen Mile Falls, is now buried by the pools impounded behind two dams. Farther upstream, the gradient flattens where the river traverses calc-alkalic plutonic rocks for about 30 km. In Connecticut and Massachusetts, stream gradients are low in areas underlain by rocks of Jurassic and Triassic age. The tributary streams entering the Connecticut River from the west head in areas of Proterozoic rock forming the Berkshire Hills. Their gradients are steeper than those of the tributary streams that enter from the east where there are large areas of calc—alkalic plutonic rock. In New Hampshire and Vermont about as far north as lat 44° N., the drainage basin of the Connecticut River is asymmetric; the western tributaries are longer than those entering the river from the east (fig. 9). The White River valley drains a large area of metasedimentary rocks and has a gentler gradient than that of the West River that has a large area of Proterozoic gneiss and quartzite in its headwaters. Near Claremont, the gra- dients of the valleys entering the Connecticut River from the west are steeper than those of either of the rivers mentioned above, probably because Proterozoic rocks and alkalic plutonic rocks are present near the river. Scattered observations suggest that streams, such as the White River, in areas of metasedimentary rocks have many rock outcrops in their beds, whereas streambeds in or near areas of Proterozoic rock or alkalic plutonic rock are covered with boulders, outcrops are scarce, and stream gradients tend to be steeper than those in areas of metasedimentary rocks. The highlands between the Merrimack River and the Connecticut River contain large areas of calc-alkalic plutonic rock, where, in general, stream gradients are lower than those in adjacent rocks. For example, the Ashuelot River (fig. 9) south of Keene, NH, has a lower gradient in the plutonic rocks than it does upstream. The gradients of streams east of Lebanon, NH, are steeper near the Connecticut River than they are to the east, where the streams are largely in plutonic rocks. A striking feature of the subenvelope map (fig. 11) is its delineation of the coastal lowlands (fig. 3). Stream gradients are gentle in the coastal lowlands and steepen rapidly along the edge of the central highlands. These features do not appear to coincide with any bedrock units. Similar rocks are found in both the coastal lowlands and adjacent parts of the central highlands. A belt of steep stream gradients extends from eastern Connecticut north and northeast to the vicinity of Mount Katahdin, Me. (fig. 5). In detail, the line where the envelope steepens extends west and northwest up the large valleys and east and southeast where valleys are small. The line varies in altitude from place to place, as follows: Altitude Area (m) Worcester, Mass 100 Concord, NH 100 South of White Mountains _________________________ 150 Southeast of White Mountains _____________________ 150 West of Rumford, Me 200 Rumford to Mount Katahdin, Me ___________________ 150 AGE OF THE LANDSCAPE 11 In Maine, the beds of the major rivers rise from less than 120 m to more than 240 m above sea level where the streams cross the 8—16-km-wide belt of steep stream gradients. In the belt, both altitude and relief rise about 300 m. The belt of steep stream gradients includes several conspicuous gaps or notches that cross the mountains (Franconia, Crawford, Grafton). At the head of the Saco River in Crawford Notch, southwest of Mount Washing- ton (fig. 11), is a prominent step that marks the Gulf of Maine-Connecticut River divide. The riser of this step is a headwater tributary of the Saco River that has a steep gradient to the south. The tread is a headwater tributary of the Ammonoosuc River that has a gentle gradient to the northwest. The Maine part of the St. John River basin is largely an area where stream gradients are low, although the altitude of the channel of the main stream ranges from about 150 to 300 m. The St. John River rises about 60 m from its mouth at St. John to Grand Falls, New Brunswick; the average gradient is about 0.17 m/km. In New Brunswick, many of the tributaries to the St. John have steep gradients near the river and gentle gradients near their headwaters. From Quebec City southwest to Montreal and south up the Champlain Valley about as far as lat 44° N., the principal northwest-flowing streams have low‘ gradients where they cross the Hudson-Green-Notre Dame highlands. In southeastern Quebec, the tributaries to the Chaudiere and St. Francois have low gradients, whereas to the south in Vermont, the tributaries to the Lamoille and Winooski have steep gradients. The Winooski River crosses the highest part of the Green Mountains. The two Quebec rivers are roughly twice the size of the two Vermont rivers in length and drainage area. The prin- cipal tributaries that enter the Hudson River from the east, Batten Kill, Hoosic River, and Kinderhook and Wappinger Creeks, have gentle gradients in their upper reaches in areas underlain largely by dolomite, limestone, and shale. Gradients are steep where the streams are in the area of shale and graywacke of the Taconic highlands just east of the Hudson River. The Hoosic River and Batten Kill head on the west slope of the Green Mountains. The headwater streams have very steep gradients and are floored with quartzite boulders as large as 3 m in diameter derived from the adjacent Cheshire Quartzite of Cambrian age (Doll and others, 1961). AGE OF THE LANDSCAPE A few widely scattered deposits of Cretaceous or Ter- tiary age on land and extensive Coastal Plain deposits largely beneath the sea suggest that the present land areas have been above sea level throughout long periods of Cenozoic and later Mesozoic time. The volume of sedi- ment under the Coastal Plain has been used to estimate rates of erosion and of uplift of the adjacent landmass. If the estimated rates of erosion and uplift are of the right order of magnitude, it is extremely unlikely that any part of the present landscape dates back before the late Miocene. The only exceptions are areas buried beneath Cenozoic and upper Mesozoic deposits that have been exhumed perhaps by stream and by glacier erosion dur- ing the later Cenozoic. The New England landscape is the result of long- continued subaerial weathering and erosion induced by long-continued uplift or upwarping of the land. Such proc sses may have gone on since the Early Cretaceous. DunEg this span of perhaps 120 million years or more, the rainage has been continually adjusting to changes in the lithologic and structural character of the bedrock as the ground surface has been lowered. In the Middle Atlantic States, there have been two major periods of gravel deposition on the Coastal Plain, one in the Early Cretaceous and the other in the Miocene and perhaps the Pliocene (Owens, in press). Similarly, on the Scotian Shelf, a thick wedge of clastic deposits of Cretaceous and early Tertiary age has been derived from a source area to the north and northwest, probably in the drainage basin of an ancestral St. Lawrence River. A thick wedge of mudstone of later Cenozoic age forms the outer part of the shelf. The base of the Upper Cretaceous sedimentary rocks (US. Geological Survey, 1967; Oldale and Uchupi, 1970) of the Coastal Plain beneath Long Island, Martha’s Vineyard, and Nantucket slopes steeply to the south (fig. 14). The base of the sedimentary rocks—the base- ment surface—if projected landward to the north shore of Long Island Sound, more or less coincides with the in- terfluves near the coast. In a 20-km-wide coastal belt, the interfluves rise steeply to the north. The belt is called the “Fall Zone” by Flint (1963) and, as shown in figure 15, is the envelope of this report. The average slope of the basement surface shown in figure 15 is about 2.3 m/km. If extended northwest, the surface clearly passes far above the envelope, suggesting, as Flint said (1963, p. 683) “* "‘ * recurrent (or continuous) arching beginning before late Cretaceous time.” A map of the basement surface south of Rhode Island (McMaster and Ashraf, 1973) shows a smooth surface in- dented by subparallel channels; the whole slopes south at about 8 m/km. Clearly, the surface has been tilted south; such a slope is far too steep for the drainage as restored by McMaster and Ashraf. Estimated rates of erosion suggest that New England has risen in later Cenozoic time. The rate at which the Appalachian Highlands have been lowered by erosion 12 GEOMORPHOLOGY OF NEW ENGLAND has been estimated by Mathews (1975) on the basis of the volume of sediment in the emerged and submerged Coastal Plain along the Atlantic coast and by Hack (1980) on the basis of the load carried by rivers draining the highlands (see fig. 15). The lowering of the highlands of Connecticut by about 500 m would require about 20 million years if Mathews’ (1975) rate of 2.7 x 10-2 mm/yr is used, whereas about 13 million years would be re- quired if Hack’s (1980) rate of 4.0x 10-2 mm/yr is used. The amount of vertical lowering of the landscape il- lustrated in figure 15 shows that in 15—20 million years, erosion would reduce Connecticut to broad lowlands unless the area was gradually upwarped during that in- terval. If the Pleistocene and Pliocene lasted about 5.4 million years and the Miocene 20 million years, clearly southern New England has been upwarped in later Cenozoic time. These erosion rates also show that when deposition of the Upper Cretaceous sediments beneath Long Island began, the land surface to the north was hundreds of meters above the position of the envelope shown in figure 15. Other evidence suggests considerable erosion of the central highlands. In a study of Paleozoic regional metamorphism in New England, Thompson and Norton (1968) suggested that as much as 15 km of rock may have been removed by erosion since the late Paleozoic. Fission-track dates from apatites from igneous and metamorphic rocks (Zimmerman and Faul, 1976) in the central highlands suggest a possible uplift and erosion of 3—5 km during the last 64—110 million years. The Gulf of Maine may be largely an erosional feature dating from Cretaceous time (Oldale and others, 1974). Oldale and Uchupi (1970, fig. 3) have prepared a reconstruction of the surface beneath the Cretaceous and younger sediments that suggests a stream-eroded landscape. They (1970, p. B—171) believe that the pres- ent floor of the gulf is the result “* * * of fluvial erosion probably during Pliocene and early Pleistocene time.” However, the Gulf of Maine may be in part a structural basin (Owens, in press) modified by erosion and deposi— tion. The western margin of the gulf follows the east side of the north-northwest-trending belt of alkalic granites (the Newport-Boston line) along which a change in topographic form and trend takes place. Perhaps the gulf was downwarped along this line. Small and widely scattered lignitic deposits in the Ap- palachian region (Pierce, 1965) suggest that this region has stood above sea level since the Late Cretaceous. The lignitic deposits at Brandon, Vt., about 20 km north of Rutland (Barghoorn and Spackman, 1950), are reported to be of Oligocene age. Lignite from a clay bed in central Nova Scotia is of Early Cretaceous age (Stevenson and McGregor, 1963). Similar deposits have been found in Pennsylvania, Tennessee, Georgia, and Alabama. At Brandon, as well as in southern Pennsylvania and in Nova Scotia, the plant remains suggest a wet depres- sion, probably a sink. The Brandon locality is in an area underlain by dolomite and limestone of Ordovician and Cambrian age. No marine fossils or any dinoflagellates or other fossils commonly associated with nearshore pollen-bearing sediments were found. Therefore, the deposits at Brandon probably accumulated in a non- marine environment. The association of the deposits at Brandon and elsewhere with carbonate rocks and the absence of any stratification or sequence of fossils in the deposits suggests that they accumulated in a sinkhole pond and have been lowered many hundreds of meters and deformed by continued solution of the underlying bedrock. Pierce (1965) suggested that the Upper Cretaceous Pond Bank lignitic deposit in southern Penn- sylvania could have been lowered more than 425 m on the basis of estimates of the average amount of material eroded from the Applachian Highlands since Late Cretaceous time. “If this amount of lowering has taken place, then the late Cretaceous position of the deposit was several hundred feet [100 m] above the highest mountains now present in the area” (Pierce, 1965, p. C155). RELATION OF COASTAL PLAIN AND GULF OF MAINE BASINS TO THE EMERGED COASTAL PLAIN OF THE MIDDLE ATLANTIC STATES The Coastal Plain and the Gulf of Maine basins of the New England region have some features in common with Chesapeake and Delaware Bays and with the Delmarva Peninsula that separates the two bays. However, the emerged Coastal Plain in the Middle Atlantic States has many characteristics that differ from those of the submerged Continental Shelf to the north. The upper Cenozoic sediments of the Delmarva Peninsula, Delaware, Maryland, and Virginia (Owens and Minard, 1975, 1979; Owens and Denny, 1979), in- clude large amounts of coarse clastic deposits laid down in fluvial and deltaic environments. The Baltimore Can- yon off the New Jersey coast about 150 km south of Long Island contains about 1,000 m of largely clastic sediments of Miocene and younger age (Scholle, 1977). South of southern New England, rocks of Tertiary age are of limited extent, are largely fine-grained sediments, including only a few small masses of fluvial gravel (Folger and others, 1978; Minard and others, 1974; Perry and others, 1975). Chesapeake and Delaware Bays have a different geologic setting from that of the Gulf of Maine. The gulf is, at maximum, only about 400 m deep and contains on- ly small amounts of Coastal Plain sediments. It is north COASTAL PLAIN, GULF OF MAINE BASINS, RELATED TO COASTAL PLAIN, MIDDLE ATLANTIC STATES 13 of the line along which the surface at the base of the Cretaceous rocks is steeply downwarped to the. southeast (fig. 14), the line being the submerged easterly extension of the Fall Line of the Middle Atlantic States (Mathews, 1975). If the Gulf of Maine is in part a struc- tural feature, it represents only a gentle downwarp. Chesapeake and Delaware Bays, on the other hand, are seaward of the Fall Line and are part of the much larger Salisbury embayment (Anderson, 1948; Robbins and others, 1975; Owens, in press). The embayment extends parallel to the coast about 280 km and at right angles to the coast for about 180 km, roughly about two-thirds the area of the Gulf of Maine. However, the embayment near the Maryland coast contains about 1,800 m of Coastal Plain sediments. In the Gulf of Maine, the surface beneath the Coastal Plain sediments, the basement surface as reconstructed by Oldale and Uchupi (1970), resembles a landscape (fig. 14) of broad valleys separated by low divides, the valleys being the seaward extension of many of those on land. Georges Bank forms most of the divide at the mouth of the gulf and is breached at two points. The eastern gap, Georges Basin and the Northeast Channel, carried the drainage from the eastern two-thirds of the floor of the gulf and from the Penobscot and St. John Rivers and the Bay of Fundy, a total drainage area of about 190,000 ka, or nearly three times that of the Susquehanna River. The western gap, Great South Channel, has a more complex Pleistocene history (Lewis and Sylwester, 1976). Nevertheless, the channel is believed to mark the position of the stream that in the Tertiary carried drainage from the western third of the floor of the Gulf of Maine, and to have been the seaward extension of the Charles, Merrimack, Androscoggin, and Kennebec Rivers. The total area that drains to the mouth (south end) of the Great South Channel is about 99,000 ka, roughly about one-third larger than the Susquehanna River drainage basin. The basement surface or floor of the Gulf of Maine, as reconstructed by Oldale and Uchupi (1970), suggests an erosional surface. If the gulf is indeed a structural depression, it appears to have been extensively modified by erosion and deposition. Erosion of large masses of Coastal Plain sediments is reasonable in terms of the amount of material that may have been removed and the size of the'streams that are believed to have done the work. Georges Basin and the Northeast Channel and the drainage basin upstream are comparable in size with similar valleys in the Coastal Plain south of the glaciated region, such as Chesapeake Bay, as shown below: Size Drainage area - (kmz) (kmz) 12,200 176,000 10,500 167,000 Georges Basin and Northeast ChanneL _________ Chesapeake Bay ___________________________ North and east of the New England region, the Laurentian Channel (Canada Hydrographic Service, 1973), similar to the Northeast Channel but on a much larger scale, follows the St. Lawrence River estuary from near Riviere-du-Loup (mouth of Riviere Saguenay) for about 1,200 km through the Gulf of St. Lawrence and enters the Atlantic Ocean between Nova Scotia and Newfoundland. Where the Channel crosses the sub- merged Coastal Plain s0uth of Nova Scotia, it'is about 80 km wide and 180—300 m deep. The Northeast Channel southwest of Novia Scotia is 32 km wide, and the walls range from 90 to 150 m in height. Above the mouth of the Saguenay, the St. Lawrence River. drainage basin below Niagara Falls is about 830,000 km2. The Lauren- tian Channel is presumed to be the result of glacial ero- sion and deposition in the ancestral St. Lawrence valley (Shepard, 1931; Emery and Uchupi, 1972; Loring, 1975). The configuration of the Continental Shelf of north- eastern North America suggests that the region has been submerged in late geologic time (Eardley, 1964). However, we do not know the position of sea level in the New England region in the Miocene when glaciers are presumed to have begun to form in the Antarctic and when glacially controlled eustatic changes in sea level became a reality. Nor do we know whether northeastern North America has returned to the same position with respect to the center of the Earth as it had before glacial loading. Studies in the Coastal Plain of the Middle Atlantic States suggest that in the Miocene the Hudson River did not enter the ocean near its present position but that it flowed southwest from New York City near the inner edge of the Coastal Plain and entered the ocean in the vicinity of the Del arva Peninsula. Beginning in the Miocene, large vol mes of fine clastic materials were deposited in the Coastal Plain of the Middle Atlantic States. The sedime ts coarsen upward, culminating in deposition of wars} clastic materials in the Pliocene. The clastic deposit ‘ came from the northwest and the north. Owens and Minard (1975, 1979) have suggested the Hudson Valley as the probable source of Miocene fluvial deposits (Bridgeton Formation or “Arkose 2”) near the inner edge of the New Jersey Coastal Plain. South of the mouth of the Hudson River, no large channel crosses the1 Continental Shelf that is similar in size to the Northeast Channel at the mouth of the Gulf of Maine. A shallow channel crosses part of the shelf, to end near the head Of the Hudson Canyon on the Con- tinental Slope (UchUpi, 1965). The channel is about 100 km long, 1 to 10 km wide, and about 20 to 40 m deep. Perhaps the Northeast Channel is large because it was widened and deepe ed by an ice sheet during Wiscon- sinan time. The ar a that may have drained seaward through the North ast Channel (176,000 kmz) is more 14 GEOMORPHOLOGY OF NEW ENGLAND than four times larger than that of the present Hudson River (34,700 kmz). Perhaps this difference in drainage area accounts in part for the difference in size of the two submerged channels. A buried valley in the Continental Shelf south of New York City, apparently a Pleistocene course of the Hudson River, is about the same size as the shallow channel on the shelf at present (Knebel and others, 1979). A third possibility is that the present course of the Hudson was established in post-Miocene time and that in the Miocene, as Owens and Minard have suggested, the river flowed southwest near the inner edge of the Coastal Plain and entered the Atlantic Ocean in the vicinity of the Delmarva Peninsula. Perhaps at the same time, other rivers were flowing across the floor of the Gulf of Maine and through the channels in the Coastal Plain to the south. LANDSCAPE EVOLUTION The landscape of the New England region is closely related to the character and distribution of the bedrock units. The relationships suggest that long-continued subaerial weathering and erosion aided by concurrent rise of the land has produced a landscape in conformity with the geologic framework of the region. These subaerial processes may have been in operation during much of post-Early Cretaceous time. The control that bedrock exerts on land form is evident throughout the area. The volcanic rocks of Jurassic and Triassic age form steep-sided narrow ridges. Shale and graywacke of Ordovician, Cambrian, and Proterozoic Z age form the Taconic highlands. Steep-sided mountains and hills are the topographic forms of alkalic plutonic rocks. Sand- stone and shale of Jurassic and Triassic age, as in the Connecticut Valley, similar rocks of Carboniferous age, as near Boston, and dolomite, limestone, and shale of Ordovician and Cambrian age, as in the Vermont Valley, commonly form lowlands. The higher parts of the southern half of the Hudson-Green-Notre Dame highlands are underlain largely by resistant beds of massive gneiss and of subordinate quartzite of Pro- terozoic age. The northern half of the highlands is large- ly Paleozoic metasedimentary and metavolcanic rocks of both amphibolite and greenschist facies. Massive in- termediate to high-grade metapelites are more resistant than are similar schists of low metamorphic grade. Calc- silicate metamorphic rocks and feldspathic plutonic rocks tend to form lowlands, although ease of disag- gregation and differences in massiveness of the plutonic rocks influence their topographic expression. The central highlands include not only the highest peaks in New England—the White Mountains and Mount Katahdin—but also large areas of low mountains and hills. The geology of the central highlands is diver- sified, and at the map scale used in this study, it has not been possible to define the lithology and structure of the central highlands adequately to permit a detailed discus- sion of the physiographic features of this unit. The White Mountains, Mount Katahdin, and the higher peaks between them are 300—800 m above the coastal lowlands to the southeast. These peaks are in the center of the New England region, roughly equidistant from the St. Lawrence River to the northwest and the Gulf of Maine to the southeast. If the principal streams radiated out from these peaks in all directions, one might suppose that they are at the center of a crustal block that has been slowly rising for a long time to more or less balance the lowering of the peaks by erosion. However, such is not the case. The Connecticut and An- droscoggin Rivers rise about 100 km north of Mount Washington. The former flows south and southwest around the west side of the White Mountains; the latter runs southwest to Berlin, NH, where it turns east to enter the ocean near Portland, Me. Although the data presented here clearly show that no part of the present landscape is probably older than the Miocene, major lowlands such as the Hudson- Champlain-St. Lawrence lowlands, the Vermont Valley, the Connecticut Valley, and the Gulf of Maine might have been in existence throughout the Tertiary Period. Streams flowing from Mount Washington and adjacent peaks west to the Connecticut River, and the river itself north of the mouth of the Passumpsic, cross a belt of resistant rocks, including the Ammonoosuc Volcanics and the Clough Conglomerate (Billings, 1955), where stream gradients are steep. Streams flowing south from the White Mountains, such as the Merrimack and the Saco, head in the largest area underlain by alkalic plutonic rocks in the New England region, rocks that clearly form steep—sided mountains. Probably these geologic relations have been causing streams to have steep gradients for tens of millions of years, and the geographic arrangement of the bedrock units has led to the formation of the White Mountains. The mountains have been buttressed to the south and west by the alkalic plutonic rocks. The metasedimentary rocks of the White Mountains and adjacent western Maine are largely am- phibolite and granulite facies. Such rocks underlie the summit of Mount Washington. In central Maine, the metasedimentary rocks in the higher mountains are greenschist facies. Many of the higher peaks are massive rocks, either metavolcanic rocks or contact-metamorphic rocks surrounding plutonic rocks. The mountains consist of somewhat isolated peaks, whereas in the White Mountains and to the south, the mountains tend to be somewhat elongate. The coastal lowlands are a half—submerged and half— emerged piedmont at the foot of the central highlands. TECTONISM 15 The lowlands may have undergone long periods of ero- sion beginning in the Early Cretaceous. The northwest border of the lowlands is, in a few places, a low, gently sloping escarpment. Throughout most of its length, however, the border is a belt 15—30 km wide, where from southeast to northwest, the relief and stream gradients increase as compared with those in the lowlands. In detail, the southeast border of the highlands appears to be an erosional feature. No structural evidence for tec— tonic movement, perhaps related to the uplift of the White Mountains-Mount Katahdin highlands, has been reported. Many of the same rock units occur in both highlands and lowlands. A belt of calc-silicate rocks of Silurian and Ordovician age underlies areas in the coastal lowlands. These fairly nonresistant rocks may be a part of the reason for the lowlands. However, south of Worcester, Mass, the calc-silicate belt is in the central highlands, and in much of Maine, the western edge of the belt is 10—40 km east of the western edge of the coastal lowlands. It is difficult to escape the conclusion that the highlands have been raised by tectonic movements, presumably some sort of arching or doming relative to the adjacent lowlands. Why many of the large rivers do not cross areas of 'calc-alkalic plutonic rock, but rather take a longer course around such areas, cannot readily be explained. Do these phenomena have a climatic explanation? Was the climate of New England warmer and wetter in the early Cenozoic than it has been since that time? Perhaps the plutonic rocks formed highlands in the early Cenozoic, which have been lowered by erosion during the cooler later Cenozoic. In spite of such a change in climate, the major streams still maintain their early Cenozoic courses around the areas of plutonic rock. Any such explanation hardly seems adequate. Are the phenomena related to the contrast between the action of a stream flowing in coarse-grained plutonic rocks and that of one flowing in fine-grained foliated rocks? As a broad generalization, one can perhaps say that modern rivers draining areas of coarse—grained rock tend to have beds and banks of sand and gravel, whereas rivers draining areas of fine-grained rock tend to have beds and banks of silt and clay. The former rivers have shallow channels and tend to migrate from side to side; the latter have deep channels and tend to maintain their courses. Perhaps such processes acting over long periods of time (10 million years) cause rivers to move from areas of plutonic rock into areas of fine- grained rock. Although the map of the New England region outlin- ing physiographic units (fig. 3) shows a narrow belt of coastal lowlands in southern Connecticut, the topography in the belt is more rugged than that in the lowlands elsewhere. The coast of southern New England trends more or less at right angles to the major bedrock units, which to the south pass beneath the Coastal Plain. Southern New England has been upwarped relative to the Coastal Plain to the south in late Mesozoic and in Cenozoic time (fig.l 14). Oldale and Uchupi (1970) show streams on the 1a (1 extending down the slope of the basement surface. he gradient of streams on the base- ment surface is much steeper than that of their possible headwater reaches: on land, suggesting that the base- ment surface has been tilted down to the south relative to the adjacent landmass. The deformation could be Late Cretaceous or younger. TECTONISM One of the major problems of New England geomor- phology is how important tectonic movements have been in the shaping of the modern landscape. The evidence for Cenozoic tectonic movements in the Coastal Plain and Piedmont of Southeastern United States (Mixon and Newell, 1977; Prowell and O’Connor, 1978), as well as in the Adirondacks (Isachsen, 1975, 1978), raises the possibility of similar tectonic activity in the New England region. The character of the Coastal Plain sediments tells us something about e tectonic history. The arrival of coarse clastic sedi ‘ents on the Coastal Plain in the Mid- dle Atlantic Statels in the late Miocene and in the Pliocene suggests the relative uplift of the adjacent Piedmont and of the Hudson River drainage basin. If the central highlands of the New England region were elevated in the late Tertiary, one might expect that coarse clastic materials should have been deposited in the Coastal Plain to the south and east. Although such sediments are not found near shore, a thick section of upper Cenozoic clastic rocks is present at the north end of the Baltimore Canyon trough. The coarse clastic sediments shed by the central highlands may have been deposited close by, that is, in the coastal lowlands, not 50—100 km to the east as part of the submerged Coastal Plain of the present day. The lowlands adjacent to the highlands contain extensive deposits of sand and subor- dinate gravel of Pleistocene age (National Research Council, Division of Earth Sciences, 1959). Perhaps some of these sediments were derived from older elastic deposits of Tertiary age. If the central highlands were elevated relative to the coastal lowlands inlMiocene and Pliocene time, it is in- teresting to note that the break between highlands and lowlands is just southeast of a belt of calc-alkalic granites. Richard Goldsmith (written commun., 1978) has suggested that, because such granites are emplaced in or near t cores of orogens, they would be the sites of former mtifuntains. Such areas commonly are gravity 16 GEOMORPHOLOGY OF NEW ENGLAND lows (Kane and others, 1972). As the mountains are lowered by erosion, they tend to rise because of isostasy. In Maine, a gravity gradient that slopes down to the northwest coincides in places with the topographic break (Kane and others, 1972). Estimated rates of erosion by streams draining to the North Atlantic Ocean (fig. 15) suggest that highlands such as the White Mountains would be reduced to hills and lowlands within about 30—40 million years. Such estimates indicate that the doming or arching of such highlands either individually or as a unit, cannot be older than middle Tertiary. No movement has been shown to have taken place along any fault planes in the New England region in later Cenozoic time. Isachsen (1975, 1978) believes that there may have been Holocene defor- mation in the Adirondack region, perhaps including the adjacent Hudson-Champlain lowlands. The bedrock geology of the Piedmont in the central and southern Appalachians (King and Beikman, 1974) is similar in many respects to that of New England. The topography, on the other hand, is different. In New England, the areas of high relief are much more exten- sive than they are in the Piedmont to the south (Hack, 1980, fig. 5), perhaps indicative of upwarping of the highlands of New England in late Cenozoic time. The St. Lawrence lowlands near Quebec City are ‘seismically active, and one wonders whether the lowlands might not be the result, in part, of tectonic movements. However, “the concentrations of earth- quake epicenters [in the lowlands] are apparently not controlled by near-surface geological elements" (Poole and others, 1970, p. 300 and fig. VI—32). REFERENCES CITED Anderson, J. L., 1948, Cretaceous and Tertiary subsurface geology: Maryland Department of Geology, Mines and Water Resources Bulletin 2, p. 1—113; appendix, p. 385—441. Ballard, R. D., and Uchupi, Elazar, 197 5, Triassic rift structure in Gulf of Maine: American Association of Petroleum Geologists Bulletin, v. 59, no. 7, p. 1041—1072. Barghoorn, E. S., and Spackman, William, 1950, Geological and botanical study of the Brandon lignite and its significance in coal petrology: Economic Geology, v. 45, no. 4, p. 344—357. Billings, M. P., compiler, 1955, Geologic map of New Hampshire: Washington, D.C., US. 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W., 1975, Possible evidence for contemporary doming of the Adirondack Mountains, New York, and suggested implications for regional tectonics and seismicity: Tectonophysics, v. 29, p. 169-181. REFERENCES CITED 17 Isachsen, Y. W., Geraghty, E. P., and Wright, S. F., 1978, Investiga- tion of Holocene deformation in the Adirondack Mountains dome [abs.]: Geological Society of America, Abstracts with Programs, V. 10, no. 2, p. 49. Jansa, L. F., and Wade, J. A., 1975, Geology of the continental margin off Nova Scotia and Newfoundland, in van der Linden, W. J. M., and Wade, J. A., eds., Offshore geology of eastern Canada, v. 2, Regional geology: Canada Geological Survey Paper 74—30, p. 51—105. Kane, M. F., and others, 1972, Bouguer gravity and generalized geologic map of New England and adjoining areas: U.S. Geological Survey Geophysical Investigations Map GP—839, scale 1:1,000,000, 6-p. text. King, P. B., and Beikman, H. 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A., eds., Offshore geology of eastern Canada, v. 2, Regional geology: Canada Geological Survey Paper 74-30, p. 11—34. Mathews, W. H., 1975, Cenozoic erosion and erosion surfaces of eastern North America: American Journal of Science, v. 275, no. 7, p. 818—824. McMasters, R. L., and Ashraf, Asaf, 1973, Subbottom basement drainage system of Inner Continental Shelf off southern New England: Geological Society of America Bulletin, v. 84, no. 1, p.187—190. Minard, J. P., Perry, W. J., Weed, E. G. A.,Rhodehamel, E. C., Rob- bins, E. I., and Mixon, R. B., 1974, Preliminary report on geology along Atlantic continental margin of northeastern United States: American Association of Petroleum Geologists Bulletin, v. 58, no. 6, pt. 2, p. 1169-1178. Mixon, R. M., and Newell, W. L., 1977, Stafford fault system- Struc- tures documenting Cretaceous and Tertiary deformation along the Fall Line in northeastern Virginia: Geology, v. 5,no. 7, p. 437—440. Morgan, 8. 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J ., 1978, Belair fault zone—Evidence of Tertiary fault displacement in eastern Georgia: Geology, v. 6, no. 11, p. 681-684. Quebec Department of Natural Resources, 1969, Geological map of Quebec: Quebec, P.Q., 2 sheets, scale 1:1,013,760. Quinn, A. W., 1971, Bedrock geology of Rhode Island: U.S. Geological Survey Bulletin 1295, 68 p. (See especially pl. 1, scale 1:125,000.) Robbins, E. 1., Perry, W. J., Jr., and Doyle, J. A., 1975, Palynological and stratigraphic investigations of four deep wells in the Salisbury Embayment of the Atlantic Coastal Plain: U.S. Geological Survey Open-File Report 75—307, 120 p. Scholle, P. A., ed., 197 7, Geological studies on the COST No. B—2 well, U.S. Mid-Atlantic Outer Continental Shelf area: U.S. Geological Survey Circular 750, 71 p. Shepard, F. P., 1931, St. Lawrence (Cabot Strait) submarine trough: Geological Society of America Bulletin, v. 42, no. 4, p. 853-864. Steams, R. G., 1967, Warping of the western Highland Rim peneplain in Tennessee by ground-water sapping: Geological Society of America Bulletin, v. 78, no. 9, p. 1111—1124. Stevenson, I. M., and McGregor, D. C., 1963, Cretaceous sediments in central Nova Scotia, Canada: Geological Society of America Bulletin, v. 74, no. 3, p. 355—356. Stewart, D. P., and MacClintock, Paul, 1969, The surficial geology and Pleistocene history of Vermont: Vermont Geological Survey Bulletin 31, 251 p. Thompson, J. B., and Norton, S. A., 1968, Paleozoic regional metamor- phism in New England and adjacent areas, in Zen, E-an, and others, eds., Studies of Appalachian geology—northern and maritime: New York, Interscience, p. 319-327. 18 GEOMORPHOLOGY OF NEW ENGLAND Uchupi, Elazar, 1965, Map showing relation of land and submarine topography, Nova Scotia to Florida: U.S. Geological Survey Miscellaneous Geologic Investigations Map 1—451, 3 sheets, scale 1:1,000,000. U.S. Geological Survey, 1967, Engineering geology of the Northeast Corridor, Washington, D.C., to Boston, Massachusetts—Coastal Plain and surficial deposits: U.S. Geological Survey Miscellaneous Geologic Investigations Map I—514—B, 8 sheets, 9-p. text. Weed, E. G. A., Minard, J. P., Perry, W. J., Jr., Rhodehamel, E. C., and Robbins, E. I., 1974, Generalized pre-Pleistocene geologic map of the northern United States Atlantic continental margin: U.S. Geological Survey Miscellaneous Investigations Series Map 1—861, 2 sheets, scale 1:1,000,000, 8-p. text. White, W. S., 1968, Generalized geologic map of the northern Ap- palachian region, in Zen, E-an, and others, eds, Studies of Ap- palachian geology—northern and maritime: New York, Inter- science, p. 453. Zen, E-an, 1967, Time and space relationships of the Taconic allochthon and autochthon: Geological Society of America Special Paper 97, 107 p. 1972, A lithologic map of the New England States and eastern New York: U.S. Geological Survey open-file map, 18 sheets, scale 1:250,000. Zimmerman, R. A., and Paul, Henry, 1976, Fission-track tec- tonics —Regiona.l uplift in eastern North America [abs]: Geological Society of America, Abstracts with Programs, v. 8, no. 6, p. 1181—1182. fi U.S. GOVERNMENY PRINYING OFFICE: l982- JGI-GM/IZ ZOZZZ VA 'U015U!IJ\1 '133118 51193 MINDS UOZl 'Aemns 1931501095 '31] 11011011111311] 10 usuan Aq 9193 101 GNV'IDNEI MEIN :IO ADO'IOHdHOWOEIE) LLVOBSVZ861*VA LNULSHH 'HAHflS WOIEJOWOED‘HOIHHWI Auuea '3 59119113 Aq A601099 186L ‘A9A1ns 1901501099 'S'n 1110119599 'uaAeH maN 1o 1samq1nos un1 31 1n0qe 91111310115 1n3113auu03 9111 s1oasxa1u1 u0113es $50.13 91.11 H.961) (39th 1931801099 '31] w011 aoeyns 1uawaseg 10861) 113911 pUQ (9L6I) smaqmw liq pa19w11sa $9 91996 u01111u1 19d uogsOJa liq adeospuq 31.11, 10 8u1xam01 123111911 10 1unowe 9111 0919 ‘19Aa1 995 moIaq 01121qu S! 63211118 1uawaseq 9‘41 U0 553119A 11193115 JO 11099301 P3113JUI ‘swe1un0w 99an9 u19111nos - 1 1 - WGPUO 'SUIWUUOW 113319 ”19113105 ‘ - w s ue mo aaualme '1s—u121du12q3—u08an-u9830 sq1dap pue aAoqe sapn1111e smoqs 912391231119A 9L1 .L snoa3e1913 Jaddn 31.1110 aseq 91.11 pug ado1anuaqns 9111 ad01aAua (OL6I) 1dn113f1 pue a1ep10 Aq pau31u1se s>1301 51108321813 10 aseq moqs sm01u03 1319 9 9 £ 2 011 99121 uame a Sutuuo 389 3902013 01 o s 301 {9 up 81), ,P p I 1 —I 9 9 _- . 1891 we Bu me a 0 draw 31 a _. 611110 uomsod smoqs uouoas 91191815110110 81qu qlnos 6111 01 amqsmonoauu03 39110 quou UDI 061noqe1u1od 2 won 30.qu ‘SIIIH 8111151199 6111 91011191118111 1108an Due 19911111011131.1891 6111111101 652 31020131019. 10 51°01 99 Pu2 659 310201310191 “54113”? 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NOKLEBERG and GARY R. WINKLER GEOLOGICAL SURVEY PROFESSIONAL PAPER 1209 Contemporaneous mean—floor sednnentatz'on, submarine volcanism, sulfide deposition, and hydrothermal alteration in Mz’ssissz‘ppz‘an time UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1982 UDHTTI)STATTESDEPARJWAENT‘OF'FHIZHQTERDOR JAAJES(3.VVAJTT,Sbcnnany GECHJ)GJCAJ.SLH{VEY Dallas L. Peck, Director Library of Congress Cataloging in Publication Data NokLebergr Warren J. Stratiform zinc-Lead deposits in the Drenchwater Creek area; Howard Pass quadrangLez northwestern Brooks Range: ALaska. (GeotogicaL Survey professionaL paper ; 1209) BibLiography: p. 21-22 Supt. of Docs. no.: I 19.16:1209 1. Zinc ores--ALaska--Drenchwater Creek region. 2. Lead ores--ALaska-- Drenchwater Creek region. I. WinkLerz G. R. II. TitLe. III. Series: United States. GeoLogicaL Survey. ProfessionaL Paper 1209. TN483.A64N64 553.4'4'097987 81-607994 AACRZ For sale by the Superintendent of Documents, US. Government Printing Office Washington, DC. 20402 CONTENTS Page Page Abstract .................................................. 1 Sulfide dePOSitS ........................................... 14 Introduction .............................................. 1 Occurrence and limits ................................. 14 Previous work ............................................ 2 Petrology --------------------------------------------- l5 Stratigraphy of zinc- and lead-bearing rocks ................ 2 Disseminated sphalerite ........................... 15 Petrology—Mississippian rocks of the Kagvik sequence ..... 5 Disseminated sphalerite, galena, pyrite, Silicified mudstone .................................... 7 and marcasite .................................. 15 Sulfidebearing chert .................................. 7 Geochemistry ......................................... 16 Sulfide-bearing metaquartzite .......................... 9 Rock, soil, and stream-sediment samples ........... 16 Tuffaceous sandstone, tuffaceous siltstone, and tuff ..... 9 Sulfide minerals .................................. 17 Keratophyre flows .................................... 10 Lead isotope analyses 0f galena -------------------- 18 Pyroxene andesite sill ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, 10 Origin and modification ............................... 18 Structure ................................................. 11 Submarine volcanogenic/ hydrothermal origin ...... 18 Major structures ...................................... 11 Geologic controls .................................. 19 Minor structures ...................................... 13 Model ............................................ 20 Origin of structures ................................... 14 Regional mineral potential and exploration guidelines ...... 20 References cited ........................................... 21 ILLUSTRATIONS Page PLATE 1. Geologic map of the Drenchwater Creek area, Howard Pass quadrangle, northwestern Brooks Range, Alaska ................................................................................................. In pocket 2. Maps showing geochemical distribution of zinc, lead, barium, and silver in rock, soil, and stream-sediment samples from the Drenchwater Creek area, Howard Pass quadrangle, northwestern Brooks Range, Alaska ............................................................................................... In pocket FIGURE 1. Index map of northern Alaska, showing location of Drenchwater Creek area ....................................... 2 2. Oblique aerial views of Drenchwater Creek area .................................................................. 3 3. Map of southern part of National Petroleum Reserve in Alaska, showing distribution of the Kagvik sequence and areas of high and low zinc-lead mineral-resource potential .................................................. '. . . 4 4. Diagram showing reconstructed stratigraphic succession in the Kagvik sequence ................................... 5 5. Photomicrographs of thin sections of Mississippian rocks of the Kagvik sequence ................................... 6 6. Ternary diagram showing modes of Mississippian clastic and volcaniclastic rocks of the Kagvik sequence ........... 10 7. Ternary diagram showing feldspar compositions in keratophyre ................................................... 11 8. Ternary diagrams showing compositions of feldspar and clinopyroxene in pyroxene andesite ........................ 11 9. Simplified structure map of Drenchwater Creek area .......................................... x. ................... 12 10. Photograph showing highly deformed dark-gray chert and shale in Mississippian rocks of the Kagvik sequence in southwestern part of Drenchwater Creek area ..................................................... 13 11. Lower-hemisphere stereograms of structures measured in Drenchwater Creek area .................................. 13 12. Photomicrographs of polished thin sections of sulfide minerals in Mississippian chert and metaquartzite of the Kagvik sequence ...................................................................................... 15 13. Graphs showing sphalerite and galena compositions .............................................................. 17 14. Diagrams illustrating model for origin and deformation of stratiform sulfide deposits in Drenchwater Creek area .................................................................................................. 20 III IV CONTENTS TABLES Page TABLE 1. Petrologic characteristics of Mississippian rocks of the Kagvik sequence in the Drenchwater Creek area ............. 8 2. Anomalous abundances of metallic elements in selected rock samples from the Drenchwater Creek area ............. 16 23. Electron microprobe analyses and structural formulas of sphalerite from the Drenchwater Creek area ............... 18 4. Electron microprobe analyses and structural formulas of galena from the Drenchwater Creek area .................. 19 54 Lead isotope ratios for galena from the Drenchwater Creek area ................................................... 19 STRATIFORM ZINC-LEAD DEPOSITS IN THE DRENCHWATER CREEK AREA, HOWARD PASS QUADRANGLE, NORTHWESTERN BROOKS RANGE, ALASKA By WARREN J. NOKLEBERG and GARY R. WINKLER ABSTRACT Major zinc-lead deposits occur at Drenchwater Creek in the Howard Pass quadrangle in the National Petroleum Reserve in Alaska (NPRA). Detailed geologic mapping ofa 81-km2 area shows that sphalerite, galena, pyrite, marcasite, and sparse barite occur irregularly in a zone at least 1,830 m long and 6 to 45 m wide. The sulfide deposits are in deep-water marine rocks of Mississippian age that consists of dark-gray chert and shale, tuff, tuffaceous sandstone, and sparsely distributed keratophyre and andesite flows and sills. These Mississippian rocks constitute the oldest part of the Kagvik sequence, which includes rocks oflate Paleozoic and Mesozoic age. The Kagvik sequence is in the lowermost structural plate of a terrane characterized by east-west-striking gently south dipping thrust faults. The bedrock of the Drenchwater Creek area is a tectonic breccia composed of a heterogeneous mixture of lenses of different rock types; these lenses are commonly several hundred meters long by a few tens of meters wide. The sulfide minerals typically are present in hydrothermally altered chert and shale adjacent to volcanic and volcaniclastic rocks. Fragments of fine-grained feldspar, pumice lapilli, and mafic volcanic rocks in the chert and shale are commonly replaced by aggregates of kaolinite, montmorillonite, sericite, chlorite, actinolite, barite, calcite, quartz, fluorite, and prehnite. Locally the chert is altered to siliceous medium-grained metaquartzite. The sulfide minerals and barite form disseminated grains, massive sphalerite-rich layers, or, more rarely, quartz-sulfide veins that crosscut cleavage. Selected samples contain more than 1 weight percent Zn and 2 weight percent Pb, as much as 150 ppm Ag, greater than 500 ppm Cd, and as much as 500 ppm Sb and 1,500 ppm Ba. Electron microprobe analyses of sphalerite show the following atomic percentages: 44.3 to 47.5 Zn, 2.0 to 5.2 Fe, 0.3 to 0.4 Cd, and 0.1 to 0.2 Mn. Analyses of galena show the following atomic percentages: 47.8 to 49.9 Pb and 0.1 to 2.2 Sb. The pyrite and marcasite are nearly devoid of trace metals. Lead isotope analyses of galena show model lead ages of approximately 200 my. and indicate derivation of the lead from an average orogene, either an island-arc or Andean-type arc environment. Field and laboratory data suggest that the stratiform deposits were formed from metal—laden hydrothermal fluids discharged onto a deep»ocean floor during submarine eruptions that yielded keratophyric to andesitic flows, tuff, and sills. Later intense deformation disrupted and partly remobilized the stratiform deposits. The sulfide deposits in the Drenchwater Creek area represent a recent discovery in a region that has not been thoroughly explored. Zones of iron staining in the Kagvik sequence and zinc anomalies in stream sediments indicate favorable areas for exploration to the east and west of the Drenchwater Creek area. INTRODUCTION During the last few years, there has been great interest in stratiform zinc-lead-copper deposits. These deposits generally occurin carbonate rocks, in dark-gray shale and chert, or in mafic to siliceous submarine volcanic rocks (Gilmour, 1971; Hutchin- son, 1973; Sillitoe, 1973; Lambert, 1976; Solomon, 1976; Urabe and Sato, 1978; Williams, 1978a, b). Deposits of this type are thought to originate from submarine volcanism through exhalation of sulfide- rich hydrothermal fluids (Sangster, 1972). This theory has led to the discovery of extensive stratiform sulfide deposits in the Yukon and Northwest Terri~ tories of Canada, including the extensive shale- hosted Howard’s Pass deposit, which holds several hundred thousand tons of 10-weight-percent com- bined Zn-Pb values (Templeman-Kluit, 1978), and the shale-hosted Tom deposit, with published re- serves of 7 million tons grading 8.4 weight percent Zn, 8.1 weight percent Pb, and 2.8 troy oz Ag per ton (Brock, 1976). During fieldwork in 1950-53’ 1976, and 1977, I. L. Tailleur (oral commun., 1977; Tailleur and others, 1977) observed iron staining from weathered pyrite, marcasite, sphalerite, galena, and minor barite in dark-gray chert and shale along Drenchwater Creek (fig. 1). During fieldwork in 1955 and 1968, Tailleur (1970) observed similar sulfide minerals in Mississip- pian rocks along Red Dog Creek in the De Long Mountains quadrangle, about 120 km west of Drench- water Creek. Because of similarities between the two deposits, Tailleur (1970) suggested that other areas along the north front of the Brooks Range where prominent iron-stained dark-gray chert and shale of Mississippian age occur might be the sites of zinc, lead, and barium deposits of potential economic significance. The metallic-mineral resource potential of the area had previously been considered to be low. Since 1970, the zinc-lead deposits at Red Dog Creek have been intensively explored (Plahuta, 1978; Plahuta and others, 1978; Nokleberg and others, 1 2 STRATIFORM ZINC-LEAD DEPOSITS, DRENCHWATER CREEK AREA, ALASKA 1979a, b). That area is now the site of extensive claim staking for stratiform zinc-lead-barium deposits; recent newspaper accounts estimate that two major companies have staked more than 5,000 mining claims. These discoveries have generated considerable inter- est in the stratiform sulfide deposits in the Brooks Range, and also in the geologic setting and genesis of these deposits in the northwestern Brooks Range. A large part of the National Petroleum Reserve in Alaska (NPRA) (fig. 1) between the Red Dog Creek and Drenchwater Creek areas contains rocks whose stratigraphy, structure, and age resemble those that host sulfide deposits in the Red Dog Creek area (Tailleur, 1977; Plahuta, 1978; Plahuta and others, 1978; Nokleberg and others, 1979a, b). In the same general area, Mayfield, Curtis, Ellersieck, and Tailleur (1979) also reported zinc-lead and barite deposits in the Ginny Creek and Nimiuktuk areas, in rocks similar to those hosting the deposits in the Drenchwater Creek and Red Dog Creek areas. The Drenchwater Creek area contains the best exposed and most abundant zinc- and lead-sulfide deposits yet discovered in the NPRA (fig. 2). Conse- quently, we have studied the area in detail to acquire basic information on the genesis of the stratiform sulfide deposits for mineral-resource assessment and exploration within that region (Nokleberg and Winkler, 1978a, b, c). The results of our studies presented here include: (1) a detailed geologic map of about a 30-km2 area at a scale of about 1:20,000; (2) petrologic analyses of host rocks and sulfide samples; (3) structural analysis of the tectonic breccia and melange that constitute most of the bedrock in the area; (4) semiquantitative analyses of whole—rock, soil, and stream-sediment samples; (5) electron micro- probe analyses of silicate minerals from igneous flows and sills; (6) electron microprobe analyses of sphalerite, galena, pyrite, and marcasite from mineral— ized rocks; (7) lead isotopic analyses of sulfide minerals; and (8) discussion of the genesis of the deposits. The detailed geologic mapping and sam- pling was done during July 1977 with about 44 man- days of effort. Drenchwater Creek flows northward from the crest of the Brooks Range, which is only a few kilometers south of the study area, into the Kiligwa River, a tributary of the Colville River. Relief in the area is moderate; low hills and ridges rise a few tens to a few hundreds of meters above the major drain— ages (fig. 2). To the south, the crest of the Brooks Range ranges in altitude from 1,500 to 2,000 m. Although vehicle movement is practicable in the winter, helicopters provide the only effective access to the area in the summer. The nearest communities 170° 165° 160° 155° 150° 145° 140° 7 I I I 1 \ BEAUFORT SEA 70° \ CHUKCHI 68° 0 100 200 KILOMETERS 0 100 MILES FIGURE 1.—Index map of northern Alaska, showing location of Drenchwater Creek area, Red Dog Creek area, Howard Pass quadrangle (shaded), and National Petroleum Reserve in Alaska (NPRA). are Kotzebue, Alaska, about 240 km to the southwest, and Umiat, Alaska, about 280 km to the northeast. PREVIOUS WORK This report is part of a mineral-resource assess- ment of the northern foothills of the Brooks Range within the NPRA and also part of the land-use study required by section 105(c) of the National Petroleum Reserves Act of 1976. Other reports include those by Churkin, Huie, Mayfield, and Nokleberg (1978a), Churkin and others (1978b), Mayfield, Tailleur, Mull, and Sable (1978), Theobald and others (1978), and Nokleberg, Plahuta, Lange, and Grybeck (1979a, b). Additional studies of soil geochemistry and of ground magnetic and ground mercury-vapor geophysics have been made by Metz, Robinson, and Lueck (1979) for the U.S. Bureau of Mines. The western part ofthe Howard Pass quadrangle was partly mapped by Tailleur, Kent, and Reiser (1966) at a scale of 1:63,360. Acknowledgments—We are indebted to the earlier mapping and studies of the region by I. L. Tailleur, C. F. Mayfield, and their associates, who gave freely of their time and expertise. Michael Churkin intro- duced us to the Drenchwater Creek area and provided excellent geologic guidance. The semiquantitative analyses were done mainly by P. K. Theobald and H. N. Barton. We appreciate the many discussions with D. K. Blasco, I. M. Lange, Uldis Jansons, Donald Grybeck, E. M. MacKevett, Jr., and J. T. Plahuta. STRATIGRAPHY OF ZINC- AND LEAD-BEARING ROCKS The bedrock of the Drenchwater Creek area com- STRATIGRAPHY OF ZINC- AND LEAD-BEARING ROCKS 3 prises mainly the Kagvikstructural sequence (Chur- kin and others, 1979), a structurally deformed map- pable unit of rock that includes unnamed rocks of Mississippian age; the Siksikpuk Formation (Per- mian); the Shublik Formation (Triassic); and the Okpikruak Formation (Cretaceous). Other bedrock units are Mississippian carbonate rocks of the Lisburne Group and minor diabase dikes (Tailleur and others, 1966; Churkin and others, 1978, 1979). The Mississippian carbonate rocks of the Lisburne Group are in fault contact with the various units of the Kagvik sequence (pl. 1). The Mississippian through Triassic units of the Kagvik sequence, which have a total thickness of about 500 m, consist mainly of chert and shale deposited in a stable deep-water marine environment. The presence of volcanic and volcaniclastic rocks within only the Mississippian unit suggests some submarine volcanism during the Mississippian. The Kagvik sequence, which forms the lowest structural plate of the northwestern Brooks Range (Tailleur and others, 1966), is discon- tinuously exposed in erosional windows at least as far west as the Red Dog Creek area in the De Long Mountains quadrangle, across the Misheguk Moun- tain quadrangle, and in most of the Howard Pass quadrangle (fig. 3). The four main sedimentary units in the Kagvik sequence are of Mississippian, Permian, Triassic, and Cretaceous age (fig. 4) The Mississippian unit consists mainly of dark-gray siliceous shale and radiolarian chert. Radiolarian chert from an area about 1.5 km east of the Drenchwater Creek area has yielded Mississippian radiolarians (B. K. Holdsworth and D. L. Jones, written commun., 1978). About 6.5 km southeast of the Drenchwater Creek area, an ammonite (Ammonellipsitespolaris), found near the headwaters of Twisten Creek in dark shale of the Mississippian unit, indicates a Mississippian age (Gordon, 1957). In the Drenchwater Creek area the Mississippian unit contains keratophyre flows, pyrox- ene andesite sills, tuff, tuffaceous sandstone, and stratiform sulfide deposits. Biotite from the kera- tophyre cropping out about 1,600 m east of Drench- water Creek (pl. 1) has been dated by potassium- argon methods at 319:17 m.y., also middle Missis- sippian. The minimum thickness of the Mississip- pian unit is approximately 150 to 200 m. Conformably overlying the Mississippian unit is the Siksikpuk Formation, composed of 100- to 150-m- thick maroon and green argillite and olive-gray chert that contain radiolarians of Permian age (D. L. Jones, oral commun., 1978). The Siksikpuk Forma- tion lithologically resembles the underlying Missis- sippian unit of the Kagvik sequence but differs in its lighter color, its greater degree of cleavage with a micaceous sheen, and the absence of obvious volcanic units. The Shublik Formation conformably overlies the Siksikpuk Formation and consists of a 100- to 150-m- thick sequence of dark-gray paper-thin shale, medi- um-gray chert, and platy micritic limestone. The limestone is easily identified by ubiquitous coquina of the Triassic pelecypod Monotis. The uppermost unit of the Kagvik sequence is the FIGURE 2.—Oblique aerial views of Drenchwater Creek area, showing prominent iron-stained zones (S) that are loci of zinc— and lead-sulfide deposits. A, View westward across Drenchwater Creek. Light areas of scree mark intense alteration from weathering of pyrite and marcasite in chert, shale, and tuff. Dark areas near left side are dark-gray shale and chert. Drenchwater Creek extends for about 1 km across lower half of photo. B, View northeastward across Drenchwater Creek toward Wager Creek. Light areas of scree mark intense iron staining. Hill (K) is underlain by keratophyre. Dark areas are outcrops of dark-gray shale, chert, tuff, and tuffaceous sandstone. Drenchwater Creek extends diagonally about 1 km across lower left of photo. 