1 TN I ^^ ' C3 H= A3 STATE OF CAIlFOBmA DEPABIMENT OF NA.TOHAL EESOOBCBS GEOLOGY Rm MINERAL DEPOSITS OF BARSTOW QUADRANGLE SAN BERNARDINO COUNTY, CAIJ^ORNIA BuHelln 165 1S54 DIVISION OF MINES FERRY BURDma SAIf FBANOSCO r^iaHHHBaBHBBHMBiaHBaaaaaBBianaaBHHBBi^Bssai .^ ^^ THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA DAVIS I 4 MMa^—^^UiteadM STATE OF CALIFORNIA GOODWIN I. KNIGHT, Governor DEPARTMENT OF NATURAL RESOURCES DeWITT NELSON, Director DIVISION OF MINES FERRY BUILDING, SAN FRANCISCO 11 OLAF P. JENKINS, Chief SAN FRANCISCO BULLETIN 165 April 1954 GEOLOGY AND MINERAL DEPOSITS OF BARSTOW QUADRANGLE SAN BERNARDINO COUNTY, CALIFORNIA By OLIVER E. BOWEN, JR. and THERMAL PROPERTIES OF CERAMIC MATERIALS FROM BARSTOW QUADRANGLE, CALIFORNIA By JOSEPH A. PASK AND OLIVER E. BOWEN, JR. LIBRARY UNHVERSITY OF CALIFORNIA DAVIS ,Ar«^ '* LETTER OF TRANSMITTAL To His Excellency The Honorable Goodwin J. Knight Governor of the State of California Sir: I have the honor to transmit herewith Bulletin 165, Geology and Mineral Deposits of Barstow Quadrangle, San Bernardino County, California, prepared under the direction of Olaf P. Jenkins, Chief, Di- vision of Mines, Department of Natural Resources. The report is ac- companied by detailed colored geolofjic and economic mineral maps, charts and cross sections, and many other illustrations. The area cov- ered by the report lies in the ]\Iojave Desert and embraces 976 sciuare miles, a 30-minute quadraujorle. The mineral deposits descril)ed consist of Limestone, dolomite, ganister (quartzite), barite, magnesite, pyro- phyllite, mica-quartz fillers and ornamental stone such as marble and granite, which are the chief non-metallic minerals of the area; gold, silver, iron, copper, lead, zinc and tungsten, the metallic minerals. The underground water supplies of the area are also discussed as they are related to the geology. The report represents one of the basic geologic map projects of the Division of Mines. It has been prepared by a member of the statf, Oliver E. Bowen, Jr. Included with Bulletin 165 is another report, representing the results of laboratory investigations of some peculiar ceramic materials found in the area. This report is entitled, Therynal Properties of Ceramic Materials From Barstow Quadrangle, California. It has been prepared by Joseph A. Pask, pro- fessor of Ceramic Engineering, University of California, in cooperation with Oliver E. Bowen, Jr., of the Division of Mines. Bulletin 165 should be of value in the development of all manner of natural resources found in the area and especially of assistance in the development of the min- eral industrv in this desert region. -o' Respectfulh' submitted, DeWitt Nelson, Director Department of Natural Resources January 12, 1954 (3 ) CONTENTS Page Geolofiv and mineral deposits of Barstow quadra ii^rle, San Ber- nardino County, California, by Oliver E. Bowen, Jr 7 Thermal properties of ceramic materials from Barstow quadrangle, California, by Joseph A. Pask and Oliver E. Bowen, Jr 186 Index 201 PLATES Plate 1. Geologic map of Barstow quadrangle. San Bernar- dino County, California^ In pocket 2. Economic map of Barstow (quadrangle, San Bernar- dino County, California In pocket 3. Geologic structure sections across Barstow quad- rangle, San Bernardino County, California In pocket 4. Geologic map of Sparkuhle Hill area In pocket 5. Geologic map of Black ^Mountain limestone conglom- erate In pocket 6. Outline geologic map of Quartzite ^Mountain, with aerial photograph In pocket 7. Geologic map of Sidewinder mine ai'ca and aerial photograph In pocket 8. Geologic map of Ilodge area and aerial jiliotograph- In pocket 9. Aerial photograph of llelendalc fault and Stoddard dike complex In pocket (5) ■ ''P\1j GEOLOGY AND MINERAL DEPOSITS OF BARSTOW QUAD- RANGLE, SAN BERNARDINO COUNTY, CALIFORNIA By Oliver E. Bowen, Jr.* OUTLINE OF REPORT Page Abstract 10 Introduction . 11 Descriptive geolopy 17 Paleozoic and Mesozoic rocks 17 Waterman gnP'ss 17 Oro Grande series 23 Fairview Valley formation 36 Hodjre volcanic series 34 Sidewinder volcanic series 42 Granitic rocks 53 Tertiary rocks 76 Miocene( ?) continential deposits 76 Miocene(?) volcanic rocks 83 Pliocene volcanic rocks 85 Quaternary rocks 88 Pleistocene alluvium 88 Recent deposits 92 Structure 93 Folds 95 Faults 103 Phj^siography and physiographic evolution 107 Geologic history 113 Mineral deposits 119 Metallic minerals 119 Copper 119 Gold 123 Iron 134 Lead-zinc-silver 136 Silver-barite 138 Tungsten 139 Non-metallic minerals 140 Asbestos 140 Barite 140 Clay 141 Dimension stone 145 Dolomite 148 Mineral fillers 150 Abrasive cleanser 150 Mica schist 151 Sericite-quartz i-ocks 152 Pyrophyllite 158 Limestone 160 Magnesite 170 Marl 172 Sand, gravel, and crushed rock 173 Silica (ganister) 174 Water 179 Petroleum 181 Bibliography 183 Illustrations Frontispiece — Aerial oblique photograph of Barstow and vicinity 6 Figure 1. Index map showing location of Barstow quadrangle — 12 la. Index map showing names of physiographic features 14 2. Stratigraphic column, Barstow quadrangle 16 3. Photo showing parallel structures in Waterman gneiss 18 4. Photo showing joints in Waterman gneiss 19 * Associate mining geologist, California Division of Mines. Manuscript submitted for publication July 1953. ( 7 ) BARSTOW QUADRANGLE [Bull. 165 Page 5. Photoniicrosraphs of Waterman gneiss ^ 20 6. Photomicrographs of hornblende diorite, "Waterman and Hinkley Hills 21 7. Photo of sedimentary breccia, Oro Grande series, Sidewinder Moun- tain 24 8. Photo of detail of sedimentary breccia, Oro Grande series 25 9. Photo of coxcomb ridge of massive quartzite, Oro Grande series, Quartzite Mountains 26 10. Photo of banded limestone, Oro Grande series west of Reserve Quarry 27 11. Photo of streaked carbonate rock, Oro Grande series. Red Seal Ridge 28 12. Photo of contorted carbonate rock deformed by plastic flow, Oro Grande series. Red Seal Ridge 29 13. Photo of uniformly banded, contact-altered limestone west of Reserve quarry 30 14. Photo of contact altered limestone. Reserve quarry 31 15. Photo of unusual joint pattern in massive limestone, Oro Grande series. Red Seal Ridge 32 1(1. I'hoto of quartz-mica schist, strongly deformed, Hinkley Hills 33 17. IMioto of limestone conglomerate, Fairview Valley formation, Black Mountain 37 18. Photo of crude bedding in Fairview Valley limestone conglomerate 38 19. Photo of t(>nsional joints filled with white calcite in a limestone lens of the lower member of the Fairview Valley formation 39 20. Photo of (|uartz porphyry dike cutting hornfels member of Fairview Valley formation 40 21. I'hotomicrographs of Hodge metadacite and Sidewinder metadacite tuff 44 22. I'hotomicrograph of Sidewinder metarhyolite and dacite 45 23. IMiotoniicrograph of Sidewinder meta latite-andesite 48 24. Phdto of psfudo-hedding in massive metadacite of Sidewinder series. Sidewinder ^Mountains 49 '2~>. Photo of comple.x jointed, hydrothermally altered felsite, Side- winder series. Split Rock Mountain 49 20. Photo of lahar or mud flow conglomerate, Sidewinder series south of P>all magnesite mine 50 27. Photo of multiple sills of fine-grained latite-andesite. Sidewinder series. Red Seal Ridge 50 28. IMioto of tournialinized quartz porphyry. Sidewinder series, Stoddard Mountain 51 29. Photomicrograph of tournialinized quarts porphyry 52 30. IMioto of alaskite intrusions cutting Oro Grande series, Red Seal Ridge 55 31. I'hoto of typical exposure of quartz monzonite, Fairview Valley, Granite Mountains 55 32. IMioto of odd weathering pattern in quartz monzonite, Granite Moun- tains 56 33. I'hoto of unusual cracking in sheeted quartz monzonite. Granite ]Moun tains 56 34. Photo sliow lug three generations of granitic rocks, Stoddard dike complex 57 3."). Photo of slieeted quartz monzonite between Victorville and Side- winder Well 58 30. Photo of (luartz monzonite crammed with quartz diorite inclusions, Quartzite Mountains 59 37. Aerial i)hoto of P.<'11 Mountain showing distribution of hornblendite and schriesheimitc 60 35. Ph. ltd of injection gneiss. Hinkley Hills 61 39. I'hotomicrographs of spessartite and quartz monzonite porphyry 62 40. Photomicrographs of alaskite and quartz monzonite 63 41. Photomicrogi-ajihs of (piartz diorUe and granodiorite porphyry 70 42. Photomicrographs of schriesheimite and gabbro-diorite 71 43. (ieologic map of the Miocene section in Kramer Hills 78 44. Photo of contorted Miocene lake beds near Calico 79 4.1. I'hoto of Miocene tuff and lake beds in the Barstow syncline 80 4(). Photoniicrographs of Miocene quartz andesite and olivine analcite .lial)ase 82 47. Photomicrographs of Pliocene dacite and rhyolite tuff 86 l!)r)4] GEOLOGY AND IVIINERAL DEPOSITS 9 Page 4S. IMiolo nf iipiici- ricistncciH" (Icposits, Piilisinlfs of the Mojave River 87 4!). riioto lit" li.isal caliclic ifiiiciilcd lircccia, uiipor ricistdcciic hcds north of C^)iiarl/.it(' .Mountain 80 .">(». riiolo sliowin;; detail of caliche-cMMiieuted brecciii, upper Pleistocene iieds inn-tli of (»uai-t/.ite Mountain 90 Til. I'hoto of a Recent talus cone cemented by caliche, north flank Quartz- ite Mountain 91 ■VJ. IMioto of (•aliehe-ceuH-nted arkose. Pleistocene beds east of Harper Lake road 92 .">:',. IMioto of scarps of the Ilelendale fault, north end Fairviow Valle.v__ 94 r>4. Photo showiui; fault contact between Oro (Jrande series and Side- winder series. Rail ma^nesite mine 98 ri.'i. Photo showiiii; flatinni of limestone, Quartzite Mountain thrustplate 100 .">(>. Photo (tf side of flat iron shown in figure ")"), northeast slope Quartzite Mountain 101 ."iT. Profile of Leuwood anticlinal dome 104 .'iS. Plioio of Stoddard ell Mountain area 108 (10. Photo of P.ell :Mountain 108 C.l. Photo of dissected pediment. Lower Narrows near Victorville 109 ('r_'. Photo of I'pper Narrows (Jor^e, Victorvill(> 110 (;:;. Photo of dissected f;in of Pleistocene alluvium overlapping basement rocks on Quartzite Mountain 111 (il. Photo of .\uiazon mine 122 (i."). Photo of Sidewinder mine 132 ()(i. Photo of cif inai-hle. Three Color (pi.-irry _ 147 (ill. Photo showinu character of rock in Marshall filler deposit 152 70. Photo of contact hclwecu altered and unaltered rock at Marshall Hllcr deposit 153 71. Photo of ni.iin i>it, INIarter Mining Company filler deposit 155 7l'. Photo of dike of unaltered latite-andesite cutting north wall of Mar- ter Mining Coinp;iuy"s main pit 156 73. Photo of dike of unaltered l;it ite-andesite in the iNIarter Mining Com- p.niy's south pit 157 74. Photo of Victorite ])yrophyllite deposit, main quarry 159 70. Photo of Ideal Cement Company's Quartzite ^Mountain limestone deiiosit „ 162 7(». Photo of Riverside Cement Comi)any's Klondike (puirry 163 77. Photo of Riverside Cement Companv's schist (piarry, Quartzite Moun- tain _■ 164 75. Plioto of Southwestern Portland Cement Company's Reserve quarry 166 7!'. Photo of dikes in limestone of Reserve quarry 166 50. Photo of Southwestern Portland Cement Company's Black ^Mountain (piarry, December 1948 168 51. Photo of Mineral ^hiterials Company's silica quarry near Oro Grande 172 52. Photo of Mineral ^Materials Company's silica quarry, detail of proc- essing eciuipment 173 83. Photo of Vitrlite marl i)it and loading platform 174 84. Photo of P.all magnesite mine, portal, main adit 175 PLATES Plate 1. Geologic map of Barstow (luadrangle, San P>ei-n;irdino County, California - In pocket 2. Economic map of Barstow quadrangle, San Bernardino County, California In pocket 3. Geologic structure sections across Barstow quadrangle, San Ber- nardino County, California In pocket 4. Geologic map of Sparkuhle Hill area In pocket 5. (Jeologic map of Black M(nintain limestone conglomerate In pocket 6. Outline geologic map of Quartzite Mountain, with aerial photo- graph In pocket 7. Geologic map of Sidewinder mine area and aerial photograph In pocket 8. Geologic map of Ilodge area and aerial photograph In pocket 9. Aerial photograph of Ilelendale fault and Stoddard dike complex In pocket 10 BARSTOW QUADRANGLE [Bull. 165 ABSTRACT Barstow quadrangle embraces 976 square miles of the southwestern Mojave Desert, lying between the San Bernardino Range on the south and Harper Dry Lake on the north. The center of the area is 42 airline miles north of San Bernar- dino or 30 miles northeast of the summit of Cajon Pass. Limestone, dolomite, ganister (quartzite), barite, magnesite, pyrophyllite, mica- quartz fillers and ornamental stone such as marble and granite are the chief non- metallic minerals of Barstow quadrangle. ^Metallic mineral deposits include gold, silver, iron, copper, lead, zinc and tungsten. "Water supplies of consequence are obtainable along the Mojave River, Adelanto district, Hinckley Valley, Apple Valley, Lucerne Valley and probably Fairview Valley. In other places, water is scarce or absent. The great are of the Mojave River is the dominant geographic feature and the numerous mountains and hill groups on both sides of its course are lai-gely isolated from each other by alluvial fill. Pre-Upper Jurassic rocks occur essentially as roof IX'udauts lying in granite, and Tertiary rocks as erosion remnants lying on the pre- Cretaceous basement. The Waterman gneiss, Hodge volcanic series, and Oro Grande series of probable Paleozoic age are the three oldest rock groups exposed in the quadrangle. The Waterman gneiss is believed to be younger than the Oro Grande series and intrusive into it ; the Hodge series is not in contact with other Paleozoic units. Unconforniably overlying the Upper Paleozoic Oro Grande series is the Permian Fairview Valley formation. This in turn is overlain by the Sidewinder volcanic series of probable Triassic age. These rock groups have been intruded by a variety of granitic rocks, chiefly quartz monzonite, quartz monzonite porphyry, and horn- blende gal>l)ro-diorite. Granitic rocks were intruded within the Upper Jurassic- Lower ("retaceous interval. Upper Miocene ( '!) continental deposits, both fluviatile and lacustrine, crop out in widely scattered patches. Quartz andesite and dacite flows are found inter- bedded with the continental deposits and olivine arsto\v. The course of the Moj.-ive River through the (piadrangle has l)een con- trolled largely l)y this structure. Broad, relatively simi)le folds having northeast- er east-trending axes are characteristic of an early (the end-I'aleozoic) period of 1954] GEOLOGY AND MINERAL DEPOSITS 11 foldiiiK and are in sharp contrast to the acute, complex, northwest-trending folds that (It'velopeil ihirinir a later iK>rio(l. Sharp local foldinj; and fatiltinji in lower and middle Pliocene time have deformed the Miocene sections nearly everywhere, and gentle Recent arching probably related to the main fault system locally has affected Pleistocene beds. Regional uplift in Recent time amounting to at least 20<) feet has resulted in deep dissection of the I'leistocene deposits and establishment of new aggradation jdains. C"ai)ture of part of the watershed of the Mojave River by Cajon Creek has changed the entire drainage pattern of the Mojave River tributaries in the southwestern part of Rarstow quadrangle. A probable southeast-flowing drainage system which may once have emptied into the Colorado River has been destroyed. Exhumed remnants of Miocene land surfaces are present north of the Mojave River in the vicinity of Hodge and Barstow and relict Pleistocene surfaces are evident east and west of Oro Grande. A lake existed in fairly recent time south of the Upper Narrows of the Mojave River at Yictorville. Marine sedimentation in the Barstow area evidently culminated in a series of disturbances that took i)lace near the end of the Paleozoic. No marine transgression is known to have reached the area since the Permian. Paleozoic deposits were folded and subjected to erosion before continental A-olcanism broke out in probable Triassic time. During the I'pper Jurassic-Lower Cretaceous interval, a second folding period ended in widespread invasion of granitic rocks which now are exposed on. or iinderlie at shallow depth, the entire quadrangle. There is no record of sedimentation or of influx of igneous material between the time of emplacement of the granitic rocks and middle Miocene time, and a long period of erosion stripped the cover from the granite in many places. Floodplain and lacustrine deposition, accompanied by volcanism, went on in a discontinuous series of basins during most of the upper Miocene and probably persisted locally into the lower Pliocene. In mid-Pliocene time these basins were destroyed by intense though probably shallow folding as well as faulting. Another widespread outbreak of volcanic activity in the upper Pliocene added many hundreds of feet of volcanic material to the Tertiary deposits. INTRODUCTION Location and Acccssihilify. Barstow qnadranp-le includes 976 square miles of the southwestern Mojave Desert, stretehinp' north from the San Bernardino Range and Lucerne Valley to Harper Dry Lake. The center of the area is 42 airline miles north of San Bernardino or 30 miles northeast of the sunmiit of Cajon Pass. Barstow is situated only a few miles from the northeast corner of tlie quadrangle and Yictor- ville is near the southwest corner. The Shadow Mountains adjoin the quadrangle on the west and the Ord Mountains on the east. U.S. High- ways 66, 466, 91 and 395 traverse the area as do the Union Pacific and Santa Fe Railroads. Climafc and Topography. Because of proximity to Cajon Pass and because of relatively high local base levels, which range from 2000 to 3200 feet, the climate of the Barstow- Yictorville area is cooler and rainier than many other parts of the Mojave Desert. Precipitation averages 5.48 inches (Simpson, 1951, pp. 487-488) at Yictorville and 4.17 inches at Barstow. Cool air coming over Cajon Pass and down Mojave River wash has its effect on most of the area. The Mojave River, which flows through Yictorville and Barstow in a great arc convex to the nortliwest, greatly modifies the arid cycle of erosion because it rises in the well-watered San Bernardino Range. Away from the river, which in most places has a flood-plain many hundreds of yards wide, the land surface consists of isolated hills and mountains or mountain groups partly buried in their own debris. Some mountain groups are separated by intermontane basins containing 12 BARSTOW QUADRANGLE [Bull. 165 D c 1954] GEOLOGY AND MINERAL DEPOSITS 13 playa lakes; others have become part of the Mojave Kiver drainage. The Sidewinder and Granite Mountains occupy much of the southeast corner of the quadrangle and summits of several peaks in this group lie above 5200 feet. The lowest part of the quadrangle is in the extreme northAvest portion at the border of Harper Dry Lake where elevations are 2040-2045 feet. Field Work and Base Maps. Geologic mapping of the quadrangle was started in August 1940 and continued intermittently until July 1952. Most of the detailed work was done between June and September of 1949. Field expenses were partly defrayed by the State Division of Mines and the University of California. The principal base map used was the 30-minute U. S. Geological Survey Barstow Quadrangle sheet surveyed in 1920 and 1932 by the U. S.' Geological Survey and the City of Los Angeles. This sheet is drawn on a scale of 1 inch equals 2 miles or 1 :125000. Supplementary detailed mapping was done on aerial photograph overlays and on topo- graphic maps supplied by Southwestern and Riverside Cement Com- panies. Acknowledgments. The helpful suggestions of Olaf P. Jenkins, Gordon B. Oakeshott, Lauren A. Wright, Charles W. Chesterman. and Mort D. Turner, staff members of the Division of ]Mines who spent several days in the field with the author, are gratefully acknowledged. The author is particularly indebted to D. F. Hewett of the U. S. Geological Survey for procurement of aerial photographs, for time spent in the field, for a great deal of comparative data on many parts of the Mojave Desert, and for maiu' helpful suggestions. Valuable inter- change of information concerning adjacent desert areas was also had with Hoyt S. Gale, Thane McCulloh, T. W. Dibblee, Robert Guillou. and the late Chester Stock. Cooperation of the staff of tlie Southwestern Portland Cement Com- pany, particularly B. H. Dunham, R. M. Willson, Felix INIcGinnis and M. Goodall. as well as R. M. Wightman of Riverside Cement Company, and R. M. Richter of Marter Mining Company, is greatly apprt>ciated. Lionel Weiss of the L^niversity of California did a petro-fabric study on some of the severely deformed rocks of the Oro Grande series east of Hinkley and the author is grateful for the use of the results ot that study. William Smiley of Stanford Research Institute kindly turned over the findings of his research on Marter ^Mining Company's filler materials. ^Marshall Maddock and Melvin Stinson then of University of California assisted in laboratory separation and testing of fine- grained mica and Dion L. Gardner made available numerous thin sec- tions of Ord ^Mountains rocks. The author is also indebted to Francis J. Turner, Howell AVilliams. Adolph Pabst, and Joseph Pask of the faculty of the University of California who have given freely of their time in discussing petro- graphic, mineralogical, field, and ceramic problems connected with tliis study. Fo.ssil determinations were made at various times by James Steele AVilliams and staff of the U. S. National :\Iuseum, Charles AV. :\Ierriam of the U. S. Geological Survey, 11. Rodney Gale of Pasadena City Col- lege, J. Wyatt Durham of the University of California and Siemon 14 BARSTOW QUADRAXGLE [Bull. 165 Figure la. Index map of the Barstow quarlranple showins: names of physiojjraphic features mentioned in the text. Underlined names are in local use but not shown on the topographic map. 1954 J GEOLOGY AND MINERAL DEPOSITS 15 W. ]\Iuller of Stanford University, all of whom have given freely of their time. Previous Works. Published works pertaining to the geology of Bar- stow quadrangle consist mainly of short statements based on investiga- tions of reconnaissance nature or else concern areas adjacent to tlie Bar- stow area. The most recent data (1946) are contained in a paper by Gale (1946) on the Kramer borate district which lies close to the north- west corner of Barstow quadrangle. Some of the rock units and his- torical events mentioned in this paper apply to the Barstow region as well. A reconnaissance report on three separate parts of Barstow (piad- rangle by Miller published in 1944 contains the only detailed descrip- tion of the immediate area embraced in this report. It contains petro- logic and petrographic descriptions of several proposed rock groups, correlation data, and some generalized maps. Gardner's (1940) lengthy reconnaissance report on the Xewberry and Ord Mountains describes a large area adjoining Barstow ciuadrangle on the east. Some rock units described therein are present in Barstow qu-adrangle. Gardner's account contains much data on petrography, structure, correlation of formations, and geologic history. Reports on mineral resources of San Bernardino County have been published by the State Division of ]\Iines from time to time ; the most recent of these appeared in 1943 and 1953 (Tucker, 1943; Wright, et al, 1953). They contain data on the geology of a number of mines and mineral deposits located in Barstow quadrangle. The State Geologic Map, compiled by Olaf P. Jenkins of the Divi- sion of Mines and published in 1938, covers Barstow quadrangle, but that part of the map is incomplete and overgeneralized. So also is the map and geologic account that accompanies Water Supply Paper 578 from which that part of the state geologic map was compiled. Yaughan (1922) described a large area in the San Bernardino ]\Ioun- tains that corners on Barstow. quadrangle to the southeast. Some rock units described in this work probably correspond to some on Barstow quadrangle and some of Vaughan's tectonic lines extend northwest onto Barstow quadrangle. A small area in the San Bernardino ^Mountains originally mapped by Vaughan has been re-mapped by Guillou (1953). Pack (1914) discussed reconnaissance geology and oil possibilities of an area north of Barstow. He also described (1914) an ornamental lime- stone deposit on the north flank of Sidewinder Mountain and included two chemical analyses of the rock described. Age relationships and petrographv were briefly discu.ssed. Darton (1915) in his guidebook for the Santa Fe route describes some of the rocks found in Barstow quadrangle. Reconnaissance maps are included. Hershey (1902) in his description of numerous crystalline rocks of southern California describes several rock units on Barstow quadrangle and discusses their correlation. Brief references to the geologic history of the southwestern Mojave Desert mav be found in the writings of A. C. Lawson (1916). AY. M. Davis (1933, 1936, 1938), C. L. Baker (1911), and J. C. Ilazzard (1936, 1937). 16 BARSTOW QUADRANGLE [Bull. 165 ERA PERIOD OR EPOCH SERIES OR FORMATION SYM- BOL COLUMN THICKNESS IN FEET LITH0L06Y - 100 Alluviimi and fanglomerate o o UJ o Recent Alluvium Qal Pleistocene Alluvium Qoal Pliocene Volcanics Tvr Miocene ? Continentol sediments and volcanic rocks. Tmc tx^'^uvium, fanglomerate and playa lakebeds Red, pink and gray dacite and rhyolite flows & pyroclastlcs -4800 White opaline and magnesitic shales, buff limestone, red & green clays, black quartz an- desite (Tma) flows, granite sands 2000 Granite sands and fanglomer- ate, red clays Oo 5M Triossic? Sidewinder volconic series 4000 Green and green! sh-b lack dac- ite and andesite tuff: red, pink and white rhyolite and dacite .. ..|i.....,.-l,.s.. T li,''liil|l»IIIIMII|l!lll|IUII> upper Paleozoic '' Hodge volcanic series hv 10,000 msimrniMh White and gray muscovite and biotite schists, reddish- brown to lavender -brown mas- sive dacite and dacite tuff, white tuffaceous sands, white, kaolinized felsite, white to pinkish quartzite; generally weathered in shades of red and lavender \\\mh:miMim' Permian o N o UJ _J «I a. Foirview Valley formation Pf Carboniferous Oro Grande series Cog Upper Paleozoic ? Woterman gneiss wg 6075 Dark gray limestone conglom- erate, gray-green hornfelsed, silty and sandy limestones, dense, black limestone in thin lenses 9670 Blue-gray and white lime- stone and dolomite, pinkish- white quartzite, black and brown quartz -mica schist, green ealc-silicate horn- fels, coarse multicolored dolomite breccia, dark brown argillite and horn- fels 4000 Black hornblende-plagioclase- quartz-mica gneiss and local diorite and pegmatite Figure 2. Stratigraphic column, Barstow quadrangle. 1954] GEOLOGY AND MINERAL DEPOSITS 17 DESCRIPTIVE GEOLOGY Rocks exposed in Barstow quadrangle range in age from Middle Paleozoic (?) to Recent. The geologic record over this span, however, is incomplete as there are no known rocks of Upper Cretaceous, Eocene, Oli'^ocene or lower Miocene age. Acid plutonic mstrusive rocks either are^exposed on or underlie at shallow depth much of the land surface between Harper Drv Lake and the San Bernardino Range. Lying m and intruded by the Jura-Cretaceous granitic rocks are metasedimen- tarv and metavolcanic roof pendants of Upper Paleozoic and Triassic (?) ao-e Lying on this old crystalline complex are scattered remnants of Miocene' and Pliocene continental sedimentary and volcanic rocks and broad expanses of Pleistocene and Recent alluvium. PALEOZOIC AND MESOZOIC ROCKS Waterman Gneiss The Waterman gneiss has been named by the author from a well- exposed section Iving south of the Camp Irwin road opposite the Wa- terman silver mine. It covers 3^ square miles of Barstow quadrangle and extends east into unmapped territory for an undetermined dis- tance The tvpe section is found in a deeply eroded, northeast-trending broad, simple anticline in which at least 4000 feet of meta-igneous and metasedimentary rocks are exposed. In the northern limb of the anti- cline almost the entire width of which is exposed on Barstow quad- rangle the lowermost 2300 feet' of the formation consists predom- inantly of strongly foliated, partly mylonitized hornblende-plagioclase gneiss The upper 960 feet of the formation in the north limb consist^ of lenses and plates of marble, mica schist and quartzite intercalated with hornblende-plagioclase gneiss. The metasedimentary plates and lenses ranoe in thickness from a few feet to more than 100 feet and are traceable along the strike from a few feet to more than 500 feet. Most of them are less than 30 feet thick. i,- -u • In the southern limb of the structure, only a small part ot which is exposed in Barstow quadrangle, 4000 feet of hornblende gneiss is over- lain by an undetermined thickness of carbonate rocks, mica schist and quartzite. Wedges of hornblende-plagioclase gneiss penetrate the meta- sedimentary beds in parallel fashion to some extent m the south limb of the structure, but for the most part continuity of the sediments ot the south limb is broken only by relatively undeformed intrusions ot quartz monzonite, quartz monzonite porphyry, and associated 1am- prophyres. Granitic rocks of these types also penetrate other parts ot the structure as dikes and sills. In the most deeply eroded crestal part of the structure, the gneiss grades imperceptibly into a much less deformed rock closely resembling hornblende diorite. 'Similar transitions occur locally higher up m the structure. Even in this granitic-appearing rock, however, foliation, or at least lineation, parallel to the bedding is never completely obliter- ated and some crushing is always evident. In the more deformed por- tions of the gneiss a conspicuous set of slip surfaces developed parallel to the axis of the anticlinal structure, i.e., at right angles to the major crustal shortening, is everywhere conspicuous. 18 BARSTOW QUADRANGLE [Bull. 165 S**V^ Figure 3. An exposure of "W^aterman gneiss showing persistent schistosity and slip surfaces. These planar structures are parallel to the bedding of the overlying metasedi- ments of the Ore Grande series. The gneiss was derived from hornblende diorite. Carbonate remnants in the AVaterman gneiss, particularly those of the north limb of the anticline, commonly show extensive contact meta- morphism with development of epidote-amphibole-garnet tactites and concentrations of specular hematite. Severely deformed granite peg- matites and aplites, present as dikes and sills a few inches to a foot or two thick, are characteristic of both the gneissic and metasedimen- tary parts of the formation, particularly in the upper part of the north limb of the structure. Intrusions of small plugs of Tertiary rhyolite and dacite have caused local alteration of the gneiss into a conspicuous blue earthy rock com- posed of tourmaline, quartz and clay, all finely divided. Veins of coarsely crystalline barite, probably associated in time and origin with the Waterman and Calico silver mineralization, cut the formation in several places. Petrography of the HornMende Gneiss. In thin section the gneiss making up the bulk of the formation is a strongly foliated, thoroughly crushed rock in which recrystallized material generally is subordinate to relict fragmental material. The proportions of hornblende and ande- sme (An 35-40) vary between 40 and 60 percent, hornblende generally being in excess of andesine. One to three percent of iron oxides, both hematite and magnetite, is invariably present; hornblende, andesine and iron oxide minerals being predominantly relict. Biotite, either relict or secondary, is rare. Quartz, largely if not wholly secondary, is present 1954] GEOLOGY AND MINERAL DEPOSITS 19 Figure 4. An exposure of Waterman gneiss near the axis of the Waterman anticline. The principal set of joints is roughly perpendicular to the schistosity and very slightly oblique to the axial trend. Slip surfaces are also strongly developed parallel to the fold axis. in variable amounts, both in lenticular, ragged folia and in crosscutting veinlets. In some quartz-rich folia, granulite texture is conspicuous. Late-stage secondary chlorite after hornblende, probably of hydro- thermal origin, is abundant, together with minor though widely dis- tributed amounts of epidote, clinozoisite and sphene. Metamorphic segregation of hornblende and andesine varies widely in completeness. Some thin sections show distinct separation of mineral species into folia whereas most show incomplete separation with large crystals or crystal clots of one species included in folia made up of smaller fragments or recrystallized mosaics of another species. Trains of fine-grained f ragmental material commonly flow around these larger crystals and obvious rotation of many large crystals in the principal plane of shear is evident. A few thin sections show almost equidimen- sional fragmentation of hornblende, andesine crystals 1-2 mm in average dimension. Bands a centimeter to a few inches wide of minutely and almost completely crushed material may be seen megascopically. Kelict grains of hornblende and andesine 4-5 mm in average dimension are not uncommon. Hornblende crystals are commonly and conspicuously twinned on [001] or [100], simple twinning being commonest but lamellar twinning being well represented. Hornblende is pleochroic in shades of dirty green or blue green and light brown. Andesine crystals almost invari- ably show complex twinning by several combinations of laws. Bent 20 BARSTOW QUADRAXGLE [Bull. 165 Figure 5A. Photomicrograph of Waterman gneiss, plane polarized light, X19. Light mineral grains are chiefly andesine and dark grains blue-green hornblende, but there is a little metamorphic quartz. Figure 5JS. Same field as in fig. 5A under crossed nicols. Crushed character of rock is clearly shown together with partly rotated relict andesine crystals about which secondary minerals are moulded. Trains of fine-grained, .^utured quartz mingled with andesine are interlami- nated with coarser-textured bands of relict, broken crystals. The large metacryst in the lower left quadrant is andesine not oriented to show twinning. 1954] GEOLOGY ANT) MIXERAT, DEPOSITS 21 Figure 6A. Photomicrograph of a relatively undeformed specimen of hornblende diorite from the Hinkley Hills, plane polarized lisrht, X19. Light-colored and mottled grains are andesine in various stages of saussuritization ; dark, translucent grains are blue-green hornblende and black grains are magnetite. Figure fiB. Gneissoid hornblende diorite from Hinkley Hills. Note the bent and fractured lamellae in the large andesine crystal in the upper right quadrant. Other specimens are much more severely crushed or made gneissoid. Plane polarized light, XI!*. 22 BARSTOW QUADRANGLE [Bull. 165 lamellae, fractures and strain shadows are common deformation features in hornblende, andesine and quartz crystals. Origin, Age and Correlation. Sedimentary remnants found in and above the AVaterman gneiss almost certainly belong to the lower part of the Oro Grande series, although no fossils have yet been found in them east of the Waterman thrust. Two miles west of the faulted end of the main structure, however, gastropod and echinoid debris of prob- able Upper Paleozoic and possible Pennsylvanian age ^ is found in lime- stone of an isolated thrust plate remnant. This remnant most probably was once connected with the overthrust block east of the Waterman fault, but the connection has been obliterated by erosion. If the fore- going assumption is correct, the fossil debris supports the lithologic evidence of correlation with the Oro Grande series. The lithology is strikingly similar to the Oro Grande series of Quartzite Mountain. Stratigraphie relationships and mineralogical composition of the hornblende-rich part of the Waterman group of rocks are suggestive of two mutually unrelated possibilities of origin. The first and less likely hypothesis is that the Waterman rocks were originally laid down as a marine series of intercalated basic volcanics and sediments. If this as- sumption is correct then the following sequence of events must have taken place : the basic volcanics were metamorphosed to coarse-grained amphibolite w^hile the sediments were changed to marble, quartzite and schist ; these metamorphics were invaded by granite intrusions of minor size ; and the whole complex was then partly mylonitized and the mylonites arched into the broad, simple structure now evident. The second and preferred hypothesis is that the hornblende gneiss is simply derived by shearing and partial recrystallization of hornblende- rich diorite, the diorite having intruded and partly cut to pieces the marine sedimentary sequence which formed its roof. As in the alterna- tive hypothesis, the sedimentary-igneous complex was crushed and thrown into broad open folds, either following intrusion or possibly as events taking place during emplacement of the diorite. Precise evidence of the time and order of these events is lacking and some of the evidence, perhaps, is contradictory. Evidence in favor of the second hypothesis may be summarized as follows : 1. Andesine crystals predominantly are complexly twinned on a wide variety of laws. Complexly twinned plagioclase is, according to Turner (1950), character- istic of igneous plagioclase rather than metainorphic plagioclase, which tends to be simply twinned or untwinned. 2. There is a lack of gradational facies between obvious metasediments and horn- blende gneiss such as would be expected if the two types of rock were laid down together as sediments and tuff ; al.so, gneissic rock transgresses both the bedding and grain of the metasedimentary remnants. 3. There is definite gradation from gneiss to relatively undeformed diorite in several places in the main structure. 4. There are contact metamorphic iron deposits in a number of the sedimentary remnants adjacent to gneiss but far from known or inferred younger granitic intrusions. The time or times of deformation of the Waterman gneiss must re- main in doubt because of insufficient and possibly contradictory evi- ' IMerriam, C. W., personal communication. 1954] GEOLOGY AND MINERAL DEPOSITS 23 dence. On a regional basis, the principal deformation period which came, in this area, near the end of the Paleozoic era resulted largely in broad, open folds having northeast-to-east-trending axes. In this respect the. Waterman anticline fits the pattern of the end-Palezoic deformation. Within the Waterman gneiss section, however, are crushed, partly re- crystallized, concordantly injected hypabyssal porphyries which closely resemble rocks of other parts of the quadrangle that are known to belong to the Upper Jurassic-Lower Cretaceous interval of granite invasion. The correlation is by no means certain because of the recrystalized condition of most sills in the Waterman gneiss and because of variations in texture and mineral content of the porphyries of Jura-Cretaceous age. Also, intrusion of similar igneous rocks of entirely different ages is possible. Met amor phi sm. It is clear that the principal deformation that pro- duced the Waterman gneiss was done under intense shearing stress, fairly low confining pressures, high temperatures, and in the presence of little or no pore fluid. Otherwise, the relict minerals and cataclastic textures could hardly have survived. Whether another period of dyna- mothermal metamorphism preceded the principal deformation of the hornblende gneiss is not known, but it is probable that it did not. It is also likely that the chief shearing was done in a more or less horizontal plane and that the (probable) subsequent crustal shortening which pro- duced the anticline was accompanied by major crustal elongation per- pendicular to the shortening. Petrofabric studies in selected horizons of the gneiss structure undoubtedly would aid materially in understand- ing the structural evolution of the gneiss, but such studies have been beyond the scope of this work. Contact metamorphism in the carbonate remnants of the Waterman gneiss, in most if not all instances, can be demonstrated to have preceded cataclastic deformation. This contact metamorphism could have been accomplished either by influx of hornblende diorite which later was converted to gneiss or by one or more of the smaller granitic intrusives which cut the gneiss but have been sheared with it. Hydrothermal alteration of the hornblende gneiss, during which hornblende was in part converted to chlorite and epidote-group min- erals, must have taken place at the time of intrusi6n of unsheared Jura- Cretaceous quartz monzonite. This rock, although not extensively ex- posed in the north limb of the anticline, is well exposed in the south limb off Barstow quadrangle and may underlie other parts of the structure. Oro Grande Series The Oro Grande series was first named by Hershey (1902, pp. 287- 288) for well-exposed sections east of Oro Grande. Baker (1911, p. 334- 335) also used the name. The series was further mentioned, unnamed, by Darton (1917, p. 163) and by Miller (1944, p. 98) who adopted Hershey 's name. None of these accounts adequately describes or gives measurements of thickness, except in the broadest terms, and Miller included in the series some rocks of several different ages. The author has measured and described in detail a type section on the east slope of Quartzite Mountain, 1 mile east of Oro Grande, to conform to Her- 24 BARSTOW QUADRANGLE [Bull. 165 *« i^?*- ' ^^4 k' iX** -- Ti^. :'^_ ?^ Figure 7. Sedimentary dolomite breccia of the Oro Grande series on the north flank of Sidewinder Mountain south of tlie Three Color marble quarry, camera facing north- east toward northern outliers of the Ord Mountains. The uniform bedding in the breccia is clearly shown. shey's early usage of the name, but has supplemented this very incom- plete section by measuring and describing other sections in the southern Shadow ]\Iountains and northern Sidewinder Mountains. The Oro Grande series is predominantly a marine metasedimentary sequence characterized by thick carbonate members, but contains nu- merous quartzite, mica schist, and hornfelsed argillaceous members as well. The various units are seldom persistent along the strike for more than half a mile except in the Shadow Mountains. East of Oro Grande many are persistent for only a few hundred feet. Consequently the stratigraphic succession varies considerably from place to place and the accompanying stratigraphic columns have iimited regional significance. Fossils have been found in only three widely separated places so that the age of many parts of the series is imperfectly established. Type Section on Quartzite Mountain. In the type section on Quartz- ite ^Mountain, the lowermost member, which is exposed in the east limb of a tightly folded, northwest-pitching syncline, consists of 1000 feet of white dolomite containing thin interbeds of white limestone. The dolomite member is in fault contact with younger pink quartzite and probably is not the basal bed of the series. Conformably above tlie dolo- mite in ascending order are 275 feet of dark brown to black mica schist, 240 feet of blue-gray limestone, 80 feet of interbedded brownish-black mica schist and green calc-silicate hornfels, 135 feet of massive, homo- geneous pink quartzite. 