X4- C 2) h3 A2> I -4- T STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES GEOLOGY OF THE QUIEN SABE QUADRANGLE CALIFORNIA BULLETIN 147 1949 muTMTiiiii i i m iiMH B™*""**' iiiiifiiiimiiini DIVISION OF MINES FERRY BUILDING, SAN FRANCICCO i i STATE OF CALIFORNIA EARL WARREN, Governor DEPARTMENT OF NATURAL RESOURCES WARREN T. HANNUM, Director DIVISION OF MINES FERRY BUILDING, SAN FRANCISCO OLAF P. JENKINS, Chief SAN FRANCISCO BULLETIN 147 OCTOBER 1949 I GEOLOGY OF THE QUIEN SABE QUADRANGLE CALIFORNIA By CARLTON JAMES LEITH QUICKSILVER AND ANTIMONY DEPOSITS OF THE STAYTON DISTRICT, CALIFORNIA BY EDGAR H. BAILEY AND W. BRADLEY MYERS U. S. DEPARTMENT OF THE INTERIOR. GEOLOGICAL SURVEY UrtVERSTTY OF CALIFORI«A LIBRARV ooijuex:e Of agkiculturf DAVIS LETTER OF TRANSMITTAL To His Excellency The IIo7iordble Earl Warren Governor of the State of California I have the honor to submit herewith Bulletin 147, Geology of the Quien Sahe quadrangle, prepared under the direction of Olaf P. Jenkins, Chief, Division of Mines, Department of Natural Resources. It is one of a series of such bulletins on specific areas in California which the Division of Mines is engaged in publishing. Accompanying this report are detailed geologic and economic mineral maps of the Quien Sabe quadrangle, which covers portions of the counties of San Benito, Merced, and Santa Clara. The author of Geology of the Quien Sahe quadrangle, Dr. Carlton James Leith, prepared this report in partial fulfillment of the require- ment for the degree of Doctor of Philosophy at the University of Cali- fornia. His work was done under the supervision of the Department of Geological Sciences and also in cooperation with the Division of Mines. The results of the work are basic and fundamental to the understanding of the state 's mineral deposits and related geological features. Included in this same bulletin is a detailed economic report prepared by the Geological Survey, Department of the Interior, Quicksilver and antimony deposits of the Stayton district, California, by Edgar H. Bailey and W. Bradley Myers. The Stayton district is located within the Quien Sabe quadrangle and is the principal commercial mineral-bearing area in it. Respectfully submitted, Warren T. Hannum, Director Department of Natural Resources May 24, 1949 67^21 CONTENTS GEOLOGY OF THE QUIEX SABE QUADRANGLE, CALIFORNIA, BY CARLTON JAMES LEITH 7 QUICKSILVER AND ANTIMONY DEPOSITS OF THE STAYTON DIS- TRICT. CALIFORNIA, BY EDGAR H. BAILEY AND W. BRADLEY MYERS 37 PLATES Plate 1. Geologic map of Qiiien Sabe quadrangle In pocket 2. Economic map of Quien Sabe quadrangle In pocket 3. Geologic structure sections across Quien Sabe quadrangle In pocket 4. Rhythmically banded Franciscan chert and shale 16-17 5. A, Spheroidal weathering of "cannonball" concretion east of Los Banos Valley. B, Massive, heavy Upper Cretaceous conglomerate, east end of Los Banos Valley 16-17 6. A, Pebbly tuffacious sandstone at base of Quien Sabe volcanics. B, Twin Peaks from east slope of Antimony Peak 16-17 7. A, Rhyolite intrusive on north side of Cathedral Peak. B, Jointed out- crop of massive agglomerate, south end of Quien Sabe Valley 16-17 8. Geologic map and section of the Stayton mining district, California In pocket 1). Geologic map and section of the upper levels of the Stayton mine, Merced County In pocket 10. Geologic map and sections fo the Gypsy mine, Merced County In pocket 11. Geologic map and section of the Comstock mine, Santa Clara County_In pocket ( •> t GEOLOGY OF THE QUIEN SABE QUADRANGLE, CALIFORNIA* By Carlton James Leith** OUTLINE OF REPORT Page ABSTRACT 9 INTRODUCTION 9 Location and geographic features 9 Climate and vegetation 10 Aclinowledgments 10 Previous literatm-e 10 GEOMORPHOLOGY 11 STRATIGRAPHY 13 Franciscan group (Upper Jurassic) 13 Upper Cretaceous 17 Vaqueros formation (lower Miocene) 21 Quien Sabe volcanics (middle? Miocene) 22 Peckham formation (upper Pleistocene) 26 Landslides (Quaternary) 28 Terrace deposits : 28 Alluvium 28 STRUCTURE 28 GEOLOGIC HISTORY 30 ECONOMIC GEOLOGY 32 Manganese 32 Antimony 33 Quicksilver 33 LITERATURE CITED 34 ILLUSTRATIONS Figure 1. Index map showing location of Quien Sabe quadrangle 8 2. Stratigraphic column, Quien Sabe quadrangle 12 Plate 1. Geologic map of Quien Sabe quadrangle In pocket 2. Economic map of Quien Sabe quadrangle In pocket 3. Geoolgic structure sections across Quien Sabe quadrangle In pocket 4. Rhythmically banded Franciscan chert and shale 16-17 5. A, Spheroidal weathering of "cannonball" concretion east of Los Banos Valley. B, Massive, heavy Upper Cretaceous conglomerate, east end of Los Banos Valley 16-17 6. A, Pebbly tuffaceous sandstone at base of Quien Sabe volcanics. B, Twin Peaks from east slope of Antimony Peak __— :l_ 16-17 7. A, Rhyolite intrusive on north side of Cathedral Peak. B, Jointed out- crop of massive agglomerate, south end of Quien Sabe Valley 16-17 * This report represents a portion of a dissertation accepted for the requirements of the degree of Doctor of Philosophy in Geology, in the Graduate Division of the Uni- versity of California, Berkeley, California. Manuscript submitted to the Division of Mines for publication August 4, 1947. ** Assistant professor, Indiana University. (7) 8 QUIEN RABE QUADRANGLE [Bull. 147 Fig. 1. Index map showing location of Quien Sabe quadrangle. Underlined quadrangle names indicate other recently published geologic quadrangle maps in the region. GEOLOGY — LEITH 9 ABSTRACT The Quien Sabe quadrangle, located 90 miles southeast of San Francisco, includes a portion of the crest of the Diablo Range of the central Coast Ranges of California, and lower rolling country toward the San Joaquin Valley to the east. The following stratigraphic units were mapped : Franciscan group. Upper Jurassic, arkosic sandstone with subordinate siltstone, shale, conglomerate, volcanic rock, radiolarian chert, basic and ultrabasic intrusive rock, and glaucophane schist ; Upper Cretaceous arkosic sandstone, conglomerate, and shale ; Yaqueros formation, lower Miocene, limestone ; Quien Sabe volcanics, probably middle Miocene, including biotite andesite, oxyhorn- blende andesite, hypersthene-augite andesite, olivine basalt, dacite, tuffaceous sediment and agglomerate, plugs and irregular intrusive masses of augite-hornblende-biotite andesite, and hydrothermally altered rhyolite plugs ; Peckham formation, upper Pleistocene, lake beds consisting of gravel, sand, silt, and limestone ; and Quaternary alluvium, terrace deposits, and Inndslides. Most of the Franciscan sandstones of the Quien Sabe quadrangle have suffered only slight metamorphism. The Ortigalita fault marks the boundary between the volcanic-capped Franciscan core of the Diablo Range and the Cretaceous rocks in the foothills to the east. Two periods of faulting are represented in the southwestern portion of the quadrangle ; post-middle Miocene northeastward-trending faults are offset by faults which show evidence of Quaternary movement and which strike northwest. Except for the Fran- ciscan, which has suffered a long and complex deformational history, folding is less pronounced than faulting. Cretaceous sediments locally are overturned against the Ortigalita fault ; their general dip in the northeast quarter of the quadrangle is moderate to the northeast. Exposures of Cretaceous rocks in the southwest portion of the area are not abundant, but the attitudes that can be seen suggest an anticlinal structure. Miocene volcanics are warped and faulted, and upper Pleistocene lake beds are undisturbed. Manganiferous Franciscan cherts have yielded a small amount of manganese ore from oxide deposits located in the south-central portion of the quadrangle. The Stayton mining district, near the northwest corner of the area, has produced minor amounts of antimony and quicksilver since 1870 ; stibnite and cinnabar occur in silieified fault zones in the Quien Sabe volcanics. Most of the properties are idle. INTRODUCTION Location and Geographic Features The Quien Sabe quadrangle (scale 1 : 62,500) of the U. S. Geological Survey, is located 90 miles southeast of San Francisco and 13 miles east of Hollister, California. It includes the southeast corner of Santa Clara County, the northeastern portion of San Benito County, and a portion of western Merced County. The corner common to the three counties is in the northwest quarter of the quadrangle. There are no towns or settle- ments within the limits of the area. The land is used chiefly for cattle grazing, but in favorable local areas, such as the wide, flat bottom lands of Los Banos Valley and Quien Sabe Valley, grain and alfalfa are grown for hay and seed. Numerous roads make the area accessible from Hollister on the west, or from Los Banos on the east. Most of these are passable in dry weather, and become impassable during the winter rainy season. Access to the southw^estern portion of the quadrangle is via Santa Ana Valley from Hollister, the road branching at the Indart Ranch. The east fork leads to Rancho Quien Sabe and Quien Sabe Valley, and the south fork to Los Muertos and Las Aguilas Valleys. State Highway 152, 'from Gilroy to Los Banos, crosses the Diablo Range through Pacheco Pass four miles north of the Quien Sabe quadrangle ; private roads and fire trails inter- secting this highway provide access to the northern and eastern portions of the quadrangle. The Comstock Road and the Lone Tree Road, both reached from Hollister, terminate in the Stayton mining district at the crest of the range near the northwest corner of the area. 10 QUIEN SABK QUADRANGLE [Bull. 147 The crest of the i:)iablo Ranj^e extends southeastward from the northwest corner of the qnadraii^'le and attains its maximum elevation of .'ISdO feet in the area centeriiifi- at Laveajia Peak (elevation 3801 feet). The lowest elevation, 400 feet, is in the noi-tlieast corner of the quadrangle where Los Banos Creek turns to the northeast and leaves the area. Climate and Vegetation The climate of the Quien Sabe region is semi-arid, the average annual rainfall at Ilollister being only 13 inches. The higher slopes of the Diubh) Eange, however, receive somewhat greater precipitation. The eastei-n side of tlie range is much more arid, and the climate is similar to that of the San Joaquin Valley to the east. (^.rassland devoid of trees has developed principally on Cretaceous chiy-shalos and sandstones in the eastern portion of the quadrangle. It is also developed locally on areas of Franciscan sandstones and shales. Savanna type vegetation, including various species of live oaks scattered among annual grasses and herbs, is more characteristic of Franciscan areas. Chajiarral occurs in dense, almost impenetrable, patches on vol- canic rocks with little soil cover. Woodland, characterized by the bay tree, is common in parts of the volcanic areas where the soil cover is well developed. Acknowledgments The writer wishes to express his thanks to Dr. N. L. Taliaferro, who suggested the problem, accompanied the writer in the field, and made valuable suggestions and criticisms. He is also grateful to Dr. F. J. Turner who helped in the petrographic studies of the igneous and meta- morphic rocks ; Dr. C. M. Gilbert made valuable suggestions concerning the separation of mineral grains. Without the financial assistance of the Board of Research of the University of California it would not have been possible to carry out this w'ork, and to this board the writer wishes to express his appreciation. Previous Literature Becker,^ the first to have written about any part of the Quien Sabe quadrangle, mentioned the Stayton mine (section 5, T. 12 S., R. 7 E., M. D.) in an 1888 survey of ciuicksilver deposits of the Pacific coast. Angel,^ in 1890, described the same area under the name "M'Leod dis- trict." lie states that the veins of this district Avere discovered in 1861, and were worked from time to time with no great success. The miner- alized region was known as the Stayton. mini}ig district in 1903, when Forstner ^ made a reconnaissance map of the area. Other writers ■* in succeeding years mentioned the Stayton district, and in 1906 the first mention of a portion of the Quien Sabe area outside the Stayton district was made in the description of a manganese prop- erty." The coming of the first World War brought an increased interest > Becker, G. F., Geology of the quicksilver deposits of the Pacific slope: U. S. Geol. Survey Mon. 13, p. 380, 1888. 