4 STRATIFORM ZINC-LEAD DEPOSITS, DRENCHWATER CREEK AREA, ALASKA Cretaceous Okpikruak Formation, which consists of coarse-grained lithic graywacke, mudstone, and minor conglomerate, and contains prominent turbi- dite structures, plant fragments, and the Cretaceous pelecypod Buchia. The minimum thickness of the Okpikruak Formation is approximately 100 m. The Mississippian through Triassic units of the Kagvik sequence probably consist of a deep-water marine assemblage (Churkin and others, 1979). The evidence for a deep-water marine origin includes abundant radiolarians, inferred slow sedimentation rates, little or no elastic component from a conti- nental source, sparse siliceous sponge spicules, rare ichthyosaur bones, and burrows typical of biotur- bated deep-water marine deposits. Neither the Kagvik sequence nor any stratigraphic unit is fully exposed in the Drenchwater Creek area because of complex folding and faulting. The thick- 69° fit that fig:— 1 Auan Hills l 68" — 162° 160° 158° 155° II IIIIIIIIIIIIIIIIIIIIIII'I:I:I.II'I'I‘III'I'I'I'I'I'I'I'I'I'II'"'I"""|'""“"""""" ImmlIiIlI’I‘IlIII'IIIIIIIIIH'IIIIIIHIII‘III oum'eI I . III I II.l.IEI‘I‘II'I'I'I'I'I'I'I'I'I'I'I'I'I'I'I'I‘I'I'I'I’I"I— HIIIIIIIIIIIII'IIIIIHIIIIIIIIIIII IIIII iI'wr''I'I‘I'I'I'I'I'I'I'I'I'I‘I'I'I‘I'I'H''I I‘I HHIHHHHH ,I I ll‘lll IIll IIIIIIIIIIIII . III lllllllllllllll 1 llllllll lll lllllllllll l'klllll HHHHHHH ‘ IIIHIIIIIII,II IIIIIIIIIIIIIIgJIIIIII IIIIIIIIIIIII I I ‘IIII """*" """"”"’ H'HHHHH I I'llllllllllllllll III IIIIQrIIIIIII llll‘l'l[ltl‘lllllllllll'l I I I llxl IIII:I:I:III:I'If\'I'I'I’I'I'I'I'I‘I'I'I'Il'I'I" I'I‘I'I‘I‘ll'l' ll. ‘ I IIIIIIIII{.;.;I;.;.:I;.;II l I I .,w.II'I’His.'fu"I’i'l'l'r'pr'wim‘“;{li's'l'l'l'l'l'll'l ”HUM” I,‘ 1|!!! IIIIII III.IIII:“=IIIIIIlI ,I,I:III|III,I. / ‘A/y' "" m‘I'I'I‘I'I'I‘Ill'I'I'I'I'I'I'"I' I|,I 7' rehte .IIIIIII.IIIIIII . / maze}: b ’, I'l'llil'lll'llllllll II ,/ I /. I I #3 \/ , ,c Noam/r River \ l a cm I l.— 0 10 20 30 40 KlLOMETERS l_.__;T_l_Lr_l 0 20 MILES EXPLANATION Northern terrane | I l l Mainly Cretaceous and younger rocks with low Zn—Pb I resource potential Central terrane Kagvik sequence Areas within Kagvik sequence with iron staining, Zn anomalies, and highest Zn—Pb mineral—resource po- tential Structurally higher thrust plates of mainly carbonate rocks with low Zn-Pb mineral—resource potential, Lisbume Group TV- llA ”i ‘ Q A Structurally higher thrust plates of mafic and ultramafic ~L.A--' rocks Southern terrane Principally regionally metamorphosed sandstone and shale Symbols ° Area of detailed geologic traverse and sampling 4“'~ Thrust fault separating major sequences of sedimen- tary rocks —————— South margin of study area — ' —'— South boundary of NPRA FIGURE 3.-—Southern part of National Petroleum Reserve in Alaska, showing distribution of the Kagvik sequence and areas of high and low zinc-lead mineral-resource potential. Adapted from Churkin, Nokleberg, and Huie (1979, fig. 1). PETROLOGY—MISSISSIPPIAN ROCKS OF THE KAGVIK SEQUENCE 5 ness and lateral extent of units in the Drenchwater Creek vary considerably, and many discontinuous tectonic lenses of different rock types occur. Gray- wacke, siltstone, and mudstone of the Cretaceous Okpikruak Formation are tectonically interleaved with all older units. In other parts of the western Brooks Range, the Okpikruak Formation unconform- ably overlies all older rocks and apparently indicates initial uplift of the ancestral Brooks Range during the Cretaceous (Tailleur, 1969, 1970; Churkin and others, 1979). In the Drenchwater Creek area, sulfide deposits occur in tuff, tuffaceous sandstone, metaquartzite, and dark-gray chert and shale that make up part of the Mississippian rocks of the Kagvik sequence. The APPROXIMATE FOSSILS THICKNESS. iNO METERS I g g Lithicsandstone, mudstone, and shale. < g 3.; Minor conglomerate. Turbidite curv i.|_.l O E a rent structures, Pelecypod Bud-la, 0: Lu .aE plant tragments,and ichthyosaur U U 6 ; bones M. Chen, shale, and limestone. Chen is U x 8 dark to medium gray, weathering (7) :3 light olive gray. Radiolarian ribbon U) .9 N chert interlayered with black shale. < 2 E Limestone is medium gray, thin E (I) .6 bedded, very line grained and gen» '_ LL erally tossiliterous, with pelagic pelecypods Manon: and Halohia. About 100 meters thick I: Olive-gray siliceous shale, mudstone, .9 argilliteiand chertMaroon andgreen .5 argillaceous strata are highly 2 E cleaved, with argillitic sheen on sur- < _ laces. Gray to greenish-gray radiola» _ o rian ribbon chert, knobby and con- 2 ”- taining rosettes ol marcasita: E 43‘ weathers maroon, orange and 250 _ D. Q, shades of green and yellow. Forma- 7“ tion is about 100 to 150 meters thick. a Barite nodules, lenses, and veins in it many places are conspicuous on er- (I) gillaceous talus slopes. Locally, for- mation is stained bright red Dark lacies. Mainly black siliceous shale and radiolarien ribbon chert, Thin beds and laminae oi light-gray turbidites and tuffaceous material in- “ terlayered with shale and chert occur (I) 'E in narrow sections of the formation. :3 3 Locally, intermediate to mafic tuft is 0 associated with intermediate to D: mafic massive porphyritic flows and u_| g breecia. Tuff is cemented by varying E E. amounts of calcite and onenz, and Z a contains chert pebbles that, together 0 .5 with layering, indicate submarine m w origin, Except for sheliy fossil frag- D: 7, ments (mainly crinoids) that make up (<2) .‘2 thin beds of elastic lime- E stone, pelagic fossils are radiola» rians, sponge spicules, and abun- dant trace fossils of Nereitu type. 500 _ Locally, galena, sphalerite, and py- rite occur in veins and lenses. Forma— tion is about 250 meters thick BASE OF SECTION NOT EXPOSED FIGURE 4.—Reconstructed stratigraphic succession, relative distri- bution of rock types and fossils, and approximate thicknesses of units in the Kagvik sequence. Vertical succession within units has been generalized. After Churkin and others (1978b, p. 23, fig. 4). sulfide minerals consist of sphalerite, galena, pyrite, and marcasite; disseminated barite also occurs with the sulfide minerals. The sulfide minerals have been observed in several units of tuff, tuffaceous sand— stone, metaquartzite, dark-gray chert, and dark-gray shale; however, intense folding and faulting, as well as poor exposures, preclude any precise determina- tion of the number of mineralized horizons. The Kagvik sequence structurally underlies nappes of carbonate rocks and calcareous sandstone of the Lisburne Group, here of Mississippian age (Churkin and others, 1979). In turn, these nappes or thrust slices of carbonate rocks are locally overthrust by apparently dismembered ophiolites, including ultra- mafic rocks, gabbro, and pillow basalt (fig. 3). These dismembered ophiolites, of late Paleozoic or early Mesozoic age, occur in the Avan Hills and in the Misheguk and Siniktanneyak Mountains (Patton and others, 1978; Roeder and Mull, 1978). PETROLOGY—MISSISSIPPIAN ROCKS OF THE KAGVIK SEQUENCE We have studied the petrology ofthe Mississippian rocks of the Kagvik sequence in detail because these rocks host the stratiform sulfide deposits not only in the Drenchwater Creek area but also in the Red Dog Creek area (fig. 3) (Plahuta, 1978; Plahuta and others, 1978). Typical petrologic characteristics of the Mississippian rocks of the Kagvik sequence (fig. 5) in the Drenchwater Creek area are listed in table 1, which summarizes the thin-section, chemical, and X-ray diffraction data. Several important relations became apparent during petrologic studies subsequent to the fieldwork: (1) Most of the fine-grained chert and shale contains low to high percentages of volcanic rock fragments, euhedral feldspar laths, and pumice. Many rocks labeled “chert” or “shale” on the geologic map (pl. 1) actually are tuffaceous sand- stone that has been intensely hydrothermally altered and silicified; this alteration causes hand specimens to resemble dark-gray chert or shale. Table 1 lists both the petrologic name (underlined) and the field map (map unit) name and symbol on the geologic map (pl. 1). The field designations “chert” and “shale” are retained on the geologic map because hand specimens were used for rock identification during mapping. (2) The entire suite of Mississippian rocks of the Kagvik sequence in the Drenchwater Creek area have been intensely hydrothermally altered. Almost all volcanic rock and pumice fragments are 6 STRATIFORM ZINC-LEAD DEPOSITS, DRENCHWATER CREEK AREA, ALASKA FIGURE 5.—Photomicrographs in transmitted light of thin sections of Mississippian rocks of the Kagvik sequence. S, sphalerite; G, galena; P, pyrite and marcasite; su, sulfide; Q, quartz; R, radiolarians; K, feldspar altered to kaolinite; pu, pumice lapilli; mv, mafic volcanic rock fragment; C, calcite; B, biotite; F, feldspar phenocryst; cp, clinopyroxene. A, Silicified mudstone. Crossed polarizers. Field of view is 1.0 mm long. B, Sulfide-bearing chert containing abundant sphalerite and recrystallized radiolarians. Plane-polarized light. Field of view is 2.3 mm long. C, Sulfidebearing metaquartzite. Plane-polarized light. Field of View is 1.0 mm long. D, Quartz with hexagonal growth zones in sulfide-bearing metaquartzite. Plain-polarized light. Field of View is 1.0 mm long. E, Kaolinite tuffaceous sandstone. Plane-polarized light. Field of view is 2.3 mm long. F, Calcareous tuffaceous sandstone. Plane-polarized light. Field of view is 2.3 mm long. G, Mafic tuff. Plane-polarized light. Field of view is 1.0 mm long. H, Ketatophyre. Crossed polarizers. Field of view is 2.3 mm long. I, Pyroxene andesite. Crossed polarizers. Field of view is 2.3 mm long. PETROLOGY—MISSISSIPPIAN ROCKS OF THE KAGVIK SEQUENCE 7 ‘ ‘3/ ti“, Jf’fiw . we 2 fl 3;. 6% y! altered to a low-temperature hydrothermal-mineral assemblage consisting of kaolinite, montmoril- lonite, sericite, quartz, chlorite, fluorite, actinolite, carbonate (mostly calcite and minor siderite), and prehnite (table 1). Feldspar is altered principally to kaolinite and lesser amounts of sericite and mont- morillonite. The alteration is observed in rocks interpreted to be submarine volcanic flows and tuff, in tuffaceous sandstone, and in chert and shale derived from a volcaniclastic source. The hydrothermal alteration probably occurred during submarine volcanism and may relate directly to simultaneous stratiform sulfide mineralization. (3) The occurrence of sulfide deposits in rocks petrographically identified as chert, tuff, tuffa- ceous sandstone, and tuffaceous siltstone strongly implies a direct link between submarine volcanism and stratiform sulfide mineralization. The Drench- water Creek area is one of the few well-exposed places in North America where stratiform sulfide deposits can be directly related to a volcanic source. Petrologic study of all samples from the Drench~ water Creek area involved microscopic examination of thin sections in transmitted light, microscopic examination of polished thin sections in reflected light, X-ray diffraction analyses of clay and related hydrothermal minerals, and electron microprobe analyses of silicate and sulfide minerals. All mineral chemical analyses were done by electron microprobe techniques, using an Applied Research Laboratory S.E.M. instrument and a theoretical corrections program developed by the US. National Bureau of Standards, as modified by M. H. Beeson and L. C. Calk. The general operating conditions were 15-kV acceleration potential, 002- to 0.03-uA sample cur- rent, fixed-beam current-integration times of about 10 s, subtraction of background counts, and use of natural or synthetic mineral standards similar in composition to the unknowns. For the sulfide anal— yses presented below, synthetic sulfide standards were provided by G. K. Czamanske. In the highly altered rocks, such as the keratophyre, great care was taken to analyze unaltered remnants ofminerals and to avoid zones of alteration or recrystallization. SILICIFIEI) .\ll'l)ST()NE The silicified mudstone contains relic feldspar microlites replaced by kaolinite in a very fine grained matrix of cryptocrystalline quartz and kaolinite (fig. 5A). The euhedral shape of the relic feldspar micro- lites indicates a nearby volcanic source. “Silicified mudstone” is the petrologic name for rocks desig- nated “dark-gray chert and tuff” in the field. Sl' LFIDE-BEARING (IHERT The sulfide-bearing chert contains disseminated sphalerite, galena, pyrite, and marcasite in a matrix of recrystallized quartz and kaolinite (fig. 5B). Kaolin— ite has replaced euhedral feldspar phenocrysts, and 8 STRATIFORM ZINC-LEAD DEPOSITS, DRENCHWATER CREEK AREA, ALASKA TABLE 1.—-Petrologic characteristics of the Mississippian rocks in the Kaguik sequence, Drenchwater Creek area, northwestern Brooks Range, Alaska [Original stratigraphic position unknown] Petrologic name (italic), map unit, map symbol Percentage of major and minor minerals Textures and structures Alterations, replacements or recrystallization Silicified mudstone Black chert, Mc Finegrained tuff, Mft Sulfide-bearing chert Black chert, Mc Black shale, Ms Sulfide-bearing meta- quartzite Black chert, Mc Silicified kaolinite tuffaceous sandstone, locally sulfide bearing Black chert, Mc Black shale, Ms Medium-grained tuff, Mmt Calcareous tuffaceous sandstone-sandy tuff Medium-grained tuff, Mmt Coarse-grained tuff, Mct Keratophyre, Mke Kaolinite lapilli tuff or tuffaceous siltstone, locally sulfide bearing Finegrained tuff, Mft Medium-grained tuff, Mmt Calcareous lapilli tuff Fine-grained tuff, Mft Medium-grained tuff, Mmt Vitric crystalline mafic tuff Mafic tuff, Mma Limestone Crinoidal limestone, Mls Cryptocrystalline quartz .............................. 60—100 Detrital quart . ........... 0—10 Kaolinite .............. 0—16 Opaque minerals 0-10 Chlorite, sericite .................. <1—4 Quartz .................................. 40—45 Sphalerite .. 25—45 Galena ........ 10—25 Kaolinite 0—10 Sericite .................................... 0—<1 Quartz .................................. 50—90 Sphalerite _ "“5-35 Galena ........................ Kaolinite .............................. 50-55 Quartz ..................... ....5—40 Volcanic fragments .0—10 Galena and Sphalerite ........ 0—30 Ankerite? ................................ O- 10 Chlorite, sericite, montmorillonite .................... <1 Calcite, siderite .................. 20—50 Quartz .............. Kaolinite .......... Opaque minerals .................. <1—1 Sericite,montmorillonite O—<1 Fluorite <1 Kaolinite .............................. 40-75 Quartz _____________ 15—40 Opaque minera s .................. 0—10 Montmorillonite, actinolite, sericite .............................. < 1— 1 0 Fluorite, barite < 1 —3 Galena .................................... 0— 1 0 Carbonate ............................ 30—55 Quartz ........................ ._.10—15 Kaolinite ................... 10-50 Opaque minerals ............... 4—20 Montmorillonite, scrim e ........ <1 Sphalerite ........................ . 0—1 Chlorite ........... . 0—5 Fluorite, barite(?) ...................... <1 Carbonate .................................. 50 Kaolinite, sericite, montmorillonite ____________________ 35 Chlorite ............................ __ 10 Quartz .............................. .. 5 Sericite, prehnite. Carbonate .................... Quartz ............... .. 3 Kaolinite ...................................... 2 Very fine grained. Detrital biotite and quartz in slightly recrystallized matrix of cryp- tocrystalline quartz and kao- linite. Relic plagioclase microlites. Very fine grained. Angular quartz, mostly recrystallized. Disseminated sulfide grains. Radiolarians replaced by quartz. Sparse tiny fluid inclusions. Medium-grained mosaic of hexagonal quartz containing interstitial sulfides. Sparse inclusions of sulfides. Galena inclusions outline growth stages of hexagonal quartz. Abundant fluid inclusions. Wavy beds or hands of sulfides. Medium-grained fragments. Very fine grained replace- ments. Relic volcaniclastic texture, pumice lapilli, and vesicles. Medium grained. Relic volcanic lapilli and detrital carbonate grains. Relic radiolarians. Relic plagioclase laths. Relic mafic minerals. Very fine to fine grained. Relic volcanic lapilli re- placed by kaolinite. Locally highly schistose. Strong pre— ferred orientation of crystals. Sparse tiny fluid inclusions. Relic mafic volcanic lapilli. Sparse relic shards. Medium grained. Relic vesicu- lar volcanic lapilli, replaced by kaolinite and quartz, in a carbonate matrix. Sparse fragments of angular detrital quartz. Medium grained. Relic vesicu- lar mafic lapilli. Relic feldspar clots. Fine to medium grained. Inter- locking mosaic of calcite containing sparse interstitial kaolinite and sparse angular detrital quartz. Matrix locally recrystallized to polycrystalline quartz. One sample completely recrystallized to metaquartzite. Sparse new growth of chlorite and sericite. Thin quartz veins. Sparse thin quartz veins contain sulfides. Sparse thin quartz veins contain sulfides. Many medium-grained angular fragments of quartz, vesicles, and feldspar, replaced by very fine grained quartz and kao- linite. Sparse new growth of seri- cite and chlorite. Thin quartz veins contain sulfides. Strong schistosity and preferred orienta- tion of minerals. Plagioclase laths replaced by kao- linite, montmorillonite, or carbonate. Radiolarians replaced by quartz. Volcanic lapilli replaced by kaolinite and quartz. Mafic minerals replaced by clay, opaque minerals, and kaolinite. New growth of sericite. Plagioclase laths replaced by kaolinite. Mafic volcanic lapilli replaced by montmorillonite, sericite, kaolinite, and actinolite. New growth of sericite. Volcanic lapilli and feldspar re- placed by kaolinite and quartz. Some lapilli and feldspar re placed by carbonate. New growth of mica. Mafic lapilli replaced by chlorite, carbonate, montmorillonite. Feldspar replaced by kaolinite and quartz, and vesicles mostly by chlorite, some by quartz and carbonate. New growth of mica. PETROLOGY—MISSISSIPPIAN ROCKS OF THE KAGVIK SEQUENCE 9 TABLE 1.—Petrologic characteristics of the Mississippian rocks in the Kagvik sequence, Drenchwater Creek area, northwestern Brooks ' Range, Alaska—Continued Percentage of major and Petrologic name (italic), _ minor minerals map unit, map symbol Alterations, re lacements Textures and structures or recrystal ization Keratophyre Albite, anorthoclase .......... 50—65 Keratophyre, Mke Sanidine .................. 20—25 Fine-grained tuff, Mft Hornblende .................................. 5 Sericite, montmorillonite, kaolinite, carbonate, chlon'te ................................ 5—10 Opaque minerals 500 >500 200 150 150 n.d. 1 ,000 500 50 200 200 30 700 >20,000 15,000 >20,000 1,000 70 n.d. 500 100 300 100 n.d. >10,000 >10,000 1,500 >10,000 >10,000 1,000 SULFIDE DEPOSITS 46 *— Z LLI Q 55 47 — n. S 2 ..° 3 E 3 o O o' l- < 43 _ - Z O '5 Pure (Zn,Fe)S m '2 49 o — O U c N :‘ 50 I 1 | O 1 2 3 4 A Fe CONTENT, IN ATOMIC PERCENT 0.40 \ \ +_ Pure (Zn,Cd)S \ E Slope of line \ o . for pure (Fe,Cd)S\\ 5 0.30 — , \ '3- \ 2 . o \\ 2 ° \ .9 ° .- \ . O < 0.20— ‘ . l .2. o .o l '_~ 0 . . \\ Z . \ uJ . E o .:.' . l\ O 0.10 . . I . \ U \ 'o l U \ i 0 | l L 0 1 2 3 4 |_ 8 Fe CONTENT, IN ATOMIC PERCENT E 2.5 o 9: Lu 0- 2.0 — ‘ 2 E O 1.5 — [— <2: E 1.0 — ,_‘ Z P: 0.5 — Z O . U o a 47 48 49 50 51 C Pb CONTENT, IN ATOMIC PERCENT 17 ppm in soil samples, and from 2,000 to more than 5,000 ppm in stream-sediment samples (pl. 2). The high values in rock and soil samples can be related to (1) nodules of barite sparsely distributed in the Siksikpuk or Shublik Formation, or (2) disseminated barite in the Mississippian rocks of the Kagvik sequence. The high values in stream-sediment samples represent placer concentrations of barite weathering from these sources. The highest values for barium, zinc, lead, silver, arsenic, cadmium, copper, and antimony are in just seven of the rock samples from the Drenchwater Creek area (table 2), and the highest values for all these elements but barium and zinc are in just two of the samples (77AMD116 and 77ANK013G), which contained abundant sphalerite and galena. Electron microprobe analyses (table 3) show that the sphaler- ite contains abundant zinc and iron and minor amounts of cadmium and manganese. The galena contains abundant lead and minor amounts of silver, arsenic, and antimony (table 4). Neither sphalerite nor galena contains any detectable copper, and no copper-bearing sulfide has yet been identified in the study area. Local malachite staining in areas of sphalerite and galena deposits may represent either weathering of very sparse copper sulfide or, less likely, primary copper carbonate minerals deposited during hydrothermal alteration. SULFIDE MINERALS The compositional variations in the major-element contents of sphalerite and galena are plotted in figure 13. In sphalerite, the antipathetic variation of zinc with iron content indicates the well—known substitu— tion of zinc for iron. Sphalerite composition ranges from essentially pure ZnS to about 2.5 atomic percent Fe and about 47.5 atomic percent Zn. Sphalerite analyses plot at small distances from the line for pure (Zn,Fe)S (fig. 13A); the distance between any given data point and the line for pure (Zn,Fe)S represents either minor-element content (principally Cd) or error in the analysis. A few large crystals show zoning, from relatively zinc rich and iron poor cores to rims richer in iron and poorer in zinc. Cadmium content varies somewhat antipatheti- cally with iron content (fig. 133), but the variation is not systematic. Systematic substitution of cadmium for zinc or iron would produce compositional trends parallel to the lines for (Zn,Cd)S or (Fe,Cd)S. A FIGURE 13.—Sphalerite and galena compositions based on electron microprobe analyses by W. J. Nokleberg. Lines with triangles show compositional changes from core to rim of large zoned crystals. A, Variation of Zn content with Fe content in sphalerite. B, Variation of Cd content with Fe content in sphalerite. C, Variation of Sb content with Pb content in galena. Sphalerite analyses from table 3, galena analyses from table 4. 18 limited trend is evident in a few analyses, parallel to the line for (Zn,Cd)S; most analyses, however, fall randomly in the field of the diagram. In galena, antimony varies antipathetically with lead content (fig. 13C). Most analyses cluster in the area near 50 atomic percent Pb and 0 atomic percent Sb, although a few analyses trend parallel to the line for (Pb,Sb)S. The maximum antimony content is just more than 2.0 atomic percent. The distance between any particular data point and the line for (Pb,Sb)S (fig. 130) most likely represents experimental error in determining small amounts of antimony in galena. Besides the minor amounts of antimony in galena, trace amounts of arsenic and silver were also found, in a range of a few tens of parts per million for each element. X-ray compositional scans on the electron microprobe show microscopic inclusions, as large as a few tens of micrometers in diameter, of an unidenti- fied sulfosalt containing abundant antimony and lesser arsenic and silver. Electron microprobe analyses of pyrite and marcasite show only iron and sulfur with no major impurities. LEAD ISO'I‘OPE ANALYSES ()F GALENA Lead isotope analyses of galena (table 5) indicate model lead ages of approximately 200 my, according STRATIFORM ZINC-LEAD DEPOSITS, DRENCHWATER CREEK AREA, ALASKA to the model of Stacey and Kramers (1975). The analyses also indicate that the lead was derived from a large volume of average-orogene material which may have included a considerable component of continental material (B. R. Doe, written commun., 1979). Derivation of the lead from an average orogene indicates either an island-arc or an Andean-type arc environment, rather than a sea-floor-rifting environ- ment, for the formation of the stratiform zinc-lead deposits in the Drenchwater Creek area. ORIGIN AND MODIFICATION Sl'BMARINE VOLCANOGEN[(I/HYDRO'I‘HERMAL ORIGIN Several lines of field and petrologic evidence indi- cate a submarine volcanic origin for the volcanic and volcaniclastic rocks, for a significant part of the dark- gray chert and shale, and for the stratiform zinc-lead deposits in the Mississippian rocks of the Kagvik sequence in the Drenchwater Creek area: (1) The keratophyre flows grade laterally into bedded tuff, tuffaceous sandstone, and tuffaceous siltstone that are interbedded with dark-gray chert and shale containing some volcaniclastic debris as well as radiolarians. (2) The tuff, tuffaceous sandstone and siltstone, TABLE 3.—Electron microprobe analyses and structural formulas of sphalerite from the Drenchwater Creek area, northwestern Brooks Range, Alaska (Analyst: Warren J. Nokleberg] Sample ............ lle 13E Grain No. ________ l-Core l-Rim 2—Core 2-Rim 3 4 la 1b 2 Ba 3b Major elements (weight percent) 32.934 33.039 33.055 32.971 33.098 33.157 32.893 32.907 32.731 33.067 33.179 .026 .043 .045 .026 .033 .032 .225 .217 .217 .101 .228 .67 1.439 .329 1.232 1.609 .865 2.238 2.262 2.543 2.702 2.256 66.156 65.494 65.491 65.504 65.039 65.528 63.914 64.140 64.022 64.070 64.043 .433 .316 .392 .367 .276 .724 .552 .783 .611 .200 .487 100.227 100.332 99.762 100.099 100.054 100.305 99.823 100.309 100.124 100.139 100.193 Structural formulas 49.970 49.983 50.295 50.014 50.136 50.226 49.980 49.850 49.675 49.983 50.153 .023 .038 .040 .023 .029 .028 .199 .192 .193 .089 .201 .591 1.250 .287 1.073 1.399 .752 1.952 1.967 2.215 2.344 1.957 49.229 48.593 49.208 48.732 48.317 48.681 47.629 47.653 47.653 47.497 47.478 .187 .137 .170 .159 .119 .313 .239 .338 .264 .086 .210 Sample ____________ 13F 13HB 13HC Grain No. ________ 1A 18 2 3 4 2a 2b 3 5 6 1 2 Major elements (weight percent) 32.908 33.022 33.050 32.991 33.119 32.998 32.980 33.028 33.075 33.020 33.191 33.028 .055 .032 .061 .039 .046 .052 .045 .029 .038 .035 .228 .238 1.559 1.474 .000 1.376 1.185 .074 .108 2.091 1,607 1.638 2.417 2.219 64.210 64.945 66.941 64.676 65.186 66.676 66.653 63.957 64.400 64.363 64.071 63.932 .314 .238 .219 .267 .226 .258 .252 .232 .391 .332 .525 .585 99.047 99.711 100.271 99.348 99.763 100.058 100.038 99.337 99.511 99.388 100.431 100.002 Structural formulas 50.306 50.181 50.093 50.291 50.286 50.114 50.099 50.288 50.330 50.303 50.074 50,071 .049 .029 .054 .035 .041 .046 .040 .026 .034 .031 .200 .211 1.368 1.286 .000 1.204 1.033 .064 .094 1.828 1.404 1.433 2.093 1.932 48.140 48.402 49.759 48.354 48.542 49.663 49.657 47.758 48.062 48.089 47.406 47.534 .137 .103 .095 .116 .098 .112 .109 .101 .170 .144 .226 .253 TABLE 4.——Electron microprobe analyses and structural formulas ofgalena from the Drenchwater Creek area, northwestern Brooks Range, Alaska [Analyst Warren J. Nokleberg] 13HC 13HB 13HA 13F 13E Sample .. 1!) 1b 1a Grain N0. Major elements (weight percent) m m ~ w wNmm NNN©§ TQfiW. m w H w 99.791 99.663 100.425 99.752 99.842 99.933 100.008 99.550 100.273 99.695 99.510 99.716 100.119 99.597 99.668 100.493 Structural formulas G5 a) V ‘1‘ $3520 aoqma O5 05 VI‘ ‘7‘ SULFIDE DEPOSITS 19 dark-gray chert, and dark-gray shale are perva- sively hydrothermally altered in areas adjacent to keratophyre flows, andesite sills, and mafic tuff. (3) Sphalerite, galena, pyrite, and marcasite are disseminated in chert that contains euhedral feld- spar replaced by kaolinite. Textural relations indi- cate that this replacement was penecontempora- neous with deposition. (4) In the metaquartzite, tiny inclusions of galena outline growth zones in hexagonal quartz that recrystallized from chert during hydrothermal alteration. (5) The sulfide minerals, volcanic rocks, tuff, tuffaceous sandstone and siltstone, and hydro- thermal-alteration minerals are intimately asso- ciated along a relatively narrow stratigraphic horizon in the Drenchwater thrust plate (pl. 1). (6) Fluid-inclusion data indicate that the mineral- izing fluids were around 100°C, that is, near boiling—a temperature compatible with submarine volcanism and mineralization. (7) Sphalerite, galena, pyrite, and marcasite occur only in tuff, tuffaceous sandstone, meta- quartzite, or dark-gray chert and shale adjacent to tuff or tuffaceous sandstone. (ili()l.()(;l(l(1().\' l’R()l.S Several major geologic controls on sulfide mineral- ization exist in the Drenchwater Creek area. First, sulfide deposition was stratiform and volcanogenic; that is, deposits were formed simultaneously with or just after sedimentation and volcanism. Second, volcanic exhalations (including magma) and hydro- thermal fluids mixing with and heating seawater were the source of the mineralizing fluids. Third, hydrothermal fluids altered the volcanic rocks, v01- caniclastic rocks, and dark-gray chert and shale in the Mississippian rocks of the Kagvik sequence to such hydrothermal minerals as kaolinite, montmoril- lonite, sericite, chlorite, actinolite, calcite, siderite, fluorite, barite, prehnite, and quartz. And fourth, intense deformation, including isoclinal folding, faulting, and dismembering of formations, has severely disrupted the former stratiform deposits. The Drenchwater Creek sulfide deposits were prob- TABLE 5.—Lead isotope ratios for galena from the Drenchwater Creek area, northwestern Brooks Range, Alaska [Analysts: Bruce R. Doe and Maryse Delevaus] Sample leth/ledpb 207Pb/ZfHPh ZUHPb/llNPb 77ANK—13H Drenchwater (lat 68°34.3’ N., long 185°41.3’ W.) 18.428 15.609 38.351 20 STRATIFORM ZINC-LEAD DEPOSITS, DRENCHWATER CREEK AREA, ALASKA ably much more extensive before that period of intense deformation. Similar tectonic lenses of sulfide deposits may be present in the subsurface along strike to the east and west of the Drenchwater Creek area. MODEL The submarine volcanic origin of the stratiform sulfide deposits is illustrated in a cartoon model (fig. 14A) that depicts penecontemporaneous sea—floor vol- canism, hydrothermal activity, and sulfide deposi- tion. Gilmour (1971), Hutchinson (1973), Sillitoe (1973a), and Solomon (1976) demonstrated that copper-zinc volcanogenic deposits are generally associated with ophiolite complexes and newly formed oceanic crust in rifting environments. On the other hand, zinc-lead (and minor copper) volcanogenic deposits commonly occur in or are associated with more felsic calc- S _ N DEEP OCEAN GLOBA L MOVING AND . OLLISION -| ARCTIC MOVIN G D O Chert Lead and sulfur Volcanic ash Volcanic flows Zinc and sulfur deposits % Thrust fault FIGURE 14.—Model for origin and deformation of stratiform sulfide deposits in Drenchwater Creek area. A, Formation of stratiform zinc-lead deposits in association with island-arc or Andean‘type arc volcanism. B, Intense thrust faulting, folding, and formation of tectonic breccia and melange in rocks hosting sulfide deposits. alkaline submarine deposits in island-arc or Andean- type are environments; the Kuroko deposits in north- eastern Japan are one prominent example (Hayakawa and others, 1974; Sato, 1974; Sato and others, 1974). Because the igneous rocks of the Drenchwater Creek area are keratophyre and pyroxene andesite, the source of the magma in that area was most likely incipient submarine Andean-type arc volcanism or, less likely, incipient island-arc volcanism rather than sea-floor rifting, which would yield basalt and pos- sibly form ophiolite complexes. During the period of Cretaceous deformation, the Kagvik sequence, including the stratiform sulfide deposits and associated rocks in the Drenchwater Creek area, was intensely deformed by thrusting, isoclinal folding, and small-scale shearing. This defor- mation extensively dismembered the stratiform sul- fide deposits, as illustrated in figure 148; the two moving trucks represent the convergent forces that caused the deformation. Churkin, Nokleberg, and Huie (1979) related the intense deformation of the Kagvik sequence during the Late Cretaceous to tele- scoping of a Mississippian continental margin, caused in part by rifting and opening of the Canada basin and in part by accretion of the schist belt in the southern Brooks Range to the Kagvik sequence. REGIONAL MINERAL POTENTIAL AND EXPLORATION GUIDELINES Significant potential for stratiform zinc-lead de- posits exists in the northwestern Brooks Range. Recent studies by Plahuta (1978), Plahuta, Lange, and J ansons (1978), and Nokleberg, Plahuta, Lange, and Grybeck (1979a, b) of the Red Dog Creek area, about 120 km west of the Drenchwater Creek area, showed that stratiform zinc-lead deposits similar to those in the Drenchwater Creek area also occur in the Mississippian rocks of the Kagvik sequence. In addi- tion, Churkin and others (1978b) showed that (1) the Kagvik sequence can be traced along a continuous east-west-trending belt in the northern Brooks Range, and (2) the Mississippian rocks of the Kagvik sequence are quite favorable for zinc-lead deposits. These relations are evident on the map of the south- ern part of the NPRA (fig. 3), which shows: (1) the extent of the Kagvik sequence, (2) the areas of prom- inent iron staining in the Kagvik sequence, and (3) the areas of significant zinc geochemical anomalies in stream sediments. Coinciding areas of iron stain- ing and zinc geochemical anomalies in the Kagvik sequence were considered by Churkin and others (1978b) as having the greatest potential for stratiform zinc—lead deposits; these areas include Spike, Kagvik, REFERENCES CITED 21 Elbow, Chertchip, Sorepaw, Drenchwater, and Safari Creeks. In addition, we propose several guidelines to further exploration for stratiform zinc-lead deposits in the northwestern Brooks Range. First, because of the stratiform nature of deposition at Red Dog Creek, Tailleur (1970) suggested that all areas of iron staining along the north front of the Brooks Range should be examined for potential economic value. We further suggest that areas underlain by the assem- blage of dark-gray chert, dark-gray shale, and tuff in the Mississippian unit of the Kagvik sequence should be examined in detail, particularly in the areas of significant zinc geochemical anomalies in stream sediments. Second, the dark-gray chert and dark- gray shale should be petrographically examined to determine areas that have been substantially hydro- thermally altered and that contain abundant, though perhaps highly altered, volcanic fragments; such areas should have a greater potential for sulfide deposits formed in conjunction with hydrothermal exhalations and submarine volcanism. Third, iron staining should not be used as the sole prospecting guide because sphalerite and galena, without acces- sory pyrite and marcasite, weather to shades of dark gray to black; consequently, every dark-gray chert and dark-gray shale should be examined directly, or indirectly by means of geochemical analyses. And fourth, because of the intensity of deformation in the Drenchwater Creek area, future exploration should concentrate on detailed geologic mapping and geo- physical or geochemical methods for locating lenses of the original deposits. REFERENCES CITED Brock, J. S., 1976, Recent developments in the Selwyn-Mackenzie zinc-lead province, Yukon and Northwest Territories: Western Miner, v. 49, no. 3, p. 9—16. Churkin, Michael, Jr., Huie, Carl, Mayfield, C. F., and Nokleberg, W. J., 1978a, Geologic investigations of metallic mineral resources of southern NPRA, in Johnson, K. 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Gordon, Mackenzie, Jr., 1957, Mississippian cephalopods of northern and eastern Alaska: U.S. Geological Survey Profes‘ sional Paper 293, 61 p. Hayakawa, Norihasa, Shimada, Ikuro, Shibata, Toyokichi, and Suzuki, Shunichi, 1974, Geology of the Aizu metalliferous district, northeast Japan, in Ishihara, Shunso, ed., Geology of Kuroko deposits: Tokyo, Society of Mining Geologists of Japan, Mining Geology Special Issue 6, p. 19—28. Hutchinson, R. W., 1973, Volcanogenic sulfide deposits and their metallogenic significance: Economic Geology, v. 68, no. 8, p. 1223—1246. Lambert, I. B., 1976, The McArthur zinc-lead-silver deposit: Fea- tures, metallogenesis and comparisons with some other strati- form ores, chap. 12 of Wolf, K. H., ed., Handbook of strata- bound and stratiform ore deposits. 11. Regional studies and specific deposits: Amsterdam, Elsevier, v. 6, p. 535—585. Mayfield, C. F., Tailleur, I. L., Mull, C. G., and Sable, E. 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Theobald, P. K., Barton, H. N., Billings, T. M., Frisken, J. G., Turner, R. L., and VanTrump, George, Jr., 1978, Geochemical distribution of element in steam sediment and heavy-mineral concentrate samples in the southern half of the National Petroleum Reserve, Alaska: US. Geological Survey Open-File Report 78—517, scale 1:500,000. Urabe, Tetsuro, and Sato, Takeo, 1978, Kuroko deposits of the Kosaka mine, northeast Honshu, Japan—products of sub- marine hot springs on Miocene sea floor: Economic Geology, v. 73, no. 2, p. 161—179. Weiss, L. E., 1959, Geometry of superposed folding: Geological Society of America Bulletin, v. 70, no. 1, p. 91—106. Williams, Neil, 1978a, Studies of the base metal sulfide deposits at McArthur River, Northern Territory, Australia: I. The Cooley and Ridge deposits: Economic Geology, v. 73, no. 6, p. 1005—1035. 1978b, Studies of the base metal sulfide deposits at Mc- Arthur River, Northern Territory, Australia: II. The sulfide-S and organic-C relationships of the concordant deposits and their significance: Economic Geology, v. 73, no. 6, p. 1036—1056. GPO 587-041/43 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 1 58°45’ 68°35 "'V'"'V" 'V--- # .V/<:;\_\\rfl/< (, A// \/ \(,// Drenchwatel' 7 v--v._ "T“T"T"‘v--T.. "'V"V"'V"" Drainage features plotted from US. Geological Survey aerial photographs, series BAR—348, 1949 Geology by W. J. Nokleberg, G. R. Winkler, C. Huie, |. Ellersieck, M. Churkin, and APPROXIMATE SCALE HQ 800 . C. Mayfield, 1977 1/2 U 1 MILE TRUE NORTH APPROerAl E MEAN DECANATlON,198? KILOMETER '2 9 Ln 0 .0 ; w -g=s.,.pd 4.24 AREA OF MAP PROFESSIONAL PAPER 1209 PLATE I CORRELATION OF MAP UNITS Os Unconformity Intrusive contact i i i-. l l Unconformity or fault — QUATERNARY CRETACEOUS f?) l CRETACEOUS l TRIASSIC PERMIAN l Kagvik equence _ T - Unconformity or fault Two Cubs All thrust plates Drenchwater thrust plate thrust plate Lisbume Egg _ ‘ Group ‘[ ]' MISSISSIPPIAN DESCRIPTION OF MAP UNITS OS SURFICIAL DEPOSITS (Quaternary)—Undifferentiated alluvium, - Medium—grained pyroxene andesite and fine—grained andesitic tuff—Occurs colluvium, glacial deposits, talus, and gravel - DIABASE (Cretaceous?)——Mafic sills and dikes forming bold outcrops and prominent rubble piles. Most outcrops are several meters to several tens of meters thick. Weathers dark brown, with dark—gray to black fresh surfaces. Major minerals: olivine, plagioclase, and pyroxene; average grain size, 0.5 to 1 mm. Diabasic texture. In places, unit grades into fine— »grained olivine gabbro. Occurs only in Gas Drum and Spike Camp thrust plates KAGVIK SEQUENCE - OKPIKRUAK FORMATION (Cretaceous)—Lithic sandstone, siltstone, and mudstone. Occurs as strongly deformed and partly fault bounded units several tens to several hundreds of meters thick. Sandstone and siltstone weather dark brown, mudstone weathers dark gray to black. Major clasts in the sandstone are plagioclase, dark chert, quartz, and unidentified lithic fragments. Coarse—ribbed Buchia and plant fragments occur along partings. Abundant cleavage; lenses formed from disrupted isoclinal folds. A unit of sheared mudstone occurs between the Spike Camp and Gas Drum thrust plates Occurs only in the Mother Bear, Spike Camp, and Gas Drum thrust plates SHUBLIK FORMATION (Triassic)——Pred0minantly medium—bedded chert, with lesser amounts of black paper shale and thin limestone. Chert weathers gray and yellow, with distinctive mottled green surfaces. Fresh surfaces are medium gray. Contains abundant Monotis on limestone partings. Commonly thinner than 50 m. Intricately folded and faulted. Occurs only in the Mother Bear, Spike Camp, and Gas Drum thrust plates SIKSIKPUK FORMATION (Permian)—Total thickness approximately 70 m (Tailleur and others, 1966). Red and green siliceous shale—Strongly cleaved and locally intensely folded and faulted Yellow, green, and gray Chert—Medium bedded, with dark-gray fresh surfaces. Contains scattered radiolarians and sparse barite concretions SHUBLIK AND SIKSIKPUK FORMATIONS, UNDIVIDED (Triassic and Permian)—Undifferentiated chert CHERT, SHALE, TUFF, KERATOPHYRE, AND MINOR LIMESTONE (Mississippian)—-Was designated “dark facies of Lisburne Group,” by Tailleur, Kent, and Reiser (1966). Specific units restricted to certain thrust plates. See correlation of map units. Original stratigraphic position of following units unknown Black medium—bedded chert—~Approximately 100 m thick (Tailleur and others, 1966). Locally forms extensive outcrops, with many folds and faults. Partially recrystallized to fine—grained quartzite along Drenchwater Creek. Weathers dark gray locally. Locally contains galena, sphalerite,and pyrite Black shalewApproximately 100 m thick (Tailleur and others, 1966). Intensely faulted and sheared. Locally contains galena, sphalen'te, and barite in veins and concretions F ine~grained felsic tuff—Maximum thickness. 80 m. Weathers bright rust, with light-gray fresh surfaces. Contains sparse microphenocrysts of biotite and feldspar, angular fragments of black chert, and disseminated pyrite Medium—grained felsic tuff—~As much as 250 m thick. Weathers light brown, with light—gray fresh surfaces. Locally grades into calcareous sandstone. Contains abundant medium—grained feldspar phenocrysts in a fine—grained matrix, and sparse fine-grained biotite phenocrysts Coarse—grained felsic tuff-As much as 200 m thick. Weathers medium gray, with green—gray fresh surfaces. Contains abundant coarse~grained feldspar phenocrysts in a fine—grained matrix, sparse biotite phenocrysts, and minor amounts of calcite cement , ’ . l Mke Keratophyre—As much as 80 m thick. Medium grayContains coarse-grained feldspar and fine-grained biotite phenocrysts in a fine—grained matrix. Occurs as sills or flows adjacent to felsic tuff. Radiometric age of 319 my. by K—Ar method on biotite (Tailleur and others, 1966) Mafic tuff—Mottled dark—green to light»gray tuff Crinoidal and coralline limestone—Light— to medium—gray, as thick as 35 m. Grades downward into fine—grained felsic tuff only in Two Cubs thrust plate. Pyroxene andesite weathers dark brown, with black fresh surfaces. Andesitic tuff weathers medium brown, with pale—olive—gray fresh surfaces. Mainly massive calcareous crystallithic tuff, with sparse pyroxene and plagioclase phenocrysts. Locally, unit consists of alternating sills, flows, and tuff. Radiometric age of 330 my. by K—Ar method on biotite _ Undifferentiated black shale of the Okpikruak, Shublik, and Siksikpuk Formations and the Mississippian unit LISBURNE GROUP KOGRUK FORMATION (Upper and Lower Mississippian)—Light— to medium—gray crinoidal limestone and calcareous shale. Several tens of meters thick; thick bedded (Tailleur and others, 1966). Occurs only in the Two Cubs thrust plate _ UTUKOK FORMATION (Lower Mississippian)—Purplish-gray thin—bedded limestone, dolomite, and sparse calcareous siltstone. Several tens of meters thick. Sparse fossils including proetid trilobite, fenestrate bryozoan, brachiopod Leptagonr‘a analoga, brachiopod comparable to Brachythyris suborbicularis, schuchertellid brachiopod, and zaphrentoid coral. Occurs only in the Two Cubs thrust plate Contact— Approximately located; dotted where concealed Fault—Dashed where approximately located; dotted where concealed —‘—‘—‘— Thrust fault—Dasled where approximately located; dotted where concealed. Sawtceth on upper plate —fl—> Overturned anticline——Showing trace of axial surface, direction of dip of limbs, and plunge. Dashei where approximately located; dotted where concealed —fl-—> Overturned syncline—Showing trace of axial surface, direction of Clip of limbs, and plunge. Dashei where approximately located; dotted where concealed Strike and dip of bes ii inclined —l— Vertical Strike and dip of clavage fir Inclined I—l Vertical Sulfide and sulfate inineral localities 0 P b Galena OZn Sphalerite 0 Ba Barite x x x x Iron stain from wezthered sulfide minerals Fossil localities 0 M Monotis 0 B Buchia 0 F Corals, brachiopods, trilobites, and bryozoans 099 Center of aerial photograph with BAR—346 series number TH R UST PLATES 1— Mother Bear 2— Two Cubs Mc Q 05 Mke Mct Os Mmt " ‘ I 3—Drenchwater 4—Spike Camp 5—Gas Drum 05/ INTERIORiGEOLUGlCAL SURVEY, RESTUN, VA 719827680416 STRATIFORM ZINC-LEAD DEPOSITS IN THE DRENCHWATER CREEK AREA, HOWARD PASS QUADRANGLE, NORTHWESTERN BROOKS RANGE, ALASKA UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 1209 PLATE 2 GEOLOGICAL SURVEY CORRELATION OF MAP UNITS — K0 - CRETACEOUS L Unconformity or fault NK14d/L‘, , _ L “We '55 — TRIASSIC Kagvik _ RPSS P55 Sequence ~ PERMIAN Psc NK14hL L/MPL 14f Unconformity or fault Mc Ms Mft Mmt Mct Mke Mls Mlu — MISSISSIPPIAN ‘ NK14c ~ ~ L \WK117 /'1 « §WK116 .NK4a /NK4b.4d L .yL ‘ K113 r ; K1121, a , iNKIxILK1-3d—g Nst , WK146a\Y.[’WKfi1£I6b WK108 MD L/ er/ /NK5b . , _ - “\f EWK11°88 hNKL13b ‘\ M0116 '\NK4g_ _ p _ ” WK109 NK13c . , _ DESCRIPTION OF MAP UNITS M- A, * NK13I] ’\N-K\~LLNK13I . '_/LNK5e L L \WK107 NK513k/‘L .‘/NK14b MD117’ Ko OKPIKRUAK FORMATION (Cretaceous)—Lithic sandstone and siltstone Mft Fine—grained felsic tuff , 'MD113 Es SHUBLIK FORMATION (Triassic)—Chert, shale, and limestone Mmt Medium—grained felsic tuft ‘ o/Wmo SIKSIKPUK FORMATION (Permian) Mct Coarse —grained felsic tuft 'WK126 Pss Shale Mke Medium—gray keratophyre Psc Chert Mls Gray limestone MD63C EPss SHUBLIK AND SIKSIKPUK FORMATIONS (Triassic and Permian)—— Mlu UTUKOK FORMATION M0633, L ‘ Undifferentiated chert ,Md'*L LL/'L L “'*_. ._ 1 CHERT, SHALE, TUFF, KERATOPHYRE, AND LIMESTONE (Missis- Contact—Dashed where approximately located 63D L sippian)—Original stratigraphic position of following units unknown . ”(0163362 WK1LL28c\; . M BI k h t Fault—Dashed where apprOXImately located WK128b/’ TEL/fig?“ c ac C er 4—‘—‘—‘- Thrust fault—Dashed where approximately located a . Ms Black shale X x X X x x Iron stain from weathered sulfide minerals ”WK148 I 2 KILOMEIERS | I I MILE Location and sample numbers of 62 rock, soil, and stream-sediment samples from the Drenchwater Creek area. I ,1. 11] 155:. {15' I I / r’ L1IV‘15V1‘II , L_ , --LL_f_*\M' ‘ 11, .. L‘5,000 7y2,000;1 5 1 MIT \\ A , e 1 1“,, 11 ,2 -\,LLL‘LL” >L10,ooo;mq L ‘4/ £004)» 0 700 N 3 1V1:11 .1 Mt: V—«nv «r we," y/ $1111 ,1 v ,1 L ‘I, 500 “>10, 000; >20 ,LOLOOm >10,ooo;2o,oo_o ‘100 ' 0 0.5 1 2 KILOMETERS I | I | 0 1/2 1 MILE 2 KILOMETERS | 1 MILE Distribution of zinc and lead in rock samples from the Drenchwater Creek area. Values in parts per million. Lead values underlined. Distribution of barium and silver in soil samples from the Drenchwater Creek area. Values in parts per million. Silver values underlined. 50010” ,1 L ~"\1,000;jg 700' 300 , ,1, , . ‘MC ., \ \H.\.I\flr.i {"f’d‘f“ , . 500; 300 , \‘ “Txrvis I: IVII .: Mir Wkfirx'v‘yT’W” "VL> y. M1500; 7- W X 70mm, .. W Nike . , TL , , 4‘ Mb ”'WLVLTNI: __ 1"". /.'LL ,\ 30mg .é_.;_ ~1000LLLL " , .9! L, 1. ‘T 1y?” _ __ fix, 41» / “R m» _ " 500 E L “ » \\ 5 000 L 1'LLL 700'3 2,000» 0 ‘\ 2,000;0.7 1,500 f 300;?” ,/ / xxx/1 _ M vaj Z KILOMETEHS 2 KILOMETERS I | I 1 Distribution of barium and silver in rock samples from the Drenchwater Creek area. Values in parts per million. Silver values underlined. Distribution of zinc and lead in stream—sediment samples from the Drenchwater Creek area. Values in parts per million. Lead values underlined. [1 “ __ / . . y/{Mc 5,ooo;5>:»/ 1582151 ' L 3'00011 1' ./ 1 I L/ M. . ._ I“ «SW/1.111? ‘ Lxx Lx X , \ 31111,, . \- _ (’11,; PST, 5,000,1_ ,2 » r- . “N /L L 11. . LEW“ ., 200 Pm ‘3} 5'000L3 f I“ .Ae5,000 .. MN; MW Wi‘v v v ML KL "v, ‘V’ TIL-74??» _ 11, «mg L,\/ x __: ‘57:» v r._ L " “ M . 7 11111,; M» wv’f‘fi' EJII ° 5,000 M11 1 M MWMAmwAmkpAN f 517*» x A v x MHM‘MQN‘ - Mr 1 f >: r .1. . ”M" L L W” x, , ,2 _ i > 5 000)\ {th if K ’ 150/ L L 111. 11 , .51.wa , we, 2 KILOMETERS 0 0-5 1 2 KILOMETEHS | I IL I I I I I I MILE 0 1/2 I MILE . . . . _ ' ' ' ' _ INTERIORaGEOLUGICAL SUFIVEY, RESTON, VA 49324380415 Distribution of Zinc and lead in 5011 samples from the Drenchwater Creek area. Values in parts per million. Lead values underlined. Distribution of barium and silver in stream—sediment samples from the Drenchwater Creek area. Values in parts per million. Silver values underlined. MAPS SHOWING DISTRIBUTION OF ZINC, LEAD, BARIUM, AND SILVER IN ROCK, SOIL, AND STREAM—SEDIMENT SAMPLES FROM THE DRENCHWATER CREEK AREA, HOWARD PASS QUADRANGLE, NORTHWESTERN BROOKS RANGE, ALASKA _ 5 3.,3_1,3..3,_,3_. -. ..,,,3.; ,11 , 1.11:»,311:,1,'1.1.1.' ,1 1>1,1,1. .1 .1 .. .3-»- 1 ...1-1. ‘5' L LLLLLL L LL L L L M .. ; .. 1- 11 , E' ‘ , . ..11 1 1 .» 3,_._,.:,-, ..-, - 1 11 1- g',.1..;.1-.:1;.3 1, , 31111131. 11:... 11: 11.1-12'. mm >1,,....1.:;111'...-..... 33 3555535533535 3 53:7,“, _ 3 ..1.1: ' 1 .3.-1.1111,:1111': 1' '>¢ -.11»..11 1 1113.13.33.31“, .1 .:1. 1 - - ::.1..1.1:11 “11111“ ,1 33:55:53,555“ ,- ._. :,.3 .. 11.-.1:.11.. $1 , :1- - , 1 .1.11111:. 1, 3 1 11+ 31-,».1--,,1»1-;1 ,.1;1,.:,1. :11:.111 1:. . .. 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' ,,.3. 33 .;3 11 ,'11 .1., 13.3 1 . . .-1»1,. -111..1- ..:. , .1 ,...,.-1,1111», , 11 , 13 11111111: ,- ..11, .,1,-,'3 11 1»1-,11 ,,, 13,,,111,_11_ , ¢ 1. 33.1.33; 3» L LL L M“ Weathering Rinds on Andesitic and Basaltic Stones as a Quaternary Age Indicator, Western United States By STEVEN M. COLMAN and KENNETH L. PIERCE GEOLOGICAL SURVEY PROFESSIONAL PAPER 1210 Weathering rind: can eflectively a’zflerentiate Quaternary deposits according to relative age and, with calibration, can be used to estimate numerical agex UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1981 UNITED STATES DEPARTMENT OF THE INTERIOR JAMES G. WA'IT, Secretary GEOLOGICAL SURVEY H. William Menard, Director Library of Congress Cataloging in Publication Data Colman, Steven M. Weathering rinds on andesitic and basaltic stones as a Quaternary age indicator, Western United States. (Geological Survey Professional Paper 1210) Bibliography: p. 39 Supt. of Docs. no.: I 19.16:1210 1. Geology, Stratigraphic—Quaternary. 2. Weathering—The West. 3. Andesite—The West. 4. Basalt—The West. 1. Pierce, Kenneth Lee, joint author. II. Title. III. Series: United States Geological Survey Professional Paper 1210. QE696.C656 551.7'9'0978 80—607840 For sale by the Superintendent of Documents, US. Government Printing Office Washington, DC. 20402 CONTENTS Page Abstract 1 Weathering-rind development and time—Continued Introduction 1 Statistical analysis Purpose 2 Nature of the weathering-rind measurement distribu- Previous work 2 tions Acknowledgments 2 Analysis of variance General description of weathering rinds on andesitic and Multiple comparisons basaltic stones 3 Summary of statistical analysis ---—-—-—-———- Factors affecting weathering-rind thickness 4 Numerical model of weathering-rind development with Sampling design and methods 5 time Structure of the data 5 Rind-thickness ratios Areas and types of deposits sampled 6 Time-stratigraphic nomenclature - Sample site selection 6 Rate curves for weathering-rind thickness —-——-——-—- Sample collection 6 Regional correlations based on ages estimated from weath- Measurement procedures 8 ering rinds Environmental factors other than time - ———- 9 Cascade Range—Puget Lowland ~~~~~ Topographic position 9 California Mountains Parent material 10 Rocky Mountains Vegetation 13 Summary Climate 13 References cited Summary 15 Appendix A.-—Weathering-rind thickness measurements The relation between weathering-rind development and time -- 15 Appendix B.—Sample locations and site data ———————————————— Weathering rinds as an indicator of relative age 15 Appendix C.—Generalized petrographic descriptions ILLUSTRATIONS FIGURE 1. Photographs showing examples of weathering rinds on andesitic rocks near Lassen Peak, Calif ————————————————— ——-—~ 2. Photographs showing examples of weathering rinds on basaltic rocks near McCall, Idaho 3. Index map of sampling localities, Western United States 4 . Photograph showing destruction of weathering rinds on stones brought to the surface of Tahoe Till near Lassen Peak, Calif 5. Diagram showing interrelations among factors affecting weathering-rind development ——————————————— 6—9. Graphs showing: 6. Rind thickness versus mean annual precipitation 7. Average weathering-rind thicknesses on fine-grained andesite against coarse-grained andesite from same sampling sites 8. Average weathering-rind thicknesses on stones from outwash against those from till, with age, rock type, and sampling area held constant 9. Average weathering-rind thicknesses on stones from sites with grass and (or) sage vegetation against those from sites with forest vegetation 10. Graphs of elevation, mean annual precipitation. and weathering-rind measurements along the Bullfrog terrace, Yakima Valley 11—13. Diagrams showing: 11. Weathering-rind measurements on basalt 12. Weathering-rind measurements on andesite 13. Average weathering-rind thicknesses for the sequence of tills and terraces recognized in each of the principal sampling areas 14. 15. 16. Graph of reproducibility of weathering-rind measurements Selected histograms of weathering—rind measurements , Diagrammatic sketch of the nested sampling design for the deposits near McCall, Idaho ------------------------------------------ — III Page 16 18 21 22 23 24 24 25 26 31 31 35 36 37 39 44 50 54 Page 03AM moo 11 12 12 13 14 16 17 19 20 20 21 IV CONTENTS Page FIGURE 17—19. Graphs showing: 17. Weathering-rind thickness versus time curves for Bohemia and West Yellowstone ------------- -—-—~——————- 26 18. Conceptual models of the weathering-rind thickness versus time function 27 19. Weathering-rind thickness versus time curves for each of the principal sampling areas ---------- ——-—————-——————- 30 20. Chart comparing ages estimated from weathering rinds in glacial deposits in this study with the deep-sea oxygen- isotope record 32 21. Correlation chart for deposits sampled in this study 33 TAB LE S Page TABLE 1. Average weathering-rind thicknesses 18 2. Skewness and kurtosis for weathering-rind thickness distributions 20 3. Analysis of variance, McCall and Lassen Peak data 22 4. Summary of results of Scheffe's multiple comparison test 23 5. Rind-thickness ratios 25 6. Characteristics of deposits considered to be about 140,000 yr old (oxygen-isotope stage 6) ~———-—~——--—-—— ~~~~~ 28 7. Deposits used as calibration points, and derivation of the rate factors used in the weathering-rind equation d = a log (0.73 + 0.038t) 29 WEATHERING RINDS ON ANDESITIC AND BASALTIC STONES AS A QUATERNARY AGE INDICATOR, WESTERN UNITED STATES By STEVEN M. COLMAN and KENNETH L. PIERCE ABSTRACT Approximately 7,335 weathering rinds were measured on basaltic and andesitic stones in Quaternary glacial deposits to assess the use of weathering rinds as a relative- and numerical-age indicator. These rinds were studied at 150 sites in 17 different areas of the Western United States. Sampling methods were designed to limit the variabili- ty of environmental factors other than time (climate, vegetation and other organisms, parent material, and topography) that affect rind development. Only andesitic or basaltic lithologies were sampled, and sampling sites were restricted to terraces or flat moraine crests in areas that differ only moderately in climate. Within the restrictions of these sampling procedures, variation in rock types among sampling areas appears to be the most important factor, other than time, that affects weathering-rind development. Differences in climate among sampling areas also have a major effect, whereas the influence of such factors as vegetation, topography, and soil-matrix texture appears to be comparatively minor. Statistical analysis demonstrates that weathering rinds are an ex- cellent quantitative indicator of age. Within a sampling area, deposit age is the most important source of variation in rind thickness, and all differences in mean rind thickness between deposits of different stratigraphic ages are important. Rind-thickness data for independently dated deposits near West Yellowstone, Mont., and elsewhere demonstrate that the rate of in- crease in weathering-rind thickness decreases with time. Because the rate decreases with time, the ratio of the rind thicknesses of two deposits in the same area provides a minimum estimate of the numerical-age ratio of the two deposits. Based on the West Yellowstone sequence, a logarithmic function appears to best repre- sent the relation between weathen‘ng-rind thickness and time. However, because of the effects of climate and rock type on rind development, a logarithmic time-function must be calibrated for each sampling area. Because of the absence of independent numerical-age estimates in areas other than West Yellowstone, the age of one deposit (with rinds >0.5 mm thick) in each area was inferred by cor- relations based on stratigraphy and relative—age criteria. The inferred age of this one deposit in each area was then used as the calibration point for the rind-thickness curve for that area. The ages of the other deposits in each area were estimated from their rind thickness and the calibrated weathering-rind curves. Ages estimated from weathering-rind thicknesses and the resulting conclusions depend on several assumptions and inferences, but the data clearly suggest that, if the rate equations can be calibrated, weathering rinds can be used to approximate numerical ages, perhaps to within 10—20 percent. In addition, age estimates based on weather- ing rinds provide quantitative comparisons that constrain regional correlations. In the areas examined, ages of glacial deposits estimated by these methods appear to group into at least four time intervals: about 12,000—22,000, about 35,000—50,000, about 60,000—70,000. about 135,000—145,000 yr ago, and possibly several older time periods. These time intervals are approximately coeval with times of high worldwide ice volume indicated by marine oxygen-isotope records. The ages also indicate that several separate ice advances oc- curred during the Wisconsin Glaciation in the Western United States, including both a mid-Wisconsin advance and an early Wisconsin ad- vance in several areas. None of the age estimates for end moraines in our sample areas fall between 75,000 and 130,000 yr ago. End moraines of a given age are not present in all areas and the number of end-moraine ages differs from area to area, probably because of dif- ferences in glacier response to local climatic variations. INTRODUCTION This study was prompted primarily by the need for better dating and correlation of Quaternary deposits in the Western United States. The paucity of material suitable for dating these deposits by available numerical‘ (mostly radiometric) methods has per- sistently hampered regional correlations. In most cases, inferences concerning ages have been drawn and correlations proposed for these deposits on the basis of the extent of weathering and of modification of mor- phology. However, weathering and erosion processes provide only a measure of relative age, because (1) their results as functions of time are imperfectly understood, (2) difficulties arise in the quantification of their results, and (3) their rates are controlled by several environmen- tal factors. Correlations based on relative ages are ten- tative at best, because rates of weathering and erosion can vary significantly, both over short distances and with small variations in parent material. In addition, relative-age differences do not indicate the magnitude of absolute-age differences. ‘Throughout this report we will use the term “numerical" for dating techniques that pro duce age estimates on a ratio scale of years, and “relative—age” for those which produce ages on an ordinal scale. (See Griffiths, 1967, p. 245—249, for a discussion of different types of scales.) We resist using the term “absolute" for any dating technique. 