270 feet of black biotite-quartz schist, 400 feet 1954] GEOLOGY AND MINERAL DEPOSITS 25 s-midMi^'- Figure 8. Detail of weathered surface of dolomite breccia shown in fig. 7. Universal angularity and heterogeneity of size (1-14 inches) of the dolomite clasts is well shown. The siliceous matrix weathers less easily than the dolomite clasts. of massive pinkish-white quartzite, and 50 feet of buff-to-gray limestone. An unknown thickness of the section has been eroded out or faulted off so the total thickness of 2450 feet in the type section is not representa- tive of the true thickness of the series. Shadou' Mountains Section. In southern outliers of the Shadow Mountains at the west central edge of Barstow quadrangle, a much thicker, apparently unbroken section of Oro Grande rocks is continu- ously exposed for nearly three miles. Half of this width is within the boundaries of Barstow quadrangle and half is within Shadow IMoun- tains quadrangle. The section is found in the east limb of a broad, openlj' folded, north-trending syncline which pitches gently to the south. It crops out over two parallel north-trending ridges of hills and an intervening pediment which is free of masking alluvium over much of its surface. The lowermost member exposed consists of 3470 feet of blue-gray, massive, crudely bedded, saccharoidal limestone which con- tains numerous cross-cutting veinlets of white calcite. The limestone member is overlain with apparent conformity by 1850 feet of reddish- brown to black mica schist and dark brown biotite-quartz hornfels. Con- formably above the dark-colored schist-hornfels member is a lighter- colored heterogeneous group of interbedded gray sandstones, white and gray limestones, buff dolomites, white and brown quartzites, grayish- white limy siltstones and green calc-silicate hornfelses, 1650 feet in total thickness. Within this member, series of beds" of any one rock type seldom exceed 4 feet in aggregate thickness and most are less than 2 26 BARSTOW QUADRANGLE [Bull. 165 &0>. » '' *'" * '- # * .^ .» ' , . > * - 7^ - . -. .^ V Figure 9. Coxcomb ridge of massive quartzite of the Oro Grande series cropping out east of Quartzite Mountain, camera facing east toward the Ord Mountains. Sidewinder Well is on the flat in the right middle-ground. feet thick. Sandy strata commonly are cross-bedded and occasionally ripple-markingc can be identified, indicating shallow water deposition. Above the thin-bedded member, again with apparent conformity, is 1600 feet of blue-gray to grayish-white limestone and finally, in the axial region of the syncline, 1100 feet of reddish-brown weathering mica schist and brown quartz-biotite hornfels. The total thickness of 9670 feet for this section makes it the thickest of any in the area studied but it does not represent all of the Paleozoic section once present. McCulloh - has mapped an apparently nnrepeated series of Paleozoic rocks more than 24,000 feet thick in Lane Mountain quadrangle, which adjoins Barstow quadrangle on the northeast. Vaughan (1922) and Guillou (1950) have described 8000-10,000 feet of Upper Paleozoic rocks in the San Bernardino Mountains a few miles southeast of Bar- stow quadrangle. Dibblee (1952, pp. 15-19) has described a section in the El Paso Range north of Randsburg that is more than 30,000 feet thick, more than half of which must be Upper Paleozoic. From these figures it is evident that there probably was 210 material thinning in Upper Paleozoic sequences from the eastern to western Mojave Desert. 2 McCulloh, Thane, personal communication. 1954] GEOLOGY AND MINERAL DEPOSITS 27 Figure 10. Banded, contact-altered limestone of the Ore Grande series lying unconformably below the Fairview Valley formation west of the Reserve quarry of Southwestern Portland Cement Company. Sidewinder Mountain Section. A third thin but important section of Oro Grande rocks crops out over several square miles on the northern slope and a northern outlier (Red Seal Ridge) of Sidewinder Moun- tain, 1 J miles east of the Sidewinder mine. It is not continuous at any one place Ijut relationships are sufficiently clear to allow reconstruction of the section. The lowermost member consists predominantly of 500 feet of hornfelsed, limy, argillaceous sediments varying in color from dark brown through dark green to black. It includes some sandy strata in various stages of metamorphism from sandstone to quartzite. The sandy strata are cross-bedded and ripple-marked and peculiar tubular and ovoid forms resembling worm burrows are abundant in some beds. Some of the hornfelsed strata may have been tuff or tutfaceous sedi- ments, from their mineral composition ; but positive evidence is lacking. The sequence is clearly a shallow-water assemblage. Because of the close proximity of granitic intrusives and because of the chemical susceptibility of the sediments of the lower member of this section, numerous streaks and patches of pneumatolytic-hydro- thermal alteration products have developed, a few inches to a few feet in longest dimension. These alteration patches consist predomi- nantly of epidote-group minerals, chietiy yellowish-green epidote, 28 BARSTOW QUADRANGLE [Bull. 165 j V \ I 1 1 \ \/ ' J ^ Figure 11. Streaked, slieared carbonate rock in the Oro Grande series, south flank Red Seal Ridge. Dark streaks are doloniitic limestone ; light streaks are calcitic limestone. grayish-green clinozoisite and rose-pink manganiferoiis elinozoisite. These minerals appear singly or together in fine-grained aggregates ^vhich are strongly colored in hand specimen but weakly colored in thin section. The rose-pink clinozoisite is particularly characteristic of cal- careous rocks of this member. Lying above the dark hornfels member is 500 feet of light gray dolo- mite and dolomitic limestone. The contact between dolomite and argil- lite members is irregular and complicated by minor interbed displace- ments. Attitudes of beds of both members appear similar but commonly are indistinct near the contact. The irregularity of the contact suggests an unconformity between the two. Over some exposed areas, the dolomite member consists of homo- geneous grayish-white dolomite but in the ridge east of the Ball mag- nesite mine the character of the dolomite differs considerably from place to place. In the eastern end of the ridge the rock consists of alter- nating black or dark gray and white bands. Dark bands seldom exceed two inches in width ; white bands range from two inches to a foot wide. A quarter of a mile farther west along the ridge, discrete banding fades out and the carbonate rock consists of light-gray dolomite streaks included in light-gray calcitic matrix. Still farther west on the north side of the ridge the banding is again 1954] GEOLOGY AND MINERAL DEPOSITS 29 L:.^ / - rwfc^St* ' Figure 12. Contorted carbonate rock deformed by plastic flow. Light layers are dolomite : dark layers are dolomitic limestone. conspicuous. Microscopic examination and partial chemical analysis of several specimens taken from both light and dark bands reveal that the coloration is probably finely divided graphite and that there is considerable chemical variation among the bands. In some specimens the dark bands are predominantly dolomitic and some are siliceous; in others the dark bands are predominantly calcitic and light bands are more siliceous or dolomitic. Consequently, color is no criterion as to the composition of the bands of the member. The origin and evolution of such an association of carbonate rocks is not clear. It is probable that vagaries of sedimentation, metasomatism and metamorphic differentiation all played their parts. It is also likely that at least part of the carbonate member of the section originally was laid do^vn as a series of alternating dark and light beds of lime- stone and dolomite (or dolomitic limestone) and that some was laid down unhanded. In several places, however, there are cross-cutting re- lationships and sharp change in granularity between banded carbonate rocks and unhanded dolomite that could only have been produced by magnesia metasomatism of predominantly calcitic rock. The relatively small streaks of dolomite present in much less magnesian limestone in some parts of the member probably are best interjireted as being an effect of metamorphic segregation under shear, but other alternatives are possible. 30 BARSTOW QUADRANGLE [Bull. 165 Figure 13. Uniformly banded, contact-altered limestone, Ore Grande series, west of Reserve quarry. Dark bands consist of yellowish-green garnet, yellow- ish-green idocrase, and green diopside. Light bands are coarsely crystalline calcite. A third, the uppermost member, uormally 200 feet thick, is a black, wliite and green sedimentary breccia made up of angular dolomite fragments set in a limy, partly silicated matrix. Because of overlapping younger volcanic rocks, stratigraphic relationships of the breccia with the underlying dolomite cannot be precisely established, but the breccia locally occupies a V-shaped canyon 500 feet deep and at least 300 feet wide cut into the dolomite. Fragments of the breccia vary from a fraction of an inch to several inches in longest dimension and are similar in appearance and composition to the underlying grayish-white dolomite. Black and green matrix colors are due largely to iron oxide and complex silicate minerals introduced into the breccia by emana- tions and solutions from penetrating hornblende-rich granite dikes. Peripheral de-dolomitization of the fragments is common. Many labora- tory specimens stained showed coronas of calcite | to |: inch thick around dolomite fragments. This dolomite breccia was described briefly by Pack (1914) when the rock was being quarried as ornamental marble. The Sidewinder ^Mountain section, then, consists of three members having an aggregate thickness of 1200 feet and separated one from the other by probable unconformities. The lapse of time represented by these probable unconformities may not be significant as fossiliferous Carboniferous and Permian sections in other parts of the Mojave Desert and in adjacent Inyo County, in which time intervals are rela- tively well-known, commonly contain local unconformities^ (Knopf, s Merriam, C. W., personal communication. 1954] OEOI.OGY AND MINERAL DEPOSITS 31 1918, pp. 40-43 V Althoiigrh the Sidewinder Mountain section differs locally from other parts of the Oro Grande series, the over-all litholo^y remains similar and the possibility of the section being radically dif- ferent in age from other sections here assigned 'o the Oro Grande series is remote. The middle dolomite of the Sidewinder section prob- ably corresponds with the lowermost dolomite member in the type sec- tion on Qnartzite ]\Ionntain and with massive dolomite members else- where in the Oro Grande series of Barstow quadrangle. Dolomite of any significant thickness invariably occupies a position low in the series. Regional and Contact Metamoi-phism in the Oro Grande Series. The Oro Grande series has been subjected to at least two major orogenies and to two corresponding periods of dynamothermal metamorphism. Xeitlier of these periods produced rocks of a more advanced stage of dynamothermal metamorphism than the biotite zone of most metamor- phic petrographers. Almost universally within the quadrangle lime- stones have become marbles, pelites have become mica schist and sand- stones and cherts have become quartzites. The abundance of fossils in the younger Fairview Valley formation, apparently derived in part FiGiiRE 14. Selective silioification of massively bedded limestone of the Oro Grande series west of the Reserve quarry. Width of the exposure shown in the photograph is approximately 1!0 feet. The narrow gray bands art' unaltered blue- gray limestone ; the mottled black and white areas are coarse intergrowths of yellowish-green garnet, idocrase, diopside, quartz and less commonly deep green uvarovite. 32 BARSTOW QUADRANGLE >J ^ L f : Figure 15. Rectangular .iointing- developed on a dip slope of dolomitic liine- stone, Oro Grande series, Red Seal Ridge. from the Oro Grande series, and the almost complete destruction in the Oro Grande series is notable. The few fossiliferous parts of the Oro Grande series are exceedingly fossiliferous, and it is probable that all of the limestones originally were somewhat fossil-bearing. Probably, dynamothermal adjustments in the Fairview Valley conglomerate, de- scribed in following pages, were made principally in the matrix while the clastic portion largely escaped recrystallization. It is also possible that heating and shearing simply happened to be less in that part of the crust occupied by the conglomerate. There may also be some con- nection between the universal recrystallization of the bedded limestones and their almost invariable content of hydrogen sulfide. Contact metamorphism has resulted in formation of mineral assem- blages of high metamorphic grade in some instances and has had little or no effect upon wall rocks in others. Pelites have become microcline (or orthoclase) — quartz-oligoclase — mica schists, gneisses and hornfelses while limestones were converted to mineral assemblages such as garnet, wollastonite, idocrase, diopside, epidote and coarse calcite. Along other granite-limestone contacts the only sign of change lies in superficial endomorphic development of garnet in granite. In general hornblende- rich intrusives have produced the greatest contact effects and leucogran- ites the least. 1954] GEOLOGY AND MINERAL DEPOSITS 33 Figure 16. Quartz-muscovite schist of the Oro Grande series in the Hinkley Hills. The Hinkley and Waterman Hills lie in a localized belt of strong deformation of alpine-type. Note the joints which are roughly perpendicular to the schistosity and the crenulated slip surfaces on the planes of schistosity. A common contact effect in dolomite is widespread, development of sulfur-yellow serpentine. In most cases serpentinization and de-dolo- mitization, with or without production of predazzite (brucitic marble), has taken place without marked development of zones. In the Hinkley dolomite deposit north of Iron Mountain, however, hornblende diorite dikes have produced narrow but marked zonal contact alteration. Next to the dikes a few inches of spinel-bearing' calcite has been irregularly developed. This grades into a zone of approximately equal width of forsterite-bearing marble, then into as much as 2|-8 feet of yellow ser- peiitinous dolomite and finally into unsilicated though coarsely crystal- line white dolomite. The most extensive contact alteration of carbonate rocks in the quad- rangle has taken place in the Oro Grande series in a north-trending ridge located just west of the Reserve quarry. The ridge, which is TOO feet wide, 200-300 feet high and 1400 feet long, is made up almost entirely of coarse-grained tactite in which brownish-yellow garnet and idocrase, green diopside, creamy white wollastonite, and coarse white calcite are the chief minerals. Muscovite, biotite, dark green uvarovite, specularite, and a green amphibole near actinolite in composition are 2 — 85919 34 BARSTOW QUADRANGLE [Rllll. Kio developed locally in minor amounts. A much larger number of contact minerals could be found in this deposit if the interior could be pene- trated. In the Reserve quarry, in which many hundreds of feet of faces are exposed, and on the hillside north of the west end of the quarry, contact minerals and mineral groups are locally developed. Pods and irregu- larly developed areas of woUastonite develop near quartz monzonite porphyry dikes. In seams and next to fracture zones adjacent to horn- blende-rich dikes (both diorite and lamprophyre), green talc, white mountain leather (fibrous tremolite), and black and pink calcite locally have been developed. The black color of the calcite is caused by numer- ous blebs of hydrous iron oxide introduced along cleavage planes. The pink color is caused by manganese ■* although the mineral lacks the characteristics of rhodochrosite. There apparenlty has been slight iso- morphous replacement of Ca"^^ by Mn++. Age and Correlation. There are no fossils in the Sidewinder Moun- tain section of the Oro Grande series with which to check the fore- going lithologic correlations, but if they are correct then the dark hornfels member of the Sidewinder Mountain section is the oldest unit in the Oro Grande series. The author believes, on both lithologic and fossil grounds, that the type section of the Oro Grande series in Quartzite Mountain is approximately equivalent to the two lower mem- bers of the southern Shadow Mountains section. Two poorly preserved brachiopods, found by the author near the top of the carbonate member of the Shadow Mountain section, w^ere examined by C. W. Merriam (April 1949) who stated that they most probably are Pennsylvanian. Brachiopod and crinoid debris of Carboniferous age was also found by the author in the upper part of the limestone section in Sparkuhle Hill two miles northw^est of the type section in Quartzite Mountain. The limestone of Sparkuhle Hill almost certainlv corresponds to the lower limestone member in the type section in Quartzite Mountain so that the greater part of the Oro Grande composite section is Pennsyl- vanian or younger. Therefore, as the Oro Grande series unconformably underlies the Permian Fairview Valley formation, described herein, the author believes that the entire series most probably is Carboniferous. The fossil locality mentioned and pictured by Miller (1944), from which poorly preserved Mississippian (?) fossils were obtained, was visited several times by the author but yielded no further material. The author believes that much of the Carboniferous ( ?) material from the clastic part of the Fairview Valley formation was derived from the underlying Oro Grande series and that the latter series was once exceedingly fossil- iferous. Widespread recrystallization by intruding granitic rocks has obliterated the fossil record throughout most of the series. "^o^ Hodge Volcanic Series The Hodge volcanic series has been named by the author from a thick homoclinal section exposed north of the Mojave River a few miles northwest of the railroad town of Hodge. Originally included by Miller (1944, pp. 79-98) in what lie called the Hodge eomplex, the series has been withdrawn by this author, renamed and redefined. The Ilodge complex, as described by Miller, was designated as a predominantly ♦ Duniiam, B. R., personal communication. 1954J GEOLOGY AND MINERAIj DEPOSITS 35 plutonic igneous assembla<>-e. The rocks herein described as the Hodge \ok'anic series clearly are predominantly volcanic rocks of tlie andesite- dacite-rhyolite association. Locally, thin dikes and sills of hornblende diorite cut the series, chiefly at the east end of the exposed mass. Only one quartz monzonite intrusion that is large enough to map on the 1 : 125,000 base map used for this work cuts the series, and none of the diorite dikes and sills are large enough. The lower half of the 10,0()()-foot-thick volcanic series consists prin- cipally of massive reddish-brown, purplish-brown, and dark green rocks. These are chiefly weakly sheared quartz latites and dacites, originally a series of vitrophyre flows and crystal vitric tuffs. The upper half consists of alternating variable thicknesses of black, white and gray-green, strongly sheared metavolcanics and tuffaceous metasedi- ments. Andesite members have been converted to black or dark gray biotite-quartz schist ; quartz latites and dacites to white muscovite schist ; thin sandstone members to white or pinkish-white quartzite, and rhyolite felsites and possibly some clay shale to muscovite schist. The various members may be as much as 550 feet thick or as thin as 10 feet, and tend to be persistent along the strike for many thousands of feet. Characteristic of the upper half of the section are several dozen widely spaced, prominently exposed quartzite members. These com- monly are 10 to 20 feet thick and not more than two or three hundred feet long, but several examples 100 to 200 feet thick and 1000 feet or more long are present. A few of the quartzite members may originally have been sandstone or chert, but a .majority are simply recrystallized quartz veins which were introduced parallel to the beds because of structural weakness in that direction. Several examples are strongly mineralized with hematite and once were probably pyritic. The origin of the iron is hydrothermal, not sedimentary. Cavities lined with coarse quartz crystals and other relict textures and structures characteristic of mesothermal veins remain in some examples. White muscovite schist members a few tens of feet thick are common and conspicuous members of the upper part of the section. These com- monly are persistent for many thousands of feet along the strike and may represent water-laid rhyolite tuff beds. The entire section of the Hodge volcanic series is exposed on well- eroded hills and on partly dissected, exhumed pediment surfaces. Con- sequently the rocks in some places are deeply weathered. "Weathered surfaces of the series commonly are higlily colored in red, yellow, cream, violet and white. The rocks are further discolored by weathering of numerous small sulfide-bearing quartz veins. At a distance they re- semble areas of Tertiary volcanic rocks also found in the Barstow area, but the resemblance ceases on close-range view. Petrography. A large part of the entire mass of the Hodge volcanic series is made up of rocks gradational between rhyolite, quartz latite, and daeite. In most thin sections these rocks are found to be composed of 30-45 percent relict phenocrysts 1-3 mm in average dimension set in wholly or partly recrystallized fine-grained granoblastic ground- mass, but in a few specimens of coarse-grained lava even the ground- mass crystals have been preserved. Of the relict phenocrysts in most specimens of rhyolite, 50 percent are slightly perthitic orthoelase, per- 36 BARSTOW QUADRANGLE [BuU. 165 haps pseudomorphous after sanidine, 30 percent are quartz and 20 per- cent are oligoclase (An 18-22). Occasional patches of magnetite dust pseudomorphous after biotite indicate that biotite phenocrysts were once present in the laA^a. Oligoclase and orthoelase laths are the usual relict groundmass minerals, oligoclase commonly being in excess of orthoelase. Outlines of the quartz phenocrysts commonly show bi-pyra- mid and short prism faces and remelt embayments typical of volcanic rocks. Broken crystals and shard-outlined quartz mosaics are present in tuff specimens although many shard-outlines must have been lost through recrystallization. In some slides of the more severely sheared rhyolite, swirl structures (curved trains of inclusions) within re- crystallized or partly recrystallized phenocryst outlines clearly show directions of rotation of the phenocryst in the fabric. The granoblastic groundweb of most rhyolite specimens consists mainly of quartz, orthoelase (?) and probably albite in fine-grained mosaic. Grain size in the groundweb is not uniform and patches vary as much as 2-3 diameters from the average. In addition to these prin- cipal groundmass minerals of the least deformed examples, wisps of dirty-green biotite, colorless muscovite, pale-green epidote, and sub- hedral magnetite are present in widely distributed but minor amounts. Proportions of micas and quartz increase rapidly with the degree of deformation that has been imposed. Thin sections of quartz latite and.dacite are similar in general ap- pearance to the rhyolite just described, but the proportion of feldspars and quartz varies in conformance with rock types of those compositions. Andesite members of the series tend to be made up of rock more thoroughly recrystallized beyond the stage where precise identification is possible, but presence of a little relict quartz suggests that the most mafic rocks of the series are most probably intermediate between dacite and andesite. Age and Correlation. Age-determining features of the Ilodge vol- canic series are few. Nowhere is it in contact with other units except where invaded by igneous intrusions. The series is cut by a small dike of Jura-Cretaceous quartz monzonite in the southwestern portion of the exposed area, by porphyritic hornblende diorite along its northern boundary, and by numerous widely distribtued pegmatite dikes and quartz veins associated with the granitic succession of tlie Jura-Cre- taceous interval. The volcanic members of the series are more per- sistent and much better bedded than those of any known section of the Triassic (?) Sidewinder volcanic series. On the whole the Hodge series is less coarsely pyroclastic and more severely metamorphosed than the Sidewinder. In addition, fold trends of the Ilodge series appear to have originated in the end-Paleozoic disturbance discussed later. The best estimate is that the Ilodge volcanic series is post-Fairview Valley and pre-Sidewinder in age, probably Upper Permian. Fairview Valley Formation North and northwest of Southwestern Portland Cement Company's Reserve quarry and west of the Sidewinder gold mine, a tightly folded series of clastic and limy sediments crops out over an area of approxi- mately three square miles. The assemblage is lithologically unlike any other group of rocks in the southwestern Mojave Desert and forms a 1954] GEOLOGY AND MINERAL DEPOSITS 37 Figure IT. Cobble conglomerate in the upper member of the Fairview Valley formation, Black Mountain. The dark patches on the boulder are silicified corals. A majority of the limestone cobbles are well rounded, varying from gravel size to boulders more than two feet in diameter. Rounded chert cobbles are found in some parts of the conglomerate. distinct formation divisible into two members. It was mapped by Miller (1944, p. 112) as part of the Oro Grande series but was not mentioned in his description of that series. The formation has been named by the author from the valley at the edge of which the type section crops out. It lies nnconformably on massively bedded limestones and quartzites of the Oro Grande series less than a quarter of a mile west of South- western Portland Cement Company's Reserve quarry, and has been intruded and overlapped by volcanic rocks of the Triassic (?) Side- winder volcanic series less than a quarter of a mile Avest of the Side- winder mine. ;38 BARSTOW QUADRANGLE [Bull. 165 ^^ ^^ Figure 18. Another exposure of limestone conglomerate of the Fairview Valley formation showing crude bedding and wide variation in clast size. A steeply dipping bed of cobbles and boulders diagonally crosses the photo from lower left to upper right corners. Over much of the mass, bedding is indeterminate. AVest of the Reserve quarry thin basal conglomerate beds of the Fairview Valley formation occurs in a zone 10-30 feet thick. The beds contain well rounded pebbles of dense, black and maroon, porphyritic andesite, quartzite, leueogranite and limestone, volcanic debris greately predominating. Pebbles make up 20-25 percent of the basal beds and the matrix consists of hornfelsed, sandy argillaceous limestone. Above the pebbly, ill-defined beds are thinly laminated hornfelsed, limy, fine- grained clastic sediments (chiefly limy siltstones) 4,725 feet in maxi- mum observed thickness. In the northwest central portion of the exposed 1954] GEOLOGY AND MINERAL DEPOSITS 39 formation, reerystallization in the lower member has been less severe and sedimentation more selective. There, hornfelses are interbedded Avith jiTayish-blaek limestone, limy shale, thin gritty limestone conglom- erate and gray sandstone. Thin lenses of black limestone and red- dish conglomerate 3 to 25 feet thick are also scattered throughout the lower member of the formation. Gray and gray-green colors prevail in freshly broken rocks throughout the formation, but sufficient iron is present to cause a rusty coating over most exposed rock surfaces. Petrographu of Rocks of the Horn f els Mcmher. The laminated horn- felses originally consisted of all gradations betw^een calcareous, arkosic sandstone and calcareous shale, but contact action of the underlying granite batholith has produced reerystallization to a degree that most hand specimens resemble chert or very fine-grained quartzite rather than limy sediment. The clastic fraction of the hornfelsed rocks varies widely in composition, as seen in thin section. Granitic debris predom- inates — quartz, mierocline and orthoclase perthites, oligoclase, musco- vite, and biotite forming the bulk of debris of this kind. In addition, rock fragments of quartzite, granite, aplite, quartz porphyry, and lime- stone are common in the coarse-grained facies. The most completely Figure 19. Bedded silty limestone of the hornfelsic member of the Pairview Val- ley formation west of Black Mountain. Tensional fractures developed roughly per- pendicular to the bedding- have been filled with white calcite. Note the cross-bedding to the right of the light meter. Major bedding dips away from the observer ; cross- bedding to the right. Beds are not overturned. 40 BARSTOW QUADRANGLE [Bull. 165 Figure 20. A quartz porphyry dike of probable Triassic age cutting steeply dipping sediments of the Permian Fairview Valley formation northwest of Black Mountain, camera facing slightly east of south. Edges of the nearly vertical strata, not conspicu- ous in this photo, strike directly away from the observer ; the dike cuts them obliquely. recrystallized rocks are typical hornfelses made up chiefly of mosaics of biotite, quartz, elinozoisite, epidote, calcite and, in some specimens, chlorite. Long- needles of tremolite are conspicuous in a few specimens. Percentages of quartz and calcite, both primary and secondary, vary widely. The upper 1,350 feet of the formation, the thickness of which is doubled by folding to 2,700 feet in the axis of the syneline, is made up almost entirely of coarse limestone conglomerate. Cobbles, boulders and pebbles of dark-gray, pinkish-gray and black limestone, together with a few white and gray pebbles and cobbles of dolomite and dolomite limestone make up more than 95 percent of the clasts. Well-rounded to subangular cobbles and pebbles of brown chert make up the remainder of the clastic fraction. The matrix consists of fine-grained light or dark gray limestone except locally where silicated and hydrothermally al- tered patches have developed. Like the chert, most of the limestone clasts are subrounded to well-rounded but some are angular and sub- angular. Compression applied during folding has greately accentuated the angularity of the clasts in some parts of the formation. According to accepted usage, the rock is clearly a conglomerate, not a breccia. Except where the conglomerate member interfingers with the hornfels member, bedding directions are difficult to follow. Crude cross-bedding further complicates interpretation of the structure, particularly in the uppermost beds which form the axial region. However, beds of the hornfels member follow around the nose of the syneline so that approxi- mate location of the axis is possible. 1954] GEOLOGY AND MINERAL DEPOSITS 41 Age Correlaiion and the Fossil Record. With the exeeption of one narrow lens containin«r small, planarly coiled immature gastropods of indeterminate type and the presence of poorly preserved i^yrinjropora ( ?), wliich are not good time markers, fossils from the Fairview Valley formation have come from the clasts of the limestone conglomerate. Three individuals have also been found in the matrix of the conglom- erate, but they themselves are worn and appear to be of clastic char- acter. Hence, the large fauna may serve only to date the rocks from which the conglomerate was derived and not the conglomerate itself. Tt should be pointed out, however, that with two exceptions, all of the forms present could have lived together in early Permian time and may not be of radically different age from forms from other parts of the formation. The two exceptions are Lower Paleozoic forms found by personnel of the cement company, one an Archeocyathid (Low^er Cambrian) and the other the coral Halysites (Ordovician-Silurian). Inasmuch as only two or three specimens of Lower Paleozoic forms have been found during many years of collecting in a formation con- taining abundant fossils, there is considerable doubt that the Lower Paleozoic forms actually came out of the formation. They could have been dropped by collectors and have come from elsewhere in the ]\rojave Desert. If they actually came from the formation, then it must have been derived from rocks of many different ages and a considerable time lapse between original deposition of the fossils and deposition of the matrix material must have taken place. Corals, brachiopods, gastropods and echinoid and crinoid debris are the commonest, most distinctive types present, but a few bryozoa and other miscellaneous forms have been found. The fossils are the most numerous and best preserved of any described from the few Mojave Desert localities west of the New York and Providence Mountains and south of the Garlock fault. Even so, silicification of the fossils in the limestone of many specimens is incomplete and in poorly silicified indi- viduals internal structures commonly have been obliterated by recrys- tallization of the limestone. A collection of fossils assembled by the writer between 1940 and 1948 was sent to the U. S. National Museum for identification. All of the fossils from this collection were placed within the Mississippian-Per- mian interval and some were listed as probably Lower Permian. They were tentatively correlated with those of the McCloud limestone of northern California and, in part, with the Wolfcamp formation of Kansas. Additional material has been collected by the author and by II. R. Gale which definitely contained Low-er Permian forms and most of the genera had a range from Mississippian or Pennsylvanian to Permian. The Fairview Valley formation is certainly younger than Pennsyl- vanian and most probably younger than Lower Permian. It is older than the intruding Jura-Cretaceous granitic rocks and older than the Triassic (?) Sidewinder volcanic series. In the absence of Mesozoic fossils, it must be presumed to be Upper Permian. The only possible alternative is that the fossils from the clasts as well as the few solitary examples found in the matrix (here interpreted as clastic also), are the same age and that the Fairview sea merely reworked its own sedi- ments. In this case, the conglomerate would be considered Lower rather 42 BARSTOW QUADRANGLE [Bull. 165 than Upper Permian. Presence of well-ronnded chert pebbles in the conglomerate make such an alternative unlikely as the amount of abra- sion necessary to produce rounded pebbles from hard chert most prob- ably would have reduced the limestone to much more finely divided particles. Fairview Valley formation fossils are listed in the following tables : Forms for irkich generic or specific names have heen determined. Name Range Authority Occurrence* Chonetes granulifera (Owen) Pennsylvanian to Permian J. S. Williams c Meekella sp. Lower Permian C. W. Merriam r Heritchia sp. {Waagenopkyllum) Permian H. Duncan a Polypora sp. Upper Paleozoic — ranee not well estaVjlished H. Duncan c Meekopora sp. Mississippian — Pennsylvanian H. R. Gale r Halysites sp. Ordovician — Silurian J. W. Durham r Composita sp.** Mississippian to Permian J. S. Williams & H. R. Gale a Aulosleges sp. (?) Permian J. S. Williams a Omphaloirochus Whitneyi Lower Permian S. W. Muller c Omphaloirochus obtusispira Permian H. R. Gale r Echinocrinus sp. Mississippian — Pennsylvanian H. R. Gale a Syringopora sp. Mississippian-Lower Permian H. R. Gale r Archeocidaris sp. Upper Paleozoic S. W. Muller c * a — ;iliiiiiii:mt (' — conimnn r — rare ** The large forms of this genus such as those in the Fairview Valley formation commonly are Permian, accord- ing to Muller. Forms for irhich only family designation has heen possible. Name Bellerophontids Straparolids Raphistomids (?) Archeocyathids Range Ordovician to Permian Silurian to Jurassic Ordovician to Silurian Lower Cambrian Authority B. Knight B. Knight W. Durham W. Durham Occurrence Sidewinder Volcanic Series Sidewinder Mountain is the type locality for rocks of this unit. The series is widely distributed throughout the southeastern part of the quadrangle and erosional remnants of the series are exposed in the Kramer Hills. The greatest thicknesses are found in the Silver Moun- tain group of hills, Sidewinder Mountains, Stoddard Mountain, and Raven Ridge. Miller (1944, p. 100) proposed the name Sidewinder Valley metavolcanics for this group of rocks but the name has been reworded and redefined for two reasons. Topographers have not used the name Sidewinder Valley on existing maps and Miller's map does not show its location. Also, Miller's Sidewinder Valley metavolcanics, as mapped, included rocks of several different ages. Miller believed the series to be interbedded with the Oro Grande series and to be Paleozoic in age. Evidence accumulated during this investigation does not sup- port either of these views. The Sidewinder series is predominantly a pyroclastic assemblage sub- aerially laid onto very irregular topography. Waterlaid members are 1954] GEOLOGY AND MINERAL DEPOSITS 43 rare and over most of the Barstow quadrangle exposures the series con- sists of overlappinjr. intorfinoerinup of iierthitie ortho- olase nystals is in the upper ri,i;lit (luadrant : zoned, partly altered iilif;in-la.se in tlic lower left (iiiadrant. Crossed nieols, XI 0. Fic.iKK 22/>. Biotite nietadacite of tlie Sidewinder series, Sidewinder .Mciuntain showing embayed quartz, zoned oliKOcluse and lathy biotite. I'lane polarized liKTht, XI 5. 46 BARSTOW QUADRANGLE [Bull. 165 Petrography of RhyoWe and Ehyolite Tujf. Chertlike porphyritic metavitrophyres and dense felsites are the most salie rocks of the series. Devitrification of the metastable glass to quartz-feldspar mosaics is universal. Phenocrysts of the metavitrophyres consist of perthitic or- thoclase, oligoclase (Anl8) and quartz. Spherulitic textures are com- mon, the spherulites commonly averaging 2-3 mm in diameter. Spheru- litic structures commonly form coronas around all three minerals found as phenocrysts. The potash feldspar is orthoclase and this is most com- monly perthitic ; orthoclase of the dacite varieties of the series is not so commonly perthitic. The microcrystalline groundvreb consists pre- dominantly of quartz and potash feldspar. Plagioclase is seldom recog- nizable and much of the potash feldspar is too fine-grained for precise identification. Shear lines, evident in the groundmass of many speci- mens are marked by zones of sutured, more coarsely crystalline quartz, proportions of various mineral species vary but an average content in the rhyolite metavitrophyre is as follows : Percent in Percent in Species phenocrysts groundmass Total Oligoclase (Anl8) 18 IS Perthitic orthoclase 12 12 Quartz 5 20 2.5 Magnetite tr tr 1 Biotite 3 8 Hornblende 1 1 Indeterminate — mainly orthoclase ( ?) 40 40 Felsites composed almost wholly of microcrystalline material are common. Observed in thin- section, these have microcrystalline pheno- crysts of quartz and feldspar just like the megascopic varieties, but the proportion of phenocrysts is small and much of the groundweb con- sists of indeterminate crystallites. One variety of coarse-grained rhyolite consists mainly of mixed euhedral and broken crystals of quartz, orthoclase. oligoclase, altered biotite and altered hornblende in a very small proportion of ground- mass — less than 20 percent. There are all gradations between rock of this sort and rock that is obviously pyroclastic. In contrast to the tuffs, however, this rock shows no relict shard outlines, no lithic fragments and the crystals are arranged in much the same fashion as in any flow lava. The broken crystals may be the result of vent brecciation followed by remelting and mixing with new vent magmas. The ferromagnesian minerals are almost invariably altered' to magnetite and hematite, probably by reheating. Petrography of Dacite and Dacite Tuff. Most dacites are pyroclastic and crystals consist predominantly of oligoclase-andesine with some quartz, orthoclase and orthoclase perthite. A greater proportion of dark accessories is normally present than in most rhyolites of the Sidewinder series. Broken, embayed, partly resorbed crystals are common but shard outlines are not commonly present because of recrystallization. Relict outlines of hornblende and biotite are numerous and together made up at least 10 percent of the crystals of some tuff specimens. Oligoclase- andesine (An32-36) is somewhat more calcic than in most of the rhyo- lite where the common plagioclase is An 18. The groundweb is often too fine for determination but quartz mosaics are usually determinable. The determinable feldspar in some specimens may be entirely oligoclase- 1954] GEOLOGY AND MINERAL DEPOSITS 47 andesiiie or potasli feldspar may be present up to 15 percent. The phenocryst-quartz content may vary from traces to 20 percent. The per- centagre of phenocrysts to gronndmass varies widely in dacites but com- monly is in proportion of 3 to 2. Petrography of Latiie-Andesite. Latite-andesites are porphyritic, dense, and black or g-reenish black when badly altered. Phenocrysts consist of sodie andesine (An32-36) with minor amounts of hornblende, biotite, and magnetite. Andesine phenocrysts may be either thick-tab- ular or lath-shaped and may average as large as 4 mm in longest dimen- sion in some rock bodies. Quartz is generally absent as phenocrysts but scattered crystals of orthoclase may be present. Hornblende and biotite together seldom exceed 10 percent of phenocrysts. The texture may be sub-traehytic or the feldspar laths may be unoriented. Groundmass feldspars usually are found to be too badly altered for precise identi- fication but they appear to be similar in composition to the phenocrysts. There may be some potash feldspar in the groundmass as indicated by the analysis in the accompanying table. This analysis, done on the freshest, most typical specimen available, shows that the potash and silica contents are a little high for normal andesite and that the rock is close to the latite-andesite dividing line. Type latite-andesite from the Average of 87 Average of 12 trachy- south side of Highland andesites after Daly audesites after Johannsen Mountain (percent) (percent) (percent) Si02 63.47 59.59 58.60 AI2O3 17.66 17.31 17.47 FeO 3.73 3.13 3.22 FeaOs 1.22 3.33 4.02 TiOo .46 .77 1.12 MnO - .07 .18 .05 CaO 4.14 5.80 4.26 MgO .92 2.75 1.26 K2O 3.74 2.04 3.67 NaaO 3.42 3.58 5.75 H2O- .23 @ 105°C H.O* .34 @ 105°C CO2 nil P=05 .14 .58 * Analysis by W. H. Herdsman, Glasgow, Scotland. Epidote-group minerals are generally present, both in groundmass groups and as spongy alteration products of plagioclase. Clots and trains of epidote, green biotite, chlorite, magnetite, and sphene are commonly present in latite-andesite and corresponding tuffs. In more severely metamorphosed specimens imperfecth' formed, ragged albite (?) is present in a ground web of finer sutured phantom grains of other .secondary minerals. Metamorphism and Hydrothermal Alteration. Dynamothermal met- amorphism has been weak in rocks of the Sidewinder series. In most places vitrophyres and other rocks containing glass and finely-divided material have merely been de-vitrified to form fine-grained mineral mosaics. Locally, hydrothermal alteration in shear zones has produced finely divided sericite or p,vrophyllite schists. Rocks of such composi- tion as to yield biotite under dynamothermal conditions only rarely have been metamorphosed to that stage. Formation of secondary biotite has been almost entirely a hydrothermal effect. Sericite, albite (?) and chlorite of probable dynamothermal origin present in specimens of 48 BARSTOW QUADRANGLE [Bull. 165 Figure 23. Photomicrograph of amygdaloidal latite-andesite of the Sidewinder series, northeast slope Split Rock Mountain. Amygdules in upper left and lower right corners have an outer rim of quartz and an inner filling of calcite. Most of the andesine pheno- crysts have been saussuritized. Plane polarized light, XI 9. some rock masses of the series indicate that metamorphism in part has progressed only as far as the low greenschist facies of Turner (1948, pp. 93-94). Both dynamothermal and widespread hydrothermal altera- tions appear to have been completed before the end of the Jura-Cre- taceous period of granitic emplacement. Contact metamorphism, where definitely related to a granite contact, has also been weak, increasing development of epidote group-minerals being the chief effect as contacts are approached. Hydrothermal altera- tion is, however, universally developed, with appearance of epidote- group minerals, sericite, biotite, and chlorite. Severe hydrothermal alteration has resulted locally in extensive con- version of almost all compositional varieties in the series to quartz- sericite, quartz-kaolinite, quartz-pyrophyllite or quartz-alunite mix- tures. Subsequent shearing has, in some cases, caused further alteration of these rocks to low-grade quartz-mica schists. In one case the end product was chiefly pyrophyllite and quartz but most commonly quartz- sericite or quartz-kaolinite mixtures resulted. Large patches of white or white and pastel-colored (reddish, lavender, etc.) material of this sort up to several hundred yards in average surface dimension are characteristic of the Sidewinder series in the Silver Mountain, Stoddard Mountain and Split Rock Mountain areas of the quadrangle. Among the pneumatolytic or hydrothermal epidote-group minerals formed, epidote and clinozoisite are the species most commonly devel- 1954] GEOLOGY AND ISIINEUAL DEPOSITS 49 Figure 24. ^Massive, planarlj- jointed nietatuff of the Sidewinder series on the northeast slope of Sidewinder ^lountain east of tlie Tliree Color marble quarry. The pseudo- bedding is not parallel to any apparent change in granularity in the tuff. FiGt'RE 25. Sheared, complexly jointed fel.site of the Siik u iiulii- series near the summit of Split Kdck Movmtain. camera facing- .southeast toward Sidewinder IMountain (right background). Some of the rock apparently was hydrothermally altered before shearing took place. 