2 Anpel, Myron, San Benito County: California Min. Bur. Kept. 10, pp. 515-517, 1890. =* Forstiu-r, William, The quicksilver resources of California : California Min. Bur. Bull. 27, pp. 12K, 147-149, 1903. ' Bradley, \V. W., and Logan, C. A., San Benito County: California Min. Bur. Rept. ir., pp. (il(;-673, 1917. •> Auijury, L. E., Structural and industrial materials of California: California Min. Bur. Bull. 38, p. 336, 190G. GEOLOGY — LEITH 11 in the mineral areas of the region. Logan ^ wrote of manganese prospects and mines, and Bradley "' again briefly mentioned the Stayton district in writing of quicksilver. In 1925, Laizure ^'* presented short descriptions of mineral properties in Merced County, and in 1926 ^ of mineral prop- erties in San Benito County. In 1939 the Stayton district was again described, this time by Ransome and Kellogg.^^ In 1912 Bailey and Myers ^^ mapped and described the Stayton district in detail as a part of the strategic minerals iuA-estigation program of the U. S. Government. In connection with this same program. Trask, Wilson, and Simons ^^ summarized the manganese properties of California, including locations within this quadrangle. A portion of the quadrangle is included in the area mapped by Anderson and Pack ^^ and described by them in 1915. The San Benito quadrangle, adjoining the Quien Sabe quadrangle on the south, was mapped by "Wilson ^'^ and the Hollister quadrangle, to the west of the Quien Sabe quadrangle, has been mapped by Taliaferro.^^ GEOMORPHOLOGY In the latitude of San Benito County the Coast Ranges have the following major divisions, from west to east : the Santa Lucia Range ; the Salinas Valley; the Gabilan Range; the Hollister basin or San Benito Valley ; and the Diablo Range. To the east, the main belt of the Diablo Range is separated from the San Joaquin Valley by lower rolling country underlain by Cretaceous and Tertiary sediments. The Quien Sabe quad- rangle includes a portion of the Diablo Range and the hills of Cretaceous rocks to the east. Los Banos Valley forms a distinct dividing line between the two in the northeast quarter of the quadrangle. There are two imjDortant drainage s^^stems within the Quien Sabe quadrangle. Los Banos Creelv, with its north and south fork and tribu- taries, drains the eastern and central portions of the quadrangle. Quien Sabe Creek joins with Canada Verde in the southwestern portion of the quadrangle and passes southward into the San Benito quadrangle where a junction is made with Los Muertos Creek. In general, the drainage pattern is dendritic, modified somewhat by the nature of the underlying rock. Quien Sabe Creek, the south fork of Los Banos Creek, and Los. Banos Creek in Los Banos Valley are all sub- sequent and roughh" parallel the structural trends of the area. The north fork of Los Banos Creek is consequent on the land surface generated by Tertiarj^ volcanism. * Logan, C. A., Manganese and chi'oniium in California: California Min. Bur. Bull. 76, pp. 59-61, 1918. ' Bradley, W. W., Quicksilver resources of California : California Min. Bur. Bull. 78, p. 96, 1918. 8 Laizure, C. McK., Merced Co.: California Min. Bur. Rept. 21, pp. 175, 181-182, 1925. B Laizure, C. McK., San Benito Co. : California Min. Bur. Rept. 22, pp. 222-223, 238, 1926. "Ransome, A. L., and Kellogg, J. L., Quicksilver resources of California: Cali- fornia Div. Mines Rept. 35, pp. 429, 451, 1939. 11 Bailey, E. H., and Myers, W. B., Quicksilver and antimony deposits of the Stayton district, California: U. S. Geol. Survey Bull. 931, pp. 405-434, 1942. 1^ Trask, P. D., "Wilson, I. F., and Simons, F. S.. Manganese deposits of California, a summary report: California Div. Mines Bull. 125, pp. 81, 83, 142, 158, 159, 1943. i^' Anderson, Robert, and Pack, R. W., Geology and oil resources of the west border of the San Joaquin Valley north of Coalinga, California: U. S. Geol. Survey Bull. 603, 220 pp., 1915. " Wilson, I. F., Geology of the San Benito quadrangle, California : California Div. Mines Rept. 39, pp. 183-270, 1943. 15 Taliaferro, N. L., Geology of the Hollister quadrangle, California : Unpublished report. 12 QUIEN SABE QUADRANGLE [Bull. 147 AGE FORMATION COLUMN THICK- NESS FT DESCRIPTION RECENT ALLUV aiERRACES ;0 000«00 0-100 Grovel, sond, cloy NOT IN CONTACT UPPER PLEISTOCENE PECKHAM FORMATION 'Tirrp , ' , ' T ' , I . -r^ 0-300 Non-marine grovel, sond, silt ond limestone- MIDDLE (?) MIOCENE. QUIEN SABE VOLCANICS LOWER MIOCENE VAQUEROS UPPER CRETACEOUS I' t^ u 1/ i/ 1^ t^ ly' I, t^ 1^ 1/ l^ 1^ l^ t^ 1^ I- l^ 1^ l^ ly 1^ iy l^ 1^ l\ 1^ ly 1^ w ly l,:^ l^ ly i^ ly l^ ly l^ 0-4000 Andesite and basalt flows, ogglomerotes; intruded by ondesite and rtiyolite. ll 0-20 Thin limestone lens. 0-6000 Dork colored clay shale, and buff concretionary sondstone with lenses of conglomerate. --^ fAULT CONTACT I^oOq 0*0*0 ^^»o^o*o^o* UPPER JURASSIC (?) FRANCISCAN GROUP BASE NOT EXPOSED Well induroted orkosic sondstone (partially re- crystallized) shole, con- glomerate, radiolorion chert, bosolt; serpentine intrusions locolly pro- ducing metosomoiic omphibole-mico schists. Fig. 2. Stratlgraphic column, Quien Sabe quadrangle. GEOLOGY — LEITH 13 Two late cycles of erosion are represented within the Qnien Sabe quadrangle. The first cycle reached a stage of late maturity, character- ized by broad alluviate'd valleys and well rounded ridges. These valleys have been entrenched over large areas bj^ actively down-cutting streams, representing the second or present cycle, which is still in a stage of youth or, in part, of early maturity. Remnants of the first cycle are represented by broad, alluviated valleys, including Los Banos Vallej', Quien Sabe Valley, Las Aguilas Valley, Dairy Flat, and Los Muertos Valley. In addition, terrace levels were developed during this cycle at various locali- ties within the quadrangle. These valleys and terraces are now being entrenched by the youthful streams of the second cj^cle. STRATIGRAPHY In the Quien Sabe quadrangle Franciscan rocks of late Upper Jurassic age form the basement and are overlain by Cretaceous sedi- ments. The Tertiary is represented by IMiocene sediments that are mostly of volcanic origin and are associated with lava flows and related intrusive bodies. The volcanics overlap both Jurassic and Cretaceous rocks. Local sedimentary remnants of a Pleistocene lake basin overlie both volcanic and Franciscan rocks. Terraces were formed in late Pleistocene or Recent time, and are now somewhat dissected. Recent alluvium is found in many of the creek bottoms, and landslides of Recent age (some may be older) scar many of the hill slopes. Franciscan Group (Upper Jurassic) Distribution. The Franciscan group is composed of arkosic sand- stones, radiolarian cherts, basalts, basic and ultra-basic intrusives, and metasomatic metamorphic rocks (glaucophane and related schists) . These rocks underlie the entire southeastern portion of the quadrangle and con- tinue northwestward between Los Banos Valley on the east and the Tertiary volcanic area on the west. The belt also extends around the northern limit of the A'olcanic area to the northwest corner of the quad- rangle. In the southern part of the quadrangle the main belt of Fran- ciscan extends westward around the southern end of the volcanic area. Sandstone. The predominant rock type in the Franciscan of the Quien Sabe quadrangle is arkosic sandstone, bluish gray or buff when fresh, weathering to yellowish brown. The structure is commonly massive, but north of the junction of the north and south forks of Los Banos Creek the sandstone is dominantly thin bedded and has a pronounced shaly parting. This rock is buff colored, characteristically fine grained, and is cut by quartz and calcite veins. In general the Franciscan sandstones are poorly sorted rocks composed mainly of angular grains of quartz and feldspar (in approximately equal amounts) and less abundant fragments of dark shale. In numerous localities within the quadrangle a blue, relatively fine-grained sandstone occurs. Shaly portions of this rock impart a bluish color to the soil that may be useful in interpreting struc- ture for limited distances. Close examination shows that throughout the whole area the Fran- ciscan sandstones have been sufficiently deformed to cause at least incip- ient recrj'-stallization of clastic materials. In thin section, the original I'lastic structure is still present, but the surviving grains of quartz, feld- spar, and fragments of shaly material are set in a fine-grained matrix in 14 QUIEN SABE QUADRANGLE [BuU. 147 which recrystallized quartz and feldspar are associated with minute crystals of muscovite, chlorite, pumpellyite, clinozoisite, and other meta- morphic minerals. The feldspar of the Franciscan sandstones occurs in clastic grains, altered to greater or less degree. Plagioclase, the dominant feldspar, commonly comprises about half the volume of the sandstone. It ranges from oligoclase to labradorite, with calcic oligoclase and oligoclase- andesine tlie usual varieties; niicroline is rare. Quartz is about equal in amount to plagioclase and sometimes exceeds it. Granulation effects are evident in some of the quartz grains, but are not uniform in intensity throughout a given thin section. Other clastic grains include dark shale fragments, igneous material that is largely glassy, and recrystallized chert (common in some sections). Minor constituents include sphene, apatite, magnetite, and epidote. Secondary calcite is found occasional!