2 WEATHERING RINDS AS A QUARTERNJARY AGE INDICATOR, WESTERN UNITED STATES These difficulties emphasize the need for, and he usefulness of, a numerical dating method based on a commonly applicable weathering parameter; previous studies have shown that weathering rinds on andesitic and basaltic stones have some potential for use in such a technique. The advantages of weathering rinds over the plethora of other time-dependent weathering and erosional features result from the potential for isolating a single weathering parameter, for objectively measur- ing that parameter, and for controlling the variables that affect it. For these reasons, weathering rinds may be a more consistent and representative measure of age than other weathering and erosional features for ages of 10“ to 105 yr. Weathering rinds were measured on andesitic and basaltic stones in this study because of certain advan- tages that result from the fine grain size and mafic com- position of these lithologies, for example: (1) a tendency for matrix and grain-by-grain alteration rather than in- tergranular staining, resulting in a relatively consistent thickness of weathered material and a well-defined “weathering front” (inner boundary of weathering); (2) a disinclination for granular disintegration, which often destroys rinds on coarser grained rocks; and (3) a relatively fast rate of weathering compared to that of more felsic rocks of similar grain size. PURPOSE This study examines the development of weathering rinds on andesitic and basaltic stones with time, with the goal of using weathering rinds as a dating method for Quaternary deposits in the Western United States. In order to accomplish this goal, the influence of variables other than time (sampling and environmental variables) on rind development must be evaluated. The study of weathering rinds as a dating technique will begin with their use as a relative-age criterion for local sequences of deposits, followed by the use of weath- ering-rind thickness as an approximate numerical-age indicator and regional correlation tool. PREVIOUS WORK A number of workers have used weathering rinds on andesite and basalt as a relative-age indicator in local areas in the Western United States (Crandell, 1963, 1972; Crandell and Miller, 1974; Birkeland, 1964; Car- rara and Andrews, 1975; Kane, 1975; Porter, 1975, 1976; and Scott, 1977). Each of these local studies proved weathering rinds to be a highly effective tool for separating deposits of different ages. In particular, Porter (1975) was able to demonstrate that weathering rinds in the Yakima Valley, Wash., were statistically consistent for deposits of one age, and significantly dif- ferent for deposits of different ages. He did not define a numerical function for the change in weathering-rind thickness with time, because of a lack of independent dates for calibration. However, he did suggest that the rate of rind formation may decrease with time. Weathering rinds on other types of rocks have also been examined for their use as potential age indicators. Obsidian hydration, which produces rinds by hydration rather than by the oxidation-hydrolysis processes predominating in the rinds examined in this study (Colman, 1977), has been used to study Quaternary deposits and found to be an effective numerical dating technique (Friedman and Smith, 1960; Pierce and others, 1976). A number of workers, including Birkeland (1973), Benedict (1973), Carroll (1974), Thorn (1975), and Burke and Birkeland (1979), among others, have studied weathering rinds on granitic rocks and demonstrated that they can be useful relative-age in- dicators. Weathering rinds on granitic rocks are, however, subject to problems associated with in- tergranular staining and granular disintegration. Desert varnish is a rind-er feature, but detailed chemical studies (Engel and Sharp, 1958; Hooke and others, 1969) have demonstrated that desert varnish is largely a surface coating, due at least in some cases to accretion of Fe- and Mn-bound clay (Potter and Rossman, 1977). Although desert varnish generally is developed to a greater degree with deposit age in a given area, large variations in rate of development ex- ist, and local measurements are commonly inconsist- ent. Consequently, desert varnish has been used only as a relative-age indicator (Hunt and Mabey, 1966). ACKNOWLEDGMENTS The writers would especially like to thank D. R. Crandell, S. C. Porter, and P. W. Birkeland, who were helpful in discussing problems and in locating sam- pling sites in areas they had mapped. Valuable com- ments on an early version of the manuscript were pro- vided by D. R. Crandell, R. F. Madole, and D. W. Moore. Thanks are also due to the members of Col- man’s doctoral committee at the University of Colo- rado, including P. W. Birkeland (chairman) and T. R. Walker, who critically reviewed early reports of the study, and J. T. Andrews, R. L. Barry, W. C. Bradley, E. E. Larson, and D. D. Runnels. W. E. Scott, R. M. Burke, and R. R. Shroba provided unpublished data and many useful hours of discussion. J. O. Kork and A. T. Miesch provided advice on statistical prob- lems. M. S. Colman and L. W. Pierce helped with field logistics. WEATHERING-RINDS ON ANDESITIC AND BASALTIC STONES 3 GENERAL DESCRIPTION OF WEATHERING RINDS ON ANDESITIC AND BASALTIC STONES A weathering rind is defined for the purposes of this study as a zone of oxidation colors whose inner bound- ary approximately parallels the outer surface of a stone (figs. 1, 2). Other weathering reactions commonly ac- company oxidation (Colman, 1977), but the rinds measured were defined primarily by visible discolora- tion. The original gray to black color of the rock is altered to colors ranging from buff through yellow to reddish (2.5Y to 7.5YR hues). The coloring of some weathering rinds is layered; but vague, diffuse inner parts of rinds were not measured. These “inner rinds” (fig. 2D) are usually dark reddish gray and are usually many millimeters thick, but they vary considerably in thickness around a single stone and are only displayed by some stones. Thin sections of the “inner rinds” show that they are usually products of alteration of olivine and (or) glass. The kind of alteration that pro- duces the “inner rinds” and the reason for their large FIGURE 1.—Examples of weathering rinds on andesitic rocks near Lassen Peak, Calif. Sampling sites for each deposit are given in Appendixes A and B. Arrow or dashed line, areas where true rind thickness is shown. Apparent variation in rind thickness is mostly a function of camera angle and unevenness of the broken surface. A. from Tioga Till (about 0.1 mm); B, from “early Tioga” (Kane, 1975) till (about 0.4 mm); C, from Tahoe Till (about 0.8 mm); D. from pre-Tahoe till (about 2.0 mm). 4 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES FIGURE 2.—Examples of weathering rinds on basaltic rocks near McCall, Idaho. Sampling sites for each deposit are given in Appendixes A and B. Arrow, area where true rind thickness is shown. Apparent variation in rind thickness is mostly a function of camera angle and uneven- ness of the broken surface. A, from Pinedale Till (about 0.3 mm); B. from Intermediate till (about 0.8 mm); C, from Bull Lake Till (about 1.8 mm); D, example of an inner rind, from Bull Lake Till. variation are not known, but in many cases deuteric alteration along joints and subsequent differential ero- sion appear likely. The hardness of weathering rinds varies from almost that of the unaltered rock to extremely soft and mushy. Weathering-rind hardness appears to decrease with time, and rinds from older deposits can often be sliced with a knife, smeared with the fingers, or crushed where hit with a hammer. FACTORS AFFECTING WEATHERING- RIND THICKNESS A large number of variables or factors potentially af- fect weathering-rind thickness. These factors can be classed into two general groups, which here will be called sampling factors and environmental factors. Elements of the sampling procedure that are capable of introducing variation into the measurement of weather- FACTORS EFFECTING WEATHERING-RIND THICKNESS ing rinds include (1) selection of sampling sites, (2) col- lection of samples from sampling sites, (3) procedures for measuring the selected samples, and (4) the operator who performs the sampling and measuring. Possible variation in rind thickness introduced by these factors was largely eliminated from this study by using a stan- dard set of sampling and measuring procedures, which will be described in the next section. The effect of dif- ferent operators will be partially evaluated in the statistical analysis section. Environmental factors that affect weathering-rind thickness are essentially identical to those postulated by Jenny (1941) as the factors in soil formation: climate, parent material, vegetation, topography, and time. Jackson and Sherman (1953, p. 241—248) have stated that the factors that control chemical weather- ing are essentially those that control soil development. Many of these factors are composed of several sub- variables. Topography includes the effects of erosion and deposition; climate includes temperature, precipita- tion, and their seasonal distribution; parent material in- cludes rock type, rock texture, and soil matrix texture. Because the purpose of this study was to examine the relationship. between weathering-rind thickness , and time, we attempted to minimize the variation in other ficmrs—by sampling them over a restricted range. For example, out of the wide range of possible lithologies, only basaltic and andesitic stones were sampled. However, variables other than time could not be com- pletely eliminated, and as a result, we attempted to evaluate the effect of residual variation in environmen- tal factors. To a large extent, the effect of time could be isolated from the effect of other variables. The evalua- tion of variables other than time will follow the discus- sion of sampling procedures. SAMPLING DESIGN AND METHODS STRUCTURE OF THE DATA The basic organization of data in this study is a nested, multi-level sampling design. This design con- sists of the following levels: 1. seven different sampling areas, 2. several stratigraphic ages of deposits within each sampling area, 3. several landforms (moraines, terraces) of each age, 4. several sampling sites on each landform, 5. many measurements at each sampling site. In some areas, the landform level was not used. The sampling design used in this study was con- ceived primarily to evaluate the relation between weathering-rind thickness and time (age). Age is therefore isolated on the second level of the nested sampling design. Variation in two important factors in rind development, rock type and climate, occurs mostly between sampling areas, so that these factors can be held nearly constant by analyzing each sampling area separately. The influence of factors other than time on weath- ering-rind thickness was investigated using several dif- ferent subsets of the rind thickness data. Some of these subsets are part of the data collected for the basic nested sampling design; other subsets were collected specifically to evaluate the influence of factors other than time. For example, the influence of climate was evaluated by comparing rind thicknesses on similar rock types in deposits thought to be about the same age in different sampling areas. However, the rock types were not identical, and the ages of the deposits are not known with absolute certainty. Therefore, the in- fluences of rock type and climate are to some extent “confounded,” that is, their influences cannot be com- pletely separated. Such evaluations of the influence of each factor are tempered by the amount of confounding in the data. Another subset of data used to evaluate the influence of factors other than time was data collected with the specific purpose of isolating one of these factors. For example, in some cases, a single deposit, such as an out- wash terrace, could be traced along a considerable climatic gradient. By sampling a single rock type at places on the deposit with different climates, rock type and age were held constant, and the influence of climate could be evaluated independently. Because we attempt- ed to keep variables such as rock type and climate relatively uniform within each sampling area in order to evaluate the influence of age, much of the data collected to specifically isolate other variables was not used in the nested sampling structure. Only sites where variables such as rock type and climate are relatively uniform were used to evaluate the influence of age. The basic data collected in this study are contained in Appendixes A and B. Appendix A provides the mean‘, ‘Mean = i = EXi/n, where X,- are individual observations, and n is the number of observations. 6 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES standard deviation", and number of measurements at each site, along with the deposit and rock type on which rinds were measured. Appendix B gives site locations and other site data. AREAS AND TYPES OF DEPOSITS SAMPLED Approximately 7,335 weathering rinds were measured at about 150 sites in 17 different areas in the Western United States. Most of the deposits sampled were either glacial or glaciofluvial because of the possibility of correlating deposits resulting from large- scale climatic fluctuations, and because of the possibility of correlating these deposits with dated paleoclimatic records. However, data collection was concentrated in seven areas because they contained well-developed sequences of deposits of different ages, because they contained abundant, relatively uniform rock types, and because they had climates conducive to rind formation. The stratigraphic ages of deposits sampled in each of the seven areas were defined by mapping of previous workers (fig. 3). These areas are (1) near West Yellowstone, Mont.; (2) near McCall, Idaho; (3) the Yakima Valley near Cle Elum, Wash.; (4) the Mount Rainier area, Washington; (5) the Satsop River drainage and adjacent parts of the Chehalis River Valley, Wash., here referred to as the Puget Lowland; (6) the Lassen Peak area, California; and (7) near Truckee, Calif. The locations and data for the other sampling areas are given in Appendixes A and B. These areas proved relatively less suitable either because of the scarcity of basalts or andesites, because of the large variability in these lithologies (especially andesites), or because of very dry climates. SAMPLE SITE SELECTION Land surface stability was the primary criterion for selecting sampling sites, and evidence of erosional or depositional disturbance of the weathering profile was minimal at most sites chosen. Sampling sites were commonly located on relatively flat moraine crests or on flat terrace surfaces. This type of site precludes burial by colluvium; sites with thick eolian mantles were also avoided. These sites were not chosen by for- mal random selection procedures from all possible sites of the above description because of access considera- tions. However, we are aware of no bias in the selection of sample sites, and the selected sites are thought to be representative. 22(x,-—)—()2 ‘/z n—1 ) 2Standard deviation = s =( Lgueer WASHINGTON WL ' . AND AYAKIMA MONTANA VALLEY MOUNT WEST 45. RA'N'ER YELLOWSTONE ~ . I "‘ AMCCALL OREGON ' 40° 120“ l 115° l 110° 105° IDAHO WYOMING ALASSEN PEAK . COLORADO UTAH L l l FIGURE 3.—Index of sampling localities, Western United States. Triangle, principal sampling area. Solid dot, secondary sampling locality. References to the surficial mapping on which the sampling was based are as follows: West Yellowstone, Mont. (Alden, 1953; Richmond, 1964, 1976; Pierce, 1973; Waldrop, 1975; Waldrop and Pierce, 1975; Pierce and others, 1976); McCall, Idaho (Schmidt and Mackin, 1970); Yakima Valley, Wash. (Porter, 1969, 1976); Mt. Rainier, Wash. (Crandell and Miller, 1974); Puget Lowland, Wash. (Carson, 1970); Lassen Peak, Calif. (Crandell, 1972; Kane, 1975); Truckee. Calif. (Birkeland, 1964). SAMPLE COLLECTION Several options existed in procedures for selecting the stones at each sampling site; these options in- cluded the type of stones selected and the position in the weathering profile from which the samples were taken. In this study, stones were collected from the soil pro- file at depths of about 20—50 cm, usually from the upper part of the B horizon, or, if a B horizon was not present, from the uppermost C (Cox) horizon. All stones encountered in the soil profile at the proper depth were removed and broken with a rock hammer. A preliminary reconnaissance of the rock types present in the deposits of a given sampling area formed the basis for selection of the lithologies on which rinds were measured. These lithologies are those that were common throughout a given sampling area, and that were relatively consistent in appearance from site to site. All stones of these lithologies encountered at each sampling site were retained for measuring rind thick- ness. Appendix C contains generalized petrographic descriptions of the lithologies used in this study in each of the principal sampling areas. The upper part of the B horizon (or the Cox horizon if a B horizon was not present) was used as the sampling FACTORS EFFECTING WEATHERING—RIND THICKNESS 7 horizon, because the B horizon is generally more weathered than lower horizons (Birkeland, 1974, p. 9) and is less subject to the problems of disturbance associated with the A horizon. The A horizon represents the zone of maximum leaching (Birkeland, 1974, p. 9), but several fac- tors—including its relative thinness, disturbance by frost or animals, loss of material by erosion, and accre- tion of loess, colluvium, or other material—make it less reliable than the B horizon as a sampling horizon. The C horizon is generally less weathered than the B horizon (Birkeland, 1974, p. 9), and weathering rinds in C horizons are thinner than those in associated B horizons. Weathering-rind thickness appears to progressively decrease with depth in the weathering profile, from the B horizon downward. In a number of locations, par- ticularly near McCall, Idaho, rind thickness was observed to decrease progressively below the standard sampling depth. (See, for example, C76—54C versus C75—104B, Appendix A.) Porter (1975) has made the same observation for rinds in the Yakima Valley. Where completely unoxidized parent material was en- countered (Cn horizon), virtually no weathering-rind development was observed, for example C7 6—54A (Ap- pendix A). In contrast to our sampling procedures, some workers have used weathering rinds on stones at the ground surface (Porter, 1975; Burke, 1979) to deter- mine relative ages. Porter (1975) observed no notice- able difference between surface rinds and shallow- subsurface rinds in the Yakima Valley. Our observa- tions support this conclusion for the Yakima Valley, where at least for the younger drifts, the rinds are almost as hard as the rock itself. However, a number of observations clearly indicate that the rinds on surface stones can yield unreliable data for studying weath- ering with time, especially for older deposits. First, the hardness of the weathering rinds obviously affects their preservation on the surface. The soft, mushy rinds produced by advanced weathering are almost certain to be eroded from surface stones. The rinds on subsurface stones in older deposits in most of the sampling areas had to be handled with care in order to preserve the full thickness of the weathering rind. In the Lassen Peak area, stones which were brought to the surface of Tahoe deposits by logging-road con- struction showed abundant evidence of flaking and removal of weathering rinds, even though they had been at the surface a few tens of years at most (fig. 4). At McCall, Pierce determined that a thin stream of warm water removed most of the soft rinds on stones from older deposits. Even where the loss of weathering rinds at the sur- face is not a problem, major differences commonly ex- ist between rinds on surface stones and those on shallow subsurface stones. On fine-grained andesitic intrusive rocks at the surface of moraines of Pinedale age in the West Yellowstone area, weathering rinds under lichen-covered surfaces were two or more times thicker than those on the undersides of the same stones. This difference is consistent with the conclu- sions of Jackson and Keller (1970), who documented greater depths of weathering under lichen-covered sur- faces than on lichen-free surfaces on basalt in Hawaii. At another Pinedale locality near West Yellowstone, rinds were measured on both shallow subsurface and surface basalts. The results were 0.44i0.22 (1 stan- dard deviation, n=41) for the subsurface sample, and 0.67 i021 (n=25) for the surface sample (collected by R. M. Burke, measured by Colman). A probability value of less than 0.01 for a Student’s t-test provides strong evidence against the hypothesis that these two samples are from the same population. Differences in thickness between rinds on surface stones and those on shallow subsurface stones may be related to differences in duration of exposure to weathering. A surface stone begins to weather as soon as it is exposed, but weathering of a subsurface stone is probably minor until the oxidation front migrates downward past the stone. Stones in unoxidized parent material have virtually no rinds (C76—54A, for exam- ple). An interval of at least several thousand years seems to be required before the oxidation zone extends to the typical 30-cm sampling depth used in this study. The formation of rinds on basaltic stones at the sur- face also may be controlled by different processes than those that control the formation of rinds on stones within the soil. Rinds on subsurface basaltic stones near Wallowa Lake,‘ Ore. (Appendix A), appeared con- siderably different than rinds on surface basaltic stones measured by Burke (1979). The surface rinds were thicker on the average, but much more variable; many stones have no rinds. The surface rinds were also harder and redder than the subsurface ones. One pos- sible explanation for the difference is the effect of grass and forest fires on the surface rinds. Because of the difficulty in controlling the variables that affect weathering-rind development on surface stones—including lichens, fire, rolling by animals, uneven wetting, and erosion of weathered material— weathering rinds were sampled from within the weathering profile in this study, as described in the WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES _ FIGURE 4.—Destruction of weathering rinds on stones brought to the surface of Tahoe Till by logging-road construction near Lassen Peak, Calif. Outer part of weathering rinds on these two stones of nearly identical lithology is quite soft. Rind on underside of stone on left is preserved, whereas rind on exposed upper side of stone on right is flaking off. preceding section. This procedure minimizes the effect of the above variables and helps to isolate time as a factor. In conclusion to this discussion, it should be noted that the sampling procedures used in this study are most appropriate for deposits in the range of 10" to 105 yr old. In younger deposits, weathering may not reach the depths sampled in this study, and rinds developed on surface stones may be more useful for deposits in the 103-yr-old range. Deposits older than about 0.5 m.y. have usually suffered considerable erosion, and their surface is probably now below the position of the original B horizon. Thus, the weathering of these deposits is not strictly comparable to that of younger deposits whose surfaces have been minimally lowered. Despite this limitation on our methods, rinds on early to middle Pleistocene deposits are usually much thicker and better developed than those in nearby late Pleistocene (about 105-yr-01d) deposits, so that rinds are still a useful age indicator for the older deposits. MEASUREMENT PROCEDURES Rind thickness was measured to the nearest 0.1 mm, using a 6—power magnifying comparator containing a scale graduated in 0.2 mm increments, on stones that were split open and sampled as described in the previous section. In most cases, only half or less of the perimeter of each stone was appropriate for measuring rind thickness. Places not considered suitable for measurement include: (1) where the broken face was not approximately perpendicular to the outer surface of the stone, (2) where part of the rind was crushed or flaked in the process of breaking the stone, and (3) where the outer surface of the stone was concave out- ward, allowing soil matrix to cling tightly to the stone. An important assumption that will be necessary in the analysis of the relation between rind thickness and time is that the stones on which rinds were measured were unweathered when entrained, or were abraded in transport, and were therefore deposited with fresh, FACTORS EFFECTING WEATHERING-RIND THICKNESS 9 unweathered surfaces. Accordingly, the measured weathering rinds developed progressively from the time of deposition. Several observations suggest that this assumption is valid, and that preexisting rinds on stones inherited from bedrock or from older, reworked deposits are rare. First, stones sampled from unweathered C (Cn) horizons exhibit virtually no rinds (C76—54A, for example). Second, stones that show evidence of weathering prior to deposition are rare. Such stones include those having rinds with asym- metric thicknesses around the stone, which suggests partial abrasion of a preexisting rind, and stones whose thicknesses are far removed from the distribu- tion of rind thicknesses for the rest of the sample. Stones with markedly asymmetric rinds (varying by more than a few tenths of a millimeter) were not measured. Exceptionally thick rinds were measured but were considered outliers to the sample rind- thickness distribution; they were not included in the calculation of sample means. On stones that exhibited no visible variation in rind thickness, the rind was measured in a single, conven- ient place. Although formal randomizing procedures were not used in the selection of the place where the rind was measured, care was taken to avoid obvious bias, and the measurements obtained in this manner are considered effectively random. In a few cases (usually 10 percent or less), rinds exhibited small but apparent variation in thickness around the stone. In these cases, a place that appeared representative was chosen in which to measure the rind. These measure- ment procedures preclude the use of formal signifi- cance levels and precise calculations for statistical analysis, but do not invalidate the usefulness of such analyses. In most cases, between 30 and 60 measurements were made at each sampling site. With repeated measurements of rinds on the same stones, individual measurements could usually be reproduced to within $0.1 to 0.2 mm, depending primarily on the sharpness of the weathering front (the inner boundary of the weathering zone). Very thin rinds, in the range of 0.0—0.1 mm thickness, are at the limit of measurement. Such rinds were recorded as 0.1 mm if surface oxida- tion of the stone obscured the texture of the rock and penetrated the stone surface. The rind was recorded as 0.0 mm thick if the texture of the rock could be seen through the slight oxidation of the surface. ENVIRONMENTAL FACTORS OTHER THAN TIME Because the main focus of this report is on the rela- tion between weathering rinds and time, we wish to first evaluate the influence of other environmental fac- tors. Besides the effect of sampling procedures, factors that affect chemical weathering features are essen- tially the same as those that control soil development (Jackson and Shaman, 1953, p. 241-248). As discuss- ed previously, these variables are climate, vegetation and other organisms, relief (topographic position), parent material, and time (Jenny, 1941, p. 15). As discussed earlier, the variability of rind thickness due to sampling techniques essentially has been elim- inated by using a standard set of procedures. In addi- tion, the sampling procedures have greatly reduced the influence of environmental factors by including only a limited range of such factors. Their remaining effect on rind thickness is the subject of the following sections. The influence of these factors is complex, because the factors themselves are interrelated (fig. 5), and their ef- fects are commonly confounded; that is, their effects cannot be completely separated. TOPOGRAPHIC POSITION Just as erosion and burial affect the development of soil profiles, our observations indicate they also affect the development of weathering rinds. The effects are essentially those described by Jenny (1941) as the relief (topography) factor. The effects of erosion and burial on weathering-rind development are illustrated by the data for sampling sites on till of Hayden Creek age near Mount Rainier. The data for these sites (Ap- pendix A) exhibit considerable scatter, which we at- tribute to the fact that all of the sampling sites except two, 076—40 and C78—116, are either being eroded or are buried by eolian deposits. The stones at C76—40 and 078—116, the two undisturbed sites, have much thicker rinds than stones at the other sites, even though 076—40 and 078—116 are on recessional moraines that are at least slightly younger than the other moraines sampled. u. m—“fl .1. . .I ORGANISMS PARENT CLIMATE (VEGETATION) MATERIAL TOPOGRAPHV TIME L l J I WEATHERING-RIND THICKNESS FIGURE 5.—Interrelations among factors affecting weathering-rind development. 10 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES Obviously, where erosion has removed the zone of maximum weathering in the upper part of the soil, the weathering rinds on remaining stones will be anom- alously thin. Sample sites were chosen to avoid ac- tively eroding areas, but especially for relatively old till deposits, completely uneroded sites probably do not exist. Despite efforts to choose sites with minimal erosion, the data suggest that minor differences in topography may have an appreciable affect on weath- ering rinds. For example, three sampling sites were located on the crest of the outermost Bull Lake moraine near McCall. In order of decreasing average rind thickness they are: C75—109 (1.96 mm), just off the crest (erosion=deposition?); C76—56 (1.69 mm), on a broad, flat part of the crest; and 076—55 (1.44 mm), on a relatively sharp part of the crest. Although other variables are probably involved, one explanation for the differences in rinds among these sites is variation in the erosion to which the sites have been subjected. However, erosion at most sampling sites does not seem to have significantly affected rind thicknesses. For sites on flat outwash terraces, an assumption of negligible erosion can be easily justified. As will be discussed in a later section, rind thicknesses from sites on outwash terraces were compared with those from sites on till of the same age. Rinds sampled from the till sites tended to be slightly thicker than those from outwash-terrace sites. Although variation in vegeta- tion and soil drainage conditions may affect these rind thicknesses, the fact that rinds from the till sites were actually thicker than those from the non-eroded outwash-terrace sites suggests that erosion of care- fully chosen moraine crest sites about 105 yr old or younger is relatively minor. Even on older deposits where some degree of erosion is unavoidable, carefully chosen sites probably yield consistent data with a minimum influence of erosion. Burial of deposits also affects the rate at which weathering rinds form in the deposit, principally by placing the upper part of the buried deposit below the zone of maximum weathering. Many of the study areas were locally covered by a mantle of eolian deposits, commonly loess. Loess-covered sites were avoided in collecting data for the analysis of the relation between weathering-rind thickness and time. However, sep- arate comparisons of loess-free sites with sites having a variety of loess thicknesses demonstrated that relatively thin eolian deposits (less than 50—100 cm) did not appreciably slow weathering-rind development in the upper part of the buried material. In contrast, where eolian deposits are greater than 50—100 cm thick, weathering rinds in the underlying deposits are commonly quite thin. This was the case with Hayden Creek deposits near Mount Rainier, cited earlier; the Salmon Springs terrace deposits in the Puget Lowland are another example. Salmon Springs gravels buried beneath thick loess (076—33, 37A) have rinds only a few tenths of a millimeter thick, whereas those beneath thin loess (C76—37B) have rinds greater than 1 mm thick. Because of these data, only sites with less than 50—100 cm of loess were used in the analysis of the rela- tion between weathering-rind thickness and time. PARENT MATERIAL We deliberately restricted the lithologies on which weathering rinds were measured to basalts and ande- sites. This restricted range of chemical composition, mineralogy, and texture automatically reduces varia- tion in weathering-rind thickness. However, basalts and andesites still have a range of lithologic variation, and the effect of this variation on weathering-rind development, along with the effect of the soil matrix, is the subject of this section. Many of the comparisons of parent material in this section also involve differences in climate, so that although the effect of climate will be discussed in detail in the next section, climate must also be considered in this section. Apparently, rates of rind development differ for basalts and fine-grained andesites of similar textures. Although basalts and andesites were seldom found together in the principal sampling areas, rind data from different areas allow some comparison of rind development for the two lithologies. When rind thick- ness is plotted against time separately for basalts and andesites for each of the study areas (see fig. 19), the curves plot in order of mean annual precipitation of the study areas. However, when basalts and andesites are considered together, the relation of the curves to precipitation is not clear. This suggests that basalts and andesites have different rates of rind development, which can obscure the relation between rate of rind development and precipitation. Comparison of rind thicknesses for deposits thought to be about the same age in different areas suggests that rinds form somewhat faster on basalt than on andesite. This observation is consistent with the generally accepted conclusion that mafic rocks tend to weather more rapidly than felsic rocks (Goldich, 1938; Loughnan, 1969, p. 93; Birkeland, 1974, p. 138). Dif- ferences in precipitation between areas complicate comparisons, but assuming increased moisture favors rind development (a point demonstrated in the section on climate) the comparisons can still be validly made. For example, the basalt-rich Indian John Member of the Kittitas Drift in the Yakima Valley and the andesite-rich pre-Tahoe till near Lassen Peak are prob- ably about the same age, and have almost identical FACTORS EFFECTING WEATHERING-RIND THICKNESS 1 1 rind thicknesses. However, the Lassen Peak area is considerably wetter than the Yakima Valley. Had the climate of the two areas been similar, the rinds on the basalt in the Yakima Valley would have been thicker than those on the andesite near Lassen Peak in deposits of the same age. The relative influence of rock type on rind develop- ment can be compared to that of other factors, whose specific effects are discussed in subsequent sections. Between sampling areas, difference in rock type ap- pears to be more important than factors such as climate, vegetation, and topography. Although the influence of climate on the weathering of basalts and andesites overrides that of rock type in some places in the Western United States (R. W. White, oral commun., 1975), in the present study, rock type appears to be a greater influence than climate. The relative effects of rock type and climate on the weathering of basalts and andesites can be assessed by comparing: (1) rind thickness for deposits of a single age in a single sampling area, and (2) rind thickness for deposits thought to be the same age (based on soils, morphology, and other relative-age criteria, and on the calibrated rind curves developed in this study) in dif- ferent areas. For the first type of data, rock type is not a factor, and climate is the only variable that affects rind thickness; for the second type of data, both climate and rock type affect rind thickness. Basalts and andesites were treated separately, so only the in- fluence of differences among basalts, or among ande- sites, was considered in the effect of rock type. The two types of data are compared in figure 6, where rind thickness is plotted against mean annual precipitation. The first type of data, that affected by climate alone, is plotted in figure 6, as well as the second type, that affected by climate plus rock type (assuming the cor- relations are correct). Only one aspect of climate, namely precipitation, is considered in figure 6. Other climatic parameters, such as temperature, may affect the lines in figure 6 significantly, but such effect re- mains largely unevaluated. The fact that the lines representing the influence of precipitation plus rock type slope much more steeply than the lines repre- senting the influence of precipitation alone in figure 6 indicates that precipitation plus rock type has a much greater effect on rind thickness than does precipitation alone. Therefore, variation in rock type (combined with unevaluated variation in climatic factors such as temperature) has a greater effect than variation in precipitation. The closeness of fit of points T, U, and V to line 8 in figure 6 might be interpreted, by itself, to indicate a strong influence of precipitation on rind thickness. However, other lines representing the influence of rock type plus precipitation (for example, line 9) sug- gest that the fit of points to line 8 is fortuitous; the lines representing the influence of precipitation alone 2.4 I 2.2—. 2.0 0.8 0.6 RIND THICKNESS, IN MILLIMETEFIS 0.4 0.2 IIIIIIIIIIITTIIIIIIII lllllllllll o I 20 4O 60 80 100 120 MEAN ANNUAL PRECIPITATION, IN CENTIMETERS O _. A 0 FIGURE 6,—Plot of rind thickness versus mean annual precipitation at sample localities in Western United States. Mean annual precipitation values are from US. Weather Bureau (1959). Points A-N are means of individual sites (Appendix A); points 0-2 are means for all sites for the given age and sampling area. Solid lines connect points of the same age, lithology, and sampling area; dashed lines connect points of the same general lithology (basalt or andesite), of the same inferred age, but from different sampling areas; fg, fine-grained andesite; cg, coarse-grained andesite; areas not marked. basalt. The two points for Hayden Creek Till (W and Y) correspond to two interpretations of the age of the Hayden Creek advance. Point Area Age Line A-F Yakima Valley, Wash. Bullfrog 1 G-H Truckee, Calif. (fg) Tahoe 2 I-J Truckee, Calif. (cg) Tahoe 3 K-L Truckee, Calif. (fg) Donner Lake 4 MN Truckee, Calif. (cg) Donner Lake 5 O McCall, Idaho Pinedale 6 P Yakima Valley, Wash. Domerie 6 Q W. Yellowstone, Mont. Deckard Flats 6 (recessional Pinedale) R Yakima Valley, Wash. Ronald 7 S W. Yellowstone, Mont. Pinedale 7 T McCall, Idaho Bull Lake 8 U Yakima Valley, Wash. Indian John 8 V W. Yellowstone, Mont. Bull Lake 8 W Mt. Rainier, Wash. (fg) Hayden Creek 9 X Lassen Peak, Calif. (fg) pre-Tahoe 9 Y Mt. Rainier, Wash. (fg) Hayden Creek 10 Z Lassen Peak, Calif. (fg) Tahoe 10 12 in figure 6 indicate a much smaller influence of precipitation. The amount of glass and olivine in the rock is another variable that appears to influence the develop- ment of weathering rinds. Examination of thin sec- tions of rinds reveals that glass and olivine are par- ticularly unstable in the weathering environment, and their alteration is the most important source of oxida- tion colors in the early stages of rind development. The basalts in the deposits in the Puget Lowland illustrate this relation. These rocks contain no olivine, and the small amount of original glass has devitrified, prob- ably by slight burial metamorphism. Compared to basalts that do contain glass and (or) olivine in deposits of comparable ages, the basalts in the Puget Lowland deposits have anomalously thin weathering rinds. Rock texture is another aspect of parent material that can affect the rate of weathering-rind develop- ment. A conscious effort was made in sampling to minimize variations in texture, but some variation was unavoidable. In areas of andesitic rocks, two arbi- trarily defined textures were sampled, based on field appearance, and were designated fine grained and coarse grained (Appendix C). Fine-grained andesites contain few or no phenocrysts and usually have a dense, aphanitic matrix, whereas in coarse-grained andesites, phenocrysts comprise more than one-third of the rock volume, and the matrix is somewhat more granular. For comparison, average rind thicknesses for fine-grained andesites were plotted against those for coarse-grained andesites from the same sampling sites (fig. 7). On the average, rinds on fine-grained andesites are 84 percent as thick as those on coarse-grained andesites. The texture of the soil matrix can also affect the rate of weathering-rind development by affecting soil mois- ture or the rate at which water moves through the soil. To evaluate the effect of soil-matrix texture, average rind thicknesses for sample sites on outwash were plot- ted against average rind thicknesses for sites on till, for each age of deposit in each sampling area (fig. 8). Rinds developed in outwash are, on the average, 89 percent as thick as those developed in till of the same age. The effect of soil-matrix texture is complicated by the fact that different soil-matrix textures often sup- port different -vegetation communities, and the in- fluences of soil matrix and vegetation on weathering- rind development are difficult to evaluate separately. However, the sample data suggest that rinds develop slightly faster in till than in outwash. This may be due to the finer texture and higher water retention capaci- ty of the till matrix, which allows the soil water more time to approach equilibration during weathering reac- tions. The effect also may be partly the result of the in- WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES 3'5 l | I l l 7.38, has" A 8 g / < 3.0— / _ II (p / E / u. 2.5— / — g / Lu / g 2.0— // _ 3 «‘7 2 / z 1‘5“ / ‘ X ‘ (,5 / (I) A/ ‘5‘ 1.0— - EXPLANATION _ (X) f . x x X A Rainier E x A . Truckee D 0.5— )9/5‘ x Lassen “ Z X o E M + Other 0“ 0 1 I l I 1 1 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 RIND THICKNESS, IN MILLIMETERS, COARSE-GRAINED FIGURE 7.—Average weathering-rind thicknesses 0n stones of fine- grained andesite plotted against those of coarse-grained andesite from same sampling sites. See text and Appendix C for description of rock types. The average ratio of rind thickness on fine-grained andesites to that on coarse-grained andesites is 0.84. 1.80 U) l I l I I I I I [ l I l I l I I m — A. E 160— //3'3' 23 E — / 1 .1 :1 1.4o—— / .1 E _ + / - 2 ~/ 120— ~\ — I” _ / - 22 -/ 3 1.00— / — '5 - / * + O 0.80— + o __ Z — /A — a 0160- // EXPLANATION - LU _ —4 E / + Truckee 9 0.40— A x McCall _ I _ . ._ A Yakima _ Q 0.20—- of?“ - Puget Lowland _ 1% _ / O Rainier _ l l I l l l l l l l l l I l I l I l o 0.20 0.40 0.60 0.80 1.0 1.20 1.40 1.60 1.80 RIND THICKNESS IN TILL, IN MILLIMETERS FIGURE 8.—Average weathering-rind thicknesses on stones from out- wash plotted against those from till, with age, rock type, and sampling area held constant. The average ratio of rind thicknesses for sites on outwash to that of sites on till is 0.89. fluence of different types and amounts of vegetation, which is commonly sagebrush or grass on outwash, and coniferous forest on till. FACTORS EFFECTING WEATHERING-RIND THICKNESS 13 VEGETATION The effect of different types of vegetation on rind development is difficult to evaluate because the amount and type of vegetation are difficult to measure and because amount and kind of vegetation are so dependent on climate and parent material. An attempt was made to compare rind development at sites bear- ing forest vegetation with that at sites bearing grass and (or) sage vegetation on deposits of the same age. However, because most contrasts in vegetation on deposits of the same age corresponded with a contrast in soil-matrix textures (between till and outwash), only five data pairs were obtained for deposits of the same age and similar texture, but with different vegetation (fig. 9). For these data, rinds developed under grass and (or) sage average 87 percent as thick as those under forest vegetation. Because of the small number of data points, however, the conclusion is tenuous. This possibly slower rate of rind formation under grass and (or) sage may explain some of the difference be- tween rinds developed in till and in outwash (fig. 8). Vegetation and soil pH are related, as are pH and the degree of weathering (Jenny, 1941, p. 216). Soil matrix pH’s (1:1, soilzwater) were measured for soil samples collected at rind sampling horizons in 1975 (Appendix B). The variation in pH is small and inconsistent; no relation to age or rind development is apparent. CLIMATE Climate is a variable that is generally accepted as a major influence on weathering processes (Jenny, 1941, p. 104; Loughnan, 1969, p. 67; Birkeland, 1974, p. 211). Climate includes a large number of interrelated variables; however, all of the principal sampling areas in this study have similar seasonal distributions of temperature and precipitation, so that mean annual temperature (MAT) and mean annual precipitation (MAP) values are considered reliable variables for pur- poses of climatic comparisons. Climatic variables at individual sites may be slightly different from those at nearby weather stations due to microclimatic, orographic, or altitudinal effects. Because most sampling sites were located on flat moraine crests or terrace surfaces, climatic differences between these sites and nearby weather stations are thought to be minimal. No field evidence that would suggest major microclimatic effects due to insolation. aspect, wind, snow drift, or evapotranspiration was observed at any of the sites used in the analysis of the relation between rinds and time. Nevertheless, other data (for sites not used in the analysis of the relation between rind thickness and time) indicate that climate can change substantially :2 °-8 I I I I I I 0.7— / _ 0.6 — / _ 0.5 '— / 0.3 — / — 0.2 —' 0.1— A — o L I I I l I l I O 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 RIND THICKNESS, FOREST, IN MILLIMETERS RIND THICKNESS. GRASS-SAGE, IN MILLIMETE FIGURE 9.—Avera.ge weathering-rind thicknesses on stones from sites with grass and (or) sage vegetation plotted against those from sites with forest vegetation. Age, type of deposit, and sampling area have been held constant. The average ratio between rinds developed under grass and (or) sage, and rinds developed under forest vegetation is 0.87. over short distances, and that such changes have an important effect on rind thickness. Two sites near West Yellowstone, Mont. (C75—102A and 102B, Ap- pendixes A, B), are only about 30 m higher in altitude than the weather station at West Yellowstone but are in a more favorable topographic position to intercept storms. The effect of soil moisture on rind thickness at these sites is indicated by snow course data (Farnes and Shafer, 1975), which suggest that they have average snow packs about 1.7 times that at West Yellowstone. The average rind thickness at these sites is 0.99 mm, compared to 0.78 for sites of the same age in a setting closer to that of West Yellowstone. Similarly near McCall, Idaho, two sites (C7 8—124 and 125) on recessional Pinedale deposits in a side valley are located about 400—450 In above McCall. Snow course data (Wilson and Carstens, 1975) suggest that the snowpack at these sites may be more than 2 times that at McCall, although the relationship to moisture is complicated by the difference in temperature be- tween the sites and McCall. Rind thickness at these sites averages 0.67 mm, compared to 0.25 mm for the youngest Pinedale deposits near McCall. A dramatic example of the effect of precipitation on the rate of weathering-rind development is found along the Bullfrog terrace (Porter, 1976) in the Yakima Valley, Wash. (fig. 10). Weathering rinds were measured at six localities along the terrace, over a distance of 45 km, in which MAP decreases by a factor of about 3, whereas MAT increases by less than 1°C 14 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES (7.9°C at Cle Elum, Wash., 8.3°C at Ellensburg, Wash.) Within the area of this climatic gradient, rind thickness decreases by a factor of about 2 (fig. 10), even though the slight increase in MAT should in- crease the rates of the chemical reactions that form rinds. Thus, the climatic gradient’s effect on weathering-rind thickness is largely due to moisture differences. The influence of moisture differences may be partly indirect, through differences in type and amount of vegetation, which varies from coniferous forest to sparse grass and sage. Near Truckee, Calif, data from terraces that tran- sect different climatic zones also demonstrate a positive correlation between MAP and rind thickness. Near Verdi, Nev., MAP is about 50 cm, compared to 80 cm near Truckee (US. Weather Bureau, 1959). Rind thicknesses measured in Tahoe and Donner Lake deposits near Verdi are generally thinner than those for deposits of the same age at Truckee (fig. 6, lines 2—5). The slope of the rind thickness versus MAP line for the Truckee-Verdi area is similar to that for the Bullfrog terrace in the Yakima Valley (fig. 6, line 1). Comparison of rates of weathering-rind development between principal sampling areas also illustrates the effect of precipitation. Rind thickness versus time curves for each area (developed in a later section) demonstrates that rates of weathering-rind develop- 2 2:53 BULLFROG END MORAINE METERS 0 CLE IELUM 700 F: BULLFROG < 2000 TERRACE ELLENSBURG 600 i. I A H 500 L“ 1500 l l l N 1 r—. (I) n: 2 Lu — (— a’E < .2 2 z LIJ 0 05m 3 E 1.0 __ .— _ E LU 0.8 -i ______ _ o 2 0 e __________ __ E E 0.4 i7. ______ in: 2 0.2 __ D o 1 l I | Z z 0 ‘0 2° 30 4o KILOMETERS c: - FIGURE 10.—Elevation, MAP, and weathering-rind measurements along the Bullfrog terrace (Porter, 1976), Yakima Valley. The precipitation profile is based on records at Ellensburg and Cle Elum, Wash., and at several stations upstream from Cle Elum (US. Weather Bureau, 1959). The rind-thickness values represent the mean 11 standard deviation for the measurements at each site, whose location has been projected into the line of profile. Trend line of rind thickness against distance down-valley was calculated by least-squares regression (r = 0.90). See figure 6, line 1, for plot of rind thickness versus MAP. ment generally increase with increasing MAP. For example, basalts in deposits thought to be about 140,000 yr old at West Yellowstone (50 cm MAP), in the Yakima Valley (55 cm MAP), and at McCall (65 cm MAP) have weathering rinds averaging 0.78, 1.05, and 1.57 mm thick, respectively. The West Yellowstone deposits have been dated by combined obsidian hydra- tion and K-Ar methods (Pierce and others, 1976), and the other deposits are thought to be about the same age based on soils, morphology, and stratigraphic rela- tions. These data are plotted in figure 6, line 8; however, as noted in the previous section, much of this variation in rind thickness is due to differences in rock type in addition to differences in climate. The influence of precipitation alone is much less than that of climate and rock type combined (fig. 6). The effect of temperature on weathering-rind devel- opment remains largely unevaluated because of sev- eral problems. First, the range of MAT for the prin- cipal study areas is rather small (between 1.7° and 10.5°C, Appendix B), and the effects of variation in MAT are usually masked by the effects of much larger variations in MAP, for example, along the Bullfrog ter- race in the Yakima Valley, Wash. What variations do exist in MAT are usually inversely related to those in MAP, and higher temperature and lower precipitation (or vice versa) have offsetting effects on rind develop- ment. In addition, the effect of temperature on rind development is difficult to separate from the effect of precipitation; for example, even with MAP held con- stant, an increase in temperature would result in a decrease in soil moisture, thus reducing or perhaps even eliminating the effect of the increase in temperature. Climatic indices combining precipitation and temperature, such as Arkley’s (1963) leaching in- dex, have been devised; but in view of the apparent dominance of precipitation over temperature as a con- trol on weathering-rind development, the use of such an index does not seem warranted. Observations in a number of secondary sampling areas (for example, along the Bighorn River near Hardin, Mont.: 30 cm MAP, 7.8°C MAT) suggest that the development of rinds is inhibited in dry, continen- tal climates, especially where calcium carbonate ac- cumulates within the soil. The presence of carbonate implies that relatively little leaching has occurred, and carbonate tends to retard the weathering of pri- mary silicates (Grim, 1968, p. 518). The later con- clusion was supported by observations in several loca- tions of thicker weathering rinds on the upper, carbonate-free sides of stones than on the carbonate- coated undersides. WEATHERING-RIND DEVELOPMENT AND TIME 15 SUMMARY Climate, organisms (vegetation), parent material, topography, and time—the five soil-forming factors (Jenny, 1941)—are the most important factors af- fecting weathering processes (Jackson and Sherman, 1953, p. 241—248), including weathering-rind forma- tion. These factors are also complexly interrelated, and most—especially climate, organisms, and parent material—contain subfactors. The sampling procedures for this study were de- signed to reduce or isolate the variation in factors other than time. Sampling sites were located within a relatively narrow range of climate, partly because the calcic soils of dry climates are not conducive to weathering-rind formation. We restricted variation in rock type, the primary parent-material factor in weathering-rind formation, by sampling only basaltic and andesitic lithologies. Most sampling sites were topographically restricted to erosionally stable sites, commonly terrace surfaces or flat moraine crests. Vegetation at the sampling sites appears to be con- trolled by climate and soil parent material, which made independent evaluation of its direct effect difficult. We attempted to isolate and evaluate the variation in factors affecting weathering-rind development that was not eliminated‘by the sampling procedures. Of the factors other than time, variation in the rock type on which rinds were measured appears to have the most important effect. Variation in climate, especially precipitation and possibly also temperature, among sampling areas also appears to have a major influence on rind thickness. The direct effect of variation in other factOrs, such as vegetation, topography, and soil- matrix texture, seems comparatively minor for our sampling sites. Within a sampling area, only data for sites with relatively uniform rock type and climate were used in the analysis of the relation between weathering-rind thickness and time. For these data the effect of time is much more important than the effect of any of the other factors, and the time factor is the subject of the rest of this report. THE RELATION BETWEEN WEATHERING-RIND DEVELOPMENT AND TIME The ultimate goal of this section is to establish a functional relation between weathering-rind thickness and time, which can be used as an approximate numerical-dating method. The analysis begins with weathering rinds as a relative-age dating method and progresses to a numerical model of weathering-rind development with time. WEATHERING RINDS AS AN INDICATOR OF RELATIVE AGE Several workers have used weathering rinds on andesitic and basaltic rocks to discriminate between deposits of different ages (Crandell, 1963, 1972; Crandell and Miller, 1974; Birkeland, 1964; Kane, 1975; Porter, 1975, 1976; and Scott, 1977). Following the procedure of the latter three workers, the data in this study will be presented in terms of means and standard deviations. This procedure appears to be the most objective and representative way of character- izing rind development for a given sampling site. Other measures of rind development, such as maximum thickness, are less easy to justify as being represent- ative, even though there appears to be a reasonably consistent relation between mean and maximum rind thickness (Porter, 1975). In addition to becoming thicker with time, weather- ing rinds tend to become softer (“mushier”), with increasing stratigraphic age. Although this effect ap- pears to be systematic, we did not develop a quan- titative method of measuring this variable. When the weathering-rind-thickness data are plotted according to the stratigraphic ages assigned by previous workers (figs. 11, 12; references in fig. 3), the data group quite well. This grouping of weathering- rind data by geologic sequence clearly demonstrates that weathering rinds are an excellent indicator of relative age, and can be used effectively to differen- tiate deposits of different ages within local sequences. The consistency of results for the same age of deposit and the consistent differences between different deposits, within a sequence, strongly imply that rind thickness is controlled by some time function. In addi- tion, the data invite comparisons between areas; for in- stance, deposits of the last major glacial advance in each area all have average weathering-rind thicknesses of between 0.1 and 0.3 mm. Average rind thicknesses for each age of deposit within each area (fig. 13; table 1) were calculated by averaging the individual measurements for all sites on each age of deposit shown in figures 11 and 12. The data in figure 13 and table 1 are the primary input for the numerical model of weathering-rind development with time. 16 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES 3 5 Carson(1970) ' WEST YAKIMA ‘ — YELLOWSTONE, MOCALL, IDAHO VALLEY, PUGET LOWLAND' MONTANA WASHINGTON WASHINGTON (Porter, 1975) 3.0— .