50 BARSTOW QUADRANGLE [Bull. 165 P"'iGi'UE 20. N'olcanic mud-flow t'unglonierate (lahar) in the Sidewinder volcanic soutli of tile Ball magne.'^ite mine. Tlie dacite cobbles and boulders range from inches to more than 5 feet in longest dimension. series a few Figure 27. IMultiple sills of fme-grained latite-andesite, Sidewinder series, south flank Red Seal Kidge east of the Ball magnesite mine. X'olcanic series has lieen faulted against dolomite of the Oro CJrande series just left of the young Joshua tree. 1954] GEOLOGY AXD MINERAL DEPOSITS 51 oped, but piedniontito (inanj^-aniferous epidote or withaniite) is (.'onimou in some places and allanite is rather widely disseminated as a minor constituent. Common epidote is developed in clots, veins and vups ap- parently isolated from vein matter. Vu<>-s connnonly are partly filled with earthy to compact masses of manjianese oxides. Common epidote and clinozoisite also are widely distributed throujrh partly recrystal- lized massive rocks in microscopic crystals and crystal groups. Figure 28. Outcrop of tourmalinized quartz porphyry of the Sidewinder series on the south flank of Stoddard Mountain near the Keystone mine. Tlie dartc bUie tourmaline dots standout from the granular quartz matrix. Iillsewliere tourmaline has also developed along fractures in the quartz porphyry. Piedmontite, a relatively rare mineral, is prominently developed in metarhyolite and rhyo-dacite tuffs and lavas of Sidewinder and Ilijzh- land Mountains. Replacement clots, streaks and disseminated crystal groups commonly are numerous enough to impart a red color to the rock. In a few places, piedmontite patches 2-3 inches in diameter may be found which contain vugs linocl witli crystals as coar.se as half a centimeter in longest dimension. Piedmontite is known to occur in Cali- fornia in a similar environment as a constituent of (luartz jiorphyries from the IMammoth Lakes district (eastern ]\Iadera aiul western Mono Counties)^ in quartz porphyry boulders from Pleistocene (?) deposits at Pacific Beach (Rogers, 1912, p. -'378) and from rhyolite and dacite ^ Chesterman, C. "W., personal communication, 1950. 52 BARSTOW QUADRANGLE [Bull. 165 Figure 29. Photomicrograph of tourmalinized quartz porphyry. Tourmaline rosettes are from 2 to more than 7 mm in diameter and are strongly pleochroic from prussian blue to bluish brown. Plane polarized light, X19. cobbles and boulders from the Poway cong-lomerate (Eocene) near Poway, San Diefjo County/' It is also found with quartz and micas in the Pelona schist of the San Gabriel and southeastern San Bernardino Mountains "' and in veins and sheared volcanics of northeastern Ma- dera County (Mayo, 1932, pp. 238-2-18). Migration of manganese in volcanic rocks of the Sidewinder series took place in two stages. Hydrothermal conditions which produced piedmontite could not have been the same as those which produced the common epidote and manganese oxides which occur together. Hutton (1938, pp. 119-124) has shown that only a minute amount of manga- nese is necessary to produce red coloration in epidote. Hence the two classes of minerals must have formed at different times and under different environments. Many vugs containing manganese minerals are superimposed on common epidote showing that in some instances, at least, the epidote formed first. The amount of manganese necessary to color the piedmontite might reasonably have come from decomposition of ferromagnesian minerals in the host rock, but the amount of man- ganese present in veinlets and vugs is sufficiently great to suggest in- troduction from some outside, perhaps magmatic, source. Age and Correlation. The Sidewinder volcanic series is traceable eastward into the Ord Mountains and northwest through the Kramer Hills to the Boron district of Kern County. It is correlative with the Ord Mountain group of Gardner (1940, pp. 266-270) and the Amargo volcanics of Gale (1946, p. 358). It is also lithologically similar to vol- canic series of pre-granite age seen by the author in the Santa Ana "First identified in 1948 by Ian Campbell, California Inst, of Technology, from mate- rial submitted by Gordon tJastil of Alpine, California. Also found in other material from the same locality examined by Bowen and Gastil in 1949. ' Hill, H. Stanton, personal communication. 1954] GEOLOOY AND MINERAL DEPOSITS 53 Mountains and the mountains of San Diepo County. The Ord Mountain group is regarded as Triassic by Gardner and tlie Amargo group simply as pre-granitic and post-Paleozoic by Oale. Within the Barstow quad- rangle there are no precise age-deteniiinating features in the Side- winder series. It is intruded by Jura-Cretaceous granitic rocks and un- conformably overlies the Permian Fairview Valley formation. It could be as old as very late Permian or as young as Jurassic, but most prob- ably is Triassic. Granitic Rocks Granitic rocks of Barstow quadrangle range from coarse-grained hornblende gabbro-diorite to medium-grained alaskite and variable- grained leucogranite pegmatite and aplite. Except for two strongly de- formed types discussed, Waterman gneiss and gneissic hornblende dio- rite under the several varieties apparently were emplaeed within the Upper Jurassic-Lower Cretaceous interval. Some were intruded earlier in this period than others. In general, the early intrusions were more mafic than those intruded later in the sequence although lamprophyric dikes and small, oval hornblendite stocks did come in near the end of the ^sequence. Biotite (juartz monzonite is by far the most broadly dis- tributed type although six others are present in masses sufficiently large to map on the scale adopted for this work. In decreasing order of abundance these are hornblende gabbro-diorite, granodiorite. quartz monzonite porphyry, granodiorite porphyry, schriesheimite (olivinic hornblendite), and hornblende-oligoclase lamprophyre. In the few local- ities where the various granitic types were too intimately mixed for mapping on the regional scale, they have been grouped under granitic rocks nndiffcrenfiated. Although chemical analyses were available for some of the rocks, norms have not been calculated because of the large proportion of in- tergrowths such as perthite and myrmekite in leucocratic varieties and because of the preponderance of minerals not calculable by normative methods in the melanocratic varieties. Gneissic Hornblende Diorite Gneissic hornblende diorite is characteristic of the basement of the Hinkley Hills and, to a lesser extent, of the basement rocks south of Hodge. It is exposed over 4 square miles and forms conspicuous, banded to massive unhanded outcrops. Hand specimens vary in appearance from unfoliated, unlineated hornblende diorite to well-banded horn- blende-andesine gneisses. The textural types grade one into the other, one extreme appearing wholly metamorphic and the other wholly ig- neous. Banding most commonly is the result of variation in hornblende content of the rock and in preferred orientation of hornblende. Segre- gation of hornblende and feldspar into distinct bands rarely is com- plete, and when complete, the monomineralic bands are locally devel- oped and only a few millimeters thick. Petrography of Chieissic Diorite. The least metamorphosed samples of rock have normal hypidiomorphic granular texture, bent twin lamel- lae in feldspar and slight cataclasis of crystal borders being the only apparent deformation effects. In most specimens, the proportion of an- desine to hornblende is about 7 : 5. Hornblende and plagioclase together 54 BARSTOW QUADRANGLE [Bllll. 165. make up more than 95 percent of the unmetamorphosed rock. The liorn- blende is pleochroic in shades of blue-j!i^-'<-~y*^' Figure 35. Sheeted (luartz monzonite sou midway between the two towns. I- *'"- ' ' ^ .„„..„ „„. ...... . „ -izonite south of the VMctorville-Sidewinder Well road, midway between the two towns. In this locality the steeply dipping, northwest and north- east-trending joint systems are much more feebly developed than the gently northeast- dipping sheeting. 11)54] GEOLOGY AND MIXKKAI- DEPOSITS 59 Figure 36. Biotite-quartz monzonite on the southeast flank of Quartzite Mountain crammed -.vith angular xenoliths of biotite hornblende quartz diorite. Except for this locality and the Stoddard dike complex, xenoliths are uncommon in quartz monzonite of Barstow quadrangle. Composition of the plagioclase in various parts of the Iron Mountain mass is fairly consistent between An50 and 56, as measured on the universal stage, although one section cut from a specimen taken on the northeast spur of the mountain near the paved road to the Hinkley dolomite deposit contained feldspar as calcic as An60-65. In the smaller individual intrusions in the vicinity of the Section 20 Hills, the com- position of the feldspar is medium to calcic andesine (An40-45), and the rock is more nearly diorite than gabbro. The labradorite crystals of the Iron Mountain stock tend to be much more lathy than in most granitic rocks, most crystals being 2-2^ times as long as wide. In some parts of the stock, however, the feldspar is much more nearly equidi- mensional and subhedral. Minor alteration products in the rock include yellow iron oxide (after hornblende), epidote, clinozoisite, and calcite after plagioclase, and sphene after titaniferous magnetite. Age and Correlaiion. Although the gabbro-diorite intrusions of Bar- stow quadrangle are similar in many respects to those in the Paradise Range south of Camp Irwin and to those in the vicinity of Chubbuck and Cronese Dry Lake in eastern San Bernardino County they may not be equivalent in age. The Iron ^Mountain stock is not in contact 60 BARSTOW QUADRANGLE [Bull. 165 fN il^ M f Figure 37. Vertical air photo of Bell Mountain showing three intrusions of schrieshei- mite and hornblendite on the north and northwest slopes of Bell Mountain. Summit of mountain is dark latite-andesite of the Sidewinder series ; other dark patches are horn- blende quartz diorite. A northwest-trending dike of hornblende-quartz diorite cuts the southwest quarter of the photo. Photo by Fairchild Aerial Surveys, courtesy U. S. Geological Survey and U. S. Army. with either the Hodge volcanic series or the Oro Grande series but probably is intruded by granodiorite porphyry. Small intrusions of gabbro-diorite cut the Triassic (?) Sidewinder volcanic series in the southeastern part of the quadrangle, so this type of rock presumably belongs to the Jura-Cretaceous period of granitic invasion. The gabbro- diorite evidently is one of the first rocks to be intruded in that period as it is cut in various places by quartz monzonite, granodiorite porphyry, and garnet pegmatite and aplite. Biotite Granodiorite Porphyry Biotite granodiorite porphyry is found in one mass covering slightly more than half a square mile, adjoining the Iron Mountain gabbro- diorite stock on the south and the Hodge volcanic series on the north. The dull dark-gray-to-greenish-black rock is less weather-resistant than the adjoining gabbro-diorite. Many examples of the granodiorite por- phyry are deceptive to identify in hand specimen, particularly those collected in the southern part of the mass. Except for presence of scat- tered large phenocrysts of orthoclase, the rock commonly resembles diorite. More normal-appearing facies of the rock are found in the northern part of the intrusion. The porphyritic character of the matrix if)r)4] GEOLOGY AND MINERAL DEPOSITS 61 rcH'k is not apparent in hand specimen as the smaller phenocrysts are I'loscly spaced. The large orthoclase perthite phenocrysts are oval to rectanpnlar in outline and average f of an inch in longest dimension. They do not make up more than 10 percent of the rock and most commonly make up only 5 percent. The large phenocrysts are set in a closely spaced mass of smaller phenocrysts 2-3 mm in longest dimension. These in turn are set in a small amount of microgranitic groundmass ; the latter is only faintly visible in hand specimen. The rock has been deuterically altered, with biotite partially converted to chlorite and plagioclase partly replaced by saussurite (finely divided carbonate and epidote-group minerals). The granodiorite porphyry has been concordantly injected into the Hodge volcanic series along the north border of that series and in that respect the mass is sill-like. Elsewhere, however, the rock is bordered by gabbro-diorite or overlapped by alluvium so that the original form of the intrusion is uncertain. The contact of the mass with the Iron Mountain gabbro-diorite is concealed in all but a few scattered places but the granodiorite porphyry probably intrudes the gabbro-diorite. Both are cut by quartz monzonite and by granite pegmatite and aplite. Petrography. In this section the large phenocrysts are found to be perthitic orthoclase which is untwinned or simply twinned on the Carls- bad law. The numerous smaller phenocrysts, which are fairly uniform at 2-3 mm in longest dimension, tend to be rectangular in outline and Figure 38. Hornblende diorite gneiss irjected by granite pegmatite, Hinkley Hills, north side Highway 466, three miles west of Barstow. Gneiss is probably Upper Paleozoic. 62 BARSTOW QUADRAXGLE [Bull. 165 'if' Figure 39.4. Photomicrogi-aph of lamprophyre (spessartite) from the vicinity of the Ball magnesite mine. The large prismatic and dia- mond-shaped crystals are green-hrown hornblende ; mottled crystals between are iiartially kaoHnitized oligoclase-andesine. Small crj'Stals of high relief at lower center of photo are epidote and clinozoisite alteration products of feldspar. Black crystals are titaniferous mag- netite. Plane polarized light, XI 9. . Figure ?.9i?. Quartz mnnzonite porphyry from the Hinkley Hills; o -^ orthoclase, ol =r oligoclase-andesine. A quartz crystal at extinc- tion lies between prominently twinned plagioclase in the upper right quadrant. Crossed nicols, X19. 1954] OKOLOGY AND MINERAL DEPOSITS 63 ) Figure 404. Kali-alaskite from an intrusion in Red Seal Ridge. Rock is made up predominantly of ortlioclase perthite and quartz, with subordinate oligoclase and an occasional biotite crystal. White grains in the central part of the photo are quartz ; orthoclase is uni- formly perthitic and everywhere conspicuous. The alaskite grades to the north into normal quartz monzonite. Crossed nicols, X19. Figure 40B. Quartz monzonite, Hinkley Hills. Most of the clear white or gray grains are quartz. A large, zonally altered oligoclase crystal is in the upper right quadrant and a mottled perthitic ortho- clase crystal at lower center. Crossed nicols, XI 9. 64 BARSTOW QUADRANGLE [Bull. 165 to be closely spaced. They consist of sodic plagioclase, greenish-brown biotite and an occasional orthoclase crystal. The microgranitic gronnd- mass consists predominantly of quartz together with lesser amounts of patchy biotite and scattered individuals of orthoclase and oligoelase ( ?). Some of the phenocrysts are zoned, part by normal transition from calcic toward sodic, but some by one or two reversals of the normal trend. Others are unzoned and are uniform in compositon at An20. Cores of zoned crystals are within the range of An25-30 ; none measured are more calcic than An30. The estimated mineral composition of the granodiorite porphyry before deuteric alteration can be summarized as follows : Large phenocrysts Small phenocrysts Groundmass Percent Percent Percent Percent Percent Percent Total Mineral of phenocrysts of rock of phenocrysts of rock of groundmass of rock in rock Orthoclase 100 5 1 <.5 15 8 13 Oligoelase 90 38 20 10 48 Quartz 9 5 40 20 25 Biotite 23 12 12 Apatite < 1 < 1 < 1 Titaniferous magnetite 2 11 The plagioclase has been extensively altered to epidote, clinozoisite and calcite. Epidote has also come in at the expense of biotite. . Age and Correlation. It is evident that the early history of crystal- lization of the granodiorite prophyry was complex. There may have been a mixing of magmas early in the sequence of invasion or there may have been significant assimilation of volcanic rocks of the Hodge vol- canic series into the incoming granitic material. The granodiorite por- phyry is not a gradational facies of any of the other rock types in the quadrangle but is a separate intrusion older than the quartz monzonite and its granitic satellites and probably younger than the gabbrodiorite of Iron Mountain. It differs somewhat in mineralogy as well as texture from other granodiorites of the quadrangle. Biotite Granodiorite Rock masses of this composition are confined to the northern part of the quadrangle. The largest is found north of the "Waterman mine where it is exposed over 4 square miles on Barstow quadrangle and extends over an area of more than 18 square miles north of the quad- rangle. Smaller masses are found scattered through the Hinkley Hills area, particularly north of the Pedry silver-lead mine. Over-all color of the granodiorite is light gray speckled with black. The ferromagnesian minerals tend to form a faint crude lineation which apparently does not have a uniform regional trend. Grain size is medium to fine for a granitic rock, ranging from 2 mm to 1 mm in longest dimension. Biotite, plagioclase, orthoclase and a little hornblende are recognizable in hand specimens. Some parts of the large mass north of the Waterman mine are crammed with mica-rich, schistose inclusions, many of which have been almost obliterated by remelting and recrystallization or by metasomatic reconstitution. The character of the least-altered inclusions indicates that they originally were slightly more mafic granodiorite than the host rock and were not sediments. 19r)4] CKOr.OfiY AND MINERAL DEPOSITS 65 Petrography. The typical granodiorite from north of the Waterman mine is a medium-jirained rock in which crystals avora<2:e .7-1 mm in loiiizest dimension. The textnre is predominantly hypidiomorphic <»ran- ular altlioujih linear and schistose metamorphic i)atches of qnartz and biotite make up a small percentage of the ht cataclasis at the borders of feldspar and quartz g-rains is almost universal in the slides examined. A little more than half of the rock i.s- made up of zoned oligoclase, the zones varying between calcic oligoclase at the center to medium oligoclase at grain borders. Orthoclase commonly makes up only 10-12 percent of the rock so the granodiorite is approaching the composition of quartz diorite. The orthoclase is slightly altered to dusty indeterminate material and is somewhat perthitic. Much of the quartz is metamorphic, crystal groups having intricate, sutured bound- aries. ]\Iost quartz grains are strain-shadowed. Primary and secondary quartz together make up 20-25 percent of the rock. Biotite makes up 3-5 percent of the rock ; it is a late stage mineral occupying interstices between quartz and feldspar grains. The mineral is trichroic-dark reddish brown to pale yellowish brown to dirty green. Minor acces- sories include magnetite and apatite. The most melanocratic phase may contain biotite up to 10 percent, together with perhaps 1 percent of relict, pale blue-green hornblende. The biotite commonly has formed at the expense of early-crystallizing hornblende. Chlorite, sphene and rutile are common minor alteration products in the more ferromagnesian. phases. Chlorite has largely formed at the expense of biotite and sphene and rutile after titaniferous magnetite and possibly biotite. Age and Correlation. Minor quartz monzonite intrusions cut small patches of granodiorite west of the Pedry silver mine in the Hinkley Hills. Elsewhere the granodiorite is not in contact with rocks older than Tertiary. It is intruded and overlapped by Pliocene volcanic rocks and covered by Recent alluvium. Except for its slightly deformed char- acter, the rock is similar to granodiorites of other parts of the south- western Mojave Desert. There is no reason to consider it older than Upper Jurassic. Biotite Quartz Monzonite Biotite quartz monzonite comprises by far the greatest bulk of the batholithic rocks of Barstow quadrangle. Almost the entire mass of the Granite Mountains is made up of this rock and it is exposed on or underlies three-fourths or more of the rest of the quadrangle. Over wide areas it is uniform in composition and general appearance. Coarse- grained porphyritic facies are uncommon although peripheral and satellitic facies commonly are granophyrie. It grades locally into rock as salic as alaskite at one extreme and as mafic as hornblende-biotite granodiorite on the other. In common with most California batholiths, small hornblende-rich segregations ranging in composition and textvire from hornblendite to the lamprophyre spe.ssartite are widely distributed in and adjacent to the quartz monzonite. These must be genetically related to the quartz monzonite. Average specimens of the quartz monzonite are medium-coarse- grained rocks made up of crystals averaging 3 mm in longest dimen- sion. The background color is creamy white to pale pinkish-white. Sur- 3 — 85919 66 BARSTOW QUADRAXGLE [Bull. 165 faces are evenly speckled with black biotite. Microcline and plajrioclase are readily identifiable in hand specimens in approximately equal proportions. Quartz makes up nearly one-third of the rock. Biotite is the only common characterizinor accessory mineral, although in the Sierra Melada of the Granite Mountains muscovite is an additional accessory present up to 2 percent of the rock. Locally developed grano- dioritic facies may carry a little hornblende. The cerium-bearing epi- dote, allanite, is present as a rare constituent in the Sierra ]\Ielada massif. Quartz monzonite exposures tend to be rounded and bouldery owing to relatively rapid disintegration along widely spaced, rectangular joint systems. One set of these joints commonly strikes northwest at near verticality, another northeast, near vertical, and a third at or near horizontal. Sheeted granite in which the near-horizontal set of joints predominates is prominently exposed along the Yictorville-Sidewinder \Vell road midway between the two towns. Partly articulated, joint'^d boulder piles stand up above the alluviated plain between Bell ]\Ioun- tain and the Sierra Melada. the last remnants of eroded granite hills. Petrography. The type quartz monzonite is a coarse hypidiomorphic granular rock having an average grain size in longest dimension of 3 mm. Quartz and feldspar grains are of approximately equal size and commonly show slight cataclasis at the borders. Quartz is commonly strain-shadowed and potash feldspar is almost invariably perthitie. Both micas and plagioclase feldspars commonly have bent lamellae. The mineralogy may be summarized as follows : Percent by volume in Degree of type specimen variation in Primary minerals (Rosiwal) other specimens Quartz 33 25-35 Microcline perthite 34 30-.35 Oligoclase-andesine (An2S) (U-Stage) 29 25-30 Biotite 3 2-4 Muscovite <1 0-2 Sphene tr <1 Magnetite tr <1 Zircou tr tr Fluorite tr tr Apatite tr tr Rutile tr tr Allanite tr tr In addition to the above list, trace§ of secondary minerals such as epidote. clinozoisite, limonite, chlorite and a clay mineral commonly are present. The more leucocratic facies of the quartz monzonite approach alaskite in mineralogical composition. These generally consist of the following minerals : Microcline or orthoclase perthite (■.5-75'/r Oligoclase 5-15% Quartz 20-309^ Biotite <1% Sphene tr Mairnetite tr The melanocratic facies commonly have the following mineralogical composition although there is greater variation among the darker phases I than in the lighter-colored variations : rangle : Oxide SiO- Conip mi'iis nf tl rangle. isite (if lli speci- fiiini variiiiis parts le Barstow iiuad- W. H. Herdsman, a-aly-t 73.14 13.62 1.74 .79 .28 .07 1.44 .64 4.1.-) 3.30 .28 (-30% QtKirtz lo-20% l?i,.rite 8-10% Ilornhleiide <1% ChonicaJ Composition. The following eheniieal analy.sps g-ivo addi- ticuial data on the composition of quartz monzonitos of Barstow (piad- Average of 34 n.uartz monzonites after Daly * 67.41 l-).76 1.96 1.93 .51 .06 3..^)4 1.43 3.76 3.45 .19 p. 4.57, New York, 1933. It is immediately apparent that the silica content is nnnsually hip:h and that the lime content is unusually low for average quartz mon- zonite'. The analytical data are more nearly like those of an alkali granite than of most quartz monzonites. Nevertheless, the approxi- mately e(|ual plagioclase-potash feldspar content classes the rock petro- graphically as quartz monzonite. Curtis '^ has noted a similar silica- lime ratio in quartz monzonites of the north central Sierra Nevada. None of the analyses listed by Larsen (1948) for the granitic rocks in the batholith of the Peninsular Ranges approach the compositions above listed for the Victorville quartz monzonite of the Barstow quad- rangle. Age an(J Corrclaiiun. . The quartz monzonite of Barstow quadrangle resembles the many other ciuartz monzonites which are broadly dis- tributed throughout the Mojave block and San Bernardino Range. These rocks have been given 'local names such as the Cactus granite of Vaughan (1922) and Gardner (1940), the Cactus quartz monzonite of Guillou (1953). the Victorville quartz monzonite of Miller (1944, pp. 105-106), and the Atolia quartz monzonite of Hulin (1925, pp. 33-42). Tile only important difference that the author has noted between char- acteristics of the (juartz monzonites of Barstow quadrangle and petro- graphie descriptions of those from other parts of the Mojave Desert is the almost universal perthitic character of the potash feldspars. If this characteristic is prominent in (piartz monzonites from other areas, no mention has been made of it ; it may or may not have any genetic [nnportance. There has been a tendency in recent years to call all of the late-intruded Mojave Desert quartz monzonites Cactus granite or Cactus quartz monzonite after Vaughan. This is a generalization that Curtis, Garni.s.s }{., personal comnn.nication. 68 BARSTOW qrAnRAXC.T.E [Bull. 165 should be avoided as there is quartz monzouite debris in rocks of the Permian Fairview Valley formation and there mar be quartz mon- zonites of several different ages within the ]\Iojave block as well as in adjoining geomorphie provinces. The author concedes that the quartz monzouite of the Barstow area may be as young as Cretaceous but the chemical and mineralogical composition of the quartz monzouite of Bar- stow quadrangle has no counterpart of any magnitude in the Penin- sular Ranges batholith. Quartz monzonites are found all the way across the Mojave Desert to the Tehachapi Mountains and quartz monzouite is a fairly common rock in the eastern and southeastern Sierra Nevada. The quartz monzonites of Barstow quadrangle are far more logically considered as correlative with the Sierra Nevada batholithic rocks than with those of the batholith in the Peninsular Ranges of San Diego County. It is quite possible that there are both Jurassic and Cretaceous granitic rocks in both the Sierra Nevada and San Diego County batholiths. V Quartz Monzonite Porphyry Rock of this type is widely distributed over Barstow quadrangle mainly as massive, Aveather-resistant dikes, but also as peripheral gra- datioual facies of quartz monzonite. It is the principal dike rock in the dike complex of the Stoddard Well vicinity and is also the principal dike rock in the Hinkley Hills. Quartz monzonite porphyry is also a gradational facies of quartz monzonite north of the Ball magnesite mine. Most facies of the rock characteristically are crammed with pheno- crysts of oligoclase-andesine and some orthoclase perthite which together make up 40 percent or more of the rock. Euhedral biotite and horn- blende and rounded quartz phenocrysts also are commonly present in the porphyry but these are generally smaller than the feldspar pheno- crysts. Some variations have no quartz phenocrysts. There are all gra- dations between rocks having megascopically conspicuous granitic grouudmass textures and rocks that appear volcanic. In thin section, however, nearly all of these dike rocks have either megagranitic or microgranitic groundmasses and without much question are derived from the same parent magma as the quartz monzonite. In a majority of dikes the rock is relatively uniform and the rectangular feldspar pheno- crysts a^'erage 4-6 mm in longest dimension. Many, however, have phenocrysts averaging as small as 3 mm in longest dimension and in these rocks the proportion of phenocrysts to grouudmass drops con- siderably. Groundmass coloration varies widely in the porphyries from dark gray or even black to cream-colored or pale pink. The darker variations contain a greater proportion of biotite and iron ores and these con- stituents are more evenly disseminated. The porphyry cropping out north of the Ball magnesite mine is the most typically granophyric of all the varieties. I\Iyrmekite and kindred quartz-feldspar intergrowths make up a considerable part of the rock. Petrography. In thin section the coarser-textured varieties are sceu to be composed of large phenocrysts of oligoclase (An'28) and ortho- clase perthite with smaller phenocrysts of euhedral biotite and horn- blende as well as subhedral, partly resorbed quartz. ^Myrmekitic inter- growths may \m\ke up 40 percent of the rock. Spherulitic intergrowths 19:)4 GEOLOGY AND MINERAL DEI'OSITS 69 of (iiiart/, and feldspar are also eomnion as are radial fibrous coronas of similar material around quartz and feldspai- phenoerysts. A typical mineral composition among coarse-grained varieties is estimated as lOlloWS : Percent of PciTciit of phenoerysts groiiiKimass (Phenoerysts — (Orciundmass — Total Mineral speeies 40% of rock) GO%ofrnek) in rock Olijrcclaso (An2S) 50 8 25 Orthoclase and orthoclase perthite 25 22 23 Quartz 15 22 19 liiotite 7 2 4 HoinliU-nde 3 4 3.6 Titaiiiffi-ous masnetite 2 1.2 Myrniekite interirrowths __ 40 24 too KM) 99.7 The finer textured varieties vary more broadly in apparent mineral composition although percentages of groundmass minerals can seldom be estimated precisely. Plagioclase is, in some cases, the only abundant mineral present as large phenoerysts, although biotite is generally present as phenoerysts intermediate in size between the plagioclase phenocl\vsts and the groundweb. In a few dikes the predominating large phenocryst mineral is perthitic orthoclase, smaller phenoerysts of quartz and oligoclase nearly always being present in rock of this variation. The groundmass of such varieties is made up of equigranular, interlocking, subhedral crystals of plagioclase, potash feldspar and quartz, together with disseminated, interstitial, late-stage magnetite and biotite. Imperfectly-formed spherulites and radial-fibrous coronas are present in some degree in all textural and compositional variations of quartz monzonite porphyry. Disseminated secondary patches or grains of magnetite, epidote, clinozoisite, sphene, sericite, hematite and chlorite are the commonly secondary minerals present. Allanite has been found in one slide as a late stage accessory mineral. Tlie following tables show comparative chemical data on quartz mon- zonite porphyries : Composite of 14 samples Type specimen of of Quartz monzonite quartz monzonite Composite of 12 quaitz poriihyry from vai ious porphyry from monzonites from Bar- paits of Barstow _ Stotiflard Well. stow quatiranij; >. Average of 8 J quadrangle. W. H. W. H. Herdsman, \V. H. Herdsman. quaitz monzonites 0.\ide Heidsmaii, analyst. analyst. analyst after Paly * SiO, 66.59 70.95 73.14 67.41 Ah(h 16.31 14.79 13.62 15.76 FeO 3.48 2.62 1.74 1.96 Kp,0, .70 .12 .79 1.93 Tin, .46 .28 .28 .51 MiiO .OS .06 .07 .06 ("a<> 2.52 .92 1.44 3.54 MfiO 1.14 .58 .64 1.43 KoO 8.76 4.88 4.15 3.76 Xa:;0 3.93 3.62 3.30 3.45 HsO- .22 ra 105°C .29 .28 HoO* .29 © 105°C .72 .32 CO2 nil nil nil I^a-. .16 .07 .07 .19 * Haly. U. \.. Igneous rocks and the depths of the earth; McGraw-Hill Book Co., Inc.. p 4.57. New York, irS.S. It is evident that there is considerable variation in chemical com- position among the various quartz monzonite porphyry dikes as might be expected in satellite rocks. The principal differences between the porphyries and quartz monzonite and also among the various dikes 70 BARSTOW QUADRANGLE ^- w' ^^ [Bull. 165 Ftgure 41.1. Phfitcimicrograph of biotite-quartz diorite from the hills two mile.s northwest of the Waterman silver mine. The larger crystals are nearly all andesine : many are multiply zoned, both normally and reverse. Cores are calcic andesine ; peripherae, sodic andesine. Most of the quartz is in small interstitial grains. Prismatic and subhexagonal biotite plates are clustered at lower center. Crossed nicols, Xl'.t. FiGTHE 41/?. Granodiorite iiorphyr>'. Iron Mountain district. Entire upper part of field consists of one large crystal section of orthocla.se poikilitically enclosing partial crystals of hornblende and biotite. Small crystals of partly altered sodic andesine are held in a granitic matri.K of fine-grained quartz and feldspar. Crossed nicols XI 9. 1954 GEOT.OOY AND ^flXERAT, DEPOSITS 71 FiGTTRE 42.4. Schriesheimite, plane pnlarized li^ht, XUI. Kiitire field consists of two preenish-lirown hornblende crystals enclosing small colorless diopside crystals and larger serpentine patches pseudo- morplious after olivine. In tlie type Bell Mountain specimen in the University of California collection (o(>-I-10). unaltered olivine is present in e.Kcess of diopside. The schriesheimite most commonly contains little relict oli\ ine. Figure 42Z?. Hornblende sabbro-diorite, crossed nicols, XI 9. Field is made up entirely of blue-green hornblende (h) and sodic labra- dorite ("1"). Crossed nicols, X19. it 72 BARSTOW QUADRANGLE [Bull. 165 themselves appears to lie largely in the ferromajinesian mineral con- tent, but there is some decrease in the silica content of most quartz monzonite porphyries as compared to the associated quartz monzonite. Age and Correlation. A study of the dike complex in the vicinity of Stoddard "Well shows that quartz monzonite porphyry dikes Avere in- truded over a considerable period of time. Kock of this sort beg'an to come in prior to invasion of normal-textured quartz monzonite, con- tinued to be emplaeed as a peripheral facies during crystallization of the main quartz monzonite mass (or masses), and continued to be in- truded as dikes after crystallization gf the normal quartz monzonite. Quartz monzonite porphyry is included as pendants and xenoliths in quartz monzonite as well as in dikes cutting it. Quartz monzonite porphyry intrusives are not common in the western part of the Mojave structural block except in the vicinity of Barstow quadrangle and the adjoining Ord ^lountains. Some of the intrusions in the Ord Mountains originally described by Gardner (1940, pp. 268- 269) as meta-porphyry and correlated by him with the Triassic (?) Ord ]\Iountain group are the same character and probably are the same general age as the quartz monzonite porphyries of Barstow quadrangle. They are much more logically correlated with the granitic rocks of the Jura-Cretaceous interval than with volcanic rocks of either the Ord Mountain group or Sidewinder volcanic series. Schriesheimite Olivine-bearing hornblendite, some of which closely approximates the schriesheimite from the Odenwald of Saxony, occurs in three small masses of circular or oval outline on the north and northwest slopes of Bell Mountain. The smallest intrusion is slightly less than 100 feet in diameter and the largest over 400. The type rock, taken from the center of the most southerly intrusion, consists predominantly of coarse-grained, subrectangular-to-oval, black liornblende crystals 6-8 mm in longest dimension. These poikilitically enclose numerous yellowish-brown olivine grains averaging .5 to 1 mm in longest dimension, together with similarly-colored pyroxene crystals of similar size. Some clinopyroxene is also present interstitially ar- ranged betAveen the much larger hornblende crystals. In some varia- tions of the type rock guest clinopyroxene is in excess of olivine. Both olivine and clinopyroxene commonly are altered, olivine to serpentine and talc, and clinopyroxene to chlorite. Fresh, unaltered guest minerals are rare in some specimens. Plagioclase is absent in the type specimen, but labradorite is present up to five percent in some parts of the largest intrusion. Peirography. The rock consists predominantly of large interlocking hornblende crystals which make up 80 percent or more of the rock. These enclose euhedral to oval, partly resorbed crystals of olivine and diopside which together make up approximately 14 percent of the rock. In many sections olivine and diopside or their alteration products are in approximately equal proportions, but in the type specimen in the University of California collection (36-1-10), olivine is considerably in excess of diopside. In a few sections diopside is the predominating host mineral. In addition to the included minerals, many hornblende crystals exhibit oval spots of different color and birefringence from the host l!)r)4j GEOLOGY AXD MINERAL DEPOSITS 78 hornblende. The material Avithin the spots is in crystallojiraphie orien- tation with the surround in*; crystal and appears to be similar to the surroundin0 Augite (titaniferous) 2.")-80 Olivine 10-15 Analcite ^- 3-5 Ilmenite 3-4 Natrolite 1 Variable amounts of alteration products such as chlorite, iddingsite, bowlingite, and chalcedony generally are present. The ilmenite tends to be in subhedral rods and plates. Age and Correlation. The diabase dikes cut the upper lakebed series in the Kramer Hills and mu.st have been intruded late in the Miocene or early in the Pliocene. They do not cut the less deformed dacites regarded as upper Pliocene. Pliocene Volcanic Rocks Dacite Erosional remnants of red, pink and gray dacite are scattered over the northern part of the quadrangle. Plugs, necks and flow remnants 86 BARSTOW QUADRANGLE [Bull. 165 $ FiGURK 47 A. Photomicrograph of Pliocene dacite vitrophyre from the Kramer Hills showing: embayed, fractured quartz phenocryst and numerous zoned sodic andesine crystals. The normally abundant biotite is sparse in this held. Crossed nicols, X19. FiGiiKF 47B. Typical vitroclastio texture in rhyo-dacite tuff from a small remnant southeast of Hodge. Larger angular grains are quartz ; lathy grains are oligoclase and the sharp, curved fragments are glass shards. Plant- polarized light, Xiy. 1954; GEOLOGY AND MINERAL DEPOSITS 87 of small size are most common, but the volcanic piles of the Waterman Hills, Hinkley Hills and Kramer Hills are made up of considerable tuff and coarser pyroclastic material. In the Hinkley and Waterman Hills such piles reach a thickness of 70 feet. The dacites are similar in appearance and age to those of the Calico Mountains, and stratified masses bear the same unconformable relation to the much more severely deformed underlying Miocene rocks as do those of the Calico Moun- tains. They intrude or overlap most of the pre-Pliocene rock units in Barstow quadrangle and themselves are overlapped by Pleistocene and Recent alluvium in which dacite debris is abundant. In general, the dacites are vitrophyric or vitroclastic rocks, some con- taining a large proportion of glass. The coarsest-grained, most nearly holocrystalline variations tend to be found in intrusive rather than extrusive masses. Through all variations, plagioclase phenocrysts pre- dominate over all others. Biotite is a common and abundant accessory and hornblende is generally present as phenocrysts in minor amounts. Quartz phenocrysts are common in some variations and rare in others. Petrography. The least glassy varieties are made up of less than 5 percent glass, 35 percent phenocrysts, averaging 1.5 mm in longest dimension and 55-60 percent of smaller groundmass crystals. The most VK^ m. Im ^ '■«iiii, « »«i A ^^ '•<( T* :,'m^:l)k0- Figure 48. Bedded upper Pleistocene deposits exposed in the Palisades of the Mojave River 4 miles north of Victorville. Scattered mastodon and horse bones have been found in these deposits near Victorville and Hesperia. 