}^, and abundant rather coarse grains of lawsonite are present in some cases. Fine-Graincd Sediments. The fine-grained sediments, including the shaly sandstones, the siltstones, and the shales, are similar to the coarser- grained arkosic sandstones in their content of determinable minerals. Some are only slightly recrystallized ; others .show a more advanced stage of recrystallization, with slight development of schistosity. The coarsest fine-grained sediments contain clastic grains of oligoclase-andesine. Clastic quartz is present in quantity equal to or greater than feldspar ; apatite and epidote are present in very minor amounts, and all contain earthy iron oxide. The detrital grains are enclosed in a matrix of fine- grained muscovite, chlorite, and indeterminate material in which possibly pumpellyite and stilpnomelane are present. Conglome7'ate. Conglomerate occurs as local lenses within the sand- stone-shale sequence. Pebbles are composed of sandstone, blue quartz, white quartz, pebble conglomerate fragments, porphyritic igneous rock, black chert, white chert, pale green chert, granodiorite, and aplite. Peb- bles and boulders range from ^ inch to 2^ feet in diameter. The most com- mon .sizes lie between 4 and 2 inches. The pebbles are rounded, and gen- erally occur in a hard sandy matrix. One conglomerate reef, within the Stayton mining district, has been unsuccessfully prospected ; in the NE^ sec. 34, T. 11 S., R. 7 E., M. D., conglomerate, occurring wdth coarse- grained arkosic sandstone, is exposed in the bottom of the canyon of the north fork of Los Banos Creek; in the southern part of the quadrangle, the crest of the hills trending southeastward and culminating at Bench Mark 3014. in sec. 21, T. 13 S., R. 8 E., M.D., is made up of a large con- glomerate lens ; and the fourth outcrop is in the northern part of the quadrangle, in sec. 29, T. 11 S., R. 7 E., M.D. Volcanic Rocks. Volcanic rocks of the Franciscan are present within the Quien Sabe area, but are not extensive or widespread. They are green to black on fresh surfaces, but oxidize readily to various shades of broAvn and red. The voleanics are easily recognized in the field by their rugged outcrops and by the red color they impart to the soil. The rocks are basaltic and are vesicular with variable texture. "With the exception of a sill-like body at the Franciscan-Cretaceous contact between Wildcat Creek and Chileno Creek, they are closely associated with cherts. Vein- lets and amygdules of quartz and calcite are common. GEOLOGY — LEITH 15 The sill-like body on the Franciscan-Cretaceous contact between Wildcat Creek and Chileno Creek is diabasic in texture, with anhedral augite grains surrounded by lath-shaped feldspars and smaller augite crystals. Much of the groundmass is composed of cloudj^, brownish yellow, devitrified glass. The larger feldspars are andesine, while the feldspar mierolites have the same composition as the most sodic of the pheno- crysts. This outcrop represents a portion of El Puerto volcanics which Taliaferro ^® mentions as common in the exposed top of the Franciscan along the east side of the Diablo Range. Chert. Some of the Franciscan shales contain chert nodules, around which the bedding of the shale is distorted. Rhythmically banded radio- larian chert has a more striking appearance. This material consists of light-colored, partly recrystallized chert bands betw^een alternate bands of shale. In some places the shale is dominant and in others it is rep- resented only as a shaly parting between chert bands. In mapping, the banded chert was not separated from the rest of the Franciscan group. The major area of chert is in the eastern half of the northeast quarter of the quadrangle. This area extends southeastward from the northeast corner of sec. 26, T. 11 S., R. 8 E., M. D., to the eastern portion of sec. 20, T. 12 S., R. 9 E., M. D. The belt reaches a maximum width of 2^ miles in Herrero Canyon and is cut near its northern end by the Ortigalita fault. Within the chert belt igneous rocks and other types of sedimentary rocks are present. Rhythmicallj^ banded chert also occurs in scattered areas elsewhere in the quadrangle and is often breceiated and slickensided. The breccia is composed of chert fragments cemented by chert of a slightly different color. Frequently the surface of the chert is coated with manganese and iron oxides, giving the outcrop a dark blue or brown color. Such an occurrence in sec. 9, T. 13 S., R. 8 E., M. D. (the Fries Ranch prospect) has been prospected for manganese, the ore occurring as oxide in the thicker chert layers. The bedding of the chert is irregular with pronounced pinching and swelling ; near the mouth of the workings the chert is breceiated and contains extensive gouge. Some of the chert fragments are well polished and rounded and resemble pebbles. At the Hendricks manganese mine in sec. 24, T. 13 S., R. 8 E., M. D., the chert again is similarh^ sheared and breceiated. Some of the chert layers are as much as 5 feet thick, and Avhere these layers are broken, less com- petent shale and thin chert are folded around the large blocks. Attitudes of the chert, wiierever they are found, are exceedinglj' variable. The chert is recrystallized and is often cut with veins of coarse quartz aggregates. Grains of magnetite are present, and locally chlorite and iron oxide stains occur between the grains in the veins. The lens-like nature of the cherts, as well as their close association and even interfingering with coarse clastic sediments, indicates shallow water conditions of deposition. The abundance of silica in the water provided favorable conditions for the growth of radiolaria. The original material containing much of the manganese associated with the cherts is neotocite, a light to dark brown manganiferous opal. Oxidation of the primary material produces the coatings of black man- ganese oxides (psilomelane, pyrolusite, and wad) previously mentioned. M Taliaferro, N. L., Franciscan-Knoxville problem : Am. Assoc. Petroleum Geolo- gists Bull., vol. 27, p. 146, 1943. 16 QUIFN SAHF, QTTADKANOLE [Bull.l4( The inaiiganiferous lenses are syugeiietie, and owe their origin to the same volcanisni which was responsible for tlie concentration of silica prodncing: the chert, lirecciation of the chert provides avenues for the downward oxidation of contained iron and manganese. Basic and Ultrabasic Intrusivcs. In tlie Quien Sabe quadrangle intrusions of basic and ultrabasic rocks have the forms of dikes, sills, and plugs. Although these masses are all represented on the map as serpentine, they include rock tj'pes ranging from diorite to serpentinized peridotite or dunite. One common varietj^, exposed along AVildcat Creek and Chileno Creek, is massive, has numerous slickensided and polished surfaces, and contains blocks of volcanic material probably derived from the El Puerto (Franciscan) volcanics with which it is in contact. Blocks of serpentine with shells of magnesite are also included in the distorted mass. The west side of hill 1012, north of Chileno Creek, is badly sheared serpentine bounded on the east by El Puerto volcanics which outcrop on the crest of the hill and continue down the east slope to the Ortigalita fault. A second variety of serpentine is coarsely crystalline and contains bastite pseudomorphs of orthorhombic pyroxene. This variety is found in sec. 2, T. 12 S., R. 8 E., M. D., where it is completelj' brecciated ; and also northwest of the Bueua Vista Ranch. In the latter locality the bastite serpentine is associated with other types of basic intrusive rocks. The area of the outcrop is clearly outlined by dark colored scrub brush. The igneous rocks apparently were intruded in sheets, which now dip steeply north- east. Extensive brecciation and distortion of the mass is apparent in the outcrop. The intrusive body also contains hornblende-biotite diorite with fresh hornblende cores surrounded by chlorite, pale biotite (chloritized in part), andesine, and minor magnetite, (ilabbro. consisting of bytownite and augite ; and olivine gabbro with labradorite, somewhat altered olivine, and augite, are other rock types present in this intrusive mass. A fourth occurrence of serpentine, a distorted mass too small to be shown on the map, contains inclusions of green Franciscan chert, Fran- ciscan sandstone, vein quartz, and basic igneous rock. The sandstone inclusions are abundant, and are somewhat rounded, ranging to a maxi- mum diameter of 8 feet. This outcrop is in an area of blue Franciscan sandstone and black shale in sec. 27, T. 12 8., R. 8 E., M. D. The serpentines are not found in rocks younger than Franciscan but tlie}' are intrusive into the Franciscan sediments. It is possible that the period of intrusion was contemporaneous with the deposition of the sedi- ments. The existence of serpentine and metasomatic rocks oldei- than some of the Franciscan sediments is proved by the presence of glaucophane as a detrital mineral in the Franciscan sandstone and the presence of both serpentine and glaucophane schist pebbles in Franciscan conglomer- ates of other areas. Glaucophane Schist and Belated Rocks. As a result of soda-iron metasomatism that has accompanied ultrabasic intrusioivs, various Fran- ciscan sediments have been converted into glaucophane schist and related rock types. The most widespread occurrence of glaucophane-muscovite schist is in the southwestern portion of the quadrangle where an aureole, terminated by faults on the northeast, northwest, and southwest sides, has developed around the intrusive body. The southeastern margin of the aureole must be inferred, as it is hidden by the soil cover. Exposures DIVISION OF MINES BULLETIN 147, PLATE 4 RHYTHMICALLY BANDED FRANCISCAN CHERT AND SHALE SW. corner sec. 9, T. 13 S., R. 8 E. 2—3163 DIVISION OK .\ii.\i:s nri.i.irnx ht, platk 5 A, SPHEROIDAL, WEATHERING OF "CANXOXBAT.I." CONTRETION EAST OF LOS BANGS VALLEY L, MASSIVE, HEAVY UPPER CRETACEOUS CONGLOMERATE EAST END OF LOS BANGS VALLEY DIVISION' OF MINKS Bin.T^ETiN 14 7, PLATE 6 . JtSM k m m tu j Aih ofinxsfniii.. i^,-fW^'0r^;~. i^.v.^ • \ 1* i A, VKBPA.Y Tl'FFACEOIJS SANDSTONE AT BASE OF QUIEN SAHE VOI.CANICS Sec. 9, T. D! S., Jl. S E. B, TWIN PEAKS FPvOM EAST SLOPE OP ANIMMCJNY I' OAK in VISK ).\ ( »!•■ MIXIOS BULLKTIX 147, PLATE 7 * ^ *»iF ■"» .1. JtilVdIJ'i'iO IXTIU'SIVK (CKNTEPo « 'X Xoimi SIDE OF CATHEDRAL PEAK /;, JOIXTKD OUTCROP OF I^IASSIVE AOC.LOMIORATE SOUTH END OF QUUOX SABK \ALLEY GEOLOGY — LEITH "17 along- the Santa Ana Creek road show unaltered sediments, while a short distance to the north there are poor outcrops of glaucophane-muscovite schist. Similar schist is found associated with actinolite schist in an isolated outcrop south of the Santa Ana Creek road, southeast of Hill 1398, 1,000 feet north of the center of the north line of sec. 4, T. 14 S., R. 7 E., M. D. Glaucophane-muscovite schist with minor chlorite and epidote, and occasionally with calcite and sphene, or with garnet, sphene, and rutile, is the type found most frequently within the quadrangle. Source, Relationships and Age. The land mass which furnished the debris for the Franciscan must have been extensive to provide for the wide distribution of uniform rock types found with the Franciscan. It must have been of considerable relief to account for the abundance, freshness, and angularitj^ of the feldspar in the accumulated material. Lack of Sierran debris in the coarser clastic sediments, and a westward coarsening of grain size of Franciscan sediments in other parts of Cali- fornia ^^ suggest that the land mass lay somewhere to the west of the geosyncline in which the Franciscan was deposited. The Franciscan is not in contact with older rocks within the Quien Sabe quadrangle. It is in fault contact with Cretaceous sediments and is overlain unconformably by Tertiary and Quaternary sediments and vol- canic rocks. Physical evidence for the Upper Jurassic age of the Franciscan group is obtained by correlation with rocks of the Sierra Nevada region through northern California and southwestern Oregon. ^^ Camp^^ has established the same age from faunal evidence in describing two Upper Jurassic (Tithonian) ichthyosaur rostra contained in worn Franciscan chert cobbles. The Franciscan of the Quien Sabe quadrangle probably represents a portion of the second stage, Upper Franciscan, as recognized by Taliaferro. 