— ,. O 0) AAA g g [I 3°: < % u: 2.5— E w 3 _ E 3 3 £2, .. ‘5‘ g 5 i .E’ E 2.0— < 3 <3 3 _ z — r-H 8 % “ E 8 ., é , a g ”21 3'“; g 2 E :E 93 (—H r-H x 1.5— s g 9, l as _ g m :33 ‘1’ 2 (i J g c '5‘ g o g» a: E 5 '1‘: a? E 10— 9 i E 8’ : A ' {E s 5 *5; § Hr” - E r—H—L—x ‘- x % .1 3 a u m LL g ‘7- FM N F5 N v- 5 L—w—J E % E E O 0 E v AA Ha», g o n: g . g 0-5— g 8 3 '5 f A I _ 8 ’5 g E FM 5 m 8 fi % § § % if i g __ FIGURE 11.—Weathering—rind measurements on basalt. Each point and bar represents the mean :1 standard deviation, respectively, of from about 30 to 60 stones measured at one site. Stratigraphic names are those of previous workers (references, fig. 3). See text and Appendix C for lithologic descriptions. Areas are arranged east to west. Numbers for McCall area denote sequence of moraines; 1, outermost. STATISTICAL ANALYSIS The data presented in the previous section suggest that weathering rinds are an effective relative-age criterion, and the associated figures provide a quali- tative visual comparison of the effectiveness of weath- ering rinds in separating deposits of different ages. The purpose of this section is, first, to quantitatively evaluate the conclusion that rind thicknesses can separate different ages of deposits, and second, to ex- amine the amounts and sources of variation in the weathering-rind thickness data. These goals will help define the effectiveness of weathering rinds as a dating technique and will suggest the amount of confidence that can be placed in the method. The data analysis1 in this study consists of “explora- tion” and “approximate confirmation.” Tukey (1977, 1The Fisher K-Statistics, Transformation, and Analysis of Variance programs of the US. Geological Survey “Statpac” (unpub. data, 1979) were used in the analysis. preface) has described the relative merits of explora- tion, approximate confirmation, and confirmation modes in data analysis. Exact confirmation requires specific circumstances and is relatively rigid, whereas the flexibility of exploration and approximate con- firmation commonly makes them more useful in data analysis. The sampling procedures and data collection for this study were designed to explore the amounts and sources of variation in rind thickness, as these data were largely unknown before the study began. The sampling and measurement procedures allow rela- tively rapid and efficient data collection, permitting evaluation of a variety of factors affecting rind thickness. However, these procedures are not suffi- ciently rigorous for precise, formal statistical tests. Such confirmatory analysis would require experiments in which involved, formal sampling procedures were used, and in which some prior knowledge of the amounts and sources of variation could be used to WEATHERING-RIND DEVELOPMENT AND TIME 17 35‘ MOUNT RAINIER ”L TRUCKEE, CALIFORNIA ' r LASSEN PEAK, CALIFORNIA WASHINGTON V 30— 8 E‘- C _1 w i E E 0 l.— uJ 2.5r— _ E _J =1 2 E 20L :1) E: -- ’— g E 13, 5 Lu 5 g I g 1.5— I—Afifla If E — .— o : - Z a I g x 10~ _> g _ 8 .53 ‘3 m E 8 E O) .: LIJ I? E T E r—Bx Q‘s—’r—Afi . E r-H a é iii M {an “ MEI O FIGURE 12.——Weathering—rind measurements on andesite. Each point and bar represents the mean i 1 standard deviation, respectively, of from about 30 to 60 stones measured at one site. Stratigraphic names are those of previous workers (references, fig. 3). Closed circles, fine-grained andesite; open circles, coarse-grained andesite. See text and Appendix C for lithologic descriptions. Areas are arranged south to north. Data for Logan Hill deposits near Mount Rainier are off the diagram. design the necessary sampling pattern. In this study, lack of prior data on the amounts, nature, and sources of variation in rind thickness precluded a confirmatory analysis. However, the exploratory analysis accom- plished here should allow precise confirmatory statistical studies to be designed in the future. Two aspects of the sampling procedures, in par- ticular, invalidate precise statistical calculations: (1) sampling sites were not chosen by formal randomiza- tion processes from all possible sites meeting the definition of a suitable sampling site, and (2) the selec- tion of the location where the rind was measured on an individual stone was not formally random. Although we would argue that little or no bias has been intro- duced by our procedures, they do preclude exact prob- ability calculations for statistical tests. Nevertheless, comparisons of the magnitudes of differences and amounts of variation are valid, especially because we believe that our sampling procedures have introduced little bias into the data. This approximate- confirmation procedure permits many useful in- ferences to be drawn about weathering rinds. The following statistical analyses will be interpreted from this viewpoint of approximate confirmation. The definition of weathering rinds and the sampling procedures described earlier were conceived partly to facilitate the reproducibility of weathering-rind meas- urements. Reproducibility is an important property of any technique of measurement, and in most cases, the usefulness of a technique depends on the reproducibili- ty of the measurements. Thus, close replication of weathering-rind measurements by different workers is critical to the usefulness of rinds as a dating technique. R. M. Burke assisted us by independently sampling and (or) measuring rinds at a number of sites. We also compared our measurements in the Yakima Valley with those of Porter (1975), who used somewhat dif- ferent sampling and measuring procedures. In addi- tion, rinds were resampled and measured at a few sites at two separate times. The results demonstrate that 18 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES TABLE l.—Average weathering-rind thicknesses [Deposit names are those of previous workers (references, fig. 3); where not specified as terrace or outwash. deposits are till. or till and outwash undifferentiated; in andesite areas. fg. fine grained, cg, coarse grained. Thickness entries are the mean 11 SD. (standard deviation) of all measurements on a given deposit. In the Yakima Valley, data are from Porter (1975). for which standard deviations are apparently for means of site means, and for which the number of sites H is not given. Last three entries for Puget Lowland from Carson (1970). in which number of sites and number of measurements H are not given] Rind thickness Total No. of Rind thickness Total No. of Deposit :1 S.D. measure- sites Deposit :1 S.D. measure- sites (mm) ments (mm) ments West Yellowstone, Mont., basalts Mt. Rainier, Wash., andesites--Continued Deckard Flats Wingate Hill (fg) ------- 3.01:0.69 80 2 (recessional Pinedale). 0.1010.07 86 2 Wingate Hill (cg)-- 3.50:0.69 39 1 Pinedale terminus ------- 0.40:0.22 80 2 Logan Hill (fg)---- 5.68:1.23 56 2 Bull Lake --------------- 0.78_+_0.19 162 3 Logan H111 (cg) --------- 8.63:1.88 15 1 McCall, Idaho, basalts Puget Lowland, Wash., basalts Inner Pinedale ---------- 04510.14 164 4 Vashon ------------------ 0.23-_t-_0.lS 68 2 Inner Pinedale outwash-- 0.24:0-12 39 1 Low Fraser terrace —————— 0.21:0.14 120 3 Average --------------- 0-2510-14 High Fraser terrace ————— 0.71:0.30 40 1 Intermediate Pinedale--- 0-3110al7 97 3 Salmon Springs ---------- 0.99i0.36 124 2 Outer Pinedale ---------- 0.3810.17 155 4 Middle Salmon Pinedale outwash- 0.35:0-13 102 3 Springs terrace ------ LOT-£0.53 38 1 Average -------- O. 35i0.l6 Average --------------- l. 01:0.40 Intermediate ------------ 0.85:0.24 238 6 Helm Creek -------------- 3.3 :2.0 — - Helm Creek terrace ------ 2.6 i2.5 - - Inner Bull Lake ————————— l.53i0.30 74 2 Wedekind Creek ---------- 6 :3 — — Intermediate Bull Lake-— 1.58:0.46 181 4 Outer Bull Lake --------- l.71+0.39 99 3 Average ________ 1.61:0.41 Lassen Peak, Calif., andesites Tioga (fg) -------------- 0.17i0-09 78 4 Yakima Valley, Wash-, basalts Tioga (cg) -------------- 0.16:0.12 156 4 "Early Tioga" (fg) ------ 0.331-0.15 150 4 Domerie ————————————————— 0.25:0.04 225 - "Early Tioga" (cg) ------ 0-3610-19 192 4 Ronald ----------- $5210.06 193 - Bullfrog ————————— 0.71:0-12 279 - Tahoe (fg) -------------- 0-7210-23 237 6 Indian John ------------- 1.0510.l7 287 - Tahoe (cg) ------ 0.82:0-25 262 6 Pre-Tahoe (fg)-- l.06iO-31 89 3 Swauk Prairie-—-— 1.10:0-11 413 - Pre-Tahoe (cg) ---------- 1.7510-63 89 3 Thorp ------------ 13610.24 346 — Pre-Thorp(?) ___________ 2'78-t0'23 70 — Truckee, Calif., andesites Mt. Rainier, Wash., andesites 'I‘ioga (fg) -------------- 0.16:0.10 38 2 Tioga (cg) -------------- 0.18:0.13 40 2 Vashon (fg) ------------- 0-1910-13 94 3 Tahoe (fg)--- 0.21:0-09 155 4 Vashon (cg) ------ 0.27:0-17 28 l Tahoe (cg) -------------- $2210.14 138 4 Evans Creek (fg) -------- 0.16:0.10 80 4 Evans Creek (cg) -------- 0.1510.12 123 4 Donner Lake (fg) ———————— 0.93:0-24 106 3 Donner Lake (cg) -------- 0.97iO.23 103 3 Hayden Creekl (fg) ------ 1.37:0-43 84 2 Hobart (buried) (fg)--—- 0.75:0.22 31 1 Hayden Creek (cg) ------- 1.95i0.54 38 l Hobart (buried) (cg)---- 1.0010.30 39 l 1Although several Hayden Creek sites were sampled, the data for only two (C76—40, C78-116) are given, because they were the only loess-free, non-eroding sites sampled. the reproducibility of weathering-rind measurements by workers using consistent procedures is quite good (fig. 14). Specific topics investigated with statistical proce- dures include (1) the nature of distributions of sampled weathering-rind thicknesses (fig. 15), using moment statistics and the x2 distribution, and (2) the impor- tance of the variation in rind thickness with time com- pared to that with other variables, using analysis of Rinds from the other sites were somewhat thinner. variance and multiple comparison tests. The detailed statistical analyses were performed on the data from the McCall and Lassen Peak areas, because of the par- ticularly detailed sampling done in those areas. NATURE OF THE WEATHERING-RIND MEASUREMENT DISTRIBUTIONS Complete moment statistics were calculated for each sampling site; the statistics used were Fisher K-statis- WEATHERING-RIND DEVELOPMENT AND TIME 19 F———-— BASALT “F AN DESITE ———-—-*| lg McCALL YAKIMA PUGET TRUCKEE LASSEN RAINIER 3.5_ 0 (Porter, 1975) LOW- — 53 5, % LAND L; a g = 9 w ‘ _l ‘3 I: 3'OL E a. ’05 1 3.. f, 2 3 9.’ O O r: 0 to § 2 2 £3 E E % +°-° 5:“ ._ 2.5— m ; g g __ g m é’ g e 3 x 3: .— 3 2 é 2 a s z 2.0— E E 9 — -_ w ‘3» <0 % 3‘” 5 f3 2 s % s 3 E 2 E ‘2 $3); a: g a c '5 ._ x g (f) 1 5!— E a) ‘ ‘ § 5 5 S 3 g V 4— u E L L _‘ I- 0' 1% r: g 5 Tu G! g Q l ‘ E g g 3‘” E I E g 3 a; E <0 i co m a: E 3 E % c 2 e = — u 9 m 1.0— 2 8 g $1 in " — é; a 2 3 g E ‘— )— I: a 0 ,, E E 5 l X,’ x E. c '33 a 3 I SI: (D a) m g e 0 5 E 5 ° 3 + z 9 o : g 0 ~ ".3 s g 8% 0 a f» a > ., ‘ E _ o >_, E o I- o: c x Q — i: ‘9 g 3 ¢ H i’ % " ‘“ ° l) i l) i H o f FIGURE 13.—Average weathering-rind thicknesses for the sequence of tills and terraces recognized in each of the principal sampling areas. Each point and bar represents the mean :1 standard deviation, respectively, of all rind measurements for each age of deposit in each sampling area. Stratigraphic names are those of previous workers (references, fig. 3). In areas of andesitic rocks, closed circles, fine- grained andesite; open circles, coarsegrained andesite. See text and Appendix C for lithologic descriptions. Areas arranged as in figures 11 and 12. Arrows indicate data off the diagram. tics, including gl (skewness) and g2 (kurtosis) (Fisher, 1954). The g1 and g2 statistics, which have expected values of zero for normal distributions, were used to examine the types of distributions represented by weathering-rind measurements. The results (table 2) indicate that the distributions of weathering-rind measurements have a slight tendency to be skewed to the left (gl positive); measurement distributions of basalt at McCall and of fine-grained andesite at Lassen Peak tend to be platykurtic (flat, g2 negative), whereas measurement distributions of the coarse-grained ande- site at Lassen Peak tend to be leptokurtic (peaked, g2 positive). Confidence limits for g1 and g2 values calculated for rind-measurement distributions can only be estimated, because of the lack of rigor in the measurement methods (p. 17), and because the variances of g1 and g2 are precise only for sample sizes greater than about 100 (Griffiths, 1967, p. 262). However, these con- fidence levels are useful for comparison. Ten of the 85 calculated gl values for the McCall and Lassen Peak areas exceed the confidence limits (Griffiths, 1962, a= 0.05) for the expected value of zero for normal distributions. Chi-square statistics were also calculated for the 10 distributions with high gl ab- solute values. Only four of the X2 values exceeded the confidence limits (a= 0.05) for normal distributions. These comparisons, while not rigorously precise, sug- gest that weathering-rind distributions can reasonably be considered normal distributions. The skewness (positive) of the distribution is especially apparent for sampling sites with very thin 20 MEAN RIND THICKNESS, IN MILLIMETERS 3.0 . I I I I I / / 2.5— / _ / / O / 2.0— / _ fi/ ~\ 1.5— o/ — / D / EXPLANATION 1.0— + . A — + + I o B E] C 05— 3/ch A D — 3,33 + E 0 I l I I I 0 0.5 1.0 1.5 2.0 2.5 3.0 MEAN FIIND THICKNESS, IN MILLIMETERS FIGURE 14.—Reproducibility of weathering-rind measurements. Data collected by S. M. Colman are plotted on the abscissa. In A, 1975 measurements are plotted on the abscissa. A, samples taken and measured by S. M. Colman in 1976 versus samples taken and measured by S. M. Colman in 1975 at the same site; B, measurements by K. L. Pierce versus those of S. M. Colman; C. measurements by R. M. Burke (written commun., 1976) versus those of S. M. Colman; D, measurements by Porter (1975) versus those of S. M. Colman; E, samples collected by K. L. Pierce versus those collected by S. M. Colman at adjacent sites; all measurements by Colman. 20 075-06 FREQUENCY E; 075-79 FREQUENCY C76-24 0 0.5 FIIND THICKNESS, IN MILLIMETERS 075-100 2.0 i . .0” . RIND THICKNESS, IN MILLIMETERS WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES TABLE 2.—Skewness (g,) and hurtosis (g,) for weathering-rind-thick- ness distributions Statistic Number Number Data set positive negative McCall, Idaho —————— g1 26 7 Lassen Peak, Calif. g1 16 1 (fine-grained). Lassen Peak, Calif., 91 15 2 (coarse—grained) . McCall, Idaho —————— 92 9 24 Lassen Peak, Calif. 92 6 ll (fine—grained) . Lassen Peak, Calif. g2 13 4 (coarse-grained) . weathering rinds (fig. 15). In an attempt to reduce the skewness in the distributions, the data were subjected to a log transformation and the moment statistics were recalculated. Compared to the untransformed data, the positive and negative values of g1 and g2 are more evenly distributed for the log transformation data, and tend to have lower absolute values. Thus, based on g1 and g2 statistics and on the )8 distribution, both the linear and log data fit the normal distribution model quite closely. Analysis of variance, discussed in the next section, was calculated for both the linear and log data; the conclusions that can be drawn from the analysis of the two sets of data are identical. However, the fact that the data are slightly 076-66 1.0 0 0.5 1.0 076-02 076-56 075-126 i451: . 1.5 0.8 1. 3.2 0.4 2.0 2.8 1.5 1.2 FIGURE 15,—Selected histograms of weathering-rind measurements. Sampling site number is given above each histogram; mean and standard deviation for each site are given in Appendix A, and site locations are given in Appendix B. Note different rind-thickness scales. WEATHERING-RIND DEVELOPMENT AND TIME 21 closer to a log-normal distribution than to a linear- normal distribution is significant and will be a useful piece of evidence in the construction of rind thickness versus time curves. ANALYSIS OF VARIANCE The nested sampling design for the McCall (fig. 16) and Lassen Peak areas was chosen so that variation in rind thickness from several sources could be compared using analysis of variance. The McCall sampling de- sign has four nested subdivisions: (1) ages, (2) moraines within each age, (3) sites within each moraine, and (4) measurements within each site; the Lassen Peak sampling design has three subdivisions: (1) ages, (2) sites within each age, and (3) measurements within each site. The importance of variance contributed from each of these levels can be evaluated by analysis of variance procedures. The calculations (table 3) were made using the general methods of Anderson and Ban- croft (1952) and Snedecor (1956) on the linear data. INNER OUTER 3 PINEDALE PINEDALE E 1570 '3 t t E 1550 E Z 1530 __ 1510 Z 9 '— < > LU _l IJJ w 3 T I: UJ l.— U] .5. .J .1 i 2 — Z (I5 0) Lu 2 X 9 F" ill 1 o T 1 i z {I H E l} E c o _ 0 | 1 INTERMEDIATE “ lglfll ‘ The general model used in the analysis of variance is a nested oneway model in which any individual measurement X(i, j, k,...r) has the value X(i, j, k,...r) = M + A(i) + B(i, j) + at j, k) +...+E(i, j, k,...r) where M is the grand mean; A, B, C,...E are random and normally distributed with zero means and variances V(A), V(B), V(C),...V(E); i, j, k,...r are the nested levels in the subdivision. Each F-ratio test in the analysis tests the null hypothesis: “These subsamples are random samples from the same normal population.” The nested levels in the sampling design isolate sources of variation and allow them to be compared. Measurement errors are confined to the measurement level, whereas local differences in rock type, climate, and vegetation are contained in the site and moraine levels. Differences in age, of course, are contained in the age level. For the McCall data, the variation in rind thickness among ages is very large (F=182) compared to that among moraines, and the variation among sites is large (F=15) compared to that within a site (among BULL LAKE AGES MORAINES — T MEASUREMENTS ? 4| KILOMETERS FIGURE 16.—Diagrammatic sketch of the nested sampling design for the deposits near McCall. Idaho. Sampling was based on mapping by Schmidt and Mackin (1970). Short line pattern. till; stipple, outwash. Measurements are summarized as the mean :1 standard deviation rather than the branches for the 30-60 measurements at each sampling site. Kilometer scale is approximate. 22 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES TABLE 3.—Ana1ysis of variance, McCall and Lassen Peak data Analysis of variance Components of variance Test of hypothesis Sum of Degrees of Mean Unit Variance Source squares freedom square Level size component Percent F—Ratio Estimated p1 McCall (basalt) Among ages ----- 314.040 2 104.680 1 3 0.36185 78.62 182.060 0.00018 Among moraines— 4.025 5 .575 2 8 .00513 .00 .544 .378 Among siteS--—— 21.132 18 1.057 3 26 .02646 5.75 14.690 1.8x10'18 Within sites-—- 81.633 958 .072 4 984 .07192 15.63 Total -------- 420.830 983 0.46024 100.00 Lassen Peak (fine-grained andesite) Among ages ----- 44.323 3 14.774 1 4 0.11971 64.74 29.719 2.1x10_6 Among sites-——— 6.462 13 .497 2 17 .01494 8.08 9.891 3.2x10'12 Within sites—-— 24.778 493 .050 3 510 .05026 27.18 Total ———————— 75.563 509 0.18491 100.00 Lassen Peak (coarse—grained andesite) Among ages----- 167.360 3 55.788 1 4 0.37108 70.55 31.969 7.3x10_7 Among sites---- 22.686 13 1.745 2 17 .04968 9.45 16.585 1.3x10-16 Within sites——- 60.396 574 .105 3 591 .10522 20.00 Total -------- 250.452 590 0.52598 100.00 1p, probability that the null hypothesis is true. measurements). However, the variation among moraines is small (F=0.5) compared to that among sites. For both the Lassen Peak fine- and coarse- grained data, the variation among ages is large (F=30 and 32) compared to that between sites, and the varia- tion among sites is large (F=10 and 17) compared to that within a site (among measurements). All com- parisons, except that between moraines and sites at McCall, allow for only a slight possibility that the null hypothesis is true. The most important conclusion from the analysis of variance is that, within a given study area, the varia- tion in rind thickness between different ages of deposits is more important than all other sources of variation, including variation due to differences in rock type, climate, and vegetation. The components-of- variance analyses in table 3 suggest that differences in age contribute about 65—80 percent of the total rind- thickness variance. Another important conclusion is that, at McCall at least, any differences in rind thickness between moraines of one stratigraphic unit are not important compared to other sources of varia- tion in rind thickness. MULTIPLE COMPARISONS The analysis of variance indicates that important differences in average rind thickness exist among sites and among ages of deposits, but it does not indicate which differences are important. Multiple compar- ison tests allow direct comparisons of differences in rind thickness and determine which differences are important. The method used in this study is that of Scheffé (1959). The derived statistic for comparison is BS: ((82) (gf) (k-l) (Fk—1,No—k, 1—a))‘/’ where D8 is the significant, or critical, difference for the comparison; S2 is the mean square residual (error mean square in the analysis of variance); C, is the coefficient of comparison of sample mean t; WEATHERING-RIND DEVELOPMENT AND TIME 23 Nt is the number of observations in sample t; k is the number of samples in the class being ex- amined; F is the F-ratio for the given probability and degrees of freedom; No is the total number of observations in the class being examined; and a is the probability level. For comparison of two means, the statistic reduces to 1 1 Ds= «82)(71 + a) (Ia—1) (Fr—1, No—k, 1-01))” The multiple comparison tests (table 4) prove the im- portance of age (time) in weathering-rind development. All differences in mean rind thickness between stratigraphic ages of deposits exceed the critical dif- ferences (Ds) calculated for a probability of 0.05 by Scheffé’s method. Differences in mean rind thickness between closest pairs of ages exceed Ds by factors ranging from 1.4 to 13.3. Clearly, weathering-rind thickness effectively discriminates between different ages of deposits. For moraines within one age of deposit, the conclu- sions are the opposite of those for ages. None of the dif- ferences in mean rind thickness between moraines of one stratigraphic age at McCall (the only area where moraines were tested) exceed Ds, except for one case. This indicates that at McCall, moraines of each stratigraphic unit are all similar in age. The exception is the outermost Bull Lake moraine, which has a mean rind thickness that exceeds Ds in comparisons with the other two Bull Lake moraines by factors of 2.0 and 3.4. Because this moraine cannot be distinguished from the other two by any method other than weathering rinds, it remains grouped with the other two Bull Lake moraines as a map unit. For sites within one stratigraphic age of deposit, comparisons of mean rind thicknesses yield mixed results (table 4). Generally, for relatively young deposits, the differences between sites of one age do not exceed D8, suggesting that the samples come from a single age population. In contrast, differences in mean rind thickness for sites of the same stratigraphic age within older deposits exceed Ds in some cases. However, the majority of comparisons do not exceed D5, and those that do commonly contradict the stratigraphic sequence of moraines within the deposit. In some cases, sites on different moraines have dif- ferences in rind thickness that do not exceed Ds, whereas the differences that exceed D8 are commonly for sites on the same moraine. Therefore, the different populations suggested by the differences in rind thickness that exceed D3 are probably not produced by differences in age but by local differences in other fac- tors such as climate, rock type, or surface stability. SUMMARY OF STATISTICAL ANALYSIS Statistical analysis demonstrates that weathering rinds are an excellent quantitative indicator of age. The rind measurements can be closely reproduced, and they tend to be nearly normally distributed, with a tendency for positive skewness. Analysis of variance indicates that, within a sampling area, the age of the deposit sampled is the most important source of varia- tion in rind thickness. Multiple comparison tests demonstrate that, within a sampling area, (1) all dif- ferences in mean rind thickness between different stratigraphic ages of deposits are important, (2) dif- ferences in mean rind thickness between different moraines of the same stratigraphic age are generally TABLE 4,—Summary of results of Scheffé’s multiple comparison test (01:0.05) Number Number not Comparison group1 exceeding exceeding DS 08 Comparisons between sites McCall inner Pinedale-—- 0 10 McCall outer Pinedale——- 0 45 McCall intermediate ----- 6 15 McCall Bull Lake -------- 17 I9 Lassen (fg) Tioga ——————— 0 6 Lassen (fg) early Tioga— 2 4 Lassen (fg) Tahoe ------- 3 12 Lassen (fg) pre-Tahoe--- 2 1 Lassen (cg) Tioga ——————— 0 6 Lassen (cg) early Tioga— Q 6 Lassen (cg) Tahoe ------- l 14 Lassen (cg) pre—Tahoe—-—— 2 1 Comparisons between moraines McCall inner Pinedale--- 0 3 McCall outer Pinedale-—— 0 3 McCall intermediate ————— 0 l McCall Bull Lake ———————— 2 1 Comparisons between ages McCall —————————————————— 6 0 Lassen (fg) ————————————— 6 0 Lassen (cg) ------------- 6 0 lfg, fine grained; cg, coarse grained. 24 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES negligible, and (3) differences in mean rind thickness between sites of the same stratigraphic age may be im- portant, but the differences are largely due to factors other than age. NUMERICAL MODELS OF WEATHERING-RIND DEVELOPMENT WITH TIME The extraction of numerical-age information from weathering-rind measurements can be done in two ways: (1) rind-thickness ratios, and (2) rate curves. Although the ratio of the rind thicknesses for two deposits does not provide numerical ages for the deposits, such ratios can provide very useful informa- tion on the magnitude of the age difference between the deposits. In addition, if the numerical age of one deposit is known, rind-thickness ratios provide limits to the possible ages of other deposits in the same area. Rate curves have the major advantage of allowing numerical ages to be calculated directly from the data, but the rate curves need to be defined and calibrated. Because of the paucity of independent age determina- tions, definition of rate curves based on several deposits within a sequence requires major assump- tions whose validity cannot at present be proven. In the following sections, we will first examine rind- thickness ratios as a means of estimating minimum and maximum probable age differences between deposits, and then we will attempt to develop rate _ curves using dated sequences from West Yellowstone and elsewhere. KIND-THICKNESS RATIOS The ratio of rind thicknesses from two deposits in the same sequence provides a simple index to their age relations. We can estimate with considerable con- fidence the minimum and maximum age ratios in- dicated by these rind ratios. Therefore, from the rind- ratio data for two deposits, we can infer either limits on their age ratio, or, if one age is known or assumed, we can infer the minimum and maximum value for the other age. Within a given local sequence of deposits, the factors of climate, vegetation, topography, and parent material at the sampling sites were generally held nearly constant; time is the only remaining major variable affecting rind thickness. However, because Quaternary climate has fluctuated, the rate of weathering-rind development may also have changed, especially between glacial and interglacial times. Therefore, deposits of different ages have been sub- jected to different climatic histories and may have weathered under different average climates. With our present information, we are not able to calculate this effect. However, the decrease in the rate of rind forma- tion due to colder temperatures during glacial times would tend to be compensated for by an increase in rate due to a probable concomitant increase in soil moisture. Assuming that the total effect of climatic change on the rate of rind development is minor, and for present purposes can be neglected, we now attempt to bracket the maximum and minimum age relations indicated by the rind ratios. Three basic types of functions can be postulated for the relationship between rind thickness and time: 1. linear: d = kt or t = kd 2. logarithmic‘: d = k log t or t = k(10)d 3. power function: d = ktl/n or t = kd" where d = rind thickness, at = time, n is an unspecified exponent, and k is a rate factor due to variables other than time. In each case, calculation of rind thickness ratios (dl/dz) eliminates k by division and leaves the age ratios (tl/tz) as a function of rind thicknesses only: 4. linear: d,/d2 = t1/t2 5. logarithmic: dlld2 = log t,/log t2 6. power function: d,/d2 = (tl/t2)1’" Rind thickness ratios for deposits sampled in this study (table 5) can therefore be used to estimate age ratios within each sampling area, where the value of the rate factor k is approximately constant. In the past, the rate of change of features due to weathering has been assumed by some workers (for ex- ample, Birkeland, 1973) to be constant, especially in the absence of independent age estimates; but many workers now believe that the rate of change of most weathering features decreases with time (Cemohouz and Solc, 1966; Ollier, 1969, p. 252; Carrara and An- drews, 1975; Birkeland, 1974, p. 176; Winkler, 1975, p. 151; Pierce and others, 1976; Porter, 1976). A cons- tant rate corresponds to a linear function (eq. 1), whereas a decreasing rate can be represented by either a logarithmic curve (eq. 2), or a power function curve (eq. 3( with n >1. The rate of change of some weathering features may decrease to values approaching zero, in which case a steady state is reached. In table 5, the rind-thickness ratios are presented in two forms: (1) the simple rind-thickness ratio, which is appropriate for estimating the age ratio if rind thick- ness is a linear function of age, and (2) the rind ratio squared, which is appropriate for estimating the age ratio if rind-thickness is a power function (n=2) of age. 1Use of the base 10 is convenient but arbitrary; the natural base (2) or other bases would be equally valid for the general case. WEATHERING-RIND DEVELOPMENT AND TIME 25 TABLE 5,—Rind-thickness ratios Rind ratio Rind ratio squared (dl/dz) (dl/dZ) Deposits (minimum age (maximumfl) age ratio) ratio) West Yellowstone (Deckard Flats/Pinedale/Bull Lake) 16 61 * Deckard Flats-Pinedale teminus——-— * Deckard Flats-Bull Lake—-----—------ {cub OQO Pinedale terminus-Bull 1ake—-------- 3.8 McCall (Pinedale/Internedlate/Bul1 Lake) * Inner Pinedale-intermediate Pinedale 1.2 1.5 *Internediate Pinedale-outer Pinedale 1.3 1.6 Pinedale average-Intemedlate--——--- 3. O 8. 8 Pinedale average-Bull Lake average-- 5-0 25 Intermediate-Bull Lake average ------ 1.7 2.9 Inner Bull Lake-outer Bull Lake ————— 1.1 1.3 Yakima Valley (Domerie/Ronald/Bullfrog/Indian John/Swank Prairie/Thorp/pre-Thorpfl )) * Donnie-Ronald ---------------------- 2.1 A. 3 '1 Damerie-Bullfrog-—- -—-- 2-8 8-1 Ronald-Bullfrog------ ———— 1 . A 1 . 9 Bullfrog-Indian John ------ ---- 1.5 2.2 Indian John-Swauk Prair1e1------——-- 1.1 1.2 Swauk Prair1e-Thorp-—o——-----————-—- 1.8 3.2 Thorp-pre-Thorp('l) ------------------ 1.4 2.0 Mount Rainier (Evans Creek/Hayden Creek/Wingate Hill/Logan 11111) 82 356 o .4 Evans Graek-Hayden Creek ——————————— 9 lib/ans Creek-Hingace H111 ____________ 9 Hayden Creek-Wingate 1-1111 ___________ 2, 1 V» ,_. l lo.3 Wingate Hill-Logan Hill--———------— .9 3.6 Puget Lowland (Vashan—Low Fraser terrace/ High Fraser terrace/Salmon Springs) * Low Fraser terrace-Vashon—------—-- 1.1 1.2 * Low Fraser terrace-High Fraser terrace—-------——-—-----—— 3.1. 11 * Vashon-Salmon Springs-——------———--- MA 19 High Fraser terrace-Salmon Springs-- 1.1. 2.0 Lassen Peak (Tings/"Early Tioga"/Tahoe/pre-Tahoe) t Hogs-"early" Tioga----———---————-__ 1 , g Tioga-Tahoe ------------------------- 1, , 2 18 Tioga-pre—Tahoe ————————————————————— 6 2 l! "Early Tiaga"-Tahoe-—-—-------------- 2.2 4.8 "Early Tioga"-pre-Tahoe 3. 2 10 Tahoe-pre-Tahoe --------------------- 1 . 5 2. 2 Truckee (Tings/Tahoe/Donner Lake) Tings-Tahoe -------- 1 . 3 1 . 7 Mega-Donner Lake— 5 . 8 31. Tahoe-Donner Lake- (“lo 20 1Swaul: Prairie deposits may have anonalous1y thin rinds due to a thick loess cover. Because the rate of rind formation almost certainly decreases with time, as is argued in the next section, the simple rind-thickness ratio (thicker rind to thinner rind) is a minimum estimate of the age ratio. The expo- nent of n=2 is appropriate for simple diffusion reac- tions, such as obsidian hydration (Friedman and Smith, 1960). Rinds appear to form by a combination of oxidation, hydrolysis, and solution processes (Col- man, 197 7), for which an exponent of two is probably a maximum; thus the rind ratio squared is probably near the upper limit of the age ratio. Therefore, table 5 pro- vides the probable upper and lower limits of the age ratios of the listed deposits. As an example of the utility of table 5, Pinedale and Bull Lake terminal moraines near West Yellowstone have rind thicknesses of 0.40 and 0.78 mm respec- tively, for a ratio of about 2, and a ratio squared of about 4. Their ages, independently determined by Pierce and others (1976), are about 35,000 and 140,000 yr, respectively, for an age ratio of 4.0. Thus table 5 can be used to place limits on the age difference be- tween the West Yellowstone Pinedale and Bull Lake deposits independently of other age estimates. Our best estimate for rind thickness versus time functions, derived in the next section, almost invariably produces age ratios between the limits of the rind ratio and the rind ratio squared proposed in table 5. The rind ratio approach to extracting numerical age information from rind data is presented before we give our preferred rate-curve model. The assumptions used in estimating the maximum and minimum age ratios are few, and, we think, readily justified. Thus, the age constraints provided by rind ratios are relatively definitive data. Age inferences or correlations incom- patible with the constraints provided by the rind ratios are therefore open to serious question. TIME-STRATIGRAPHIC NOMENCLATURE Because of lack of agreement in the usage of time ter- minology for the Quaternary, we will define the time terms that will be used in the following sections on numerical ages and correlations. Our primary reference is the marine oxygen-isotope record (Emiliani, 1955, 1966; Broeker and van Donk, 1970; Emiliani and Shackleton, 1974; Shackleton, 1977a), which has been shown to be dominantly a record of worldwide ice volume (Shackleton and Opdyke, 1973). Figure 20 (p. 32) shows four such oxygen-isotope records plotted on a common time scale. We consider the last inter- glaciation to be equivalent to all or part of isotope stage 5, the period independently dated as between about 75,000 and 125,000 yr ago. The Toba Tuff in North Sumatra has been dated by K-Ar as 7 5,000 yr old, and occurs in deep-sea cores at the stage 4—5 boundary (Ninkovich and others, 1978); oxygen- isotope values for stage 5e and for the corals at the high sea stand in Barbados (dated by U-series methods as 125,000 yr old) demonstrate their equivalence (Shackleton, 1977b). The isotopic record demonstrates that there were fluctuations in ice volume during\stage 5, and some workers have argued that only the earliest part, stage 26 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES 5e, represents the last interglaciation, and that stages 5b and (or) 5d represent early phases of the last glacia- tion, especially at high latitudes (see references in Suggate, 1974). For temperate latitudes, such as the locations of the sampling areas in this study, we provi- sionally accept the arguments of Suggate (1974) that the last major interglacial-to—glacial transition oc- curred at the boundary between stages 5 and 4, about 75,000 yr ago. This agrees with the estimates of Willman and Frey (1970) and Dreimanis and Karrow (1972) for the beginning of the Wisconsin Glaciation. The temperate-latitude Wisconsin thus encompasses isotope stages 2—4. In our usage, early Wisconsin refers to glacial culmination(s) within stage 4, about 60,000 to 70,000 yr ago, and late Wisconsin refers to glacial culmination(s) within stage 2, about 12,000 to 22,000 yr ago. Our mid-Wisconsin glacial advances oc- curred during' the middle part of stage 3, between about 30,000 and 50,000 yr ago, and would be approxi- mately correlative with the late Altonian advance in the mid-continent, which culminated about 32,000 yr ago (Willman and Frey, 1970; Dreimanis and Karrow, 1972). Most oxygen-isotope records indicate that ice volume during stage 6 (about 130,000—150,000 yr ago) was at least as great as that during any time since. We consider glacial deposits correlating with stage 6 to be latest pre-Wisconsin, sometimes called the penulti- mate glaciation. RATE CURVES FOR WEATHERING-RIND THICKNESS The paucity of independent numerical ages for Quaternary deposits in the Western United States pre- sents a major obstacle to determining the exact rela- tion between rind thickness and time. The only glacial sequence examined in this study for which there are numerical ages older than the last major advance is that at West Yellowstone. This sequence has been dated by Pierce and others (1976) using combined obsidian-hydration and K-Ar dating. A curve for the development of weathering rinds with time has been constructed for basalts in Bohemia by Cemohouz and Solo (1966), using seven ages rang- ing from 600 yr to about 2,000,000 yr. They do not state the basis for the ages, so it is difficult to evaluate their data; but their curve fits their data points ex- tremely well (fig. 17). This rate curve is of the form d=A log (1 +Bt) where d=rind thickness, t=time, and A and B are constants. 2»4I]I]1]I[1)I[IIIIIIIII 2'21—BOHEMIA ((YDERNOHOUZ+ 50m, 1966) 20— d=4.64 LOG (1+0.01 t) .8 + WEST YELLOWSTONE d : LOG (0.734- 0038 t) l | l l i 1 l l i l l l l Jml l I l 20 4o 60 so 100 120 140 160 180 200 220 TIME (103 YEARS B. P.) Ill Illlll RIND THICKNESS, IN MILLIMETERS l l l l FIGURE 17 —Weathering- -rind thickness versus time curves for Bohemia and West Yellowstone. The Bohemia curve is from Cer- nohouz and Solo (1966), and is based on the four points shown in ad- dition to three points with ages greater than 220, 000 yr. The West Yellowstone curve is based on the logarithmic form of the Bohemia curve, on obsidian-hydration ages (Pierce and others, 1976), and on rind-thickness data from this study. The difference between the two curves results from differences' in rock type, climate, and other factors between the two areas. Error bars on data points are from Cemohouz and Sole (1966) for Bohemia; for West Yellowstone, time error bars are from Pierce and others (1976) and rind- thickness er- ror bars are :1 stande deviation (this study, table 1). The West Yellowstone data (fig. 17) demonstrate that rind thickness is not a linear function of time; the rate of rind formation clearly decreases with time. We attempted to fit (by inspection) various types of power function and logarithmic curves to the data, and of these curves, a logarithmic curve of the same form as the curve for Bohemia (Cemohouz and Sole, 1966) ap- peared to fit the data best. A date of about 35,000 yr was used for the Pinedale deposits at West Yellowstone, rather than about 30,000 yr as calculated by Pierce and others (1976) using a maximum temperature correction. The rind thickness for the terminal Pinedale deposits is somewhat higher than would be expected for a loga- rithmic curve through the data for the other West Yellowstone deposits. This may be due to the fact that, unlike Deckard Flats (recessional Pinedale) and Bull Lake deposits, which are basalt rich, the terminal Pinedale deposits consist of scattered basalt clasts in a rhyolite-rich deposit. The rhyolitic material appears to alter very slowly, and the weathering in these deposits seems to be concentrated in the scattered basaltic clasts, which may thus exhibit slightly thicker than ex- pected rinds. Unlike the Bohemia curve, which intercepts the origin, the West Yellowstone curve has been con- structed with the zero rind-thickness intercept at 7,000 yr (fig. 17). The curve with this intercept is meant to approximate a curve with two segments; that is, one WEATHERING-RIND DEVELOPMENT AND TIME 27 whose rate begins slowly but which eventually attains a logarithmic form (fig. 18). Three arguments suggest that a curve similar to curve C in figure 18 is ap- propriate. First, some time is necessary for weathering processes, especially oxidation, to reach the depths sampled in this study. Second, because weathering rinds are initially a surface phenomenon, it is reasonable to expect that much of the early surface weathering will take place on grains in the soil matrix, which have a much greater surface area than the larger clasts. Third, the fact that most of the late glacial deposits, on the order of 12,000—15,000 yr old, have very thin weathering rinds (for example, 0.1 mm for Deckard Flats (recessional Pinedale) deposits near West Yellowstone) suggests that the early stages of rind formation are very slow at the depths sampled. The figure of 7,000 yr for the intercept may not be precisely applicable to all sampling areas because of differences in climate and soil parent material, but in many cases variations due to these factors tend to off- set each other. Also, the ages estimated from the rind curves for deposits older than the last major glacial ad- vance change only slightly if the intercept value is changed. Therefore, 7 ,000 yr was used as the intercept for all the rate curves; inaccuracies in age estimates due to the intercept value are small compared with other uncertainties in the rate curves. Birkeland (1974, p. 176) presented several inflected curves similar to curve B (fig. 18) as models for weathering and soil development processes. Winkler (1975, p. 148—151) reviewed several weathering studies and concluded that weathering rates may initially in- crease exponentially, and probably eventually decrease exponentially. The fact that the distributions of weathering-rind measurements tend to be log normal supports the logarithmic form of the rate curve. Because climate affects rind development, fluctua- tions in climate in the past have had an effect on the rate of rind formation. Because data for evaluating this effect are not available, the rate curves that will be constructed instead average the climate in each area through time. The sampling areas are all in the same basic weather pattern today, and the parallelism of past and present snowlines in southern Washington State (Porter, 1964) suggests that general climatic pat- terns have not changed drastically. If climatic change has been approximately concordant for the areas sampled, the rind curves are valid for comparison and correlation purposes. The pluvial lake record of the Western United States indicates that precipitation during glacial times could not have been much less than that of the present in- terglacial (G. 1. Smith, oral commun., 1977). Similar precipitation and colder temperatures would have resulted in greater effective soil moisture in glacial times than in interglacial times. The effects of lower temperatures and the effects of higher effective soil moisture (or vice versa) on weathering-rind develop- ment are offsetting. These arguments suggest that, if the actual rate curves could be plotted in detail, they probably would fluctuate around the average rate curves that will be presented, but the fluctuations probably would be small and concordant between curves. The fact that the two curves in figure 17 indicate dif- ferent rates of rind formation is reasonable because of differences in climate, rock type, and other variables between the two areas. Because factors affecting rind- development rates are different for each area, a separate curve of rind thickness versus time will be developed for each sampling area in this study. The form of these curves will be the same as that for the dated model for West Yellowstone (fig. 17). The curves will be calibrated using one deposit in each area as a calibration point whose age will be independently infer- red from other data. The resulting rate curves will then be used to estimate the ages of the other deposits in each area. The calibration procedure empirically eliminates the need to account for the variation due to factors other than time, assuming that these factors are reasonably constant within each area. In the absence of independent numerical ages, the calibration point for each curve must be inferred by correlation. The ages of the deposits representing the last glacial maximum (oxygen-isotope stage 2) are known or inferred with greater certainty than those of .0 at _( .0 on l l .0 b l l P m .0 N O '.. RIND THICKNESS, IN MILLIMETEHS O O _‘ O 20 30 40 TIME (103 YEARS B. P.) FIGURE 18.—-Conceptual models of the weathering-rind thickness ver- sus time function. A, model used by éemohouz and Solo (1966); B, conceptual model used in this study for early stages of rind development; C, simple log function, similar to A, used to approx- imate B. Rind thickness scale approximate. 28 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES any other deposits in the areas sampled. Numerical age estimates exist for some of these deposits, and their correlation is relatively straightforward. However, these deposits were unsuitable for use as calibration points for the following reasons: (1) the uncertainty of individual rind measurements (i0.1—0.2 mm) is of the same magnitude as the average rind thickness for these deposits (0.1-0.4 mm), and (2) the age of these deposits is relatively close to zero, so that a small uncertainty in their position as a calibration point results in large uncertainty in the position of the rest of the curve. A more useful calibration point is the deposits repre- senting the glacial maximum about 135,000—140,000 yr ago, just prior to the last interglaciation. These deposits correspond to oxygen-isotope stage 6, and to dated times of glacial maxima in Hawaii (Porter and others, 1977) and at West Yellowstone (Pierce and others, 1976). Most oxygen-isotope records indicate that ice volumes during stage 6 were at least as great as those during any time since. (For example, see fig. 20.) Therefore, it seems reasonable that moraines or terraces representing stage 6 should be preserved in most areas, although exceptions are known (for exam- ple, Pierce, 1979). Deposits of about this age also appear to have a minimum percent-error in weathering- rind measurements, and are near the middle of the apparent useful range of rind thickness (table 2); they are thus a convenient calibration point. We have assigned this age to a number of sampled deposits based on soil development, morphology, sequence of deposits, loess distribution, terrace heights, and other relative-age indicators (table 6), in addition to stratigraphic relations. These data are primarily those described by previous workers in each of the study areas (references, fig. 3), supplemented by our own observations. On the basis of the criteria listed in the preceding paragraph, the following deposits are considered cor- relative: Bull Lake at West Yellowstone, Bull Lake near McCall, Indian John in the Yakima Valley, pre- Tahoe near Lassen Peak, and Donner Lake near Truckee. These correlations appear to be relatively sound, but correlations in the Puget Lowland and near Mount Rainier are less certain for reasons that will be discussed later, in the section on correlations. Two interpretations will be presented for these areas, cor- responding to a calibration age of either early Wiscon- sin (65,000 yr) or pre-Wisconsin (140,000 yr) for the Salmon Springs and the Hayden Creek deposits. The correlations used for calibrating ages are for the most part consistent with the opinions of previous workers in these areas, as expressed both in the origi- nal references (fig. 3) and in later communications (S. ‘C. Porter, written commun., 1976; K. L. Pierce, written commun., 1976; P. W. Birkeland, written com- TABLE 6.—Characteristics of deposits considered to be about 140,000 yr old (oxygen-isotope stage 6) [Starred entries, observations of authors: other entries from references. figure 3] Area Depth of Maximum (MAT, MAP)1 Deposit oxidation hue Bt horizon Loess2 Morphology (In) West Yellow- Bull Lake ——————— *1—2 7.5—10YR Moderately 0.3-1 m Subdued. stone (1.7, developed, (b). 50). 15-30 cm thick. McCall —--do ——————————— *2 *5—7.5YR Well developed, Locally 2 m* Subdued.* (4.4, 65). 50 cm thick. (b). Yakima Valley Indian John 1-3+ 7.5YR Well developed, 1—3 m Very (7.9, 55). (Porter, 1975). 20—30 cm thick, (b). subdued.* Truckee Donner Lake ----- 3 7.5YR Well developed, None ———————— Do. (6.0, 80). 50 cm thick. Lassen Peak Pre—Tahoe ——————— 5 SYR Well developed-—-- -—-do ------- Very (7, 120). subdued. Mt. Rainier Hayden Creek3--— 2 7.5-10YR Weakly developed-— Locally Subdued. (9, 130). >3 m (b?).* Puget Lowland Salmon Springs3 3 7.5YR Well developed(?)* Up to 6 m Very (10, 150). locally.* subdued. 1MAT, mean annual temperature (08); MAP, mean annual precipitation (cm). 2(b), buried soil at least as well developed as the surface soil is locally recognizable beneath loess. An optional interpretation, discussed later, is that Hayden Creek and Salmon Springs deposits are early Wisconsin (60,000-70,000 yr) in age. WEATHERING-RIND DEVELOPMENT AND TIME 29 mun., 1976; D. R. Crandell, oral commun., 1976). Cran- dell and Miller (1974) favored a latest pre-Wisconsin age for the Wingate Hill Till, an age that appears to be too young based on its very thick weathering rinds. Crandell (1972) implied that Tahoe Till at Lassen Peak could be either early Wisconsin or latest pre-Wiscon- sin; we consider either correlation possible, but favor assigning the pre-Tahoe to the latest pre-Wisconsin. Weathering-rind thickness versus time curves were constructed for each area (fig. 19), using the inferred ages of the deposits discussed above as calibration points (one point per curve). The logarithmic form of the curves is based on the model for the dated West Yellowstone sequence (fig. 17). The West Yellowstone curve appears in figure 19 as it did in figure 17, and each of the other curves was obtained by simply multiplying the West Yellowstone curve by a rate fac- tor (table 7) so that it would pass through the ap- propriate calibration point. For example, the Bull Lake deposits at West Yellowstone, average rind thickness 0.78 mm, are correlated with the Indian John deposits in the Yakima Valley, average rind thickness 1.05 mm. The Yakima Valley curve was obtained by multiplying the West Yellowstone curve by 1.05/0.78, or 1.35. The rate factor of 1.35 accounts for the difference in the rate of rind formation between West Yellowstone and the Yakima Valley, and for the difference in rind thickness between Bull Lake and Indian John deposits, which are thought to be about the same age. Finally, the rind thicknesses for the other deposits in each area were plotted on the curve constructed for that area. Thus, the numerical age of one deposit in each area has been inferred using multiple correlation methods and stratigraphic relations, and the ages of the other deposits have been estimated from weathering-rind curves. The ages estimated by this method for the glacial deposits from the different areas of this study appear to be concentrated in discrete time intervals, in- dicated by the histogram in figure 19. The usefulness of weathering rinds as a dating technique decreases towards both ends of the time scale in figure 19. For young ages, the method is limited by the ability to measure very thin rinds. The thinnest rinds that could be measured using the pro- cedures in this study were 0.1 mm thick, which limits the usefulness of the method for deposits less than about 10,000 yr old. The decreasing rate of change with time implied by the logarithmic form of the weathering-rind curves limits the ability of weathering-rind thickness to discriminate between older deposits. In addition, few deposits older than about 0.5 my in the Western United States have well- preserved weathering profiles. Consequently, the use TABLE 7.—Deposits used as calibration points, and derivation of the rate of factors used in the weathering-rind equation d=a log (0.73+0.038t) Age Rind Rate Deposit used for calibration (103 thickness factor yr) (mm) (a) 2 W. Yellowstone Bull Lake ------ 140 0. 78 1.00 McCall Bull Lake ------------ - 140 1.61 2.06 Indian John ----------- - 140 1.05 1.35 Pre—Tahoe (Lassen)---- - 140 1.06 1.36 Donner Lake ------------------- 140 .93 1.19 Hayden Creek (option 1) ------- 65 1.37 2.71 Hayden Creek (option 2)--- 140 1.37 1.76 Salmon Springs (option 1) ----- 65 1.01 2.00 Salmon Springs (option 2) ----- 140 1.01 1.29 1Bull Lake deposits near West Yellowstone are about 140,000 yr old, based on combined obsidian hydration and K-Ar methods (Pierce and others, 1976). Other deposits are inferred to be the same age based on relative-age methods and stratigraphic relations. The Hayden Creek and the Salmon Springs deposits may be younger than 140,000 yr; if so they are probably early Wisconsin (about 65,000 yr old). ZRate factors are derived from the calibrated West Yellowstone curve. Rate factors are computed by dividing the rind thickness for a given deposit by the rind thickness for the equivalent age at West Yellowstone. of weathering rinds for age estimates is generally limited to deposits younger than about 0.5 m.y., although weathering rinds may be useful in separating different ages of deposits up to about 1.0 m.y. if relatively stable (uneroded) sites can be found. The curves in figure 19 are a major result of this study. Before discussing the conclusions that can be drawn from the curves, it seems appropriate to review the assumptions upon which the curves are based. These assumptions include (1) that in each sampling area, the sampling procedures, and the mapping upon which the sampling plan was based, produce measurements that are representative of the principal ages of deposits present. (2) that factors other than age are relatively constant throughout each sampling area, (3) that the form of the curves for rind thickness versus time based on the West Yellowstone data is correct and can be applied to other areas, and (4) that the age estimates and correlations used for calibration are cor- rect. All of the conclusions based on the weathering- rind curves are qualified by the validity of these assumptions; however, these assumptions appear to be reasonable based on the evidence presented earlier. The rind thickness versus time curves are presented not because we are absolutely sure that they are cor- rect, but to provide a reasonable model that can be tested. Because of the consistency of the rind measurements, we believe that approximations of the numerical ages of the different deposits arecontained 30 RIND THICKNESS. IN MILLIMETERS FREQUENCY WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES 3.0 2.8 2.6 2.4 2.2 2.0 0.8 0.6 0.4 0.2 I I I I I I I I I I I I I I I I I I I I I I I I I I /// / \ I // / Option 1 Rainier (130) Option 2 ’ Lassen I120) Truckee I80) // ,/>'”” I A 'West YelIowstone (50) I I I I IAL l I I I l I l I l I I I I l I l I I ' I ' I ' I ' I ' I r I fl ' I ' I ' I ' I T I ' I ' I ' I __r_1 _ I | r—1 _| I | | _ I I I | _ I I I._.l I I _ I_.I I I I I I >5oo—> _ _ l l I I — ‘1 r—‘I I | I - r-1 _ I I r- -1 I l 14‘ I J 0 20 40 60 BO 100 120 140 160 180 200 220 240 260 230 300 TIME (103 YEARS BF.) FIGURE 19.