88 BARSTOW QUADRANGLE [BuU. 165 glassy varieties are about ^ glass. About 70 percent of the phenocrysts are sodic to medium andesine which commonly is zoned. Both normal and reverse zoning is conspicuous in the plagioclase phenocrysts and many are full of remelt patches. Groundmass andesine, slightly more sodic than that of the phenocrysts, generally is not zoned. Fifteen to twenty percent of the phenocrysts are biotite, pleochroic in shades of brown, and 10 percent or less are quartz, commonly corroded and em- bayed. Brown hornblende phenocrysts may be present up to 3 percent ; optical properties of these crystals are between those listed for common hornblende and oxyhornblende. Groundmass crystals are predominantly sodic andesine with some quartz and a little sanidine. Magnetite is commonly present as dis- seminated dust. Some textures are pilotaxitic, others subtrachytic and still others normal vitrophyric. Replacement patches of jarosite are present in some specimens. As in many volcanic rocks, the magmatic history of the Pliocene dacites has been complex. The multiple and reverse zoning in the feldspars reflects numerous fluctuations in physico- chemical conditions in the parent magma and neither the plagioclase nor the quartz phenocrysts were in equilibrium with the melt at the time of final lithification. Although no analyses of the dacites are avail- able and although the submicroscopic material in many of the dacites is large, it is probable that the dacites are nearer the over-all composi- tion of rhyolite than the composition of the plagioclase would indicate. The proportion of potash mica is high and it is possible that much of the glass and submicroscopic material might have yielded more quartz and sanidine had crystallization gone nearer to completion. Quaternary Rocks Pleistocene Deposits Deeply dissected Pleistocene alluvium is widely distributed over the quadrangle, particularly along the course of the Mojave River between Victorville and Helendale and in the Vitrlite marl quarries which are north of Helendale across the Mojave River. Four facies of the Pleisto- cene deposits are recognized : 1. Coarse fanglomerate from the upper parts of alluvial fans. 2. Buff to red floodplain clays, silts and gravelly sands. 3. Light yellowish-gray, limy clays, commonly containing salines and alkalies, the fine-grained evaporite material from extinct superficial playa lakes. 4. Thin-bedded white opaline shales, carbonate rocks and tufifaceous (?) sands, all of lacustrine origin. The four types interfinger one with another and grade to some extent one into the other, but gradations generally are rapid. The facies most commonly exposed along the Palisades of the Mojave River consists of clay, silt and gravelly sand, the floodplain deposits of the Pleistocene Mojave River. These, on the whole, are weakly consolidated or uncon- solidated except for local, caliche-cemented strata a few feet thick. North of Helendale in the vicinity of the Vitrlite marl pits the flood- plain facies may be seen to interfinger with white lakebed clays, marls, opaline shales and tuffaceous (?) sandstones in beds a few feet thick. These mark the position of part of a former lake basin of considerable size. They apparently have been raised somewhat along the upthrown side of tiie Helendale fault and in all probability are slightly lower 1954] GEOLOGY AND MINERAL DEPOSITS 89 0^-' •^- -.-«-** -*•■-" -c^^- -••>' -r^ ■-; 4--^^^ -^fc*-. -T ■-. y" : :^ .'■^]^i^'^^ ■*- ■^- -4' 1 4««gt &■' 'V #4k%'yi;.ifii;^ir^' Figure 49. Basal caliche-cemented breccia in upper Plei-stocene fanglomerate north of Quartzite Mountain and south of Sparkuhle Hill. Groundwater derived from intermittent rains dissolves calcium carbonate from areas of exposed lime- stone and tends to redeposit it by evaporation above bedrock or above some other impervious horizon. stratigraphically than any of the upper Pleistocene beds exposed in the Palisades of the Mojave River. Althouofh the lacustrine facies of the Pleistocene deposits resembles to some extent the upper Miocene ( ?) lakebeds of the Kramer Hills, the Pleistocene beds are undeformed except by very gentle tilting whereas the Miocene ( ? ) beds everywhere are strongly deformed. In addition, there is Pliocene volcanic debris in the beds and there can be little doubt of the interdigitate relation be- tween the lakebeds at the Vitrlite pits and the adjacent Pleistocene floodplain alluvium. South of the Upper Narrows of the Mojave River thin, light yellowish- gray limy siltstone and claystone are distributed over several acres, indicating the former existence in very late Pleistocene or Recent time, of a shallow lake. This may have been the result of uplift (damming) on the Victorville fault. Caliche-cemented horizons are common in Pleistocene sediments, particularly in the upper parts of alluvial fans draining limestone terrain. Basal caliche breccias more than 20 feet thick are character- istic in walls of canyons cutting alluvial fans northeast of Oro Grande. Thinner, perched caliche breccias are also commonly found at various distances above bedrock where they overlie clay-rich horizons of low 90 BARSTOW QUADRANGLE [Bull. 165 Figure 50. Detail of coarse caliche-cemented Pleistocene fanglomerate in the Sparkuhle Hill vicinity. permeability. A low, sinuous, ealiche-cemented ridge several miles long, roughly following the northwest-trending course of a present-day wash, is a conspicuous feature in air photos of and on the ground in the middle of T. 8 N., R. 5 W. (between Helendale and the Shadow Moun- tains). It marks the course of a Pleistocene stream whose bed became caliche-cemented by intermittent, carbonate-laden wash waters. Regional uplift and differential erosion in Recent time has resulted in rise of the former streambed to form a ridge standing 20 to 40 feet above the slope of the present wash. Thin partings and fracture fillings of gypsum and caliche are char- acteristic of Pleistocene deposits along the Victorville Sidewinder Well road northwest of Bell Mountain. Gypsiferous beds are uncommon elsewhere. The rock types present in the Pleistocene alluvium vary broadly from place to place as they reflect the bedrock character of the high- lands from which they were derived. In the Palisades of the Mojave, the debris reflects the lithologic assemblages currently exposed in the San Bernardino Range and San Gabriel Range plus minor percentages of debris derived locally from tributary washes draining the Victorville district. Southeast of Lenwood the folded Pleistocene beds consist raainlv of metavolcanic debris derived from the Stoddard Mountain- 19541 GEOLOGY AND MINERAL DEPOSITS 91 r ^ '<■ FiGURE 51. Caliche-cemented alluvial fan flanking a small limestone hill north of Quartzite Mountain. The apparent dip of the deposit is the normal angle of repose for debris of that coarseness and angularity. Sidewinder Mountain vicinity. North of the Mojave River north of Barstow and within a one-mile arc of the town on the south, the allu- vium contains debris derived largely from the north, including material from the Waterman gneiss, Oro Grande series and the Pliocene dacite remnants. Age and Correlation. Pleistocene alluvium closely resembles Recent alluvium and much of the latter is reworked Pleistocene material. How- ever, most Pleistocene deposits have been uplifted and dissected whereas Recent deposits are being built into a new base level of different aspect and elevation. Scattered occurrences of mammalian remains serve to date the deposits. A horse metapodial was found west of the Victor- ville cement plant and miscellaneous mastodon bones were found at scattered points between Victorville and Plesperia. These remains are in the Los Angeles Museum at Exposition Park. They were regarded as upper Pleistocene by the late Chester Stock.^^ The deposits of the Palisades of the Mojave River unquestionably are the finer-grained out- wash continuation of the tremendous alluvial fans (Inface gravels) so well exposed in roadcuts at the summit of Cajon Pass. The maximum thickness of Pleistocene alluvium is not known, but more than 800 feet " Personal communication, 1948. 92 BARSTOW QUADRANGLE [BuU. 165 ■^^.juts^i^ ■-.3i' "**^-— • t***^ Figure 52. Caliche-cemented Pleistocene arkose cropping out east of the Harper Lake road seven miles north of Helendale. of probable Pleistocene material has been penetrated in wells at the edge of the quadrangle due south of Victorville. At the southwest corner of the quadrangle a thickness in excess of 1000 feet might be expected. Recent Deposits Recent deposits of several sorts cover large areas of Barstow quad- rangle. Alluvium, laid partly by streams and parth' by the wind, has the broadest distribution. It generally has the same character as the Pleistocene alluvium described in preceding paragraphs, but grades more commonly into coarse fanglomerate around the bases of the moun- tains and scattered buttes and is found on aggradation plains ob\i- ously of Recent development. Thin playa silts and alkali-rich e vapor ites are found in several local, closed basins in Apple and Fairview Valleys. The larger Harper and Mirage dry lakes which border the quadrangle to the north and west contain somewhat thicker accumulations of like character. None are notably saline. Sand dunes have accumulated in several scattered areas, notably along the ^Mojave River in the vicinity of Lenwood, at the western edge of the quadrangle northwest of Adelanto, and north of Highway 466 between the railroad and Harper Dry Lake. Only those north of Len- wood cover any great acreage. The dune sands commonly are poorly 1954] GEOLOGY AND MINERAL DEPOSITS 93 sorted and consist of one-fourth clay-size particles and three-fourths fine sand. The sand particles consist of pranitic debris, Tertiary vol- canics and older metavolcanics deflated mainly from the Mojave River wash or from beds of dry lakes. Lijjht-buff wind-laid sands, not deposited in dunes but plastered onto hillsides and blown into gullies, are conspicuous on the landscape north and east of Harper and Mirage Dry Lakes. In the "ranitie hills 2 miles northwest of the Waterman mine, gullies 10 to 15 feet deep have been buried in blow-sand. Another conspicuous feature of Recent surfaces in areas of low relief are the so-called desert pavements. These are relatively flat surfaces, a few square rods to several acres in extent, from which all particles smaller than gravel size have been removed. The subangular pebbles and cobbles are tightly w^edged together and are further held in place by finer particles which have gravitated into the interstices. Desert pavements are largely the work of deflation aided by occasional rains and sheetfloods. Pebbles of the pavements commonly are coated with desert varnish, a mixture of iron and manganese oxides polished by wind abrasion. Structure Regional Structural Setting Barstow quadrangle is in the south central part of the ]\Iojave struc- tural block. This block as defined by Hewett ^^ is wedge-shaped, being bounded on the northwest by the Garlock fault, on the southwest by the San Andreas fault, and (partially) on the east by the thrust-fault system that passes south to southeasterly east of the Avawatz and Soda Mountains. Elements of the block probably do not extend much east of the 116° meridian (w^est longitude) although insufficient geologic mapping has been done south of the Ivanpah and Avawatz quadrangles to establish precise structural trends there. Within the Mojave block the predominant trend of the topographic features, as w-ell as the faults which control them, is northwest. Al- though this northwestern trend is conspicuously a Quaternary feature still tectonically active, there is considerable evidence, particularly in Barstow cjuadrangle, that the northwestern structural trend was estab- lished as far back as the Jura-Cretaceous orogeny. Hewett,^^ who has done extensive work in the ]\Iojave Desert, has concluded that the Mojave block has been rising over a period starting at least as far back as Paleocene and possibly as far back as Cretaceous, with major rise and eastward thrusting in late Pliocene. Hewett also suggests that the active, northwest-trending system of faults has devel- oped along older tectonic lines of weakness in response to gravitational adjustments within the eastward-moving Mojave block. The structural features of Barstow quadrangle in general seem in harmony with the regional setting as pictured by Hewett, but the ap- parent strike-slip movement on the northwest-trending faults of the quadrangle, particularly along the Ilelendale fault, and the westward thrusting along the Waterman thrust have yet to be resolved into Hewett 's Mojave block concept. " Hewett, D. F., personal communication, 194 8. "^ Hewett, D. F., personal communication, March 1953. 94 BARSTOW QUADRANGLE [Bull. 165 i I f 1954] GEOLOGY AND MINERAL DEPOSITS 95 Folds Folds Produced at op Near the Close of the Paleozoic The earliest period of foldinji: in Barstow quadran<;]e that can be dated with any precision is reflected by the angular unconformity seen between the Carboniferous Oro Grande series and the Permian Fair- view Valley formation northwest of Southwestern Portland Cement Company's Reserve quarry. The extent and severity of this folding cannot be determined conclusively because of the small area over which the unconformity is exposed. It is probable that, in common with other Permo-Carboniferous sections in the Mojave Desert and Inyo County where local unconformities are relatively common, the unconformity represents a local disturbance and hence has little regional significance. This folding could have taken place either in Lower Permian or Upper Permian time depending upon whether the fossils in the cobbles of the Fairview Valley limestone conglomerate are interpreted as being the same approximate age as the formation itself or as being older. Elsewhere in Barstow- quadrangle the earliest recognized folding affects the Oro Grande series, Waterman gneiss and Hodge volcanic series, all believed to be of Upper Paleozoic age, and the deformation or deformations involved most probably belong to the end-Paleozoic orog- eny. Axes of folds produced during the orogeny commonly trended northeast to east in contrast to later periods of crustal shortening which produced folds trending predominantly northwest. Although later fold- ing, faulting and igneous intrusion have tilted or otherwise obscured the original shape of many of the folds, it is fairly clear that, with some exceptions, they were broader and more gentle than the acute folds produced in Jurassic and Tertiary disturbances. The principal arc of the Mojave River bed as it crosses Barstow quadrangle reflects bedrock structures produced in the end-Paleozoic orogeny. Rocks which went through the end-Paleozoic orogeny in general have suffered far greater metamorphism than those younger than Paleozoic. The principal examples of folds, or parts of folds, stemming from this orogeny are the relatively simple anticlines so conspicuous in the hills south of the Waterman mine (northeast of Barstow), the more complicated anticline of the Hinkley Hills, the homocline in the Hodge volcanic series northwest of Hodge, and the syncline in the Oro Grande series of the southeastern Shadow Mountains. The Oro Grande series of the Quartzite Mountain vicinity and the Fairview Valley formation west of the Sidewinder mine were also deformed in the end-Paleozoic orogeny, but the shape and trend of the end-Paleozoic folds in those areas have been considerably modified by Jura-Cretaceous and later deformations. The Waterman anticline is an unusual structure in that, although it is essentially a simple arch complicated, at least on Barstow quadrangle, by few sub-structures, the rocks which make up the arch are severely sheared, some to the degree of mylonites. In the light of their highly deformed condition, the simplicity of the arch is remarkable and it must be assumed that the shearing stresses were applied in a more or less horizontal plane prior to the time of the principal arching. The principal anticline of the Hinkley Hills is much more compli- cated and acutely folded than the Waterman anticline and it is dis- rupted by numerous small faults as well as by igneous intrusions. Effects of interbed slipping are conspicuous and widespread, ruptured 96 BARSTOW QUADRANGLE [Bull. 165 septa from the more competent beds having pierced and crumpled the less competent layers both parallel to and diagonally across the bedding planes. Petrofabric studies carried on by Weiss ^^ in the western part of the Hinkley Hills indicate that some of the folds are complicated, northeast-trending, northeast-pitching, partly recumbent alpine, types deformed under extreme conditions. "Weiss summarizes the results of his petrographic studies as follows : The fabric study has confirmed that these rocks have undergone an intense penetrative deformation. The most important penetrative structure within the area is a marked lineation which pervades all the rock types, and which has been shown by fabric analysis to be a true B-axis. This B-axis always plunges shallowly, and it is an axis of small and large scale folding as well as one of marked elongation. Folding is most pronounced in the marble bodies, but is present throughout. The style is disharmonic and the folds tend to be polyclinal. The rocks have only one marked s-plane, which takes the form of a mega- scopic foliation usually folded about the B-axis. It is everywhere parallel to a differential compositional layering which represents original bedding in the case of those rocks derived from sediments, and the product of chemical or mechanical metamorphic differentiation in other cases. No undoubted axial plane foliation has been observed. In some rocks, especially in the pure white quartz- ite lenses within the marble bodies, the foliation is so intricatel.v contorted as to possess no planar significance. In such cases the lineation is the only visible penetrative structure, and the rocks have a markedly fibrous texture. Some of the massive quartzites within the area show crossed [OKI] girdles for [0001] in quartz, similar to those characteristic of granulite fabrics. The fabrics throughout suggest that, though flow of the rock mass has been extreme, tectonic transport has been slight or negligible. The rock mass as a whole has undergone intense elongation parallel to B with a small but variable amount of transport normal to it. The tectonic stresses have been transmitted as strong axial squeezing about B with slight penetrative shear normal to it. The tendency for the symmetry of the fabric to be orthorhombic or weakly monoclinic supports this view. It is suggested that the rocks under consideration were deformed at a mod- erate to deep tectonic level in a major axial mountain building movement of Alpine type. Nowhere else in the quadrangle and adjacent areas are rocks of apparent Paleozoic age so severely deformed as in the Hinkley and Waterman Hills. The homocline involving 10,000 feet of the Hodge volcanic series, cropping out seven miles to the southwest and having , similar structural trends, is far less deformed. | This broad homocline trending N. 10° E. and dipping 60° to 70° northwest is complicated by minor crenulations only. It is cut by a branching dip slip fault system which has been somewhat warped by later folding and by metamorphic shear and recrystallization in the wall |. rocks. Consequently the fault traces, as seen in the accompanying photo- graph, more nearly resemble a stream pattern than a fault pattern. Faults of like character cut the gneiss complex south of Hodge. The Hodge homocline is terminated along its northern border by granitic rocks and is cut by numerous small intrusions near its eastern ex- tremities. The broad syncline in the southeastern Shadow Mountains, involv- ing more than 9000 feet of Oro Grande metasediments, overlaps the common boundary of Barstow and Shadow Mountains quadrangles and has its axis on Shadow Mountains quadrangle. Consequently, only the east limb lies within Barstow quadrangle. It is a canoe-shaped fold having a north-trending axis, a steep southerly pitch, and a northwest- " Weiss, Lionel, personal communication, November 19o2. 1954] GEOLOGY AND MINERAL DEPOSITS 97 trending warp at its northern end. One probable nose structure affect- ing the east limb of the main structure (on Barstow quadrangle) is suggested by a broad salient of rocks of the carbonate group which alter the (otherwise) north trend of the overlying schist member. Attitudes are, however, too uncertain in that vicinity for positive interpretation of structure. Farther north in the Shadow Mountains, folds in the Oro Grande series are cut by northwest and west-trending faults whereas the southeastern outliers apparently are not faulted. Another fold which originated in the end-Paleozoic orogeny but which may have been greatly modified during the Jura-Cretaceous dis- turbance is the syncline involving the Fairview Valley formation in the vicinity of Black Mountain (west of the Sidewinder mine). It is a northwest-trending fold probably pitching moderately to the north- west but disrupted by complex normal and lateral movements on the Sidewinder fault. The syncline began to form long before Jurassic time inasmuch as the metavolcanics of the Sidewinder series overlap the upturned edges of the syncline in the saddle between Black Mountain and the mountain on which the Sidewinder mine is located. Jura- Cretaceous folding as well as lateral movements on the Sidewinder fault may well have shifted the axial direction of the Fairview syncline from north to northwest. Folds and Related Structures Produced in the Jura-Cretaceous Orogeny The fundamental northwest structural trend so conspicuous in the southeastern quarter of Barstow quadrangle was first established early in the Jura-Cretaceous orogeny. This northwest trend is evident in the ' igneous complex of the Stoddard Well vicinity, in the joint patterns of the granitic rocks and some roof pendants, and in a number of northwest-trending folds. Igneous Complex of the Stoddard Well Vicinity. The linear ar- rangement of the swarm of lenticular igneous rock masses which stand out from the granitic country rock in the vicinity of Stoddard Well is one of the most conspicuous features of the accompanying map. It is I a structural pattern originally imposed by folding upon the rocks of the batholith roof, chiefly in rocks of the Sidewinder volcanic series, and the strike of the upturned edges of the folds controlled the em- placement of dikes and the alignment of the xenoliths in the complex, i Although a majority of the lenticular, sheet-like masses are dikes of I quartz monzonite porphyry, some are inclusions of metavolcanic rocks of the Sidewinder volcanic series and some are simply large inclusions of quartz monzonite porphyry. The less weather-resistant country or I matrix rock in which these parallel-aligned rock masses are found is a ; coarse-grained, deuterically altered, porphyritic quartz monzonite, a rock probably contaminated during crystallization by materials derived from metavolcanic roof rocks. The quartz monzonite porphyry dikes cut this granitic material and the large xenoliths are included in it. Both the dikes and inclusions are well-exposed through Ja vertical dis- tance of several hundred feet in newly eroded youthful canyons so there can be no doubt as to their form or their persistence in depth. Where exposed, contacts between porphyry bodies and Sidewinder vol- i canic remnants show that the porphyry intruded the Sidewinder series. ; 4 — 85919 98 BARSTOW QUADRANGLE [Bull. 165 i In order to account for the field features just described, an unusual sequence of events must have taken place. It is clear that emplacement of quartz monzonite porphyry dikes began in the rocks of the Side- winder series soon destined to form the batholith roof, that the porphyry dikes so emplaced were broken up and included as large xenoliths to- gether with xenoliths of the Sidewinder volcanics, and that after crys- tallization of the outer parts of the batholith quartz monzonite porphyry continued to be injected into the partly cooled outer shell. The linear pattern of dikes and remnants (xenoliths) must have been established in the roof rocks prior to invasion of quartz monzonite, possibly by shearing but more probably by tensional fracturing along lines of strati- fication or schistosity tilted to near-verticality by folding. The granitic rocks could then have welled up along the fractures and assimilated, tuffaceous material from the Sidewinder series, such material being' already finely comminuted and more susceptible to assimilation than the porphyry dikes. Positive effects of metasomatism are hard to find along the granite-remnant contacts, and a general lack of parallel struc- tures in the granitic matrix as well as overwhelming predominance of sharp contacts between this rock and the included remnants indicates: that metasomatism (granitization) on a large scale was not operative.- Folds in the Sidewinder Volcanic Series. Because of a general lack' of stratification in the Sidewinder volcanic series the trend of folds can' only be surmised in broad terms. A majority of strikes are northwest in both bedding and schistosity. Several small folds found in the Slash-Xi Mountains trend northwest and suggest a complex anticlinorium in that vicinity. Stoddard Mountain appears to have been eroded from a steeply west-dipping homocline. Silver Mountain is most probably syn- clinal with gentle dips but the north-trending axis was not located. Figure 54. Fault contact between dolomite (white) of the Oro Grande series anc metavolcanics of the Sidewinder series, Ball magnesite and magnetite mine, earners facing slightly south of east. The white dumps were driven on pods and stringers o; magnesite cutting dolomite. 1954] GEOLOGY AND MINERAL DEPOSITS 99 Mapping of the light and dark units of the Silver Mountain area on a map of considerably larger scale than that used in this report would better establish the structure there. The attitudes obtainable in Side- winder Mountain were insufficiently distributed to reveal the structure there, but the pattern is complex. Strnctures of Quarfzite Mountain and Sparkuhle Hill. The acutely folded, multiply faulted rocks of the Quartzite Mountain vicinity east of Oro Grande are unusually well exposed, and as the lithologic units of the series are more distinctive than elsewhere in the quadrangle, the essential features of the structural complex can be deciphered with some confidence. The dominating features are a series of tight, north- west-trending folds truncated on the north by an east-trending zone of parallel and en echelon faults and overridden, probably from the north- east, b}' a now-warped thrust plate. Two synclines pitching gently northwest are conspicuously exposed in the main mass of the mountain, the intervening anticline having been faulted and the limbs greatly displaced. West of the two major synclines in the vicinity of the Klondike quarries of Riverside Cement Company, the Oro Grande series is too complexly deformed and too haphazardly exposed to be adequately expressed on available base maps. A probable south-plunging anticline has been crumpled and multiply fractured by both transverse and bed- ding faults. Septa broken from competent beds have been driven both concordantly and discordantly into adjacent less competent strata. In- tense but unequal pressures applied to the carbonate members of the series has resulted in local thickening and thinning of them by plastic flow. East of the two principal synclines of Quartzite Mountain, the Oro Grande series is faulted off by a vertical northwest-trending fault and structural trends change from northwest to northeast. East of this fault the structure is essentially homoclinal with dips to the northwest. This northeast areal trend is, of course, disrupted in many places by transverse and bedding faults and by small granitic intrusions. The conspicuous coxcomb ridge comprising the long northeast spur of Quartzite Mountain has been eroded from a thick, strike-warped, cross- faulted quartzite unit belonging to the upper part of the Oro Grande section. Interbed slipping of competent against incompetent beds is well shown in the walls of limestone quarries east of Quartzite Mountain, operated intermittently by Southwestern Portland Cement Company. The homoclinal structure there is, however, not so badly confused by transverse fractures and crumpled substructures as the quarry area west of Quartzite Mountain, probably because the weak mica-schist members were thinner and less well distributed through the section. The most puzzling feature of the Quartzite Mountain structure is the warped thrust plate which overrides northern ends of the principal northwest-trending folds. Overriding flatirons of limestone and quartz- ite lap onto the ends of the folds in the vicinity of Southwestern Port- land Cement Company's No. 12 quarry. The base of the plate dips north toward the canyon axis with apparent inclinations varying be- tween 20 and 30 degrees. The trace of the thrust is lost in canyon alluvium but another trace is readily picked up north of the canyon 100 BARSTOW QUADRANGLE [Bull. 165 ^T:'^ -^ .- ■■■■ r --^ *-»'^ '1» - <•*» -- / .\---.5i - •««»-'«► .'-<*. i • «*, !.;>V ■• -"-^^.'^ 'r-'^ - ••'O Figure 55. A flatiron of limestone of the Oro Grande series overriding the up- turned edges of quartzite, schist and limestone members of the Oro Grande series in a low-angle thrust plate. Northeast flank, Quartzite Mountain, camera facing slightly west of south. where it dips gently to the south. On this side of the Canyon Oro Grande rocks have been thrust across granite, &. zone of breccia 10-20 feet wide marking the contact. Although a strongly developed zone of vertical faulting and drag in which mineralized veins have been de- posited can be followed in a northeast direction until it apparently passes beneath the thrust plate, the two faults appear to be unrelated. The northeast line of faulting antedates the invasion of vein matter whereas the thrust is post-mineral. The areal distribution of the Ore Grande series in the vicinity indicates that the thrust plate must have moved in from the northeast but the magnitude of the movement is unknown. There is marked contrast between the structure of Quartzite Moun- tain and that of Sparkuhle Hill which lies one mile to the north. Spark uhle Hill is essentially a gentle, northwest-trending, northwest-pitchi.if syncline cut, but not seriously disrupted, by northeast-trending faults From the position of the two patches of the Fairview Valley formatior northeast of the hill, it is probable that this formation once overlapped the Oro Grande series there just as it does south of the type section but the angular difference between younger and older units is mucl 1954] F GEOLOGY AND MINERAL DEPOSITS 101 Figure 56. A side view of the same flatiron seen in fig. 55 (extreme right middle- ground) showing the 30° inclination. The apparent dip slope above the flatiron is an illusion enhanced by a talus cone of broken quartzite. less at Sparkuhle Hill. The Oro Grande and Fairview Valley rocks of Sparkuhle Ilill are also overlapped and intruded by elements of the Sidewinder volcanic series and these rock groups stood out in relief above the surface onto which the Sidewinder series was laid. The exact time at which most of the episodes in deformation of the rocks of the Quartzite Mountain and Sparkuhle Hill areas took place cannot be well established. The Paleozoic rocks had certainly been folded to some extent before deposition of the Sidewinder volcanic series probably in Triassic time ; they presumably were deformed in the end-Paleozoic orogeny. The principal fold axes fit the northwest pat- tern of deformation known to be of Jura-Cretaceous origin in the east- ern half of the quadrangle but these may have been modified from a trend set previously. The time of low-angle thrusting is later than the emplacement of the granitic rocks and earlier than deposition of Pleis- tocene alluvium. It is a type of deformation believed to be Pliocene elsewhere in the quadrangle (see under Waterman thrust). The north- east faults cutting the northwest-trending structure in the Sparkuhle Hill vicinity are probably Quaternary as there is surface expression on the principal example in the form of a low, north-facing scarp. 102 BARSTOW QUADRANGLE [Bull. 165 The Mio-Pliocene Deformation Within Barstow quadrangle, as well as in most other parts of the southwestern Mojave Desert, the continental Miocene and lower Pliocene rocks have been severely deformed w^hereas those younger than middle j Pliocene are undisturbed or very gently disturbed. All of the patches i of continental Miocene in Barstow quadrangle are found in tilted fault ' blocks where the strata are alw^ays homoclinal. These homoclines tend to be arcuate to the northeast, that is, apices of the arcs point northeast. The repeated homoclinal attitude of the Miocene beds in the Kramer Hills may be the result of gravitational faulting of a major arch, the simplest and most probable explanation, or, less probably, the various fault blocks could have been individually tilted to produce a like effect. In the Hinkley and Waterman Hills the distorted homoclinal patches of Miocene sediments tend to be more contorted and more haphazard in their distribution so probably never were elements of any one struc- ture. In these areas, as well as in some places in the Kramer Hills, the strata appear to dip steeply down and abut the granite surface ; in such cases the only probable explanation is that they were crumpled and pushed into verticality by slipping across the underlying granite. It seems clear that in order to deform incompetent strata over com- petent granite at depihs of 4000 feet or less, yield in the granite must take the form of faulting and of minor but multiple displacements along joint and minor fracture systems. In several parts of Barstow quadrangle nearly all the joint surfaces show" polished surfaces, indi- cating slight shearing movements along them. This mode of bedrock . deformation has received too little attention in the literature. The acute ' Mio-Pliocene folds must, therefore, be the result of combined bedrock faulting, small bedrock displacements along joints and minor fractures plus slipping, dragging and thrusting of weak sediments over the stronger crystalline bedrock. Late Quaternary Arching Several low, oval domes involving Pleistocene rocks are present in Bar- stow quadrangle. Two of these are well-defined and the presence of a third is inferred. All trend northwest and all are probably related to faulting rather than to fundamental compression in the area. The Len- wood anticline extends southeast from just east of the town of IjCu- wood and off of Barstow quadrangle. It is located along a fault zone which is still active and a late break- cuts the crest of the structure somewhat west of the axis and roughly parallel to it. Beneath the sim- ple, relatively thin Pleistocene arch are complexly folded, continental ■ Miocene rocks which appear in small windows south of Highway -166 near Lenwood. East of Barstow quadrangle much of the Pleistocene cover has been stripped away from the Miocene core, but within the quadrangle only the small windows are exposed. Dips on the east side of the structure do not exceed 8° except where strongly disturbed in minor fault zones. On the western slope the dips reach 12° so the struc- ture is slightly asymmetrical with steepest dips in the region of the most recent faulting. The near-surface closure on northern domal part of the anticline is 200 feet or slightly more. It seems clear that the Lenwood anticline has developed along a line of weakness at least as old as mid-Pliocene and that the folding has 1954] GEOLOGY AND MINERAL DEPOSITS 103 been in response to Recent movements of small magnitude in the under- lying bedrock rather than to any fundamental compression of the area. Another domal anticline with even more perfect surface closure is present west of the Harper Lake Road, extending in a northwest direc- tion six to ten miles northwest of Helendale. It lies astride the Helen- dale fault and is remarkably like the Lenwood dome except that no Miocene rocks are exposed on it; they may or may not be present at depth. The C. C. Hamilton Emcap No. 1 well was drilled on a north- west nose of the structure to a depth of 2800 feet. No fossils were re- covered and the Avell bottomed in rock described in the well logs as "hard sand." Rock penetrated from 2074 to 2800 feet was also described as "hard sand." There are no well-cemented sandstones of any such thick- ness in any of the Tertiary or Quaternary sections in Barstow quad- rangle, the nearest being in Cajon Canyon of the San Bernardino-San Gabriel Ranges. It is probable that the material described as "hard sand" is actually granite in various stages of weathering and decom- position. The crest of the dome is sufficiently well eroded to expose 30-40 feet of stratigraphic thickness but the unconsolidated character of the allu- vium and the indistinctness of the gravel beds makes measurements of dips and strikes uncertain. The trace of the Helendale fault is faintly visible on the ground and in aerial photographs where it cuts the west flank of the structure. There is no apparent surface displacement, but rocks of slightly different color and character have been brought into contact, probably by strike-slip movement. Conditions of formation of the dome appear to parallel those of the Lenwood anticline. A third dome similar to that just described and adjoining it on the south is inferred from topography but dissection has not progressed far enough to expose the attitudes of the beds. This structure may well be in the process of formation at the present time. Faults Pre-Granite Faults The oldest known faults in the quadrangle cut the Hodge volcanic series north of Hodge and the gneissic hornblende diorite south of Hodge. They preceded the end-Paleozoic deformation and their sur- faces were deformed by it. Consequently, traces of these early faults more nearly resemble stream patterns than fault patterns. Quartz mon- zonite evidently found its way in along one of these old faults south of Hodge (sees. 15 and 16, T. 8 N., R. 4 \V.) as the sharp curvilinear con- tact transgresses the schistosity of the gneissic diorite. The branching fault whicli cuts the Hodge series is essentially a vertical one along which the downthrown side is to the east and the vertical displacement in excess of 500 feet. Sidewinder and Related Faults. The Sidewinder fault system is unique among the faults of the quadrangle in that it shows left lateral, strike-slip movement of significant magnitude. The left lateral move- ment is clearly shown in the saddle north of Southwestern Portland Cement Company's Black Mountain limestone deposit where the strata of the conglomerate member of the Fairview Valley formation have been dragged from a N. 55 °W. trend to an almost west trend next to the fault zone. East-striking, north-dipping strata of the Oro Grande 104 BARSTOW QUADRANGLE [Bull. 165 '.1t><':\A v>p Figure 57. Profile of the recently formed Lenwood denial anticline, camera facing southwest across the town of Barstow. Crest of the dome is approximately at the center of the skyline. series have been brought into contact with the truncated ends of the Fairview beds so the vertical component must have b'een great as well as the strike-slip movement. There are no sure marker beds present on both sides of the fault but drag on the conglomerate member and dis- placement of the synclinal structure of the formation as a whole indi- cate an offset of more than 1500 feet. The trace of the fault on the map as it crosses north of Black Mountain is distorted because of errors in the contours of the topographic base map. The topography indicated on the map shows the canyon traversed by the fault as trending some- what north of east whereas it actually trends due east. The Black Mountain segment of the fault undoubtedly connects with the fault that crosses the north slope of Sidewinder Mountain and passing west just north of the Sidewinder mine. It may also connect with the faults passing south of the Ball magnesite mine although no left lateral dis- placement can be proved there. Waterman Thrust. The trace of the Waterman thrust is exposed in numerous places along the west front of the "Waterman Hills southeast of the Camp Irwin road. Northwest of the Camp Irwin road the trace is not exposed but is presumed to continue beneath the alluvium near the base of the hills. Where the fault is exposed, it strikes N. 55° W. and has an apparent dip of 45° NE.; it coincides over part of its length with the Harper Lake fault which is not a thrust. The Waterman thrust was active as far back as upper Pliocene time as gouge of the fault zone has been mineralized at scattered points by the Pliocene barite-silver mineralization. During the period of overthrusting, probably long extinct, the hanging wall block rose sufficiently to give the Waterman Hills much of their present height above the thinly alluviated erosion surface lying to the west. It is probable that the fault flattened rapidly toward the west to give rise to the solitary, flat-floored thrust-plate J 1954] GEOLOGY AND MINERAL DEPOSITS 105 remnant (klippe) currently Ij'inj? 2^ miles west of the exposed trace at the extreme east end of the Hinkley Hills. This klippe, made up entirely of ^rray dolomitic limestone lies on remnants of a Tertiary, probably Miocene, continental formation a few tens of feet thick which in turn is lying on a gneissic diorite basement. It not only resembles carbonate rocks of the Oro Grande series lying above the Waterman gneiss in the Waterman anticline east of Barstow quadrangle, but con- tains sufficient poorly preserved fossil debris to leave little doubt that it belongs to that series. The medium-to-loAv-angle thrusting, believed to be a Pliocene feature long since dead, has been supplanted in Quaternary time by vertical faulting of quite a different character, probably involving both normal and strike-slip movements. Normal faulting in fairly recent time along the Harper Lake fault in which the valley side has been downthrown is undoubtedly responsible for laying bare the trace of the Waterman thrust. Strike-slip movements along the Harper Lake fault, although not measurable, are suspected because the upthrown and downthrown sides change at various places along the' trace northwest of Barstow quadrangle. Helendale and Related Faults of the Dominant Northwest System.. The most conspicuous and certainly the most important fault system insofar as topography and structure are concerned is the northwest system typified by the Helendale fault. Members of this system strike N. 40°-50° W. and approach verticality. All of the northwest-trending ridges in the eatsern half of the quadrangle probably are bounded by faults of this system, but in the case of the Section 20 Hills and some other probable horsts, the bordering faults cannot be located because of burial under extensive alluvial fans. Consequently some have been left off the accompanying maps and structure sections. Many faults of this system show recent displacements involving ag- grading alluvial fans and hence are active faults. Changes in apparent upthrown and downthrown sides from place to place along the Helen- dale and Harper Lake faults suggest lateral movement as well as nor- mal movement. The system has had its greatest development in late Quaternary time but may have come into being in late Tertiary time. The Helendale fault is traceable from Cushenbury Canyon in the San Bernardino Range across Lucerne Valley and diagonally across Bar- stow quadrangle from near the southeast corner to the vicinity of the Kramer Hills. Recent movement with development of scarps in allu- vium is evident along this fault from the Slash X Ranch almost to the playa in Fairview Valley, a distance of more than 10 miles. Within this segment the downthrown side is to the east, but northwest of Helendale the downthrown side is to the west and Pleistocene lakebeds have been uplifted along the east side of the trace. In Lucerne Valley the horizontal movement can be traced by differences in appearance between the alluvium within and outside of the fault zone even though no vertical displacement has occurred." The trace is very conspicuous from the air over most of its length. The total displacement on the Helendale fault cannot be measured in the absence of markers on opposite sides of the fault. Topographic expression of fault scarps indi- cates a vertical displacement greater than 400 feet. " Vaughan, F. E., personal communication, 1949. 