2^ Upper Cretaceous General Distribution and Stratigraphic Relationships. The Upper Cretaceous in the Quien Sabe quadrangle is represented by a minimum of 6,000 feet of brownish concretionary arkosic sandstones, interbedded dark clay shales, and heavy conglomerates. These beds represent a portion of the Panoche formation of Anderson and Pack.-^ Since later work has shown that the Panoche as mapped bj^ these workers includes Knoxville (Upper Jurassic), Paskenta (Lower Cretaceous), and Horsetown (Lower Cretaceous), and extends across several disconformities, the writer pre- fers the classification proposed by Taliaferro "- in which the Upper Cretaceous is divided into a lower Pacheco group and an upper Asuncion group, separated by an orogenic interval. According to Taliaferro,--^ the 1" Taliaferro, N. L., Franciscan-KnoxviUe problem: Am. Assoc. Petroleum Geolo- gists Bull., vol. 27, p. 187, 1943. 18 Taliaferro, N. L., Geologic history and correlation of the Jurassic of southwestern Oregon and California : Geol. Soc. America Bull., vol. 5.3, pp. 71-112, 1942. 1" Camp, C. L., Ichthyosaurs from tlie Franciscan formation of central California (abstract) : Geol. Soc. America Bull., vol. 52, p. 1945, 1941. 20 Taliaferro, N. L., Geologic historv and structure of the central Coast Ranges of California: California Div. Mines Bull. 118, pp. 126-127, 19 41. . . . Franciscan-Knoxville problem : Am. Assoc. Petroleum Geologi.«ts Bull., vol. 27, pp. 215-216, 1943. 21 Anderson, Robert, and Pack, R. W., op. cit. pp. 39, 42-45. — Taliaferro, N. Ij., Geologic historv and structure of the central Coast Ranges of California : California Div. Mines Bull. 118, pt. 2, p. 130, 1941. -^ Oral communication. May 1947. 3—3163 IS . QUIEN SABE QUADRANGLE [Bull. 147 heavy conglomerates in the eastern part of the quadrangle are an exten- sion of Asuncion conglomerates to the southeast, but since no strati- graphic break or faunal record was found in the Quien Sabe Cretaceous, tlie entire assemblage is mapped as undilTerentiated Upper Cretaceous, the inference being that it is part of the Asuncion group. The Upper Cretaceous crops out over a triangular area of 17 square miles in the northeast corner of the quadrangle, and is also exposed in the southwest corner and in limited patches along the western boundary. Later sediments, volcanics, terrace deposits, landslides, and allu- vium commonly overlap the Upper Cretaceous sediments but the Creta- ceous is in fault contact with volcanics near the south end of Quien Sabe Valley and in see. 7, T. 12 S., R. 7 E., M. D. The Franciscan-Cretaceous contact is a fault wherever it is exposed, with the possible exception of the small area in sec. 30, T. 11 S.. R. 7 E., M. D. In this locality the contact is obscured by a small andesite plug, landslides, and thick soil cover, but has been mapped to correspond to the highest position of Franciscan debris on the soil covered hill slope. Description and Distribution of LitJiologic Units. The northeastern quarter of the quadrangle provides the best picture of the relationships of tlie various lithologic types of the Upper Cretaceous sediments. A strip of brown clay shale in Los Banos Valley parallels the creek for a distance of more than four miles. It appears at the edge of the second terrace level, and although it forms no outcrops, it can be traced by the brown color imparted to the soil and by the presence of shale chips in the soil. At the north end of the valley, beyond the margins of the terrace deposits, it forms the gentle .slopes of the hills, and crops out in gullies immediatelj' to the north of the quadrangle, in sec. 4, T. 11 S., R. 8 E., M. D. Lenses of feldspathic sandstone, bluish-gray in color and weathering to buff, occur locally within the .shale, as at the contact with the Franciscan at the north end of Los Banos Valley-. The sand is composed of medium sized, fairly well sorted, angular to subangular grains of quartz, intermediate plagioclase, bleached biotite (.some altering to chlorite), muscovite. recrystallized chert fragments, and organic material. Minute calcite A'eins are present, and the cementing material appears to be calcareous clay. At the south end of Los Banos Valley, ea.st of the Ortigalita fault, bluish arkosic sandstone, shaly sandstone, and black shale strike north- west with a vertical or steep northeasterly dip. Conglomerate occurs at the Franciscan-Cretaceous contact. Northeast of Los Banos Creek is a nearly uniform sequence of gray to bluff concretionary sandstone, with some interbedded shale. The sandstone contains numerous "cannonball" concretions which have dark iron-stained surfaces and weather out of the .sandstone outcrops. In places the stratification is uniform and regular, with beds 2 to 4 inches thick. Elsewhere beds are much thicker. Locally they are as much as 5 feet thick and are separated by several inches of silty material. Resistance to weathering and erosion varies within a single bed, resulting in hollows and lumps on the surface of the outcrop. Frequently the sand- stone shows cut-and-fill lensing, with even-grained fine sandstone making up the lenses. Occasional .shale fragments are found in the sandstone layers, and are particularly abundant within the more shaly facies of GEOLOGY — LEITH 19 the sandstone or where thinly stratified sandstone and shale are inter- bedded. The Cretaceous sandstones northeast of Los Banos Creek are typically medium- to coarse-grained, M'ith a fair degree of sorting. Grains are angular to subangular, and include clouded feldspar (oligoclase to andesine), quartz, biotite, recrystallized chert fragments, shale frag- ments, organic material, and lesser amounts of muscovite, epidote, chlorite, and hornblende. Matrices are generally calcareous and yellow limonite stain is common. Heavy mineral concentrations contain magne- tite, zircon, augite, tourmaline, garnet, zoisite. and apatite. In the Ei sec. 20, T. 11 S., R. 9 E., M. D., Los Banos Creek, as it leaves the quadrangle, has cut a gorge through thick conglomerate lenses striking northwest and dipping to the northeast. Within the limits of the Quien Sabe quadrangle the conglomerate crops out in two lenses sep- arated by silty shale and having an aggregate thickness of at least 350 feet. More lenses appear to the east in the Ortigalita Peak quadrangle. The conglomerate is massive and heavy, and contains numerous well- stratified sandstone lenses. Some lenses reach 80 feet in length and 6 feet in thickness. Some are pebbly; others are not. The matrix of the conglomerate is sand, and is well cemented, hard, and coherent. The pebbles and boulders are well rounded but poorly sorted; they are commonly coated with a brown polish, range in size from 1 to 12 inches, and average 2 to 4 inches in diameter. The debris includes granodiorite, various types of porphyritic igneous rocks, aplite, pegmatite, dark chert, red chert, green chert, and white chert. Some of the red chert pebbles contain radiolaria, and Franciscan volcanic rocks are also represented. In addition, Cretaceous debris is present and includes poorly consolidated sandstone and pebbles of dense limestone similar to limestones in the Horsetown (Lower Cretaceous), Paskenta (Low^er Cretaceous), and even in the lower Upper Cretaceous formations.^'* A specimen of sandstone from a lens within the conglomerate contained quartz and clouded sericitized feldspar in about equal amounts, biotite, muscovite, and chlorite. The heavy portion of the sample was composed of magnetite, zircon, clouded epidote, brown tourmaline, zoisite, augite, green horn- blende, garnet, and minor sphene and apatite. The materials present in this conglomerate are all of types that occur within the Coast Ranges, and there is a complete absence of anything resembling Sierran debris. The nature of the conglomerate with its included sand lenses suggests rapid deposition with frequent shifting of channels. There is no stratigraphic break at the base ; the deposit appar- ently represents an uplift somewhere to the west, with no break in sedi- mentation. The Cretaceous sediments are in contact with the Franciscan to the west along the Ortigalita fault.^^ In almost every exposure of the fault Franciscan is brought into contact with a heavy Cretaceous conglom- erate. Like the conglomerate described above, it is composed of pebbles with a brown polish and embedded in a sandy matrix. The pebbles include dark blue and black chert, various porphyritic igneous rocks, grano- diorite, pegmatite, and aplite, as well as some weathered diabase or -* N. Li. Taliaferro, oral communication, May 19 47. -'^ TaUaferro, N. L., Geologic history and structure of the central Coast Ranges of California : California Div. Mines Bull. 118, pt. 2, p. 162, 1941. 20 QUIEN SABE QUADRANGLE [BuU. 147 •rabbro (luubtliilly referred to a Franciscan source. Tlie pebbles range from 1 incli to 1^ feet in diameter and average 2 to 6 inches. There are also lenses of fine pebble coii Taliaferro, X. L., Geologj' of the Hollister quadrangle, California: Unpublished report. :" Wil.'^on, I. P., op. cit. p. 24S. =>= Taliaferro, N. L.., Geologic history and structure of the central Coast Ranges of California: California Div. Mines Bull. 118, pt. 2, pp. 142-144,1941. GEOLOGY — LEITH 23 Lithology and Petrography. The various rock types represented in the volcanic series fall within the following groups: (a) andesitic flows, including biotite andesite, oxyhornblende andesite, and hypersthene- augite andesite; (b) basaltic flows, classified as such because of the pres- ence of olivine, since chemical analyses are not available ; (c) dacite flows, with quartz and indeterminate feldspar phenocrysts and oligoclase microlites; (d) sediments, including agglomerates, conglomerates, and tuffaceous sandstones; (e) andesitic intrusives, in the form of plugs and irregular masses; (f) rhyolitic intrusives, hydrothermally altered plugs. The effusive rocks cannot be divided into stratigraphic units charac- terized by a dominance of a particular rock type, as representatives of each group are found throughout the sequence and there are no major stratigraphic breaks. The writer found no evidence for the presence of an unconformity between a lower basaltic unit and an upper andesitic unit as reported by Bailey and Myers.