—Weathering—rind thickness versus time curves for each of the principal sampling areas. A. areas containing andesitic rocks; B, areas containing basaltic rocks. Numbers in parentheses after area name are the approximate mean annual precipitation (cm) for that area. Calibration points (solid symbols) for West Yellowstone are based on obsidian hydration ages by Pierce and others (1976); other calibration points are by correlations to deposits of known age. Open symbols represent deposits plotted on the rind curves according to their mean rind thickness. Because of uncertainties as to the age of the Hayden Creek and the Salmon Springs deposits. which were used as calibration points. two interpretations (op- tions 1 and 2) are presented for the Puget Lowland and Mount Rainier areas. Different symbol shapes correspond to different sampling areas. C. histogram of age estimates. Dashed, unshaded areas repre- sent estimates from both options for the Puget Lowland and for Mt. Rainier, and thus include two estimates for each deposit. REGIONAL CORRELATIONS 31 in the rind data; although independent numerical age estimates do not at present exist to test our model, they may in the future. We feel an obligation to offer a model that may make it possible to extract the age in- formation from the rind data and to offer age estimates for different deposits in the sequences studied. A number of independent observations can be made from figure 19 that support both the method used to construct the curves and the assumptions upon which the method is based. First, the ages determined from the weathering-rind curves for the last major glacial advance in each area generally are consistent with radiocarbon age estimates for those advances. Second, the curves show that the rate of weathering-rind for- mation generally increases with increasing mean an- nual precipitation. An exception is in the Puget Lowland, where the basalt is significantly different from other basalts used in the study (see Appendix C). Finally, the pattern of times of glacial advance, shown by the histograms in figure 19, is consistent with most marine oxygen-isotope records (fig. 20). REGIONAL CORRELATIONS BASED ON AGES ESTIMATED FROM WEATHERING-RINDS The data in figure 19 can be transformed easily into a correlation chart (fig. 21) by simply labeling the data points. Some of the correlations in figure 21, however, are in conflict with earlier interpretations. The fol- lowing discussion examines those conflicts, along with other pertinent conclusions concerning the ages of the deposits. The deposit names used in this discussion are those used by previous workers and are used primarily to identify specific deposits. The conclusions and cor- relations we suggest apply to the deposits we sampled, but not necessarily to all deposits to which a given name has been applied. CASCADE RAN GE—PUGET LOWLAN D Weathering-rind methods do not resolve the age dif- ference between the Evans Creek advance from Mount Rainier and the Vashon advance of the Cordilleran ice sheet. Stratigraphic relations between deposits related to the two advances demonstrate that the Evans Creek advance is somewhat older than the Vashon advance (Crandell, 1963), whereas the weathering-rind data, if anything, suggest the reverse. The discrepancy is probably due to differences in the rocks and climate of the two areas and to the inability of weathering rinds to resolve differences of only a few thousand years. The numerical age estimates of Crandell and Miller (1974, table 3) are retained for the two advances. Considerable controversy persists regarding the cor- relation of all but the youngest glacial advances in the Puget Lowland—Cascades area (for example, Porter, 1976). Much of this controversy results from diffi- culties in interpreting very old (50,000 yr or more) radiocarbon ages, and from differing concepts of the amounts of weathering and morphologic change ex- pectable from the range of deposits of Wisconsin age. In addition, strong climatic gradients, variability of rock types, and variable thickness and extent of eolian mantles in the area make the interpretation of most relative-age criteria extremely difficult. These factors also hinder the interpretation of weathering-rind data, but weathering rinds are probably at least as good as any other age criterion available for determining the ages of deposits near or beyond the limit of the radio- carbon method. The following discussion examines the problems of age estimates in the Puget Lowland and the Cascade Range (including the Mount Rainier area and the Yakima Valley) and discusses the correlations between these areas. We will present the interpreta- tions that we favor, from weathering-rind thickness and other weathering data. Crandell and Miller (197 4, p. 55—56) favored a 40,000 to 80,000 yr age (oxygen-isotope stage 4) for the Hay- den Creek advance and suggested that the Wingate Hill advance occurred just before 125,000 yr ago (dur- ing oxygen-isotope stage 6). Hayden Creek deposits ex- hibit large variations in weathering-rind thicknesses between sites (Appendix A), due in part to burial by eolian deposits at some sites and to erosion at others. Sites 076—40 and 078—116 were chosen as represent- ative of the weathering interval since Hayden Creek time, because they were the only stable, loess-free sites examined. Rinds at these sites, which are several kilometers upvalley from the Hayden Creek terminus (Crandell and Miller, 1974, pl. 1), average 1.37 mm on fine-grained andesite. In general, the soils in Hayden Creek deposits con- tain IOYR to 7.5YR colors, and a weakly developed argillic B horizon. Locally, these deposits are covered by thick (>2 m) eolian deposits (loess?), which are red- dish (7.5 YR), clayey, and weathered to depths of more than 2 m. We did not find any unambiguous exposures of a buried soil beneath the surface loess on Hayden Creek deposits, but the overall weathered appearance of the loess may make it difficult to recognize a buried soil. However, the following facts indirectly suggest that a buried weathered zone may exist beneath the loess on Hayden Creek deposits: (1) locally, the presence of relatively thick weathering rinds (as much as 1.0 mm average) beneath loess more than 2 m thick, (2) rapid lateral variation in weathering-rind thickness beneath the loess in places, suggesting erosion of a weathered zone, and (3) the common occurrence of a zone of increased compaction (Bt horizon?) near the 32 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES -2.o ' ‘ I l 100 200 300 400 500 600 700 Ir'IIII' || I'll III IIII II I I I I I I I II | I | | | I I I I I I II I I I I I I I I I I I II I I I I I I I I I I I II I . I I I - I I I I I1 I1*.—"—.*I I ,_'_I__._I__I_. I I I I | I #4“ II I__'_._'—_'_II I I I I I lI—o—I | | *—'—' I I I42 I I I I I (4)>5oo I I I .2 I I I l I ‘I I | I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I I . I . I I I I I I I I I I I I A II I I III I I II II 1 I I I 41 STAGES12 3 4ab2de 6 7 a 9 1o 11 12] 13 14 15 16I17 18 I19I20 I II I I I I I I l | | I I 100 200 300 400 500 600 TIME (103 YEARS B.P.) V28-23812 3 9 0 11 12 13 14 V28-239 1 1 4 171201 V12-122 1 2 9 10 11 12 P6304-9 1 2 9 DEPTH, IN M ETERS FIGURE 20.—Comparison of ages estimated from weathering rinds in glacial deposits in this study with the deep-sea oxygen-isotope record. A. ages of glacial deposits estimated from figure 19. Error bars on ages were obtained by projecting i- 1 standard deviation of the weathering-rind measurements to the curves in figure 19. Closed circles are the calibration points of figure 19, whose ages are known from independent age estimates or are inferred by correlation; open circles represent ages estimated from weathering-rind thicknesses (fig. 19). Numbers at the ends of the error bars refer to the optional interpretations for the Puget Lowland and Mount Rainier areas in figure 19. B, oxygen-isotope records of four deep-sea cores (V28-238 and 239, Shackleton, 1977a; VIZ-122, Broeker and van Donk, 1970; and P6304-9, Emiliani, 1966). The isotope records have been plotted on a common time scale according to the estimated ages of stage boundaries given by Hays and others (1976) for stages 1 to 13, and by Shackleton and Opdyke (197 3) for stages 13 to 20. Shaded portions of the curves represent isotope values heavier than an arbitrary value (the low value of stage 2 plus 25 percent of the difference between stage 1 and stage 2). the shaded areas are intended to highlight times of high ice volumes. C, The four cores plotted on a common depth scale, with the oxygen-isotope stages numbered. Shaded portions are those that are magnetically reversed (below the Brunhes- Matuyama boundary (ar- row in C, and long dash-short dash line in B)). REGIONAL CORRELATIONS 33 1 2— WEST MCCALL YAKIMA LASSEN PEAK TRUCKEE PUGET LOWLAND MOUNT RAINIER —— 3_YELLOWSTONE VALLEY OPTION 1 I OPTION 2 OPTION 1 I OPTION 2— 4— i .— 5— _ ‘3— l i Z ‘1‘ l I t 10— l l — 15 Deckard Flats Pinedale Tloga Tioga Vashon Vashon _ — Domerie E 20— Pine dale 2 Tahoe Low Fraser terrace Evans Creek 1' I I 2 30— Early lTIoga i I _ CI: 40—. Pinedale Ronald l High Fraser[ 1 _ < terrace / E 50:— l l 5, 6°" Inlennediate Bullfrog Tahoe Salmon iHigh Fraser Hayden Crl — 9 38— Springs terrace l __ $1007— I _ E I I :150—\ Bull Lake Bull Lake Indian John Pre-Tahoe Donner Lake lSalmon Spgs lHayden Cr,= 200-— Outer Bull Lake Swauk Prairie 7 7 I _ I l i i . W— m 7 i 7 Pro-Tahoe Hobart 7 | Hill l ..._ l l I _ 500—- ) —— ? _r 500— . 533- “WP _ __ ____.aen@ek Inner-sen ___' Wm“; mo; Pre'BU" Lake Pre-Thorp(?) .Wedekind Wedekind Logan Hill 395%.. Creek Creek FIGURE 21.—Corre1ation chart for deposits sampled in this study. The chart was produced from the age estimates in figure 19. Horizontal lines enclose deposits thought to be about the same age. Arrows suggest other possible correlations, queried where uncertain, discussed in the text. Stratigraphic names are those of previous workers. (See fig. 3 for references.) Vashon deposits (Mount Rainer) are slightly younger than Evans Creek deposits (Crandell, 1963); weathering-rind thicknesses are not consistent with this difference. Rinds in Swauk Prairie deposits are only slightly thicker than those in Indian John deposits. However, Swauk Prairie deposits are thickly mantled with loess, and therefore may be significantly older than the rind thickness suggests (S. C. Porter, oral commun., 1977). Pre-Tahoe deposits at Lassen Peak probably include deposits of more than one age. Rinds were measured only for the youngest (innermost) of these deposits. base of the loess. Although the soils and weathering characteristics of the Hayden Creek deposits vary con- siderably due to the eolian mantle and to erosion, no systematic change suggestive of discrete ages within the Hayden Creek was noted. In estimating the age of the Hayden Creek advance, the rind thicknesses of both younger (Evans Creek) and older (Wingate Hill) deposits and also the fact that the rate of rind development decreases with time must be considered. Because weathering rinds are so thick» (and soft) an Wingate Hill deposits (> 3.0 mm average), Crandell and Miller’s (1974) correlation of the Wingate Hill deposits with isotope stage 6 (about 140,000 yr old) implies an extremely rapid rate of weathering rind development. This rate is not supported by the very thin rinds (0.1—0.2 mm) on Evans Creek deposits. Because the age of the Wingate Hill deposits is uncer- tain but probably much greater than 140,000 yr, the data for the Hayden Creek deposits were used for the calibration points in figure 19. Two interpretations (op- tions) of the age of the Hayden Creek deposits are shown in figure 19: (1) early Wisconsin (about 65,000 yr old) as suggested by Crandell and Miller (197 4) and (2) latest pre-Wisconsin (about 140,000 yr old). An age of 140,000 yr for the Hayden Creek deposits (fig. 19, option 2) is considerably older than Crandell and Miller’s (1974) estimate, and it leaves the much less extensive Evans Creek end moraines as the sole representative of the Wisconsin Glaciation. However, this option is favored by (1) the thickness (1.37 mm average) of weathering rinds at the few undisturbed sites sampled on the Hayden Creek deposits, (2) the large ratio, about 9:1, in weathering-rind thickness be- tween the Hayden Creek and the Evans Creek deposits (table 2; fig. 12), (3) the development of an argillic B horizon on the Hayden Creek deposits, in contrast to the lack of clay enrichment in the weak soil on the Evans Creek deposits, (4) thick, weathered loess on some Hayden Creek deposits, and (5) some suggestion of a buried weathering zone beneath the loess on Hayden Creek deposits. 0n the other hand, if the Hayden Creek deposits are about 65,000 yr old (isotope stage 4), then the Wingate Hill deposits must be 250,000 or more yr old, if the rate of weathering-rind formation is logarithmic. These ages imply the absence of any recognized glacial deposit (end moraine or outwash terrace) representing an advance about 140,000 yr ago; this advance appears 34 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR. WESTERN UNITED STATES to be widely represented elsewhere. In addition, an age of about 65,000 yr (isotope stage 4) for the Hayden Creek deposits leads to the conclusion that the glacial advance representing isotope stage 4 was nearly twice as extensive as that representing isotope stage 2 (Evans Creek). However, Crandell and Miller (1974) favored an early Wisconsin age for the Hayden Creek deposits, primarily because of the weak development of an argillic B horizon, and correlation with the Salmon Springs deposits in the Puget Lowland, which were thought to be early Wisconsin. In summary, the age of the Hayden Creek advance(s?) remains unresolved but is probably either about 65,000 or 140,000 yr. The possibility remains that the Hayden Creek deposits include deposits of both ages, but no data supporting this hypothesis have been found. Based on weathering data, an age of about 140,000 yr rather than 65,000 yr seems more probable. The Wingate Hill deposits are surely pre-Wisconsin, and are probably much older than 140,000 yr. If the Hayden Creek deposits are about 140,000 yr old, then our rind development curve (fig. 19) places Wingate Hill at more than a half million years old. An analogous situation exists in the Puget Lowland, where the age of the Salmon Springs Drift is the sub- ject of controversy. Traditionally, it has been con- sidered early Wisconsin (Birkeland and others, 1970), but Porter (1976) suggested that it could be pre- Wisconsin, at least in part. The arguments for these alternative interpretations are much the same as those presented earlier for the Hayden Creek deposits. One difference between the two areas is that the Salmon Springs and Vashon advances were similar in size, whereas the Hayden Creek and Evans Creek advances were markedly different in extent. Salmon Springs Till appears to have a moderately well developed argillic B horizon and has weathering rinds about 1 mm thick on basalts. It is commonly capped by thin, weathered eolian deposits, and both the till and eolian deposits are oxidized to 7.5 YR col- ors. On the other hand, the equivalent outwash terrace (middle Salmon Springs; Carson, 1970) is covered by thick, relatively unweathered eolian deposits (loess?), locally as much as 6 m thick. The gravels at the gravel- loess contact are oxidized, but in most places the ox- idation appears to be ground-water alteration rather than a buried soil. At one locality (C76—37 B) on the ter- race margin where the loess is thin, weathering rinds in the gravel are comparable to those on stones in Salmon Springs Till (1.07 mm average thickness). The Puget Lowland receives considerably more pre- cipitation than the other sampling areas in this study, but the basalt in the deposits there contains almost no olivine or vitric glass, and therefore it probably weathers more slowly than the basalt in other areas sampled. The net effect of these rock type and precipitation factors on weathering—rind-development rates is uncertain, but the two factors have opposite ef- fects, and thus tend to cancel each other. In any case, average rind thicknesses on stones from the Salmon Springs deposits are about the same as those on stones from deposits considered to be 140,000 yr old in the Yakima Valley. The latter area receives one-half to one- third as much precipitation as the Puget Lowland but contains basalt that apparently weathers faster than that in the Salmon Springs deposits. Two buried drifts are exposed in the type section of the Salmon Springs Drift. The relation of the Salmon Springs surface till examined in this study to the two drifts in the type area is uncertain. The two drifts in the type area are separated by a peat tentatively estimated to be about 50,000 yr old on the basis of radiocarbon determinations (Crandell and Miller, 1974, p. 18). However, a more recent determination of about 71,500 yr has been obtained by 1‘C enrichment tech- niques (Stuiver and others, 1978). No evidence was found, either in this study or in Carson (1970), to sug- gest that more than one age of Salmon Springs Till ex- ists at the surface. Carson also argued against an earlier, less extensive Salmon Springs advance being represented by one of the multiple outwash terraces emanating from the Salmon Springs Till margin. He argued that the three terraces are related to one main Salmon Springs advance, a recessional stage of that advance, and a slightly older advance from the Olym- pic Mountains. Marine deposits in the area of Gray’s Harbor, Wash., provide useful information concerning the age of the Salmon Springs deposits. Three sampling sites on the first marine terrace, about 20—25 m above sea level, produced an average weathering-rind thickness of 0791042 mm, although basalts in these deposits were scarce and the measurements ranged more widely than those for most other sample sites. These deposits have not been mapped or studied in detail, and sea level curves for areas this close to the continental ice margin are different from those for areas where high sea stands have been dated. However, it seems unlike- ly that the terrace sampled could be younger than the last series of high sea stands, associated with isotope stage 5 (see fig. 20). At Willapa Bay, about 60 km south of Gray’s Harbor, Kvenvolden and others (1977) suggested that the first (20-m) marine terrace is Sangamon in age based on amino acid enantiomeric ratios. In addition, samples we collected of clayey deposits overlying the lower Salmon Springs Terrace near Grays Harbor have pollen spectra suggestive of an interglacial climate (L. E. Heusser, oral commun., REGIONAL CORRELATIONS 35 1979). These data suggest that Salmon Springs de- posits, with an average rind thickness of 1.01:0.40 mm, may be older than the last interglaciation and the first marine terrace, and thus may be about 140,000 yr old. Two different interpretations (options) of the chronology in the Puget Lowland are presented in figures 19 and 21. The similarity in weathering data for the Hayden Creek and the Salmon Springs deposits suggests that the two are at least partially equivalent. We interpret the available data as favoring an age of about 140,000 yr (option 2) rather than 65,000 yr (op- tion 1) for both of these deposits. In the Yakima Valley, Porter (1976) considered all members of the Lakedale Drift (Hyak, Domerie, Ronald, and Bullfrog Members) to be late Wisconsin, equivalent to the Vashon and Evans Creek advances on the other side of the Cascades. He also considered the Kittitas Drift (Indian John and Swauk Prairie Members) to be pre-Wisconsin (written commun., 1976) and to correlate with the Salmon Springs Drift; hence he suggested that the latter may be pre- Wisconsin at least in part (Porter, 1976). A pre- Wisconsin age for the Kittitas Drift is strongly sup- ported by evidence based on soil development, buried soils, loess stratigraphy, morphology, terrace profiles, and position of this drift in the stratigraphic sequence. These data also suggest that the younger of the two Kittitas members (Indian John) is latest pre-Wisconsin in age, or about 140,000 yr old. Relative-age criteria for the Indian John deposits are very similar to those of the 140,000-yr-old Bull Lake deposits at West Yellow- stone (table 6). Porter (1976) grouped the two members of the Kit- titas Drift because they have similar weathering and erosional characteristics. Weathering rinds on stones in the Swauk Prairie Member are only slightly thicker than those on stones from the Indian John Member. However, Porter (1976; oral commun., 1977) also in- dicated that the Swauk Prairie Member may conceiv- ably be at least one full glacial cycle (about 105 yr in the marine record) older than the Indian John Member. If that is the case, then the rinds in the Swauk Prairie Member are anomalously thin, probably due to burial .by a thick mantle of loess. Data that suggest a major age difference between the Swauk Prairie and Indian John Members include the following: (1) Our observa- tions suggest that the Swauk Prairie Member locally may contain two buried soils (one in the till and one within the overlying loess) indicating three episodes of weathering separated by two episodes of loess deposi- tion. No more than one buried soil was observed associated with the Indian John Member. (2) The Swauk Prairie terrace is twice the height of the Indian John terrace above present drainage and is more than 25 m above the level of the Indian John terrace. Differences in weathering-rind thickness indicate that significant age differences exist between the members of the Lakedale Drift. The three older members (Domerie, Ronald, Bullfrog) have average rind thicknesses differing by factors of about 1, 2, and 3 (0.25, 0.52, 0.71 mm) respectively. As discussed earlier, the rate of weathering-rind development decreases with time, so the three members must differ in age by factors of more than 1, 2, and 3, respectively. Therefore, because the Domerie Member is about 14,000 yr old (Porter, 1976), the three members prob- ably span the entire time of the last glaciation, and the Bullfrog Member probably dates from early in that glaciation (early Wisconsin). CALIFORNIA MOUNTAINS Tahoe and Tioga deposits traditionally have been considered to be early and late Wisconsin in age, respectively (Birkeland and others, 1970). The weathering-rind data suggest that, for two areas ex- amined in this study, these previous interpretations need to be reexamined. In the Truckee, Calif, area, Tahoe deposits have only slightly thicker rinds than Tioga deposits. Soils and other weathering data for the two deposits are also similar according to recent work by Burke and Birkeland (1979). They have now con- sidered much of what was originally mapped as Tahoe (Birkeland, 1964) to be equivalent to Tioga, so that much of what was previously mapped as Tahoe near Truckee may not be correlative with Tahoe deposits mapped elsewhere in the east-central Sierra Nevada region. However, Burke and Birkeland (1979) have also discovered a more intensely weathered deposit that could be early Wisconsin. Weathering-rind thicknesses measured by Burke (1979) for this deposit appear to be similar to those of Donner Lake deposits. Thus, this newly recognized deposit in the Truckee area that is possibly intermediate in weathering characteristics and age between the Tioga and the Donner Lake may be the equivalent of the Tahoe of the east-central Sierra Nevada. In the Lassen Peak area, deposits originally mapped as Tahoe by Crandell (1972) were subdivided into Tahoe and “early Tioga” by Kane (1975). This sub- division appears to be valid because the two deposits were shown to have distinctly different soil colors, depths of oxidation, and weathering-rind thicknesses. The weathering-rind data presented here suggest that the Tahoe deposits of this area are early Wisconsin, and the “early Tioga” deposits are intermediate be- tween late and early Wisconsin (fig. 19). 36 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES The Tahoe deposits near Lassen Peak could possibly be pre-Wisconsin (Crandell, 1972), but this interpreta- tion creates several problems. First, a pre-Wisconsin age for the Tahoe would demand an exceptionally slow rate of weathering-rind formation (fig. 19). This rate would be anomalous considering the large amount of precipitation in the Lassen Peak area. No lithologic reason was noted that could account for such a slow rate of rind formation. Second, a pre-Wisconsin age for the Tahoe (and the Wisconsin age of the “early Tioga”) would place the last interglacial within what Crandell (1972) mapped as a single unit (Tahoe). Crandell (1972) recognized that his Tahoe unit probably contained deposits of more than one age, but evidently con- sidered other age differences to be more important. Therefore, although characteristics such as subdued morainal form, oxidation to more than 1 m, and 7.5 YR colors suggest that the Tahoe at Lassen Peak could be as old as the Bull Lake deposits at West Yellowstone, we consider the Tahoe deposits at Lassen Peak to be early Wisconsin in age. The wetter climate at Lassen Peak appears to increase the rate at which weathering and erosional characteristics are attained. Cursory observations of weathering and erosional features suggest that pre-Tahoe deposits in the Lassen Peak area could encompass more than one pre- Wisconsin age. However, all pre-Tahoe sampling sites were located immediately beyond the limit of Tahoe deposits in order to sample the youngest deposit in case of multiple ages. Rind thicknesses from these sites suggest that the pre-Tahoe deposits sampled are latest pre—Wisconsin in age (about 140,000 yr old). ROCKY MOUNTAINS The age of the Bull Lake Glaciation has been the subject of considerable controversy because of the lack of numerical-age determinations. Also, correlations based on differing relative-age criteria in areas of dif- fering climates and rock types have proved problem- atical. The term Bull Lake was originally defined by Blackwelder (1915) to designate the older, morpholog- ically muted moraines of the two sets of well-preserved moraines at Bull Lake, Wyo., on the flanks of the Wind River Range. Since that time, a conceptual definition of the characteristics of Bull Lake deposits, based on terrace heights, moraine morphology, and soil develop- ment appears to have evolved. These characteristics were thought to represent an early Wisconsin to intra- Sangamon age (Richmond, 1965). The belt of moraines that wrap around Horse Butte in the West Yellowstone Basin have been described as Bull Lake by all workers who have examined them (Pierce and others, 1976, references). Apparently, these deposits fit the concept of the Bull Lake rather well, although no outwash terraces associated with the moraines are preserved in the subsiding West Yellow- stone Basin. Problems of correlation and nomenclature arose when the deposits near West Yellowstone were dated at about 140,000 yr old by combined K-Ar and obsidian-hydration methods (Pierce and others, 1976). Obviously, this age is not compatible with an early Wisconsin age for the Bull Lake. Although Richmond (1976, 1977) has recently favored correlation of the West Yellowstone deposits with the late stade of the Sacajawea Ridge Glaciation, he stated (1976, p. 373) tha “surficial and weathering characteristics***do not exclude possible correlation with the broad smooth moraines of the early stade of the Bull Lake as locally developed at Bull Lake.” In addition, “type” Saca- jawea Ridge deposits on the east side of the Wind River Range are associated with the 600,000-yr-old Pearlette “type-O” ash (Pierce, 1979). Also, Bull Lake deposits in the type area remain undated, and their cor- relation with deposits in other areas is uncertain. Therefore, the belt of moraines that wrap around Horse Butte are here called the Bull Lake deposits at West Yellowstone because of their well-established similarity to the type Bull Lake deposits. In view of the present conceptual difficulties, the use of the name Bull Lake for deposits near West Yellowstone and McCall does not necessarily imply that the conclu- sions reached for these deposits are applicable to all the Bull Lake deposits in the type area, or to all deposits mapped as Bull Lake in the Rocky Moun- tains. In the McCall area, the pronounced development of an argillic B horizon and the thickness of the weather- ing rinds in most of the Bull Lake deposits strongly suggests that they are at least as old as the West Yellowstone Bull Lake. A younger age for the Bull Lake deposits at McCall would require an unrea- sonably rapid rate of weathering-rind formation (fig. 19). However, small portions of the deposits at McCall mapped as Bull Lake by Schmidt and Mackin (1970) appear to be early Wisconsin. Weathering-rind meas- urements at sampling sites on the moraines mapped partly as the innermost of the large group of Bull Lake moraines and partly as the outermost of the Pinedale moraines were consistently thinner than those at sites on the rest of the Bull Lake moraines. The average rind thickness for these moraines (here called “inter- mediate”) results in an age of about 60,000 yr on the McCall curve in figure 19. Thus, in the two areas examined in this study, the deposits that have been mapped as Bull Lake and that fit the conceptual definition of Bull Lake, with the ex- ception of the innermost moraine at McCall, evidently are pre-Wisconsin. This age is contrary to that usually SUMMARY 37 assigned to the Bull Iiiake Glaciation (Richmond, 1965, 1976; Birkeland and others, 1970). In addition, the Bull Lake—Tahoe correlation (Birkeland and others, 1970) appears to be uncert 'n because (1) most of the Bull Lake deposits exami ed in this study are believed to be pre-Wisconsin, although some deposits grouped with Bull Lake are probably early Wisconsin, and (2) the Tahoe deposits ‘ amined in this study are prob- ably early Wisconsi or younger, although Tahoe deposits in some areas may be pre-Wisconsin (Burke and Birkeland, 1979). iUMMARY A large number of‘ environmental factors, including climate, parent ma rial, vegetation, position in the weathering profile, and time affect weathering-rind development, just as they do soil development and other near-surface weathering processes. Because the focus of this paper is )on the influence of time, sampling procedures were designed to reduce, eliminate, or isolate the variation due to all the factors other than time. Even though mucl'i of the variation in rind thickness due to factors other han time was eliminated, that re- maining is clearly important, although difficult to evaluate quantitatively. Of the remaining variation, that due to litholo 'c variation in the rocks sampled appears to be the ost important, even within the limited range of lithologies and textures studied. Variation in rind thickness due to differences in climate is also imp ‘rtant, especially that due to dif- ferences in precipit tion. The effect of temperature could not be evaluated independently; it may have a considerable influence on rind thickness. Variations in soil matrix texture, vegetation, and erosion and (or) deposition also cont 'bute small amounts of variation in rind thickness. More than 7,335 weathering-rind measurements at about 150 sampling fites in the Western United States were analyzed to demonstrate the usefulness of weathering-rind thickness as a relative-age criterion. Of the 17 areas examined, 7 had the most favorable rock types and cli ates and were studied in detail. Weathering-rind me urements can be closely repro- duced by different Workers if they adhere to the same procedures. The distribution of weathering-rind measurements at in 'vidual sites tends to be log nor- mal, with a tendencE' for positive skewness. Within a sampling area, depo it age (the time factor) is by far the most important source of variation in weathering- rind thickness. All differences in mean rind thickness between stratigraphc ages within a sampling area are important. Differences in mean rind thickness between moraines are generally negligible, whereas such differ- ences between sites may be important, but are largely due to factors other than time. Therefore, weathering rinds are an excellent quantitative indicator of relative age. Two approaches can be used to extract numerical age information from the weathering-rind data for a given area: (1) age constraints provided by rind- thickness ratios, and (2) estimation of the precise rind thickness versus time function. With only few and minor assumptions, rind-thickness ratios can be used to determine with near certainty the minimum and maximum age ratios between two deposits. Thus, if the age of one deposit in a sequence is known or postulated, the minimum and maximum age of another unit can be determined. This ratio method, although not precise, provides both useful information on ages and constraints on correlations. Thus, even if a reader is unable to accept the assumptions necessary for the construction of our thickness versus time curves, more certain but less definitive information on age relations can still be obtained from the rind-ratio data (table 5). A logarithmic model of weathering-rind develop- ment with time appears to be most consistent with the processes involved and with independent age controls. The rind thickness versus time curves (figs. 17, 19) are our best approximation of the age information con- tained in the rind-thickness data; they are presented as a model to be evaluated, refined, or rejected as more in- formation on radiometric ages and rates of weathering processes is obtained. The model of weathering-rind development with time, based on several assumptions, can be used to estimate numerical ages. 0n the basis of rind data for deposits of known age at West Yellowstone and in Bohemia, rind thickness increases with time according to a logarithmic function. Because of differences in rock type and climate, individual logarithmic curves were constructed for each area, using one deposit in each area as a calibration point. The ages of the calibra- tion points in areas other than West Yellowstone were inferred by correlation using traditional relative-age methods and stratigraphic relations. The correlations are based on data from previous workers and on our own observations. The ages of all deposits other than the calibration points were estimated from the weathering-rind curves in figure 19. The curves in figure 19 depend on a number of assumptions, including: (1) that the sampling pro- cedures produced representative data, (2) that factors other than time are relatively constant within each sampling area, (3) that the form of the curves is cor- rect, and (4) that the age estimates for the deposits used for calibration are correct. To the degree to which 38 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES these assumptions are valid, the model of weathering- rind development results in a number of important conclusions: 1. The Wisconsin Glaciation in the Western United States appears to be complex. Convincing evidence exists for a mid-Wisconsin glacial ad- vance between about 35,000 and 50,000 yr ago in several areas, including West Yellowstone (Pinedale) and the Yakima Valley (Ronald). The “early Tioga” deposits in the Lassen Peak area appear to be younger than 35,000 yr, but are clear- ly older than the late-Wisconsin Tioga deposits. In the Puget Lowland, the high Fraser terrace may represent a mid-Wisconsin advance from the Olympic Mountains. At West Yellowstone, this mid-Wisconsin advance was the largest one in Wisconsin time (Pierce and others, 1976). These advances are similar in age to the late Altonian ad- vances in the midcontinent (Willman and Frey, 1970; Dreimanis and Karrow, 1972). 2. Age estimates based on weathering rinds indicate an advance about 60,000—70,000 yr ago (early Wisconsin) in several areas, including the McCall area, the Yakima Valley, the Lassen Peak area, and possibly the Puget Lowland and Mount Rainier areas. This advance is probably cor- relative with oxygen-isotope stage 4 of the marine record, a time of high worldwide ice volumes. 3. In the seven principal areas examined in this study, the rind data (fig. 19) do not indicate any end mo- raines dating from the period between about 75,000 and 130,000 yr ago, based on our age estimates, and the attendant assumptions. We found no stratigraphically distinct deposits with rinds in the range of 5-25 percent thinner than the deposits we correlate with oxygen-isotope stage 6. Lack of end moraines does not imply that glacial expansions did not occur during this interval 75,000—130,000 yr ago, which is generally equivalent to stage 5 of the oxygen-isotope record, a time of relatively low worldwide ice volumes. Richmond (1976) identified and approximately dated glacial events in the Yellowstone area that he correlated with oxygen-isotope stages 5b and 5d (fig. 20); however, these events are not directly related to preserved end moraines. On the basis of ice-contact features of the West Yellowstone rhyolite flow (R. L. Christiansen, written commun.,_ 1972), glaciers were sizable 115,000i7,000 yr ago (Pierce and others, 1976; Richmond, 1976). In the areas examined in this study, glacial advances during oxygen-isotope stage 5 apparently were not sufficiently extensive to leave a preserved end-moraine record: 4. Our correlations suggest that an advance about 140,000 yr ago is widely represented. These cor- relations are based on traditional relative-age criteria, and are the basis for calibrating the weathering-rind model. However, the ages of the Hayden Creek and Salmon Springs deposits in the Mount Rainier-Puget Lowland area are uncertain. These deposits may date either from about 65,000 or from about 140,000 yr ago; if they are 65,000 yr old, then no representatives of a 140,000-yr-old ad- vance has been found in these areas. Weathering data and stratigraphic relations with interglacial deposits appear to favor an age of about 140,000 yr for Salmon Springs and Hayden Creek. A widespread occurrence of glacial deposits about 140,000 yr old is consistent with the marine oxygen-isotope record (stage 6), which indicates that worldwide ice volumes were at a maximum during that time. Most oxygen-isotope records in- dicate that ice volumes during stage 6 were equal to or greater than those of any subsequent time. 5. End moraines in some areas were deposited during times that are not represented by such features in other areas. This probably results from dif- ferences in glacier response due to local climatic variations in different areas, although it could result from inadequate sampling or from inade- quate mapping on which the sampling was based. Deposits of one glacial advance may be preserved in some areas, or eroded or buried in others by a succeeding advance of about the same size, ‘ depending on relatively small differences in the response of the glaciers to local climatic condi- tions. As a result, correlation by sequence of deposits alone (finger-matching) will inevitably ' lead to errors. The approximate ages estimated from weathering rinds conflict with some previous interpretations and agree with others. Weathering rinds appear to be par- ticularly helpful in distinguishing early Wisconsin deposits from latest pre—Wisconsin deposits in many areas. Relatively few deposits older than 140,000 yr have weathering profiles preserved well enough to be useful for numerical age estimates from weathering rinds. The decreasing rates of weathering-rind forma- tion with time also limits their use for very old (>0.5 m.y.) deposits. In the Mount Rainier-Puget Lowland area, Hayden Creek and Salmon Springs deposits are probably at least partially correlative, but whether they are early Wisconsin, pre-Wisconsin, or include both is uncertain. The available weathering and stratigraphic data favor a pre—Wisconsin age. Wingate Hill and Helm Creek REFERENCES CITED 39 deposits are certainly pre-Wisconsin and are probably at least several hundred thousand years old. On the east side of ‘the Cascade Range, Kittitas Drift is almost certainly p e-Wisconsin, and the Indian John Member is probably latest pre-Wisconsin. The Lake- dale Drift appears to span most of the Wisconsin, with the Bullfrog Membe probably being early Wisconsin. In the Sierra Nivada-southem Cascades region, Tahoe deposits at L sen Peak appear to be at least as old as early Wisconsin, but the Tahoe sampled at Truckee is consider bly younger, unlike most Tahoe deposits in the Sirra Nevada-southem Cascades region. The two are sampled in this region contain some of the few deposits in the Sierra Nevada-southern Cascades that can be convincingly correlated with late pre-Wisconsin ‘ (Donner Lake and pre-Tahoe, respectively). In the Rocky Mountains, most deposits mapped and commonly accepted as being Bull Lake at McCall and West Yellowstone ar pre-Wisconsin in age. A moraine intermediate betwee the Pinedale and the Bull Lake moraines at McCall is probably early Wisconsin. Pinedale deposits at West Yellowstone are somewhat older , than the late ‘ Wisconsin Pinedale deposits at McCall. ‘ In conclusion, weathering rinds have been shown to be an excellent indicator of relative age. As is the case with all relative-age criteria, factors other than time cause variation in dud thickness. However, time is much more important than any other factor in deter- mining rind thickness. With weathering rinds, varia- tion due to factors 0 her than time is easier to isolate, account for, or eli 'nate than with many other relative-age criteria.‘ By calibrating the curves of weathering-rind thickness versus time with independ- ent age estimates, t e influence of factors other than time can be elimina d, and weathering-rind thickness can be used to estim te the numerical ages of deposits. The wide applicability of weathering rinds and the numerical age estim tes that can be made from them . make weathering ri ds a useful correlation tool for Quaternary deposits ‘in the Western United States. REFEFIENCES CITED Alden, W. C., 1953, Physiography and glacial geology of Western Montana and adjacent areas: US. Geological Survey Professional Paper 231, 200 p. ‘ Anderson, R. 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Ollier, C. D., 1969, Weathering: Edinburgh, Oliver and Boyd, 304 p. Pierce, K. L., 1973, Surficial geologic map of the Mammoth quadrangle and part of the Gardiner quadrangle, Yellowstone Na- tional Park, Wyoming and Montana: US. Geological Survey Miscellaneous Geological Investigations Map I—641. _1979, History and dynamics of glaciation in the northern Yellowstone National Park area: US. Geological Survey Profes- sional Paper 7 29—F, 90 p. Pierce, K. L., Obradovich, J. D., and Friedman, 1., 1976, Obsidian hydration dating and correlation of Bull Lake and Pinedale Glacia- tions near West Yellowstone, Montana: Geological Society of America Bulletin, v. 87, no. 5, p. 703—710. Porter, S. C., 1964, Composite Pleistocene snow line of Olympic Mountains and Cascade Range, Washington: Geological Society of America Bulletin, v. 75, p. 477—482. 1969, Pleistocene geology of the east-central Cascade Range, Washington: Guidebook for Third Pacific Coast Friends of the Pleistocene Field Conference, 54 p. 1975, Weathering rinds as a relative-age criterion: Application to subdivision of glacial deposits in the Cascade Range: Geology, v. 3, no. 3, p. 101—104. 197 6, Pleistocene glaciation of the southern part of the north Cascade Range, Washington: Geological Society of America Bulletin, v. 87, no. 1, p. 61—75. Porter, S. C., Stuiver, M., and Yang, I. C., 1977, Chronology of Hawaiian glaciations: Science, v. 195, p. 61—63. Potter, R. M., and Rossman, G. R., 1977, Desert varnish: the impor- tance of clay minerals: Science, v. 196, p. 1446—1448. Richmond, G. M., 1964, Glacial geology of the West Yellowstone Basin and adjacent parts of Yellowstone National Park: US. 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APPENDIXES A-C 44 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES APPENDIX A.—WEATHERING-RIND THICKNESS MEASUREMENTS [3, finegrained andesite; b. coarse-grained andesite; c, andesite. undivided; d. granular basalt; e, dense. glassy basalt; f. basalt, undivided; g. quartizite: h. other; N in measurement columns, not measured or not given] Measurements (mm) Sample Rock Remarks No. Standard type Mean deviation Number Deposit West Yellowstone, Mont., Wyo. C76-74 0.11 0.08 34 Deckard Flats d Pinedale recessional deposits. -74 .10 .06 31 —-—do ------- f -74 .13 .13 32 —--do ------- h Gallatin intrusives. -75 .10 .07 21 —-—do ——————— f C75—97 .35 .23 39 Pinedale—--- d Pinedale terminal deposits. -98 .44 .22 41 —-—do ——————— d -98 .67 .21 25 ---do ------- d Surface stones. —99 .67 .24 11 --—do ------- f Do. —101 .59 .21 15 —-—do ——————— f Varying rock types, poor site. —94 .25 .14 35 Bull Lake——- d Eroding site. -95 .76 .17 56 ---do ——————— d -96 .78 .21 51 -——do ------- d —100 .81 .20 55 ———do ——————— d -102A 1.04 .18 34 -—-do ------- d Wetter site. -102B .93 .19 30 ---do ——————— d Do. McCall, Idaho C78—125 .74 .13 36 Pinedale---- e Side-valley recessional moraine. —124 .60 .20 39 ———do ——————— e Do. C75—106 .29 .14 40 ———do ------- e Inner moraine. C76 -51 .20 .08 63 -—-do ------- e Do. —52 .26 .16 22 ---do ------- 6 Do. —69 .29 .14 39 ---do ------- e Do. C78-l41 .24 .12 39 ---do ------- e Outwash from inner moraine. C76 -62 .27 .19 33 -—-do ------- e Intermediate moraine. -63A .31 .16 25 ---do ------- e Do. -633 .45 .21 28 ———do ------- e Intermediate moraine, angular stones. -64 .35 .16 39 ---do ------- e Intermediate moraine. C75—105 .39 .17 50 ---do ------- e Outer moraine. C76 -65 .39 .18 33 —--do ------- e Do. -68 .40 .16 34 —--do ------- e Do. C78-l34 .35 1.16 38 --—do ——————— e Do. C75—107 .30 .15 31 --—do ------- e Outwash. C76 -66 .40 .ll 36 --—do ——————— e Do. -67 .35 .13 35 -—-do ------- e Do. —59 .97 .32 38 Intermediate e Innermost moraine. —60 .75 .24 40 ---do—--—--- e Do. -61 .53 .23 47 —--do ------- e Innermost moraine, stones from loess above till. -71 .93 .30 56 —--do ------- e Innermost moraine. APPENDIX A 45 MeaJurements (mm) Sample ‘ Rock Remarks No. grandard type Mean eviation Number Deposit ‘ McCall, Idaho--Continued 1 C78-121 .84 .19 39 —--do ------- e Do. -135 .84 .16 32 ---do ------- e Do. -137 .71 ‘ .15 33 -——do ——————— e Do. -136 .59 .22 36 -—-do ------- e Innermost moraine, eroding site, ‘ reworked stones. 1C75-108A 1.41 .28 44 Bull Lake--- 6 Inner moraine, no loess. 1 -108B 1.71 .32 30 ---do ------- e Inner moraine, beneath 2 m loess. 1 -104A 1.23 I .45 43 ---do ------- e Intermediate moraine. lC76 -54B 1.85 ‘ .61 32 ---do ------- e Intermediate moraine, SMC3 measurements. 1 —54B 2.13 .65 32 ---do ------- e Intermediate moraine, KLP3 measurements. -54A .02 ‘ .05 24 ---do ------- e Intermediate moraine, unoxidized till. 1 -57 1.35 .33 36 ---do ------- e Intermediate moraine. 1 -58 1.52 .29 38 -——do ------- e Do. 2C75—109 1.96 ‘ .40 36 -—-do ------- e Outer moraine. 2C76 -55 1.44 .30 31 ---do ------- e Do. 2 -56 1.69 .47 32 —--do ------- e Do. 1075-1048 1.18 ‘ .35 38 Not known—-- e C horizon of soil buried by Bull Lake Till. lC76 —54C 1.42 .29 40 —--do ——————— e B horizon of soil buried by Bull Lake Till, SMC3 measurements. 1 -54c 1.50 I .26 40 --—do ------- e Soil buried by Bull Lake Till, B horizon, ‘ KLP3 measurements. ‘ Yakima valley, Wash. C75-131 0.25 0.04 225 Domerie ————— e Data from Porter (1975). -130 .52 1 .06 193 Ronald ------ e Do. —130 .43 1 .21 31 ---do ------- e This study. -133 .71 .12 279 Bullfrog---— e Data from Porter (1975). C76 -43 .78 ‘ .19 31 --—do ------- e End moraine, this study. -42 .71 .16 30 --—do ------- e Outwash terrace. -44 .65 .15 34 -—-do ------- e Do. -45 .68 .22 41 —--do ------- e Do. —46 .30 ‘ .14 36 -—-do ------- e Outwash terrace, variable lithologies, ‘ thick loess cover. -47 .40 .18 38 ——-do ------- e Outwash terrace. C75-134 1.05 1 .17 287 Indian John- e Data from Porter (1975). -l35 1.10 .11 413 Swauk Prairie e Do. -140 1.96 .24 346 Thorp -------- e Do. None 2.78 ‘ .23 70 Pre—Thorp(?)- e Do. 1 Mount Rainier, Wash. c75—123 0.23 1 0.16 34 Vashon ...... a -123 .27 .17 28 ——-do ------- b -124 .16 .11 38 —--do ------- a -116 .13 .09 27 Evans Creek— a -116 .08 .06 27 —--do ------- b 46 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES Measurements (mm) Sample Rock Remarks No. Standard type Mean deviation Number Deposit Mount Rainer, Wash.-~Continued -119 .15 .12 11 ~--do ------- a ~119 .17 .11 32 ~--do ——————— b ~129 .14 .08 24 -——do ------- a -129 .12 .09 38 —--do ——————— b C76 -41 .21 .15 18 --—do ------- 3 ~41 .24 .24 26 —--do ------- b C78-118 .17 .12 22 ---do ------- a Outwash. C77 ~44 1.03 .18 21 Hayden Creek a C75—120 .63 .25 16 ---do ------- a Slightly eroding site. -120 .84 .33 28 --~do ------- b Do. -122 .53 .29 33 ~--do——---—— 3 Deposit buried by about 1 m of loess. —122 .65 .29 35 -—-do ——————— b Do. -128 1.05 .39 36 —-—do~~---—~ a Slightly eroding site, may be mixed ' with older till. 1C76—40 1.45 .56 41 -~-do ------- a Inner moraine. ~40 1.95 .54 38 -—-do--——--- b Do. C78-115 .78 .20 38 --—do ------- a Outwash, stones from within loess. -115 .82 .21 31 —--do ------- b Do. 1 -116 1.03 .31 34 --~do ------- a Stones from within thin loess. ~116 .99 .24 26 —--do- —————— b Do. 1 -116 1.29 .30 43 -~-do ------- a Stones from within till beneath thin loess. -ll7 .34 .29 43 ---do~———--- a Recessional outwash. ~117 .31 .28 19 —--do ——————— b Do. 2 ~ll9 2.09 .68 33 Hayden Creek(?) a Oldest of three Hayden Creek(?) terraces downstream from terminus. 2C75-121 3.99 .71 36 Wingate Hill a 2 —121 3.50 .69 39 -——do ——————— b 2 -126 2.69 .71 44 —--do ------- a 2 —125 4.66 1.19 35 Logan Hill—- a 2 -118 7.38 1.43 21 ~--do ------- a 2 -118 8.63 1.88 15 ~--do ------- b Puget Lowland, Wash. C76 ~29 0.86 0.53 27 Not known--— f First marine terrace(?), Grays Harbor. ~30 .90 .53 13 —--do ------- f Do. C78~110 .68 .28 32 -~—do ------- f Do. C76 ~22 .26 .17 31 Vashon ------ f ~24 .21 .14 37 ---do- —————— f ~28 .16 .09 44 Lower Fraser f terrace. ~32 .24 .14 31 --—do ------- f ~39 .25 .19 45 --—do- ------ f Replicate of C76—32. ~38 .71 .30 40 High Fraser f terrace. 1 -26 1.13 .38 56 Salmon Springs f 1 —27 .87 .35 68 -~-do ------- f -33 .34 .22 55 Middle Salmon f Buried beneath 5 m of loess. Springs terrace - APPENDIX A V 47 Measurements (mm) Sample Rock Remarks No. tandard type eviation Number Deposit 9-0) Mean Puget Lowland, Wash.--Continued -37A .57 .48 37 ---do ------- f Buried beneath 3 m of loess. 1 -37B 1.07 .53 33 -_-do _______ f None-— 3.3 2.0 N Helm Creek-— f Data from Carson (1970). Do-- 2.6 2.5 N -——do ------- f Data from Carson (1970); outwash. Do-— 6 3 N Wedekind Creek f Data from Carson (1970). Lassen Peak, Calif. C75 -84 0.19 0.10 15 Tioga 3 -84 .20 1 .18 50 --—do ------- b —92 .15 .10 23 -—-do— ------ a —92 .11 .11 46 -—-do ------- b C76 -07 .17 .10 23 —--do ------- a "07 .14 010 22 ---d0 ------- b —12 .18 .07 17 ---do ------- a -12 .17 ‘ .08 38 ---do ------- b -06 .52 .35 10 ---do---——-- a Probably thin, older deposit. -06 .57 .38 21 ---do ——————— b Do. C75 -89 .40 1 .16 35 "early Tioga" a -89 .48 .21 32 ---do ——————— b C76 -08 .24 .11 38 -—-do ------- a —08 .27 .12 34 _—-do _______ b —13 .42 .22 23 ---do ------- a —13 .39 .22 60 ---do ------- b -11 .30 .15 27 ---do ------- a SMC3 measurements, replicate of C75-89. -11 .29 .14 27 ---do ------- a KLP3 measurements, replicate of C75-89. —11 .35 .18 33 —--do ------- b SMC measurements, replicate of C75-89. -11 .31 .18 33 --—do ------- b KLP measurements, replicate of C75-89. C75 -87 .61 1 .22 32 Tahoe— ------ a ‘87 .81 .21 33 ———do ——————— b -88 .84 .27 44 ---do ------- a —88 1.01 1 .36 31 ---do ------- b -85 .57 .20 43 —--do ——————— a -85 .62 .26 26 ---do ------- b C76 -10 .70 .24 39 ---do ------- a -10 .61 1 .29 7 —--do ------- b -09 .77 .24 45 ---do ——————— a -09 .71 .27 11 ---do ------- b -14 .74 .23 17 ---do— ------ a SMC measurements. -14 .86 .20 17 —--do ------- a KLP measurements. -14 .84 .27 77 —--do ------- b SMC measurements. -14 .84 ‘ .22 77 —-—do ------- b KLP measurements. 1c75 —86 .96 ‘ .27 32 pre—Tahoe--- a 1 -86 1.45 .49 31 —-—do ——————— b 1 -90 1.37 .48 26 -——do- ------ a 1 —90 2.23 .92 31 ---do--—---- 1, 48 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES Measurements (mm) Sample Rock Remarks N0 o Standard type Mean deviation Number Deposit Lassen Peak, Calif.—-Continued 1 -91 .91 .23 31 —-—do ------- a 1 -91 1.53 .46 27 ---do ------- b Truckee River, Calif., Nev. C75 -75 0.15 0.06 17 Tioga ------- a -75 .16> .07 40 -——do ------- b -81 .16 .08 21 ---do ------- a Outwash. -81 .16 .08 40 ---do ------- b Do. -76 .24 .11 38 Tahoe ------- a -76 .35 .23 36 --—do ——————— b —80 .19 .09 43 ———do ——————— a Outwash. —80 .20 .13 37 -——do ——————— b Do. —83 .22 .10 32 ——-do ------- a Do. —83 .16 .09 40 ———do- —————— b Do. C76 -04 .18 .08 42 ---do ——————— a -04 .18 .09 25 ---do ------- b 1075 ~79 1.06 .29 41 Donner Lake- a 1 -79 1.16 .31 37 ——-do ------- b 1 -78 .89 .22 32 ---do ------- a Outwash. 1 -78 .89 .22 27 ——-do ------- b Do. 1 —82 .80 .21 33 -—-do— ------ a Do. 1 —82 .85 .17 39 ——-do ------- b Do. 1 -77 .75 .22 31 Hobart ------ a Buried. 1 -77 1.00 .30 39 --~do ------- b Do. C76 —05 .36 .16 23 Not known—-- a Buried beneath Donner Lake Till. -05 .60 .33 33 ---do ------- b Do. Bighorn River, Mont. (Mapping of Hamilton and Paulson (1968)) C75 —62 0 N N First terrace h Miscellaneous metavolcanics. -58 .26 0.26 33 Second terrace h Do. —60 .32 .31 32 Third terrace h Do. -59 .28 .29 35 Fourth terrace h Do. -61 .46 .33 30 Fifth terrace h Do. Mammoth, Calif. (mapping of Curry (1971) and Burke (1979)) C75 -72 0.23 0.17 42 Tioga ------- f Inner moraine. -72 .21 .10 21 -—-do ------- g Do. -63 .25 .11 20 ———do ------- g Outer moraine. -63 .22 .12 17 -—-do ------- h Outer moraine, quartz latite. -63 .17 .08 7 ——-do ——————— f Outer moraine. —73 .18 .ll 25 Tahoe ——————— g -73 .26 .17 15 ———do------- f —65 .50 .29 32 Casa Diablo— g —65 .50 .39 26 --—do ------- f APPENDIX A 49 Measurements (mm) 1 Sample 1 Rock Remarks N0. Standard type Mean deviation Number Deposit West Walker River, Calif. (mapping of Clark (1967)) 1 C75 -69 0.18 ‘ 0.15 34 Tioga _______ c -68 .26 .31 40 Tahoe ------- c -70 .25 1 .23 41 —--do ------- c —67 .40 .27 36 Deep Creek-— c -66 .43 ‘ .27 36 Grouse Meadows c -66 .37 .22 30 ---do ------- g -71 .38 .34 25 Huntoon Gravel c f -71 1.72 ‘ .92 15 ---do— ------ Wallowa Lake, Ore. (mapping of Crandell (1967)4) 075-115 0.26 0.19 29 Wt“ --------- f -113 .38 ‘ .33 33 Tto --------- f -114 063 I37 43 Jt -------- f -112 .94 .36 38 Cto —————————— f Grand Mesa, Colo. (mapping of Yeend (1969)) C76 -01 0.08 1 0.06 39 Late Pineda1e f Grand Mesa Formation. —03 .95 .23 42 Pinedale—--—- f Do. 1 -02 1.39 ‘ .37 56 Bull Lake—--— f Land's End Formation. Siletz River, Ore. C76 -18 1.87 0.78 27 Not known—-— e Buried gravel below second(?) terrace. -19 .44 ‘ .14 40 ---do ------- e 15—m (first?) terrace. -21 .27 1 .09 26 ---do ------- e Do. -21 2.38 .80 14 --—do— ------ f lS-m (first?) terrace, diffuse inner rinds. ‘ Spokane, Wash. C76 -50 0.06 ‘ 0.06 27 Not known--— e Gravel from last Missoula flood. -50 .07 .06 21 ---do ------- d Do. ‘ South Fork Shoshone River, Wyo. C76 -76 0.08 ‘ 0.07 24 Pinedale(?)— a -76 .08 .08 20 -—-d0 ------- b Warm River Butte Area, Idaho, Wyo. (mapping of Richmond (1973a, b)) C78-100 0.32 1 0.13 36 Middle Pinedale f —101 .29 .13 31 —--do --------- f —102 .29 .12 36 Early Pinedale f f -108 .24 ‘ .10 34 -—-do _________ —109 .32 .11 30 ---do ————————— f 5O WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES Measurements (mm) Sample Rock Remarks No. Standard type Mean deviation Number Deposit Warm River Butte Area, Idaho, Wyo. (mapping of Richmond (1973a, b))--Continued -103 .26 .10 33 Bull Lake ----- f -106 .34 .13 42 —-—do— -------- f -107 .32 .13 25 ———do——-----—- f 1 -98 1.04 .20 32 Sacagawea Ridge f 1 -99 .99 .16 34 --—do ------- —- f 1 -104 .76 .16 37 ---do— -------- f - 97 .14 .19 27 —--do --------- f In calcareous soil, buried by 3 m of loess. -105 .53 .21 25 ---do- ------ f Buried by 2.5 m of loess. 1Outer part of weathering rind is soft. 2Outer part of weathering rind is very soft. 3SMC, s. M. Colman; KLP, K. L. Pierce. ‘'14, T, J, C, arbitrary letter designations of units from Crandell (1967); t, till; 0, outwash. APPENDIX B.—SAMPLE LOCATIONS AND SITE DATA [Climatic data for principal sampling areas given in headings in the form (Station, MAP, MATL where MAP is mean annual precipitation (cm) and MAT is mean annual temperature PC); N/A, not applicable. Data from US. Weather Bureau (1959). Where all topographic maps are in the same State as sampling area. State name not. given] Site No. Location Topographic map Vegetation Altitude Soil (m) le West Yellowstone, Mont., Wyo. (West Yellowstone, 53.7, 1.7) C76— 74 1.0 km NW. of Indian Creek Campground ----- Mammoth 15’, Wyo.-— Pine ———————— 2,245 —— — 75 Junction, Grand Loop and Bunsen Peak Roads —--do -------------- Grass, sage- 2,115 —— C75— 97 0.3 km SW. of Cougar Creek Patrol Cabin—-— Madison Junction Pine, grass- 2,110 5.0 15', Wyo. - 98 0.6 km SSW. of Cougar Creek Patrol Cabin-- -—-do —————————————— -——do ------- 2,100 -— - 99 0.7 km NNE. of Madison Range Overlook ----- ——-do -------------- —-—do ——————— 2,080 —— -101 1.0 km SSW. of Madison Range Overlook ----- ---d0 -—-d0 2,065 —- — 94 NW1/4SWl/4NW1/4, sec. 25, T. 12 3., R. 4 E. Tepee Creek 15', Grass, sage- 2,015 -— Mont. — 95 NW1/4NW1/4NW1/4, sec. 15, T. 12 S., R. 4 E. --—do —————————————— --—do ------- 2,015 5.8 - 96 NWl/4SW1/4SW1/4, sec. 15, T. 12 S., R. 5 E. --—do -------------- ——-do ------- 2,020 -- -100 SW1/4SE1/4SE1/4, sec. 10, T. 12 S., R. 5 E. ---do —————————————— Grass, fir-- 2,090 5.6 -102 NEl/4SE1/4NEl/4, sec. 6, T. 14 8., R. 5 E. West Yellowstone Pine, grass- 2,050 5.7 15’, Wyo. McCall, Idaho (McCall, 69.4, 4.4) C78—125 Center sec. 12, T. 15 N., R. 2 E. ————————— Cascade 15’ ———————— Grass, fir-- 2,050 —- C78-124 SW1/4SWl/4NW1/4, sec. 7, T. 15 N., R. 3 E. ---do -------------- Fir, grass-— 1,970 —- C75-106 NWl/4SW1/4NW1/4, sec. 3, T. 18 N., R. 3 E. McCall 7 1/2’ ------ Pine ———————— 1,540 5.7 C76- 51 NW1/4NW1/4SW1/4, sec. 2, T. 18 N., R. 3 E. ---do -------------- Pine-fir—--— 1,545 -— — 52 NEl/4NEl/4SEl/4, sec. 3, T. 18 N., R. 3 E. —-—do -------------- —--do ------- 1,540 -— — 69 NW1/4NW1/4NEl/4, sec. 3, T. 18 N., R. 3 E. ——-dc ---dc 1,540 -- C78—141 SW1/4NW1/4SE1/4, sec. 3, T. 18 N., R. 3 E. ---d0 —--d0 1,530 —- C76— 62 NWl/4SEl/4SW1/4, sec. 9, T. 18 N., R. 3 E. -—-do -------------- -—-do ------- 1,540 —- APPENDIX B 51 Site No. ‘ Location Topographic map Vegetation Altitude 5011 (m) pal ‘ ‘ McCall, Idaho (McCall, 69.4, 4.4)--Cont1nued — 63 NE1/4SE1/4S 1/4, sec. 8, T. 18 N., R. 3 E. —--do ---------- Fir, pine—-- 1,535 -- — 64 NWl/4SW1/4S 1/4, sec. 8, T. 18 N., R. 3 E. -—-do -------------- Pine-fir—-—- 1,540 -- 075-105 SW1/4NE1/4NW1/4, sec. 16, T. 18 N., R. 3 E. ---do Pine 1,540 6.1 C76 -65 SWl/4NW1/4NW1/4, sec. 16, T. 18 N., R. 3 E. ---do -------------- Pine, fir--- 1,545 -- -68 NW1/4NEl/4NEI/4, sec. 16, T. 18 N., R. 3 E. -—-do -------------- ---do ------- 1,555 -- 078-134 NE1/4NEl/4S 1/4, sec. 7, T. 18 N., R. 3 E. Meadows 7 1/2' ----- -—-do ------- 1,550 -— 075-107 SE1/4NW1/4SE1/4, sec. 16, T. 18 N., R. 3 E. McCall 7 l/2’—- Grass, sage— 1,535 5.5 C76— 66 SW1/4NW1/4S 1/4, sec. 16, T. 18 N., R. 3 E. ---do ------- 1,525 -- - 67 SE1/4SEl/4N 1/4, sec. 16, T. 18 N., R. 3 E. ---do ------- 1,540 —- - 59 NE1/4SWl/4NWl/4, sec. 15, T. 18 N., R. 3 E. Pine, aspen- 1,560 -- — 60 SW1/4NE1/4 1/4, sec. 15, T. 18 N., R. 3 E. 1,560 -- - 61 SW1/4NE1/4N 1/4, sec. 15, T. 18 N., R. 3 E. 1,560 —- - 71 SE1/4NE1/4N 1/4, sec. 15, T. 18 N., R. 3 E. 1,560 -— C78-121 SWl/4NE1/4SE1/4, sec. 7, T. 18 N., R. 3 E. Meadows 7 1/2' ----- Grass, sage, 1,550 -— pine. -135 NW1/4NE1/4S 1/4, sec. 7, T. 18 N., R. 3 E. ---do -------------- Grass, pine, 1,550 -- fir. -137 NE1/4NW1/4NW1/4, sec. 15, T. 18 N., R. 3 E. McCall 7 1/2' Pine -------- 1,570 -- —136 SE1/4NW1/4N%1/4, sec. 16, T. 18 N., R. 3 E. -—-do -------------- Pine, fir--- 1,555 -- C75-108 NW1/4NW1/4SW1/4, sec. 15, T. 18 N., R. 3 E. Grass, aspen 1,550 6.0 -104 NW1/4SEl/4S 1/4, Sec. 22, T. 18 N., R. 3 E. Pine 1,585 5.9 C76- 54 NWl/4SEl/4S 1/4, Sec. 22, T. 18 N., R. 3 E. --—do ------- 1,585 -- — 57 SW1/4SE1/4N 1/4, sec. 22, T. 18 N., R. 3 E. Pine-fir-——- 1,585 -- - 58 NW1/4NW1/4NE1/4, sec. 22, T. 18 N., R. 3 E. —--do ------- 1,585 -- C76-109 SW1/4SEl/4flE1/4, sec. 33, T. 18 N., R. 3 E. Lake Fork 7 1/2’--- Grass ------- 1,550 5.6 - 55 NWl/4NEl/4SE1/4, sec. 33, T. 18 N., R. 3 E. ---do -------------- —-—do ------- 1,550 —- — 56 NW1/4SW1/4NWl/4, sec. 34, T. 18 N., R. 3 E. ---d0 -------------- ---d0 ------- 1,555 -- Yakima Valley, Wash. (Cle Elum, 56.0, 7.9; Ellensburg, 23.0, 8.3) C75—131 SW1/4NWl/4SEl/4, sec. 2, T. 20 N., R. 14 E. Kachess Lake ------- Pine, grass- 690 5.8 -130 SW1/4NW1/4 W1/4, sec. 18, T. 20 N., R. 15 E. Easton 15' ----- ---do ------- 675 6.0 -133 NW1/4NW1/4 E1/4, sec. 29, T. 20 N., R. 15 E. Cle Elum 15'—-- ---do--- 655 6.0 C76— 1.2 do ---do -------------- -—-do ------- 655 —— — 43 SW1/4NE1/4 W1/4, sec. 19, T. 20 N., R. 15 E. Easton 15' --------- Pine, fir-—— 695 ~- - 44 SE1/4SEl/4 El/4, sec. 34, T. 20 N., R. 15 E. Cle Elum 15' ------- Pine, gtass- 625 -- - 45 NEl/4SW1/4 E1/4, sec. 33, T. 20 N., R. 16 E. Pine-grass-— 570 -— - 46 NW1/4NEl/4NE1/4, sec. 14, T. 18 N., R. 17 E. Thorp 15' ---------- Grass-sage-- 505 -- — 47 NEl/4SW1/4in/4, sec. 35, T. 18 N., R. 18 E. --do -------------- Grass—sage?- 470 —- C75-134 SE1/4SW1/4 E1/4, sec. 1, T. 19 N., R. 15 E. Cle Elum 15' ------- Grass ------- 645 6.2 —135 SW1/4SWl/4NW1/4, Sec. 29, T. 20 N., R- 17 E. Thotp 15' --------------- do ----- 750 6.3 Mount Rainier, Rash. (Puyallup 103, 10.5; Buckley, 126, N/A; Longmire, 209, N/A; Stampede Pass, 234, 4.2) 075-123 NE1/4NWl/4NW1/4, sec. 8, T. 17 N., R. 4 E. Chop Valley 15'---- Mixed forest 200 5.2 -124 NEl/4NE1/4 El/4, sec. 16, T. 20 N., R. 6 E. Lake Tapps 15' ----- Grass ------- 200 -- -116 NE1/4NW1/4 E1/4, sec. 28, T. 12 N., R. 6 E. )flneral 15’ -------- Fir --------- 280 5.8 -119 NW1/4SE1/4 E1/4, sec. 28, T. 15 N., R. 6 E. Kapowsin 15’ ------- Mixed forest 515 5.8 —129 1.6 km E. f Ranger Creek Camp ------------- Greenwater 15’ ----- 905 -- C76- 41 NW1/4SE1/4EE1/4, sec. 11, T. 16 N., R. 6 E. Kapowsin 15' ------ 590 -— - 40 SW1/4NE1/4 E1/4, sec. 31, T. 16 N-, R- 6 E. --d0 -------------- 610 -- C78-118 NE1/4NW1/4NE1/4, sec. 23, T. 12 N., R. 1 E. Onalaska 15' ------- 110 -- 077— 44 SE1/4NE1/4tW1/4, sec. 9, T. 12 N., R. 2 E. -—-do -------------- 165 -- C75—120 SE1/4SW1/4 W1/4, Sec. 11, T. 15 N., R. 4 E. Ohop Valley 15'---— 380 5.4 -122 NE1/4SE1/4NW1/4, sec. 9, T. 14 N., R. 5 E. Mineral 15' -------- 445 -- -128 sec. 5, T. 19 N., R. 8 E. Enumclaw 15' ------- 465 —— NE1/4NE1/4FEl/4, 52 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES Site No. Location Topographic map Vegetation Altitude 3011 (m) pH Mount Rainer, Wash. (Puyallup, 103, 10.5; Buckley, 126, N/A; Longmire, 209, N/A; Stamfiede Pass, 234, 4.)