106 BARSTOW QUADRANGLE [Bull. 165 Figure 58. Stoddard dike complex on the north .slope of Raven Ridge just east of Stoddard Well, camera facing slightly west of south. A broad series of parallel dikes and large xenoliths may be seen protruding from the snow. Low hill in front of the ridge is a hybrid phase of the quarts; monzonite making up the core of the ridge. Faults of the Raven Ridge Pediment of Northern Lucerne Valley. A series of parallel northwest-trending faults across the pediment near B the southern base of Raven Ridge. Only the western ends of these faults are present on Barstow quadrangle, most of their length lying to the east on the proposed Aztec Spring quadrangle. Each fault is well marked by a line of brush growing in the alluvium which sparsely covers the pediment. There is no surface expression of these faults other than the brush, but the lines of brush can hardly be present because of any process other than faulting. Traces of several of the faults are visible for five miles or more. It is probable that these are extinct faults in which the gouge acts as a barrier to groundwater percolating down the pediment (along joints as well as along the weathered surface), causing the water, to rise closer to the surface and allowing support of a greater concentration of vegetation than normal. The general strike of these inactive (?) faults (N. 65° W.), if pro- jected westward across alluvial fill, would be truncated by the major northwest-trending active fault system, so that the faults of the Raven Ridge pediment presumably are older than those of the predominating northwest system. The Victorville Fault and Others of the Northeast System. The few northeast-trending faults on the quadrange are relatively unimportant features, both topographically and structurally. None are traceable for more than 2^ miles and their relationships to other faults are not clear. In and north of Sparkuhle Hill several of these faults cut the other- wise northwest-trending structures. In one case, a graben of Fairview Valley formation rocks has been dropped down into surrounding Oro 1954] GEOLOGY AND MINERAL DEPOSITS 107 Grande sodiiiients. The fault tliat eiits the Sparkidde Hill syueline has an apparent displacement of 100 feet, the searp having- been modified but little by erosion. It is probably a Recent fault although it is not traceable in the alluvium. The Victorville fault has topographic expression clearly seen in aerial photographs where it cuts across a group of granitic hills. It is not traceable in the alluvium or in the terraces of the Mojave River, but, if projected, it passes close to the Upper Narrows of the Mojave River and may have been responsible for damming of the Mojave River to form the lake that once existed south of the narrows. This is the only clue as to which is the upthrown and which is the downthrown side. If the foregoing surmise is correct, then the upthrown side is to the southeast and the vertical displacement is 100 feet or more (based on the transverse profile). PHYSIOGRAPHY AND PHYSIOGRAPHIC EVOLUTION Although the present-day landscape of Barstow quadrangle is largely the product of forces acting in late Tertiary and Quaternary time, some of its features reflect events which took place long before Tertiary. The last known marine transgression ended in the Permian, or possibly in the early Triassic, and Barstow quadrangle and environs, without much doubt, has been emergent continuously since that time. AVith the pos- sible exception of early middle Miocene time, the region has never approached planation except locally, and mountain ranges of very ro- bust proportions have graced the Barstow landscape throughout much of geologic time. The end-Paleozoic orogeny, largely ignored by other authors who have written on the Mojave Desert and possibly inoperative except in the western part of the province, produced bedrock structures that have controlled the course of the Mojave River across Barstow quadrangle throughout the river's history. This orogeny unquestionably affected the region now occupied by the San Bernardino and San Gabriel Ranges as well as a belt at least 50 miles wide adjoining these ranges on the north. The Jura-Cretaceous orogeny, known also as the Nevadan revolution, had a profound effect over most of the Mojave Desert region, produc- ing great mountainous areas which in the Barstow quadrangle area have never entirely disappeared. In Barstow quadrangle, northwest- trending folds and fractures in both the granitic core and in the strati- fied cover were produced which greatly influenced the development of fault systems in Tertiary and Quaternary time. The last crustal folding of any great intensity in the general vicinity of Barstow quadrangle took place in mid-Pliocene time. Fold moun- tains as well as fault-block mountains undoubtedly were produced which still remain, but they have been so modified by erosion and later fault- ing that the old erosion surface (or surfaces) almost everywhere is not recognizable. Since middle Pliocene the landscape has largely been modified by tilting, elevation or depression of blocks bounded by the major northwest-trending fault system and by aggradation or degrada- tion of these blocks through normal erosional processes. The single ex- ternal agency which modified erosion, as it normally would progress in an arid region, is the Mojave River which rises in the San Bernardino Mountains, an area of much more abunda,nt rainfall. 108 BARSTOW QUADRANGLE [BuU. 165 Figure 59. Insell>erg topography between Black Mountain and the San Gabriel Range, camera facing southwest. Bell Mountain in the right middleground and Mt. San Antonio (Old Baldy) in the center background. Figure 60. Symmetrical profile of Bell Mountain suggestive of an eroded volcanic neck. The mountain does not, however, have a core of intrusive lava, but rather is capped by a remnant of latite-andesite of the Sidewinder series that has been in- truded by a variety of granitic rocks. 1954] GEOLOGY AND MINERAL DEPOSITS 109 Cycles of Erosion. Little can be reconstructed as to tlie progress of erosion cycles following soon after the end-Paleozoic oroj^eny except that the relief was still considerable at the time of accumnlation of the Sidewinder volcanic series in probable Triassic time. Black ^lonntain and Sparkuhle Hill (see oeo Extrusion of olivine basalts in Lucerne Valley SE. of Barstow quadrangle. Intrusion and extrusion of dacite and rhyolite lava and tuff over northern part of quad- rangle. Extrusion of quartz andesite of Kramer Hills; intrusion of ohvine analcite diabase. -a o Z 1 o Z 1 1 1 o Z 3 a 3 •a § Up to 200 feet in early Recent time. e- i c a 8 £ o Z £ o Z ■i o g o Z c o a 3 a Folding only in and adja- cent to fault systems. Active faulting partic- ularly on NW. system. Similar to Recent. Profound in lower; weak or absent in upper. Upper (?) Miocene beds strongly deformed. I'hrust faulting along base of Waterman Hills. ■ Probably began in upper Miocene. 1 o Z ■2 O £ o Z 3 1 Erosion Stripping of uplifted Pleis- tocene alluvium; con- tinued erosion of buttes. c B. "o 09 ■s O h a-o 5 i > o < Probably active through- out. i < i ■< .1 < i 1 1 o. la >S 3 1! a > 3 . -o _a c Jo s Similar to present day but at least one additional lake basin was re- ceiving sediment from the Mojave River. Limited intervolcanic flood-plain and lacustrine deposition in upper Plio- cene; sedimentation continuous from Miocene to lower Pliocene in adjacent areas — no known lower Phocene record in Barstow quad- rangle. Lacustrine and Soodplain; fanglomer- ate. O ■2 8 o o H ■g ft- a •s .1 d> a ID £ .1 o 93 i 1 1 3 Lower Cretaceous 1 oiozonag 1954] GEOLOGY AND MINERAL DEPOSITS 115 S a =a '5 ^ ^ !■.§ g a b H :^ c3 t- "3 rt o D, -a a o 1) V ~ t« ~ 3 = .■S o 5 -5 CO o ' 5 -i- & 2 2-3 ■a •; "^ a; S 'o -o ^ ja c S " ffl "^ ■ •a .2 i I • c >> tn L. fA ^j "S H« a ^ > "S 3 =« o "g 3 OS s r"* a i o 0-? .2 „ > "O QJ .2 1a 5 W ?? b4 OJ o. *^ ^ T3 8 w 13 > .a La 6 Z J3 o to O M z-gr. C c '*■ '-' o '^ S ic (5 CO ^c2 s. «--±? a ° -e o c m . *" 2 o S ' D. -a ii a £ >. ca » o .2 J-p-o o 013 , I 7 I 6 •a oiozosap^ oiozoajcj 116 BAESTOW QUADRANGLE [Bull. 165 Mesozoic. After the end-Paleozoic orogeny, an erosion period of unknown length greatly modified the land surface. Onto this surface, which had considerable relief, the Sidewinder volcanic series was ex- truded. Again the dacite-rhyolite association persisted. Volcanoes of explosive violence must have been numerous as the volcanic products are predominantly pyroclastic. The climate most probably was arid, as neither lacustrine nor fluviatile deposits of any magnitude are found in the Sidewinder series. However, there was sufficient rainfall from time to time to produce large scale mud flows. The volcanic period that gave rise to the Sidewinder series could have taken place in either Triassic or Jurassic time insofar as evidence on Barstow quadrangle is concerned, but indirect evidence in surrounding areas favors the Triassic (Hazzard et al. 1938, pp. 278-279). A lapse of time of unknown length followed accumulation of the Sidewinder volcanic series for which there is no record, but the land surface presumably was rugged and was being actively eroded. Then came the Jura-Cretaceous orogeny, the duration of which cannot be well established in Barstow quadrangle. The Sidewinder volcanic series and all older rocks were folded to some extent into structures having a predominant northwest trend. Granitic rocks began to be intruded and pulsatory compressional forces continued to act through- out the period of granitic intrusion. Field evidence indicates that the granites were emplaced mainly in liquid or partly liquid form, partly by stoping, partly by assimilation and, locally, by forceful injection between septa of stratified wall rocks. The relative importance of these methods was not determined. Metasomatic emplacement (granitiza- tion) can only be demonstrated in masses of small size. Gabbroic and dioritic intrusions came in early in the sequence and quartz monzonite, lamprophyre and schriesheimite late. Quartz mon- zonite porphyry dikes and other porphyry intrusions of variable shape were intruded both into the wall rocks and into the peripheral quartz monzonite throughout the period of granitic emplacement. Also em- placed late in the period were aplite and pegmatite dikes, gold and simple sulfide-bearing quartz veins, quartz tourmaline veins and the quartz-epidote-pyrolusite veins of Sidewinder Mountain. All of these veins were of mesothermal type. The vein and contact magnetite and specularite deposits also formed indirectly as a result of granitic in- vasions, but their time of formation within the Jura- Cretaceous period is not known. Cretaceous and Early Tertiary. Following the Jura-Cretaceous orog- eny, which left the region mountainous, there is a long gap in the geologic record, no further deposition being recorded until middle Miocene time. There is no trace of marine transgression during the Cretaceous-Miocene interval nearer than Cajon Junction in Cajon Pass. Although fluviatile deposits of possible Eocene age are found at scattered points in the western Mojave Desert and environs, notably in the western part of the El Paso Range and in the Holcombe Valley region of the San Bernardino Mountains, it is probable that Barstow quadrangle was included in a mountain mass that persisted well into the Miocene and that erosional conditions prevailed. In Eocene time neither the San Bernardino nor eastern San Gabriel Ranges had any- thing like the relief they now possess and drainage may well have been 1954] GEOLOGY AND MINERAL DEPOSITS 117 southward from a liifrhland that extended as far west as Littlerock and as far east as the Ord Mountains. Miocene. By middle Miocene the highland that had persisted through the early Tertiary had been worn down to a surface of moder- ate to low relief. Granite mountains had been in part worn down to buttes and low domes with broad plains and lake basins between. The long, rather narrow, northwest-trending Barstow trough (adjoining Barstow quadrangle on the north) had come into being and was re- ceiving sediment from both north and south. The middle and upper Miocene deposition, therefore, went on in lake basins and on river flood- plains that were for the most part disconnected from each other. Con- sequently the character of the deposits varied considerably from basin to basin, some basins being recipients of volcanic products in quantity and some being relatively free of volcanic debris throughout much of their span of existence. The fossil faunas and floras taken from Miocene rocks adjacent to Barstow quadrangle, indicate that the climate, though semi-arid, was more humid than that of the present day. The larger lacustrine basins were recipients of notable thicknesses of chemically deposited sediments including limestone, magnesian lime- stone, magnesite, opaline and jasperoid chert, and, in the Boron district, borates. By far the greatest amount of mineral matter in these chem- ically precipitated deposits must have been derived from sub-lacustrine volcanic mineral springs and from emanations from lavas themselves. In contrast to the acidic lavas produced in late Paleozoic, Triassic and Pliocene periods of volcanism, the ejectamenta from many of the Mio- cene volcanoes was intermediate to" basic in composition, olivine basalt, olivine-analcite diabase and quartz andesite greatly predominating over dacite and rhyolite. Aside from the pToducts of volcanic springs and emanations, however, non-volcanic sediments greatly exceeded water- laid pyroclastic or other volcanic material. The great northwest-trending block-fault systems which had become the predominant topographic control by Pleistocene time may have had their beginnings during middle Miocene time : the coarse fanglomerates, that in numerous places interdigitate or else are interbedded with lacus- trine sediments, are indicative of rapidly increased relief. Pliocene. Climate and depositional conditions of the upper Miocene continued into the Pliocene, the climate becoming increasingly arid as the San Gabriel and San Bernardino Ranges to the south began to rise. Sometime during middle Pliocene the Mio-Pliocene sediments were complexly folded and faulted, a line of overthrusting breaking out along the base of what is now the Waterman range of hills. How such acute and complex folds could have evolved under an overburdeti of less than 4000 feet of sediment and above a relatively rigid basement of strong crystalline rocks is one of the problems in the structural geology of the western Mojave Desert. The author believes that it was largely accom- plished in three ways : 1. By complex fault movements in the basement involving reverse, lateral and normal movements. 2. By small displacements along the fundamental northwest-trending joint systems established in the granites during the Jura-Cretaceous orogeny. (Joint surfaces are slickensided over large areas). 3. By slipping of the incompetent Tertiary deposits above the crystalline basement by compression and torsional movement between fault blocks. 118 BARSTOW QUADRANGLE [Bull. 165 The middle Pliocene deformation was the last severe period of fold- ing in the Barstow area, although gentle folds were produced in upper Pliocene as well as Quaternary time (largely in response to bedrock faulting). The severe middle Pliocene disturbance probably was a fore- runner in the series of events that resulted in re-elevation of the San Bernardino and San Gabriel Ranges, culminating in middle Pleistocene time. The ancestral Mojave River came into being with the initial re- elevation of the San Bernardino and San Gabriel Ranges sometime dur- ing Pliocene time. Volcanism was renewed over an area extending from somewhat west of the Kramer Hills east to the Calico Mountains, and from somewhat north of Stoddard Mountain north across the Barstow structural trough. Several of the vents were within the limits of present-day Bar- stow quadrangle where several necks and at least two eroded exogenous domes are conspicuously exposed. Volcanic vents were also present in the vicinity of the Waterman mine, Hinkley Hills and the old town- site of Kramer Hills. Dacite was the only rock type extruded within Barstow quadrangle during this period. The volcanoes erupted with explosive violence at times and at others quiet, dome-like upwellings of viscous, unvesicular lava predominated. The epithermal silver-bearing barite veins found in the Hinkley Hills, Waterman mine vicinity and Calico Mountains were emplaced as a late episode connected with the upper Pliocene volcanism. It is probable that the epithermal lead-zinc-copper-silver vein system at the Pedry sil- ver mine originated at this time. Upper Pliocene sedimentary deposits so far have not been recognized although their presence in Barstow quadrangle was expected. They may be buried beneath the Pleistocene and Recent alluvium or it may be that, in the general absence of fossils and the probable similarity of Pliocene, Pleistocene, and Recent deposits, that some have been included with the Pleistocene. Quaternary. The dominant, northwest-trending fault system which currently is the chief topographic control over the western Mojave Desert developed principally during the Pleistocene, but many faults, such as the Helendale, have remained active to the present day. They are faults along which movements have been predominantly of normal or gravity type, but right lateral movements have also taken place. The present course of the Mojave River was developed principally during the Pleistocene after the San Bernardino Range had gained much of its present height, but during that epoch the lands bordering the river had more adjacent lake basins into which the floodwaters of the Mojave River could drain, than are now present. One of these lakes developed north of Helendale and another behind the Upper Narrows of Victorville. The latter lake, however, probably developed as a result of uplift and damming on the Victorville fault very late in the Pleisto- cene or possibly in Recent time. Volcanism broke out sporadically in the western Mojave Desert in ■ | the late Quaternary and although there are no known vents in Barstow quadrangle, olivine basalts were extruded by fissure flows in Lucerne Valley close to the southeast corner of the quadrangle. Two events in late Quaternary time served to alter the drainage, particularly in the southwest quarter of the quadrangle and in the area 1954] GEOLOGY AND MINERAL DEPOSITS 119 between Victorville and Cajon Pass. These were regional uplifts of the area, amounting to two or three hundred feet, and the partial capture of the headwater tributaries of the Mojave River by the branches of Cajon Creek. In Pleistocene time a great braided system of washes led down from the alluvial fans bordering the San Bernardino Range and connected, at various points from Victorville to Helendale, with the Mojave River. Beheading of some of these washes by Cajon Creek and intrenching of the main Mojave River channel north and west of Hesperia because of regional uplift, deprived almost all of these washes of their water supply so that they now carry water only during storms. MINERAL DEPOSITS Metallic Minerals Copper Copper occurs in numerous localities scattered throughout the south central and eastern parts of the quadrangle. In most of these occur- rences it is found in small amounts in accessory minerals of gold quartz veins, but in a few localities it is the predominant metal in the deposit. Copper minerals are found in three distinct types of deposits : 1. Mesothermal gold quartz veins where chalcopyrite, bornite, pyrite and free gold are associated ; 2. Mesothermal veins and replacements where chalcopyrite is deposited chiefly in fractured magnetite ; 3. Epithermal veins in which chalcopyrite, chalcocite and pyrite are associated with vuggy quartz, chalcedony, opal and, less commonly, barite. The upper parts of most of the deposits have been oxidized with for- mation of secondary malachite, brochantite, chrysocolla, chalcanthite and chalcocite in various associations. The mesothermal deposits are related to the Jura-Cretaceous emplacement of granitic rocks whereas the epithermal veins are much younger and probably formed at the time of the upper Pliocene volcanism. Amazon Mine (Copper Mountain, Copper King, Lucky Rose). Lo- cation : half-a-mile southwest of Southw^estern Portland Cement Com- pam-'s No. 1 limestone. quarry near the center of the NE^, sec. 15, T. 6 N., R. 4 W., S.B. Mine is on the south face of the northeast-trending coxcomb ridge about halfway down from the summit to the piedmont below. The only means of access is a pack trail leading northwest from the cement company's shale quarry. Ownership : unknown ; the last known owner was F. H. Cline, Oro Grande, California. The most easterly of the properties was claimed (1948) by Blane A. Frazier and R. R. Percival, address unknown. According to Storms (1893, p. 363) the mine was first worked by Mormons in the early 1880 's. Housmann (1908, pp. 333-334) places the date as 1880. It was active between 1890 and 1895, but there is no record of production for that period. During the period 1912-1916, three hundred tons of oxidized ore were mined and shipped by the Copper Mountain Mining Company of San Bernardino (Cloudman, 1919, p. 784). There is no record of production since that time and, cis the shafts have no means of access, the underground workings were not examined. 120 BARSTOW QUADRANGLE [Bull. 165 (/) H 05 o Q. UJ Q -I < z ~ — o 2 .2 O ;:| z 5 UJ 11. o > tc < Zi (0 _e _>, -ki c s 03 t- t4 a 0. B CQ £> O •d >, C5 2 ri e "s > -»d c Lh '-«:> O c d o. V '-*3 B .3 c 3 a T3 o c -t.^ 'g u a o 2 •5 M £) § c £ c 'qq d _E o ^ o _o '-4J w <^fl '.4^ CD TJ *j ° >. 3 £ 3 1^ tJ '■S ■a ^^ 2 01 V, 2 2 O ^2 a > •0 0. ■3 u ca u 0) u as ■3 1 3 n CO an Iti >J OD c o "•*j cS s u o QO 3 3 3 8 IS 3 0) c a> a) K c o u V H (3 5 V « u«S u a, k. Li o c s c^ o *> « a £1 tJ .^ u .X C e OQ O a 'S Oi flj 'i OD -S n -^ (D ;3 00 gs ss g 3 3 3 3 i-J ►^ ■-5 Pi Si 1-5 OD ca -4^ G QQ g n 1 03 -^ B d a 3 § :§! s Ut ii 00 O 'a ■3 £ E "o d Ut "^ c 'S > _ 00 G 'S > _ & .• 03 _^ 00 s a £ ■s _ d § £ « § S3 E — « £^1 £ « c 00 « E j= « 2 |.S B 'd _o *i o -^ O to tf ■-a' 3. E -.^ '3. S 3 'a >i 08 m K hH tf W un H T3 1 B 1 -^ • ■^ _o o 4) ■♦a OD ia L. . ■a J3 a U3 £ 3 s i *J be M a o .2 i 3 ^ B 00 t> OS E 'S ^3 O rt ;Sg CO a a |8 J3 -0 &>. Sal -0 B 03 B 01 ■a B oi is B 4) '1 3i «4- 3 > > u O B a ■C;i: O o c a •a •c o o T3 B 2 T3 >. J3 O B > H c 1 s "a "oi a 1 a . ■*^ _ c ^ S .H a 3 « B U 4) a -g a .2 2 O 03 .&a 2 ° 4) jn o ■« o ja 8 a 2 §»■ "s'S. 09 ^ 4) ll a-a B a 1 Ih o 1 Oi a "a 4 3 03 o a o g ■a •3 a •a >> ■a s 2 QQ 1 o a 3 & o 01 o; 2 -c > 2 . o S «-aii , So a ^13 §5 43 ° B B ■c 2 8! '^S II B 4} s s r a i B > & o 43 s a ffi s S § K Q a S 'S 03 OS 43 o 0) fi- a *S Ih •s 1 o 2 i a s "o , -4-3 QQ B 01 4 .2 4) g •l T3 C 1 o lb GO 1 > 0! c o 1 ^ a c "c C B S E 1 B § ) 1 s J5 ct 1 03 C 11 01 122 BARSTOW QUADRANGLE [Bull. 165 Figure 64. Iron hoisting frame and tiorse-\\ himsey at tlie Amazon copper mine on the south flank of the coxcomb ridge extending- northeast from Quartzite Mountain. Wall rocks are limestone and schist intruded by black hornblende lamprophyre. There are two centers of mineralization on the claims approximately 1500 feet apart. The most easterly mineralized zone (apparently on the Copper King claim) is found along a fault which strikes N. 10-20° W. along the bottom of a gulch. The fault offsets slightly a quartzsite- limestone group of beds, belonging to the Upper Paleozoic Oro Grande series, which trend N. 10-20° E. and dip 45-50° NW. Ore crops out over a quarter of an acre in pods and bunches "replacing fractured limestone and a schistose, black hornblende lamprophyre intrusive. The mineral- ized zone is somewhat elongated parallel to the northeast-trending con- tact of the quartzite and limestone members of the Oro Grande series, and the quartzite may have acted as a barrier to the mineralizing solutions. Most of the best ore is in the black intrusive. According to Housmann (1908, p. 333) the ore shoots dip 60° NW. Fifteen hundred feet S. 26° W. of the eastern center of mineralization is another center localized along a vein system striking N. 63° E. and dipping 60° NW. Ore is found in and along an intrusion of blue-black meta-andesite of the Triassic (?) Sidewinder series. The meta-andesite intrudes quartzite and mica schist of the Oro Grande series. Ore in both locations consists chiefly of chalocopyrite occupying fractures and replacement patches in magnetite ; these are generally accompanied by some secondary malachite and chrysocoUa. 1954] GEOLOGY AND MINERAL DEPOSITS 123 The eastern ore bodies are developed by drifts from two vertical shafts rouyhly 150 and 60 feet deep, respectively. According- to Cloudnian's account (1908, p. 784) there were (1914) two shafts 265 and 175 feet deep, respectively. One of these may have been on the western ore body but the east shaft, clearly caved at roujihly the 150-foot level, and the 60-foot shaft may once have been deeper. The western ore bodies are developed by shaft, inclined at 60° NW and more than 100 feet deep, and by several short tunnels and open cuts. Several tons of ore of good grade lay on the dumps in 1951. A. C. Price Group. The Price group of copper claims are scatteTcd along a series of vertical, en echelon fissures extending west from behind the center of Southwestern Portland Cement Company's Reserve quarry. Most of the claims are in the NWi SEi sec. 8, T. 6 N., R. 2 W., 8.B. Concentrations of copper are found chiefly at the eastern and western ends of the fracture zone which is slightly more than half a mile long. The most easterly group of claims is OAvned by Southwestern Portland Cement Company ; ownership of the western group of claims was not determined. 5sone have been developed beyond the prospect stage, development work consisting of shallow shafts and short tunnels or else shallow open cuts. No sizeable ore bodies were uncovered but the mineralization is interesting. The most easterly group of prospects un- covered irregular pods and veins of white barite in which chalcocite, chrysocolla, malachite and chalcedony have been introduced in and adjacent to fractures in the barite. The veins are strongly colored by products of oxidation but the weight of copper minerals per ton of vein matter is small. The deposits at the western end of the fissure zone are found in irregular veins and replacement pods of black opal and chalcedony. Malachite and brochantite are the chief ore minerals but chrysocolla and azurite are generally present. Presence of a little relict pyrite and chalocopyrite is some clue as to the nature of the primary ore. Masses of bright yellow, ochrous jarosite are conspicuous in some of the veins, apparently an alteration product of iron and copper sulfides. Gold Mesothermal gold-bearing quartz veins have been found and worked on various scales at numerous places in Barstow quadrangle. In general production has been intermittent and not large. Upper, oxidized parts of the veins have yielded most of the better grade ore, enrichment having been by decomposition and removal of valueless sulfides. The deeper mines were worked in ore of low tenor, generally less than .3 oz, of gold per ton. Small pockets of high grade ore have been found in some of the mesothermal deposits. Ore bodies occur in fissure veins most of which strike roughly north or east; dips are generally steep — from 60° to vertical. Veins vary in width from 4 feet down to stringers less than an inch thick. Ore is found in what may be termed ore shoots of variation, that is, dis- tributed somewhat haphazardly through vein matter that is barren of valuable minerals. Primary ore minerals consist of pyrite, chalcopyrite, sphalerite and rarely bornite, as well as free gold, the sulfides commonly acting as hosts for deposition of gold. Oxidized minerals commonly are limonite and malachite. Gangue material is predominantly milky quartz 124 BARSTOW QUADRANGLE [Bull. 165 go 5 2 « T Ji o o S > n e o. . .5 _o C3 _, "« fr S >■ o a; » C s> Q .M S S.2 I- QJ j= «2 -a -*^ .-^ ""^ C QJ " 2 3 o o o i2 a rt « c 3 pa S o J3 > s J3 K . m W a '§■ " • ^ s 5 .2 J>1 :3 4i ° ■g Si M --, m CD ^ «« I O 05 •5 m Kq 11 ■t3 O o tm ja _ E -^^ ' C3 c Oi ni O " 'S 2 "!!! o S S ^3 S *^ g>'-s s, T ° e ■= a ^ 5 aj -^^ *; ta c o m S 2 -o — >. c . oa c« = JJ •2 -oQ •* £■« c e4 O § g-g- — ' 2 S o G « ■ ■-CO) £ ■ S S , •^ . < so m -O ^ o a> , rt O.S cy S =2 M " 3 O. « a-2. .§ > s- ^ flj (I' I "^ o ■- -r ^ S3 Q Q, a ' o ;§ ' a r4 -*^ O ^:5 g a a o . - a •8 oa C3> IS e 0! e 03 »5 o o i-g o « a a a a o a a a m CO B3 BQ oa CO pa CO m CO m oa pa «3 pa en d .pa z CO [x] z, o o pa w Q. m ID £ pa (U J3 3 UJ [^ T3 o" H o a „,-v Q 1=^ n ■S ^ R js ta o PQ a. a o O c3u -a .2 .X OJ > ■< a o d a 3 a CO tf o h4 T3 C 02 ■a a <« bi O o O & o o o > pa o o aa a S a o m o pa ^ ^-^ o Q W pa 03 z^ — \ o a M a 3 -a -a 1954] GEOLOGY AND MINERAL DEPOSITS 125 .B'S •- t« a:3 T3 o >, "" >, L. O -° a. w O S " C 2 1 CD .— 00 e - a o S °c? J E 2 ^ oc "rt O a. 2 > 3 00 E c ""- ^ ■ — CD • '-' ^ >> 3 — ■3 TJ =o > £" t» 9. D. rt , "3 ■;? ^ a> o 2 o .E c.-e a D.- 5 to S'S M « a a ^ ce ^ „ o. .£ 8 Si ■^ o.- 3 D. D.-3 o C.-3 - 8 M c o Q 3 s ^^ O) rt ^ » as ^ __ r2 — ■ «^ ^ 3 a> ^ »i '^ "£ o •** -* o rt «>.'-£: " "S ° ^ .5 2 S - 3 el o • — tS o w y > o ta 2 g S £ a « o ^ TO >i J3 0; ■g' sis .S3 -c O a S^ <" II, a.S. g a ■SI to !: a.t: -*s ■n ^■a a "> B a a Z ■n^ > S m t- .^1? ft &;S; 1^ ^ m 5: •i i^ 5 >■ •s. ■0 -) ■2 a c: OJ -O a fl 2 S O M ij ,— . Y a> « *j _ a " H O m 8 a-S OS >; S 5 g a a 5 Si C H" :2 i 03 na CO pa CO n (a 00 ^ fc & ^ ^ ■^ ^ •>«< ^ ■* ^ ■^ Z z Z z to Z to Z z to •>6 o. < ■3 o 00 a o a a a O 5 I ^ 3 Ed »— J as s'E t2 ° < 5a 52 or O J 08 J3 Co . o u O ,? O1 d -oo . oa o CO 10 a o O O O c 3 03 ■3 o •a '3 ■oto c CO ■© C 5 CO O 126 BAKSTOW QUADRANGLE [Bull. 165 B <2 t; " .2 .> _ > So o OO , I" > ^ ■ s = 'C >« ^ -a be ;§-- ^S 3 > .= cS -S^ » c S 2 '" .i c9 c c c= fc -sis u •_ o c 5 »^ 2 S ^ '2 T >• 'd. b o 0) ~ .- T3 g a o I £ c i-S: o o «S S a&2 > « -O , N ir -^ n (L> oi 03 ' Ih ™ - 1. 1^ -c 5 ! £ - "- _ a M I o - ^ ' M S . i.S £-3 ) fJ -*J ■ — : "2 .S "*- •CO' , O OJ c- ' " B S ■ i s i ■« S 5 g s; 1 1 '^ ; ® ** -^rt 2 <^ M ' t = 1s ■ - o <« .E , !=! S fe B ^ ^ u b < ■^ S " * ; o go '■3 "2 •g "is a "^ ■ ■res li — ° -. o o o =a ■n « 5; •2-<, E ■S .Si > ti _2 CR 11 !0 .O y a> £^ O fc- ct '■a -3 ■g; i^ a i O M S (M _ .S J3 J3 — -g >, o T5 3 a 5 Q Q..2- °- ^ ^ Qj tn — kri rt flj g 05 -is to »^ .£i . rS 4j; c=3 S; § 2 to ^ bC o 3 - o e s :? e 03 03 03 03 03 03 CO -Jv 00 03 z o Lri 1 C T3 o p3 ^ 2 CO C _ V V -tJ o rt ^O C9 3 a a o O a "S •3) SI "O) (.J w o M <; X J OJ i s a 03 1^ X> Q c c« c^ J3 C9 (M Q ro c SJ JS a a ■s -a a OS 3 H 03 c3 fli S. OS n » >> ^__^ a r-) •^ o. OS a u .^ bO u ■a S K a . n .£3 d -«-' i' to M ^ (5 o a O ci 'S <=• "2 « 4? N S <^ Si ^ o. BQ >: as 2; Gj .- to . CO •- e . p J2 — ' c ^ o . *j CO D. 5 •» CQ 02 CO 02 m CQ 03 fe ^ I ^ I z CO pa « CD o 05 — fe O L-. r~j w r IM Sf m -3 cr: m C Ed •n r : c OS 1 - >> c ca Q. 1 s o O CO OJ a 1 § 0) -c: o ■rr 1J a: > 05 > > e c5 fe ■ £ IM o a> 1 > 13 S „ p~i S ji ^ < ■p.^ (5 a ndeter Los A 1 ^ CO 1^ s 1 ^ I a I a o I O o o o^ -r) o OJ T) c C R s O C o D o E CO ■T3 -o C c<9 !« O c o o O C 128 BARSTOW QUADRANGLE [Bull. 165 8 S •♦A o 1 o •9 e as S o o e ringers and e in a ver- ;ed material Wall rocks inder series ted to have shaft at 70 1940. Small t 1888. See Div. Mines 1 d 07 C*^ 2 1 =?§'?>_ &^ >,3;r- 1 1 PS d C 1 O Set: i 'c o 5 EO -* g t^c B£ -1 "2 >i; a s 2 =5 "s ^ - .2 s tc c o s "s e s •go a cr E U) i to -a CO o O ^~ 3 3 Q CO •^ •a H ca CO aa CK m «= OT pj S: S: S: ^ fe C f CO ■-f c^ ■^ o Z ■ z z Z z J H to eo r^ CO to c5 ^ CO CO _^ MS OT •Z few » mt« ■T3 c « C4 ■§c3 O ■V 3 « ■^ « "2 C£ OS c; a c o y <; 1 s" J ra J 0^ ■5 §^ > 1-2 fc < o -1 13 O rt 3 ►J CO CO "^ CO O s o £ e S Oi ID 09 .^ CO OS i S V3 Of 'E — -*3 3 rt '.5 2« o Co 1 s V d< a; J3 did tf "r; » o ^ 1 ^ £3 ' :s T3 "3 a* S 1 s is C =B i s| g ; -gta o s t£ i ; b? s Q 1 c g ■3 ■ l5 A e« (A ■fc S kd M OT e o >• . H *■• # *»*^' Figure 65. Dumps of the Sidewinder gold mine on the north slope of Highland Moun- tain just east of Black Mountain. This is the largest gold mine in Barstow quadrangle. and idle again until 1927 when a mill and cyanide plant were built. The last period of activity, 1927-1942, ended with War Production Board Limitation Order L-208 (Wright et al., 1953). All equipment had been removed prior to 1952. The Sidewinder mine is by far the most extensive and has the greatest recorded production of any gold mine in the Barstow quadrangle. Total production compiled from U. S. Bureau of Mines statistics is approximately $60,000. Values were in gold and silver. The principal accessible working is a tunnel driven due south from a point 140 feet south and slightly west of the massively timbered ore bin. This bin was the only substantial structure remaining on the prop- erty in October 1952. The main tunnel, which is 5 feet wide and 6h feet high, strikes south 180 feet from the portal to intersect an inclined shaft, the Dohney, sunk on the vein from the surface. If it was ever driven beyond the shaft that portion is caved. The portion of the Dohney shaft above the tunnel was partly caved and inaccessible in 1952 so that the shaft is usable only as a winze from the tunnel level. At the intersection of the tunnel with the Dohney shaft, drifts have been run east and west on the vein, exposing it for a distance of more than 1000 feet. At this level the vein strikes N. 70° W. and dips 50° S., but steepens to 60° or 70° as exposed in the winze. The vein has been stoped almost the entire length of the drifts on the tunnel level, chiefly by overhand stopes but also by occasional shallow underhand 1954] GEOLOGY AND MINERAL DEPOSITS 133 stopes. Over much of the length of the drifts 1-3 feet of milky quartz is exposed although it widens locally to as mueh as 5 feet. The only visible metallic minerals present in any quantity are pyrite and limonite although small amounts of chalcopyrite, brochantite, chalcocite ( ?) and pyrolusite are locally disseminated through the vein material. Workings below the tunnel level from the Dohney shaft appeared to be open but were not accessible to the author because of a lack of hoist- ing equipment. According to Tucker and Sampson (1930, p. 252) there is 400 feet of drift on the third level (presumably 100 feet below the tunnel) and 300 feet on the fourth level, the shaft reaching a total depth (1929) of 200 feet below the tunnel level. Several hundred feet east of the Dohney shaft, also open but not accessible without hoisting equipment, is a second winze. In 1929 this had been sunk 308 feet below the tunnel level (Tucker and Sampson, 1930, p. 252). The east drift of the tunnel level is lagged over much of its length but has not been adequately enlarged for a haulageway. Tucker and Sampson also men- tioned that a 700-foot tunnel had been driven from the east winze to the surface, but if this work was ever done the surface entrance has been obliterated. About 700 feet west and slightly south of the main tunnel is a partly caved inclined shaft and open stope of unknown depth. East of this, a distance of 175 feet, is an open inclined shaft more than 100 feet deep. Six to eight feet of vein matter is exposed in this shaft which strikes N. 80^ E. and dips 65° S. Two hundred feet S. 30° E. of the shaft just described is another steeply inclined shaft on a vein striking N. 63° E. and dipping 80° S. Two hundred feet S. 40° E. of the main tunnel is another partly filled shaft sunk on a shear zone striking N. 80° E. and dipping from 64° to 80° south. No vein matter was exposed in this shaft. A short tunnel driven to the vein 30 feet east of this shaft exposes 8-14 inches of vein matter, and there are two more shallow shafts on the same vein several hundred feet farther east. These expose vein material of similar width. Although neither mine maps nor detailed base maps were available to the author it is fairly clear that the main workings as well as those east of the tunnel are all on the same vein and that the strike of the vein at the surface is predominantly N. 80° E. Below the land surface, strikes and dips of this segment of the vein tend to be more variable, and in the vicinity of the Dohney shaft the strike has swung to N. 80° W. To the west of the Dohney shaft, however, the trace of the vein at the surface is discontinuous so that the two most westerly shafts may be sunk either on a branch of the Sidewinder vein or on a vein parallel to it. In the vicinity of the Dohney shaft the hanging-wall rocks are meta- dacites and metafelsites of the Triassic (?) Sidewinder volcanic series and the footwall rock is quartz monzonite porphyry. In the most east- erly workings both walls are hydrothermally altered felsite of the Side- winder series. Both walls are quartz monzonite porphyry in the most easterly of the three west shafts. The quartz monzonite porphyry is intrusive into the Sidewinder series and it is evident that the vein did not follow the volcanic-quartz monzonite porphyry contact over much of the vein length. The main tunnel is driven entirely in quartz mon- 134 BARSTOW QUADRANGLE [Bull. 165 zonite porphyry (180 feet), but a vertical fault roughly paralleling the main vein crosses the open cut just north of the tunnel portal and north of this fault the rocks are Sidewinder metavolcanic. Iron Magnetite and magnetite-specularite deposits are found at five scat- tered localities in the quadrangle. In three of these mineralized areas the deposits are replacements in carbonate rock near granite contacts. Tn the other two areas the ores occur in veins or wall rock replacements adjacent to veins. Only one series of deposits is known to contain a significant quantity of ore although two others contain pods and bunches of high-grade ore amounting to a few hundred to a few^ thousand tons. None of the deposits is sufficiently well explored to allow a reliable esti- mate of the reserves. In addition to the deposits described in detail in following paragraphs there are occurrences of specularite ores in the NWi sec. 28 and S^^^, sec. 21, T. 7 N., R. 2 W., and in S^ sees. 16, 17, and Ni sees. 20. 21, T. 10 N., R. 1 W., S.B. Altuda (Glnherson) Deposits. Location: sec. 1, T. 7 N., R. 3 W., S.B., two miles northwest of Stoddard Mountain or 15 miles northeast of Victorville. Deposits are best reached by a dirt road joining High- way U. S. 66 midway between Hodge and Wilde siding. Ownership : Nathan Gloverson, Alhambra, and Robert Gold, Los An- geles, own two claims. Several to the west of these have been located by R. V. and IT. L. ]\Iorrow, Oro Grande, and others by R. !Mc Williams, 122 E. Anaheim Boulevard, Wilmington. The Altuda deposits were worked in a small w^ay in 1942 ; 100 tons of selected ore was sliipped to Alhambra for use in steel castings. Since that time tlie properties have been idle except for assessment work. Ore occurs in a series of five en echelon vein systems, and adjacent wall rock replacements, that strike N. 55-85° E. and are either vertical or dip steeply north. The mineralized zones pinch and swell as followed along the strike getting increasingly irregular in width and increas- ingly variable in iron content toward the west. Pure magnetite or mag- netite-specularite veins from stringers a fraction of an inch to several feet wide cut black iron-impregnated rock which itself constitutes low- grade ore. The parent rock is chiefly metadacite and meta-andesite of the Sidewinder series (Triassic?) which forms the walls of the mineralized zones. Deposits on the Altuda claims appear to be the richest in the area. They are developed by a 40-50 foot vertical shaft and connecting short drifts. The ore zone on the Altuda claims strikes N. 85° E. and is ex- posed for a distance of 160 feet. It averages 20-25 feet wide and con- tains ore varying from 65 percent Fe-Oa to partly impregnated wall rock carrying perhaps 25 percent FeoO.;. The author estimates that there is 50,000 tons of ore of variable grade in the Altuda ore body for each 100 feet of depth. Owing to insufficient development work and lack of sam])ling'data, no valid estimate can be made as to the probable per- centages of ore of various grades within the ore body. The four en echelon ore zones west of the Altuda claims also contain substantial reserves of ore, but the width, persistence and grade of the ore bodies appear to decrease to the west. The other ore zones are offset from one another from 50 to 250 feet. Three of them strike N. 65° W. 1954] GEOLOGY AND MINERAL DEPOSITS 135 Figure 66. An outcrop of massive hematite-magnetite iron ore near tile Glob- erson mine, two miles north of Stoddard Mountain. and the most westerly zone strikes N. 55° W. They are opened here and there by pits and open cuts a few feet to a few tens of feet deep. The Altuda ore zone is terminated on the west by another vertical mineralized shear zone of different character striking N. 40° E. Rocks in and adjacent to the shear zone have been pneumatolytically and hydrothermally altered to a variety of products of irregular distribu- tion. In general, there is an outer zone 2-10 feet wide consisting of muscovite-quartz albite(?) greisen. The quartz tends to lie in fist- sized clots associated with coarse crystals of intense blue lazulite. Vein- lets of specularite commonly cut the greisen zone. The bulk of the shear zone is made up of pale-green talc-tremolite rock that is also criss-crossed in numerous places by specularite veinlets. Small bodies of quartz monzonite porphyry have intruded the Side- winder volcanic series at several places in the vicinity of the ore zones. It seems clear that the iron ore originated in a late hydrothermal stage connected with greisening of the metavolcanics along the shear zone in the vicinity of quartz monzonite porphyry intrusions. The talc-tremo- lite rock appears to be entirely a hydrothermal product as there are no basic or ultrabasic rocks in the Sidewinder series. Afuazon Deposits. These have been described in detail under copper. There is a considerable tonnage of high-grade magnetite in the work- ings of the Amazon mine that might be salvaged as a by-product in possible future copper-mining. Much of it does not appear to be badly contaminated with sulfides. Ball (Red Seal) Magnetite Deposits. Location: NE| sec. 4, T. 6 N., R. 2 W., S.B., low down on a northwest-trending spur of the Sidewinder 136 BARSTOW QUADRANGLE [Bull. 165 Mountain group about 1^ miles northeast of the Sidewinder mine or 14 airline miles northeast of Victorville. Ownership: Patented claims (U.S. Mineral Survey No. 6453-B3) are owned by 0. H. Ball, 2024 West 62nd Street, Los Angeles, California. The Ball deposits are a group of small, superficially explored pods of nearly pure magnetite that have replaced dolomite and lamprophyre near the contacts of two types of intrusives, hornblende lamprophyre and quartz monzonite porphyry. The dolomite is part of the Upper Paleozoic Oro Grande series and the intrusives are of Upper Jurassic or Lower Cretaceous age. Structure is not discernible in the dolomite in the vicinity of the deposits and the dolomite is complexly fractured, seamed and intruded by igneous rocks. Workings consist of several tun- nels and shallow pits none of which have penetrated more than 30 feet below the surface. Magnetite pods crop out over a quarter of an acre, and ore in them is exceedingly rich. Adjacent to a series of sills strik- ing N. 80° AV. and dipping 20-30° SW. are large areas of black, mag- netite-impregnated rock of variable grade in which the principal gangue minerals are serpentine and a colorless, iron-lean chlorite. Because of the magnesian, and hence refractory nature of the gangue, these prob- ably do not constitute ore. Reserves of high-grade magnetite currently exposed probably do not exceed 10,000 tons and highly selective mining would be necessary. The deposits have not, however, been adequately explored and larger ore bodies might be encountered beneath the tab- ular mass of lamprophj^re. Lamprophyre and quartz monzonite porphyry intrusives are found in mutually cross-cutting relations so that their times of intrusion over- lap. The iron mineralization may have been connected with a sequence of related events which included igneous intrusion of rocks of widely variable character as well as hydrothermal introduction of iron. There are also dark-colored felsite intrusions related to the Sidewinder (Trias- sic?) series near to the iron deposits, but these unquestionably pre- date the iron mineralization. Lead -Zinc -Silver Only a few properties in the quadrangle are known to contain lead- zinc-silver ores in commercial quantities, although small amounts are recovered from time to time from ores mined primarily for gold, silver and copper. There is one small district in the Shadow Mountains, one vein system in the Hinkley Hills and one small district east of Oro Grande. Some of the deposits most probably are related to the Jurassic- Cretaceous period of granitic intrusion, and at least one is an epithermal deposit probably related to the upper Pliocene volcanism. Anaco (Red Rover, Red Raven). Location: SW^ sec. 31, T. 7 N., R. 5 W., S.B., 5 miles north and 2 miles west of Adelanto and half a mile west of Highway 395. Location is marked on Barstow topographic sheet. Ownership: 12 claims are held by Colonel Frank Whitmore, Holly- wood, California (1950). This mine is known to have been active in the late 1920 's and early 1930 's. Some development work was done during the early 1940 's. The tonnage of ore shipped was small and the property was idle in 1951. 