^^ The biotite andesites consist of phenocrysts of zoned plagioclase, andesine to labradorite, and yellowish-brown biotite set in a groundmass of feldspar microlites and brownish glass. The plagioclase microlites of the groundmass range from oligoclase to andesine. The oxyhornblende andesite flows contain phenocrysts of zoned plagioclase, ranging from oligoclase to andesine. The groundmass consists of feldspar microlites and altered brownish glass. The hypersthene-augite andesites contain normally zoned feldspar phenocrysts ranging from andesine at the cores to oligoclase in the mar- ginal zones. Plagioclase microlites in the hyalopilitic groundmass hve oli- goclase. Prismatic hypersthene phenocrysts are weakly pleochroic, from pale yellow to pale green ; inclusions are common but lack the regular arrangement typical of schiller structure. Oxyhornblende, epidote, augite, and biotite are present in minor amounts. Olivine basalt is a common roek type of the Quien Sabe voleanics. Some have phenocrysts only of olivine (often partially altered to idding- site), while in others phenocrysts of plagioclase, augite, oxyhornblende, and biotite also occur. Plagioclase phenocrysts are zoned and range from andesine to labradorite. Plagioclase microlites in the microcrystalline to glassy groundmass are oligoclase to andesine. Near the base of the Quien Sabe voleanics, close to the northwest corner of sec. 35, T. 11 S., R. 7 E., M. D., is an outcrop of light-colored, gray to pink rock in which a few quartz phenocrysts and occasional feldspar crystals are visible with a hand lens. In thin section the quartz phenocrysts are clearly visible, but the feldspar phenocrysts are too altered to be determined. The groundmass contains much calcite and finely divided quartz, some chlorite, and laths of altered feldspar. The rock is a dacite, hydrothermally altered. The flows of the Quien Sabe voleanics are interbedded with agglomer- ates and water-deposited sediments. The agglomerates generally are mas- sive and erode to a miniature pinnacles type topography in many parts of the quadrangle. This massive character makes it difficult to obtain reliable strike and dip measurements from a single outcrop ; it is often more satisfactory to observe attitudes from a distance, where bedding and jointing can be seen in their true perspective. Crude stratification, "■■ Bailey, E. H., and Myers, W. B., op. cit. p. 40!"). 24 QUIEN SABE QUADRANGLE [Bull. 147 slight rouiuliiijr of pebbles, and inclusion of extraneous material suggest that Avater had a part in the process of deposition of some of these rocks. The agglomerates are eomiiosed of mineral and rock fragments in a tufl'a- ceous matrix. The larger fragments are more resistant to erosion than the glassy, honeycombed matrix. Eock fragments include tutf, andesite, ba.salt, and some pre-voleanic rock types, the diameter of the coarser debris averaging 1 to 3 inches but sometimes reaching as much as 3 feet. The mineral content of the agglomerates, when determinable, is similar to the lavas Avith Avhich they are associated. Olivine, hypersthene, augite, oligoclase-andesine, and quartz are present in a specimen collected in sec. 25, T. 11 S., R. 7 E.. M. D. Rock fragments in the same specimen include fine-grained feldspathic sandstone, recrystallized chert, and olivine basalt ; the presence of quartz and olivine in the same rock, there- fore, is not surprising. Antimony Peak is composed predominantly of crudely bedded agglomerate containing pebbles and blocks of volcanic debris set in a tuffaceous matrix. Mineral fragments in this rock are of small size, are angular and broken, and include plagioclase (oligoclase to labradorite) and augite. The augite is sometimes included in pumiceous masses. At the south end of the row of hills separating Quien Sabe Valley and Little Quien Sabe Valley, olivine basalt is overlain by agglomerate containing olivine basalt and pumice fragments 1 to 2 inches in diameter, and crystals of olivine and sericitized andesine. Conglomerate, interbedded with coarse tuffaceous sand, crops out in a gully in sec. 24, T. 11 S., R. 7 E., M. D. The conglomerate is composed of poorly rounded pebbles and boulders of volcanic debris that are enclosed in a buff-colored matrix ; pebbles range from ^ inch to 2 feet in diameter. Similar conglomerate, apparently slumped, is found in sec. 25, T. 11 S., R. 7 E., M. D. About 50 feet of conglomerate, composed of sub- round andesitic fragments half an inch to 2 feet in diameter in a clay matrix, is overlain b}^ platy lavas on the north side of Mariposa Peak. Interbedded pebble conglomerate and tuffaceous sand occurs in sees. 8 and 9, T. 13 S., R. 8 E., M. D. Three types of andesitic intrusive bodies are found within the quad- rangle. One type has sharp contacts, nearly circular outline, and arches the surrounding rocks. Bodies of this type, a good example of which occurs at the head of Quien Sabe Valley, may best be described as plugs. A second type is represented b}^ the intrusive mass at the head of the north fork of Los Banos Creek. The rocks surrounding this type are somewhat altered as a result of the intrusion, and numerous small dikes border the Tiiass. The third type, represented by a body in the area north of ]\Iariposa Peak and Cathedral Peak, has sharply angular contacts, with no altera- tion effects. The intrusive bodies are younger than some of the volcanics, and in other cases the relationships cannot be determined. They appar- ently served as vents and feeders, supplying the material which was poured out on the surface. The andesitic intrusive activity is believed to have occurred contemporaneously with the accumulation of the extrusive rocks. The snuill knob of intrusive andesite near the center of sec. 29, T. 11 S., R. 7 E., M. D., is composed of plagioclase phenocrysts and pri.smatic limonite pseudomorplis in a cryptocrystalline groundmass. The plagio- clase ranges from andesine to labradorite and contains irregular patches of ealcite. GEOLOGY — LEITH 25 The large intrusive body north of Mariposa Peak is an augite- hornblende-biotite andesite. The augite shows marked dispersion, is twinned, and is sprinkled with magnetite inclusions. Feldspar pheno- crysts are andesine ; some are zoned, and some are noticeably saussuri- tized. Feldspar microlites in the microcrystalline groundmass are andesine. Augite-hornblende-biotite andesite also occurs in an intrusive mass in sec. 20, T. 12 S., R. 8 E., M. D. It is porphyritic with a microcrystalline to glassy groundmass, containing phenocrysts of zoned plagioclase, augite, and chloritized hornblende and biotite. The plagioclase of the phenocrysts is normally zoned oligoclase, Avith the outer rims about 3 per cent richer in soda than the cores. Feldspar microlites in the groundmass are of the same range of composition as the plagioclase of the phenocrysts. Apatite is present in minor amount. An andesite plug occurs on the Comstock road at the west line of the quadrangle, in sec. 30, T. 11 S., R. 7 E., M. D. In this rock phenocrysts are oligoclase to andesine, and prismatic limonite-chlorite pseudomorphs. A few small grains of biotite and subhedral apatite are present. Feldspar microlites in the microcrystalline groundmass are andesine. On the east- ern slope of the Diablo Range intrusive andesite has been exposed by headward erosion of the north fork of Los Banos Creek. This andesite contains phenocrysts of andesine in zoned crystals; saussuritization is shown by patches of calcite, sericite, and finely divided epidote. Deeply pleochroic oxyhornblende phenocrysts are partially chloritized and con- tain abundant inclusions of opaque iron ore. The groundmass contains microlites of andesine, chlorite flakes, finely divided epidote, magnetite dust, and limonite stain. Secondary quartz locally fills open spaces within the rock. St. Marys Peak is an andesite plug which has baked the intruded sediments and volcanics near its contacts. Phenocrysts are predominantly andesine but occasionally consist of augite. They are enclosed in a micro- crystalline to cryptocrystalline groundmass that contains microlites of andesine and microcrystalline augite. Limonite patches and magnetite grains are scattered throughout the groundmass. Two small plugs of rhyolite were found in the Quien Sabe quad- rangle, one forming the steep-sided point of Mariposa Peak, and the other cropping out on the north side of Cathedral Peak. The rhyolite is intru- sive into all other types of igneous rock within the area, and is therefore the youngest of the Quien Sabe volcanics. The straight boundaries of the Cathedral Peak plug are striking and suggest that its shape was influ- enced by pre-existing fractures. Jointing and banding, approximately vertical and parallel to the intrusive contact, are characteristic features of the rhyolite. As seen near the base of the exposed rhyolite on the south side of Mariposa Peak the joints curve outward from the major part of the body. Here the joints at the bottom of the outcrop strike N. 37° W. and dip 85° SW. ; 50 feet higher the same joints strike N. 43° W. and dip 79° NE. At the top of Mariposa Peak, the nearly vertical set of joints is accompanied by a second set dipping approximately 20° north. The rhyolite of Cathedral Peak is cut by two sets of joints, one striking N. 35° E. and dipping 64° SE., the other striking N. 32° W. and dipping 76° SW. 26 QUIEN SABE QUADRANGLE [BuU. 147 The rhyolite is chalky white to gray in color, with brown iron oxide stains. Occasional phenocrysts of quartz, feldspar, and biotite may be seen in the hand specimen, and thin sections reveal a porphyritic texture with small phenocrysts of sanidine and oligoclase. Quartz is sparsely dis- tributed in somewhat rounded and fractured grains. Biotite is present, but commonly has been converted to bauerite. A few chlorite flakes and hexagonal grains of apatite are present. The groundmass of the rhyolite is a mixture of opal and glass with a few laths of orthoclase. The baueritization of the biotite and the opalization of the glass are visible effects of hydrothermal alteration of the rhyolite. Andesite inclusions are common in the Mariposa Peak rhyolite. These are somewhat brecciated when near the intrusive contact, but are in the form of lens-shaped schlieren striking N. 30° E. with vertical dip when found nearer the center of the intrusive mass. A specimen from one of the schlieren jjroved to be andesite with phenocrysts of andesine and chloritized hornblende and biotite, and with microlites of oligoclase- anclesine in a glassy groundmass containing magnetite dust. The con- taminated host rock immediately adjacent to this inclusion is intermedi- ate in color between the dark gray included material and the light gray to white rhyolite. It is porphyritic, with some phenocrysts of oligoclase and some of andesine, and patches of chlorite which appear to be psuedo- morphic after biotite and amphibole. Orthoclase microlites, granular epidote, magnetite dust, and limonite patches occur in