--Cont. C78—115 NE1/4SW1/4SEl/4, sec. 10, T. 12 N., R. 2 E. Onalaska 15' ------- 165 -- -116 NW1/4NW1/4NWl/4, sec. 15, T. 12 N., R. 3 E. Morton 15' --------- 270 -- -117 Nw1/4NEl/4NEl/4, sec. 2, T. 11 N., R. 5 E. Spirit Lake 15’--—— 260 —- -ll9 NEl/4SWl/4NE1/4, sec. 21, T. 12 N., R. 1 E. Onalaska 15' ------- 135 -- 075-121 Center sec. 2, T. 15 N., R. 4 E. ----------- Ohop valley 15’---- 425 5.6 -126 NW1/4SE1/4NWl/4, sec. 35, T. 20 N., R. 7 E. Enumclaw 15' ------- 475 —- —125 Nw1/4SWl/4NE1/4, sec. 35, T. 20 N., R. 7 E. --do 490 —- -118 Center border sec. 26-35, T. 13 N., R. 1 E. Onalaska 15' ——————— 200 5.5 Puget Lowland, Wash. (Oakville, 139, 10.5; Blue Glacier, 397, 1.6) C76— 29 NEI/4SE1/4NEl/4, sec. 27, T. 19 N., R. 12 W. Copalis Beach Mixed forest 20 —- 7 1/2'. — 30 SW1/4NE1/4NE1/4, See. 29, T. 20 N., R. 12 W. Moclips 7 1/2' ----- ———do—--———- 25 -- C78-110 NW1/4NE1/4SW1/4, sec. 14, T. 19 N., R. 12 W. --dc ---dc 20 -- C76- 22 SW1/4NW1/4NW1/4, sec. 11, T. 20 N., R. 6 W. Elma 15' ----------- Fir --------- 140 -- — 24 NWl/4SE1/4NEl/4, sec. 8, T. 20 N., R. 5 W. ---do -------------- Mixed forest 150 -- — 28 SE1/4SWl/4SEl/4, sec. 18, T. 19 N., R. 6 W. ---dc Fir 65 -- - 32 NE1/4NW1/4NEl/4, sec. 2, T. 17 N., R. 7 W. Montesano 15’ ------ Mixed forest 10 -- — 39 do -——do --—dc 10 -- — 38 NEl/4SE1/4NW1/4, sec. 33, T. 18 N., R. 8 w. Wynoochee ———do ------- 25 —- Valley 15'. — 26 NE1/4NEl/4SE1/4, Sec. 6, T- 19 N., R. 6 W. Elma 15' ----------- Fir --------- 105 -- — 27 SWl/4SW1/4SW1/4, sec. 3, T- 19 N., R. 6 W. ---do -------------- Mixed forest 130 -- - 33 SE1/4NW1/4SE1/4, sec. 25, T. 18 N., R. 7 w. ——-dc ——do 35 -- - 37 NW1/4NW1/4SW1/4, sec. 28, T. 18 N., R. 8 w. Wynoochee --—do ------- 50 -- Valley 15'. Lassen Peak, Calif. (Mineral, 131, 8.0; Manzanita Lake, 108, 6.5) 075— 84 SW1/4NWl/4NWl/4, sec. 34, T. 30 N., R. 4 E. Lassen Peak 15’-——— Pine, grass- 1,995 5.1 — 92 NW1/4SE1/4NEl/4, sec. 10, T. 31 N., R. 4 E. Manzanita Lake 15’— Pine -------- 1,790 5.2 C76- 07 SWl/4SEl/4SEl/4, sec. 4, T. 29 N., R. 6 E. Mt. Harkness 15'-—- Pine, grass- 1,560 -- - 12 SEl/4SW1/4SW1/4, sec. 35, T. 31 N., R. 3 E. Lassen Peak 15’—--— Fir ————————— 1,855 -— - 06 NE1/4NE1/4NWl/4, sec. 4, T. 29 N., R. 6 E. Mt. Harkness 15’--- Pine ———————— 1,560 —- C75- 89 NW1/4SEl/4SEl/4, sec. 22, T. 29 N., R. 4 E. Lassen Peak 15'---- ---do ——————— 1,525 5.9 C76- 08 SE1/4SE1/4NE1/4, sec. 21, T. 29 N., R. 6 E. Mt. Harkness 15'--- ——-do ——————— 1,540 -- - l3 NW1/4SWl/4SE1/4, sec. 35, T. 31 N., R. 3 E. Lassen Peak 15’---- Fir --------- 1,900 -- — 11 NW1/4SEl/4SE1/4, sec. 22, T. 29 N., R. 4 E. --do Pine 1,525 5.9 c75— 87 SW1/4NEl/4NE1/4, sec. 28, T. 29 N., R. 4 E. —--do -------------- ---do ------- 1,625 -— - 88 SW1/4SWl/4SWl/4, Sec. 22, T. 29 N., R. 4 E. --—d0 ---d0 1,575 -- - 85 SW1/4SWl/4NE1/4, Sec. 20, T. 29 N., R. 4 E. —--do -------------- ---do ------- 1,605 5.9 C76— 10 SW1/4SEl/4SW1/4, sec. 27, T. 29 N., R. 6 E. Mt. Harkness 15'--- Pine, fir——- 1,485 —- - 09 NE1/4SE1/4NE1/4, sec. 34, T. 29 N., R. 6 E. —--dc Pine 1,480 ~- - l4 NW1/4NEl/4NEl/4, sec. 3, T. 30 N., R. 3 E. Lassen Peak 15'—-—— Fir, pine-—— 715 —- C75- 86 SE1/4SW1/4NEl/4, sec. 20, T. 29 N., R. 6 E. ---dc Pin: 1,625 6.1 — 90 NEl/4NW1/4NE1/4, sec. 28, T. 29 N., R. 6 E. ---d0 --—d0 1,660 5.3 — 91 SW1/4SW1/4SE1/4, Sec. 16, T. 29 N., R. 6 E. ---do -------------- -—-do ------- 1,705 -- Truckee River, Ca1if., Nev. (Truckee, 80.0, 6.0; Reno, 18.0, 9.5) C75- 75 SW1/4SW1/4NW1/4, sec. 16, T. 17 N., R. 16 E. Truckee 15', Pine -------- 1,800 6.1 Calif. - 81 NE1/4SE1/4NWl/4, sec. 16, T. 17 N., R. 16 E. ---do -------------- --—do ——————— 1,795 5.8 - 76 NEl/4NW1/4SW1/4, sec. 16, T. 17 N., R. 16 E. -—-d0 ---d0 1,825 -- - 80 Nw1/4NW1/4SW1/4, sec. 5, T. 17 N., R. 17 E. —--do -------------- Sage, grass- 1,775 -- - 83 NEl/4SEl/4SEl/4, sec. 7, T. 19 N., R. 18 E. Verdi 7 1/2', Nev.- Grass, pine- 1,485 6.2 C76— 04 SWl/4SEl/4NW1/4, sec. 9, T. 17 N., R. 16 E. Truckee 15', Calif. Pine -------- 1,900 -- APPENDIXB 53 Site No. ‘Location Topographic map Vegetation Altitude Soil (m) pHl Trxckee River, Calif., Nev. (Truckee, 80.0, 6.0; Reno, 18.0, 9.5)——Continued C75- 79 SE1/4NW1/4S /4, sec. 11, T- 17 N-, R. 16 E. —--do -------------- ---do ------- 1,785 6.4 - 78 SE1/4SE1/4SE1/4, sec. 25, T. 18 N., R. 16 E. -——do -------------- Sage, grass— 1,755 -— - 82 NEl/4SW1/4S /4, sec. 18, T. 19 N., R. 18 E. Verdi 7 1/2', Nev.- —--do ------- 1,510 6.2 — 77 SWl/4SW1/4SE1/4, Sec. 10, T. 17 11., R. 16 E. Truckee 15', Calif. Pine -------- 1,800 6.0 C76- 05 SE1/4NW1/4Sfl1/4, Sec. 11, T. 17 N., R. 16 E. ---do -------------- --—do ------- 1,785 -- Bighorn River, Mont. C75- 62 NEl/4SE1/4Sél/4, sec. 33, T. 5 5., R. 31 E. Yellowtail Grass ------- 970 —— Dam 7 1/2’. - 58 NE1/4SE1/4SW1/4, sec. 1, T. 6 5., R. 31 E. Mountain Pocket Grass, sage- 990 -- Creek 7 1/2'. — 60 SWl/4SE1/4821/4, sec. 19, T. 4 S., R. 31 E. Lemonade Grass ------- 1,005 -— Springs 7 1/2'. - 59 SWl/4SE1/4SVl/4, sec. 19, T. 4 5., R. 31 13- ---do -------------- —--do ------- 1,025 -— — 61 NE1/4SEl/4S 1/4, sec. 2, T. 4 S., R. 31 E. Woody Creek Sage, grass- 1,085 —— Camp 7 1/2'. ‘ Mammoth, Calif. C75- 72 SW1/4SE1/4N21/4, sec. 2, T. 4 5., R. 27 E. Mt. Morrison 15'--- Sage, man- 2,390 —- zanita. - 63 SEl/4SEl/4S 1/4, sec. 2, T. 4 5., R. 27 E. —--do -------------- —-—do ------- 2,450 —- — 73 SEl/4SEl/4S 1/4, sec. 36, T. 3 5., R. 27 E. ———do -------------- Sage, grass- 2,305 -- - 65 SE1/4NE1/4S 1/4, See. 31, T. 3 s., R. 28 E. —--do -------------- ---do ------- 2,270 -— ‘ West Walker River, Calif. C75- 69 SW1/4NE1/4SLl/4, sec. 21, T. 6 N., R. 23 E. Fales Hot Sage, grass- 2,105 -- Springs 15'. — 68 SEl/4NW1/4S 1/4, sec. 21, T. 6 N., R. 22 E. Sonora Pass 15'-——— -—-do ------- 2,635 -— - 70 NWl/4SW1/4NF1/4, sec. 23, T. 6 N., R. 23 E. Fales Hot ---do ------- 2,195 -— Springs 15'. — 67 NEI/hSW1/4NE1/4, sec. 22, T. 7 N., R. 23 E. ---dO -------------- ---do ------- 2,220 ~— — 66 NW1/4NW1/4NW1/4, sec. 5, T. 6 No, R. 23 E. --d0 -------------- ---d0 ------- 2,610 -— — 71 SE1/4SW1/48F1/4, sec. 35, T. 6 No, R. 24 E. ---d0 -------------- ---do ------- 2,105 -- Wallowa Lake, Ore. C75-115 SEl/4NW1/4 El/4, sec. 5, T. 3 8., R. 45 E. Joseph 15' ————————— Grass ------- 1,340 -- -113 SE1/4SW1/4NE1/4, sec. 9, T. 3 S., R. 45 E. --do -------------- Grass, sage- 1,535 -— -114 NW1/48E1/4NE1/4, sec. 9, T. 3 So, R. 45 E. -—-do -------------- --—do ------- 1,500 —- -112 NWl/4SW1/4WW1/4, sec. 15, T. 3 5., R. 45 E. --do -------------- Pine, grass- 1,455 —- \ Grand Mesa, Colo. C76— 01 0.2 km N. #f Bonham Reservoir —————————————— Grand Mesa Spruce-fir-- 2,980 —— , 7 1/2’. - 02 SE1/4NW1/4SW1/4, sec. 4, T. 12 S., R. 96 W. Lands End Grass, spruce 3,140 -— 7 1/2'. - 03 NE1/4SE1/49W1/4, sec. 3, T. 12 S., R. 96 W. Skyway 7 1/2' ------ Spruce, grass 3,185 -- Siletz River, Ore. C76- 18 NEI/4SE1/4fiW1/4, sec. 24, T. 8 8., R. 11 W. Euchre Mt. 15’ ----- Mixed forest 15 -- - 19 NE1/4SW1/4 E1/4, sec. 21, T. 9 5-, R. 10 W. --d0 -------------- ---do ------- 20 -- - 21 NW1/4NE1/4SW1/4, sec. 33, T. 9 So, R. 9 W. Toledo 15' --------- —-do ------- 65 —- Spokane, Wash. 076- 50 SE1/48Wl/4NE1/4, sec. 29, T. 25 N., R. 42 E. Medical Lake 15’--- Grass ------- 705 -— 54 WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES Site No. Location Topographic map Vegetation Altitude 8011 (m) le South Fork Shoshone River, Wyo. C76- 76 1.5 km E. of mouth of Ishawooa Creek ——————— Ishawooa 15' ——————— Grass ------- 1,890 -- Warm River Butte Area, Idaho, Wyo. C78—100 0.6 km NNW. of Bechler River Ranger Station Warm River Butte Pine -------- 1,966 —— 15', Idaho—Wye. —101 1.0 km NNW. of Bechler River Ranger Station ——-do -------------- --—do ------- 1,969 —— -102 NE1/4NWl/4NE1/4, sec. 11, T. 9 N., R. 45 E. ---do— ------------- Pine, aspen— 1,868 -— -108 NW1/4NE1/4NWl/4, sec. 3, T. 47 N., R. 118 W. ---do -------------- Pine, grass- 1,960 -- —109 NW1/4SE1/4NW1/4, sec. 4, T. 47 N., R. 118 W. ——-do -------------- Grass, pine- 1,966 —- -103 NE1/4NE1/4NW1/4, sec. 19, T. 9 N., R. 45 E. ---do -------------- Fir, aspen, 1,743 -- sage. —106 NEI/4NW1/4NW1/4, sec. 3, T. 8 N., R. 45 E. ---do -------------- Pine, aspen, 1,902 -— grass. -107 NW1/4NE1/4NE1/4, sec. 2, T. 8 N., R. 45 E. —--do -------------- —--do ------- 1,935 -- - 98 NW1/4NE1/4NW1/4, sec. 33, T. 47 N., R. 118 W. McReynolds Res. Pine -------- 2,109 —- 7 1/2’, Idaho—Wye. — 99 NE1/4SW1/4SW1/4, sec. 28, T. 47 N., R. 118 W. Warm River Butte --—do ------- 2,097 -- 15', Idaho—“yo. —104 NW1/4NWl/4SE1/4, sec. 24, T. 10 N., R. 44 E. ---do -------------- Aspen, grass- 1,878 —— - 97 SE1/4NE1/4SE1/4, sec. 32, T. 8 N., R. 44 E. Drummond 7 1/2’, Sage, grass-- 1,783 —- Idaho. —105 SW1/4SW1/4NW1/4, sec. 5, T. 8 N., R. 45 E. Warm River Butte Grass, pine—- 1,993 -- 15’, Idaho—Wye. 1 1:1 soil-water mixture, <0.2 um fraction; leaders (—-), not measured. APPENDIX C.—GENERALIZED PETROGRAPHIC DESCRIPTIONS The following are generalized petrographic descrip- tions of the rock types in each of the major study areas on which weathering rinds were measured. cent, olivine, 5—10 percent; glass and chlorophaeite, 5—10 percent; and opaque minerals about 10 percent. McCALL BASALTS Rocks examined near McCall, Idaho, are extremely WEST YELLOWSTON E Basalts examined near West Yellowstone, Mont., were derived from the Madison River Basalt (Chris- tiansen and Blank, 1972). The rocks contain scattered phenocrysts of plagioclase as much as 1 mm long, and less commonly phenocrysts of olivine as much as 0.5 mm in diameter, locally in glomeroporphyritic clusters. The matrix consists of plagioclase, in laths 0.1—0.2 mm long; crystals of clinopyroxene, olivine, and opaque minerals, about 0.05—0.1 mm in diameter; and irregular-shaped masses of basaltic glass and chlorophaeite. Matrix textures are mostly in- tergranular to intersertal, and less commonly subophitic. Visual estimates of the modal composition are: plagioclase, 45—55 percent; pyroxene, 25—30 per- uniform in texture and composition and are probably derived from the upper part of the Yakima Basalt Subgroup of the Columbia River Basalt Group (John Bond, oral commun., 1976). The rocks are mostly aphanitic, consisting of plagioclase laths 0.1 to 0.2 mm long (with scattered microphenocrysts up to 0.5 mm long); crystals of clinopyroxene, olivine, and opaque minerals 0.05-0.01 mm in diameter; and irregular-shaped masses of glass, chlorophaeite, and calcite. The textures are mostly intersertal to hyaloophitic; less commonly intergranular to subophitic. Visual estimates of the modal composition are plagioclase, 45—55 percent; pyroxene, 20—30 per- cent; olivine, 0—5 percent; calcite, 0—5 percent; glass and chlorophaeite, 15—20 percent; opaque minerals, 10—15 percent. APPENDIX C 55 YAKIMA VALLEY Rocks examined from the Yakima Valley are derived from the Eocene Teanaway Basalt (Foster, 1958; Porter, 1975). They are mostly aphanitic, but some contain scattered phenocrysts of plagioclase or opaque minerals 0.3—0.5 mm in longest dimension. Grain size generally ranges between 0.05 and 0.2 mm, and tex- tures are mostly intersertal; less commonly textures are intergranular, hyaloophitic, and subophitic. Visual estimates of the modal composition are: plagioclase, some of which is zoned, 45—55 percent; clinopyroxene, 25-35 percent; olivine, 0—10 percent; opaque minerals, 5-10 percent; glass, chlorophaeite, and (or) chlorite, 10—20 percent; and rare (<1 percent) potassium feldspar. PUGET LOWLAND The precise source of the basalt in the Puget Lowland drifts is not known, but it is probably mostly derived from the Eocene Crescent Formation in the Olympic Mountains. The basalt contains microphenocrysts of plagioclase, 0.5-0.8 mm long, and clinopyroxene, 0.3—0.5 mm in diameter. The matrix consists mostly of thin plagioclase laths (0.3—0.5 mm long); equant clinopyroxenes (0.05—0.1 mm in diameter); and irregular-shaped masses of devitrified glass, chlorophaeite, and chlorite. Glass is rarely present. Textures are mostly interser- tal, less commonly hyaloophitic. Visual estimates of the modal composition are: plagioclase, 40—55 percent; clinopyroxene, 25-35 percent; olivine, 0—1 percent; opaque minerals, 5—10 percent; and altered glass and chlorite, 10—20 percent. ANDESITES Weathering rinds from sampling areas containing andesitic rocks were measured on two groups of stones: “coarse grained” and “fine grained." The two textural groups represent an arbitrary field classifica- tion based on phenocryst content and matrix texture. See p. 12 for definition of these textural groups. MOUNT RAINIER Most of the rocks examined from the Mount Rainier area were derived from andesite of the Mount Rainier volcano (Fiske and others, 1963), although some weathering rinds were measured on stones derived from older volcanic rocks. The andesite of the Mount Rainier volcano is a hypersthene andesite and is remarkably uniform in composition. The fine-grained andesites contain scattered phenocrysts 0.5—1.5 mm in largest dimension, whereas microphenocrysts 0.1-0.3 mm long are more abundant. Plagioclase is the most abundant phenocryst, with lesser amounts of pyroxene, and a few crystals of amphibole and olivine. Both the plagioclase and the pyroxene are typically zoned, with plagioclase showing a wide range in degree of zoning. Both ortho- and clinopyroxenes are present; slightly pleochroic orthopyroxene (hypersthene?) is more abun- dant. Amphiboles and some pyroxenes exhibit reaction rims of iron oxides. The matrix is very fine grained (0.01—0.05 m in size) and appears to consist mostly of plagioclase, pyroxene, Opaques, and glass. Visual estimates of the modal composition are: plagioclase, 45—50 percent; pyroxene, 30—35 percent; Opaques, 5—10 percent; glass, 5—10 percent; amphibole, 0—1 percent; and olivine 0-1 percent. Textures are primarily hyaloopilitic. Coarse-grained andesites are similar compositionally to fine-grained andesites. The grain size is highly bimodal, with abundant large (0.5—3.0 mm) phenocrysts of plagioclase and pyroxene, and rare phenocrysts of olivine and opaque minerals, in a very fine grained (0.01—0.03 m) matrix. The pyroxene phenocrysts commonly occur in glomeroporphyritic clusters. Textures range from hyaloopilitic to pilotax- itic. LASSEN PEAK Rocks examined from the Lassen Peak area were derived from a variety of andesitic flows which make up the volcanic complex around Lassen Peak (Williams, 1932). The mineralogy of these andesites is moderately variable. The fine-grained andesites are nonporphyritic to weakly porphyritic. Phenocrysts, if present, range from 0.3 to 1.5 mm in size; plagioclase (some of which is zoned) is generally the largest and most abundant phenocryst; phenocrysts of clino- or orthopyroxenes and olivine are less common. The matrix is typically fine grained (0.08—0.1 mm) and consists of plagioclase, pyroxene, opaque minerals, glass, and rarely calcite, potassium feldspar, and olivine. In rocks containing calcite or olivine, clinopyroxene is more abundant than orthopyroxene. Textures are mainly pilotaxitic to in- tergranular. Visual estimates of the modal composi- tion are: plagioclase, 40—60 percent; pyroxene, 25—40 percent; Opaques, 5—10 percent; glass, 0—15 percent; potassium feldspar, 0—10 percent; calcite, 0—5 percent; and olivine, 0—15 percent. The coarse-grained andesites have similar miner- alogy, except that they contain very little glass. 56 Phenocrysts are abundant, the most common being plagioclase (1.0—2.0 mm long), which is commonly zoned. Pyroxene (clino- more abundant than ortho-) and olivine phenocrysts range from 0.6 to 1.2 mm in size. The matrix grain-size is about 0.1—0.2 mm. Tex- tures are mostly intergranular to pilotaxitic. TRUCKEE The rocks examined from near Truckee, Calif., were derived mostly from the late Tertiary andesites that are abundant in the area. A few basalt clasts (those without olivine phenocrysts) from the Pliocene and Pleistocene Lousetown Formation (Birkeland, 1963) may have been included with the fine-grained andesites. The fine-grained andesites contain microphenocrysts 0.1—0.3 mm in size and a few scattered phenocrysts up Am I . . it | ., 4.1 EARTH Qfilfifllg‘ES-llngY WEATHERING RINDS AS A QUARTERNARY AGE INDICATOR, WESTERN UNITED STATES to 2 mm in size. The phenocrysts are plagioclase, pyroxene, olivine, and amphibole in varying propor- tions; the microphenocrysts are plagioclase (most abundant) and pyroxene. A few of the plagioclase and pyroxene phenocrysts are zoned. Clinopyroxene is commonly more abundant than orthopyroxene. The matrix is very fine grained (0.02—0.07 mm) and con- sists mostly of plagioclase, pyroxene, and opaque minerals. Glass is scarce. Visual estimates of the modal composition are: plagioclase, 50—65 percent; pyroxene, 20—35 percent; Opaques, 5—10 percent; olivine, 0-10 percent; amphibole, 0-5 percent; glass, 0—5 percent. Textures are primarily pilotaxitic to trachytic. The coarse-grained andesites are similar mineralogi- cally and texturally to the fine-grained andesites. They contain abundant phenocrysts of plagioclase and pyroxene 0.5—2.0 mm in size, in a matrix whose grain size is generally 0.01—O.1 mm. .9007 a LLS. GOVERNMENT PRINTING OFFICE: 1930—777034/36 EM“ 7 DA Y5 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19-20, 1977 Report prepared jointly by the U.S. Geological Survey and the National Oceanic and Atmospheric Administration U.S. DEPARTMENT OF THE INTERIOR O U.S. DEPARTMENT OF COMMERCE 4m Josue/1:11.15 DEP/mylizziifl i ”1.7,. ,‘ H , <-_ J . i f < .‘LEF’OSI TORY rial/‘1 9 1982 ‘_ HENRY ummsm or CALIFORNIA GEOLOGICAL SURVEY PROFESSIONAL PAPER 1211 JOHNSTOWN—WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19-20, 1977 By L. RAY HOXIT, ROBERT A. MADDOX, CHARLES F. CHAPPELL, National Oceanic and Atmospheric Administration, and STAN A. BRUA, U.S. Geological Survey GEOLOGICAL SURVEY PROFESSIONAL PAPER 1211 Report prepared jointly by the U.S. Geological Survey and the National Oceanic and Atmospheric Administration UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON:1982 UNITED STATES DEPARTMENT UNITED STATES DEPARTMENT OF THE INTERIOR OF COMMERCE JAMES G. WATT, Secretary MALCOLM BALDRIGE, Secretary GEOLOGICAL SURVEY NATIONAL OCEANIC AND ATMOSPHERIC ADMINISTRATION Dallas L. Peck, Director John V. Byrne, Administrator Library of Congress Cataloging in Publication Data United States. Geological Survey. Johnstown-western Pennsylvania storm and floods of July 19—20, 1977. (Geological Survey professional paper ; 121]) Bibliography; p. Supt. of Doc. no.: I 19.1621211 1. Johnstown metropolitan area, Pas—Storm, 1977. 2. Johnstown metropolitan area, I’a.--Flood, 1977. I. lioxit, Lee R. 11. United States. National Oceanic and Atmospheric Administration. HI. Title. W. Series: United States. Geological Survey. Professional paper ; 1211. QC943.5.U6U53 551.48’9’0974877 80—607777 For sale by the Distribution Branch, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 CONTENTS Page Page Glossary IV The floods of July 19-20, 1977—Continued Abstract 1 Determination of peak discharges ____________________ 30 Introduction 1 Descriptions of the floods 30 Acknowledgments 1 Allegheny River basin _________________________ 30 Conversion factors 3 Conemaugh River basin __________________________ 31 The meteorology 3 Susquehanna River basin _______________________ 39 General meterological conditions _____________________ 3 Potomac River basin 39 Mesoscale analysis 8 Summary of flood stages and discharges ________________ 40 Distribution of rainfall 21 Breached dams 40 Discussion and summary 28 Historical floods 43 The floods of July 19—20, 1977 ___________________________ 29 Deaths and damages 54 Recurrence intervals 29 References 55 ILLUSTRATIONS Page FIGURE 1—5. Maps showing: 1. Location of flood area in western Pennsylvania 2 2. Surface analyses 4 3. Five-hundred-millibar analyses 5 4. Stability indices 9 5. Precipitable-water analyses 10 6. Plots of Pittsburgh rawinsonde data 11 7. Graph showing vertical profiles of equivalent potential temperature derived from the Pittsburgh rawinsonde data _____ 13 8. Maps showing regional mesoscale analyses, 1400 EDT, July 19, through 0400 EDT, July 20, 1977 _________-________ 14 9. Geostationary Operational Environmental Satellite (GOES) photographs, 1400 EDT, July 19, through 0400 EDT, July 20, 1977 18 10. Maps showing hourly positions of major thunderstorm outflow boundaries 22 11. Maps showing hourly rainfall analyses 23 12. Graphs showing observed hourly rainfall at three stations within the heavy rainfall area _________________________ 27 13—15. Maps showing: 13. Total rainfall indicated by meteorological radar 29 14. Total observed rainfalls 30 15. Locations of flood-determination sites in western Pennsylvania 32 16. Graph of maximum discharge versus drainage area for flood of July 19—20, 1977, and for other known floods __________ 34 17. Photograph showing remains of several homes and a church along Little Paint Creek in Scalp Level _________________ 35 18. Hydrographs of stage and discharge of Stony Creek at Ferndale 36 19. Photograph showing aerial view of breach in Sandy Run Dam 37 20. Hydrographs of stage and discharge of Little Conemaugh River at East Conemaugh 38 21—27. Photographs showing: 21. Flooded business establishments in downtown Johnstown at Park Place 39 22. Flooding at Franklin Street United Methodist Church in J ohnstown 40 23. Flooding at Johnstown's Lee Hospital 42 24. Stony Creek near the height of the flood 43 25. Maximum heights of the 1889, 1936, and 1977 floods at Johnstown’s City Hall 44 26. Destruction along an unnamed tributary to the Conemaugh River between the Coopersdale and Minersville sec— tions of Johnstown 45 27. Laurel Run Dam 46 28—30. Graphs showing: 28. Hydrographs of stage and discharge of the Conemaugh River at Seward 48 29. Flood-crest profile below Laurel Run Dam 49 30. Flood-crest profile below Sandy Run Dam 50 III IV CONTENTS FIGURES 31—34. Photographs showing: Page 31. Flood damage downstream from the Laurel Run Dam 51 32. Eastbound lanes of State Highway 56, near Johnstown’s eastern corporate boundary, undermined by flood- waters from Solomon Run 52 33. Home damaged by flooding from Solomon Run in the Walnut Grove section of J ohnstown _____________-____ 53 34. Flooding in the Homerstown section of J ohnstown 54 TABLE S Page TABLE 1. Summary of flood stages and discharges 41 2. Breached dams 43 3. Losses in individual severe floods in the United States since July 1902 54 4. Site descriptions and gage-height and discharge data 59 5. Floodka data 64 GLOSSARY Acre-foot (acre-ft). The quantity of water required to cover 1 acre to a depth of 1 foot. It is equal to 43,560 ft? (cubic feet), 325,851 gal (gallons), or 1233 m3 (cubic meters). Altimeter settling. The pressure required to make an altimeter indicate zero altitude at an elevation of 10 ft above mean sea level. Cirrus anvil. High clouds that spread outward from the tops of thunderstorms. Continuous-record station. A gaging site where a record of the flood hydrograph is collected systematically. Convection. Vertical motions and mixing resulting when the at- mosphere becomes thermodynamically unstable. Crest-stage station. A stream-gaging site where only information on crest stage and peak discharge is collected systematically. Cubic feet per second (ft3/s). A rate of discharge. One cubic foot per second is equal to the discharge of a stream of rectangular cross sec- tion 1 ft wide and 1 ft deep, flowing at an average velocity of 1 ft per second. Cubic feet per second per square mile. ((ft3/s)/mi2). The average number of cubic feet of water per second flowing from each square mile of area drained by a stream, with the assumption that the runoff is distributed uniformly in time and area. Current meter. An instrument for measuring the velocity of flowing water. Datum of the gage. The elevation of the “zero” reading of a stream- flow—gaging station above the National Geodetic Vertical Datum of 1929. Dewpoint (or dewpoint temperature). The temperature to which a parcel of air must be cooled at constant pressure and constant water- vapor content in order for saturation to occur. Drainage area of a stream at a specific location. The area, measured in a horizontal plane, that is enclosed by a topographic divide. Drainage area is given in square miles. Echoes. In radar terminology, a general term for the appearance on a radar indicator of the electromagnetic energy returned from a target. Equivalent potential temperature. The temperature an air parcel would have after undergoing the following processes: dry-adiabatic expansion until saturated, pseudo-adiabatic expansion until all moisture is precipitated out, then dry adiabatic compression to a pressure of 1,000 mb (millibars). Flood-wave routing model. A mathematical model for determining the timing and shape of a flood wave at successive points along a stream. Front. Boundary separating two different air masses. Gage height. The water-surface elevation referred to some arbitrary gage datum. Gage height is often used interchangeably with the more general term “stage,” although gage height is more appropriate when used with a reading on a gage. Gaging station. A particular site on a stream, canal, lake, or reservoir where systematic observations of gage height or discharge are ob- tained. Hydrograph. A graph showing gage height or stage, discharge, velocity, or other property of water with respect to time. Inversion (temperature inversion). A layer in the atmosphere in which the temperature increases with height. Isobar. A line of equal or constant barometric pressure. Isotherm. A line of equal or constant temperature. K Index. A stability index defined as KI = (Tam — T500) — (T— Td)7oo+ T4350, where T“o is the 850-mb temperature, Two is the 850-mb dewpoint temperature, Two is the 500-mb temperature and (T — T3,.» is the difference between the 700-mb temperature and 700-mb dewpoint temperature. Lifted index. A stability index based on the difference, in degrees Celsius, between the 500-mb environmental temperature and the temperature of a parcel of air lifted adiabatically from or near the surface to the 500-mb level. Mesa-high (“bubble high”). A small high pressure system with typical horizontal dimensions of 50—500 km. The high pressure is produced by the cold outflow from thunderstorms and is best defined near the Earth’s surface. Mesoscale. A general term used to define the intermediate scales of atmospheric motion, such as thunderstorms, squall lines, and hur- ricanes. Millibars (mb). A pressure unit, equivalent to 1,000 dyn (dynes) per square centimeter, convenient for reporting atmospheric pressure. Miscellaneous site. A site where data pertaining only to a specific hydrologic event are obtained. National Geodetic Vertical Datum of 1929 (NGVD of 1929). A geodetic datum derived from a general adjustment of the first order CONTENTS V level nets of both the United States and Canada, formerly called “Sea Level Datum of 1929” or “Mean Sea Level.” Precipitable water. The total atmospheric water vapor contained in a vertical column of unit-cross-sectional area extending from the sur- face up to a certain pressure level, usually 500 mb. Radiosonde. A balloon-home instrument package for measuring and transmitting meteorological data. Rawinsonde. Meteorological data-collection system including a radiosonde and reflectors for measuring winds by radar. Recurrence interval. In this report, the average interval of years within which a given flood discharge will be exceeded once. Runoff. That part of the precipitation that appears in streams. Runoff, given in inches, is the depth to which the drainage area would be covered if the runoff for a given time period were uniformly distributed over the surface. Sounding. A single complete radiosonde observation of the upper atmosphere. Stage-discharge relation. The relation between stage or gage height and the flow rate of water in a channel. Temperature. Expressed in degree Farenheit (°F), Celsius (°C), or kelvins (K). Relationships between these temperature scales are listed in the section titled Conversion Factors. Time of day. Expressed in 24-hour time. For example, 12:30 am. is 0030 hours; 1:00 pm. is 1300 hours. All time noted is eastern daylight time (EDT). Trough. An elongated area of relatively low atmospheric pressure. VIP. Video Integrator Processor. 1336.1 nwfll JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 By L. RAY HOXIT, ROBERT A. MADDOX, and CHARLES F. CHAPPEL, National Oceanic and Atmospheric Administration, and STAN A. BRUA, U.S. Geological Survey ABSTRACT Dynamics associated with a weak mid-tropospheric short wave trig- gered widespread thunderstorms across Pennsylvania between the afternoon of July 19 and the morning of July 20, 1977. During this period, two major squall lines moved across the State. The western part of the outflow boundary produced by the second line became almost stationary in western Pennslyvania, resulting in 6 to 9 hours of nearly continuous thunderstorm activity. More than 6 inches of rain fell over a 400-square-mile-area of western Pennsylvania. In the hills just north and east of J ohnstown, rainfall totals were high as 12 inches. Flash flooding was severe as the storms moved slowly southeastward across the Allegheny, Susquehanna, and Potomac River basins. Runoff rates exceeding unit discharges of 1,000 cubic feet per second per square mile were determined for eight streams with drainage areas as large as 10 square miles. The greatest com- puted rate for natural conditions was 2,390 cubic feet per second per square mile for a site on Sandy Run, about 5 miles east of Johnstown. A unit discharge of 3,360 cubic feet per second per square mile was computed for a site downstream from Laurel Run Dam — the largest of seven earthfill, gravity-type dams that were breached. Floods were also severe on larger streams, such as the Conemaugh River at Seward, which had a peak discharge of 115,000 cubic feet per second from a drainage area of 715 square miles. Recurrence intervals for this discharge and for peak discharges at seven other gaging stations are estimated to be 100 years or more. At least 78 deaths were attributed to the floods, and eight persons were still listed as missing 1 year later. Total damages in the eight- county flood area were extremely high and might exceed $330 million. This report describes the storm and the associated flooding. Included are detailed analyses from surface raingages, National Weather Serv— ice radar, and synoptic charts. Descriptions of flooding are supported by peak stage and discharge data at 30 streamflow-gaging stations and 27 miscellaneous sites. A brief discussion of the deaths and damages resulting from the flood is also presented. INTRODUCTION A series of intense thunderstorms formed over western Pennsylvania during the evening and early morning of July 19—20, 1977. These storms, triggered by a mesoscale, quasi-stationary thunderstorm outflow boundary, produced an elongated northwest-southeast pattern of heavy rainfall. Regional topography probably played a role in focusing the heaviest rains in the moun- tains just north and east of J ohnstown. In parts of In- diana and Cambria Counties, shown on the map in figure 1, as much as 12 in. of rain fell in 6 to 9 hours, resulting in some of the worst flooding ever known in the north- eastern United States. Previously known maximum flood flows were surpassed at 12 of the 30 streamflow- gaging stations in the area. The flash floods that oc- curred on many small streams were especially severe, causing numerous deaths and much structural damage. The steep terrain of the J ohnstown area was a major factor contributing to the severity of much of the flooding. Undoubtedly, steep channel slopes resulted in destructively high velocities. Average stream velocities of 10—15 ft/s (feet per second) were common and, in some places, exceeded 20 ft/s. Runoff rates were also af- fected to some extent by both the steep channel slopes and hillsides. Many streams that drain areas less than 10 mi2 (square miles) had peak runoff rates greater than 1,000 (ft3/S)/mi2 (cubic feet per second per square mile). Some severe flooding also resulted from the failure of seven earthfill, gravity—type dams. The most disastrous failure occurred just north of J ohnstown on Laurel Run, where about 40 persons are known to have lost their lives. Much destruction was also reported downstream from a breached dam on Sandy Run, several miles east of Johnstown. However, the effects of the dam failures on the peak-flood level in downtown J ohnstown were not significant. Peak stage and discharge data collected at 57 sites are compiled in this report to document the flooding. Flood- crest elevations are also provided for reaches of selected streams. One of the most notable aspects of the flooding was the great monetary loss incurred over such a small area. Estimates of damage indicate the total physical losses may be in excess of $330 million in a 1,000—mi2 area around Johnstown. The large losses can be attributed mostly to extensive industrial and commercial develop- ment on the flood plains. ACKNOWLEDGMENTS Meteorological data presented herein are mostly a condensation of an Environmental Research 1 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 79" »_ {bu Hm Rn __ ’5 ~ / ~1CLEARFIELD \ fsgnfianser‘ Yullvh "Mn.” ‘{:>\\ i / I A Rimlnfrg r -———-.A:...."..n.._._“_/T___(”1‘______ [5— MARYLAND WEST . VIRGINIA i 30 MILES I Base 1mm US. Geological Survey 1500.000, State base map, 1977 | 30 4O KILOMETERS o——o FIGURE 1. —Location of flood area in western Pennsylvania. THE METEOROLOGY 3 Laboratories Technical Report titled “Meteorological Analysis of the Johnstown, Pennsylvania Flash Flood, 19—20 July 1977” (Hoxit and others, 1978). This technical report resulted from a combined effort of the Environmental Research Laboratories (ERL), the Na— tional Weather Service (NWS), and the National En- vironmental Satellite Service (NESS). Most of the hydrologic data were collected by the US. Geological Survey (USGS) as part of cooperative pro- grams with the Pennsylvania Department of En- vironmental Resources and the US. Army Corps of Engineers. Some data collected by the cooperating agencies are also included and noted in the report. The photographs were furnished by the Johnstown- Tribune Democrat or the Pennsylvania Air National Guard, as noted, or were taken by USGS personnel. Information on flood damage was furnished by the Greater Johnstown Chamber of Commerce and the Pennsylvania House of Representatives. Casualty figures were provided by the American Red Cross. CONVERSION FACTORS The meteorological data in this report are presented using both the inch-pound units and International System (SI) units. Measures are expressed in the type of units most commonly used for the given application. The hydrological data uses inch-pound units entirely. Fac- tors are provided in the following table for converting inch-pound to SI units. Inch-pound units may be con— verted from SI units by “dividing” the number of SI units by the factor listed in the table: Multiply inch-pound um'ts By To obtain SI units Length inch (in.) 25.4 millimeter (mm) 2.54 centimeter (cm) foot (ft) mile (mi) nautical mile (nmi') meter (m) kilometer (km) kilometer (km) square mile (mi?) 2590 square kilometer (km?) acre 4047 square meter (m3) 0.4047 square hectometer (hm?) Volume cubic foot (fts) 28.32 cubic decimeter (dms) ' g 0 02832 cubic meter (m3) million gallons (10‘ gal) 3785 cubic meter (m3) acre-foot (acre-ft) 1233 cubic meter (m3) Flow cubic foot per second (ftS/s) 28.32 liter per second (l/s) 28.32 cubic decimeter per second (dm‘ls) _ 0.02832 cubic meter per second (ms/s) cubic foot per second per square 0.01093 cubic meter per second per square mile [fts/symiz] square kilometer [(m3/s)/km2] Velocity foot per second (ft/s) 0.3048 meter per second (m/s) knot (kn) 1.852 kilometer per hour (km/h) Pressure millibar (mb) 0.1 ldlopascal (kPa) Temperature data are expressed in degrees Fahrenheit (°F), degrees Celsius (°C), or kelvins (K). Following are several expressions that can be used to convert the data from one of these scales to another: °F=9/5 °C+32.0; °C= 5/9 (°F —32.0) or °C=K—273.16 Eastern daylight time (EDT) is used throughout this report. Greenwich Meridian Time, commonly used for meterological analyses, may be obtained by adding 4 hours to the times shown. Elevations used in this report are referred to National Geodetic Vertical Datum (NGVD) of 1929, unless other- wise qualified. At gaging-station sites, elevations of the water surface may be obtained by adding the gage height to the datum of the gage given in table 4. THE METEOROLOGY‘ GENERAL METEOROLOGICAL CONDITIONS The evolution of larger-scale processes beginning at 0800 EDT on July 19 and extending through 0800 EDT on July 20, before and during the intense rainfall over southwest Pennsylvania, is shown in figures 2 and 3. These standard meteorological analyses provide a general setting and background for the detailed meso- scale analyses presented in the next section. Most of the eastern United States was under general anticyclonic flow around a large subtropicalhigh in the western Atlantic—a fairly typical midsummer pattern. The major storm track was across central Canada, and associated frontal systems lay across east-central Canada southwestward into the northern High Plains of the United States. Early on July 19, a weak surface trough, associated with an upper-level low pressure area, extended northeastward through Louisiana and Mississippi. This low pressure area moved slowly north- westward to the Arkansas region by 0800 EDT on July 20. A small, separate high-pressure area persisted dur- ing this period along the western slopes of the Ap- palachian Mountains in West Virginia and eastern Ken- tucky. Dewpoint temperatures of 70°F or greater ex- tended northward into the Great Lakes region and into a small part of southeastern Canada. Low-level moisture flux into the Pennsylvania region was from the southwest. Major thunderstorm outflow boundaries were gen- erated in the Lake Erie region and moved southeast- ward across the mid-Atlantic States. A mesoscale high pressure system (“bubble high”) was evident at both 2000 EDT on July 19 and 0800 EDT on July 20. The flow pattern in the middle troposphere (500 mb) was again fairly typical for midsummer (fig. 3A—C). At 0800 EDT on July 19, a broad, large-scale ridge existed over the central and eastern United States. A weak 4 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 91]" 85: 50“ Mi“ B 2000 EDT, JULY 19,1977 9 i9 “ MU ELSE '5??? H M ’ii%' "I: J‘fil‘ EXPLANATION Area where dewpoint temperatures exceed 70 degrees Fahrenheit —16-— Line of equal atmospheric pressure at sea level. —16=1016 millibars. Interval 2 millibars — — Trough line ——--v— Cold Frontedashed where dissipating —-—---— Warm Front-dashed where dissipating _._.._,— Stationary Front-dashed where dissipating H Geographic center of high-Pressure System Geographic center of low-pressure system —v—"-v— Thunderstorm outflow boundary. Frontal symbols indicate whether cool thunderstorm air or warmer environmental air is advancing FIGURE 2.—Surface analyses at indicated times. A, 0800 EDT, July 19, 1977. B, 2000 EDT, July 19, 1977. 0,0800 EDT, July 20, 1977. Frontal positions, outflow boundaries, pressure centers, and isobars for 2-mb intervals (numbers represent the last two digits of pressure in millibars, 16 a 1,016 mb) are shown in black. Frontal symbols are added to conventional squall line notations to indicate whether cool thunderstorm, outflow, or warmer environmental air is advancing. Regions having dew points 2 70" are shaded in red. THE METEOROLOGY 5 A 0800 EDT, JULY 19,1977 FIGURE 3.—Five-hundred-millibar analyses at indicated times. A, 0800 EDT, July 19, 1977. B, 2000 EDT, July 19, 1977. C, 0800 EDT, July 20, 197 7. (Figure 3A is shown above. Figures 33, 3C, 3D are on following pages.) closed low pressure area over the southern Mississippi Valley and a short—wave trough (meso-a scale) over the eastern Greak Lakes region constituted small pertuba- tions in this mean pattern. A moderately strong wester- ly current extended across southern Canada. The short-wave over the Lake Huron and Lake Erie region at 0800 EDT on July 19 played a key role in the formation of the flash—flood-producing thunderstorms. This system moved east-southeast at 15—20 knots across _ Pennsylvania during the next 24 hours. The wave axis remained tilted (from northeast to southwest) through- out this period. Strong, warm advection in the lower troposphere was indicated to the west and northwest of the short-wave trough. As warmer air moved under the relatively cool air aloft, the atmosphere became more unstable. This flow regime was somewhat uncharac- teristic, as low-level warm advection typically occurs in advance (east) of short-wave troughs embedded in JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 B 2000 EDT, JULY 19,1977 FIGURE 3. — Continued. THE METEOROLOGY --582—- _..10_ —8.3 591 we C 0800 EDT, JULY 20,1977 EXPLANATION Area where dewpoint temperature was within 6-degrees Celsius of air temperature Contour showing altitude of 500-millibar surface. 582:5820 meters. Contour interval 30 meters. Datum is mean sea level Line of equal air temperature. Interval 2 degrees Celsius Axis of Pressure Trough Geographic enter of highest altitude of 500-millibar surface GeOQraphic center of lowest altitude of 500-millibar surface OBSERVATION STATION—Upper left number is air temperature, in degrees Celsius. Lower left number is depression of dewpoint temperature, in degrees Celsius; X shown when depression greater than 30 degrees Celsius. Upper right number is altitude of 500-millibar surface, in meters; 581 =5810 meters. Shaft indicates wind direction. Barbs on shaft indicate wind speed, in knots. Long barb—10 knots; short barb=5 knots; Flag=50 knots; M in- dicates missing data FIGURE 3. — Continued. 8 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 westerly flow. At the same time, the upward vertical motion in advance of the trough axis acted to destabilize the atmosphere further and to trigger widespread con- vection during the afternoon and evening of July 19. Analyses of stability indices computed from standard rawinsonde data (fig. 4) shows the development of a very unstable air mass ahead of the advancing short- wave trough. By 2000 EDT on July 19, the air mass over eastern Pennsylvania was characterized by Lifted Index values of —4 or less and K Index values of 236. These values are comparable with those associated with out- breaks of severe thunderstorms. Precipitable water in the surface to 500-mb layer was substantially greater than climatological mean values along and ahead of the upper-level trough axis (fig. 5). High precipitable-water values propogated southeast- ward and increased in areal coverage during July 19. Values greater than 4.4 cm were found over a wide area extending from northeastern Kentucky through much of New York by 2000 EDT on July 19. The 4.6 cm measured at Pittsburgh at 2000 EDT was approximately 172 percent of the July average documented by Lott (1976). Data from three upper air soundings taken at Pitts- burgh during this 24-hour period are shown in figure 6. Note that the winds shifted in the 850—400-mb layer from west-southwest to northwest and north as the short-wave trough passed. Abundant moisture up to almost 500 mb was evident in the 2000 EDT sounding (fig. 6B). The surface inversion evident in the tem- perature and moisture profiles at 2000 EDT resulted from earlier thunderstorms and was topped by strong, westerly winds immediately above. Strongest winds were in the 700—950-mb layer, and weak wind shear was present from the top of the inversion to nearly 300 mb. Profiles of equivalent potential temperature at Pitts- burgh (fig. 7) further show the unstable environment over western Pennsylvania. Equivalent potential tem- peratures of more than 360 K are characteristic of tropical boundary layer. The 2000 EDT sounding indi- cated a value of 362 K at the top of the surface inversion. A conditionally unstable atmosphere, uncommonly high moisture content, and the slow moving short-wave trough all contributed to thunderstorm development over a rather large area on the afternoon and evening of July 19, 1977. This area included most of Pennsylvania and parts of several surrounding States. However, the atmospheric structure over this region differed in the following ways from that generally associated with a major tornado outbreak: (1) Moisture content was relatively high up to nearly 500 mb, which contrasts with the strong inversion and dry air above, often observed between 700 and 850 mb in the pre-tornado en- vironment, and (2) wind shear was small in the convec- tive cloud layer (from cloud base to nearly 300 mb). The precipitation efficiency of convective clouds in this en- vironment is greater than for clouds embedded in the highly sheared environment commonly associated with tornadoes, strong surface winds, and large hail (Mauritz, 1972); that is, a greater percentage of the water vapor condensed in the updrafts eventually reaches the ground as precipitation. However, two important questions cannot be answered by the synoptic scale analyses just presented: (1) Why did the convective processes focus on a relative- ly small area around Johnstown, and (2) What distin- guished this region from the surrounding region, which apparently had the same general potential for heavy thunderstorms? The answers to these questions may lie in the evolution of mesoscale weather processes preceding and during the storm. MESOSCALE ANALYSIS Surface and radar charts at 2-hour intervals for the period 1400 EDT, July 19, to 0400 EDT, July 20, are shown in figure 8. Analyses of the pressure fields (altimeter settings) and the major thunderstorm outflow boundaries were based on surface observations (both hourly and special), radar data, and satellite photo- graphs. Small systematic errors in the altimeter settings were suspected at several stations (for example, Brad- ford, Pa., and Binghamton, NY). However, no correc- tions were made, so that analyses would be based as closely as possible on information available under opera- tional conditions. Radar analyses are composites prepared from radar- scope photographs taken at National Weather Service WSR—57 radar sites at Pittsburgh, Pa., Buffalo, N.Y., New York City, N.Y., Atlantic City, NJ, and Patuxent, Md. A small region of central Pennsylvania and south- ern New York was not covered by any of the 125-nmi— range scopes. Geostationary Operational Environmental Satellite (GOES) imagery for the same general time period is shown in figure 9. Routine maintenance procedures were underway during the period 0030 to 0330 EDT on July 20, and satellite imagery was not available. Visible imagery is shown through 1800 EDT, July 19; the THE METEOROLOGY 9 C 0800 EDT, JULY 20,1977 FIGURE 4.—Stability indices at indicated times. Regions having K-Index values 236 are shaded. A, 0800 EDT, July 19, 1977. B, 2000 EDT, July 19, 1977. C, 0800 EDT, July 20, 1977. _____\ / / " 32/123/ zn/ /zo 18 ’ B 2000 EDT, JULY 19,1977 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 .2 10 C 0800 EDT, JULY 20,1977 FIGURE 5. —Precipitable water analyses (surface to 500 mb) in cen- timeters for indicated times. Regions having more than 4.4 cm are shaded. A, 0800 EDT, July 19, 1977. B, 2000 EDT, July 19, 1977. C, 0800 EDT, July 20, 1977. B 2000 EDT,JULY 19,1977 Pressure :mbi Pressure (mb) THE METEOROLOGY K Index = 29 Lmeu Index = 4:2 “ix; N W». \ k' ._ V Ni Precipitable Water (surlace t0 SUD mh) = 3.3 cm ‘1‘ / , ~ . /‘«. \ ,2 {III 1000 K Index = 39 Lilted Index = 76.8 \ gm Precipilahle Water [surface in 500 mb) = 4.6 cm .1 .’\ ' \ B 2000 EST, JULY 19, 1977 EXPLANATION Dewpoint temperature (left profile) Air temperature (right profile) Moist-adiabat scale, in degrees Celsius Dry-adiabat scale, in degrees Kelvin Air temperature scale, in degrees Celsius SEMEHJIAMEW flfffffffxf 1WD Wind—Direction and speed observation. Shaft indicates wind direction; north is at top. Barbs on shaft indicate wind speed, in knots; long barb=10 knots; short barb=5 knots FIGURE 6.—Plots of Pittsburgh rawinsonde data at indicated times. A, 0800 EDT, July 1977. B, 2000 EDT, July 19, 1977. C, 0800 EDT, July 20, 1977. Temperature profile in degrees Celsius is shown by solid lines. Red lines show plotted wind and dew point temperatures. 11 12 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OFJULY 19—20, 1977 lllll PIPSSUW 1mm / has \ , 'Cx » by ' Kludex=27 Lmeu Index: 74.8 900 . Pvecrpllable Wale: (surface In 500 mbl = 4.0 cm \ ,/ / ‘,/A.‘ \ \ \\' /. /. O’—‘\ , , (V O/\ \. JQ V. j . as. M f .1 ._ ' , k0 K \ / ‘ :F VZEQ /)\:\\~. J\5° l % ., \ky "\ KJI/ \‘ Vi. ivfi K.,/“, 0\ C 0800 EST, JULY 20, 1977 FIGURE 6. —Continued. remainder of the satellite data are enhanced infrared im- agery. By early afternoon (1400 EDT, July 19), convective ac- tivity was already organized and widespread over north- western Pennsylvania and southern New York (figs. 8A and 9A). Thunderstorms along the southern shore of Lake Erie in the morning (fig. 2A) had spread east- southeastward and expanded into a squall line extending from just north of Johnstown into south-central New York. In J ohnstown, however, only a few hundreths of an inch of precipitation was recorded as this line moved through the area. The cool outflow attending the first squall line ex- tended in two arcs from near Lake Ontario southwest- Ward to a meso-low pressure center over north-central Pennsylvania, then southwestward to near Johnstown before curving northwestward to near Youngstown, Ohio. An elongated meso-high, or “bubble”—high, pressure area was north of the outflow boundary, While an area of light precipitation was forming in extreme northwestern Pennsylvania, southwestern New York, and northeastern Ohio. During the afternoon, this first line of convective storms and their associated c001 outflow boundary con- tinued to move eastward at 30—40 kn (fig. 10A). By 2000 EDT, the leading edge of cooler air extended from southwestern Vermont through extreme southeastern New York to the eastern Pennsylvania border. The southwestern part of the outflow boundary moved back toward the northeast and assumed the characteristic of a shallow mesoscale warm front. At about 1600 EDT, an isolated thunderstorm formed just west of Pittsburgh. This storm moved east— southeastward at about 50 kn, affecting the Pittsburgh region from 1700 to 1800 EDT and dropping about half an inch of precipitation on J ohnstown between 1800 and 1900 EDT. At 2000 EDT, the small meso—high produced by this storm had reached the area near J ohnstown, and the storm was dissipating. Meanwhile, clouds and precipitation over north- western Pennsylvania had moved slowly southeastward and organized into a second major squall line. Several strong cells were indicated by Pittsburgh radar (fig. 80, D), and the late afternoon satellite imagery indicated several overshooting tops embedded in the line (fig. QC). By 2000 EDT, this activity had progressed into the northern parts of the Conemaugh River basin. The behavior of the second squall line differed from the first in several ways. It propagated toward the southeast (instead of east) and at a slower speed than the first line. More importantly, the western section of the outflow boundary was nearly stationary along the Ohio-Pennsylvania border. The quasi-stationary char- acter of this outflow boundary northeast of Pittsburgh continued during the remaining hourly analyses (figs. 8E-H). By 2200 EDT, the first series of intense thunder- storms had moved across the Johnstown region (fig. 8E). A well-defined meso—high attending these storms was located slightly northwest of J ohnstown, while the associated outflow boundary (second of the series) was oriented along the southern Pennsylvania border, north- westward to just east of Pittsburgh and Youngstown, Ohio. This boundary, produced by the cool downdrafts from the thunderstorms, remained quasi-stationary and nearly perpendicular to the low—level flow of moist air THE METEOROLOGY 13 11 10 -“ 0800 EST JULY 19 — 2000 EST JULY 19 ---- 0800 EST JULY 20 HEIGHT ABOVE NATIONAL GEODETIC VERTICAL DATUM OF 1929, IN KILOMETERS 'Efi 0 ” 320 325 330 335 340 345 350 355 360 365 EQUIVALENT POTENTIAL TEMPERATURES, IN KELVIN FIGURE 7. —Vertical profiles of equivalent potential temperatures in Kelvin, derived from the Pittsburgh rawinsonde data. streaming into western Pennsylvania from Ohio. By 0000 EDT, July 20, a mesoscale “wake” low had formed in east-central Pennsylvania (fig. 8F). The two-hourly analyses and satellite photos, along with the summary analyses presented in figure 10B, il- lustrates the quasi-stationary and concentrated nature of the J ohnstown flood-producing storms. As the warm, unstable air from the west was lifted over the cool outflow boundary, new thunderstorms were triggered. Once these storms formed, they moved with the mean midtropospheric flow southeastward over the Con- emaugh River basin. Maddox and others (1979) and Mogil and Groper (1976) have found that quasi—stationary thunderstorm outflow boundaries contribute to many flash floods. These boundaries, as in the Johnstown instance, focus the thunderstorm development and resulting heavy rains over relatively small regions. The part of these boundaries most likely to become stationary is that part parallel to the midtropospheric winds. (Text continued on page 21.) JOHNSTOWN—WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 95 mm .. . 7| 91 30:1;90'16 ./J 001%.», 30.19 ’22 -'_C K ' 30.25 30.22 30.1111 30.13 A 1400 EDT;JULY19, 1977 19 :12 29.95 29.95 £0.99. ”,5” 29.92 R321:” 99 u 58 29.95 g. 29.98% ”30.01 30.25 0-19 311.10 30.07 B 1600 EDT, JULY19, 1977 88 72 Area 30,05 jTE Thunderstorm EXPLANATION covered by radar echoes. Light shad- ing : video intergrator processor (VIP) Level 1 or greater; dark shad- ing=VlP Level 3 or great- er Line of equal altimeter set— ting, in inches of mercury, interval 0.03 inch outflow boundary. Frontal sym- bols indicate direction the boundary is moving Geographic center of high- pressure system Geographic center of low- pressu re system Observing station upper left number is air temperature in degrees Fahrenheit. Lower left number is dewpoint temperature in degrees Fahrenheit. Upper right number is al- timeter setting in inches of mercury. Middle left symbols indicate current weather conditions using standard meteorological surface weather code. Lower right often con- tains additional ab- breviated comments about current weather FIGURE 8. — Regional mesoscale analyses for indicated times. A, 1400 EDT, July 19, 1977. B, 1600 EDT, July 19, 1977. C, 1800 EDT, July 19, 1977. D, 2000 EDT, July 19, 1977. E, 2200 EDT, July 19, 1977. F, 0000 EDT, July 20, 1977. G, 0200 EDT, July 20, 1977. H, 0400 EDT, July 20, 1977. Outflow boundaries, pressure centers, pressure troughs, and pressure analysis (altimeter settings in intervals of 0.03 in.) are in black. Areas of shading indicate area covered by radio echoes (light shading, VIP level 1 or greater, and dark shadings, VIP level 3 or greater). THE METEOROLOGY I "0 HI 1 {Clam 59 river» (U 30.04 :9; 33mm 59 an ,, sum 6 ___,_ . 3.122 . I30.07 30.22 30.16 1 30.07 D 2000 EDT,JULY 19,1977 FIGURE 8. — Continued. 15 16 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 BS 19 99 %? 30.25 30-1539-103037 30-“ 30.04 E 2200 EDT,JULY 19,1977 A: 30.10 30.07 i F 0000 EDT, JULY 20, 1977 FIGURE 8. —Continued. THE METEOROLOGY 30.13 0 70 o 1,? 30.03 107,8 UMK 7:"(9 '1'“ 2998 ‘. 0:1: ,. ‘ ISN 11w 9 I33 990.117 76 F903”: 30.04 ‘ M” 72 30.07 “76 7- 31107 £030.09 ' ' 71 ~.._,~_ .7 ‘ 1 30.01 n' W 10,130 ‘. 1 N 30” ?‘3© 30.16/~ ”-4”: 30-22 30. 5 30.19 1 30.10 30.07 30.04 G 0200 EDT, JULY 20,1977 . 039 1 1 ‘ i (v 9 {rd {x , .. 3232”“ 1. \gflozam 2““‘11‘ m 256 29.90 55 m 11 15,2990 2995 _ _.. an m: 29.96 $10.00 '; ' ' ' s. a 0' s‘o\ 6:7 19.9 ...- ___ 29.90 6 2 .95 $3093”? 3001 30.07 30.04 30.01 H 0400 EDT, JULY 20,1977 FIGURE 8. —Continued. 17 18 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 FIGURE 9.—Geostationary Operational Environmental Satellite (GOES) photographs for indicated times. Visible imagery 1400—1800 EDT, July 19 (1-km resolution at satellite subpoint). Enhanced infrared imagery 2000 EDT July 19 to 0400 EDT July 20 (2-km equivalent resolution at satellite subpoint). A, 1400 EDT, July 19, 1977. B, 1600 EDT, July 19, 1977. C, 1800 EDT, July 19, 1977. D, 2000 EDT, July 19, 1977. E, 2200 EDT, July 19, 1977. F, 0000 EDT, July 20, 1977. G, 0400 EDT, July 20, 1977. THE METEOROLOGY FIGURE 9. — Continued. a. on n g g... . - 19 20 J OHNSTOWN-WESTE RN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 «u u u 'n u a an. .. a c... FIGURE 9. —Continued. THE METEOROLOGY 21 FIGURE 9. — Continued. The thunderstorm cells moved roughly parallel to the outflow boundary and nearly perpendicular to the western slopes of the Allegheny Mountains. Orographic lift probably enhanced storm intensities and helped con- centrate the heavy rain in the hills north and east of Johnstown. However, orography was probably not as important in triggering these thunderstorms as it was in causing the Big Thompson and Rapid City floods (Mad- dox and others, 1978). Radar indicated that 12 separate thunderstorm cells moved over the J ohnstown area between 2000 EDT, J u- ly 19, and 0500 EDT, July 20 (Greene and Saffle, 1978). The downdrafts and cool outflow from each successive cell reinforced and helped maintain the thermal and wind discontinuities along the outflow boundary. As the short-wave trough moved to the east of Johnstown, drier, subsiding midtropospheric air moved into the region. Convective activity was suppressed, and the meso—high moved toward the southeast and slowly dissipated. Shortly after 0500 EDT, the heavy rain in Johnstown ended abruptly. DISTRIBUTION OF RAINFALL Temporal and spatial distributions of the rainfall over western Pennsylvania before and during the major flooding are now examined. Hourly and daily rainfall totals from the rain-gage network are shown, as well as rainfall estimates from the National Weather Service Digitized Radar Experiment (D/RADEX) radar facility at Pittsburgh (Greene and Saffle, 1978). D/RADEX values were computed and available during the storm. Many surface observations of rainfall were not available until after the flood. (Text continued on p. 28.) JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19-20, 1977 *3? l L {gm 0 \jm mm o ,g \“3 lé \\\\\ M E 13 , v_,_. \x _ /' T~\ = \x J V ‘1 ,‘rJ’I‘ FIGURE 10. —Hourly positions'of major thunderstorm outflow boundaries. A, First major bound- ary: 1400 EDT, July 19, 1977, to 2000 EDT, July 19, 1977. B, Second major boundary: 1600 EDT, July 19, 197 7 , to 0500 EDT, July 20, 1977; red shading defines region where 24—hr rain- falls exceeded 2 in. THE METEOROLOGY 23 B 1500—1600 EDT, JULY 19, 1977 D 1700—1800 EDT, JULY 19, 1977 FIGURE 11. —Hourly rainfall analyses (in inches) for indicated times. Plotted data are observed rainfalls. Anal yseSJshow'D/RADEX rainfall ac- cumulations. A, 1400—1500 EDT, July 19, 1977. B, 1500—1600 EDT, July 19, 1977. C, 1600—1700 EDT, July 19, 1977. D, 1700—1800 EDT, July 19, 1977. E, 1800—1900 EDT, July 19, 1977. F, 1900—2000 EDT, July 19, 1977. G, 2000—2100 EDT, July 19, 1977. H, 2100—2200 EDT, July 19, 1977.1, 2200—2300 EDT, July 19, 1977. J, 2300—2400 EDT, July 19, 1977. K, 0000—0100 EDT, July 20, 1977. L, 0100—0200 EDT, July 20, 1977. M, 0200—0300 EDT, July 20, 1977. N, 0300—0400. EDT, July 20, 1977. 