1954] GEOLOGY AND MINERAL DEPOSITS 137 Ore occurs at or near the contact of severely altered quartz porphyry dikes of unknown age and blue-gray crystalline limestone of the Upper Paleozoic Oro Grande series. The apparent strike of the limestone is N. 23° W. with steep dips to the west, but attitudes in the massive limestone are by no means certain. General strike of the dikes is parallel with the limestone, but they dip steeply east. Most of the dike rock is friable and thoroughly decomposed and there is spongy quartz- jarosite- limonite vein matter along the dike contacts and along fractures in the limestone. Limonite obscures the nature of the mineralization at the surface. Fragments of unoxidized ore on the dump consist of galena, sphalerite and pyrite. The galena presumably is argentiferous. Workings consist of a 100-foot shaft surmounted by a headframe and ore bin and a 70-foot shaft sunk 300 feet south of the main shaft. Both shafts are inaccessible. The most complete early account of the work- ings is recorded by Tucker and Sampson (1931, p. 340). Carhonate Mine. This mine is discussed in detail under gold. Sub- stantial amounts of lead were shipped in complex lead-silver-gold ores. It is the only mine in the quadrangle that has had any sustained pro- duction of lead. Golden Witch (San Antonio, Pedry) Deposits. Location : sees. 7, 18, T. 10 N., R. 2 W., S.B., 4i airline miles northeast of Hinkley. Ownership: William ifile et al., Nipton, California. Under lease (1952) to 0. C. Fredericks, 3050 Lincoln Drive, San Bernardino, California. The Pedry vein system crops out continuously for more than a mile, striking N. 23° W. and dipping east from 70° to near- vertical. It is conspicuously exposed on a low ridge made up of several types of granitic and volcanic rocks. Surface exposures of vein material vary from 2 to 10 feet wide. The lead-zinc mineralization appears, from sur- face exposures, to be concentrated in the southern half of the vein, with increased quartz, subordinate copper and sparse lead-zinc showings to the north. Wall rocks along the southern half of the vein are chiefly gray quartz monzonite porphyry approaching a quartz latite in tex- ture, but this rock includes pendants of hornblende gneiss and is cut by thin dikes of white felsite. The northern half of the vein is chiefly in slightly gneissie, light gray granodiorite. It is also cut by white felsite dikes and is intruded along its south contact by the quartz monzonite porphyry. Vein matter is chiefly brecciated quartz mingled with wall rock frag- ments. Relict primary minerals in the main workings include galena (probably argentiferous), sphalerite and pyrite with chalcopyrite com- ing in only along the northern half of the vein. The vein has been oxidized for the entire depth penetrated and the principal ore minerals are now cerussite and anglesite. Gangue minerals include barite, calcite and limonite as well as quartz. Vein matter is full of vugs and comb structures and the environment of deposition is clearly epithermal. Workings consist of a 270-foot inclined shaft near the most southerly exposure of the vein, a partly caved vertical shaft of unknown depth 100 feet north of the main shaft,, a third shaft inclined 70° E. situated I of a mile north of the main shaft (described by Wright (1953) as being 200 feet deep and having short drifts at several levels) and numerous 138 BARSTOW QUADRANGLE [Bull. 165 shallow pits and crosscuts. Most of the recent activity is confined to workings connected with the main shaft. This is equipped with a head- frame, ore bin and hoist and is readily accessible by ladder. Its gen- eral inclination is 70° E. but this dip changes as much as 10° in some places. There are 5 levels spaced approximately 50 feet apart consist- ing of short drifts 30 feet long or less. A crosscut was driven west from the main shaft 40 feet to intersect a parallel vein. The shaft is full of water below the 250-foot level. Insufficient development work has been done to gain much of an idea of tonnage reserve in the mine and the author did not have access to either the lower workings or to the parallel vein underground. The latter is discontinuously exposed at the surface for a hundred feet or more and the gossan outcrops contain high-grade ore. Several feet of high-grade ore were observed at each of several levels and the amount and quality of the ore exposed is notable. Several small shipments were made during the period 1950-53. Silver- Barite Epithermal silver-barite veins similar in character, origin, age, and regional environment to those of the Calico district are found in and near the Waterman mine, 4 miles north of Barstow, and in the Hinkley Hills 1 mile north and 3 miles east of Hinkley. Ore bodies of commer- cial interest so far have been discovered only at the "Waterman mine. Veins cut either middle Miocene (?) continental sediments or upper Pliocene voleauics, and there invariably are dacitic volcanics in the vicinity of the veins. The mineralization is clearly linked to the upper Pliocene volcanism. Waterman Mine. Location : NE^ sec. 13, T. 10 N., R. 2 W., 4 miles north of Barstow via the Camp Irwin road. Ownership : Robert W. Waterman, Box 15, Dagget, California, owns 2 patented (the Alpha and Omega) and 2 unpatented claims. The Waterman mine has the largest production of any metal mine in the quadrangle. Discovered in 1880, it was worked chieflly prior to and during the heyday of the Calico silver district, producing approx- imately $l,700,000"between 1880 and 1887. ^^ Except for a small amount of barite recovered from mill tailings in 1931, there has been no known production since 1887. The owner recently has rehabilitated the No. 2 shaft and installed hoisting equipment. ]Most of the workings down to the 400-foot level are accessible and all of. them are dry. The principal ore-bearing vein roughly follows the bedding of a sequence of dacitic tuffs, lakebed clays and siltstones, and granitic fanglomerate probably belonging to the middle ^Miocene Piekhaudle formation.^" These have been folded into a near-vertical attitude that is arcuate, commencing at the south with a northerly strike and veering toward the northwest. The vein matter, which consists chiefly of massive and comb barite, follows a massive-to-laminated jasper zone which may or may not be vein matter. In some places the jasper appears bedded and may have been an original member of the Piekhaudle for- mation. In all the places examined by the author the barite and metallic minerals have formed later than the jasper. At nearly all points the vein dips generally 75-85° west although dips flatten and steepen lo- "■ Waterman, R. W., personal communication, 1950. iBMcCuIloh. Thane, per.sonal communication, 1951. Pickhandle formation is a name proposed by McCulloh in an unpublisiied report. 195-i] GKOLOGY AND MINEKAL DKPOSITS 139 cally. In the vicinity of tlie 200-foot level the vein rolls (is Avarped into a shallow, narrow troujih) and then resumes its steep westerly dip. Aeeordin*!' to the owner the highest : '^-■?3^^J'i Figure 68. Dolomite marble breccia at the Three Colored marble quarry on the north slope of Sidewinder Mountain. White, green and black colors prevail. Blocks larger than 10 feet across can be obtained l)etween joints. The green coloration of the rock is caused chiefly by epidote-group minerals and a very fine-grained mesh of minerals of the serpentine- chlorite series. Black coloration in the matrix is largely disseminated magnetite dust whereas most purple or pink material yields qualitative tests for manganese. The black dolomite fragments are colored by finely divided organic matter. The dolomite fragments commonly show peri- pheral zones of white calcitic marble up to a quarter of an inch wide. This material could have been added by accretion at a time when the breccia was unconsolidated or might simply be the product of hydro- the»mal dedolomitization. A quarry or open cut 20-30 feet broad driven 25 feet into the ridge is the only working. This is situated high on a steep, north-trending ridge 150 feet above the canyon floor. In view of the extent and distri- bution of the marble, the choice of a quarry site seems poor. Large chunks up to 9 feet in longest dimension were broken from the quarry walls by blasting and were then rolled down the steep ridge to a staging area on the canyon floor. There the blocks were loaded by means of block, tackle, mast and boom onto wagons or trucks. Cutting and polish- ing was done elsewhere, probably in Colton. Marble is exposed over several acres, but several spots would have to be tested to determine the best quarry site. In the quarry there is an east-striking, steeply south-dipping joint system which somewhat 148 BARSTOW QUADRANGLE [Bull. 165 limits the size of the blocks. Other parts of the breccia mass do not have prominent joints, at least at the surface. Verde Antique (Kimhall, Gem, Alamo Consolidated) Deposit. Loca- tion : Wi sec. 28, T. 7 N., R. 2 W., S.B., 3 miles north of the Side- winder mine and 15 miles northeast of Victorville via the Stoddard "Well road. Ownership : undetermined. The quarry has been abandoned for many years. This deposit, first discovered about 1890, had produced about 400 tons by 1904 (Aubury, 1906, p. 147). The marble was used to decorate buildings in Los Angeles and San Francisco. The rock quarried is a serpentinous marble derived by contact meta- morphism of a roof pendant of dolomite of the Oro Grande series. It is surrounded by quartz monzonite and quartz monzonite porphyry and is penetrated in several places by hornblende-rich granitic dikes. Much of the coloration minerals formed by interaction of emanations from the hornblendic dikes with the parent dolomite. In addition to the deposit developed by the quarry, similar undeveloped roof pendants of marble of like character are found lower the flanks of the hill to the north- west and southeast. Contact minerals such as epidote, garnet, actino- lite and specularite are irregularly distributed in the dolomite near the granitic contact, but generally do not interfere with quarrying opera- tions. Coloration of the marble varies considerably, there being various combinations of sulfur yellow, chocolate, black, pale blue, red, gray, cream, rose and white. The predominating colors, however, are yellow, white and brown. According to Irelan (1892, pp. 363-364) the original outcroppings stood 10-20 feet above the adjacent country rock, the northwest-striking, southwest-dipping bands of marble and serpentine of various colors ranging from 3 to 6 feet wide. The crushing strength of the serpentinous rock was listed by Irelan at 28,000 pounds per square inch. The chief working is a level quarry, irregular in plan, driven near the top of an 1100-foot high mountain. It is 60 to 100 feet wide and extends more than 50 feet into the hill. The west-dipping east face, 75 feet high, follows a thin, black dike of lamprophyre that has been almost wholly altered to epidote-group minerals. This dike-rock is similar to that found in dikes which cut the dolomite at the Ball magnesite de- posits. Rock in the quarry was handled by a pair of masts equipped with booms, blocks and tackle. A fair road once led to the deposit but this has been gutted by storm water and is impassable. A large volume of marble of variable quality remains in the vicinity of the quarry and yellow and white ophicalcite of good quality occurs in quantity in two other undeveloped deposits to the northwest of the quarr3^ Dolomite White and. gray dolomites are broadly distributed over Barstow quadrangle in carbonate members of the Upper Paleozoic Oro Grande series. There are all gradations between nearly pure dolomite and nearly pure cak'itic limestones, but calcitic rock greatly predominates over dolomite in most carbonate sections of the series. The largest reserves of high-grade dolomite occur in bedded deposits assumed to be original 1954] GEOLOGY AND MINERAL DEPOSITS 149 products of marine sedimentation. Certain smaller masses unquestion- ably are hydrothermal replacements of limestone or of mixed carbonate rocks and there are extensive masses of carbonate rocks in which caleitic and dolomitic rocks are interlaminated in thin bands and streaks ^yhich are partly metamorphie in origin. The latter cannot be selectively mined and are of current economic value only as magnesian limestones. Some deposits of this type may ultimately be beneficiated into caleitic and dolomitic fractions. Large deposits of high-grade dolomite are found on the north flank of Sidewinder IMountain. in the Shadow Mountains, in the hills north of Iron Mountain, and, to a lesser extent, in Quartzite Mountain. Hinkley Deposit. Location : SWj sec. 12, T. 9 X.. R. 4 W., S.B., 4 miles south and three miles west of Hinkley or 1^ miles X.W. of Iron Mountain. Accessible by good paved road from the paved Hodge-Hink- ley road. Ownership: A. R. Mills, 3859 Main Street, Riverside, California, owns two unpatented placer claims. This deposit was worked briefly in 1944 as a source of basic flux for the Fontana plant of Kaiser Steel Company. The 25-ton-per-day capacity crushing and screening plant built in 1943-44 has been re- moved from the property. Massive, white, coarsely crystalline, dolomite occurs with schist and quartzite as a roof pendant in quartz monzonite. The.se metasediments are remnants of the Oro Grande series which in this area strikes north- east and dips steeply southeast. The dolomite crops out on the south- east side of a northeast-trending ridge rising 150-200 feet above the local base level. In the quarry vicinity a series of shallow benches has been driven into the dolomite in an operation that covered several acres. The dolomite varies in thickness from a few feet to more than 200 feet and extends below local base level for an unknown distance. It crops out discontinuously over ten acres or more. High-grade dolo- mite occurs in discontinuous masses each containing from a few tens of thousands of tons to several hundred thousand tons. Numerous, hornblende-rich, granitic intrusions as well as quartz monzonite in- trusions cut the dolomite which is badly faulted and fractured. Atti- tudes obtained on the dolomite in the quarry area are not reliable. Close to the hornblende-rich intrusions, chiefly small dikes and sills, the dolomite has been converted to sulfur-yellow serpentine and, within a few inches of the contact, to f orsterite and spinel. These contact prod- ucts are, however, not extensive and are not as troublesome in quarr}-- ing operations as the granitic intrusions themselves. Dolomite from the various high-grade masses probably will aggregate several million tons above the local baselevel with an unknowni but sub- stantial amount occurring below the base of the ridge within reasonable quarrying depth. Selective mining must be practiced in order to pro- duce a large tonnage of rock of high uniform grade. Unaltered rock tends to vary in chemical composition within the following limits : Si02 .36- 1.07 R2O3 .18- .58 (R = Al-f Fe) CaO 30.3 -30.8 MgO 21.0 -21.9 Ignition loss 46.7 -47.2 (Chiefly CO2) 150 BARSTOW QUADRANGLE [Bull. 165 Klondike Quarry. Location: NWi sec. 17, T. 6 N., R. 4 W., S.B., li miles northeast of Oro Grande. Ownership : Riverside Cement Company, 621 South Hope Street, Los Anp'eles, California. Dolomite is found below the commercial limestone of the Klondike quarry in thickness varying from 100-200 feet.-^ Much of the rock runs 15-18 percent MgO but some is nearer a magnesian limestone with 6-11 percent MgO. The Klondike quarry is operated principally for lime- stone but a substantial tonnage of dolomite could be quarried if demand for it should arise. Sidewinder Mountain Deposit. Location: sec 11, T. 6 X., R. 2 W., S.B., on the north slope of Sidewinder Mountain. Accessible by partly graded dirt road joining the Barstow-Lucerne Valley Road. Ownership : undetermined. Light gray to white dolomite and magnesian limestone is exposed underneath the dolomite breccia of the Three Color marble quarry. Near the south end of the deposit, the dolomite reaches a thickness of 400 feet above the canyon bed and it is exposed continuously for 1400 feet. It is one of the carbonate members of the Oro Grande series which in this vicinity strikes N. 40-50° E. and dips 50° NW. into the ridge. More than 4,000,000 tons of dolomite and magnesian limestone are exposed without overburden above canyon level and presence of several times that amount is inferred from the attitude of, the beds. Some of the rock is nearly pure dolomite and some contains as little as 7 percent MgO. Systematic sampling would be necessary to determine the extent of the reserves of high-grade dolomite. Miscellaneous Dolomite Deposits. Extensive exposures of carbonate rock in which dolomite predominates are found in sections 26, 27, 28, T. 10 N., R. 2 W. ; sees. 2, 3, 4, T. 6 N., R. 1 AV. ; and in the SEi sec. 10, T. 6 N., R. 4 W., all, S.B. The quantity and distrbution of the various grades of carbonate rocks in these areas has not been determined. Mineral Fillers There is increasing demand for white mineral materials of some chemical iuertness for use as extenders and fillers in manufacture of such materials as paint, paper, rubber, cleansers, and floor coverings. There are a number of deposits of white rocks of several sorts in Bar- stow quadrangle which have been explored and tested for such pur- poses, and still others which so far have not been utilized. These include quartz-sericite, pyrophyllite and kaolinite-quartz rocks — the hydrother- mal alteration products of ancient volcanic rocks; sericite and quartz- sericite schists, the dynamothermal metamorphic products of siliceous volcanic rocks; white marl, a product of weathering of calcareous shale; the impure magnesite of the Kramer Hills ; and white limestones and dolomites. The latter three carbonate rocks are considered under sepa- rate headings on other pages of this bulletin. Abrasive Cleanser Black Mountain Deposit. A white, mildly abrasive, powdery marl suitable for blending with soap in prepared cleansers and for some ^' Wightnian, R. H., personal communication, 1949. I 1954] GEOLOGY AND MINERAL DEPOSITS 151 filler uses is found in two general areas underlain by the lower (horn- felsie siltstone) member of the Permian Fairview Valley formation. These hilly areas are in the W^ sec. 6, NE^ sec. 7, T. 6 N., R. 4 W., 8.B. ; parts of these areas are marked off by claims of unknown ownership and parts are on unclaimed land. The white, friable marl is a product of weathering: of hornfelsic limy siltstone and claystone which every- where underlie the marl. It forms surficial deposits varying from a few feet to more than 30 feet thick. The material crops out on or underlies surface talus in an area aggregating more than 50 acres. As the north- ern and largest area covers 40 acres, a large tonnage probably could be blocked out by trenching and test stripping of a few feet of overburden. The marl could be mined rapidly and cheaply by surface earth-moving equipment and loaded with a minimum of handling through use of bulldozers, ramps and haulage pits. A substantial part of the reserves could be handled free or nearly free of adulterating detritus and more could be prepared by screening mixed material. A typical sample col- lected by the author, consisting predominantly of clay, quartz, car- bonates, feldspar and miscellaneous rock fragments had the following chemical composition : Silica (SiO.) 26.42 Alumina (AI2O3) 8.41 Iron oxide (Fe.Os) 0.79 Barium oxide (BaO) nil Calcium oxide (CaO) 27.30 Maf^nesium oxide (MsO) 7.11 Sodium oxide (Xa,0) 0.52 Potassium oxide (K2O) 1-94 Manfranous oxide (MnO) 0.06 Titanium oxide (Ti02) 0.38 Phosphorus pentoxide (P2O5) 0.12 Sulfuric anhydride (SO3) 0.05 Carbon dioxide (CO2) 24.86 Fluorine ( Fo) nil Ignition loss 27.43 (Analysis by California Testing Laboratories, Los Angeles) Mica Schist Hodge Deposits. Sericite and muscovite schists, occurring in the upper part of the Upper Paleozoic (?) Hodge volcanic series, have been explored and superficially developed by small pits and quarries at scattered localities in a 2-to-3-square-mile area northwest of Hodge. The deposits lie principally in sec. 31, T. 9 N., R. 3 W., and sec. 36, T. 9 X., R. 4 AV., both S.B., although they extend discontinuously northeast from see. 31 as much as 2 miles. Some of the schist-bearing land is owned by AV. E. Leahy, 4238 Edgehill Drive, Los Angeles; some by Kennedy Minerals Company, 2550 East Olympic Boulevard, Los Angeles; and some is of unknown ownership. The schist occurs as steeply dipping, tabular masses 20 to 70 feet wide and many hundreds of feet long, striking X. 65-70° E. and dip- ping very steeply northwest. Parallel and en echelon belts of schist are numerous. The coarseness of grain varies gradationally from place to place and there is also gradational mineralogical variation, so that the rock passes from nearh' pure muscovite schist througli finer-grained sericite schist to quartz-muscovite and quartz-sericite schists. The best quality rock is a uniform pearly white muscovite schist, but iron oxide- 152 BARSTOW QUADRANGLE [Bull. 165 bearing groundwater has penetrated and discolored the schist over large areas to an unknown depth. None of the quarries or pits has penetrated deep enough to offer much data on the probable depth of discoloration. Inasmuch as a uniform light color is required in most mica fillers and lubricants, only the least discolored areas of schist have been explored. A small tonnage of schist has been removed from the Kennedy Minerals Company properties, probably for experimental and test purposes for a covering on asphalt-base roll-roofing. Sericite-Quartz Rock Dewillihie Deposits. Location : SEi NE^ see. 3. T. 6 X., R. 4 ^., S.B., on the west slope of Silver Mountain, 4 airline miles NE of Oro Grande, adjacent to Marshall and Davis deposits on the east. Ownership: a 160-acre placer claim was held (1946) by Dewillibie Mining and Milling Company, 5253 Baltimore Street, Los Angeles, California. The properties have been prospected by several small open cuts which expose white sericite-quartz rock, the hydrothermal alteration product of felsitic andesites and dacites of the Triassic ( ?) Sidewinder volcanic series. The apparent strike of the volcanics is N. 80° W. and the dip is m. V* ■.•-%**f < # f r / ^•r '■^'■■^^ 'S? "2cj(Cv" Figure 69. A quarry face of sericite-quartz rock in the Marshall filler deposit east of Sparkuhle Hill. The rock is a hydrothermal alteration product of latite and dacite tuffs. Dark sills of unaltered dacite or quartz latite cut the white rock at the lower left quadrant of the photo. 1954] GEOLOGY AND MINERAL DEPOSITS 153 22° NE. The white material occurs in selectively altered bands and distribution appears to be sporadic. The best material is similar to that found in the Marshall and Marter deposits described in detail in fol- lowing paragfraphs. No estimation of reserves is possible without further development work. It would be necessary to construct half a mile of road in order to reach the deposit with power equipment. Marshall and Davis Deposits. Location: center sec. 3, T. 6 N., R. 4 W., S.B., three and one-half airline miles northeast of Oro Grande or one mile northeast of Sparkuhle Hill. Adjoin the Ozark mine on the northeast. Ownership : the Keystone claims were held in 1944 by Kenneth Mar- shall, 907 California State Building, Los Angeles. A series of 17 ad- joining claims were controlled (1950) by the Davis Exploration Com- pany, Oro Grande ; these claims total 337i acres. The claims, located in 1896 ^* primarily because of scattered copper showings, seem to show greater promises as sources of filler material. A considerable but unknown tonnage of material was mined in 1935, processed at Bryman and shipped to Los Angeles for use as filler in "Tucker, W. B., unpublished notes dated April 14, 1944. il Figure 70. A sharp contact between tlie sc-rn iic-quartz alteration product and relatively unaltered metadacite at the Marshall filler deposit. The contact may be an ancient line of Assuring or the physical characteristics of the overlying rock at the time of alteration may have made it much less susceptible to alteration. 154 BARSTOW QUADRANGLE [Bull. 165 paint, rubber, and paper. The principal working is an open cut 100 feet long and roughly half an acre in plan with faces 10-20 feet high. A smaller open pit adjoins this working on the east. Part of the high-grade material is covered by 6 feet of alluvial over- burden, and the principal clay-bearing series is overlapped by unaltered or superficially altered metavolcanics of the Sidewinder series. The white material, which is chiefly hydrothermally altered dacite felsite, is interlaminated by tabular intrusions of unaltered dacite and andesite so that a considerable amount of waste material must be handlefl in quarrying. The unaltered bands and presumably the Sidewinder series itself strikes N. 30-40° W. and dips 17 to 25° northeast. The alteration older than some lavas of the Sidewinder series and therefore is earlier than the granitic intrusions which crop out in the vicinity. Both the Marshall and Marter-White deposits probably formed during the Triassic (?) volcanic period which gave rise to the Sidewinder lavas themselves. Volcanic vapors and solutions working along shear zones probably caused the alteration. According to Tucker,^^ selected material yielded the following analysis by Smith-Emery Company of Los Angeles : Si02 69.60 AI2O3 16.55 Fe^Os 0.73 Ti02 0.72 MnO 1.54 Na^O 2.46 K2O 5.40 Moisture and | 2.80 combined H2O | 100.00 Other samples collected by the author contained several percent of CaCOa, in the form of calcite. The rock is predominantly sericite and quartz, sericite somewhat exceeding quartz. It is very similar to the material described in following paragraphs under Marter-White deposits. Marter-White (Velvet White) Deposits. Location: Sj sec. 26; S^ sec. 27; NEi sec. 34; Si, NW^ sec. 35, all T. 7 N., R. 4 W., S.B., 3^ miles east and slightly south of Bryman siding on the Santa Fe rail- road. Bryman is 11 miles north of VictorvilLe. Ownership : the original 160-acre Velve-t White placer claim is owned by Sylvan Gordon, Los Angeles, California, and leased to Marter Min- ing Company, 530 West 6th Street, Los Angeles, California. Marter Mining Company also holds 640 acres adjoining the Velvet White properties. The material known commercially as Marter-White occurs in hydro- thermally altered zones in metadacite and meta-andesite of the Triassic (?) Sidewinder volcanic series. The white masses are discontinuously distributed in a sinuous belt as much as 1000 feet wide and more than 3 miles long. The degree of alteration within the various rock masses of the belt varies considerably and uniformly altered masses of large size have been found in only two or three localities. Commercial ma- terial has developed along shear zones of irregular shape through action of hot vapors and solutions rising from a deeper source, per- «> Tucker, W. B., unpublished notes dated April 14, 1944. 1954] GEOLOGY AND MINERAL DEPOSITS 155 kP^SIs-' >g4^ji||,^' ^gj^i.aS3 iw i < » af -> .^i^iaKiag iy ' ''1ji^ii| jKa»^ ' ..<": / M li^ Figure 71. Main quarry at Marter Mining Company's sericite-quartz filler deposit, camera facing southeast. The ore body strikes diagonally across the field of view from left to right and dips away from the observer at a moderate angle. haps the same source that gave rise to the parent volcanic rocks thern- selves. The alteration is older than at least part of the adjacent granitic intrusions (Jurassic or Cretaceous) as unaltered granite dikes cut the altered material in the south quarry. In the north quarry thin, un- altered purplish dacite dikes of the Sidewinder series also cut altered material so that the time of alteration most probably was during the Triassic ( ?) period of volcanism. In the south quarry, alteration has been more selective than in the north pit; controls apparently were the degree of fracturing and the original porosity of the rock. The best white material has been derived chiefly from dacite tuff; felsite and relict phenocrysts of quartz and phantom igneous textures and structures remain in the altered rock. The apparent strike of the Sidewinder series in the south pit is N. 80° W. and the dip is 20-25° N. The belt of alteration, however, trends N. 65-70° W. southeast of the pit and arcs around slightly to the north- east north of the main pit. South of the Marter properties the belt arcs around near the base of Silver Mountain and passes through the Mar- shall and Dewillibie properties. The main pit, which is roughly 100 x 80 feet in plan, is sunk in remarkably uniform compact-to-friable white material. Stripping and 156 BARSTOW QUADRANGLE ■jWfcS^-'^w Figure 72. A cross-cutting dike, 8 to 12 inches wide, of felsitic dacite or quartz latite in the north wall of the main pit in the Marter deposit. The dike trans- gresses all other planar structures in the ore body. Both altered rock and dike rock are parts of the Triassic ( ?) Sidewinder series. test holes have revealed the presence of more than 1,000,000 tons of hio'h-grade white material. The trend of the ore body cannot be pre- cisely established because of 1 to 6 feet of alluvial overburden and because of overlying unaltered volcanic rock, but it is elongated in a northerly direction and dips moderately east. The unaltered volcanic overburden thickens markedly toward the east. Because of the unique nature of the Marter-White and the numerous potential uses for it, both the owners and the Division of Mines have engaged in extended laboratory studies of the material; the Division of Mines has studied a number of related materials as well. The results of these studies appear in the following paper in this bulletin. The owners engaged Stanford Research Institute to work on new uses for Marter-White and the Division of Mines is grateful to both the owners and the Institute for access to the results of that research. The crude rock, as mined, breaks down rapidly and completely when treated dry under moderate heat or when agitated in water. Thus broken down the crude material screens more than 90 percent minus 32r)-inosh and more than 75 percent minus 10 microns. After dry- grinding, 99.5 percent of the material passes 325-mesh screens. The particles are largely laminar in shape because of the presence of a mica in the serieite-illite series which forms more than half of the rock. 1954] GEOLOGY AND MINERAL DEPOSITS 157 _Mt ■ 'm^^'^^W0'^* '^',' '•. . 5--:? il^U /j^ Figure 73. A quarry face in the most southeasterly of Marter Mining Company's pits showing the sharp contact between hydrothermally altered rock and intruding felsitic lava. The alteration was contemporaneous with the accumulation of the Sidewinder series. There is no contact effect from the intruding dike because of the refractory nature of the sericite-quartz rock. Mica, quartz and probably amorphous silica are interleaved together in all particle sizes so that the chemical and physical characteristics of the particles are quite uniform. Minor proportions of calcite, feldspar, magnetite, limonite, pyrite, and hematite are generally present. Scat- tered grains of epidote, clinozoisite, andalusite, zircon, sphene, rutile, jarosite, chloritized biotite, ilmenite and thorite have been noted in microscopic examinations. Chemical analyses of the material tend to vary as follows : Silica (SiOs) 67.70 -71.55 Alumina (AI2O3) 15.76 -16.90 Lime (CaO) 1.40 - 2.10 (Occasionally hiRher) Magnesia (MgO) 0.50 - 1.00 Iron oxide (FesOs) 1.15 - 2.60 Soda (Xa^O) 0.20 - 0.63 Potash (K:;0) 4.36 - 5.20 Barium oxide (BaO) 0.13 - 0.20 Manganous oxide (MnO) 0.003- 0.08 Titanium dioxide (TiO^) 0.04 - 0.05 Phosphoric pentoxide (PzOb) 0.006-0.14 Water soluble chlorides 0.003 or less Ignition loss 0.53 - 3.80 158 BARSTOW QUADRANGLE [Bull. 165 Physical characteristics are as follows : -^ Oil absorption — (1) Gardner-Coleman 39.00 (2) Standard rub-out 38.40 pH 8.8 Specific gravity 2.67 Mean refractive index 1.565 Fusing point 2400° F. Electrical character positive Approximate particle size of milled material : Micron diameter Percent finer 50 99.7 40 99.3 30 99.0 20 98.3 10 80.3 5 38.5 2.5 18.5 Annual production of Marter- White has been 4000 to 5000 tons over the past few years but production is expected to increase. The material has been used chiefly as filler or extender material in manufacture of rubber asphalt tile, pipe and wire coatings, paint, insecticides, phono- graph records and plastics. It is of potential use in the manufacture of paper, oil-well drilling fluids, and ceramic ware when properly proc- essed. Snow White Deposit. Location: NW^ and S^ sec. 26; SEJ sec. 27, T. 7 N., R. 3 W., S.B., 1^ miles northwest of Split Rock Mountain or 12 airlane miles northeast of Victorville. Ownership : C. L. Longfellow and A. L. Berry, address unknown, own several claims. The claims were originally located for gold but have been mined intermittently for white filler material. Four hundred tons were mined and shipped in 1949. The rock is similar to Marter-White in most respects but contains a higher percentage of quartz. The origin and geological setting are identical to those in the Marter Mining Company and Marshall deposits. The rock is unlike that in the nearby Victorite pyrophyllite deposit. Filler material has been developed in an east- trending fracture zone, but the mass is irregular in shape and dips steeply under a capping of silicified felsite of the north side of the deposit. The fracture zone crosses almost perpendicular to the schis- tosity of the Sidewinder lavas that form the wall rocks of the deposit. An open cut 20 to 50 feet wide and more than 100 feet long is the only working. Although several tens of thousands of tons of rock have been removed, the deposit is not materially depleted in depth, but faces will become excessively lofty in the eastern half of the deposit if the open cut is materially deepened. Pyrophyllite Victorite Deposit. Location: NEi sec. 25, SEi sec. 24, T. 7 N., R. 3 W., S.B., I mile north of Split Rock Mountain. Accessible from the Victorville-Stoddard Well road via three miles of graded dirt road. Ownership : 640 acres in sec. 25 are owned by Southern California Minerals Company, 320 South Mission Road, Los Angeles, California, ^ Supplied by Marter Mining Company. i9r)4] GEOLOGY AND MINERAL DEPOSITS 159 ;i*r^ Figure 74. A quarry face at the Victorite pyrophyllite deposit 2| miles soutli\ve.'^t of Stoddard ^Mountain. The massive white rock is predominantly pyrophyllite with variable amounts of quartz. It is a weakly metamorphosed, hydrotliei-mal alteration product of latite-andesite having; a similar history to other altered Triassic ( ?) lavas of Barstow quadrangle. The end-product \aries with the composition of tiie original rock and with the physico-chemical conditions prevailing at the time of alteration. 160 BARSTOW QUADRANGLE [BuU. 165 under lease (1952) to Mineral Materials Company, 1145 Westminster Avenue, Alhambra, California. Mineral Materials Company also owns 5 claims in sec. 24. White pyrophyllite rock is found in a broad shear-zone in volcanic rocks of the Triassic ( ?) Sidewinder series. The zone trends N. 35° W. and carries downward almost vertically. It varies from 30 to 60 feet wide and has been exposed by bulldozing for more than 100 feet of strike length. Within the zone hydrothermal pyrophyllitization of ande- site and dacite tuff and felsite has advanced to various degrees of com- pleteness so that there is uneven distribution of material of different grades. Relict fragmental and phenocrystine quartz remains in some parts of the deposit which detracts from the value of the material for some uses. A typical chemical analysis, as furnished by the owners, is as follows : Silica 75.96 Aluminum oxide 18.93 Iron oxide .12 Calcium oxide .18 Magnesium oxide .23 Sodium oxide .58 Potassium oxide .16 Ignition loss 3.70 Total 99.86 Development work consists of a quarry, roughly 700 square feet in plan with faces from 5 to 15 feet high, and bulldozed surfaces aggregat- ing about half an acre. Insufficient work has been done at depth to gain an accurate estimate of reserves, but several hundred thousand tons of white material of variable grade is present above quarry level and there is reason to believe that it continues downward well beyond the limits of practical open cut mining. Presence of a large, partly altered dike of quartz monzonite porphyry along the west wall of the shear zone suggests that the altering solutions may have been derived from a granitic source in late Jurassic time. Limestone Crystalline limestone deposits of commercial or potential commercial quality currently are the most valuable mineral resources in the quad- rangle. They occur in either the Upper Paleozoic Oro Grande series or the Permian Fairview Valley formation. Deposits are widely distributed in the quadrangle and reserves of rock of some grades are immense. The largest, most uniform deposits are in the Shadow Mountains, the Victorville-Oro Grande district and the Black Mountain district south and west of the Sidewinder gold mine. Smaller deposits of high-calcium rock are also found 3-4 miles east of Victorville, 2 miles east of Hinkley, and 6 miles southwest of Hinkley. The large body of carbonate rock at and east of the Ball magnesite mine (in sees. 2 and 3, T. 6 N., R. 2 W., S.B.) consist of intimately mixed dolomite, dolomitic limestone and calcitic limestone that cannot be selectively mined ; at present it is not of economic importance. Mixed carbonate rocks are also found in the Hinkley Hills 6 miles east of Hinkley. The yellow and brown carbonate rocks in Miocene erosion remnants north of Barstow probably are too impure to be of current or future importance. Deposits now being exploited are those most favorably situated in respect to terrane and to rail or truck transportation. The large reserves 1954] GEOLOGY AND MINERAL DEPOSITS 161 in the Shadow Mountains are not likely to be exploited on a large scale until tliose of the Victorville-Oro Grande district are exhausted. The commercial limestones of the Barstow area tend to fall into four general classes which may grade one into the other. These are : 1. Coarse-grained white rock that has been strongly affected by contact meta- morpliisni ; grain size varies from 3 mm to 3 centimeters or more in average dimension. 2. Medium-to-coarse-grained blue-gray rock which commonly decrepitates dur- ing calcining, but wliich may have a very high CaCOs content. 3. Medium-to-fine-grained blue-gray or even black rock which holds its shape during calcination ; it is simply a less severely metamorphosed rock than that in classes 1 and 2. 