the microcrystal- line to crj^ptocrj^stalline groundmass. Peckham Formation (Upper Pleistocene) Name, Distribution, and Relationships . The name Peckham forma- tion is proposed for the non-marine silts, sands, gravels, and limestone occurring near the center of the quadrangle. The name is derived from Peckham Ridge, an eastward trending spur of the Diablo Range which marks the northern limit of the exposures of the sediments. The formation is flat-lying and rests with as much as 90° angular discordance upon the Franciscan, and as much as 25° upon the Miocene volcanics. It is undis- turbed, the top of a portion of the formation forming a level surface. Exposures of the Peckham formation occupy two geographic areas, each of which covers approximately 2 square miles. The northern area lies east of St. Marys Peak and north of Lookout Mountain ; the southern area is principally on the eastern side of the south fork of Los Banos Creek, south of Lookout Mountain. The maximum thickness of the forma- tion is 300 feet. The poorly consolidated sediments are less resistant to erosion than the older rocks and are cut by sharp gullies developing on the slopes of rounded hills. Soil cover is thin or absent on the slopes and grassland is found on the flatter areas. LitJioIogy. The gravels of this formation are poorly cemented, with well-rounded pebbles and boulders that have a maximum diameter of 1 foot ; the average size of the pebbles is i inch to l^ inches. In sec. 17, T. 12 S., R. 8 E., M. D., the gravels rest directly on the Quien Sabe volcanics, and the pebbles are composed almost entirely of volcanic debris, while in sec. 27, T. 12 S., R. 8 E., M. D., the formation rests on the Franciscan, and pebbles in the gravels include an appreciable amount of Franciscan sandstone and some chert, in addition to Tertiarv volcanic material. The GEOLOGY — LEITH 27 coarser material is enclosed in a matrix of pebbly sand. Channeling, cut- and-fill strnctures, and cross-bedding are characteristic features of many of the exposures. The gravels are interbedded with pebbly sands, clays, and silts, which also contain small pebbles of volcanic debris. Volcanic material is everywhere the most abundant constituent of the coarse grains and pebbles, but smaller amounts of Franciscan material are present where tlie formation rests upon the Franciscan terrain. A specimen from the northern area contained grains of clouded feldspar, quartz (in less amount than feldspar), and a hea\y fraction including augite, hyper- sthene, green hornblende, magnetite, epidote, and biotite, with minor amounts of garnet, zircon, glaucophane, and a grain or two of rutile. A similar assemblage occurs in the finer-grained sediments of the southern area, except that here no garnet was noted and brown horn- blende, in addition to green hornblende, was present. The similarity of the mineralogy of these sediments with that of the contiguous Quien Sabe volcanics is an indication that the latter provided the principal soiirce of the material which collected within the local basin. A contribution from the Franciscan, on a smaller scale, is indicated by the presence in the sediments of a small amount of clastic glaucophane. A dense, fine-grained, gray limestone, Avith scattered small sub- angular grains of clastic quartz crops out near the center of sec. 16, T. 12 S., R. 8 E., M. D. This appears to be a typical lacustrine limestone. Environment of Deposition. Salients of lava project upward through the Peckham formation in sec. 17, T. 12 S., R. 8 E., M. D. In the southern area of the Peckham formation, rugged masses of Franciscan rocks also project upward into the younger sediments. These are exposed by the downward cutting of the southfork of Los Banos Creek. Exposures in which the sediments overlap the older rocks show that the younger formation accumulated on a very irregular surface, in part Franciscan, and in part volcanic. The stratification, cross-bedding, lensing, and chan- neling, of the sediments are strongly indicative of deposition by water. This deposition probably took place in a lake occupying this portion of the quadrangle in late Pleistocene time. Although no definite proof of the existence of a landslide dam was found, water may have accumu- lated behind such a dam near the northern end of the south fork of Los Banos Creek, flooding lower country to the south and west. Around the margins of the lake, deposits were built above the lake level, the trans- porting streams cutting migratory channels and forming cut-and-fill structures such as are found on present day floodplains and deltas. Age. No fossils were found in the Peckham formation and its exact age can not be determined. In the Hollister quadrangle to the west and in the San Benito quadrangle to the south Plio-Pleistocene San Benito gravels are gently folded and faulted. The Peckliam sediments are not deformed and are probably younger than the deformation affecting the San Benito gravels. The Lower Pleistocene is separated from the Upper Pleistocene by a diastrophism which was more pronounced in the southern part of California than in the central portion of the state,^^ but which nevertheless noticeably disturbed the Plio-Pleistocene gravels of the Hollister-San Benito region. No statement can be made regarding the upper limit of age for the Peqkham formation. 3* Bailev, T. L., Late Pleistocene Coast Range orogenesis in southern California : Geol. Soc. American Bull., vol. 54, pp. 1549-15C8, 1943. 28 QUIEN SABE QUADRANGLE [Bull. 147 Landslides (Quaternary) Quaternary landslides are common, particularly in the western half of the quadrangle where Franciscan and volcanic slopes are steep. Numerous small slides scar hill slopes composed of Franciscan sandy shales and shaly sandstones, as in the northwest corner of the quadrangle. The sliding and slumping of the volcanics has already been discussed. Only the more prominent of the landslides were mapped. The largest slide occurs on the north side of Peckham Ridge west of Twin Peaks, reaches a length of 2| miles, and has an average width of a half mile. The mass does not represent material that was all once near the top of the ridge, but is more correctly pictured as a continuous zone ni which the surface material has moved some distance dovm the slope from its original location. Three other large slides are present in the high country of the northwestern portion of the quadrangle ; all are composed of volcanic debris. Terrace Deposits Quaternary terrace deposits, consisting of unconsolidated gravel, sand, silt, and clay, occupy much of Los Banos Valley where three levels were mapped. The first occurs at a height of 20 feet, the second at 100 feet, and the third at 120 feet above the level of the stream. Terrace deposits also occur around the common corner of sees. 28, 29, 32, and 33, T. 12 S., R. 8 E., M. D., in sees. 19 and 20, T. 13 S., R. 9 E., M. D., and in Los Muertos Valley, but different levels were not differentiated in these localities. Alluvium Recent alluvium, composed of unconsolidated gravel, sand, silt, and clay, is present in the beds of many of tlie streams of the area, and forms the flat bottom lands of the larger valleys. Quien Sabe Valley is floored with the largest expanse of alluvium in the quadrangle. STRUCTURE The Quien Sabe quadrangle is a portion of one structural unit of the Coast Ranges, the Diablo Range. This range has a basement of folded Franciscan strata, overlain by several thousand feet of later sediments and volcanic rocks. It has been deformed by folding and thrust faultnig, with pronounced overturning in places. The Ortigalita fault, in the northeastern quarter of the quadrangle, is one of the most important structural features in the area. It continues along the eastern front of the Diablo Range, to the north and south of the Quien Sabe region, and marks the Franciscan-Cretaceous contact. Thrust movement on this fault has moved Franciscan rocks to the north- east oyer the later Cretaceous sediments, overturning the Cretaceous rocks in the process. Additional displacement has occurred on a fault paralleling the Ortigalita fault, usually at the base of the El Puerto volcanics within the Franciscan. These faults will be considered together, as they are closely related. The Ortigalita fault is exposed within the Quien Sabe quadrangle, from the vicinity of Carrisalito Spring to the southwest corner of sec. 24, T. 11 S., R. 8 E., M. D. It has an average strike of N. 15° AV. and dips steeply to the southwest. The secondary fault within the Franciscan is exposed over the same area, paralleling the strike of the Ortigalita fault, but dipping 50° to 55° SW. The amount of displacement on both is inde- GEOLOGY^ — LEITH 29 terminate, but movement on the Ortigalita fault has sheared the con- glomerate at the base of the Cretaceous, and slickensided, sheared serpen- tine marks the position of the parallel fault at the base of the El Puerto volcanics ; chert immediately to the west of the serpentine is also sheared and brecciated. In general, slickensides are very poorly preserved., but indicate an upward movement of the hanging wall. The stratigraphic position of the Franciscan above the Cretaceous, separated by the fault, also indicates thrust movement. A short distance to the east of the Ortigalita fault the Cretaceous beds dip 50 to 65 degrees to the east. The beds are vertical closer to the fault, and at the fault on the north side of Chileno Creek the beds are overturned 65° NW. The strike is affected somewhat by a minor cross- fault which offsets the Ortigalita fault slightly to the east on the south side of Chileno Creek. The overturning is apparently a drag effect pro- duced by the movement on the Ortigalita fault. There are no indications of recent movement on either of these faults. As Upper Cretaceous sedi- ments are involved in the movement, the age of the disturbance is post- Upper Cretaceous. No Tertiary rocks occur near the fault within this quadrangle, but in other portions of the Coast Ranges Paleocene and Upper Cretaceous sediments have the same geographic distribution, and are lithologically similar. There is no evidence of any great disturb- ance.^^ The compressive forces which began to affect the Coast Ranges in the early Tertiary reached their peak in the late Pliocene, at which time the ranges were uplifted by folding and thrusting of their margins. Direct evidence of this peak is present in the San Benito quadrangie.