0, 0400—0500 EDT, July 20, 1977. P. 0500—0600 EDT, July 20, 1977. 24 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 E 1800—1900 EDT, JULY 19,1977 F 1900—2000 EDT, JULY 19,1977 H 2100—2200 EDT, JULY 19,1977 FIGURE 11. — Continued. THE METEOROLOGY 25 J 2300—2400 EDT, JULY 19, 1977 L 0100—0200 EDT, JULY 20,1977 FIGURE 1 1. — Continued 26 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 N 0300—0400 EDT, JULY 20, 1977 P 0500—0600 EDT, JULY 20, 1977 FIGURE 11. — Continued THE METEOROLOGY 27 TIME (GMT) I July 19 I July 20 14 15 18 20 22 00 02 04 06 08 ll] 12 2-“ I I I I I I I I I I I El RAINFALL, IN INCHES 10 12 14 15 13 20 22 00 02 04 V 05 0810 A TIME (EDT) TIME (G MTI I July 19 I July 20 j' 3 014 16 18 20 22 00 02 04 06 08 10 12 14 ' I | | I I I I | I I I RAINFALL, IN INCHES 10 12 14 16 18 20 7 ’22 oo 02 04 06 08 In B TIME.(EDT) FIGURE 12.-—Observed hourly rainfall at three stations within the heavy rainfall area. A, Public Safety Building, Johnstown, Pa. B, Strongstown, Pa. C, Dunlo, Pa. 28 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 TIME (GMT) I July 19 , I4 16 18 20 22 00 July 20 ——-| [12 04 06 08 ID 12 I4 we” . - | I I I I RAINFALL, IN INCHES I 10 12 14 IS 18 20 I I I I I | 22 00 02 04 08 08 II] C TIME (EDT) FIGURE 12. -Continued. Analyses of the hourly rainfalls, obtained from D/RADEX for the period 1400 EDT, July 19, until 0600 EDT, July 20, are presented in figure 11. Hourly rain- falls observed at stations in and surrounding the Con- emaugh River basin are plotted for the period 1800 to 0600 EDT. During the afternoon, the hourly D/RADEX totals clearly show the eastward movement of the first squall line out of western Pennsylvania and the development and eastward extension of the second line over north- western Pennsylvania. As the second line moved into the J ohnstown area dur- ing the late afternoon and early evening, spatial agree- ment between the hourly rainfall, estimated by radar, and observed amounts is reasonably good. Hourly rain- fall totals at three stations (fig. 12) indicate that the bulk of the rain fell in 6—9 hours. A comparison of 24-hour rainfall amounts from D/RADEX data with an isohyetal analysis of surface rain-gage data is shown in figures 13 and 14. The pat- tern of heavy rainfall is similar in both analyses. However, observed maximum totals are more than 12 in., whereas the maximum radar-determined accumula- tion is slightly more than 8 in. Figures 11 and 12 suggest that radar estimates were somewhat low during the early evening but compare more favorably with the observed values in the 0100 to 0600 EDT, July 20, time period. Analyses presented in figures 12 and 14 show the in- tensity of the rain during the 6—9-hour period and the localized nature of the rainfall. For example, Nanty G10, about 10 miles north of Johnstown, received approx- imately 12 inches of rain during the 24-hour period, whereas locations 30 miles to the southwest received little or none. DISCUSSION AND SUMMARY The July 19—20, 1977, flash floods in southwest Penn- sylvania resulted when large-scale and mesoscale proc- esses combined to focus excessive convective rains over a relatively small area. Circulation patterns associated with the large surface high off the Atlantic coast and the long-wave upper-tropospheric ridge over the eastern United States provided a conditionally unstable at- mosphere having abundant moisture over a large area of the Ohio Valley and central Appalachian Mountain region. Dynamic processes associated with a slowly moving short-wave trough destabilized the atmosphere and acted to trigger and maintain organized convention during the morning and afternoon of July 19. THE FLOODS OF JULY 19—20, 1977 29 FIGURE 13.—Total rainfall (in inches) indicated by meteoro- logical radar (D/RADEX). Time period 0800 EDT, July 19, to 0800 EDT, July 20, 1977. In response to the convective activity during the after- noon and early evening, mesoscale pressure systems and low-level baroclinic zones were generated. In western Pennsylvania, the boundary separating the rain-cooled air generated by previous thunderstorms became quasi-stationary nearly perpendicular to the warm, moist, low—level flow streaming in from Ohio. As this unstable air ascended over the rain-cooled air, new thunderstorms were triggered, which then moved southeastward parallel to the outflow boundary. Each thunderstorm cell reinforced the temperature gradient along the outflow boundary and maintained the trigger- ing mechanism in a quasi-stationary position. The 1 - tions for which at least 10 successive years of peakflow storms moved upslope into the western parts of the Ap- palachian mountains, releasing maximum rainfall in the hills north and east of JohnstoWn. This process con- tinued for several hours, subjecting the region to a series of storms. The quasi—stationary nature of the storm was even- tually terminated as the short-wave trough moved into eastern Pennsylvania. Advection of somewhat drier midtropospheric air and development of weak sub- sidence with the trough passage over western Penn- sylvania eventually suppressed formation of new cells. The meteorological conditions leading to the flood- producing rains around Johnstown were those present during most significant flash floods (Maddox and others, 1979). These storms commonly have several important characteristics: (1) very moist and conditionally unstable conditions, with precipitable water substantially above normal from the surface to 500 mb; (2) a weak short— wave trough (meso-a scale) moving through a large- scale ridge that provides lifting and air mass destabiliza— tion; (3) weak wind shear through much of the cloud layer, which contributes to high precipitation efficien- cies; (4) topographic features, frontal boundaries, or cool outflow boundaries produced by earlier or existing con- vection, which trigger additional storms and focus heavy rain over a relatively small ,area; (5) several cells that typically move over the same area, and (6) the tendency for rainfall that produces flashfloods to occur at night. THE FLOODS OF JULY 19-20, 1977 To document the extreme floods in western Penn- sylvania on July 19—20, 197 7 , stream-stage and discharge data were collected at 57 sites in the Allegheny, Susquehanna, and Potomac River basins. Thirty of these sites are at gaging stations, where both stage and discharge data are available, and the re— mainder are miscellaneous sites, for which only peak discharges are available. Numbers have been assigned to these sites for locating them on a map (fig. 15) and referencing flood data. Floodmark data consisting of peak-flood elevations throughout selected reaches of 27 streams in the Mahoning Creek and Conemaugh River basins are also presented. Descriptions of the tables con- taining these data are provided in the section Summary of Flood Stages and Discharges. RECURRENCE IN TERVALS Recurrence intervals were computed at all gaging sta- data were available; they provide an indication of the severity of flooding on the respective streams. The recurrence interval, as applied to flooding, is the average interval of years within which a given peak discharge will be exceeded once. It is inversely related to the chance of the given discharge being exceeded in any year. For example, a flood having a recurrence interval of 50 years, would have one chance in 50 (2 percent chance, or 0.02 probability) of being exceeded in any year. The occurrence of floods is erratic; a flood of a given magnitude may occur in any year, it may occur in successive years, or it may not occur within a period much greater than the designated interval. Recurrence intervals were computed using a log-Pearson type III distribution, a regionalized skew coefficient, and other guidelines of the US. Water Resources Council (1977). 30 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 DETERMINATION OF PEAK DISCHARGES At 34 sites (27 miscellaneous sites and 7 gaging sta- tions), peak discharges for the July 1977 flood were determined by indirect methods. These methods are based on principles that relate streamflow to observed water-surface elevations and to the hydraulic properties of a stream or a structure that crosses the stream. They include the (1) slope—area, (2) contracted-opening, (3) flow-over-dam, and (4) flow-through-culvert methods de- scribed in Dalrymple and Benson (1967), Matthai (1967), Hulsing (1967), and Bodhaine (1968), respectively. Peak discharges for the remaining gaged sites were deter- mined from previously established stage-discharge rela- tionships. DESCRIPTIONS OF THE FLOODS ALLEGHENY RIVER BASIN Flooding was severe in much of a 70-mile long by 25-mile wide area along the Allegheny River basin’s eastern divide. Allegheny River tributaries affected in- clude Redbank, Mahoning, and Crooked Creeks. The Conemaugh River, a tributary to the Kiskiminetas River in the southeast part of the basin, had the worst flood. The main stems of the Allegheny and Kiskiminetas Rivers were not flooded owing to flood—control reser- voirs near the mouths of Mahoning and Crooked Creeks and the Conemaugh River. More than 200,000 acre-feet of runoff from this storm was stored in these three reservoirs. Flooding was moderate in the Redbank Creek basin. At the gaging station on Big Run near Sprankle Mills (site 1), the peak discharge from a drainage area of 7.38 mi2 was 960 ft3/s. Although this discharge is the highest since record collection began in 1963, its recurrence in— terval is estimated at only 15 years. The peak flow for the main stem of Redbank Creek at St. Charles (site 2) was 19,000 ft3/s. A recurrence interval of 5 years was estimated for this discharge. Flooding was extreme in the upper half of the Mahon- ing Creek basin, where as much as 6 inches of rainfall was recorded. Stump Creek, at the town of Big Run (site 3) had a peak flow of 5,240 ft3/s from a drainage area of 26.8 miz, which corresponds to a unit discharge of 196 (ft3/s)/mi2. On the main stem of Mahoning Creek at Punxsutawney (site 4), the peak flow was 12,700 ft3/s, the second highest flow since at least 1936. This is con- siderably less than the record discharge of 17,300 ft3/s during a flood in June 1972, but a change in the carrying capacity of the stream resulted in a peak stage for the FIGURE 14.—Total observed rainfalls (in inches) from 0800 EDT, July 19, to 0800 EDT, July 20, 1977. A, Western Pennsylvania. B, Conemaugh River basin. July 1977 flood that was 0.3 ft higher than the previous record. A recurrence interval of 40 years is estimated for the July 197 7 peak discharge at this site. The peak flow of 5,770 ft3/s on Little Mahoning Creek at McCor- mick (site 5) was also the second highest for its period of record, which extends back to 1939. However, it is only 7 percent less than the previously known maximum dis- charge of 6,200 ft3/s, in June 1972. The July 1977 peak discharge at this site is estimated to have a recurrence interval of 20 years. Downstream from Little Mahoning Creek, the peak flow of Mahoning Creek was greatly reduced by the ef- fects of Mahoning Creek Lake. About 28,500 acre—feet of flood-control storage was utilized to reduce the peak flow below Mahoning Creek Dam (site 6) to 6,560 ft3/s on July 22. Flooding was significant throughout the Crooked Creek basin. At Shelocta (site 7), in the central part of the basin, the peak discharge on Crooked Creek was estimated to be 9,940 ft3/s, or 85 (ft3/s)/mi2 from a drainage area of 117 miz. Farther downstream at Idaho (site 8), the peak flow on Crooked Creek was 8,860 ft3/s, a unit discharge of 46 (ft3/s)/mi2 from a drainage area of 191 miz. The recurrence interval for this peak is estimated at 10 years. A recurrence interval of about a year is estimated for the peak discharge of 4,150 ft3/s downstream from Crooked Creek Dam (site 9) on July 22. More than 17,000 acre-ft of flood runoff was stored in Crooked Creek Lake, which prevented flooding downstream. THE FLOODS OF JULY 19—20, 1977 31 1.24 Parker's anding 4.531 Creekside 5.27 Indiana -0 . Sutersville 0.90 Connellsville 0 10 |__I_l Miles 1’ .553 Ph ipsburg Wnlfshurg 4.]0 Bu alo Mills FIGURE 14. —Continued. CONEMAUGH RIVER BASIN Peak flows on streams in the Conemaugh River basin, over which the storm centered, were among the greatest known in the Northeast. The relations of the 1977 peak discharges in the Conemaugh River basin to size of drainage areas are shown in figure 16 and are compared with those outside of the basin and to other known floods in the Northeast. On the main stem of the Conemaugh River and its three principal tributaries, Stony Creek, Little Conemaugh River, and Blacklick Creek, recurrence intervals of the peak discharges are estimated to be 100 years or more. Many deaths and much property damage resulted from flooding in the lower half of the Stony Creek basin. Along Paint Creek and its tributaries, many homes were either destroyed or extensively damaged. (See fig. 17.) 32 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 , Malamw «ml.- - I...» C , WESTMORELAND if" j/ / “‘ 7 I ./'\'”“" .7 i: ,, < b I an \ ,.f . kink] ’r \ 40' 1 I \ '7 ‘ .1,» Mummy, [IQ/I” >"i >’ I < -: L‘ 7 IV , ‘ ,. :____.E|_51‘§N_SYL_ wm<30m Z_ . _m an >2 my I + ++ ++ + + :72 :12 :83; :22 .m:_m2:_mo 6:00. 866 3ch H H I + + + ++ uwmgcto: mp: 52 :3: mam Ucm cwaato >9 umm: 2mm. + I m I + w + 5me 52m smszwcoo 9: II + mu+ + V6 3650 coo: Rm: >3“. L2 .383: 02m ucm ESQ Sun. ~F< + + ++ + EMU + + + + ,uocomofi E0: Emwmesou Emma 62m zmsmEocoo I + 9: E coo: R9 >3... .8 .6355: 95 new Eon 2mm mmo I + + tnr wcoEucon. .239. L8 Ewan 33m :msmEmcoo I w 00 > I + ++ + 5 E v c R? .2. .8 53:5: gm Ucm EBQ Ema wen M f:___ __:___ V __:_w_ :__:,_ _:__r_ I 8F com coo F ooom oood _. ooodm ooo.oo_. ooodom CINOOES HEld 133:! OIEOD NI 'SDHVHOSIG >|VE|d THE FLOODS OF JULY 19—20, 1977 35 FIGURE 17. —Remains of several homes and a church along Little Paint Creek in Scalp Level. (Johnstown Tribune-Democrat photograph.) Sandy Run, a tributary to the South Fork Little Con- emaugh River, had the maximum known natural-runoff rate in the entire flood area—2,390 (ft3/s)/m2. This was determined for a site just upstream from a breached water-supply dam (fig. 19). The peak flow at this site (site 21) was 14,000 ft3/s from a drainage area of 5.86 miZ. The failure of the dam probably caused little modification of the natural peak discharge. One mile downstream from the dam (site 22), the peak flow was 15,300 ft3/s, or only 10 percent greater than the upstream inflow. Additional information on this and six other dam failures is included in the section Breached Dams. The peak flow of the Little Conemaugh River at East Conemaugh (site 23), about 9 miles downstream from the South Fork, was 40,000 ft3/s, as shown by the discharge hydrograph in figure 20. This is 40 percent higher than the previously known maximum in 1936 and is probably the largest since 1889, when a large dam on the South Fork failed. Johnstown, at the confluence of Stony Creek and the Little Conemaugh River, had its worst flood since March 1936. Four to 8 ft of water, and much debris, covered most of the downtown area (figs. 21—24). At the City Hall building, the peak-flood level was about 10 ft below that of the 1936 flood and about 17 ft below the level of the disastrous 1889 flood (fig. 25). Flooding along the Conemaugh River in the northern part of Johnstown was 3 to 7 ft below that of 1936. After the 1936 flood, channel improvements were made on the lower 4 miles of Stony Creek, the lower 11/2 miles of the Little Conemaugh River, and on the Con- emaugh River for another 31/2 miles. Without these im- provements, the US. Army Corps of Engineers (1978) estimated that the 1977 flood in downtown Johnstown would have been about 11 ft higher, or 1 ft higher than the 1936 flood level. Small streams in the northern part of J ohnstown and in adjacent communities also experienced extremely high floodflows. For example, the peak flow of Elk Run in the Morrelville section of Johnstown (site 24) was 1,900 ft3/s from a drainage area of 1.99 miz, or 955 (ft3/s)/mi2. Flood severity along one of several streams 36 J OHN STOWN-WE STE RN PENNSYLVANIA ISTORM AND FLOODS OF JULY 19—20, 1977 24 GAGE HEIGHT, IN FEET 70 l 26 60— D 5 so 0 _ LLI (D D: I.IJ n_ _ '— Lu LLI LL 0 5 40— D U LL 0 _ U) D Z < 8 o 30— I '— Z LLI _ (D O: < 5 g: 20— D 10.— 20 21 JULY, 1977 FIGURE 18. —Hydrographs of stage and discharge of Stony Creek at Ferndale (site 13). just east of Johnstown is indicated by the destruction shown in figure 26. Flooding was most disastrous downstream from Laurel Run Reservoir on Laurel Run, which flows into the Conemaugh River at the north end of Johnstown. High inflows, which exceeded the discharge capacity of the spillway, resulted in the overtopping and subsequent erosion of the dam’s earthen embankment (fig. 27). About 2,000 ft upstream from the dam (site 26), the peak flow was estimated to be 10,500 ft3/s from a drainage area of 7.56 miz. The peak discharge about a mile downstream from the dam (site 28) was computed to be 37,000 ft3/s, more than three times as great as the upstream inflow. (See section Breached Dams for addi- tional information.) Red Run, a tributary to Laurel Run between the dam and the downstream measurement site, had the second highest of known natural-runoff rates. The peak flow at its mouth (site 27) was 4,000 ft3/s, or a unit discharge of 2,000 (ft3/S)/mi2. However, its contribution at the time of THE FLOODS OF JULY 19—20,1977 37 FIGURE 19. -Aerial view of breach in Sandy Run Dam (Pennsylvania Air National Guard photograph.) the dam failure is considered to have been negligible. Another tributary to Laurel Run, Wildcat Run, had a peak discharge at its mouth (site 29) of 2,440 ft3/s, or a unit discharge of 1,240 (ft3/s)/mi2 from a drainage area of 1.97 miz. Flooding on the Conemaugh River between Johns- town and Conemaugh River Lake was also very severe. Flood levels were 3 to 6 ft higher than the previously known maximum levels of March 1936. The peak flow of 115,000 ft3/s at Seward (site 30), which was about 50 percent greater than the peak of 1936, is equivalent to a unit discharge of 161 (ft3/s)/mi2. The recurrence interval for this peak flow is estimated to be greater than 100 years. Stage and discharge hydrographs for the July 1977 flood at Seward are shown in figure 28. Severe flooding also occurred along Blacklick Creek, which empties into Conemaugh River Lake about 20 miles downstream from Seward. At Josephine (site 31), just upstream from Two Lick Creek, the peak flow was 45,700 ft3/s or 238 (ft3s)/mi2 from a drainage area of 192 miz. This discharge has a recurrence interval greater than 100 years and is more than twice the maximum discharge during Hurricane Agnes in June 1972, the previous maximum since the gage was established in 1952. Recurrence intervals greater than 100 years were estimated for the peak discharges at three other gaging sites in the Blacklick Creek basin. Peak discharges, drainage areas, and comparisons With the 1972 flood discharges (the previously known maximums at these sites) are as follows: Little Yellow Creek near Strongstown (site 35)— 4,250, ft3/s from a drainage area of 7.36 miZ, 5.2 times greater; Yellow Creek near Homer City (site 36)— 15,000 ft3/s from a drainage area of 57.4 miz, 3.7 times greater; and Two Lick Creek at Graceton (site 38)—32,000 ft3/s from a drainage area of 171 miZ, 1.6 times greater. 38 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 80 | l — 20 70 — — 18 60 — — 16 /Gage height a Z _ 8 LU 0’ 14 SE a_ 50,—- [— LLI I.IJ U- l— Lu 0 .— E 12 'le D U z 8 '5‘ 40 7 g 8 <2): I ‘3 _ 10 g 0 (D I I— z '1 30 — 8 m 8 < I o _. 13 o 20 — 5 /Discharge 4 10 *- 2 0 19 20 21 JULY, 1977 FIGURE 20. —Hydrographs of stage and discharge of Little Conemaugh River at East Conemaugh (site 23). Discharge records before 1951 are not available at dicate that 1977 peak flows in at least the lower reaches present gaging sites in the Blacklick Creek basin. of Blacklick and Two Lick Creeks were the highest since However, flow records for a discontinued gage on at least 1905, when the record began. Blacklick Creek at Blacklick (Jarvis and others, 1936) in- No flooding occurred downstream from Conemaugh THE FLOODS OF JULY 19—20, 1977 39 FIGURE 21. —Flooded business establishments in downtown Johnstown at Park Place. The peak stage was about 8 in. higher than the water level shown. (Johnstown Tribune-Democrat photograph.) River Lake because of storage in the reservoir. The maximum discharge from the dam, determined at the gaging station 2 miles downstream (site 39), was 23,600 ft3/s. This is 16 percent less than the flow the U.S. Army Corps of Engineers (1978) considers to be downstream bankfull capacity. More significantly, it corresponds to an 88 percent reduction of the peak reservoir inflow of 194,000 ft3/s, as computed by the U.S. Army Corps of Engineers (1978). About 170,000 acre-feet of runoff was stored in the reservoir, utilizing 64 percent of the total available flood-control storage. SUSQUEHANNA RIVER BASIN Peak stages and discharges in the West Branch Susquehanna River basin, although significant, were generally much less than those during previous major floods. At Bower (site 42), the peak flow on the main- stem West Branch Susquehanna River was 19,200 ft3/s, the fourth highest since at least 1889, when records were first collected. The estimated recurrence interval of this discharge is 30 years. The peak stage of 16.23 ft was 3.5 ft lower than the previously known maximum in March 1936. Significant flooding was also reported on two east bank tributaries, Chest and Clearfield Creeks. A recurrence interval of 15 years is estimated for the peak discharge of 602 ft3/s on Bradley Run near Ashville (site 44), a tributary to Clearfield Creek. Peak flows on other Clearfield Creek tributaries farther downstream were even more significant, as illustrated in figure 16, for two ungaged sites, Brubaker Run at Dean (site 45) and North Witmer Run at Irvona (site 46). On the main stem of Clearfield Creek, downstream from these tributaries, the magnitude of flooding decreased rapidly. Near the mouth of Clearfield Creek, at Dimeling (site 47), the recurrence interval for the peak flow of 9,210 ft3/s is only 4 years. The elongated rainfall pattern by the storms of July 19—20, 1977 extended well into the Raystown Branch Juniata River basin and resulted in severe floods on several streams. The peak flow of Dunning Creek at Belden (site 56) was 19,400 ft3/s from a drainage of 172 mi2, the highest discharge since at least 1936. The recur- rence interval of this flow is estimated to be greater than 100 years. POTOMAC RIVER BASIN Moderate to extreme flooding was reported on several small streams in the Potomac River basin, but because the area is so sparsely populated, damages were minor. A recurrence interval of 70 years is estimated for the peak flow of 3,000 ft3/s on Little Wills Creek at Bard 4O JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 FIGURE 22. —Flooding at Franklin Street United Methodist Church in J ohnstown. (Johnstown Tribune-Democrat photograph.) (site 57). The corresponding peak stage of 11.00 ft is about 2 ft higher than any other since the record began in 1961. SUMMARY OF FLOOD STAGES AND DISCHARGES Peak stage and discharge data for the sites shown in figure 15 are presented in table 1. Data for the max- imum flood previously known are included for each of the gaged sites. The 8-digit numbers listed in the second column of the table are permanent USGS station numbers. These are the same as those used in the annual USGS Water Data Report for Pennsylvania and were assigned to each site according to its downstream order. Additional stage and discharge data for many of the sites are included in table 4, which also includes detailed site locations, gage descriptions, and other pertinent ‘ facts about each site. Data in this table can be used to construct stage and discharge hydrographs for most gaged sites, generally for the period July 19—23, 1977. The volume of runoff for the specified periods is also shown. Floodmark data are included in table 5 and can be used to estimate maximum flood levels along selected reaches of the following 27 streams in the Mahoning Creek and Conemaugh River basins: Mahoning Creek basin: Mahoning Creek Stump Creek Conemaugh River basin: Conemaugh River Stony Creek Shade Creek Paint Creek Seese Run Weaver Run Little Paint Creek Sams Run Solomon Run Little Conemaugh River Spring Run Trout Run North Branch Little Conemaugh River South Fork Little Conemaugh River Sandy Run St. Clair Run Laurel Run Blacklick Creek North Branch Blacklick Creek South Branch Blacklick Creek Two Lick Creek North Branch Two Lick Creek Buck Run Dixon Run Yellow Creek BREACHED DAMS Extremely high flows in the Conemaugh River basin resulted in the failure of seven earthfill gravity-type dams. The locations of the breached dams are shown on the map in figure 15B and are given in table 2, which also gives the age and size of each structure. Peak discharges were determined at sites upstream and downstream from the Sandy Run and Laurel Run Dams and downstream from three other dams. Site numbers for referencing the peak-flow data are given in the last column of table 2. Figure 29 and 30 show profiles of the maximum water- surface elevations downstream from Laurel and Sandy Run Dams. Floodmark data used to construct the pro- files are included in table 5. Because of the destruction and deaths caused by these failures and by others in the past, flooding caused by the Laurel Run Dam was analyzed in detail. Flood THE FLOODS OF JULY 19—20, 1977 TABLE 1. —Summary of flood stages and discharges Maximum flood previously known 41 Flood of July 1977 Drainage Month Gage Gage Unit Recurrence Site area and height Discharge height Discharge discharge interval (fig. 15) Station Stream and place of determination (mil) Period year (feet) (ftals) Date (feet) (ftS/s) ((ft3/s)/mi2) (years) Redbank Creek basin 1 03031950 Big Run near Sprankle Mills _________ 7.38 1963—77 Feb. 1966 6.23 822 19 6.22 960 130 15 Feb. 1975 6.12 858 2 03032500 Redbank Creek at St. Charles ________ 528 1910—77 Mar. 1936 118.60 50,000 20 14.72 19,500 37 5 Mahoning Creek basm 3 03033220 Stump Creek at Big Run ____________ 26.8 __ _--_ 5,240 196 _____ 4 03034000 Mahoning Creek at Punxsutawney __ 158 1936—77 June 1972 15.94 17,300 20 16.22 12,700 80 40 5 03034500 Little Mahoning Creek at McCormick __ 87.4 1939—77 June 1972 13.20 6,200 20 12.77 5,770 66 20 Feb. 1977 214.03 _______ 6 03036000 Mahoning Creek at Mahoning Creek 344 1938—77 Mar. 1942 8.10 310,400 22 7.35 36,560 19 3 Dam. Crooked Creek basin 7 03037300 Crooked Creek at Shelocta _________ 117 __ ____ 9,940 85 _____ 8 03038000 Crooked Creek at Idaho ______ -_ 191 1936—77 Mar. 1936 18.6 19,400 20 13.38 38,860 46 10 9 03039000 Crooked Creek at Crooked Cr. Dam ___ 278 1909—77 Mar. 1936 17.86 21,000 22 7.65 4,150 15 1 Conemaugh R1ver Basm 10 03039200 Clear Run near Buckstown __________ 3.68 1961—77 Feb. 1961 I5.30 _______ 20 5.03 366 99 30 June 1972 4.53 266 11 03039910 Seese Run at Windber ______________ 4.66 __ ____ 5,760 1,240 _____ 12 03039914 Paint Creek at Windber _ 21.8 __ ____ 19,000 872 _____ 13 03040000 Stony Creek at Ferndale 451 1913—77 Mar. 1936 l30.26 359,000 20 23.21 348,000 106 100 14 03040016 Sams Creek at Geistown _ 1.28 __ ____ 1,600 1,250 _____ 15 03040018 Sams Run at Lorain ________________ 2.17 __ ____ 2,960 1,360 _____ 16 03040095 North Branch Little Conemaugh .80 __ ____ ‘1,040 1,300 _____ River tributary near Ebensburg. 17 03040300 Little Conemaugh River at Summerhill 91.1 __ -___ 8,670 95 _____ 18 03040420 Otto Run at Salix __________________ 3.70 __ ____ 42,120 573 19 03040430 South Fork Little Conemaugh 1.70 __ ___4 44,300 2,530 River tributary at St. Michael. 20 03040500 South Fork Little Conemaugh River at 52.6 __ ____ 24,000 456 _____ Fishertown. 21 03040503 Sandy Run above Sandy Run Reservoir 5.86 _, ____ 14,000 2,390 _____ near St. Michael. 22 03040505 Sandy Run below Sandy Run Reservoir 7.61 ,_ ____ 415,300 2,010 _____ at St. Michael. 23 03041000 Little Conemaugh River at East 183 1936—77 Mar. 1936 _______ 328,800 20 18.85 340,000 219 > 100 Conemaugh. June 1972 10.48 316,600 24 03041030 Elk Run at Morrellville _____________ 1.99 __ ___- 1,900 955 25 03041038 Laurel Run at Chickaree ____________ .055 __ 19 345 26 03041039 Laurel Run above Laurel Run 7.56 __ ____ 10,500 1,390 Reservoir near Coopersdale. 27 03041040 Red Run near Coopersdale __________ 2.00 __ ____ 4,000 2,000 28 03041043 Laurel Run below Laurel Run 11.0 __ ___- 437,000 3,360 Reservoir near Coopersdale. 29 03041046 Wildcat Run at Coopersdale ________ 1.97 __ _-,_ 2,440 1,240 _____ 30 03041500 Conemaugh River at Seward __ _ 715 1936—77 Mar. 1936 22.95 375,000 20 27.06 3115,000 161 >100 31 03042000 Blacklick Creek at Josephine _________ 192 1952—77 June 1972 13.99 20,800 20 19.89 45,700 238 >100 32 03042170 Stoney Run at Indiana ______________ 4.39 1963—77 Sept. 1974 8.87 505 __ 510—11 ___________________ 33 03042180 Two Lick Creek near Homer City _____ 95.5 __ ___fi 16,500 173 34 03042198 Little Yellow Creek tributary at .76 __ _”_ 1,450 1,910 Strongstown. 35 03042200 Little Yellow Creek near Strongstown 7.36 1959—77 June 1972 6.10 820 20 9.31 4,250 577 36 03042280 Yellow Creek near Homer City _______ 57.4 1967—77 Feb. 1971 28.37 _______ 20 12.60 315,000 261 >100 June 1972 7.46 4,100 37 03042282 Ferrier Run near Homer City ________ 2.14 __ ___ 890 416 _____ 38 03042500 Two Lick Creek at Graceton _________ 171 1951-77 June 1972 14.69 319,600 20 18.65 332,000 187 >100 39 03044000 Conemaugh River at Tunnelton ______ 1,358 1939—77 Mar. 1945 21.0 359,200 21 11.98 323,600 17 3 West Branch Susquehanna Rlver basin 40 01540600 West Branch Susquehanna River at 25.8 __ ____ 2,400 93 _____ Barnesboro. 41 01540650 West Branch Susquehanna River at 58.8 _______ June 1972 _______ 6,790 __ _______ 6,000 102 _____ Cherrytree. 42 01541000 West Branch Susquehanna River at 315 1889—1977 Mar. 1936 19.74 31,500 20 16.23 19,200 61 30 Bower. 43 01541200 West Branch Susquehanna River at 367 1955—77 Mar. 1964 14.19 15,700 23 8.47 35,660 15 3 Curwensville. 44 01541308 Bradley Run near Ashville ___________ 6.77 1967—77 June 1972 3.82 679 20 3.65 602 89 15 45 01541321 Brubaker Run at Dean _____ 3.82 __ ____ 1,370 359 _____ 46 01541365 North Witmer Run at Irvona 30.8 __ ____ 10,000 325 _____ 47 01541500 Clearfield Creek at Dimeling _____ 371 1913-77 Mar. 1936 118.49 30,600 20 11.27 39,210 25 4 48 01542000 Moshannon Creek at Osceola Mills 68.8 1940—77 June 1972 14.25 5,120 20 1.97 339 5 1 42 TABLE 1. —Summary of flood stages and discharges — Continued JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 Maximum flood previously known Flood of July 1977 Drainage Month Gage Gage Unit Recurrence Site area and height Discharge height Discharge discharge interval (fig. 15) Station Stream and place of determination (miz) Period year (feet) (fta/s) Date (feet) (ft3/s) ((ft3/s)/mi2) (years) Juniata River basin 49 01556000 Frankstown Branch Juniata River 291 1889—1977 June 1889 19.1 35,500 20 8.11 2,930 10 1 at Williamsburg. 50 01556400 Sandy Run near Bellwood ___________ 5.58 1962—77 Sept. 1967 6.25 900 20 5.89 550 99 10 51 01556500 Little Juniata River at Tipton ________ 93.7 1946-77 June 1972 9.24 6,140 20 9.07 5,580 60 10 52 01557100 Schell Run at Tyrone _______________ 1.68 1958—77 July 1969 3.00 225 20 1.97 45 27 1 53 01557500 Bald Eagle Creek at Tyrone _________ 44.1 1936—77 Mar 1936 ‘15 _______ 20 1.41 112 3 1 Nov. 1950 17.5 5,140 __ _,__ ___________________ 54 01558000 Little Juniata River at Spruce Creek ,_ 220 1936-77 Mar. 1936 19.1 39,800 20 7.52 5,760 26 3 55 01559700 Buflalo Run tributary near 5.28 1961—77 Sept. 1967 4.26 1,010 20 5.12 1,120 212 20 Manns Choice. 56 01560000 Dunning Creek at Belden ____________ 172 1936—77 Mar. 1936 ‘517.8 16,900 20 14.15 19,400 113 >100 Potomac River Basin 57 01600700 Little Wills Creek at Bard ___________ 10.2 1961—77 Sept. 1967 8.91 1,100 20 11.00 3,000 294 70 1 Different site or datum. 2 Backwater from ice. 3 Regulated by reservoirs upstream. ‘ Downstream of breached dam. 5 Peaked 1—2 feet above gage. 5 Backwater from Raystown Branch Juniata River. FIGURE 23.—Flooding at Johnstown’s Lee Hospital. The dark line across the center of the photograph shows the maximum flood level. (J ohnstown Tribune-Democrat photograph.) HISTORICAL FLOODS 43 TABLE 2. -Bre¢whed dams [Data furnished by the Pennsylvania Department of Environmental Resources] Surface Storage Number of area at capacity site at normal at which peak Drainage pool spillway flow data Date area elevation elevation Height are provided Stream and location Latitude Longitude built (miz) (acres) (10‘ gal) (feet) (see table 1) Sandy Run near St. Michael _______ 40°19’40" 78°48'10" 1915 ______ 5.6 8 15 28 21, 22 Laurel Run near Coopersdale _____ 40°23'05” 78°54’55" 1914 ______ 7.9 22 101 42 26, 28 Otto Run at Salix _______________ 40°17’40” 78°45’35” 1956 ______ 1.9 2 2 19 18 South Fork tributary at St. Michael 40°19’30” 78°46’20” Unknown __ 1.5 2 1 6 19 North Branch tributary 40°28’20” 78°41'30” Unknown __ .65 2.2 6 18 16 near Ebensburg. Peggys Run at Franklin __________ 40°20’10” 7 8°53’00" Unknown __ 1.1 <1 <1 12 None. Little Paint Creek at Elton _______ 40°16’50” 78°47’15” Unknown __ 1.5 3 3 10 None. FIGURE 24. — Stony Creek near the height of the flood. View is of Haynes Street bridge looking downstream toward Johnstown’s business district. (Johnstown Tribune—Democrat photograph.) hydrographs describing inflow to the reservior and the flows of major tributaries were constructed from rain- fall data collected in and near the Laurel Run basin. These data were used, along with reservoir and channel cross-sections, to verify a dam-break flood-wave-routing model. Armbruster (1978) gives a brief discussion of the model. HISTORICAL FLOODS Throughout its history, the area discussed in this report has had an uncommonly high frequency of flooding. The relatively narrow, steep—sided valleys characteristic of much of the area are probably a major factor contributing to its high flood potential. The FIGURE 25.-Maximum heights of the 1889, 1936, and 1977 floods at Johnstown’s City Hall at northeast corner of Main and Market Streets. (US. Geological Survey photograph.) severity of floods just west of the Ohio River—Sus— quehanna River drainge divide has also been attributed to increased rainfall intensities resulting from orographic uplift. Other factors are the area’s position relative to the tracks of most Northeastern United States storms and its proximity to a large source of moisture, the Great Lakes. Flood plain development has also increased the damage potential of flooding in many parts of the report area, especially in the Johnstown area, which has had three devasting floods within the last 90 years. The May 31, 1889 flood, commonly referred to as “the J ohnstown Flood”, was one of the worst catastrophies ever in the United States. About 2,200 persons died, and nearly 1,000 persons were reported missing, and be- lieved to have died as a result of the failure of an 80 ft high dam on the South Fork Little Conemaugh River, 13 miles upstream from J ohnstown. Just before the failure, JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 ' Johnstown and surrounding areas were experiencing severe floods as a result of 6 to 8 in. of storm rainfall the preceding day. Runoff from the storm had also caused the water level behind the South Fork Dam to rise far above normally safe levels. As the water level continued rising, leaks were reported in the dam’s earthen em- bankment. Accounts of the failure (Shank, 1972) state that the leaks progressively worsened and that at about 3:00 pm. (May 31), the dam suddenly burst, releasing about 20 million tons of water on the flooded valley below. The resulting flood wave estimated at 30 to 40 ft. Seven small towns were destroyed as the wave travelled the 13 miles to Johnstown in about 15 minutes. Down- town J ohnstown, at the mouth of the Little Conemaugh River and directly in the path of the flood wave, was almost destroyed. A stone, multi—arched railroad bridge over the Conemaugh River in Johnstown was able to withstand the wave, which greatly reduced damages farther downstream. Though overshadowed by the catastrophe at Johns- town, floods on other streams in the area on May 31 and June 1, 1889, were also severe. It was the highest known flood on the Frankstown Branch Juniata River at Williamsburg (site 49), where the peak stage was at least 0.5 ft higher than any that have occurred since 1889, and the second highest known on the West Branch Susquehanna River at Bower (site 42). Flooding occurred frequently in the Johnstown area during the next four decades, but not until March 1936 was flooding severe and widespread enough to rival that in 1889. Nearly the entire Northeast was affected by floods during March 1936, which resulted from combina- tions of snowmelt and storm runoff. Although there was some melting of the abnormally deep snowpack by the end of February 1936, the major thaw did not begin until March 9, initiated by unseasonably warm temperatures and 1 to 2 in. of rain— fall. The snowmelt and runoff associated with the first storm did not cause flooding, but they did increase the potential for flooding. The second series of storms beginning on March 16 brought 5 to 8 in. of rain, most of which fell on March 17. Runoff from these storms, com- bined with further melting, produced floods comparable to that of 1889 in much of the area. Downtown J ohnstown was inundated by 15 to 20 ft of water, the maximum known for a naturally produced flood. It was the greatest known flood on Stony Creek at Ferndale (site 13), where records are available since 1913, and also at seven gaging sites in the report area but outside the Conemaugh River basin. At J ohnstown, Stony Creek and the Little Conemaugh and Conemaugh Rivers were realigned and partly paved, so that flood flows equivalent to the March 1936 flood would be contained within their channel banks. (Text continued on p. 54.) HISTORICAL FLOODS 45 FIGURE 26.—Destruction along an unnamed tributary to the Conemaugh River between the Coopersdale and Minersville sections of Johnstown. The drainage area above this site is about 0.5 mil. (Pennsylvania Air National Guard photograph.) 46 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS FIGURE 27. —(See caption on facing page.) OFJULY 19—20, 1977 HISTORICAL FLOODS 47 FIGURE 27. —Laurel Run Dam. A,The left photograph shows the vie Guard photograph). B, The right photograph shows the eroded do Survey photograph.) w looking downstream through the breach. (Pennsylvania Air National wnstream face of the dam. The breach is at the far end. (U.S. Geological 48 DISCHARGE, IN THOUSANDS OF CUBIC FEET PER SECOND JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 160 30 140 fi 120 — 100 E 60— 40— 20* 19 20 21 JULY, 1977 FIGURE 28. —Hydrographs of stage and discharge of the Conemaugh River at Seward (site 30). GAGE HEIGHT, |N FEET 49 HISTORICAL FLOODS cam Hmon__>>I manta .m>< EncooI manta .w>< hoaooul Immvtn .w>< Lwaoou m ImmEE .w>< .maooo MAXIMUM RESERVOIR ELEVATION=1437.8 IEE 8m _>_ 0_._.m_n_0w0 4Om< mm“. 2. .ZO_._.<>m_._w 1200 1100 DISTANCE, IN MILES ABOVE MOUTH FIGURE 29. —Flood-crest profile below Laurel Run Dam. 50 ELEVATION, IN FEET ABOVE NATIONAL GEODETIC VERTICAL DATUM OF 1924 1900 1800 1700 1600 1500 JOHNSTOWN—WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 UM RESERVOIR ELEVATION: 1810.5 bfidge I SANDY RUN DAM— J E E US. Route 219 US. Route 219 overpass Right bank tributary —— Embankment of old dam— Starte Route 869 bridgeI 2 1 DISTANCE, IN MILES ABOVE MOUTH FIGURE 30. —Flood-crest profile below Sandy Run Dam. HISTORICAL FLOODS 51 ‘q¥~¢ , n & "1 FIGURE 31. —Flood damage downstream from the Laurel Run Dam. The foundations of two homes that were washed away are Visible in the upper left corner (Pennsylvania Air National Guard photograph). 52 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 FIGURE 32. — Eastbound lanes of State Highway 56, near J ohnstown’s eastern corporate boundary, undermined by floodwaters from Solomon Run (Pennsylvania Air National Guard photograph). HISTORICAL FLOODS 53 FIGURE 33.—Home damaged by flooding from Solomon Run in the Walnut Grove section of Johnstown (Johnstown Tribune-Democrat photograph.) 54 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 FIGURE 34.—Flooding in the Hornerstown section of Johnstown (J ohnstown Tribune—Democrat photograph.) Since its completion in 1943, this channelization was twice credited with preventing serious floods at Johnstown, once in October 1954 and again in June 1972. DEATHS AND DAMAGES The Great Johnstown Flood of 197 7, as described by many residents, was among the more devasting floods in the history of the United States, as shown in table 3. It is especially noteworthy when one considers the size of the area affected. Most of the property damage occurred within a 200-mi2 area, whereas other floods listed in table 3 generally occurred over areas that are 10—1,000 times larger. Although damages have not been officially compiled in detail, the total may exceed the estimated $330 million (National Oceanic and Atmospheric Administration, 1977), as indicated by the following estimates. A spokesman for the Greater J ohnstown Chamber of Com- TABLE 3. —Losses in individual severe floods in the United States since July 1902 [Adapted from National Oceanic and Atmospheric Administration (1977) and includes only those floods resulting in 60 or more deaths or property losses in excess of $200 million] Property damage Lives (thousands Date Location lost of dollars) May—June 1903 Kansas, lower Missouri, and upper Mississippi 100 40,000 Rivers. Mar. 1913 Ohio River and tributaries 467 147,000 Dec. 1913 Texas rivers _ 177 9,000 June 1921 Arkansas Rive n State of Colorado 120 25,000 Sept. 1921 Texas rivers _________________ 215 19,000 Spring, 1927 M" ‘ ‘ ri Valley 313 284,000 Nov. 1927 New England rivers _______________ 88 45,578 May—June 1935 Republican and Kansas Rivers _____ 110 18,000 Main—Apr. 1936 Rivers in Eastern United States _______ ____ 107 270,000 Jan—Feb. 1937 Ohio and lower Mississippi River basins _ 137 417,685 Mar. 1938 Streams in Southern California ______ __ 79 24,500 July 1939 Licking and Kentucky Rivers ________________ 78 1,715 May—July 1947 Lower Missouri and middle Mississippi River 29 235,000 basins. June—July 1951 Kansas and Missouri _______________________ 28 923,224 Aug. 1955 Hurricane “Dianne” floods in the northeastern 187 714,079 United States. Dec. 1955 West Coast rivers _________________________ 61 154,532 Dec. 1964 California and Oregon ____ ____ 40 415,832 June 1965 South Platte River basin ____ 16 415,076 Jan—Feb. 1969 Floods in California ______________ ____ 60 399,233 Feb. 1972 Bufialo Creek, West Virginia ______ ____ 125 10,000 June 1972 Black Hills of South Dakota _________________ 237 164,947 June 1972 Hurricane “Agnes” floods in the eastern 105 4,019,721 United States. Spring, 1973 Mississippi River basin _____________________ 33 1,154,770 June—July 1975 Red River of the North basin ________________ <10 273,114 Sept. 1975 Hurricane “Eloise” floods in Puerto Rico and 50 470,274 northeastern United States. June 1976 Teton Dam failure in southeast Idaho _________ 11 1,000,000 July 1976 Big Thompson River in Colorado _______ 139 30,000 Apr. 1977 Southern Appalachian Mountains area __ 22 424,000 July 1977 Johnstown-Western Pennsylvania ____________ 78 330,000 merce, reported that 640 dwelling units were destroyed and another 2,600 sustained major damages, a loss of about $26 million. Also, 405 business structures were destroyed, of which more than half were in downtown Johnstown, where business damages totalled $136 million. In addition, the Bethlehem Steel Corp., the area’s largest employer, estimated that damages to its facilities would total $35—40 million. A report by the Pennsylvania House of Represen- tatives (1976) lists railroad damage at $20 million and states that damages to the area’s utilities were in excess of $20 million, mostly properties of the Pennsylvania Electric Co. Other estimates of damage listed in the Johnstown Tribune-Democrat include $94 million of roadway and bridge repair and $62.7 million for repairs to public facilities. Also, 3,300 motor vehicles and 8.2 million pounds of food were estimated to have been destroyed. The photographs in figures 31—34 show scenes of the destruction in the J ohnstown area. At least 78 lives were lost as a direct result of the flood. Also, eight others, who were listed as missing 1 year later, probably died. Flooding along Laurel Run, downstream from the breached dam, was responsible for about half of the fatalilties. Many also died along Solomon Run, in the south part of J ohnstown, and along " the Conemaugh River near Seward. REFERENCES 55 REFERENCES Armbruster, J. T., 1978, Model of the flooding caused by the failure of the Laurel Run Reservoir dam, July 19—20, 1977, near J ohnstown, Pennsylvania: Preprints, conference on Flash Floods: Hydrometeorological Aspects: American Meterorological Society, Los Angeles, Calif., p. 190—193. Bailey, J. F., Patterson, J. L., and Paulhus, J. L. H., 1975, Hurricane Agnes rainfall and floods, June-July 1972: US. Geological Survey Professional Paper 924, 403 p. Bodhaine, G. L., 1968, Measurement of peak discharge of culverts by indirect methods: US. Geological Survey Techniques of Water- Resources Investigations, book 3, chap. A3, 60 p. Brua, S. A., 1978, Floods of July 19—20, 1977 in the Johnstown area, western Pennsylvania: US. Geological Survey open-file report, 62 p. Crippen, J. R., and Bue, C. D., 1977, Maximum flood flows in the con- terminous United States: US. Geological Survey WaterSupply Paper 1887, 52 p. Dalrymple, Tate, and Benson, M. A., 1967, Measurement of peak discharge by the slope-area method: US. Geological Survey Techniques of Water-Resources Investigations, book 3, chap. A2, 12 p. Greene, D. R., and Saffle, R. E., 1978, Radar analysis of the 1977 Johnstown flash flood: Preprints, Conference on flash floods; Hydrometeorological Aspects, American Meteorological Society, Los Angeles, California, p. 176—180. Hoxit, L. R., and others, 1978, Meteorological analysis of the Johns- town, Pennsylvania, flash flood, July 19-20, 1977: NOAA Technical Report ERL 401—APCL 43, 71 p. Hulsing, Harry, 1967, Measurement of peak discharges at dams by indirect method: US. Geological Survey Techniques Water- Resources Investigations book 3, chap. A5, 29 p. Jarvis, C. S., and others, 1936, Floods in the United States, magnitude and frequency: US Geological Survey Water-Supply Paper 771, p. 170—171. Langbein, W. B., and Iseri, K. T., 1960, General introduction and hydraulic definitions: US. Geological Survey Water-Supply Paper 1541—A, 29 p. Lott, G. A., 1976, Precipitable water over the United States, Volume 1: Monthly means: National Oceanic and Atmospheric Administra- tion Technical Report NWS 20, 1973 p. Maddox, R. A., Hoxit, L. R., Chappel, C. F., and Caracena, F., 1978, Comparison of meteorological aspects of the Big Thompson and Rapid City floods: Monthly Weather Review, v. 106, p. 37 5—389. Maddox, R. A., Chappel, C. F., and Hoxit, L. R., 1979, Synoptic and meso-a scale aspects of flash flood events: Bulletin of the American Meteorological Society, v. 60, no. 2, p. 115—123. Magor, B. W., 1959, Mesoanalysis: some operational analysis tech- niques utilized in tornado forecasting: Bulletin of the American Meteorological Society, v. 40, p. 499—511. Matthai, H. F., 1967, Measurement of peak discharge at width contractions by indirect methods: US. Geological Survey Tech- niques of Water-Resources Investigations, book 3, chap. A4, 44 p. Maurwitz, J. D, 1972. Precipitation efficiency of thunderstorms on the high plains. Journal de Recherches Atmospheriques (Dessens Memorial Issue), v. 6, p. 367—370. Mogil, H. M., and Groper, H. S., 1976, On the short range prediction of localized excessive convective rainfall: Preprints, Conference on Hydrometeorology: American Meteorological Society, Fort Worth, Tex., p. 9—12. National Oceanic and Atmospheric Adminstration, 1977, Climato- logical Data, National Summary, Annual Summary: v. 28, no. 13, p. 119—120. Pennsylvania House of Representatives, 1977, House Speaker’s Ad Hoc Committee on the eight county flood of July 19—20, 1977, final report, Wednesday, December 14, 1977: 30 p. Shank, W. H., 1972, Great Floods of Pennsylvania, 1972 Flood Edi- tion: Buchart—Horn Publication, 88 p. US. Army Corps of Engineers, Pittsburgh District, 1974, Flood plain information, Conemaugh and Little Conemaugh Rivers, Stony and Bens Creek, City of Johnstown and Vicinity, Cambria and Somerset Counties, Pennsylvania: 59 p., 5 p1. 1977, Floodmark data for Flood of July 19—20, 1977 [unpublished] onfile in Pittsburgh, Pa., office, US. Army Corps of Engineers. 1978, The 1977 Southwestern Pennsylvania Flood: 75 p. US. Geological Survey, 1974, Hydrologic Unit Map—1974, State of Pennsylvania: scale, 1:500,000. U.S. Water Resources Council, 1977 Guidelines for determining flood flow frequency: Bulletin 17A of the Hydrology Committee, Washington, DC, US. Government Printing Office, 197 p. TABLES 4 AND 5 TABLES 59 TABLE 4. —Site descriptions and gage-height and discharge data. [Site numbers used in this table are the same as those used in table 1 and figure 15. Hydrologic Unit numbers are included in the site description for each continuousArecord gaging station. This number designates a geographic area representing part or all of a surface drainage basin or distinct hydrologic feature as delineated by the Office of Water Data Coordination, U.S. Geological Survey (1974). If needed, hourly stage and discharge data for times other than those shown should be determined either graphically or by linear interpolation] SITE 1.—03031950. Big Run near Sprankle Mills, Pa. Location. — Lat 40°59’30”, long 79°05’26”, Jefferson County, Hydrologic Unit 05010006, on the right bank at the downstream side of a highway bridge 0.5 mi (0.8 km) downstream from McCracken Run and 1.3 mi (2.1 km) southeast of Sprankle Mills. Gage. —Water-stage recorder and crest-stage gage. The altitude of the gage is 1,290 ft (393 m), from a topographic map. TABLE 4. —Site description and gage-height and discharge data- Continued SITE 3.—03033220. Stump Creek at Big Run, Pa. Location—Lat 40°58’39”, long 78°50’48”, Jefferson County, at the Baltimore and Ohio Railroad bridge 0.5 mi (0.8 km) upstream from the mouth, 1.0 mi (1.6 km) northeast of Big Run, and 5.6 mi (9.0 km) south of Sykesville. Gaga—Miscellaneous site. SITE 4.——03034000. Mahoning Creek at Punxsutawney, Pa. [NOTE: Gage height and discharges are estimated beginning at 1800 hours on July 21] Location. — Lat 40°56’21”, long 79°00’31", Jefferson County, Hydrologic Unit 05010006, on the right bank 75 ft (23 m) downstream from Williams Run, 1.9 mi (31 km) downstream from Sawmill Run, and 2 mi (3 km) west of Punxsutawney Gage.—Water-stage recorder. Datum of the gage is 1,206,14 ft (367,631 In) NGVD of 1929. (Corps of Engineers bench mark). Prior to October 1, 1946, the gage was at a site 2.9 mi (4.7 km) upstream, at a datum 13.30 ft (4.054 m) higher. Gage Dis- Gage Dis- Gage Dis: Gage Dis- Gage Dis- Gage Dis- Time height charge Time height charge Time height charge Time height charge Time height charge Time height charge (ft) (ft3/s) (ft) (ft3/s) (ft) (ft3/s) (ft) (ft’ls) (ft) (ft3/s) (ft) (ftS/s) July 19: July 20: July 21: July 19: July 20: July 21: 0600 2.12 6.2 0100 5.38 588 0200 2.57 45 0100 2.77 478 0100 642 2,970 0200 7.40 2,760 1200 2.12 6.2 0200 5.69 706 0600 2.50 38 0600 2.68 442 0200 8.22 4,610 0600 6.60 2,240 1400 2.22 12 0300 5.86 774 1200 2.41 30 1200 2.60 410 0300 10.20 6,740 1200 6.34 2,080 1600 2.75 57 0400 5.71 714 1600 2.36 26 1300 2.58 403 0400 11.30 8,170 1800 6.00 1,900 1700 2.68 50 0500 5.27 550 1400 2.60 410 0500 12.52 8,860 2000 590 1,850 1800 2.51 35 0600 4.37 304 1600 2.89 526 0600 13.62 9,740 2200 625 2.030 1900 2.41 26 0800 3.53 160 1800 3.06 610 0700 1478 11,200 2400 6.40 2,120 2000 3.26 114 1000 3.29 126 2000 3.26 710 0800 15.68 12,200 July 22: 2100 5.66 674 1200 315 108 2100 3.58 878 0915 16.22 12,700 0600 5.95 1,880 2200 6.07 838 1400 299 90 2200 4.21 1,300 1000 16.13 12,400 1200 5.50 1,650 2230 6.22 960 1600 2.88 78 2300 4.92 1,790 1100 16.00 12.100 1800 5.10 1,450 2300 6.13 905 1800 2.78 67 2400 5.44 2,160 1200 15.57 11,200 2400 4.70 1,250 2400 5.69 706 2000 2.68 56 1400 14.46 9,750 July 23: 2200 2.63 51 1600 13.14 8,170 0600 4.40 1,100 2400 2.60 48 1800 11.78 6,780 1200 4.05 925 _ , 2000 10.44 5,440 1800 3.70 750 TOW "mom “1 mehes 1'96 2200 9.22 4,320 2400 3.50 670 2400 8.14 3,350 Total runoff, in inches 3.16 SITE 2.—03032500. Redbank Creek at St. Charles, Pa. Location—Lat 40°59’40", long 79°23’40”, Armstrong County, Hydrologic Unit 05010006, on the left bank 400 ft (120 m) downstream from a highway bridge on Legislative Route 03117 at St. Charles, 0.3 mi (0.5 km) downstream from Leatherwood Creek, and 3 mi (5 km) west of New Bethlehem. A water-quality sampling site is 400 ft (120 m) upstream. Gage.—Water-stage recorder. Datum of the gage is 97314 ft (296.613 m) NGVD, datum of 1912. Prior to July 10, 1940, a nonrecording gage was at a site 500 ft (150 m) upstream, at a datum 3.10 ft (0.94 m) higher. SITE 5.—03034500. Little Mahoning Creek at McCormick, Pa. Location.-Lat 40°50’10”, long 79°06'37”, Indiana County, Hydrologic Unit 05010006, on the left bank 200 ft (60 m) upstream from the highway bridge at McCormick, 1 mi (2 km) west of Georgeville, 1.7 mi (27 km) upstream from Ross Run, and 4 mi (6 km) southeast of Smicksburg. Gaga—Water-stage recorder. Datum of the gage is 1,164.88 ft (355.055 m) NGVD of 1929, (Corps of Engineers bench mark). Prior to May 10, 1940, a nonrecording gage was at a site 200 ft (60 m) upstream, at the same datum. Gage Dis- Gage Dis- Gage Dis- Time height charge Time height charge Time height charge Gage Dis- Gage Dis- Gage Dis- (ft) (ftS/s) (ft) (ft3/s) (ft) (ft3/s) Time height charge Time height charge Time height charge July 19: July 20: July 22: (ft) 105/5) (“1 (fig/5i (ft) 0W5) 0100 4.74 830 0900 14.65 19,300 0200 777 3,800 July 19: July 20: July 21: 0600 4.63 775 1000 14.50 18,800 0600 7.56 3,530 0100 2.00 58 1000 12.42 5,420 1400 5 19 767 1200 4.51 715 1100 14.18 17,700 0800 7.42 3,350 0600 1.94 53 1100 1268 5,680 1500 5 10 740 1800 4.50 710 1200 13.78 16,400 1200 7.23 3,100 1200 1.89 48 1200 12.76 5,760 1600 5.75 960 2000 4.54 730 1400 12.83 13,700 1800 6.88 2,660 1800 1.91 50 1230 12.77 5,770 1800 7.15 1,520 2100 4.76 840 1600 11.94 11,400 2400 6.62 2,340 1900 1.92 51 1300 12.77 5,770 2000 7.64 1,720 2200 5.19 1,070 1800 11.21 9,760 July 23: 2000 2.23 82 1400 12.68 5,680 2200 8 19 2,030 2300 5.82 1,560 2000 10.60 8,500 0600 6.40 2,100 2100 2.33 94 1500 12.53 5,530 2400 8 80 2,400 2400 6.75 2,500 2200 10.03 7,450 1200 6.19 1,890 2200 2.66 138 1600 1230 5,300 July 22: July 20: 2400 9.52 6,540 1800 5.97 1,680 2300 3.15 230 1700 12.00 5,000 0200 9.20 2,650 0100 7.79 3,830 July 21: 2400 5.75 1,500 2400 3.97 425 1800 11.63 4,630 0230 9.21 2,660 0200 8.98 5,570 0200 9.11 5,800 July 24: July 20: 2000 10.69 3,750 0300 9.19 2,640 0300 10.86 9,020 0400 8.78 5,250 0600 5.55 1,340 0100 5.69 896 2200 9.48 2,850 0400 9.04 2,540 0400 12.46 12,700 0600 8.52 4,830 1200 5.37 1,200 0200 6.86 1,400 2400 8.24 2,060 0600 8.43 2,180 0500 13.23 14,800 1200 7.98 4,070 1800 5.21 1,090 0300 7.70 1,750 July 21: 1200 6.43 1,230 0600 13.67 16,100 1800 7.79 3,830 2400 507 1,000 0400 8.77 2,380 0200 7.15 1,520 1800 5.57 888 0700 14 15 17,500 2000 7.82 3,870 0500 9.81 3,080 0400 6.51 1,260 2400 4.92 686 0800 14 52 18,900 2200 7.90 3,970 0600 10.35 3,480 0600 6.14 1,120 July 23: 0830 14 72 19,500 2400 7.82 3,870 0700 10.80 3,840 0800 5.85 1,000 0600 4.54 572 To... mm, mm... 1.65 3333 fig: 33:3 333 g~gg :33 120° 4-27 498 Total runoff, in inches 2.99 60 TABLE 4.—Site description and gage-height and discharge data— Continued J OHNSTOWN-WE STE RN PENNSYLVANIA SITE 6.—03036000. Mahoning Creek at Mahoning Creek Dam, Pa. Location-Lat 40°55’39", long 79°17’29”, Armstrong County, Hydrologic Unit 05010006, on the left bank at the downstream side of the highway bridge at McCrea Furnace, 700 ft (213 m) downstream from Camp Run, 0.9 mi (1.4 km) downstream from Mahoning Creek Dam, 1 mi (2 km) southwest of Eddyville, and 2.1 mi (3.4 km) upstream from Pine Run. Gage.—Water-stage recorder. Datum of the gage is 1,003.39 ft (305.833 m) NGVD of 1929 (Corps of Engineers bench mark). Prior to February 1, 1940, a nonrecording gage was at the same site and datum. Remarks—Flow has been completely regulated since 1941 by Mahoning Creek Lake, 0.9 mi (1.4 km) upstream. STORM AND FLOODS OF JULY 19—20, 1977 TABLE 4.—Site description and gage-height and discharge data- Continued SITE 9.—03039000. Crooked Creek at Crooked Creek Dam, Pa. Location—Lat 40°43’13", long 79°30’42”, Armstrong County, Hydrologic Unit 05010006, on the right bank 0.4 mi (0.6 km) downstream from Crooked Creek Dam, 3.5 mi (5.6 km) south of Ford City, and 6.7 mi (10.8 km) upstream from mouth. . Gage. — Water-stage recorder. Datum of gage is 79951 ft (243.691 m) NGVD of1929. Prior to August 1, 1933, a nonrecording gage was at a site 2 mi (3 km) downstream, at a different datum. From July 31, 1933, to December 5, 1939, a nonrecording gage was at a site 1.5 mi (2.4 km) downstream, at a different datum. Remarks—Flow has been completely regulated since 1940 by Crooked Creek Lake, 0.4 mi (0.6 km) upstream, and since 1968, by Keystone Lake; the combined capacity of the lakes is Gage Dis- Gage Dis- Gage Dis- Time height charge Time height charge Time height charge (ft) (ft3/s) (ft) (ft3/s) (ft) (re/s) July 19: July 20: July 22: 0100 3.84 1,020 1200 3.55 815 0100 6.88 5,400 0600 3.83 1,010 1400 3.53 801 1200 6.88 5,400 1200 3.81 998 1600 3.89 1,060 1345 7.35 6,560 1300 3.20 590 1800 3.94 1,100 1400 7.35 6,560 1800 3.08 530 2000 4.86 1,930 1700 7.35 6,560 2400 3.31 656 2200 4.90 1,970 1800 6.85 5,330 July 20: 2400 4.93 2,000 2400 6.90 5,440 0100 3.49 773 July 21: July 23: 0200 4.32 1,420 0200 4.94 2,010 0600 6.99 5,660 0300 4.60 1,670 0400 4.95 2,030 1200 7.00 5,690 0400 4.13 1,250 0900 4.97 2,050 1800 7.00 5,690 0500 3.85 1,030 1000 5.74 3,080 2400 7.01 5,720 0600 3.75 955 1200 5.76 3,120 July 24: 0800 3.68 906 1300 6.88 5,400 0600 7.01 5,720 1000 3.60 850 2400 6.88 5,400 1200 7.02 5,740 1800 7.02 5,740 2400 7.02 5,740 Total runoff, in inches 2.47 SITE 7.