4. Slightly siliceous limestone conglomerate of variable tenacity usable chiefly in Portland cement. A fifth class might be added to include the interlaminated calcific and dolomitic limestones of the Devils Gorge vicinity east of Ball mag- nesite mine in sees. 2 and 3, T. 6 N., R. 2 "W., S.B., which may have future importance as a source of magnesian lime for plaster. They may also be ultimately used as source material from which carbonate minerals could be separated. Chemical grades of limestone, here re- garded as those containing in excess of 98 percent CaCOa, are broadly distributed but generally must be selectively mined. The largest re- serves of limestone in Barstow quadrangle are in rock containing from 1-3 percent MgO and 92-96 percent CaCOs- The Portland cement industry currently is the lat-gest consumer of limestone in the area, limestone for this purpose being quarried at the rate of nearly 2,000,000 tons annually. Substantial amounts are also consumed in metallurgy, glass manufacturing, roofing granules and mineral fillers. Hinkley Limestone Deposits. Location: NE^ sec. 27, T. 10 N., R. 3 W., S.B., 2 miles east of Hinkley. Ownership : Undetermined. White to grayish-white crystalline limestone crops out on two oval hills each covering several acres. The massive beds strike N. 65-75° W. and are nearly vertical. There are more than 500,000 tons of limestone without overburden in the two hills above the local base level. Most of this rock appears to be high-calcium material from qualitative tests made by the author, but no chemical analyses are available. No attempt has been made to quarry the limestone in either hill. The terrane is favorable for low-cost quarrying operations and rail facilities are half a mile to the south. Limestone is associated with mica schist in a series of roof pendants of the Oro Grande series. These are surrounded by granitic rocks and partly buried under alluvial overburden of variable thickness. Iron Mountain Deposits. Location: NE^ sec. 13, T. 9 N., R. 4 W., S.B., 1 mile northwest of the summit of Iron Mountain and 1 mile southeast of the Hinkley dolomite deposit. Ownership : Undetermined. The Iron Mountain limestone is the uppermost member in a roof pendant of metasediments of the Oro Grande series. These rocks strike N. 40-60° E. and dip very steeply north (75° to vertical). There has 6 — 85919 162 BARSTOW QUADRANGLE [Bull. 165 been no development on the deposits to date. The exposed section con- sists of 25 feet of micaceous gneiss and schist ; 325 feet of white to gray dolomite, which includes lenses of quartzite and mica schist ; and 365 feet of white limestone also including minor lenses of schist and quartz- ite. Dikes of light-colored granitic rocks of several compositions cut the metasedimentary section in numerous places but large masses of carbonate rock contain no adulterating material. The following analyses are of two spot samples, No. 1 from the center of the limestone member and No. 2, 10 feet from the confining quartz monzonite. These analyses were made by B. H. Dunham, Chief Chemist for Southwestern Portland Cement Company. Several other samples from other parts of the limestone gave similar analyses. No. 1 No. 2 SiOa 1.88 1.74 AI2O3 0.56 0.82 FesOs 0.38 0.46 CaO 54.20 52.80 MgO 0.82 1.18 Ignition loss 42.49 42.69 Total 100.33 99.69 .-{-■•• ^, , t. jr- *'■•' / . ^r- ' . ; '^k Figure 75. A quarry face at Ideal Cement Company's limestone deposit on the north slope of Quartzite Mountain adjacent to Southwestern Portland Cement Company's No. 12 quarry. Prior to acquisition by Ideal, the property furnished substantial amounts of rock to sugar refineries in southern California. The mas- sively bedded limestone, part of a thrust plate of Oro Grande rocks, dips 20-30° away from the observer. 1954] GEOLOGY AND MINERAL DEPOSITS 163 T^^K,^ Figure 76. Riverside Portland Cement Company's Klondike limestone quarry at Ore Grande, observer facing southeast. The hill capping is massive quartzite. The dark lenticular beds beneath the capping- near the top of the photo are weathered limestone. The section is down-faulted at the extreme right of the photo. Limestone crops out on a low ridge rising 30-40 feet above local base level. The 365-foot limestone member crops out over several thousand feet of strike length. Several hundred thousand tons of commercial limestone are exposed in the deposit, but much of the tonnage lies below the local base level and would have to be quarried in an open cut of considerable depth. Intrusions of granitic rock and inclusions of schist and quartzite would have to be allowed for in some parts of the deposit. A substantial tonnage of high-magnesian dolomite might also be de- veloped. Riverside Cement Company Deposits. Location : the principal hold- ings of the company are in sees. 4, 8, 9, 16, 17, T. 6 N., R. 4 W., S.B., near Oro Grande; sec. 25, T. 6 N., R. 4 W., 4 miles northeast of Victor- ville; and sec. 9, T. 6 N., R. 6 W.. S.B., in the southwestern outliner of the Shadow Mountains west of Barstow quadrangle. The deposits northeast of Victorville are currently under lease to other operators and are discussed separately. Ownership : Riverside Cement Company, 621 South Hope Street, Los Angeles, California. 164 BARSTOW QUADRANGLE [Bull. 165 «-«^>l , ^'^^^ ■••TJ{^*f •' «*»*""«"'**i;^ •-^, ^ ■* J^ .♦ t-^ 7->. •it " Figure 77. Highly contorted, ruptured schist beds of the Ore Grande series at Riverside Cement Company's "shale" quarry half a mile northeast of the Klondike limestone quarry. Material is used to supply the aluminous and siliceous fraction of the Portland cement mix. The quarry is driven in an east-trending vertical fault zone which cuts the north base of Quartzite Mountain. The properties now owned by Kiverside Cement Company were first operated for production of lime in the late 1880 's. According; to Irelan (1888, p. 225) there were 8 kilns having a daily capacity of 450 barrels of lime in operation near Oro Grande in 1889. Oro Grande Lime and Stone Company operated a lime kiln in the early 1900 's. Ruins of this operation still remain a few hunch-ed feet northeast of Riverside Cement Company's newest smokestack. Manufacture of portland cement at Oro Grande began in 1910 with completion of Golden State Portland Cement Company's 225,000- barrel-per-year plant. Riverside Cement Company had purchased lime- stone holdings in the Oro Grande district prior to 1915 and in 1923 acquired the properties of the Golden State company. The plant was closed down in 1928 and remained idle until 1942 (Logan, 1947, p. 295). During World War II the old plant was rehabilitated and put into operation. After a brief shutdown at the close of the war, full- scale modernization began and by 1948 three 10 x 350-foot dry process kilns had been completed. A fourth kiln was scheduled for completion in 1952. Early operations at the Riverside Cement Company properties uti- lized limestone and schist from just north of the Carbonate gold-silver- 1954] GEOLOGY AND MINERAL DEPOSITS 165 lead mine. During the postwar period of activity limestone has been obtained largely from the Klondike quarry, three-fourths of a mile east of the mill. The Klondike quarry, about half a mile long, consists of a series of pits and benches driven mainly in a blue-gray, medium-grained crys- talline limestone member of the Oro Grande series varying from 200 to 450 feet thick. The limestone is overlain by pinkish-Avhite quartzite and black mica schist and is interbed'ded with these rocks to some extent. It is underlain by 200 feet of dolomite. The general trend of the meta- sedimentary series is northwest but it is cut by east-trending cross faults at both the north and south ends of the quarry. The regional trend is further disrupted by smaller strike and transverse faults and by sharp, commonly ruptured minor folds. Several granitic intrusions cut the sedimentary section in the west central part of the quarry. Most of the limestone contains less than 1.64 percent MgO and much of it contains less than 1 percent,^" magnesium being the chief deleterious ingredient in limestones used for cement. The calcium carbonate eon- tent of clean rock ranges from 92 to more than 98 percent. The Sparkuhle Hill deposit is a very large, undeveloped occurrence of limestone exposed about 3^ miles northeast of the mill or two miles northeast of the Klondike quarry. Blue-gray to black limestone, exposed almost continuously over more than 200 acres, occurs in a gently folded, northwest-trending, northwest-pitching syncline. The limestone is over- lapped on the north and west by Pleistocene alluvium and is bordered on the east by the Triassic ( ?) Sidewinder volcanic series. Low on the southeast side of the hill dikes and sills of black to dark-green andesite and dacite intrude the limestone. Most of the limestone is blue-gray and sugary-textured, but ranges locally into fine-grained, black or coarse- grained, white varieties. Few data are available on the chemical composition of the Sparkuhle Hill limestone mass. Most of the rock is believed to run much lower than the critical 3 percent MgO although locally some rock may exceed this amount of magnesia. The dense, fine-grained variety of limestone is well suited for blast furnace and vertical kiln use as it will not de- crepitate under calcining temperatures. Sparkuhle Hill contains the largest mass of fine-grained lime rock in the quadrangle. The hill is estimated by the author to contain a minimum of 106 million tons of : carbonate rock above the lowest exposure at the extreme north end of the deposit. Over the northern half of the deposit the limestone should ' continue downward several hundred feet below present exposures. Presence of additional limestone is indicated beneath the Pleistocene alluvium between Sparkuhle Hill and the Klondike quarry. Southivestern Portland Cement Company Deposits. Location: sees. 5, 6, 7, 8, T. 6 N., R. 2 W., Black Mountain and Reserve quarries ; sees. i 2, 10, 11, 14, 15, 16, T. 6 N., R. 4 W. ; Quartzite Mountain area; and ! see. 2, T. 6 N., R. 6 W., and sec. 35, T. 7 N., R. 6 W., in a southeast outlier of the Shadow Mountains, all S.B. Ownership : Southwestern Portland Cement Company, 727 West 7th , Street, Los Angeles, California. [ The Victorville plant of Southwestern Portland Cement Company ; was placed in operation in 1916. Up to 1942 raw materials were ob- " W^ightman, R. H., personal communication, 1949. i 166 BARSTOW QUADRANGLE [Bull. 165 .-r^o '"^i-lC- -^^ . .:-M& 4. '•»*•*' ,- PiGUREj 7 8. Composite photograph of Southwestern Portland Cement Company's Re- serve quarry, camera facing northwest. The white limestone, part of the upper Paleo- zoic Oro Grande series, is cut by dark hornblende-quartz diorite dikes. The dike rock is unusable in cement because of its magnesium content, so the dikes are an obstacle in quarrying operations. tained chiefly from quarries just east of Quartzite Mountain, 6 miles north and slig:htly east of Victorville. In 1942 a heavy-duty road was opened to the Reserve deposit 9 miles east of the Quartzite Mountain quarries. During the period 1947-48, the company railroad was ex- tended 5 miles east toward the Reserve quarry and rail-loading facili- ties were constructed at Sidewinder Well. Between 1948 and 1950 very large limestone deposits were explored and developed at Black Moun- tain, half a mile northeast of the Reserve quarry, and a new kiln was completed that increased the mill capacity to 3,000,000 barrels annu- ally. During 1951 the railroad was extended another 6 miles to the base of Black Mountain and quarrying of limestone at the Quartzite Moun- tain and Reserve quarries was largely discontinued. d']^.' Figure 79. Detail of dikes in the face of the Reserve quarry; these dikes coalesce farther up the hill. Most of the limestone in the Reserve deposit is not, however, cut by dikes and the limestone is commonly more than 98 percent CaCOs. 1954] GEOLOGV AND MINERAL DEPOSITS 167 Twelve quarries were worked in the Quartzite ^Mountain area. There limestone occurs in lenticular masses interbedded with quartzite and mica schist. The limestone beds pinch and swell markedly and the entire sedimentarj' series has been severely folded and faulted. Parts of a northeast-trendinj:: anticlinal structure still remain. The limestone has been converted to taetite near contacts with intrusive granitic masses. Limestone, tactite, schist, quartzite and even granite have been utilized from time to time in various cement mixtures. The crystalline lime- stone is a medium-grained, blue-gray rock which, where unaltered, averages about 52.0 percent CaO, 2.4 percent MgO, 2.7 percent Si02, 1.6 percent AI2O3, 0.7 percent FeoOs, and 40.6 CO2 plus combined water (ignition loss). In addition to rock taken from the 11 quarries in the main Quartzite IMountain quarry area, several million tons of limestone were taken from Quarry No. 12, a mile west of the main quarry area. The lime- stone averages slightly higher in magnesia and silica than unaltered rock from the main quarries. A spur track which once connected with Quarry 12 has been removed. Rock from this quarry is part of a thrust plate which overrides the north slope of Quartzite Mountain. Adjacent to the No. 12 quarry on the south is another 240-foot bed of limestone of similar grade which has never been quarried because of the steep- ness of the slope and because of the thick quartzite overburden. Quarry- ing to the west of the No. 12 quarry was limited by the boundary of a former sugar-rock property now owned by Ideal Cement Company, Denver, Colorado. The Reserve Quarry, 5 miles east of Sidewinder Well, is in a north- east-trending ridge 200-300 feet high and more than 2000 feet long. Most of the ridge is made up of coarsely crystalline, white limestone of the Oro Grande series which has a general northeast strike and is steep northwest dip. Quarrying has been hindered by dikes of hornblende diorite and quartz diorite porphyry which are too magnesian for use in cement. The unaltered limestone of the Reserve quarry contains less magnesia than most limestone from the Quartzite Mountain area and much of it contains more" than 98 percent CaCOs. Although quarrying of limestone from the Reserve quarry has been suspended, more than half of the readily accessible reserves remained. Quarries were opened in 1950 on the steep south slope of Black Mountain half a mile northeast of the Reserve quarry. Black Moun- tain attains a height of more than 800 feet above local base level and occupies an area of nearly a quarter of a square mile. The entire moun- tain is made up of the limestone conglomerate member of the Permian Fairview Valley formation. The 1350-foot-thick conglomerate occupies the axial region of a tightly folded, symmetrical syncline trending about N. 40° W. parallel to the long axis of the mountain. The total thickness of the conglomerate is thereby doubled to 2700 feet. In spite of its detrital origin, the limestone is sufficiently uniform in chemical com- position to be usable in manufacture of portland cement. Except for a small proportion of brown chert pebbles and cobbles and interstitial silicification, the rock is entirely limestone. The average composition, based on company analyses made from 1600 feet of diamond drill cores, shows 46.0 percent CaO, 3.3 percent MgO, 11.0 percent silica, 1.7 per- cent AlaOs, 0.8 percent Fe203, and 37.2 percent CO2 and combined 168 BARSTOW QUADRANGLE [Bull. 165 .* *: ^. I* . , /^t it 'y^t . i P O O ft 1954] GEOLOGY AND MINERAL DEPOSITS 169 water (icrnition loss). More than 300,000,000 tons of limestone is pres- ent above the lowest exposure on the mountain. Southwestern Portland Cement Company's Shadow Mountains de- posits, formerly known as the Adalanto or Whitlock deposits, are in a 200-400 foot hiprh, north-trending ridge, a southeastern outlier of the Shadow Mountains. Massive, blue-gray limestone occurs in beds strik- ing north to N. 10° W. and dipping 45° W. In this area the limestone is the lowermost member of the Oro Grande series and unless it is re- peated by concealed strike faults, the limestone member is at least 3470 feet thick. Total thickness of limestone in the ridge is about 2500 feet but some of this may not be on company property. Reserves above local base level are well in excess of 50,000,000 tons and the limestone ex- tends indefinitely downward. The deposit has not been systematically sampled but cement company analyses show much of the limestone has the following approximate composition : Si02, 2 percent ; AI0O3, 0.7 per- cent; Fei.08, 0.3 percent; CaO, 54.4 percent; MgO, 1.0 percent; and COo and combined water (ignition loss) 42.5 percent. A few small granitic intrusions cut the limestone and in scattered spots small sul- fide-bearing veins contaminate the limestone. Vicforville Lime Rock Company Deposits. Location: sees. 25, 35, T. 6 N., R. 4 W., S.B., 4^ miles northeast of Victorville via the paved Sidewinder AVell-Stoddard Well road. Properties totaling 120 acres in the SWt see- 25, are owned by Riverside Cement Company, 621 South Hope Street, Los Angeles, California, and leased by Victorville Lime Rock Company; properties in sec. 35 are owned by Victorville Lime Rock Company, 5225 Wilshire Boulevard, Los Angeles, California. From 1924 to 1943 Victorville Lime Rock Company quarried lime- stone from properties leased from Riverside Cement Company. In 1943 quarries were opened on property acquired by the company. In 1945 the company became a subsidiary of E. K. Williams Company, East St. Louis, Missouri. The present mill, located at railside close to the Upper Narrows in Victorville was constructed in 1947. Crystalline limestone is discontinuously exposed in a group of low hills in a belt of irregular width and 1^ miles long. The attitude of the beds is obscure but carbonate rocks crop out in an arc convex to the southeast. The limestone is coarse-to-medium-grained and blue-gray to white. To date only the coarse, rhombic-grained white rock has been quarried. ^luch of this white material is more than 99 percent CaCOs and is used in glass manufacturing. Because of the distribution of gra- nitic intrusions, contact altered zones and alluvial overburden, esti- mation of reserves is difficult, but several million tons of high-grade rock lie above the lowest point in the quarry area. Rock is removed in a series of low benches and hauled by truck to the company mill. In some places 5 to 15 feet of overburden must be removed. The dry-grinding mill is equipped with air-separating equipment and has a 24-hour daily capacity of 40,000 tons of crushed limestone of various particle sizes. Glass sand, white filler, chicken grit, roofing granules, and limestone for stucco and lime are the principal products marketed. White Lime Rock Company Deposits. Location: NW^ sec. 25, T. 6 N., R. 4 W., S.B. ; adjoins Victorville Lime Rock Company deposits on the north. 170 BARSTOW QUADRANGLE [BuU. 165 Ownership : properties are leased from Riverside Cement Company, 621 South Hope Street, Los Angeles, California, by "White Lime Rock Company, 5953 Crenshaw Boulevard, Hollywood, California. White Lime Rock Company quarries, crushes and sizes white lime- stone chiefly for roofing granules in an operation which began in 1949. Limestone is quarried in an open pit and trucked to Victorville for reshipment to the Los Angeles area. The limestone is a continuation of the belt in which the Victorville Lime Rock Company deposits are located. Only the whitest rock is utilized and selectiA'e mining and hand sorting are necessary to pro- duce a uniform, pure-white product. The deposit is cut by light and dark-colored granitic dikes which interfere with quarrying operations and w^hich tend to discolor the adjacent limestone. Considerably more than 100,000 tons of rock have been removed from the main pit, partly by the present operators and partly in previous operations. Reserves have not been materially reduced but additional benches must be cut in selected parts of the quarry area to maintain a steady production of top-quality rock. The main pit was approaching the economic limit in depth late in 1951. Magnesite Porcelainous magnesite is found in Barstow quadrangle in two types of deposits of different age and origin. The purest material comes from hydrothermal veins and irregular replacements adjacent to such veins. The deposits cut dolomite or dolomitic limestone of the Oro Grande series near hornblende-rich lamprophyre dikes, strongly suggesting a genetic relationship between the dikes and the magnesite. Magnesite is also found in beds of variable purity in the Miocene ( ?) lower lakebed series of the Kramer Hills district where it must be pre- sumed to be a precipitate from lake waters contaminated by volcanic hot springs. Ball (Red Seal) Deposits. Location: N-J sec. 3, T. 6 N., R. 2 W., S.B., 13 miles northeast of Victorville via Sidewinder Well or 1^ miles northeast of the Sidewinder mine. Owner: 0. H. Ball, 2064 West 62nd Street, Los Angeles (1943). Sev- eral claims are patented under U. S. Mineral Survey No. 6453-B4. Development work on the claims was done mainly in 1940 when the property was under lease to Westvaco Chlorine Products Corporation, now Westvaco Chemical Division of Food Machinery Corporation. Numerous tunnels and open cuts w-ere made which blocked out less than 500 tons of magnesite. Work was discontinued in November of 1940 and the properties have since been idle. The magnesite commonly occurs at or near the contact of dolomite with dikes or sills of hornblende lamprophyre; some magnesite veins crosscut the lamprophyre but never extend very far into the wall rock. Most of the dikes strike north to N. 35° E. and dip east at angles vary- ing between 10 and 30 degrees. The lamprophyre intrusions are uni- formly tabular and vary in thickness from 8 inches to 3 or 4 feet. The magnesite may be found along the foot-wall or hanging wall contact, or both, in veins and stringers varying from a few millimeters to as much as 5 feet thick. The veins tend to pinch and swell rapidly along the strike and rarely are persistent for more than 40 or 50 feet ; many 1954] GEOLOGY AND MINERAL DEPOSITS 171 lenticular masses contain only a few tons. The ma^nesite is of excellent quality, most of it being: between 98 and 99.5 percent Mf^COs. Bunches of ore crop out on hilly terrane over an area 5 acres or more in extent, but none of the workin;i's encountered ore-bodies of notable size. The most extensive workinjj: is a tunnel 162 feet lon<; driven in an attempt to crosscut two west-dippin*i: ore bodies. The first 23 feet of tunnel is driven N. 50° W. and the remainder N. 30° W. There is a 10-foot raise 20 feet from the end of the tunnel ; with the exception of some 1-2-inch stringers, this did not encounter ore. The dolomite walls are fractured and somewhat cavernous the entire length of the tunnel and the dolomite is serpentinized from an interval 47 to 63 feet from the portal. Near the portal the tunnel crosscuts an ore body, 1 to 2^ feet thick, lying- above a lamprophyre sill. Several other veins and stringers are exposed deeper in the tunnel, but there are no other size- able ore bodies. About 75 feet higher up the hill north of the main tunnel is a second tunnel 35 feet long which strikes N. 43° W. and is inclined slightly downward toward the face. It crosscuts a 3-foot wade multiple lampro- phyre sill striking N. 35° E. and dipping 15-20° N. The hanging wall vein swells in one place to more than 4 feet wide and several inches of magnesite have developed between the planes of the multiple dike. Additional crosscutting veins, 1-3 inches wide, extend out into the cav- ernous wall rock. This ore body is probably the most extensive one on the properties. Seven or eight open cuts of variable size explore lenses of magnesite in the general vicinity of the main and upper tunnels just described. One-fourth of a mile east and higher up an abutting ridge are two other tunnels driven east. The most northerly is 80 feet long and the other is about 30 feet long. These crosscut numerous lamprophyre sills and magnesite veins, a few inches to a foot thick, as well as several small stockworks of magnesite veinlets but no ore bodies of notable size have been exposed. Kramer (Ball Kramer, Kramer Hills) Deposit. Location : S| sec. 3, T. 9 N., R. 6 W., S.B., 2 miles east of U. S. Highway 395 or 5 miles south and slightlv west of Jingrev siding on Highway 466. Owner: 0. H. Ball, 2064 West 62nd Street, Los Angeles (1943). This property was explored in the late 1930 's by the Ball (Red Seal) Chemical Company and a private report was made on it by the late Hoyt S. Gale of Eagle Rock, California. No shipments other than test samples were made. The magnesite occurs in the lower series of the Miocene ( ? ) Kramer Hills lakebeds. The series strikes N. 80° E., dips 50°-60° S. and is over- lain by a prominent flow of black ({uartz andesite. White, porcelainous magnesite occurs in beds a few inches to a few feet thick interbedded with green and white clay shale, opaline chert, fanglomerate and mas- sive, laminated dolomite beds up to 10 feet thick. The magnesite beds grade from nearly pure magnesite to argillaceous magnesite or white opaline chert. Only a small percentage of the material is as pure as most vein magnesite, but reserves of marginal grade are large. The only development work is an. open cut approximately 200 feet long and from 2 to 7 feet deep ; this crosscuts the strike of the strata. The magnesite-bearing beds are interspersed through 50 feet or more 172 BARSTOW QUADRANGLE [Bull. 165 r Figure SI. Mineral :Material.s Company's Atlas silica quarry near Oro Grande, camera facing southeast toward Qiuirtzite Mountain. Rock is fractured pinkish- white quartzite of the Oro Grande series. Quarry adjoins Riverside's Klondike quarry. of the lakebed section, but selective ininin<]r and processinfj -would be necessary to get rid of worthless interbedded material. The most serious impurity from the point of vie-vv of separation or beneficiation is opaline chert which is as thoroughly indurated as the magnesite and in some cases closely resembles magnesite. Marl Vitiiite Marl Deposits. Location : Sees. 8 and 9, T. 8 X., R. 4 AV.. S.B., 3 miles northwest of AVilde siding or 17 miles north of Victorville. Ownership: undetermined. Last known owner (1931) was ]\Iojave ]\Iarl Company. 374 Court Street, San Bernardino, California. ]\Iojave ]\Iarl Company operated the properties in the late 1920 's and early 193()'s. shipments at one time reaching 35-50 tons per day (Tucker and Sampson, 1930. p. 311). The marl was marketed chiefly in Orange County as a soil additive. The deposits have been idle for more than 15 years. Marl occurs in a bedded Pleistocene playa lake assemblage of cal- careous clays, sands, tufa, limestone and fanglomerate. Fresh water limestone beds several feet thick associated with thin bands of white to colorless opal and chalcedony are characteristic of the lakebed series. ¥ 1954] GEOLOGY AND MINERAL DEPOSITS 173 Figure S2. Crushing, sizing and storage macliinery at Mineral ^laterials Com- pany's Atlas silica quarry, camera facing east. The hillside to the east is made up of northeast-dipping schist, limestone and quartzite of the Oro Grande series. The beds strike roughly x. 70° AV. and dip 3 to 10° north. The marl (limy elay"!, "which oecnrs in beds 10 to 30 feet thick, is friable and easily removed by power equipment. A large law-crusher, screens, conveyor belt, loadinp' hopper, loading platform and bagging chnte were on the property in 1949. The total amount of material marketed is not known, but the reserves of marl have not been materially depleted. Sand, Gravel and Crushed Rock Sand, gravel and rock suitable for road base, concrete, railroad bal- last, macadam and similar uses are present in the ciuadrangle in large quantities. Clean sand and gravel are found chiefly along the ]\Iojave River but strong, abrasion-resistant rocks crop out in most parts of tlie quadrangle. The sand and gravel in the ]\Iojave Kiver Wash is com- posed chiefl}' of granitic debris but in most places there is a variable fraction of quartzite, ancient metavoleanics (chiefly metadacite), and a variety of crystalline gneisses and schists. Crystalline rocks that have been quarried and crushed include quartzite. limestone and dolomite from the Oro Grande series, metadacite from the Sidewinder series, quartz monzonite (called granite in the trade) and Pliocene dacite from the Barstow vicinity. 174 BARSTOW QUADRANGLE [Bull. 165 ^ 'r'':'Z Figure S3. Crushing machinery and loading: platform at the Vitrlite marl deposit three miles north of Helendale. The property, now idle, formerly pro- duced soil conditioning- material for use in orange groves of Orange County. Sand and gravel have been taken in small amounts from the Mojave River bed in the vicinities of Victorville and Barstow, but production has been intermittent and there are no established pits. Crushed lime- stone is produced for both local and export consumption from the White Limestone Company and Victorville Lime Rock Company prop- erties 8 miles northeast of Victorville. Crushed quartzite, limestone, dolomite and tactite is also sold from time to time by the cement com- panies at Victorville and Oro Grande. As populated areas within the quadrano'le are small the volume of local business in stone materials is small. A large, sustained production of road base and railroad bal- last was made by Southwestern Portland Cement Company between 1942 and 1952 to supply material for new company roads and railroads. Quartzite from quarries at the eastern end of Quartzite IMountain was utilized to a major extent for these purposes. Rubble and riprap have been produced from time to time from both the Lipper and Lower Nar- rows vicinities, chiefly for use by the railroad companies. Silica (Canister) Iligh-silica deposits of notable size are found in the Quartzite Moun- tain district, the Iron Mountain district south and southwest of the mountain, and in the northeastern part of the Section 20 Hills. The 1054] GEOLOGY AND MINERAL DEPOSITS 175 silica deposits are of two types. The most extensive deposits are mas- sively bedded quartzites found in the Upper Paleozoic Oro Grande series. A few large deposits are partly metamorphosed quartz veins found cuttinp: the upper part of the Upper Paleozoic (?) Hodg:e vol- canic series just west of the Ilodge-IIinkley road 2 miles north of Hodge. Commercial quartzite in the Oro Grande series is a pinkish-white-to- pinkish-lavender, tough, massive rock derived chiefly from sandstone. The silica content ranges from 98.5-99.1 percent SiOo and the rock would be suitable for chemical as well as refractory use. The cost of crushing the rock, however, makes its competitive position with silica sand deposits difficult. So far the quartzites have been utilized chiefly for Portland cement and for silica refractories where a silica content of 98 percent and AI0O3 + combined alkalies content of less than 0.60 is required. The commercial vein quartz found in the Hodge volcanic series is massive, milky white, coarse-to-medium-crystalline material M'ithout ap- parent impurities over considerable distances. Sporadic distribution of rutile' and tourmaline needles might make some material unsuitable for commercial use. The vein deposits have not been thoroughly sampled and are largely undeveloped. Atlas (Western Refractories Company) Deposit. Location: SE^, sec. 17. T. 6 X.. R. 4 W., S.B., adjoins Riverside Cement Company's Klon- dike properties. /•^ ■ -■— 'm Figure S4. Portal of main adit at Ball magnesite mire showing position of the mag- nesite ore bodies (m) in relation to the hornblende lamprophyre sill ("1") and the dolo- mite country rock (d). Lamprophyre sillis 2 J -3 feet wide. 176 BARSTOW QUADRANGLE [BuU. 165 Ownership : the deposits are controlled by Mineral Materials Com- pany, 1145 Westminster Avenue, Alhambra, California. The property has been active since 1989 prodncinji' silica for refrac- tories and for various types of portland cement. The silica is shipped to Colton and Los Angeles. Quartzite is found in a lenticular mass 100-250 feet thick interbedded with limestone and schist. These rocks are metamorphosed marine sedi- ments belons:ing' to the Oro Grande series. At the north end of the quarry the apparent strike of the quartzite is east and the dip is 45 de F0,O:, O.IS TiOo 0.04 CnO 0.28 MliO O.OS Alkalies 0.24 The main quarry consists of an oval area roughly 100 feet wide by 300 feet long excavated at the summit of a hill 350 feet high. There is more than 400 feet of working face 30-50 feet high. Between 100,000 and 150,000 tons of material had been taken from the hill up to 1952 and the reserves are estimated at roughly 2.000,000 tons above the 3100- foot contour. The quartzite is thickest at the north end, where it dips most steeply, and thinnest at the south e-nd at the hill. Golconda (Emsco Gonisicr, Leahy Ganistcr) Deposit. Location: SW] sec. 36, T. 9 N., R. 4 W., S.B.,"3 miles north and 1 mile east of Wild siding or 4 miles west of Ilodge. Ownership : W. E. Leahy, 4238 Edgehill Drive, Los Angeles, Cali- fornia. The deposit was operated for a short period in 1930 by Emsco Re- fractories Division of Gladding McBean and Company but has since been idle. Massive, piukisli Avliite (juartzite, similar to the deposits of the Quartzite Mountain district, occurs in a series of discontinuous lenses striking N. 65° E. and dipping very steeply north. The lens nearest \Vild(^ siding is the only one (piarried to (bite on the Golconda properties. The lenses -dvc metamorphosed sandstones occurring in the Upper Paleozoic (?) Ilodge volcanic series. 1954] GEOLOGY AND MIXER AL DEPOSITS 177 Qiiartzite crops out in a ri(lg:e that stands about 100 feet above a gfently south-slopinjr pediment worn on weaker mica schists and meta- voleanit's. The r'uV^e is developed at the west end by an open cut and tunnel U^ss than 50 feet lonp-. Althou-< j3 CM cm" >^ a -0 3 ST ■V "a H c c "o a "E C 03 .J . a) CC ^ -^ .-^ Jo 10 CM t~ CM co" a T3 £ a-. CO co' .^ ■a 3 Total depth 2,800 ± feet. Drillers reported "hard sand" in bottom of well but this may have been granite. Total depth 3,216 feet. Bottomed in granite. Water- bearing sands and gravels 0-730 feet; sandstone and sandy shale 730-1,350; and crystalline limestone, schist and granite below 1,350 feet. -a c -a a 5 ■5 Q CO CO -a a; c ■* -a CM C — -C . C3 c OK 00 0: CO 0-. CO CM CM CO CO CM CO 0-. c <== S 1^ to CO 0: -T3 3 Q CO CO — ■ Oj § 8 0: CO c 3 1-5 05 0: CM ^- c^. in 00 -a ■>»• a) o> c: ^ e>- "0 "o £ 0! £ a 'w 03 PQ > '0 d T3 o n ca m CO oa pa m 03 10 10 10 ^ •<1" ^ CO H 12; a: 2: 2; OS Z, in 03 CM " ^ " CO ■* CM CM CM 1954] GEOLOGY AND MINERAL DEPOSITS 183 anil wliilc there is reason to believe that there is from GOO to 2000 feet of ^lio-Pliocene continental sandstone (Cajon formation?) beneath Pleis- tocene alhivinm. in the southwestern corner of the qnadranfrle, none of the lous examined from the west central or northwest parts of the quad- ranpfle fxavo any indication of presence of marine strata other than Paleozoic. Altlunip'h oil showings have been reported from time to time in several different wells, these reports have never been verified. The accompanying table summarizes the known data on wells drilled in Rarstow quadrangle. BIBLIOGRAPHY Aulmrv. L. E.. lOOS. The copper resources of California : California Min. Bur. Bull. 50. hCM pp. Anbury, T>. E., 1000. The structural and industrial materials of California : Califor- nia Min. Bur. Bull. 38, 412 pp. Axelrod. D. T.. lO.'iO, Piru Gorge flora of southern California : Carnegie Inst. Pub. .")90, pp. l.")r)-204. Baker. C. L.. 1011. Notes on the later Cenozoic history of the Mojave Desert region in , southeastern California : T'niv. California, Dept. Ceol. Sci.. Bull., vol. 6, pp. 338.381. Blackwelder. Eliot. 1031, Desert plains: .Tour. Geology, vol. 39, pp. 133-140. Blaclvweldor. Eliot. 1027. Desert weathering: (abstract) Geol. Soc. America Proc, vol. .38. no. 1, pp. 127-128. Blackwelder, Eliot, 1929, Origin of piedmont plains of the Great Ba-sin : (abstract) Geol. Soc. America Proc, vol. 40, no. 1, pp. 168-160. Blackwelder, Eliot. 103."i. Talus slopes in the Basin-Range province: (abstract) Geol. Soc. America Proc. p. 317. Cloudman. II. C and others, 1010. San Bernardino County : California Min. Bur. Kept. l.">. pp. 77.5-890. Darton. Nelson H., 101.5, Guidebook of the Western United States, part C. the Santa Fe Route: V. S. Geol. Survey Bull. 613, pp. 162-165, sheets 23-24. • Davidson, Pirie, 1023. Alticnnielus alexniidrae, a new camel from the Barstow upper Miocene of the Mohave Desert : I'niv. California. Dept. Geol. Sci., Bull., vol. 14, no. 12. pp. .307-408. Davis, AV. M., 1033. Geomorphic processes in arid regions and their resulting forms and products: XVI Int. Geol. Cong. Rept., vol. 2, pp. 703-714. Davis, W. M., 10.30, Rock floors and arid and humid climates : .Tour".. Ge'plogv, vol. 38, pp. 1-27, 136-1.38. Davis. W. M., 1036, Geomorphology of mountainous deserts : 16th International Geol. Cong. Rei)t.. vol. 2, pp. 703-714. Davis, AV. M., 1038, Sheetfloods and .streamfloods : Geol. Soc. America Bull., vol. 49, pp. 13.50-1.353. 1.3.58. 1381-82. Davis, W. ^I., 10.33. Granite domes of the Mojave Desert. Calif. : San Diego N.at. Hist. Trans., vol. 7, no. 20, pp. 211-258. Degroot, H.. 1800, San Bernardino County: its mountains, plains and valleys: Calif. Min. Bur. Rept. 10, pp. 518-530. ' . Dibhlee, T. W.. 10.52, Geologv of Saltdale quadrangle, California : Califo/Yiia Div. Mines Bull. 160. Dietrich. AValdemar, 1028, The clay resources and the ceramic industry of Califor- nia : California Div. Mines and Mining Bull. 00. Eric, John H., 1048. Tabulation of the copper properties in California : California Div. Mines Bull. 144, pp. 100-351. Gale, Hoyt S., 1048, Geology of the Kramer Borate district, Kern County, Calif. : California Jour. Mines and Geology, vol. 42, pp. 325-378. Gardner, Dion L., 1040, Geology of the Newberry and Ord Mountains, California: California Div. Mines Rept. 36, pp 257-202. Guillou, Robert B., 1053, Geology of the Johnston Grade area, San Bernardino Mountains, California ; Calif. Div. Mines Spec. Rept. 31, 18 pp. 184 BARSTOW QUADRAXGLE [Bull. 165 Hazzard, J. C, 1037. Paleozoic section in the Xopah and Resting Springs Mountains, Inyo County, California : California Div. Mines Rept. 33, pp. 284-339. Hazzard, J. C, 19.38, Paleozoic section in the Providence Mountains, San Bernardino County, California: (abstract) Geol. Soc. America proc, 1937, pp. 240-241. Hazzard, J. C, Gardner, D. L., and Mason, J. F., 1938, Mesozoic metavolcanic and metasedimentary rocks in San Bernardino and Riverside Counties, California : (abstract) Geol. Soc. America proc, 1937, pp. 278-279. Hershey, Oscar H.. 1902, Some crystalline rocks of southern California : American Geologist, vol. 29, pp. 283, 286-289. Housmann, A., 1908, San Bernardino County copper claims : California Min. Bur. Bull. no. Hulin. Carlton D., 1925, Geology and ore deposits of Randsburg quadrangle of Cali- fornia : California Min. Bur. Bull. 95. Hutton, C. Osborne, 1938, On the nature of withamite from Glen Coe, Scotland: Mineralogical Magazine, vol. 25, No. 162, pp. 119-124. Hutton, C. O., and Bowen, O. E., Jr., 1950, An occurrence of jarosite in altered volcanic rocks of Stoddard Mountain, San Bernardino County, California : Am. Mineralogist, vol. 35, pp. 556-561. Hyatt, Edward S., et al., 1934, The Mojave River investigation : California Div. Water Resources Bull. 47, 249 pp. Irelan, Wm., Jr., 1888, California Min. Bur. Rept. 8, San Bernardino County, pp. 490-512. Jenkins, O. P., 1938, Geologic map of California: scale 1:500.000: California Div. Mines. Jenkins, O. P., et al., 1942, Tabulation of the tungsten deposits of California : Cali- fornia Div. Mines Rept. 38, p. 352. Johannsen, Albert, 1937, A descriptive petrography of the igneous rocks ; vol. 3, the intermediate rocks : Univ. Chicago Press, 365- pp. Knopf, Adolph, 1918, A geological reconnaissance of the Inyo Range and the eastern slope of the Sierra Nevada, California : U. S. Geol. Survey Prof. Paper 110. Larson, Esper S., 1948, Batholithic and associated rocks of Corona, Elsinore, and San Luis Rey quadrangles, southern California : Geol. Soc. America Memoir 29. Lawson, Andrew C, 1916, The epigene profiles of the desert : Univ. California, Dept. Geol. Sci. Bull., vol. 9, no. 3, pp. 23-48. Logan, C. A., 1947, Limestone in California : California Jour. Mines and Geol., vol. 43. pp. 175-357. McGee, W. J., 1897, Sheet-flood erosion ; Geol. Soc. America Bull., vol. 8, pp. 87-112. Mayo, Evans B., 1932, Two new occurrences of piedmontite in California : Am. Mineralogist, vol. 17, pp. 238-248. Merriam, J. C, and Pack, R. AV., 1913, Suggested paleontologic correlation between continental Miocene deposits of the Mohave region and marine Tertiary beds of the San Joaquin Vallev, California: (abstract) Geol. Soc. America Bull. 24, p. 128. Merriam, J. C, 1919, Tertiary mammalian faunas of the Mojave Desert : Univ. California, Dept. Geol. Sci., Bull., vol. 11, no. 5, pp. 437 a-e, 438-585. Miller, William J., 1944, Geology of parts of the Barstow quadrangle, San Bernar- dino Countv, California : California Jour. Mines and Geol., vol. 40, no. 1, pp. 72-112. Pack, Robert W., 1914, Ornamental marbles near Barstow, California : U. S. Geol. Survey Bull. 540, pp. 363-368. Paige, Svdney, 1912, Rock-cut surfaces in desert ranges: Jour. Geology, vol. 20, pp. 442-4.50. Reed, Ralph D., 1933, Geologv of California : Am. Assoc. Pet. Geol., Tulsa, esp., pp. 17, 24-26. Reed, R. D., and Hollister, J. S. 19.36, Structural evolution of southern California: Am. Assoc. Petroleum Geologists Bull., vol. 20, no. 12, pp. 1529-1704. Rogers, A. F., 1912, Notes on rare minerals from California : Columbia school of Mines Quart., vol. 33, p. 378. Simp.son, T. R., et al., 1951, Water resources of California : Calif. Water Resources Board Bull. 1. Pertinent pages are 481-524. 1954] GEOLOGY AND MINERAL DEPOSITS 185 Storms. "\V. H., 1803, San Bernardino County : California Min. Bur. Kept. 11, pp. 337-869. Thoini)son, David G.. 1920, The Mojave Desert region : U. S. Geol. Survey Water- Supply Paper r>78, pp. 330-303, 424-426. Tucker, W. R., and Samiison, R. J., 1043, San Rernardino County : California Div. Mines Kept. 39, pp. 42T-r)49. Tucker, W. R., and Samp.son, R. J. 1930, San Rernardino County : California Div. Mines Rept. 26. pp. 202-325. Turner, Francis J., 1048, Evolution of the metamorphic rocks : Geol. Soc. America Mem. 30, 342 pp. Turner, Francis J., 1050, Observations on twin laws commonly exhibited by plagio- clase in metamorphic rocks: (abstract) Geol. Soc. America Rull., vol. 61, p. 1511. Vander Leek. Lawrence, 1021, Petroleum resources of California, with special refer- ence to unproved areas : California Min. Bur. Rept. 80, pp. 153-154. VauKhan, Francis E., 1022, Geology of the San Rernardino Mountains north of San Gorgonio Pass : University Calif., Dept. Geol. Sci., Rull., vol. 15. Woodford, A. O., and Harris, T. F., 1928, Geology of Rlackhawk Canyon, San Rer- nardino Mountains, California : University Calif., Dept. Geol. Sci., Rull., vol. 17, pp. 265-292. Wright, L. A., et al., 1953, Mines and mineral deposits of San Rernardino County : California Jour. Mines and Geol., vol. 49, nos. 1 and 2. Yerkes, Robert F., 1951, Geology of a portion of the Cajon Pass area, California: Unpublished M. A. Thesis Claremont Graduate School, Pomona College. THERMAL PROPERTIES OF CERAMIC MATERIALS FROM BARSTOW QUADRANGLE, CALIFORNIA By Joseph A. Pask * and Oliver E. Bowen, Jr.