^^ Although there may have been earlier movements along the Ortigalita fault, the features observed today probably were produced during the late Pliocene disturbance. In the southwestern corner of the quadrangle, Franciscan rocks are thrust to the northwest over Cretaceous sediments along a fault trending northeast. This fault is offset by later, northwestward- trending faults, along which a portion of the Miocene Quien Sabe vol- canics is thrust over Cretaceous and Franciscan rocks to the south. Northwest of Little Quien Sabe Valley, a northeastward-trending fault has offset the contact between the Cretaceous sandstone and the Quien Sabe volcanics. This dates the northeastward-trending set of faults as later than the middle ( ?) Miocene volcanic series, and as these are offset by northwestward-trending faults, the northwestward-trending faults postdate the first set. Sag ponds and short trough-like valleys mark the position of the later faults and suggest active movement as recent as Quaternary. Dikes occur in some of the fault zones and the mineraliza- tion of the Stayton mining district is localized along certain of these faults. The structure of the Franciscan is generalized on the cross sections accompanying this report. This group of rocks is intricately folded and and faulted and in the time available it was not possible to work out in detail all of the relationships existing within this group. Attitudes are exceedingly variable over a short distance. A small east-west-trending, nlunging anticline, eroded along its axis, occurs in sec. 9, T. 11 S., R. 8 E., M. D., and forms an amphitheater-shaped valley opening into the north 35 Taliaferro, N. L,.. Geologic historv and structure of the central Coast Ranges of California : California Div. Mines Bull. IIS, pt. 2, p. 153, 1941. 33 Wilson, I. F., op. cit. pp. 253, 254. 30 QUIEN SABE QUADRANGLE [Bull. 147 end of Los Banos Valley. West of Wildcat Creek are an anticline and syn- cline in the Franciscan, the axes trending roughly east-west ; dips on the north limb of the anticline range from 50° N. to vertical, and on its south limb average 60° to 65° S. In this area interpretation of the structure was aided by the presence of a blue sand horizon which could be used as a marker over a limited area. The Cretaceous sediments in the northeastern corner of the quad- rangle dip fairly uniformly to the northeast. No pronounced structural features stand out in this area except the overturning of the beds against the Ortigalita fault. Exposures of the Cretaceous in the southwest quar- ter of the quadrangle are very poor, except in road cuts. Hills are rounded -with very few outcrops, and the flatter land has been under cultivation for so long that exposures of the rock through the soil are almost non-existent. Along the Santa Ana Creek road dips are moderate to the northeast, while on the road to Little Quien Sabe Valley there is moderate southeastward dip. Comparison of the map accompanying this report with the geologic map of the Hollister quadrangle ^'^ suggests an anticline in the Cretaceous of this area, as dip symbols on the two maps, though sparsely scattered, are opposed in a regular manner. The Quien Sabe volcanics are broadly warped and in places, extensively faulted. A broad curving downwarp at the east end of Peck- ham Kidge is reflected by the attitudes of the volcanics in this area, and slight upwarps and downwarps are present in other localities ; not all of them are indicated on the map. The north half of an eroded east-west anti- cline, plunging to the west, can be followed along the outcrops of light colored tuff aceous agglomerates on the north side of the north fork of Los Banos Creek, in sees. 23 and 27, T. 11 S., R. 7 E., M. D. The fold is not traceable on the south side of the creek, as it is obscured by a large land- slide. GEOLOGIC HISTORY During Upper Jurassic time a thick sequence of terrigenous sedi- ments, predominantly arkosic sandstone (Franciscan group), was deposited. The freshness of the feldspar, angularity of grain, and thick- ness of accumulation indicate a source region of strong relief with a rigorous climate. The character of the material, the coarsening of the sediments to the west,^^ and the absence of Sierran type debris in the Franciscan conglomerates are evidences that the source region lay to the west of the basin of accumulation, The climatic conditions in the source region probably ranged from low temperatures and heavy precipitation in the highlands to more moderate temperatures favoring wooded areas on the lower slopes. The sandstones and shales of the Franciscan com- monly contain carbonized wood and plant fragments. Mechanical disinte- gration predominated over chemical decomposition in the rugged area from which the Franciscan was derived. The basin of deposition of the Franciscan group was a geosyncline occupying a position between the ancestral Sierra Nevada and the present coast line. This geosyncline came into existence as a result of the Nevadan orogeny. West of the present coast line, a new high and rugged land mass came into existence, or an 37 Taliaferro, N. L., Geology of the Hollister quadrangle, California : Unpublished report. 38 Taliaferro, N. L., Franciscan-Knoxville problem : Am. Assoc. Petroleum Geolo- gists Bull., vol. 27, p. 187, 1943. GEOLOGY — LEITH 31 old land mass in this position was strongly uplifted. The thickness of the Franciscan in the Quien Sabe quadrangle is unknown, as nowhere within the area is it in contact with older rocks. On the basis of incomplete sec- tions which are exposed and which measure 10,000 feet,''^^ an estimate of 25,000 feet for the total thickness of the Franciscan is not excessive.^" Volcanic activity reached a maximum near the middle of this period of accumulation of clastic material, then lessened. Basic flows poured out, probably on the sea floor, and were accompanied by sills and other hypabyssal and shallow types of intrusions, all of which combined were responsible for the large contribution of silica that resulted in thick lenses of radiolarian chert. The entire sequence was intruded by ultrabasic magma that was commonly serpentinized either at the time of intrusion or shortly thereafter. Many of these intrusions metasomatically meta- morphosed the wall rock and produced glaucophane schists and related rock types. The deformation of the Franciscan is in marked contrast to that of the younger formations. At least two orogenic disturbances which took place between the Upper Jurassic and the Upper Cretaceous are recorded in other portions of the Coast Ranges. Although these disturbances did not greatly affect the position and extent of the geosyncline, they may have been the cause of the deformation and slight regional metamorphism of the materials deeply buried in the geosyncline. The weight of the over- lying sediments has probably caused the slaty appearance of many of the Franciscan shales. Furthermore, the presence of rigid intrusive masses within the Franciscan may account for the greater deformation of these sediments, as the rigid masses w^ould act as buttresses against which the sediments would be crushed during succeeding periods of deformation. Knoxville (Upper Jurassic) and Lower Cretaceous rocks are absent within the quadrangle and may never have been deposited in this area ; or they may have been completely removed by erosion prior to the deposition of the Upper Cretaceous sediments. A second sequence of arkosic clastic sediments with, thick conglom- erate lenses was deposited during Upper Cretaceous time. The conglom- erate, which contains Franciscan and Lower Cretaceous debris, probably reflects uplifts in the land area bordering the basin of deposition. The abundance of shale and fine- to medium-grained sandstones of Upper Cretaceous age indicates derivation from a comparatively low land mass, but the arkosic and f requentl}^ coarse nature of these sediments suggests rapid erosion of the source area by large streams. Early Tertiary sediments are absent in this region but the presence of the lower Miocene sea is indicated by the thin bed of Vaqueros lime- stone in a small area in the western portion of the quadrangle. Either the remainder of the area was above sea level during Vaqueros (lower Miocene) time, or erosion has completel.y removed what material was deposited. Volcanic activity was pronounced following the lower Miocene (Vaqueros), and extensive andesitic and basaltic debris accumulated along what is now the crest of the Diablo Range. Some of the pyroelastie material was deposited or reworked by streams flowing on the new land 39 Wilson, I. F., op. cit. p. 195. *^ Taliaferro, N. L., Franciscan-Knoxville problem: Am. Assoc. Petroleum Geolo- gists Bull., vol. 27, pp. 185-186, 1943. 32 QUIEN SABE QUADRANGLE [Bull. 147 surface. Plugs and irregular masses of intrusive andesite, centering in the northwestern portion of the quadrangle, were the feeders for this volcanic activity. A later phase of the volcanism consisted of intrusion of rhyolite into both intrusive and extrusive andesite. No flows, or pyroclasties, of rhyolitic material remain on the surface today ; they may never have been extruded, or perhaps active erosion in the region has removed whatever originally was present. Antimony and quicksilver mineralization, localized along faults which resulted from the disturb- ance accompanying the igneous activity, represents the final volcanic phase. Mineral veins are fractured and often brecciated. The present features of Ortigalita fault probably were developed during the upper Pliocene elevation of the Coast Kanges, when the Franciscan core of the Diablo Range was thrust outward over the border- ing Cretaceous sediments. The maximum deformation occurred along the margins of the mountain blocks. The cap of Quien Sabe volcanics at the center of the Diablo block was much less affected, but in places it was also thrust outward over Cretaceous sediments. .Faulting of the volcanic area continued into Quaternary time, but the upper Pliocene faulting and uplift in large part determined the present topography and was responsible for the establishment of a drainage pattern which, except for minor modifications, has continued to the present time. Gravels, sands, silts, and limestone accumulated in an upper Pleisto- cene lake in the central portion of the quadrangle. Terraces were formed along the edges of the valleys of the main streams of the area and two cycles of erosion ensued. The first reached a stage of late maturity, the second a stage of late youth or early maturity. ECONOMIC GEOLOGY Manganese Hendricl's (Cleveland) mine is located in sec. 24, T. 13 S., R. 8 E., M. D. The property covers 80 acres, with manganese occurring in rhythmically banded Franciscan chert in which some bands are as much as 5 feet thick. The workings consist of a caved inclined shaft on the hillside, and a trench 75 feet long, 20 feet wide and 20 feet deep, cut along the top of the outcrop. The shaft, 50 feet below the trench, report- edly w'as driven 135 feet and encountered the deposit about 80 feet from the collar, according to Bradley .