—03037300. Crooked Creek at Shelocta, Pa. Location. —Lat 40°39’35”, long 79°18’40”, Indiana County, 0.4 mi (0.6 km) upstream from State Highway 156 bridge and 0.5 mi (0.8 km) northeast of intersection of US. Highway 422 and State Highway 156, at Shelocta. 115,910 acre-ft (143 hma). Gage. — Miscellaneous site. SITE 8.—03038000. Crooked Creek at Idaho, Pa. [NOTEz Gage heights and discharges estimated from 1800 hours on July 20 to 1000 hours on July 21] Location.— Lat 40°39'17”, long 79°20'56”, Armstrong County, Hydrologic Unit 05010006, on the right bank at the downstream end of the old bridge abutment at Idaho, 0.4 mi (0.6 km) downstream from Keystone Generating Station, 1.5 mi (2.4 km) downstream from Plum Creek, and 2.4 mi (3.9 km) west of Shelocta. Gage.—Water-stage recorder and concrete weir control. Datum of the gage is 961.04 ft (292.925 m) NGVD of 1929. (Baltimore and Ohio Railroad bench mark). Remarks. — Flow has been regulated to some extent since March 1968 by Keystone Lake, 7 mi (11 km) upstream, which has a usable capacity of 22,010 acre-ft (27.1 hm3). Evaporation from the operation of a steam-electric plant 0.4 mi (0.6 km) upstream, which began during Gage Dis- Gage Dis- Gage Dis- Time height charge Time height charge Time height charge (ft) (ftS/s) (ft) (fts/s) (ft) (ft3/s) July 19: July 21: July 23: 0600 1.23 99 0200 4.09 1,260 0600 7.51 4,010 1200 1.23 99 0400 4.12 1,280 1200 7.44 3,940 1800 1.24 101 0600 4.17 1,310 1800 7.36 3,860 1900 1.24 101 0800 4.19 1,320 2400 7.28 3,780 2000 1.33 120 1000 5.36 2,140 July 24: 2100 1.31 115 1200 5.40 2,170 0600 7.19 3,690 2200 1.28 109 1400 6.68 3,200 1200 7.07 3,570 2300 1.29 111 1600 6.70 3,220 1800 6.97 3,470 2400 1.29 111 1800 6.69 3,210 2400 6.85 3,350 July 20: 2000 6.68 3,200 July 25: 0600 1.29 111 2200 6.68 3,200 0600 6.71 3,230 0800 1.31 115 2400 6.68 3,200 0900 6.63 3,160 1000 2.41 474 July 22: 1000 4.76 1,720 1200 2.42 478 0200 6.69 3,210 1100 4.83 1,770 1400 2.45 490 0400 6.69 3,210 1200 4.74 1,720 1600 3.91 1,160 0600 6.69 3,210 1300 3.79 1,090 1800 3.99 1,200 0800 6.69 3,210 1400 3.77 1,080 2000 4.01 1,220 1000 6.69 3,210 1600 3.79 1,090 2200 4.05 1,240 1200 6.72 3,240 1800 3.81 1,100 2400 4.09 1,260 1300 7.62 4,120 2000 3.84 1,110 1400 7.65 4,150 2200 3.87 1,130 1600 7.64 4,140 2400 3.90 1,150 1800 7.62 4,120 2000 7 .59 4,090 2200 7.59 4,090 2400 7.57 4,070 Total runoff, in inches 2.23 SITE 10.—03039200. Clear Run near Buckstown, Pa. Location-Lat 40°02'49", long 78°50°00”, Somerset County, Hydrologic Unit 05010007, on the left bank at the downstream side of the bridge on State Highway 160, 0.8 mi (1.3 km) south of Reels Corners and 2.3 mi (3.7 km) southeast of Buckstown. Gage.-Water-stage recorder, crest-stage gage, and concrete control. Datum of the gage is 2,339.24 ft (713.00 In) NGVD of 1929. From July 6, 1960, to Aug. 31, 1964, a crest—stage gage was at a site 50 ft (15 m) upstream, at the same datum. July 1967, can amount to as much as 30 ft3/s (0.85 mS/s). Gage Dis- Gage Dis- Gage Dis» Time height charge Time height charge Time height charge (ft) (ft3/s) (ft) (ft3/s) (ft) (ft3/s) July 19: July 20: July 22: 1200 2.48 51 1400 12.44 7,730 0200 7.52 3,510 1500 2.61 72 1500 12.79 8,150 0400 7.66 3,610 1800 2.76 102 1600 13.10 8,520 0600 7.75 3,680 1900 2.76 102 1700 13.38 8,860 0700 7.76 3,680 2000 2.80 111 1800 13.25 8,700 0800 7.73 3,660 2100 3.38 340 1900 13.04 8,450 0900 7.63 3,590 2200 4.33 951 2000 12.62 7,940 1000 7.46 3,480 2300 5.59 1,920 2100 12.01 7,260 1200 6.92 3,040 2400 6.85 2,980 2200 11.40 6,650 1400 6.28 2,500 July 20: 2300 10.78 6,030 1600 5.82 2,110 0100 7.48 3,480 2400 10.22 5,500 1800 5.50 1,850 0200 7.93 3,800 July 21: 2400 4.83 1,310 0300 8.30 4,060 0200 9.33 4,780 July 23: 0400 8.68 4,330 0400 8.54 4,230 0600 4.45 1,040 0500 9.08 4,610 0600 7.77 3,690 1200 4.25 895 0600 9.54 4,930 0800 6.98 3,080 1800 4.05 755 0700 9.93 5,240 1000 6.19 2,420 2400 3.87 629 0800 10.30 5,570 1200 5.44 1,800 July 24: 0900 10.67 5,920 1400 5.03 1,470 0600 3.74 544 1000 11.06 6,310 1500 4.95 1,410 1200 3.67 502 1100 11.44 6,690 1600 5.24 1,640 1800 3.56 436 1200 11.82 7,070 1800 6.18 2,410 2400 3.48 390 1300 12.13 7,380 2000 6.86 2,990 2200 7.11 3,190 2400 7.30 3,340 Total runoff, in inches 2.65 Gage Dis- Gage Dis— Gage Dis- Time ~ height charge Time height charge Time height charge (ft) (ftS/s) (ft) (fta/s) (ft) (fta/s) July 19: July 20: July 20: 0100 2.18 0.51 0400 2.38 1.7 1400 3.20 66 1200 2.18 .‘51 0500 3.81 23 1600 3.06 50 1800 2.17 .48 0530 5.03 366 1800 2.97 40 2200 2.16 .45 0600 4.68 296 2000 2.91 33 2300 2.31 1.1 0700 4.31 222 2200 2.86 28 2400 2.27 .88 0800 4.14 196 2400 2.82 24 July 20: 0900 3.92 163 July 21: 0100 2.29 .99 1000 3.68 129 0600 2.74 17 0200 2.34 1.3 1100 3.53 108 1200 2.66 11 0300 2.34 1.3 1200 3.41 91 1600 2.62 8.8 Total runoff, in inches 0.76 SITE 11.—03039910. Seese Run at Windber, Pa. Location. —Lat 40°13'44”, long 78°49’43”, Somerset County. at the bridge on State Highway 160 in Windber, 0.4 mi (0.6 km) upstream from the mouth. Gage. — Miscellaneous site. SITE 12.—03039914. Paint Creek at Windber, Pa. Location. — Lat 40° 14’33”, long 78°50‘47", Somerset County, along State Highway 56, 0.4 mi (0.6 km) upstream from State Highway 601 near the northwest corporate boundary. Gage. — Miscellaneous site. ‘ TABLES 61 TABLE 4.—Site description and gage-height and discharge data— Continued SITE 13.—03040000. Stoney Creek at Ferndale, Pa. [NOTE1 Gage heights and discharges are estimated beginning at 0800 hours on July 20] Location. — Lat 40°17'08”, long 78°55’15", Cambria County, Hydrologic Unit 05010007, on the right bank 50 ft (15 m) upstream from the highway bridge at Ferndale, 0.4 mi (0.6 km) doownstream from Bens Creek, 1.2 mi (1.9 km) upstream from the Johnstown city limits, and 5.2 mi (8.4 km) upstream from the confluence with the Little Conemaugh River. Gage.—Water-stage recorder. Datum of the gage is 1,184.06 ft (360.901 m) NGVD of 1929. Prior to March 19, 1936, a nonreeording gage was at a site 3.5 mi (5.6 km) downstream, at a different datum. From December S, 1938, to January 30, 1940, a nonrecording gage was at a site 50 ft (15 m) downstream, at the present datum. Remarks. Regulation is by mine pumpage and reservoirs and by diversion above the station; the four largest reservoirs have a combined capacity of 42,360 acre-ft (52.2 hms). Gage Dis— Gage Dis- Gage Dis- Time height charge Time height charge Time height charge (ft) (ft‘ls) (ft) (ft5/s) (ft) (ftsls) July 19: July 20: July 21: 0100 2.26 97 0600 18.27 38,800 0600 6 50 4,050 0600 2.23 92 0700 23.21 48,000 1200 6.00 3,280 1200 2.19 84 0800 21.50 45,500 1800 5.64 2,530 1800 2.19 84 0900 20.10 43,000 2400 5.32 2,090 1900 2.26 97 1000 18.80 40,200 July 22: 2200 2.27 99 1100 17.40 36,300 1200 4.79 1,520 2300 2.53 169 1200 16.10 32,300 2400 4 46 1,190 2400 2.99 350 1400 13.30 22,600 July 23: July 20: 1600 10.70 14,100 1200 4 18 924 0100 3.72 796 1800 9.15 9,710 2400 3.94 732 0200 4.64 1,640 2000 8.20 7,430 0300 5.07 2,070 2200 7.58 6,060 0400 5.38 2,420 2400 7.20 5,300 0500 8.99 9,330 Total runofl‘, in inches 1.98 SITE 14.—03040016. Sams Run at Geistown, Pa. Location. — Lat 40°17'20", lon 78°52'58”, Cambria County, 0.4 mi (0.6 km) upstream from the G corporate boundary at the tate Highway 756 bridge in Geistown. age—M' " site SITE 15.—03040018. Same Run at Lorain, Pa. Location -Lat 40'17’42", long 78°54'04”, Cambria County, in an artificial channel between city residence numbers 369 to 375 along State Highway 756 in Lorain. Gage. - Miscellaneous site. SITE 16.—03040095. North Branch Little Conemaugh River tributary near Ebensburg, Pa. Location -Lat 40°28’05", long 78°41’81”, Cambria County, at a dirt road crossing 0.1 m‘: (0.2 km) downstream from the Tong Club dam, 1.2 mi (1.9 km) upstream from the mouth, 2.0 mi (3.2 km) southeast of Ebensburg, and 2.1 mi (3.4 km) west of Munster. Gage. —M' " site. SITE 17.—03040300. Little Conemaugh River at Summerhill, Pa. Location. -Lat 40°22'19”, long 78°46’00", Cambria County, at the State Highway 53 bridge southwest of Summerhill, 500 it (150 m) upstream from the Conrail bridge, 0.6 mi (1.0 km) downstream from Laurel Run, and 1.5 mi (2.4 km) above South Fork Little Conemaugh River. Gage. —M' " site. SITE 18.-03040420. Otto Run at Salix, Pa. Location — Lat 40° 1743”, long 78°45’SO’, Cambria County, at a bridge on a aved road 0.5 mi (0.8 km) southeast of Salix and 300 feet (90 m) downstream from a. smal reservoir. Gage. -M' “ site. SITE 19—03040430. South For]: Little Conemaugh River tributary at St. Michael, Pa. Location. - Lat 40°19‘35”, long 78°46'23", Cambria County, 400 ft (120 m) downstream from a reservoir, 0.6 mi (1.0 km) south of Saint Michael, 0.7 mi (1.1 km) upstream of mouth, and 2.8 mi (4.5 km) southeast of South Fork. Gage. -M' " site. SITE 20.—03040500. South Fork Little Conemaugh River at Fishertown, Pa. Location. -Lat 40°2054”, long 78°46’82”. Cambria County, at the old South Fork Reservoir dam site at Fishertown and 0.1 mi (0.2 km) upstream from U.S. Highway 219. Gaga. —M‘ " site. SITE 21.—03040503. Sandy Run above Sandy Run Reservoir near St. Michael, Pa. Location—Lat 40°19'30’. long 78°48’09’, Cambria Count , 0.2 mi (0.3 km) upstream from Sandy {tun Reservoir and 1.8 mi (2.9 km) southwest of t. Michael. Gaga -M “ site. TABLE 4,-Site description and gage-height and discharge data— Continued SITE 22.—03040505. Sandy Run below Sandy Run Reservoir at St. Michael, Pa. Location-Lat 40°20’10”, long 78°47'21”, Cambria County, just upstream from the U.S. Highway 219 bridge, 0.9 mi (1.4 km) west of St. Michael, and 0.9 mi (1.4 km) northeast of Sandy Run Dam. Gage. — Miscellaneous site. SITE 23.—03041000. Little Conemaugh River at East Conemaugh, Pa. Location. - Lat 40°20’37”, long 78°53’07”, Cambria County, Hydrologic Unit 05010007, on the right bank 100 ft (30 m) downstream from the bridge on State Highway 271 at East Cone- maugh, 0.3 mi (0.5 km) downstream from Clapboard Run, and 2.5 mi (4.0 km) upstream from the confluence with Stony Creek. Gage. —Water-stage recorder. Datum of gage is 1,208.29 ft (368.287 m) NGVD of 1929. Prior 60 February 1, 1940, a nonrecording gage was at a site 100 ft (30 m) upstream, at the same atum. Remarks. -Flow is regulated by reservoirs and by diversion above the station; the two most effective reservoirs have a combined capacity of 5,640 acre-ft (6.95 hm’). Gage Dis- Gage Dis- Gage Dis- Time height charge Time height charge Time height charge (ft) (fa/s) (ft) (fix/s) (ft) (to/s) July 19: July 20: July 22: 1800 1 66 140 1100 10.21 15,500 0600 3.31 2,820 2100 1.66 140 1200 9.39 13,800 1200 2.95 2,280 2200 1.87 191 1400 8.45 11,900 1800 2.60 1,790 2300 2.62 542 1600 7.63 10,300 2400 2.35 1,460 2400 3.65 1,340 1800 7.16 9,400 July 23: July 20: 2000 6.80 8,740 0600 2.20 1,260 0100 3.75 1,460 2200 6.49 8,180 1200 2.03 1,040 0200 5.77 4,240 2400 6.16 7,590 1800 1.87 856 0300 9.27 13,000 July 21: 2400 1.92 904 0400 10.60 16,300 0300 5.84 7,010 July 24: 0500 12.35 20,400 0600 5.58 6,540 0600 1.72 664 0600 18.09 37,100 0900 5.37 6,170 1200 1.68 618 0615 18.85 40,000 1200 5.19 5,840 1800 1.66 596 0700 17.45 34,700 1500 4.82 5,210 2400 1.64 574 0800 15.12 27,400 1800 3.77 3,530 0900 12.86 21,700 2100 3.64 3,360 1000 11.37 18,100 2200 3.67 3,420 2400 3.64 3,360 Total runofl', in inches 4.70 SITE 24.—03041030. Elk Run at Morrellville, Pa. Location. — Lat 40°20’33", long 78°56’39”, Cambria County, just upstream from Fairview Ave. and St. Columbus Cemetery in Morrellville. Gage. —Miscellaneous site. SITE 25.—03041038. Laurel Run at Chickaree, Pa. “ .—Lat 40°26’54”, long 78°53’09”, Cambria County, at a culvert on the road between Chickaree and Vintondale, 0.25 mi (0.40 km) northwest of Chickaree. Gage. — Miscellaneous site. SITE 26.—03041039. Laurel Run above Laurel Run Reservoir near Coopersdale, Pa. Location. — Lat 40°23’16”, long 78°54’34”, Cambria County, at the inlet to Laurel Run Reser- voir, 1,900 ft (580 m) upstream from the dam and 2.5 mi (4.0 km) north of Coopersdale. Gage. — Miscellaneous site. SITE 27.—03041040. Red Run near Coopersdale, Pa. Location—Lat 40°22'57", long 78°55’09”, Cambria County, at the mouth, 0.3 mi (0.5 km) southwest of Laurel Run Dam and 2 mi (3 km) northeast of Coopersdale. Gage. — Miscellaneous site. SITE 28.—03041043. Laurel Run below Laurel Run Reservoir near Coopersdale, Pa. Location. — Lat 40° 2245”, long 78°55‘07“, Cambria County, 300 ft (90 m) downstream from the Cooper Ave. bridge, 0.9 mi (1.4 km) upstream from Wildcat Run, 1.6 mi (2.6 km) above the mouth, and 1.5 mi (2.4 km) northeast of Coopersdale. Gage. - Miscellaneous site. SITE 29.—03041046. Wildcat Run at Coopersdale, Pa. Location. — Lat 40°22’10”, long 78°55’58”, Cambria County, at the mouth, 1.0 mi (1.6 km) north of Coopersdale and 300 ft (90 m) downstream from Cooper Ave. Gage. —Miscellaneous site. 62 JOHNSTOWN-WE STERN PENNSYLVANIA TABLE 4.—Site description and gage-height and discharge data— Continued SITE 30.—03041500. Conemaugh River at Seward, Pa. Locution.— Lat 40°25'09”, long 79°01’35”, Westmoreland County, Hydrologic Unit 05010007, on the left bank at the upstream side of a bridge on State Highway 56 at Seward, 2.0 mi (3.2 km) downstream from Findley Run and 9 mi (14 km) northwest of Johnstown. Guge.— Water-stage recorder. Datum of the gage is 1,076.01 ft (327.968 m) NGVD of 1929. Remarks. — Flow is regulated by steel mills and by reservoirs above the station; the eight most effective reservoirs have a combined capacity of 51,850 acre-ft (63.9 hm3). Gage Dis- Gage Dis- Gage Dis- Time height charge Time height charge Time height charge (ft) (ft3/s) (ft) (re/s) (ft) (ft3/s) July 19: July 20: July 21: 0100 2.47 529 1200 21.73 65,500 1200 8.02 7,260 0600 2.42 494 1300 19.90 54,500 1400 7.86 6,690 1200 2.37 459 1400 18.23 44,500 1600 7.72 6,380 1800 2.34 438 1500 16.74 37,300 1800 7.78 6.520 2200 2.38 466 1600 14.70 29,300 2000 7.72 6,380 2300 2.55 585 1700 13.29 24,400 2200 7.72 6,380 2400 3.61 1,690 1800 12.52 22,100 2400 7.85 6,670 July 20: 1900 11.88 18,800 July 22: 0100 6.16 6,250 2000 11.38 17,500 0600 7.48 5,860 0200 6.83 7,730 2100 10.98 15,900 1200 7.13 5,160 0300 7.55 9,440 2200 10.60 15,200 1800 6.82 4,540 0400 12.76 23,100 2300 10.30 13,900 2400 6.52 3,940 0500 22.09 68,300 2400 9.98 12,900 July 23: 0600 24.40 86,600 July 21: 0600 6.28 3,340 0700 25.65 98,000 0200 9.48 10,200 1200 6.12 3,060 0800 27.06 115,000 0400 9.08 9,990 1800 5.92 2,720 0900 25.85 99,500 0600 8.80 9,560 2400 5.78 2,660 1000 24.75 88,800 0800 8.46 8,260 1100 23.74 80,100 1000 8.20 7,660 Total runoff, in inches 3.10 SITE 31—03042000. Blacklick Creek at Josephine, Pa. Location.- Lat 40°28’24”, long 79°11’01”, Indiana County, Hydrologic Unit 05010007, on the right bank on the upstream side of an old concrete dam at Josephine, 0.9 mi (1.4 km) upstream from Two Lick Creek and 5 mi (8 km) northeast of Blairsville. A water-quality sampling site is 820 ft (250 m) downstream. Gage. — Water-stage recorder and crest-stage gage. Datum of the gage is 975.82 ft (297.430 m) NGVD, datum of 1912. Prior to August 25, 1953, a nonrecording gage was at the same site and datum. Remarks.— Some regulation at low flow is by mine pumpage above the station. Gage Dis- Gage Dis- Gage Dis- Time height charge Time height charge Time height charge (It) (ftS/s) (ft) (fta/s) (ft) (fta/s) July 19: July 20: July 21: 0100 4.06 251 1200 17.94 34,200 2200 6.70 1,600 0600 3.84 180 1300 17.34 31,200 2300 6.76 1,660 1200 3.62 118 1400 16.29 26,300 2400 6.91 1,810 1800 3.59 111 1500 14.55 19,300 July 22: 2100 3.63 121 1600 13.65 16,300 0100 7.01 1,910 2200 4.16 289 1700 12.50 12,700 0200 7.00 1,900 2300 6.46 2,280 1800 11.80 10,800 0300 6.97 1,870 2400 10.87 10,600 1900 11.05 8,780 0800 6.83 1,730 July 20: 2000 10.35 7,260 1200 6.47 1,380 0100 11.90 13,200 2100 9.65 5,860 1800 6.19 1,150 0200 11.79 12,900 2200 9.05 4,730 2400 5.93 944 0300 11.90 13.200 2300 875 4,240 July 23: 0400 12.55 15,000 2400 8.50 3,840 0600 5.74 804 0500 14.45 21,100 July 21: 1200 5.62 732 0600 16.15 27,100 0200 8.40 3,700 1800 5.47 642 0700 17.70 33,800 0400 7.93 3,040 2400 5.36 576 0800 19.15 41,300 0600 7.68 2,720 July 24: 0830 19.89 45,700 0800 7.47 2,460 0600 5.25 515 0900 19.55 42,800 1000 7.29 2,250 1200 5.19 485 1000 19.00 39,500 1200 7.13 2,060 1800 5.14 460 1100 18.30 36,000 1800 6.80 1,700 2400 5.14 460 Total runoff, in inches 4.93 SITE 32.—03042170. Stoney Run at Indiana, Pa. Location.— Lat 40°36‘31”, long 79°09‘49”, Indiana County, at the southwest edge of Indiana, 300 ft (90 in) west of U.S. Highway 119 and 0.1 mi (0.2 km) below Marsh Run. Gage. — Crest-stage. STORM AND FLOODS OF JULY 19—20, 1977 TABLE 4.—Site description and gage-height and discharge data— Continued SITE 33.—03042180. Two Lick Creek near Homer City, Pa. LOCILIIOYL.—L3.I. 40°33’51”, long 79°09’42”, Indiana County, at a bridge on US. Highway 219, 4.2 mi (6.8 km) south of Indiana. Gage. — Miscellaneous site. SITE 34.—03042198. Little Yellow Creek tributary at Strongstown, Pa. Location—Lat 40°33’33", long 78°56’19“, Indiana County, at a highway culvert on US Highway 422, 2,000 ft (610 m) upstream from the mouth, 0.8 mi (1.3 km) northwest of Strongstown, and 1.5 mi (2.4 km) southeast of Nolo. Gage—Miscellaneous site. SITE 35.—03042200. Little Yellow Creek near Strongstown, Pa. Location. vLat 40°33’45", long 78°56’44”, Indiana County, Hydrologic Unit 05010007, on the right bank 100 ft (30 m) downstream from a concrete box culvert on U.S. Highway 422, 1.4 mi (2.3 km) northwest of Strongstown, 6 mi (10 km) upstream from the mouth, and 11 mi (18 km) southeast of Indiana. Gage. —Water-stage recorder and creststage gage. Datum of the gage is 1,586.83 ft (483.666 m) NGVD. From August 25, 1959 to August 31, 1960, a low-flow gage and, from November 6, 1959 to August 31, 1960, a crest-stage gage were at a site 100 ft (30 m) upstream, at the same datum. Gage Dis- Gage Dis- Gage DisA Time height charge Time height charge Time height charge (ft) (ft3/s) (ft) (ft3/s) (ft) (ft3/s) July 19: July 20: July 21: 1400 1.61 3.7 0500 8.37 2,690 1800 4.53 120 1500 1.83 8.7 0600 7.19 1,390 2000 4.42 103 1600 1.92 12 0700 6.59 903 2200 4.35 93 1700 1.95 13 0800 6.08 600 2400 4.29 85 2000 10 0900 5.73 452 July 22: 2100 252 1000 5.50 360 0600 4.15 68 2200 470 1200 5.14 252 1200 4.05 56 2300 560 1800 4.67 140 1800 3.96 47 2400 506 2400 4.45 108 2400 3.88 39 July 20: July 21: July 23: 0100 7.84 2,040 0600 4.31 87 0600 3.84 36 0200 7,92 2,120 1200 4.17 70 1200 3.74 27 0300 7.57 1,770 1500 4.11 63 1800 3.69 23 0400 9.31 4,250 1600 4.41 102 2400 3.65 21 Total runoff, in inches 3.65 SITE 36.-—O3042280. Yellow Creek near Homer City, Pa. Location—Lat 40°34’18”, long 79°06’13”, Indiana County, Hydrologic Unit 05010007, on the left bank, 0.3 mi (0.5 km) upstream from the Central Indiana County Water Authority dam and 3.5 mi (5.6 km) northeast of Homer City. Gage—Waterstage recorder. Altitude of the gage is 1,140 ft (347 m), from a topographic ma . ngrks.vFlows are not adjusted for the effect of Ferrier Run following a fiood~induced break in the Ferrier Run diversion project. Ferrier Run now enters Yellow Creek between the dam (flow measurement site) and the gaging station, instead of downstream from the dam. Gage Dis- Gage Dis- Gage Dis- Time height charge Time height charge Time height charge (ft) (ftS/s) (ft) (Eta/s) (ft) (ft3/s) July 19: July 20: July 21: 1200 2.62 48 0700 12.60 15,000 0200 7.02 3,330 1800 2.64 51 0800 12.25 14,000 0400 6.79 3,050 2000 2.65 53 0900 12.02 13,400 0600 6.57 2,780 2100 3.06 148 1000 11.61 12,300 1200 5.98 2,080 2200 3.79 455 1100 11.28 11,500 2400 5.40 1,500 2300 5.12 1,470 1200 10.85 10,500 July 22: 2400 5.39 1,740 1400 10.01 8,620 1200 4.83 1,030 July 20: 1600 9.17 6,840 2400 4.31 686 0100 5.55 1,900 1800 8.59 5,760 July 23: 0200 6.85 3,370 2000 8.11 4,980 1200 3.95 485 0300 8.21 5,140 2200 7.70 4,320 2400 3.69 366 0400 9.53 7,770 2400 7.39 3,850 July 24: 0500 11.11 11,100 1200 3.50 290 0600 12.03 13,400 2400 3.36 236 Total runoff, in inches 7.69 SITE 37.-—03042282. Ferrier Run near Homer City, Pa. Location—Lat 40°34’18”, long 79°06’13”, Indiana County, at an artificial channel near the mouth near Yellow Creek near the Homer City gaging station, 3.5 mi (5.6 km) northeast of Homer City and 4.5 mi (7.2 km) southeast of Indiana. Gage. — Miscellaneous site. TABLES 63 TABLE 4.-Site description and gage-height and discharge data— Continued SITE 38.—03042500. Two Lick Creek at Graceton, Pa. NOTE: [Gage heights and discharges estimated from 1600 hours on July 20 until 0600 hours 7 on July 21.] Location— Lat 40°31’02”, long 79°10’19”, Indiana County, Hydrologic Unit 05010007, on the right bank 0.8 mi (1.3 km) upstream from a highway bridge on the road leading west from Graceton, 1.1 mi (1.8 km) downstream from Tearing Run, 1.5 mi (2.4 km) upstream from Cherry Run, and 8 mi (13 km) northeast of Blairsville. A water-quality sampling site is at a bridge 0.8 mi (1.3 km) downstream Gage.—Water-stage recorder. Datum of the gage is 98163 ft (299.201 m) NGVD of 1929. Remarks—Diurnal fluctuation is caused by mine pumpage and by a sewage-disposal plant above the station. Flow has been regulated since December 1968 by Two Lick Creek Reser- voir, 10 mi (16 km) upstream, which has a capacity of 16,240 acre-ft (20.0 hma), and since July 1971, by Yellow Creek Lake, 11 mi (18 km) upstream, Gage Dis- Gage Dis- Gage Dis» Time height charge Time height charge Time height charge (ft) (ft3/s) (ft) (fa/5) (ft) (fta/s) July 19: July 20: July 21: 0100 2.45 160 0800 17.75 29,500 1800 7.50 3.400 0600 2.42 151 0900 18.30 31,000 1900 7.71 3.610 1200 2.43 154 0930 18.65 32,000 2000 7.72 3,620 1400 2.46 163 1000 18.33 28,500 2100 7.55 3,450 1600 2.52 181 1100 18.08 27,000 2200 7.39 3,290 1700 2.55 190 1200 17.60 24,000 2400 7.16 3,080 1800 2.56 193 1400 17.00 21,600 July 22: 1900 2.53 184 1600 15.80 17,800 0600 6.77 2,720 2000 2.97 320 1800 14.40 13,900 1200 6.50 2,480 2100 5.53 1,700 2000 12.90 10,700 1800 6.25 2,280 2200 8.55 4,460 2200 11.40 8,200 2400 4 15 795 2300 10.12 6,540 2400 10.30 6,650 July 23: 2400 10.60 7,500 July 21: 0600 3.93 685 July 20: 0200 9.50 5,520 1200 3.70 590 0100 10.28 6,860 0400 9.08 5,050 1800 3.54 526 0200 10.34 6,980 0600 8.69 4,620 2400 3.40 470 0300 11.55 9,680 0700 8.50 4,410 July 24: 0400 12.68 12,800 1200 7.73 3,630 0600 3.31 434 0500 13.79 16,200 1400 7.47 3,370 1200 3.23 402 0600 15.16 20,500 1600 7.25 3,160 1800 3.14 366 0700 16.78 26,300 1700 7.23 3.140 2400 3.08 343 Total runoff, in inches 5.34 SITE 39.—03044000. Conemaugh River at Tunnelton, Pa. Location.—~ Lat 40°27’16”, long 79°23’28”, Indiana County, Hydrologic Unit 05010007, on the right bank at the downstream side of a highway bridge at Tunnelton, 0.9 mi (1.4 km) downstream from Boatyard Run, 2.0 mi (3.2 km) downstream from Conemaugh River Dam, 3.8 mi (6.1 km) southeast of Saltsburg, and 5.5 mi (8.9 km) upstream from the confluence with Loyalhanna Creek. Gage. — Water-stage recorder. Datum of the gage is 844.64 ft (257.446 m) NGVD of 1929. Prior to October 1, 1952, a nonrecording gage was at the same site and datum. Remarks. —Flow has been regulated since 1971 by Yellow Creek Lake; since 1952, by Cone- maugh River Lake, 2 mi (3 km) upstream, and by reservoirs above the station, the nine most effective of which have a combined capacity of 68,090 acre-ft (840.0 hma). Evaporation from the operation of the Homer City and Conemaugh generating stations, which began during 1969 and 1970, respectively, can amount to as much as 45 ft3/s (1.3 m3/s). Gage Dis- Gage Dis- Gage Dis- Time height charge Time height charge Time height charge (ft) (ftB/s) (ft) (ftS/s) (ft) (fta/s) July 19: July 21: July 24: 1200 3.62 1,510 2200 11.89 23,300 0300 11.34 21,400 1800 3.61 1,500 2300 11.98 23,600 0600 11.29 21,200 2400 3.63 1,530 2400 11.98 23,600 0900 11.23 21,000 July 20: July 22: 1000 10.31 18,100 0300 3.75 1,720 0600 11.97 23,600 1100 10.09 17,400 0600 3.88 1,950 0900 11.94 23,500 1200 10.05 17,300 0900 4.01 2,870 1200 11.91 23,400 1500 10.00 17,100 1200 4.56 3,170 1500 11.87 23,300 1800 9.96 17,000 1500 5.99 6,140 1800 11.84 23,100 2400 9.86 16,700 1800 7.34 9,450 2100 11.81 23,000 July 25: 2100 8.62 12,800 2400 11.77 22,900 0600 9.76 16,400 2400 9.15 14,500 July 23: 1200 9.72 16,200 July 21: 0300 11.73 22,700 1300 8.78 13,300 0300 9.51 15,500 0600 11.69 22,600 1400 8.58 12,700 0600 9.99 17,100 0900 11.64 22,400 1500 7.60 10,100 0900 10.24 17,800 1200 11.59 22,300 1600 . 7.36 9,500 1200 10.35 18,200 1500 11.54 22,100 1800 7.33 9,420 1500 10.77 19,500 1800 11.50 22,000 2000 7.33 9,420 1800 11.27 21,200 2100 11.44 21,800 2200 7.32 9,400 2100 11.62 22,400 2400 11.39 21,600 2400 7.32 9,400 Total runoff, in inches 2.82 SITE 40.-—01540600. West Branch Susquehanna River at Barnesboto, Pa. Location—Lat 40°40’10”, long 78°47’29”, Cambria County, at the 22nd St. bridge in Barnesboro. Gage. —Miscellaneous site. TABLE 4.-Site description and gage-height and discharge data— Continued SITE 41.—01540650. West Branch Susquehanna River at Cherry Tree, Pa. Location. — Lat 40°43’34”, long 78°48’20”, Indiana County, at State Highway bridge 5H580 in Cherry Tree, 200 ft (60 m) downstream from Cush Cushion Creek. Gage. —Miscellaneous site. SITE 42.—01541000. West Branch Susquehanna River at Bower, Pa. Location—Lat 40°53’49", long 78°40’38", Clearfield County, Hydrologic Unit 02050201, on the right bank at the downstream side of the highway bridge at Bower, 4.6 mi (7.4 km) downstream from Chest Creek and Mahaffey. Gage.—Water-stage recorder. Datum of the gage is 1,207.14 ft (367.936 m) NGVD of 1929. Prior to October 17, 1929, a nonrecording gage was at the same site and datum. Gage Dis- Gage Dis- Gage Dis- Time height charge Time height charge Time height charge (ft) (ft3/s) (ft) (ft3/s) (ft) (ft3/s) July 19: July 20 July 21: 0600 5.24 313 0500 15.50 17,000 2100 10.10 4,740 1200 5.14 278 0600 15.18 16,000 2200 10.27 5,000 1300 5.12 271 0700 14.98 15,400 2300 10.23 4,940 1400 5.13 274 0800 14.85 15,100 2400 10.15 4,820 1500 5.12 271 0900 14.82 15,000 July 22: 1800 5.13 274 1200 14.83 15,000 0300 9.88 4,420 1900 5.16 285 1500 14.63 14,400 0600 9.39 3,740 2000 5.37 362 1800 14.52 14,100 0900 8.93 3,150 2100 5.65 474 2100 14.44 13,900 1200 8.64 2,800 2200 6.35 832 2400 14.32 13,600 1800 8.27 2,400 2300 9.60 4,030 July 21: 2400 7.84 1,980 2400 13.00 10,200 0300 14.02 12,700 July 23: July 20: 0600 13.10 10,400 1200 7.24 1,450 0100 16.12 18,900 0900 11.40 6,850 2400 6.84 1,150 0130 16.23 19,200 1200 10.35 5,120 July 24: 0200 16.15 19,000 1500 9.77 4,270 1200 6.55 958 0300 15.98 18,500 1800 9.46 3,830 2400 6.30 802 0400 15.80 17,900 1900 9.55 3,960 2000 9.85 4,380 Total runoff, in inches 3.37 SITE 43—01541200. West Branch Susquehanna River at Curwensville, Pa. Location—Lat 40°57’41”, long 78°31’10”, Clearfield County, Hydrologic Unit 02050201, on the left bank 30 ft (9 m) downstream from the bridge on State Highway 453, 0.85 mi (1.37 km) downstream from Curwensville Lake, 1.1 mi (1.8 km) south of Curwensville, and 1.8 mi (2.9 km) upstream from Anderson Creek. A water-quality sampling site at bridge is 30 ft (9 m) upstream. Gage. —Water-stage recorder. Datum of the gage is 1,124.52 ft (342,754 In) NGVD of 1929. Prior to August 24, 1956, a nonrecording gage and a crest-stage gage were 30 ft (9 m) upstream at same datum. Remarks—Flow is regulated by Curwensville Lake, 0.85 mi (1.37 km) upstream. SITE 44.—01541308. Bradley Run near Ashville, Pa. Location. — Lat 40°30’33”, long 78°35’02", Cambria County, Hydrologic Unit 02050201, on the right bank 200 ft (60 m) downstream from the bridge on State Highway 53 at Syberton, 0.2 mi (0.3 km) upstream from the mouth and 4.5 mi (7.2 km) southwest of Ashville. Gage. —Water-stage recorder. The altitude of the gage is 1,770 ft (539 m), from a topographic map. SITE 45.—01541321. Brubaker Run at Dean, Pa. Location—Lat 40°37’20”, long 78°30’12”, Cambria County, at a culvert on State Highway 53 at Dean, 01 mi (0.2 km) upstream from the mouth. Gage. —Miscellaneous site. SITE 46.—01541365. North Witmer Run at Irvona, Pa. Location. —Lat 40°46’12”, long 78°32’59”, Clearfield County at the mouth at Irvona. Gage. —Miscellaneous site. SITE 47.—01541500. Clearfield Creek at Dimeling, Pa. Location—Lat 40°58’18”, long 78°24’22”, Clearfield County, Hydrologic Unit 02050201, on the right bank at the downstream side of the highway bridge at Dimeling, 600 ft (180 m) downstream from Little Clearfield Creek, and 4 mi (6 km) southeast of Clearfield. Gage.—Water-stage recorder. Datum of the gage is 1,146.08 ft (349.325 m) NGVD of 1929. Prior to October 17, 1928, a nonrecording gage and from October 17, 1928, to October 25, 1967, a water-stage recorder were at a site 200 ft (60 m) upstream, all at the same datum. Remarks—Flow regulated by Glendale Lake, about 25 mi (40 km) upstream. SITE 48.—01542000. Moshannon Creek at Osceola Mills, Pa. Location—Lat 40°50'58", long 78°16’05”, Clearfield County, Hydrologic Unit 02050201, on the left bank 10 ft (3.0 m) upstream from the CONRAIL bridge at Osceola Mills and 0.1 mi (0.2 km) downstream from Trout Run. Gage—Water-stage recorder. Datum of the gage is 1,446.98 ft (441.040 m) NGVD of 1929. SITE 49.—01556000. Frankstown Branch Juniata River at Williamsburg, Pa. L “ —Lat 40°27’47”, long 78° 1200”, Blair County, Hydrologic Unit 02050302, on the left bank 10 ft (3 m) downstream from highway bridge at Williamsburg and 2.5 mi (4.0 km) upstream from Clover Creek. Gage.—Water-stage recorder. Datum of gage is 831.78 ft (253.53 In) NGVD of 1929 (Penn Central Railroad bench mark). Prior to August 14, 1928, a nonrecording gage was at the same site and datum. Remarks—Regulation at low flow by a mill above the station. 64 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 TABLE 4.—Site description and gage-height and discharge data— Continued SITE 50.—01556400. Sandy Run near Bellwood, Pa. Location—Lat 40°33’47”, long 78°20’35”, Blair County, at a bridge on a private road 0.6 mi (1.0 km) above the mouth and 2.5 mi (4.0 km) south of Bellwood. Gage. — Crest-stage. SITE 51.—01556500. Little Juniata River at Tipton, Pa. Location—Lat 40°37’40”, long 78°17’38”, Blair County, at Tipton, 100 ft (30 m) below the bridge on State Highway 220 and 150 ft (46 m) downstream from Tipton Run. Gage.—Water-stage recorder and crest~stage. Datum of the gage is 946.76 ft (288.57 In) NGVD of 1929. SITE 52.—01557100. Schell Run at Tyrone,Pa. Location, —Lat 40°40’00”, long 78°15’00”, Blair County, 0.2 mi (0.3 km) above U.S. Highway 220 between 5th St. and Shippen St, in Tyrone. Gage. —Water-stage recorder. Datum of the gage is 91911 ft (280.14 m) NGVD of 1929. SITE 53.—01557500. Bald Eagle Creek at Tyrone, Pa. Location. — Lat 40°41’01”, long 78° 1402", Blair County, Hydrologic Unit 02050302, on the left bank 0.2 mi (0.3 km) upstream from the plant of the West Virginia Pulp and Paper Co. at Tyrone, 0.2 mi (0.3 km) upstream from Laurel Run, and 1.3 mi (2.1 km) upstream from the mouth. Gage. —Water-stage recorder. Datum of the gage is 921.80 ft (280.965 m) NGVD of 1929. From October 1, 1944 to November 15, 1950, a water-stage recorder and, from November 16, 1950 to November 30, 1952, a nonrecording gage were at a site 0.5 mi (0.8 km) downstream, at a datum 17.99 ft (5.483 in) lower. SITE 54.—01558000. Little Juniata River at Spruce Creek, Pa. Location. — Lat 40°36’45”, long 78°08’27", Huntingdon County, Hydrologic Unit 02050302, on the right bank 150 ft (46 m) downstream from the CONRAIL bridge, 05 mi (0.8 km) north» west of village of Spruce Creek, and 0.5 mi (0.8 km) upstream from Spruce Creek. A water» quality sampling site is 0.4 mi (0.6 km) downstream. Gage. —Water-stage recorder. Datum of the gage is 75115 ft (228.951 m) NGVD of 1929. SITE 55.—01559700. Buffalo Run tributary near Manns Choice, Pa. Location. —Lat 39°58’40”, long 78°37’08”, Bedford County, Hydrologic Unit 02050303, at the left downstream end of the bridge on State Highway 96, 2,000 ft (610 m) upstream from the mouth, 23 mi (3.7 km) south of Manns Choice, and 11 mi (18 km) southwest of Bedford. Gage. —Water-stage recorder and crest-stage gage. The altitude of the gage is 1,230 ft (375 m), from a topographic map. Gage Dis- Gage Dis- Gage Dis- Time height charge Time height charge Time height charge (ft) (ft3/s) (ft) (ft3/s) (ft) (fta/s) July 19: July 20: July 21: 1200 0.39 0.34 0800 2.02 156 1200 0.69 14 1800 .38 .28 0900 1.66 102 1700 .64 11 2400 .48 .77 1000 1.37 67 2000 .69 14 July 20: 1100 1.23 53 2400 .65 12 0300 2.85 326 1200 1.15 45 July 22: 0400 2.73 298 1500 .96 30 1200 .59 8.6 0500 3.47 495 1800 .85 23 2400 .55 6.9 0600 3.68 560 2100 .80 20 July 23: 0620 5.12 1,120 2400 .77 18 1200 .52 5.7 0700 2.74 300 2400 .49 4.6 Total runoff, in inches 1.09 SITE 56.—01560000. Dunning Creek at Belden, Pa. Location. — Lat 40°04’18”, long 78°29’34", Bedford County, Hydrologic Unit 02050303, on the left bank 10 ft (3 m) upstream from a highway bridge, 0.8 mi (1.3 km) southeast of Belden, 3.8 mi (6.1 km) north of Bedford, and 4.3 mi (6.9 km) above the mouth. Gage. —Water-stage recorder. Datum of the gage is 1,051.16 ft (320.394 m) NGVD of 1929. Gage Dis- Gage Dis- Gage Dis- Time height charge Time height charge Time height charge (ft) (its/s) (ft) (ft3/s) (ft) (ft3/s) July 19: July 20: July 21: 1200 1.33 21 1100 13.84 17,500 1800 4.07 944 1800 1.35 23 1115 14.15 19,400 2100 4.04 934 2100 1.35 23 1130 13.91 18,000 2400 4.54 1,110 2400 1.47 39 1200 13.83 17,500 July 22: July 20: 1300 13.75 17,000 0100 4.63 1,110 0100 1.66 71 1700 12.35 10,900 0300 4.45 1,040 0200 2.02 157 1800 11.99 9,770 0600 3.90 840 0300 3.59 756 2100 10.83 6,470 0900 3.61 724 0400 6.47 1,790 2400 9.79 4,520 1200 3.44 648 0500 8.59 3,190 July 21: 2400 2.95 440 0600 9.33 3,940 0300 8.43 3,050 July 23: 0700 10.30 5,350 0600 6.48 1,790 1200 2.75 328 0800 11.34 7,820 0900 5.27 1,330 2400 2.56 261 0900 12.57 11,700 1200 4.71 1,160 July 24: 1000 13.53 15,800 1500 4.32 1,030 1200 2.46 228 2400 2.38 204 SITE 57.—01600700. Little Wills Creek at Bard, Pa. Location—Lat 39°55’35”, long 78°39’40”, Bedford County, at the bridge on State Highway 96 at Bard. Gage. —Crest-stage. Datum of the gage is 1,264.2 ft (385.3 m) NGVD of 1929. TABLE 5. —Floodmarlc data [Elevations of selected floodmarks are provided in this table for defining flood profiles on reaches of 27 streams in the Mahoning Creek and Conemaugh River basins. Each elevation is referenced by a stream mile, which is the distance upstream from its mouth. The stream bank on which the floodmarks were located is given for many sites and is designated as right (R) or left (L) bank (determined as if one were facing downstream). Unless otherwise noted, the data in this table were furnished by the U.S. Army Corps of Engineers (1977)] Elevation in Stream feet above Stream and location mile NGVD Mahoning Creek North Point, at highway bridge ____________ 36.93 1,156.94 Hamilton (R) ___________________ 40.95 1,174.2 At highway bridge _____________________ 41.03 1,174.65 Valier, at highway bridge _________________ 43.63 1,184.92 At highway bridge between Valier and Fordham ___________________________ 45.22 1,194.32 Sportsburg(R) __________________________ 50.09 1,216.5 Punxsutawney, at U.S. Geological Surve gaging station (R) ______________ 51.28 1,222.44 Railroa Bridge _______________________ 52.70 1,229.38 #114 Water St. (R)- 52.99 1,231.0 Punxsutawney (R) _______________________ 53.07 1,230.40 At U.S. Highway 119 bridge _____________ 54.06 1,231.17 At Mahoning St. bridge _________________ 54.77 1,232.56 Cloe, at highway bridge __________________ 57.48 1,252.0 Bells Mills, at highway bridge __ 58.94 1,263.19 At highway bridge ________ 59.88 1,270.88 At railroad bridge _______________________ 60.63 1,275.70 Big Run, at Mill St. bridge ________________ 62.57 1,284.18 McCardy Rd. bridge ____________________ 63.52 1,290.07 Stump Creek At State Highway 410 bridge __ ___ 1.48 1,307.9 At road bridge near Cramer _______________ 2.71 1,312.3 Cramer, downstream from State High- way 952 bridge (L) ___________________ 4.00 1,322.14 Upstream from State Highway 952 bridge (L) __________________________ 4.03 1,323.41 Sykesville, at road bridge _________________ 6.09 1,335.8 Park St. bridge ________________________ 7.05 1,341.97 Bridge at confluence of Sugarcamp Run 7.30 1,345.1 Stanley, at road bridge ___________________ 9.16 1,365.7 Conemaugh River Blairsville, at old U.S. Highway 22 bridge ____ 20.10 958.8 State Highway 217 bridge _______________ 21.45 958.6 Strangford, at mouth of Toms Run (L) _______ 24.40 961.81 Robinson, downstream side of State Highway 259 bridge (R) _______________ 30.13 1,024.8 Upstream side of State Highway 259 bridge (R) __________________________ 30.13 1,028.1 Bolivar RD #1 (L) _______________________ 32.34 1,042.74 At downstream side of railroad bridge (L) __ 32.35 1,045.5 At upstream side of railroad bridge (L) _____ 32.35 1048.4 Along legislative Route 32008 at Craw- ford Road __________________________ 34.43 1,060.6 New Florence, at downstream side of railroad bridge (L) ____________________ 36.09 1,067.0 At upstream side of railroad bridge (L) _____ 36.09 1,068.7 Huff, at small tributary (R) ________________ 37.59 1,073.23 New Florence, at highway bridge ___________ 37.68 1,072.2 At #209 9th St. (L) _____________________ 38.01 1,076.5 At Seward Generating Plant, pump house (R ___________________________ 39.23 1,082.83 Robindale (R) ___________________________ 41.00 1,093.0 Seward, at Penelec generating plant (R) _____ 41.82 1,097.96 TABLES 65 TABLE 5.—Floodma'rk data—Continued TABLE 5. —Floodmark data—Continued Elevation in Elevation in Stream feet above Stream feet above Stream and location mile Stream and location mile NGVD Conemaugh River—Continued Paint Creek—Continued Seward, at U.S. Geological Survey gaging Paint-Continued station at upstream side of State Gas company plant on 3rd St- (R) ————————— 2.87 1,672-0 Highway 56 bridge (L) ________________ 42.85 1,103.1 At brick house just upstream Windber, at #702 Lin001n St. (R) ___________ 3.14 1,676.0 from State Highway 56 bridge (L) _______ 42.89 1,104.20 #100 Tenth St. (R) _____________________ 3.35 1,679.6 #301 12th St. (R) ______________________ 3.50 1,684.1 Johnstown, at downstream side of railroad 12th St. bridge ________________________ 3.51 1,686.3 bridge at north corporate boundary ______ 49.32 1,154.6 Corner of 17th St. and Graham Ave. Upstream side of railroad bridge __________ 49.32 1,156.9 (L) 3.87 1,689.0 Bethlehem Steel Co.’s wire mill (R) ________ 50.35 1,158.74 #705 Graham Ave. (L) __________________ 3.92 1,692.0 State Highway 403 bridge _______________ 50.71 1,162.1 Somerset Ave. bridge __________________ 3.97 1,695.0 Church at corner of 8th Ave and #1010 17th St. (R) _____________________ 4.23 1,702.3 Chestnut St. (L) ____________________ 51.40 1,163.87 Se R Downstream side of Fourth St. “e “‘1 ’bridge 51.69 1,165.2 Windber, at corner of 17th St. and Upstream side of Fourth St. Jefferson Ave. (R) ____________________ 0.13 1,688.2 bridge 51.69 1,166.3 Windber (R) .33 1,693.4 Church at corner of Fourth Ave. and Downstream side of 22nd St. bridge Chestnut St. (L) _____________________ 51.70 1,164.23 (R) .50 1,699.4 Footbridge at Roosevelt Blvd. and 24th St. bridge ________________________ .67 1,707.8 McConaughy St ______________________ 52.07 1,167.7 #2604 Jackson Ave. (R) _________________ .79 1,717.1 Along State Highway 56 at railroad Corner of 28th St. and Jackson Ave. overpass (L) ________________________ 52.33 1,168.2 (R) .97 1,725.7 St C k Comer of Village St. and Jackson °“Y "e Ave. (R) 1.16 1,741.2 Johnstown, 50 ft downstream from Wash- #3104 Graham Ave ____________________ 1.26 1,746.1 ington St. bridge (R) __________________ 0.03 1,170.5 Main St. bridge ________________________ 1.66 1,780.3 Bridge to incline plane (R) _______________ .38 1,171.4 State Highway 56 bridge ________________ 2.12 1,821.6 State Highway 56 bridge ________________ .57 1,172.1 Central High School (L) _________________ .74 1,173.2 At Spruce St. bridge _____________________ 2.24 1,833.0 City Hall (R) __________________________ .86 1,172.3 At downstream side of Graham Ave. #86 Haynes St. (L) _____________________ 1.03 1,173.9 bridge 2.41 1,851.0 Corner of Homer St. and Poplar St. At upstream side of Graham Ave. (R) 1.51 1,175.4 bridge 2.42 1,852.3 Central Ave. bridge ____________________ 2.98 1,181.0 Johnstown (R) __________________________ 3.42 1,183.0 , weav‘" R“ Windber (R) 0.05 1,698.5 Ferndale, downstream side of State At State Highway 56 bridge _____________ .06 1,700.9 Highway 403 bridge (L) _______________ 3.81 1,188.0 Windber (R) .10 1,701.2 50 feet upstream from State Highway Windber (L) . .43 1,713.4 403 bridge __________________________ 3.83 1,191.0 At road budge ________________________ .68 1,728.4 Railroad bridge _______________________ 4.19 1,192.8 At wooden, road bridge ___________________ .88 1,743.3 Railroad bridge _______________________ 5.13 1,203.5 - - #373 Michigan Ave. (R) _________________ 5.15 1,204.8 “a“ Pm“ cm" Fire Co. Building on Liberty Ave. Scalp Level (R) ——————————————7—_— ———————— 0-03 1,660.4 (R) 5_40 1,206.3 At Methodist Church school bmlding on Maln st. (R) ______________________ .18 1,667.2 At State Highway 403 bridge ______________ 5.91 1,212.8 Rallroad budge _______________________ .27 1,674.1 Riverside RD #3 (R) ______________________ 6.45 1,216.6 Scalp Level (L) ——————, ____________________ .35 1,677.7 Krings (L) 7.44 1,238.6 At coal company bOiler house (R) _________ .67 1,704.5 Krings Road bridge ____________________ 7,49 1,242.3 Mine #40; at #1204 3rd St. (R) ____________ .87 1,723.6 Ingleside, at sewage disposal plant (R) _______ 8.97 1,288.4 . At road bridge __________________________ 10.70 1,329.82 At road bridge ————,— _____________________ 1.87 1,813.7 At transformer station (L) ________________ 2.51 1,885.2 Shade Creek At downgtrdeam side of State Highway . . 160 ri ge __________________________ 2.88 1,930.6 3335601366?ifid_g_e_‘f’_:::::::::: 0:32 £2333 Atupttream side ofState Highway 160 Camp Hamilton, at Windber Area Elt bringe 2'88 1’933-0 School District Building _______________ 3.02 1,646.8 m0“ (R) 3-88 20500 Old mill building _______________________ 3.16 1,653.8 Elton ( ) . . 4-01 2,061.3 At road bridge __________________________ 5.20 1,777.0 on, at Vlllal‘d St- bridge ________________ 4.33 2,062.5 Paint Creek Sams Run . . Johnstown at railroad brid e ______________ 0.03 1 184 1 At railroad bridge _______________________ 0.06 1,325.3 ’ g ’ ' Scalp Level, at confluence with Little €77 Dupont SA“ (R) --------------------- '10 1,1854 Paint Creek (R) ______________________ 2.52 1,660.4 Omer 0f 01110 St. and CBDtI‘al Ave. Paint, at Main St. bridge over State #5253 C '16 1'185-7 Highway 56 (L) ______________________ 2.63 1,665.3 013m? Ave. (R) ————————————————— -31 1»193'6 Fire Dept building at #807 Main St. Corner of Ohio St. and Grove Ave. (R) _____ .33 1,206.2 (R) 2.64 1,670.7 #544 Grove Ave _______________________ .36 1,209.2 66 JOHNSTOWN-WE‘STERN PENNSYLVANIA STORM AND FLOODS OF JULY 19-20, 1977 TABLE 5. —Floodmark data - Continued Elevation in Stream feet above Stream and location mile NGVD Sams Run—Continued J ohnstown — Continued Corner of Ohio St. and Grove Ave. (R) _____ .33 1,206.2 #544 Grove Ave _______________________ .36 1,209.2 Corner of Ohio St. and Highland Ave. (R) .49 1,223.3 Corner of Ohio St. and Forest Ave. .70 1,255.0 Forest Ave. bridge _____________________ .73 1,260.1 #239 Ohio St. (R) ______________________ .78 1,271.4 Woodland Ave. bridge __________________ .7 8 1,274.3 Lorain, at #409 Valley St _________________ 1.00 1,308.9 #437 Valley St _________________________ 1.10 13205 Solomon Run Johnstown, at #837 Horner St. (R) __________ 0.03 1,192.7 #821 Oak St. (R) _______________________ .18 1,191.2 #722 Ash St. (R) _______________________ .27 1,204.6 #714 Von Lunen St. (R) _________________ .37 1,217.0 #255 David St _________________________ .52 1,230.6 Corner of Bedford St. and Cummins St. .55 1,238.6 Walnut Grove, at #366 Arthur St. (R) _______ .76 1,248.9 #1005 Jacoby St. (R) ___________________ .91 1,264.8 Maple Park school building (R) ___________ .97 1,277.9 Bridge between State Highway 56 and Bedford St _______________________ 1.01 1,289.0 #141 Purse St _________________________ 1.05 1,292.0 #1088 Solomon St. (L) __________________ 1.08 1,300.7 #1139 Solomon St. (L) __________________ 1.19 1,316.2 Apartment building #6 (L) _______________ 1.39 1,342.2 Apartment building #9L (L) _____________ 1.53 1,360.4 #350 Solomon St. (L) ___________________ 1.72 1,386.9 #1418 Solomon St. (L) __________________ 1.85 1,415.8 #1446 Solomon St. (L) __________________ 1.91 1,430.1 Little Conemaugh River Johnstown (R) __________________________ 0.08 1,171.4 Johnstown, at Johns St. bridge _____________ .14 1,172.1 Corner of Locust St. and Walnut St. (L) .30 1,172.5 Walnut St. bridge ______________________ .31 1,173.9 Downstream side of railroad bridge _______ .38 1,173.6 Upstream side of railroad bridge __________ .38 1,178.9 Corner of Locust St. and Franklin St. (L) .51 1,173.4 Johnstown (R) __________________________ .66 1,179.3 Johnstown (L) __________________________ .66 1,180.9 Downstream side of State Highway 271 bridge __________________________ 1.09 1,187.8 Upstream side of State Highway 271 bridge 1.09 1,191.0 School, 300 ft downstream from rail- road bridge _________________________ 1.40 1,196.8 Downstream side of railroad bridge _______ 1.44 1,199.9 50 ft upstream from State Highway 271 bridge __________________________ 2.01 1,214.0 East Conemaugh, at #500 Railroad St. (R) 2.40 1,220.2 US. Geological Survey gaging station, 100 ft downstream from State Highway 271 bridge (R) ________________ 2.56 1,226.8 Along Railroad St. (R) __________________ 2.71 1,228.9 Along railroad tracks (R) _________________ 4.03 1,266.9 At downstream side of railroad bridge _______ 4.87 1,289.4 At upstream side of railroad bridge _________ 4.87 1,293.2 Along railroad tracks, 470 ft upstream from railroad bridge to slag dump (L) _________ 5.13 1,316.8 TABLE 5. —Floodmark data— Continued Elevation in Stream feet above Stream and location mile NGVD Little Conemaugh River— Continued At Brookdale Mine #77 (R) ________________ 6.71 1,361.4 Mineral Point, downstream from highway bridge (R) __________________________ 7.52 1,380.4 First house upstream from highway bridge (L) 7.57 1,379.3 Mineral Point (R) ________________________ 7.90 1,385.2 At water supply dam _____________________ 11.22 1,470.1 South Fork, at downstream side of railroad bridge 11.91 1,478.6 Upstream side of railroad bridge __________ 11.91 1,479.2 Grant St. bridge _______________________ 12.14 1,480.2 Ehrenfeld, at end of “A” St. (R) ____________ 12.84 1,497.6 Summerhill (R) _________________________ 13.88 1,526.4 Summerhill (R) _________________________ 14.28 1,531.6 Summerhill, at service station upstream from State Hi hway 53 bridge (R) ___________ 14.40 1,536.8 At railroa bridge _____________________ 14.48 1,538.7 At downstream side of railroad bridge _______ 14.85 1,540.2 At upstream side of railroad bridge _________ 14.85 1,541.6 At downstream side of State Highway 53 bridge 14.96 1,541.7 At upstream side of State Highway 53 bridge 14.96 1,542.7 At State Highway 53 bridge _______________ 15.81 1,546.9 At downstream side of State Highway bridge _ 16.47 1,553.1 At upstream side of State Highway 160 bridge 16.47 1,554.7 Wilmore, at State Highway 160 bridge ______ 17.47 1,556.7 Downstream side of railroad bridge _______ 17.65 1,556.2 Upstream side of railroad bridge __________ 17 .65 1,560.2 Along Crooked St. (R) ____________________ 18.09 1,564.2 Along State Highway 53 (R) _______________ 18.63 1,570.7 Along State Highway 53, upstream from Trout Run (R) ____________________________ 19.40 1,596.0 Portage, at State Highway 53 bridge ________ 20.34 1,602.1 At downstream side of State Highway 160 bridge 20.81 1,610.8 At upstream side of State Highway 160 bridge 20.81 1,612.5 At road bridge upstream from Noels Creek ___ 22.28 1,647.3 Oil City, at Bens Creek confluence (L) _______ 23.53 1,734.1 At downstream side of railroad bridge _______ 23.72 1,744.5 At upstream side of railroad bridge _________ 23.72 1,747.1 Cassandra, at downstream side of highway bridge 24.10 1,774.4 Upstream side of highway bridge _________ 24.10 1,778.6 At downstream side of railroad bridge _______ 24.36 1,801.4 At upstream side of railroad bridge _________ 24.36 1,803.6 Spring Run Portage, at road bridge, 950 ft upstream from mouth 0.19 1,607.8 State Highway 164 bridge _______________ .31 1,616.7 Road bridge ____________________________ .50 1,638.9 Trout Run Portage, at athletic field (L) _______________ 0.25 1,620.9 500 ft downstream from Caldwell Ave bridge (L) .49 1,643.4 Downstream side of Caldwell Ave. bridge __ .58 1,655.2 Upstream side of Caldwell Ave bridge _____ .58 1,658.0 Gillespie Ave. bridge ___________________ .67 1,668.6 Jefferson Ave. bridge __________________ .76 1,679.8 Conemaugh Ave. bridge ________________ .83 1,688.1 Sonman Ave. bridge ___________________ .91 1,700.5 State Highway 164 bridge _______________ .97 1,709.5 TABLES 67 TABLE 5. —Floodmark data—Continued TABLE 5.—Floodmark data—Continued Elevation in Elevation in Stream feet above Stream feet above Stream and location mile NGVD Stream and location mile NGVD North Branch Little Conemaugh River Sandy Run—Continued Wilmore 50 ft downstream from railroad 20 ft downstream from unnamed left bank trib- bridge 0,11 1,555.8 utary (L) ——————————————————————————— 1-92 1,741-8 50 ft upstream from railroad bridge _______ .13 1,556.7 600 ft downstream from Sandy Run Dam (R) _ 2.11 1,766.0 State Highway 53 bridge _________________ .30 1,556.8 350 ft downstream from Sandy Run Dam 50 ft downstream from State Highway 160 (R! .L) 2'16 11776-8 bridge '62 1'558'6 ESE‘Eirfi‘s’iierif'i‘fififi 3.233113 de"'(12)'"" 3‘33 i's‘ib‘i - am ____ . , . 100 giiggztream from State Highway 160 .65 1’ 559.6 140 ft upstream from centerline of dam (L) ___ 2.25 1,810.5 South Fork Little Conemaugh River St' Clair Run South Fork, at Post Office (R) _____________ .08 1,486.9 JOhHSFOWD’ at confluence With Conemaugh Maple St. bridge _______________________ .09 1,487.2 Rlver . . 0-00 1,162-1 South Fork (R) __________________________ .40 1,4957 Intersectlon of Beatty Ave. and Enterprise Soukesburg, at downstream side of State St‘ (L) . . ‘22 1'164'8 Highway 53 bridge ___________________ 1.68 1,547.5 $33938"; dengf Chandler St- bridge (R) —-— 32 1173'; - . - ' 1 _ . r1 ge ______________________ . , . Upstream Slde of State Highway 53 budge _ 1 68 ,548 8 Corner of “1,, SF and Bheam Ave. (R) ______ '45 1,188.9 _ ~ f - Downstream Slde of Fairfield Ave. bridge __ .60 1,207.4 St fill-(53;: 1’ 80 ft downstream rom railroad 3.20 1,580.4 Upstream s1de of Fairfield Ave. bridge _____ .61 1,211.5 80 ft upstream from railroad bridge _______ 3.23 1,582.3 Road bridge at corporate boundary ——————— 1-07 11261-5 Fire Dept. building (L) __________________ 3.39 1,584.3 , - At unnamed left bank tributary ____________ 1.38 1,302.9 Creslo, 80 ft upstream from road bridge (L) __ 3.80 1,598.6 At road bridge __________________________ 2.04 1,382.1 - _ ~ . h 1 At downstream side of road bridge _________ 2.58 1,486.1 SldTfi?’ at Adams Summerhlll ngh SC 00 420 1,618.9 At upstream side of road bridge ____________ 2.59 1,489.8 100 ft upstream from railroad bridge ________ 4.57 1,642.3 Laurel Run 4010f? downstream from State nghway 869 4 1 1 643 8 [Data collected and compiled by the us. Geological Survey] 30 Rdlfifstream from State Highway 869 '6 ’ ' At confluence with Conemaugh River at John- bridge 4.62 1 647.3 stown’s north corporate boundary (L) _'___ 0.00 1,166.6 Along road parallel to railroad tracks (R) _____ 4.73 1,651.9 90 f:f1{1)pstream from State ng‘hway 403 bridge 0 8 1 164 1 Allendale, 150 ft downstream from railroad 90 ft upstream from State Highway 403 bridge bridge 5.99 1,760.1 60 ftla t f d . f -32 1’181-6 50 ft upstream from railroad bridge _______ 6.03 1,763.6 C owns Areal?) 33”“ Igwnstream Slde ° 47 1 199 0 Along State Highway 869 (L) ______________ 6.60 1,814.5 60 ft 009:1” V‘} “ ge (t ) ————.—d——-f— ——————— - , - Beaverdale, 50 ft downstream from State Cups rezm rkomdupslream SI e 0 Highway 160 bridge __________________ 7.74 1,922.2 001’” ve- “ ge( ).— ——————————————— ‘49 1,2009 50 ft upstream from State Highway 160 290 ft downstream from W1ldcat Run (R) ____ .68 1,221.5 bridge 7‘74 1 922.2 140 ft upstream from Wildcat Run (L) _______ .76 1,229.4 Lloydell, 50 ft downstream from State High— 3131§n§ left bank ---—--------.- ----------- 1'01 1’252'5 way 869 bridge ______________________ 8.53 2029.3 1 Al; 0%??reafil from centerllne 0f Cooper 50 ft upstream from State Highway 869 At ve. r1 ge ( ) -------------.- -------- 1'28 1’278'6 bridge 8.55 2 0337 upstream s1de of Cooper Ave. bndge (R) __ 1.31 1,280.8 ’ Along left bank ________________________ 1.49 1,315.7 Sandy Run fiong {11$th bink ______________________ 1.57 1.3322 1 d d . .s. G 1 . 1s ong e t an ________________________ 1.63 1,334.4 300 ft upstrZ:1:6:ecddfl:;pcfl:dv:1ytllleslduth eo ow way] A: Kfigegmtsdhe “1033‘?“ Ave' bfidge (L) __ 23; 1362': _ . e 0 1s urc __________________ . , . Fork Little Conemaugh River near 220 ft upstream from Red Run (L) __________ 2.33 1,392.8 Soukesburg (R) ___—___? —————————————— .06 11551-7 30 ft downstream from centerline of Laurel 150 ft upstream from road bridge (L) ________ .12 1,555.3 Run Dam (R) ________________________ 2.51 1,400.8 At dowgsttrfilg 51?? {if ”“2133 g“ etrllitfi)ce 20 1 570 5 Centerline of Laurel Run Dam _____________ 2.52 ______ ma 0 ‘ ' 1g WEW ou ----- ' ’ ' 80 ft upstream from centerline of dam (R) ____ 2.53 1,437 .5 800 ft upstream from L1berty Park pool (L) "- ’52 1'594’7 120 ft upstream from centerline of dam (R) _-_ 2.54 1,437.8 260 ft dfwnstrflamrfrim US Highway 219 77 1 623 6 Blacklick Creek roa wa 0 ve __________________ . , . . . . 760 ft dowrlbtream fr(on)1 US Highway 219 At road budget) Blalrsvflle ------------7-- 0'72 958.8 bridge (R) __________________________ _90 1,630.0 At TOWUShlp Llne brldge near Campbells MlllS 6.37 958.9 230 ft downstream from US. Highway 219 At road brldge near Grafton --------------- 9-85 969.8 bridge (R) __________________________ 1.00 1,643.1 At U.S_- nghway 119 brldge _______________ 10.78 976.0 70 ft upstream from US. Highway 219 bridge Josephlne (R) --------------------------- 1129 994-8 (L) 1.10 1,662.2 H . . . eshbon, at State Highway 259 brldge ______ 17 .93 1,254.3 600 $322633. from U'S' nghway 219 1 20 1 668 5 Dias, at State Highway 56 bridge ___________ 21.33 1,309.2 ' ’ ' gilltowlsifilat State. Highway 403 bridge (L) ___ 25.55 1,350.7 At embankment of old dam (L) _____________ 1.40 1 689.0 ong l town-Vintondale Road (R) -------- 27-97 14357-5 ,, - ’ Alon Dllltown-Vintondale Road (L) ________ 29.56 1 364.9 _ . 2 . g . . , 400 ft downstream from 18 culvert drain (R) 1 76 1,7 6 8 At new highway budge near Wehrum _______ 3050 1,369.5 68 JOHNSTOWN-WESTERN PENNSYLVANIA STORM AND FLOODS OF JULY 19—20, 1977 TABLE 5. —Floodma'rk data — Continued TABLE 5. —Floodmark data — Continued St Eflevtatigm in Elevation in 1' Stream and location . fl . mile!“ elquavgve Stream and location 833:," feetGa‘llioDve North Branch Blacklick Creek Two Lick Crcck—Continued At highway bridge near Vintondale _________ 0.05 1,392.5 Corner of 4th St. and Sherman St. (L) _______ 22.86 1,220.1 Red Mill, at highway bridge _______________ 2.92 1,498.9 State Highway 286 bridge _______________ 23.15 1,225.8 At U.S. Highway 422 bridge near mouth of Elk Diamondville, along Water St., at 2nd dwell- Creek 4.34 1,568.1 ing downstream from Diamondville bridge Adams Crossing bridge ___________________ 5.61 1,613.2 (R) 26.65 1,282.0 South Branch Blacklick Creek North Branch Two Lick Creek Vintondale, at #1002 Main St. (R) ___________ 0.06 1,395.8 Wandin Junction (R) _____________________ 0.13 1,303.5 #119 Main St. (R) ______________________ .30 1,396.2 Starford, at #408 City Ave ________________ 2.00 1,340.6 Church upstream from Main St. bridge (L) __ .47 1,403.1 Road bridge 2.18 1,347.5 #637 Main St _________________________ .58 1,404.3 Lovejoy 2.54 1,369.5 Commodore, at #19 Smith St ______________ 3.32 1,399.2 Twin Rocks, at road bridge ________________ 4.67 1,644.7 Seamentown (R) ________________________ 4.05 1,424.4 At highway bridge near Twin Rocks ________ 5.13 1,659.4 Seamentown (R) ________________________ 4.20 1,425.6 Nanty G10, at corner of Rodgers St. and Lloyd Seamentown, at road bridge _______________ 4.22 1,428.6 St 7.15 1,709.0 State Highway 271 bridge _______________ 7.27 1,713.7 Buck Run #18 McCoy St. (R) _____________________ 7.62 1,714.5 Buck Run, at double 5-ft diameter pipe culvert 1.26 1,324.5 At road bridge near Beula _________________ 12.33 1,842.2 At bridge on private road _________________ 1.35 1,330.7 T L' k k At State Highway 286 bridge ______________ 1.89 1,373.9 Coral at highway bridge wo in one 2 26 985 0 At downstream side of road culvert _________ 2.28 1,404.0 Graceton, at highway bridge _______________ 4.00 9943 At upstream Side of road culvert ___________ 2.28 1,407.1 U.S. Geological Survey gaging station (R) __ $.79 1,000.3 Dixon Run Homer City .07 1,008.3 At FMC plant downstream from State High- Clymer, at #13 Lee St (L) ----------------- 0'37 1,3302 way 56 bridge (L) ____________________ 6.40 1,012.1 Wfienelgc 561939th (R) —————————————————— 4515 122% #50 Indiana St. (L) _____________________ 6.85 1,015.4 A303, 3 “ ge1____d_ ------------------- 1-55 112447 Jacksonville St. bridge __________________ 6.95 1,017.9 R 1” g9 0“ ““3 m. ---—------.- -------- - . - embrant, at State Highway 403 bridge _____ 2.10 1,250.0 Along old U.S. Highway 119 (L) ____________ 7.96 1,028.7 . . . . At old U.S. Highway 119 bridge ____________ 8.47 1,033.4 Dfifmugg 2190;1“119 figoieblfigdgafig -- 3:; 32:2 Along U.S. Highway 119 at bridge over Stoney R orégb 'd e 1g way a r1 ge '- 3.82 1’277'9 Run (R) 9‘51 1,0469 Id .32.. £53: 5515;551:5555; ““““ 4‘61 {3081 Upper Two Lick, at first dwelling downstream A ta 3 d b . d p p ———————— 5'01 1’321'2 from State Highway 954 bridge (L) ______ 11.81 1,080.2 At W90 in’droan. 1" g9 ------------------- 5-74 1370- 4 First dwelling upstream from State Highway priva e we ing “““““““““““““ ' ’ ' r 91514363321 """ 5 ‘ia~‘"';a“‘zni $3 19332 “11°“ ka WO 1C a ion, a pump ul mg a am i ’ - Homer City, at railroad bridge _____________ 0.30 1,015.9 White Pine Park, at old U.S. Highway 422 (R) 15.90 1,188.8 #216 N- Mam St- (R) ———————————————————— -39 1.020-7 At Allen Road bridge ____________________ 18.16 1,189.4 #36 Maple Are ——. —————————————————————— -43 1,021-4 At road bridge 0.5 miles upstream from Penn Private dwelllng 1115t downstream from Run 2042 1,195.1 Mazza St. bridge (R) __________________ .72 1,027.2 Sample Run 21.69 1,208.2 a; 1: Wat? Sdt- (R) ———————————————————— g; 1,333 At St I: H' h 286 b 'd ______________ 22.38 1,215.8 a er-wor 5 am ————————————————————— - v - a e ‘g way I” ge Water-works building (L) _______________ .92 1,033.6 Clymer, at first dwelling upstream from State U.S. Highway 119 bridge ——————————————— -93 1’034-1 H' h 286 b 'd R _______________ 22.40 1,218.9 , . , 853,113in 45:13 Efiégg _______________ 22,69 1,219.4 Lucerne Mines, at railroad bridge __________ 1.59 1,039-5 At State Highway 954 bridge ______________ 3.44 1,090.1 Heilwood, at State Highway 403 bridge ______ 20.25 1,501.3