** OUTLINE OF REPORT Page Abstract 186 Introduction 187 Description of samples and thermal analysis curves 187 Characteristics after firing 19S Conclusions 198 References 199 Illustrations Page Fig. 1. Differential thermal analysis curves for samples of series 1 188 2. Differential thermal analysis curves for sample 2 and samples of series 3 - 190 3. Differential thermal analysis curves for acid-tested samples of series 3 compared with type curves for pyrophyllite, muscovite, illite, and sericite_ 191 4a. Differential thermal analysis curves for mixtures of quartz with quartz sericite rock 193 4b. Calibration curve for determination of amount of quartz in mixtures, based on a — ^ quartz inversion 193 5. Differential thermal analysis curves for samples of series 4 through 7 196 ABSTRACT A -number of white, hydrothermally altered dacitic volcanic rocks of potential economic importance were tested by means of differential thermal analysis in order to determine the identity and some of the physical characteristics of the finely divided claylike or micaceous matter making up the bulk of the rocks. The thermal analytical approach was wholly successful in many cases and partially successful in others. All the samples except one were found to contain one or more minerals of the layer-lattice structural type. From the experimental data, some samples are believed to contain minerals transitional between conventional micas and clay-family minerals. Results of the research suggest that silica sheets may occur interleaved between the structural layers of many minerals in much the same relationship as that described by Hendricks (1936) for anauxite. As some of the rocks have poten- tial ceramic use, their fired characteristics were also recorded. Acknowledgments. Expenses of the research were defrayed partly through research grants from the Institute of Engineering Research in the College of Engineering at the University of California at Berkeley and partly through funds of the California State Division of mines. Grateful acknowledgment is extended to Maurice F. Warner and Stephen P. Mitoff, Research Engineers with the Institute, who ran the differential thermal analysis curves and determined the quartz cali- bration curve; Marshall B. Maddock, University of California, who made certain mineral separations and supplied some X-ray diffraction data ; Melvin Stinson, geologist of the California Division of Mines, who made a series of mineral-grain separations ; and William Smiley and C. 0. Hutton of Stanford Research Institute, who made available inde- pendent research data on samples from the Marter Mining Company properties. Mr. Warner also made the X-ray diffraction determinations for alunite. • Professor of Ceramic Engineering, University of California, Berkeley, California. *• Associate Mining Geologist, Calitornia Division of Mines, San Francisco, California. (186) 1954] CERAMIC MATERIALS 187 INTRODUCTION There has been increasing interest in recent years in a variety of white California rocks of some chemical inertness for use as fillers and extenders in paint, paper, rubber, and insecticides. White hydrothermal alteration products of dacite and latitic flow and fragmental volcanics of the Triassic (?) Sidewinder series are concentrated in more than six localities in Barstow quadrangle in potential commercial quantities. Several deposits have been commercially exploited in the past and at least three are currently active (1953). Although, with one exception, the rocks from the various localities look very much alike, some varia- bility was anticipated. By far the greatest bulk of rock was found to consist of minerals too finely divided and too intimately mixed for pre- cise identification by the usual chemical and petrographic means ; con- sequently more elaborate methods of identification were deemed neces- sary if the mineralogy of the rocks was to be determined and the chemical and physical behavior of the materials under use were to be anticipated. Inasmuch as the rocks were thought to be chiefly mixtures of one or more clay minerals and quartz, and inasmuch as the rocks were believed to have potential ceramic as well as filler uses, the authors thought that the most information could be obtained by adopting dif- ferential thermal analysis techniques. Differential thermal analysis curves were made under the direction of the senior author for sixteen samples from seven different localities. It was soon apparent from the curves that, although quartz was present in quantity in all but one specimen, micaceous minerals were probably present in many more specimens than clay minerals. Alunite was found to be present -in quantity in two samples: Some of the samples are of unusual fundamental interest because they suggest mineral transitions, particularly between members of the illite-mica group. The samples also substantiate previous ideas deduced from studies on layer-lattice structure minerals, that properties of a majority of samples collected in the field approach but do not fully duplicate so-called typical or type minerals. The experimental technique of differential thermal analysis has been previously described (Spiel, 1945). Samples generally have received no treatment other than fine grinding. In a few cases they were acid treated to remove carbonates that might mask the thermal peaks of other minerals. Classification of minerals not precisely identified by petrographic means was accomplished by comparison of experimental curves with those of samples of known identity and by interpretation. Such chemical data as were available are included but chemical analyses were not available fcr all of the samples tested. DESCRIPTION OF SAMPLES AND THERMAL ANALYSIS CURVES Samples of Series 1. Series 1 samples are from the Atwood (Ex- cello) clay deposit in the S^ sec. 2, T. 6 N., R. 4 W., S.B., six and a half miles north and slightly east of Victorville. Sample lA came from the east wall of the main tunnel near its end ; sample IB from the main tunnel next to the portal winze; and sample IC from the west tunnel near the portal. Microscopic examination of sample lA in pulverized form in oils of known refractive index shows that most of the material in the sample 188 BARSTOW QUADRANGLE [Bull. 165 M F I B 70% AljOs FiGiRE 1. Differential thermal analysis curves for samples of series 1. 1954] CERAMIC MATERIALS 180 is clay-like, bein«r in opa(|iie afrf?re<2:ates or faintly birefringont, finely divided wisps. Less than 10 percent of the sample appears to be quartz, present as anjrular grains and submicroscopie (at 360 diameters) aggre- gates intergrown with clay. Red and brown iron oxide is present in dust and in minute globules totaling less than 2 percent. Scattered grains of pyrite, tourmaline, and rutile are also present. Sample IB is petrographically si)nilar to lA but with a slightly larger increment of quartz. Red iron oxide in globular grains is slightly more abundant than in sample lA. Sample IC contains a larger percentage of clay- like mineral than either lA or IB and correspondingly less quartz ; more flaky red and yellow iron oxide is present in IC than in lA and IB, sufficient to impart a pinkish color to the unfired materials. Scat- tered grains of nontronite ( ?) epidote and clinozoisite are also present. The D.T.A. curves for samples lA, IB and IC are shown in figure 1. The curve for sample lA is similar to that of a known kaolinite but with a tendency for the curve to approach that of halloysite. The curve for sample IC matches the tvpe curve obtained for alunite (KoO-AloOs- 4803-611,0), as shown by Knizek and Fetter (1946). X-ray diffraction examination of the sample, using the powder camera technique and copper-target tube, substantiated this identification. Kao- linite was not detected in either type of test. The curves for sample IB alone and for a sample of IB material mixed with 70 percent by weight of AI2O3, to reduce the intensities of the peaks, indicate presence of both kaolinite and alunite in approximately equal quantities. Again, X-ray diffraction confirmed the identification. The slight bulge on the low temperature side of the endothermic peak of sample lA suggests the presence of a small amount of alunite with the kaolinite. Sample 2 and Series 3. Sample 2 is from the Dewillibie prospect in the SE^ sec. 3, T. 7 N., R. 4 W., S.B., \ mile northwest of the At- wood deposit and a few hundred yards southeast of the Marshall de- posit, represented by samples 4A and 4B. Sample 2 is similar in many respects to samples of series 3 and hence will be discussed with them. Sample 2 when examined under the microscope at 360 diameters magnification appears to consist chiefly of partly isotropic clay. Dis- crete grains of quartz are not abundant and the iron oxide is very finely divided and less abundant than in series 1 samples. It contains little or no carbonate minerals but there are a few scattered grains of jarosite. With the exception of the clay mineral and quartz, impurities appeared to be present in trace amounts only — in the several fields examined. Samples of series 3 are all from Marter Mining Company's prop- erties in sec. 27, T. 7 N., R. 4 W., S.B., 3 miles southeast of Bryman or 10 miles north of Victorville. Sample 3A is from the east wall of the main pit, 3B from the floor of the main pit, 3C from the w'all at the southeast corner of the main pit, and 3D from the south quarry near a granite intrusion. Sample 3A, under the microscope, consists predominantly of a mica- ceous mineral and quartz. A carbonate, probably calcite, yellow and red iron oxides are widely distributed but in very minor amounts to- gether with occasional grains of pyrite, sphene, rutile, epidote, andalu- site, tourmaline, and biotite (altering to chlorite). The carbonate min- eral is present in coarse grains but both the mica and quartz are very finely divided. 190 BARSTOW QUADRANGLE [Bull. 165 M.F 2 28%Quortz M.F. 3A 35% Ouartz M.F 3B 33% Quartz M.F 3C 40% Quartz M.F 3D 25% Quartz FiGi'RE 2. Differential thermal analysis curves for sample 2 and samples of series 3. i!):)4j CERAMIC MATERIALS 191 MUSCOVITE SERlCITE SCHIST 75% Quortz ILLITE PYROPHYLLITE M.F. 3A (ACID TREATED) 35% Ouortz M.F. 38 (ACID TREATED) 40% Quartz M F 3C (ACID TREATED) 50% Ouortz M F 3D (ACID TREATED) 25% Quartz FiGURB 3. Differential thermal analysis curves for acid-treated samples of series 3 compared with type curves for pyrophyllite, muscovite, illite, and sericite. 192 BARSTOW QUADRANGLE [Bull. 165 Sample 3B is mineralogically similar to 3A with a slightly higher carbonate content and a noticeable increment of jarosite; still, how- ever, in very minor amounts. Sample 3C is much like 3A, and 3D is mineralogically similar to the other samples of the series except that the original feldspars of the volcanic parent rock have not been com- pletely replaced. Both relict plagioclase and relict orthoclase are spar- ingly present. D.T.A. curves for samples 2, 3A, 3B, 3C, and 3D are pictured in figure 2. Curves for acid-treated series 3 samples are shown in figure 3 together with those of coarse-grained muscovite from pegmatite, mus- covite-quartz schist, an illite and pyrophyllite. The general similarity among all these curves, with the exception of pyrophyllite, is striking. The main difference is m the positions of the two upper endothermic peaks. The small peak in the neighborhood of 560-570° C, experimen- tally measured, is caused by the alpha-beta quartz inversion. The shape of the curves is intermediate between known muscovite and illite but much closer to the former, suggesting that they are structvirally nearer mica than clay. On comparing these curves with the curve for pyro- phyllite, which does not show similar activity between 800° and 1200°C, it is believed unlikely that the .samples of series 3 are related to the pyrophyllite structure. The skewness of the curves as compared with type minerals, although it may be caused by varying degrees of fine- ness among the powdered materials, suggests that there are transi- tional varieties between micas and clays, and that the transitional types are not always those that would be expected under progressively severe hydrothermal alteration. The quartz content, as determined bj^ D.T.A. analysis, is indicated by the curves in figures 3 and 4. The amount of quartz present is de- termined on the basis of the height of the alpha-beta quartz inversion peak as measured on the high-temperature side. A calibration curve was first obtained by making runs with quartz, prepared mixtures of sample 3A and quartz, and also mixtures of 3A and alumina to deter- mine the effect of addition of pure substances in influencing the shape of the curve and to check the intensity of the alpha-beta inversion peak where a known amount of quartz was added. This procedure of forming synthetic mixtures for calibration purposes has been described in the literature a number of times. Assuming a linear relationship between the peak height and the amount of quartz in the sample, 3A contained 35 percent quartz. The probable quartz contents were then calculated from chemical analyses on this basis and plotted against the corre- sponding peak heights. The resulting linearity of the curve substan- tiated the procedure. However, because of possible untested factors that may be brought out in additional experimentation and because of limi- tations in the accuracy of the experimental method used, the degree of accuracy is not fully established ; it might be oft' as much as plus or minus 20 percent of the quartz increment. The quartz content, as determined by D.T.A. experimentation, is con- siderably less than the figure obtained by calculation, using the avail- able chemical analyses of the rock and the assumed formulas of the constituent minerals, as shown in table I. Petrographic examination proved to be of little use in solving the discrepancy because the mica- ceous mineral and quartz were found to be intergrown down to the 1954] CERAMIC MATERIALS 193 50% MR 3A 50%Al203 (175% Quartz Tot) 100% M F 3A (35% Quortz Tof.) 75%M F 3A 25% Quartz (52% Quartz Tot.) 50%M.F 3A 50% Quartz (67 5% Quortz Tot.) 100% Quortz Figure 4a. Differential thermal analysis curves for mixtures of quartz with quartz sericite rock. . 14 > Q 12 !=? 10 en cr 8 rsi 6 I- o: o c?^ 2 I 20 40 60 AMOUNT OF QUARTZ. % 80 100 Calibration curve for determinotion of amount of quartz in mixture based on <^- /9 inversion. Figure 4b. Calibration curve for determination of amount of quartz m mixtures, based on a — g quartz inversion. 7 — 85919 194 BARSTOW QUADRANGLE [Bull. 165 smallest particle size with which it was practical to work. All of the samples could be improved for ceramic use by acid treatment to remove carbonates and by electromagnetic separation of iron and manganese- bearing; constituents. The increments of these constituents in most materials tested is small — commonly less than two percent and in some cases much less than one percent. Chemical analyses and tnineral calculations. Cleanest Fraction Chemical analyses M.F. SB M.F. SB M.F. 7A Si02 67.7 75.96% AI2O3 16.9 12.34% 18.93 FezOa 2.6 .12 BaO 0.15 CaO 2.1 .18 MgO 0.5 .23 Na^O 0.2 0.40 .58 K-0 5.2 4.36 .16 MnO Ti02 0.5 P0O5 0.14 SO3 .04 CO2 F2 Loss on Ignition 3.8 3.7 Mineral calculation Muscovite 44.2 30 Orthoclase 5 Pyrophyllite 67 Balance by difference, Silica 47.7 65 31 D.T.A. determination Quartz 33 40 25 Excess silica can be accounted for in two ways. One, some mineral or minerals may be present that has (have) not been noticed either by D.T.A. or petrographically ; the chances of this seem very small. The other, the excess silica may be tied up as sheets of silica (not in the form of quartz) interleaved with the micaceous layers. These would not show up petrographically except possibly to modify the optical characters slightly. The latter hypothesis is a logical one because such an interleaving of silica sheets with kaolinite layers is generally ac- cepted as the explanation of the structure and composition of anauxite (Hendricks, 1936) which contains an excess of silica beyond that nec- essary for kaolinite but which does not appear on D.T.A. curves as qi;artz. This phenomenon requires further study. The series 3 untreated samples showed presence of some carbonate with an endothermic peak at about 800-875°C. These were removed upon leaching with HCl (compare figs. 2 and 3). Samples of Series 4. Samples of series 4 are from the Marshall de- posit in the S.W. i sec. 3, T. 6 N., R. 4 W., S.B. ; locality is adjacent to the Dewillbie deposit (series 2 samples) and 2 miles south of the Marter deposit (series 3 samples). Petrographic examination of sample 4A discloses presence of a finely divided micaceous mineral which appears to make up more than 90 percent of the rock. Quartz is so intimately intergrown with mica that it is almost indistinguishable except for occasional scattered patches. 1954] CERAMIC MATERIALS 195 The iron oxide content is low and there are no carbonate minerals or jarosite. Scattered grains of clinozoisite, tourmaline, sphene, zircon and apatite crystals are present as well Tas patchy white opaque ma- terial resembling leucoxene. Sample 4B is similar to 4A but is slightly higher in iron oxide content. The curves for samples 4A and 4B are shown in figure 5. They are much less diagnostic of any particular mineral than curves for samples of series 2 and 3. Sample 4A appears to be micaceous although the thermal behavior is nearer typical illite than the series 3 samples taken to be sericite. It also contains 23 percent quartz as determined by the height of the alpha-beta inversion endothermic peak. Sample 4B is indeterminate. There is a possibility of presence of pyrophyllite and also a micaceous mineral whose properties approach those of illite more closely than of any other sample. Quartz is present, probably to the amount of 15 percent. Samples of Series 5. Samples of series 5 come from a deposit on the northwest flank of Stoddard Mountain in the S.W. |, sec. 7, T. 7 N., R. 2 W., S.B. ; the deposit is close to the City of Los Angeles electric transmission line road 14 miles northeast of Victorville. Rocks in this deposit appeared less altered than those of other deposits and although the material showed little promise of economic value the samples were collected for comparative purposes. Petrographically the series 5 samples are texturally dissimilar to the other samples described in this study. They are coarser and more vari- able in grain and both quartz and the micaceous-appearing mineral particles do not appear to be so intimately intergrown. Optical proper- ties of the coarsest material are nearest those for muscovite but there is also a large increment of clay-like material. Some of the mica is probably relict from a metamorphism that preceded the hydrothermal alteration. Except for dusty to globular iron oxide the rock is quite free of minor accessory minerals. There is a moderate amount of relict feldspar, probably both potash and soda lime feldspar present in vari- ous stages of alteration to clay and mica. There is more mica in sample 5B than 5A. The curves for samples 5A and 5B, shown in figure 5, are practically identical. The only difference is in the size of the endothermic peak at approximately 570° C ; this may or may not be due to the increment of coarse mica. The samples appear to be basically kaolinitic, the curves ' being modified by small amounts of minerals other than kaolinite and quartz and possibly by slightly different molecular structure in the micaceous and clay minerals from normal type minerals such as muscovite and kaolinite. Samples of Series 6. The Snow White deposit, located 3^ miles southwest of Stoddard Mountain in SW^ sec. 26, T. 7 N., R. 3 W., S.B., provided samples of series 6, taken from two places on the north wall of the open cut. Under the microscope these are seen to consist predominantly of a micaceous mineral but also contain a substantial amount of quartz slightly larger in grain size than the mica. Iron oxide is widely dis- tributed but in very minor amounts — much less than in samples 5A and 5B. Both 6A and 6B contain a carbonate mineral ; this is very i 196 BARSTOW QUADRANGLE [Bull. 165 MP 4A 25%-30% Ouortz m M F 4B 2i — 25% Ouortz MR 5 A PYROPHYLLITE Figure 5. Differential thermal analysis curves for samples of series 4 through 7. 1954] CERAMIC MATERIALS 197 finely divided in 5A and more abundant and coarser in 5B. There are scattered g:rains of sphene, zircon, rutile and possibly a zeolite. Figure 5 shows curves for samples 6A and 6B. These are similar to curves for samples of series 2, 3 and 4, especially 3. The mineral caus- ino: the major endothermic peak does not, however, seem to be exactly the same as the one causing a peak in the same region in series 3, although it is acid-soluble and was identified petrographically as a car- bonate mineral. The mineral is present in greater amounts in 6B than 6A. The estimated quartz contents as determined by D.T.A. are indi- cated with the curves (30 to 38 percent). Samples of Series 7. These are from the Victorite pyrophyllite de- posit in the east central part of sec. 26 T. 7 N., R. 3 W., S.B., f of a mile east and slightly north of the Snow White deposit 3 miles south- west of Stoddard Mountain. The hand samples have all the charac- teristics of schistose to massive pyrophyllite and the quantitative analy- sis shown in table I bears out the presence of pyrophyllite as well as the thermal curves. Under the microscope sample 7A is found to consist almost wholly of a micaceous mineral and quartz, quartz being moderately abundant in small angular grains. The micaceous mineral is not readily identified petrographically because of its finely divided condition. There is a little red iron oxide and a few scattered grains of chlorite and sphene. Sam- ple 7B contains only minute amounts of miner-als other than the mica- ceous mineral. Curves for samples 7A and 7B, shown in figure 5, most closely resemble pyrophyllite because of the large endothermic effect, with a peak at 760 °C and slight thermal activity beyond it. Calculation of the pyrophyllite content from the chemical analysis of sample 7A (table I) indicates an excess of silica, over that necessary to satisfy the pyrophyllite formula, of 31 percent. This figure is 6 percent greater than the content estimated from the thermal curve. The broadness of the endothermic peak and the slight activity in the range of 1200° C suggests that a small amount of mica may be present. This activity is accentuated in the curve for sample 7B. Color and Physical Characteristics of Samples. Sample No. MF-IA MF-IB MF-lC MF-2__ MF-3A MF-3B MF-3C MF-3D MF-4A. MF-4B MF-5A MF-5B MF-6A VIF-6B VIF-7A VIF-7B Fired color White Off white. White Resin light brown. Resin light brown. Tan and brown Tan and brown Resin light brown. Resin light brown. Resin light brown. Beige Beige Resin light brown. Resin light brown. Pearly off white Pearly off white Color irregularities Some dark brown spots Small brown specks, evenly tributed dis- Few large black spots. Few large black spots. Color variable Color variable Few large black spots. Some brown spots Iron stains Iron and manganese stains. Manganese spots. Light iron stains. Light iron stains. Physical condition Sintered Slightly sintered Powdery Partially vitreous Partially vitreous Partially vitreous Partially vitreous Partially vitreous Partially vitreous Partially vitreous Slightly vitreous Slightly vitreous Partially vitreous Partially vitreous Partially vitreous Partially vitreous I 198 BARSTOW QUADRANGLE [Bull. 165 CHARACTERISTICS AFTER FIRING Inasmuch as many of the rocks appeared to be potentially useful in ceramic mixes, color and other physical characteristics of the various samples wi^re recorded after firing to 1175°C and "soaking" for one hour. These characteristics are listed in the accompanying table. CONCLUSIONS All samples but one were found to contain one or more minerals essentially of the layer-lattice structural type. With the exception of samples lA, kaolinite, IC, alunite, and 7A, pyrophyllite, the D.T.A. curves did not precisely duplicate those of recognized minerals set up as standards. Many of them did, however, resemble standard curves in many respects. This similarity but not complete matching is believed to have some diagnostic significance, as in the case of sample 3C, the micaceous mineral identified by D.T.A. checked with results obtained by X-ray difi^raction.^ The unkno-v\Ti micaceous mineral in series 2, 3, 4 and 6 appears to be nearer sericite than illite or any other clay mineral. The variations and similarities have been discussed through- out the report and it may be that micaceous minerals tend to vary both structurally and chemically between mica and clay depending upon the physico-chemical environment of origin. It may be that the slight varia- tion in optical properties of the micaceous mineral in samples of series 3 as observed by Hutton,- using special petrographic equipment, is due to an isomorphous gradation between sericite and illite. It is also possible that complete gradation between various clay minerals and micas is to be expected in products of hydrothermal environments where the physico-chemical conditions would be expected to vary in time and space. Because of the limited scope of the laboratory investigations on the various hydrothermal products examined and because of limited com- parative D.T.A. data available in the literature on mineral mixtures, the practical value of the foregoing data must remain open. The exact mineral constitution of some of the samples was not established but the authors feel that some progress was made toward identification of certain types of micaceous and clay minerals in intimate mixtures that are not readily separable into their respective constituents. The brief study has brought to light some interesting problems in mineral transi- tions that should be fruitful in further research. One of the most in- teresting suggestions that has come out of the research is that silica sheets may occur interleaved between other molecular layers in min- erals other than anauxite. Further research should be made along this line. 1 Separation of 0.1 gram of the micaceous mineral was made by Marshall E. Maddock in the mineralogical laboratories of the University of California and an x-ray powder pattern was made. Maddock states that : "there is a close correspondence between the pattern of sample 3C and the x-ray Diffraction Data Card for muscovite pub- lished by the American Society for Testing Materials." « Hutton, C. O., working for Stanford Research Institute, found that the mica appeared to have an optic axial angle somewhat smaller than that for common muscovite and that the refractive indices varied somewhat from normal. 1954] CERAMIC MATERIALS 199 REFERENCES Hendricks. S. B., 1936, Concerning the crystal structure of kaolinite, Al:;03-2Si02- 2H2O, and the composition of anauxite : Zeitschr. Kristallographie, band 95, p. 247. Knizek, Jan O., and Fetter, Hans, 1946, Properties of natural alunitic clays : Am. Ceramic Soc. Jour., vol. 29, pp. 308-313. Spiel, Sidney, Berkelhamer, L. H., Pask, J. A., and Davies, Ben, 1945, Differen- tial thermal analysis — its application to clays and other aluminous minerals: U. S. Bur. Mines Tech. Paper 664, 81 pp. INDEX A. C. Price group of claims, 123 Adelanto deposits, 169 Alamo Consolidated deposit, 148 Alaskite, photo of, 55 Altuda deposits, 134-135 Amazon mine, 119, 135 photo of, 122 Anaco mine, 136-137 Andesite, 83-84, 117 photomicrograph of, 82 relation wit"h Kramer Hills lakebeds, 77, 81 Apple Valley, recent deposits in, 92 Asbestos, 140 Atlas (ganister) deposit, 175-176, 177 Atwood deposits, 141-142 photo of, 142 thermal tests on, 187 Ball Chemical Company magnesite property, 77 Kramer deposit, 171 magnesite deposits, 148, 170-171 photo of, 98, 175 magnetite deposits, 135-136 Barite, 138, 140-141 veins, emplacement of, 118 Barstow, lakebed limestone near, 80 quadrangle, economic map, pocket geologic map, pocket Basalt, 117 Bell Mountain, 112 photo of, 60, 108 quartz monzonite in, 66 schriesheimite in, 72-73 Black Mountain, 103-104, 109 ; see also geographic names map, 14 limestone deiwsits on, 167 ; see also Southwestern Portland Cement Company limestone conglomerate, geologic map of, pocket quarry, photo of, 168 (marl) deposit, 150-151 Borates, deposition of, 117 Branch mine, 130 ; water in, 180 Breccia, in Oro Grande series, 30 photo of, 24 Cajon Creek, 119 Calico Mountains, geologic history, 118 Carbonate mine, 129-130, 137 Chert, deposition of, 117 Clay, 141; 186-199 Conda deposits, 140 Conglomerate in Fairview Valley formation, 38 Copper, 119 King mine, 119 Mountain mine, 119 Dacite, 85-88, 186-199, 117-118 in Hodge volcanic series, 35-36 in Sidewinder volcanic series, 43, 46-47 near Lenwood, 84-85 photomicrograph of, 86 relation with diabase, 85 (201 ) i 202 BARSTOW QUADRANGLE [Bull. 165 Del Oro mine, 130 Desert pavement, 93 Devil's Gorge deposits, 146 Dewillibie (serioite-quartz) deposits, 152-153; thermal tests on, 189 Diabase, 85, 117 photomicrograph of, 82 relation with dacite, 85 lakeheds, 85 Differential thermal analysis curves, 188, 190, 191, 193, 196 Dimension stone, 145 Diorite, 53-54, 116 photo of. 70 Dolomite, 148-149 in Oro Grande series, 24-34 photo of, 25, 28, 29, 30 Domes, 111-112 Dunes, 92-93 Economic mineral deposits, table of, 120-121 Emsco Ganister deposit, 176 Quartzite deposit, 178 Erosion, cycles of, 109-111 Excello deposits, 141-142 Fairview Valley, recent deposits in, 92 formation, 36-42 at Black Mountain (marl) deposit, 151 fossils from, 41-42 geologic historv, 113 photo of, 37, 38, 39, 40 quartz monzonite debris in, 68 relation with Oro Grande series, 34, 37, 95 Sidewinder volcanic series, 37, 101 structure, 95, 100-101, 103-104 type section described, 37-41 Fleetfoot deposits, 140 Fossils in Fairview Valley formation, 41-42 Pleistocene deposits, 91 Four Brothers mine, 130 Gabbro, intrusion of, 116 -diorite, 54-60 ; see also Iron Mountain stock photo of, 71 relation with granodiorite porphyry, 61 Sidewinder volcanic series, 60 Ganister, 174-175 Gem (marble) deposit, 148 Geologic events, table of, 114-115 Gladding McBean deposit, 144-145 Globerson deposits, 134-135 Gneiss, photo of, 61 ; see also granite gneiss Waterman, 17-23 Gold, 123-129 -bearing veins, emplacement of, 116 Bullion mine, water in, 180 mines, table of, 124-128 Golden Witch deposits. 137-138 Golconda (asbestos) deposits, 140 clay deposit, 142-143 (ganister) deposit, 176-177 Granite, 145 gneiss, 75-76 Mountains, old surface, 110 quartz monzonite in, 65-68 spring in, 180 1954] ' INDEX 20;j Gninitic rocks, 53-76, H.l photoof, f)?, 61, 106 CJraiuxliorite, 64-6r> relation with Miocene rocks, SI Pliocene volcanic rocks, 65 porphyry, 60-64 photo of, 70 relation with Kuhbro-diorite, 61 Hodge volcanic series, 61, 64 Gravel, 173-174 Hamilton, C. C, Emcap no. 1 well, 103 Harper Lake, recent deposits in, 92, 93 fault, 105 Helendale fault, 88, 93, 103, 105 ; see also geofrraphic names map, 14 photo of, 94 ; photo (aerial) of, pocket Hematite in Waterman gneiss. 18 Hicks deposits, 140, 143-144 Hinkley dolomite deposit, 33, 149 Hills, barite in, 141 dacite in, 87 diorite in, 53 geologic history, 118 granodiorite in, 64-65 photo of gneiss in, 61 quartz monzonite porphyry in, 68 structure, 102, 105 anticline, 95-96 limestone deposits, 161 Hodge area, geologic map and aerial photograph of, pocket homocline, 96 (mica schist) deposits, 151-152 volcanic series, 34-30 at Conda mine, 140 Golconda clay deposit, 142 (ganister) deposit. 176 Hodge (mica schist) deposits, 151 Kennedy dei)osit, 177 Millet deposit, 143 geologic history, 113 quartz in, 175 relation with granodiorite porphyry. 61. 64 Iron Mountain stock, 59-60 structure. 95. 103 Hornfels, in Fairview Valley formation, 39 Oro Grande series, 24-34 Ideal Cement Company, photo of quarry, 162 Inselberg topographv, photo of, 108 Iron, 134 Mountain, 112 dolomite in, 149 gabbro-diorite stock in, 54-58 limestone deposits, 161-163 stock, 59-60 Johnson, W. H. Company, 145 Kennedy (ganister) deposit, 177 Keystone mine, 140 Kimball deposit, 148 Klondike quarry, 150 ; photo of, 163 204 BARSTOW QUADRANGLE [Bull. 165 Kramer Hills, andesite in, 83-84 dacite in, 87 diabase in, 85 map of, 78 structure, 102 deposit, 171 lakebeds, 77-79 magnesite in, 170 paleogeography, 109 (magnesite) deposit, 171-172 Lahar, in Sidewinder volcanic series, 43 Lakebeds, 77-83 relation with diabase, 85 Lamprophyre, intrusion of, 116 Lamprophyric dike rocks. 73-75 Latite, in Hodge volcanic series, 35 -andesite, in Sidewinder volcanic series, 47 Lead, 136 Leahy Ganister deposit, 176 Lenwood, dacite near, 84-85 Miocene sediments near, 79-80 anticline, 102-103 ; photo of, 104 Limestone, 160-161 at Amazon mine, 122 deposition of, 117 in Fairview Valley formation, 39, 40 Oro Grande series, 24-34 ; photos of, 27-32, 100-101, 122 lakebed, 80, 83 Lucky Rose mine, 119 Magnesite, 170 deposition of, 117 Magnetite, 116 Manganese, 116 Marble, 146 in Waterman gneiss, 17 ornamental, 30 Marl, 172 Marshall and Davis (sericite-quartz) deposit, 153 ; photos of, 152, 153 ; thermal tests on, 194-195 Marter-White (sericite-quartz) deposit, 154-158 ; photo of, 155, 156, 157 ; thermal tests on, 189-194 Millet deposits, 143-144 Mineral deposits, table of, 120-121 fillers, 150 Materials Company, photo of silica quarry, 172, 173 Mines, gold, table of, 124-128 Miocene lakebeds, photo of, 78-80 rocks, 81 Mirage Lake, Recent deposits in, 92, 93 Mojave River, faulting, 107 history of, 118 Pleistocene deposits, 88, 89, 91 Valley, photo of. 111 structural block, 93-94 1954] . INDEX 205 Oil and gas, table of holes drilled for, 182 Oro Grande, photo of, 111 I mine. 180-131 II mine, 131 series, 18, 23-34 at Amazon mine, 122 Anaco mine, 137 Ball mine, 136 Carbonate mine, 129 Devil's Gorge deposits, 146 Hinkley (dolomite) deposit, 149 limestone deposits, 161 Iron Mountain limestone deposits, 161-163 Oro Grande II mine, 131 Riverside Cement Company deposits, 165, 177 Three Colored marble deposits, 146 Verde Antique deposit, 148 correlation, 22 ganister in, 175 geologic history, 113 on Shadow Mountains, 169 photo of, 24-32, 55, 111, 162, 164, 166, 172 thrust in, 100, 101 relation with diorite, 54 Fairview Valley formation, 34, 37, 95 granite gneiss, 75 Iron Mountain stock, 59-60 Sidewinder volcanic series, 101 ; photo of, 98 remnants in Waterman gneiss, 22 structure, 95-97, 99-101, 103-104 type section described, 24-25 Ozark mine, water in, 180 P.C.E.. see pyrometric cone equivalent Pediments, 110-111 photo of, 109 Pedry deposits, 137-138 water in mine, 180 Petroleum, 181 Pickhaadle formation, 138 Piedmontite, in Sidewinder volcanic series, 51-52 Pleistocene alluvium, photo of, 111 deposits, 88-92 marl in, 172 photo of, 87, 89, 90, 92 Pliocene volcanic rocks, relation to granodiorite, 65 Miocene rocks, 81 Predazzite. in Oro Grande series, 33 Price. A. C, 123 Pyrolusite veins, emplacement of, 116 Pyrometric cone equivalent, definition of, 143 Quarry Mountain, see geographic names map, 14 Quartz monzonite, 65-68, 103, 116 photo of, 55, 56, 58, 59, 111 relation with Fairview Valley formation, 68 porphyry, 68-72 at Sidewinder mine, 133 206 BARSTOW QUADRANGLE [Bull. 1^5 Quartzite, see also under silica in Hodge volcanic series, 35 Ore Grande series, 24-25, 27, 31 photo of, 26, 100, 101 Waterman gneiss, 17 Mountain, 112 ; see also geographic names map, 14 Mountain, dolomite in, 149 limestone deposits in, 167-169 Oro Grande series in, 24-25 pediments, 110-111 photo of, 111 structure, 99-101 Raven Ridge, see geographic names map, 14 photo of, 106 old surface, 110 Sidewinder volcanic series, 42 pediment, 111 ; faults of, 106 Recent deposits, 92-93 photo of, 91 Red Raven mine, 136-137 Rover mine, 136-137 Seal (magnesite) deposits, 170-171 magnetite deposits. 135-136 Ridge, see geographic names map, 14 photo of, 28 Reserve quarry, 33-34 see also Southwestern Portland Cement Company Rhyolite, 117 at Carbonate mine, 129 in Hodge volcanic series, 35-36 Sidewinder volcanic series, 43, 46 Riverside Cement Company, 129 (ganister) quarry, 177-178 photo of. 111 (limestone) deposits, 163-165 photo of quarry, 163 Rock, crushed, 173-174 R-Z mines, water, 180 San Antonio deposits, 137-138 Sand, 173 Sandstone, in Fairview Valley formation, 39 Oro Grande series, 25, 31 Schist, 151-152 in Hodge volcanic series, 35 Oro Grande series, 23-34 ; photo of, 100-101 Waterman gneiss, 17 Schriesheimite, 72-73 intrusion of, 116 photo of, 71 relation with Sidewinder volcanic series, 73 Section 20 Hills, see geographic names map, 14 gneiss in, 75 granitic rocks in, 59 structure, 105 (ganister) deposits, 178-179 Sericite-quartz, 186-199 Serpentine, in Oro Grande series, 33 Shadow Mountains, 113 limestone deposits on, 169 Oro Grande series in, 25-27 pediments, 111 syncline, 96 1954] INDEX 207 Sidewinder fault, 103-104 mine, 131-134 geologic map and aerial photograph of, pocket photo of, 132 Mountain, 104 dolomite in, 149 emplacement of veins, 116 photo of, 147 old surface, 110 Mountains, Oro (Jrande series, 27-34 Sidewinder volcanic series, 42 Valley, 42 volcanic series, 36, 42-53 at Altuda deposits, 134 Amazon mine, 122 Atwood deposits, 141 Branch mine, 130 Carbonate mine, 129 Dewillibie deposit, 152 Marshall deposit, 154 Marter-White deposit, 154, 155 Snow White deposit, 158 Sidewinder mine, 133-134 Three Buttes deposit, 144 Colored marble deposits, 146 geologic history, 116 paleogeography, 109 photo of, 60, 142 photomicrograph of, 44, 45, 48 related andesite at Oro Grande II mine, 131 rocks at Oro Grande I mine, 131 relation with Fairview Valley formation, 37, 101 gabhro-diorite, 60 Oro grande series, 101 photo of, 98 schriesheimite, 73 springs, 180 structure, 97-99 use of, 187 water in, 180 Well, photo, 26 Sierra Melada, quartz monzonite of, 66 see geographic names map, 14 Silica. 174-175 Siltstone, in Fairview Valley formation, 38 Silver, 136, 138 -bearing veins, emplacement of, 118 Mountain pediments. 111 Sidewinder volcanic series, 42, 48 structure, 98 Slash X Mountains ; see geographic names map, 14 Snow White (sericite-quartz) deposit, 158 thermal tests on, 195, 197 Southwestern Portland Cement Company, 123 (ganister) deposit, 178 (limestone) deposits, 103, 165-169 photo of, 166 structure of, 99 Reserve Quarry, 37, 38, 95 Sparkuhle Hill, 109 ; see also geographic names map, 14 geologic map of, pocket limestone deposits, 165 structure, 99-101, 106-107 Split Rock Mountain, see geographic names map, 14 Sidewinder volcanic series, 43, 48 208 BARSTOW QUADRANGLE [Bull. 165 Springs. 179-180 Stoddard dike complex, photo of, 57, 106 (aerial) photo of. pocket quartz monzonite porphyry in, 68-72 Mountain, homocline, 98 Sidewinder volcanic series in, 42, 48 thermal tests of sericite-quartz rock from, 195 Well, water from, 180 Structure, sections showing, pocket Tactile in Waterman gneiss, 18 Three Buttes deposit. 144-145 Colored marble deposits, 146-148; photo of, 147 Thrust, photo of. 100, 101 Tuff, in Hodge volcanic series, 35 Sidewinder volcanic series, 43 photomicrograph of, 86 Tungsten, 139-140 Verde Antique deposit, 148 Veins, 76 Velvet White deposit, 154 Victorite ( pyrophyllite ) deposit, 158-159 photo of, 159 Victorville fault, lOG-107 Lime Rock Company (limestone) deposits, 169 pyrophyllite deposit, thermal tests on, 197 Vitrlite marl deposits, 88-89, 172-173 ; photo of, 174 Vitrophyre. 77 Volcanic rocks, in Hoclge volcanic series, 34-36 Sidewinder series, 42-53 Water, 178 Waterman anticline, 19. 23, 95-96 gneiss, 17-23 photo of, 18, 19 structure, 95 type section described. 17 Hills, see geographic names map, 14 dacite in, 87 structure. 102. 104-105 mine. 17, 138-139 : barite in, 141 Miocene ro^ks in. 80-81 thrust. 22. 104-105 Western Refractories Company deposit, 175-176 Whatnot mine, 130 White Lime Rock Company (limestone) deposits, 169-170 Whitlock deposits, 169 Zinc, 136 printed in califohnia state printing office 85919 9-53 2M I Jl II I ill II IB ^ m DIVISION OF MINES OLAF P. JENKINS, CHIEF STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES BULLETIN 165' PLATE 3 Oal Tmc / Tmc Qql qm Tvi qm Qal qm #:^^ Cog^ Cog C KRAMER HILLS QUARTZITE MTN. QUARTZITE MTN. D Oal WATERMAN MINE Waterman \ Anticline (j Tvr Tmc Cog ,^g dg E WATERMAN THRUST "^Tvr WATERMAN HILLS HINKLEY HILLS Sierro Meloda qm BlacK Mtn Qal PL.„-„,,-^--Jl^ Qal '''" Raven Ridge qmp "ftsv qmp "ftsv IRON MTN. Lenwood Anticline Qal Qoaj. ■ Qoal Borstow HELENDALE FAULT SIDEWINDER FAULT GRANITE MOUNTAINS TO BARSTOW STRUCTURE SECTIONS BARSTOW QUADRANGLE HELENDALE FAULT SIDEWINDER FAULT 8 9 MILES SCALE BLACK MOUNTAIN EXPLANATION Qal - olluvium, Qoal - old alluvium. Tmc - continental deposits Pf - Fairview Valley fm Cog - Oro Grande Tvr- rtiyolite and docite, Tma - black quartz andesite. "Ssv - Sidewinder volcanics. hv - Hodge volconics qmp- quartz monzonite porphyry qm -quartz monzo- nite grd- granodiorite. dg - gneissic hornblende- dionte, wg- Waterman gneiss, qn - granite gneiss. LIBRARY p, ^ p „ . UNIVEfiSITV OF CALIFORNIA °>' ^ '- °°'"^Ti :o«: ? ) I DIVISION OF MINES OLAF P. JENKINS, CHIEF STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES '-, BULLETIN 165 ^"^ PLATE 6 ''^ EXPLANATION Qolf = alluvial fans; Qal = alluvium, Qoal = old alluvium qm = quartz monzonite; gr=Qlkali granite(Upper Jurassic or Lower Cretaceous) ■Ssv= Sidewinder volcanic series, docite, rhyolite, lotite (Tnassic) Pf=FQirview Valley formation, limestone conglomerate, I i mestone ( Permian) Cog = Oro Grande series, limestone, quortzite, mica schist (Carboniferous) gn:granite gneiss ( Paleozoic ?) =niarker beds LIBRARY .JJMIVERSITY OF CALIFORNIA DAVIS AERIAL VIEW AND GEOLOGY OF THE ORO GRANDE AREA BARSTOW QUADRANGLE, CALIFORNIA %-' DIVISION OF MINES OLAF P. JENKINS, CHIEF STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES tiUIUIUI , C3> BULLETIN 165 A"?. PLATE 7 '''*• EXPLANATION Qal = alluviutrn Qalf = alluviol fans hl= hornblende lamprophyre; hbd: hornblendite^ qm = quartz monzonile, grd=granodiorite } ^^^^' '""°^^"' °' qmp = quartz monzonite porphyry ' J '-°*^' Cretaceous ■Rsv= Sidewinder volcanic series } Triassic Pfc=Fairviey» Valley limestone conglomerate \ P'f'= " " hornfelsic silty limestone j^^™'°'^ CogqUOro Grande series, quartzite ond limestone'^ Cogl= " " , limestone Cogb= " " " .dolomite breccia )■ Carboniferous Cogd= " " " .dolomite Coga= " " " .orgillite AERIAL VIEW AND GEOLOGY OF THE SIDEWINDER AREA BARSTOW QUADRANGLE, CALIFORNIA LIBRARY UNIVERSITY Of CALiFORNI4 DAVIS DIVISION OF MINES OLAF P. JENKINS, CHIEF STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES BULLET I N leS'mAi)^ PLATE 8 EXPLANATION Qd = sand dunes, Qal = alluuium, Qt = terroces-, Qool = old alluvium Tpv = docile dike (Pliocene), Tmc = red fanglomerote(Miocene) qm = quortz monzonite; grdp = biotite gronodiorite porphyry,". Upper Jurossic or gd = hornblende gabbro-diorite; q« = quart2 vein J Lower Cretaceous Cog=Oro Gronde series (Carboniferous) dg = dlorite gneiss (Paleozoic ?) hv=Hodge volcanic series, dacite and andesite flows and tuffs (Upper Paleozoic) AERIAL VIEW AND GEOLOGY OF THE HODGE AREA BARSTOW QUADRANGLE, CALIFORNIA LIBRARY UNIVERSITY OF CALIFORNIA DIVISION OF MINES OLAF P. JENKINS, CHIEF STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES BULLETIN 165 PLATE 9 A- A. Vertical air photo of tile Ilel.ii.lali- fault wlji'ii- it cri)»»fs tlu' SlJewiiicler \V.-ll-Sl.,.ler left (juudraut has dikes only oa its northeast sli.pes even tliou^'h made up of mctavolcanic and eranitic rocks older than the dikes. The Lucerne Valley and Stodihinl Well r(uids join in the uiiper center of the photograph. Photo hy FairchM Aerial Surveyg, courtesy U. .S. Oeotogical Survey and V. S. Army. LIBFMY UMVEBSITY OF CAUFORMUL •- DAWSi S' .al w COLUTE Calif omia. Division Mines* ^ J Bulletin. rrni nflT GEOLOGI Call Number: TN2ii C3 A3 THZ4- C3 A3 / 75 00644 1649 114424 ^ I ■^iiiMr II m li«i •hrtr^ ■'■ "* •^ i?»/- ».,■.•. J- fr^w ■ v¥^^..JMI^^J&£k »R a '85 THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.00 ON THE SEVENTH DAY OVERDUE. -N 6 ISSS Mt mo ■:mi] I 197* SBP2 ^^74 OCT 7REC'D JAN 6 1988 JAN 14 PHYS SCI LIBRARY -Hfcrti-to pet JUL 1 6 i?;j Book Slip425wi-7,'53(A8998s4)458 _J I 12hh2L COLUTE California. Division ox Mines* Bulletin. rrni nflY GEOLOGI f3 Call Number: TN2ii C3 A3 A3 / 114424