^^ Four or five truck loads of ore were removed from the trench in 1944. The ore is typical Franciscan oxidized, manganiferous chert, containing carbonate and bementite (hydrous manganese silicate), oxidized to psilomelane near the surface. Fries Ranch Prospect. At the Fries Ranch prospect in the southwest quarter of sec. 9, T. 13 S., R. 8 E., M. D., a trench has been cut in man- ganiferous Franciscan chert. The ore is a puuky oxide derived from neotocite and occurs primarily in the thicker beds of the rhythmically bedded chert. An inclined shaft about 8 feet deep terminates in a stope at one end of the open cut. The dump is grown over with grass and weeds and the prospect apparently has not been worked in recent years. Manganese stain is pronounced on the Franciscan cherts cropping out in Herrero Canyon and Hoffman Canyon, near the eastern edge of the quadrangle, and in sees. 5 and 8, T. 13 S., R. 8 E., M. D. " Bradley, "W. "W., et al., Manganese and chromium in California : California Min. Bur. Bull. 76, p. 61, 191S. GEOLOGY — LEITH 33 Antimony Am'brose Mine. The Ambrose mine, also known as the Rip Van Winkle mine, is in see. 30, T. 11 S., R. 7 E., M. D. The last production from the mine was during' the first World War, but an attempt to recover stibnite from the dump was made during the recent war. The ore mineral is stibnite which, with a little milky quartz, occurs in a vein that strikes X. 20° W. and dips 65° SW. The country rock is intrusive andesite. Workings consist of adits on three levels, the lowest one flooded, and the upper one caved. In the second level, run about 250 feet into the hill- side, the stibnite vein pinches out 200 feet from the portal. Shriver mine, located in sec. 31, T. 11 S., R. 7 E., M. D., is caved and inaccessible. AVorkings apparently consist of two tunnels with drifts on the vein. The property was first exploited for quicksilver, and the ore also carried values in gold and silver.'*^ Blue Wing mine is in sec. 5, T. 12 S., R. 7 E., M. D., a short distance southwest of the Stayton mine. Workings are flooded, but according to Bailey and Myers ^■'' the ore is in northward-trending quartz-stibnite \eins which have been opened by a 75-foot vertical shaft with short drifts to the north and south. The ore is low grade. In November, 1948, the mine was again being worked, with the ore being hand sorted with the intent of shiiDping all better than 50 percent antimony. Other antimony properties within the Quien Sabe quadrangle include the Florence mine group in sec. 8, T. 12 S., R. 7 E., M. D., the French antimony group in sec. 5, T. 12 S., R. 7 E., M. D.. and the Gleason mine in sec. 6, T. 12 S., R. 7 E., M. D.^^ The ore in all cases is stibnite- bearing quartz of low grade. These properties are idle at the present time, with the exception noted. Quicksilver Staijton mine, in sec. 5, T. 12 S., R. 7 B., M. D., is being worked by the owner, Mr. R. B. Knox, and an assistant. Production is very small, approximately 1400 flasks having been recovered since 1880. A 12-ton furnace and retort is located on the property. The ore is cinnabar in quartz veinlets that fill fractures in basalt along a normal fault. Pyrite and stibnite occur with the quartz and cinnabar. The mine was located originally as an antimony property in 1870. The general strike of the veins is north-south with a steep dip to the west. Underground workings reportedly consist of an inclined shaft 250 feet deep, with levels at 70 feet, 150 feet, and 235 feet, and drifts of 150 feet, 775 feet, and 10 feet in length respectively.'*'' At present the deeper levels are either flooded or filled with waste. An adit 70 feet north of the main portal intersects what is probably the northerly extension of the main Stayton vein. The portal of the Yellow Jacket mine is about 500 feet northwest of the portal of the Stayton mine, in see.- 5, T. 12 S., R. 7 E., M. D. This mine has produced very little ore. Workings consist of an adit and a crosscut which are entirelv in nearlv barren basalt. ^- Angel, Myron, San Benito County: California Min. Bur. Kept. 10, pp. 516-51", 1890. *^ Bailey, E. H., and Myers, AV. B., op. cit., pp. 425-426. *^ Bradley, W. W., and Logan, C. A., San Benito County: California Min. Bur. Rept. 15, pp. 616-67.3, 1917. ^= Bradley, W. W., Quicksilver resources of California : California Min. Bur. Bull. 78, p. 96, 1918. 4 — 3163 34 QUIEX SABE QUADRANGLE [Bull. 147 Gypsy mine is about 2400 feet north of the Stayton mine and on the same fracture zone. The ore is cinnabar, associated with quartz and opal. Production has been small and workings consist of a stope open to the surface, several short drifts, and two adits. Comstock mine is in see. 19, T. 11 S., R. 7 E., M. D., in the south- eastern corner of Santa Clara County. The workings are flooded and par- tiall.y caved. The ore is cinnabar in silica-carbonate rock produced bj' the alteration of Franciscan serpentine. A northeast-trending fault, dipping moderately to the south, has localized the ore in the silicified serpentine of the hanging wall.^^ Crosscuts extend east and west from an inclined shaft immediately above the fault zone, and old stopes follow fractures in the silicified mineralized zone. Mariposa Mine. There is no record of production from the Mariposa mine, in sec. 28, T. 11 S., R. 7 E., M. D. The lower level of workings consists of three shafts connecting with an adit ; a raise joins this level with an upper level consisting of three adits, all caved. The principal shear zone consists of several closely spaced faults striking northwest and dipping moderately northeast. Very little cinnabar is present and no stibnite was seen. The same altered zone continues to the southeast where, about 1400 feet from the Mariposa mine, there are three shafts. One shaft is timbered and flooded. A caved adit and a prospect pit comprise the other workings at this locality. Other prospect pits are located in the northwestern portion of the Quien Sabe quadrangle. The Franciscan conglomerate in the northwest quarter of sec. 29, T. 11 S., R. 7 E.. M. D.. has been prospected with no apparent success. On the west side of Cathedral Peak, sec. 21, T. 11 S., R. 7 E., M. D., a caved shaft penetrates andesite at the contact with the rhyo- lite intrusive. A small amount of quicksilver "paint" was observed on some of the waste material. A small shear zone has been prospected in sec. 32, T. 11 S., R. 7 E., M. D., but the workings are now completely caved. Some of the veins of the Stayton mining district contain only anti- mony (Ambrose mine), some contain both antimony and quicksilver (Gypsy and Stayton mines) , and some contain only quicksilver (Mariposa mine) . The antimony and quicksilver deposition took place during several successive stages following the intrusion of andesite masses and along faults in andesite plugs. Thus the mineralization is later than all other igneous activity, with the possible exception of the rhyolite intrusions. A period of fracturing separates the time of quicksilver deposition from that of the earlier antimony. LITERATURE CITED Ander.son, Rol)ert. and Pack, R. W., Geology and oil resources of the west border of the San .Toaquiu Valley north of Coalinga, California : U. S. Geol. Survey Bull. 603, 220 pp., i;n."). Angel, Mvron, San Benito County : California Miu. Bur. Kept. 10, pp. 515-517, 1890. Aubury, L. E., Structural and industrial materials of California : California Min. Bur. Bull. 38, p. 336, 1906. Bailey, !•]. H., and Myers, W. B., Quicksilver and antimony deposits of the Stayton district, California :"u. S. Geol. Survey Bull. 931, pp. 40-5-434, 1942. Bailey, T. L., Late Pleistocene Coast Range orogenesis in southern California : Geol. Soc. America Bull., vol. 54, pp. 1549-1568, 1943. J» Bailey, E. H., and Myers, "VV. B., op. cit., p. 435 GEOLOGY — LEITH 35 Becker, G. F., Geology of the quicksilver deposits of the Pacific slope : U. S. Geol. Survey Men. 13, 486 pp., 1S88. Bradley, W. W., Quicksilver resources of Califoruia : California Min. Bur. Bull. r 78, p. 96, 1918. Bradley, W. W.. et al., Manganese and chromium in Califeins immediately belov^' the contact between the two volcanic units might uncover additional deposits of medium-grade quicksilver ore. 1 A flask contains 76 pounds. i STAYTON DISTRICT — BAILEY AND MYERS 39 INTRODUCTION The Stayton quicksilver and antimony district is on the crest of the Diablo Range 90 miles southeast of San Francisco and 13 miles northeast of Hollister, California (fig. 1). It is in Tps.ll and 12 S., R. 7 E., in the northwestern corner of the Quien Sabe quadrangle. The district lies mostly in northeastern San Benito County, but it also includes parts of southeastern Santa Clara County and western Merced County. The only good road into the district extends from Hollister, on the Southern Pacific 4oMiles Fig. 1. Index map showing the location of the Stayton district and tlie approxi- mate extent of the Miocene (?) volcanic field. Solid black shows area mapped ; ruled area shows volcanic field. Railroad, to the Stayton mine, which is the largest in the district ; other roads are passable only during the dry summer months. Little geologic work has been done hitherto in the region. Becker - briefly mentioned the mines, and Forstner^ made a reconnaissance map of the area in 1903. - Becker, G. F., Geology of the quicksilver deposits of the Pacific slope : U. S. Geol. Survey Mon. 13, p. 3S0, 1888. ■' Forstner, William, The quicksilver resources of California: California Min. Bur. Bull. 27, pp. 128, 147-149, 1903. 40 QUIEN SABE QUADRANGLE [Bull. 147 The field work furnishing the basis for this report was done during approximately two months in the spring of 1941. The areal geology was plotted on airplane photographs and later fitted to photographic enlarge- ments of the Quien Sabe topographic sheet. The operators and miners in the district, especially Mr. K. B. Knox, owner and operator of the Stayton mine, were uniformly courteous and helpful. The writers are indebted to E. B. Eckel of the Geological Survey for advice during the field work and the preparation of this report. HISTORY AND PRODUCTION The veins of the Stayton district were mined for antimony w^hen first worked, between 1870 and 1875, but the more valuable cinnabar was soon discovered. By 1876 the Stayton Mining Company had gained con- trol of the Gypsy, Stayton, and several smaller mines, and the company is rejDorted^ to have produced about 1,000 flasks of quicksilver before 1880. The Comstock mine in the northern part of the district was also discovered in the seventies and produced about 300 flasks prior to 1880. The production of the district from 1880 to 1920 is not known but is believed to have been very small. An accurate record is available only for the Stayton mine, which has produced 390^ flasks since the revival of mining in 1920. Tdhle 1. Pinducf ion of quicksilver, in flasks, from the Stai/ton mine. J92n-J,- o UJ o CO z o O UJ (O o z < < u o o _J o bJ o + :> ) 9 o < o 3 o o o UJ o UJ z < o CO o a < o o _J o llJ (9 OLAF P, JENKINS. CMIE U.S.OEP'T. OF THE INTERIOR GEOLOGICAL SURVEY BULLETIN 147 PLATE II Cinnabar only in silicif.ed zone above ^ Caverag^ faulx -^ ^ S 1720 1700' 1690' 1680- - V ^ ^ ^ -terpentine ' ^ — + 25 50 Feet + GEOLOGIC MAP AND SECTION OF THE COMSTOCK MINE SANTA CLARA COUNTY, CALIFORNIA DIVISION OF MINES OLflF P JENKINS, CHIEF STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES BULLETIN 147 PLATE 3 LEGEND >- — 5 UJ » a! -J Qls z Qol H < a QP Terroces (Numbers indicate levels) Peckhom formotion Pleistocene lake beds -T^'+"] itfusive rhyolite Intrusive andeslte Quien Sabe volcanics Andesile and basolt flows ond agglomerate Tvq Voqueros formotion r^Ku ^^ Upper Cretaceous l'^ -'^~^) Sondsfone, stiole ond conglomerote *> / ' ' .•i