Z4 
 
 C3 - 
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 STATE OF CALIFORNIA 
 DEPARTMENT OF NATURAL RESOURCES 
 
 GEOLOGY OF THE 
 
 TESLA QUADRANGLE 
 
 CALIFORNIA 
 
 SURE 
 
 BULLETIN 140 
 
 1948 
 
 DIVISION OF MINES 
 
 FERRY BUILDING, SAN FRANCISCO 
 
LJBRAK i 
 
 UNIVERSITY OF CALIFORNIA 
 
 DAVIS 
 
STATE OF CALIFORNIA 
 EARL WARREN, Governor 
 
 DEPARTMENT OF NATURAL RESOURCES 
 
 WARREN T. HANNUM, Director 
 
 DIVISION OF MINES 
 
 FERRY BUII-DING, SAN FRANCISCO 
 
 OLAF P. JENKINS, Chief 
 
 SAN FRANCISCO 
 
 BULLETIN 140 
 
 JULY 1948 
 
 GEOLOGY OF THE 
 
 TESLA QUADRANGLE 
 
 CALIFORNIA 
 
 By 
 ARTHUR S. HUEY 
 
 LIBRARY 
 
 JJNIVERSJTY or CALIFORNIA 
 DAVIS 
 
LETTER OF TRANSMITTAL 
 
 To His Excellency 
 
 The Honorable Earl Warren 
 
 Governor of the State of California 
 
 Sir: 
 
 I have the honor to transmit herewith Bulletin 140, * ' Geology of the 
 Tesla Quadrangle, California", prepared under the direction of Olaf P. 
 Jenkins, Chief, Division of Mines, Department of Natural Eesources. 
 This report includes detailed geologic and economic mineral maps of a 
 specific area in Alameda and San Joaquin Counties. It is one of a series 
 of such reports on specific areas in California which the Division of Mines 
 is publishing. Three previous reports covered the San Benito, Jamesburg, 
 and San Juan Bautista quadrangles. 
 
 The following report and geologic and economic mineral maps of the 
 Tesla quadrangle have been prepared by Arthur S. Huey in partial fulfill- 
 ment of the requirement for the degree of Doctor of Philosophy at the 
 University of California. The report is of particular interest because it 
 describes many typical features of the California Coast Ranges and 
 includes a description of economic mineral resources such as coal, clay, 
 chromite, glass and foundry sand, gravel, lime rock, magnesite, manga- 
 nese, and tuif . The results of this investigation are basic and fundamental 
 to the understanding of the state 's mineral deposits and related geological 
 features. 
 
 Respectively submitted, 
 
 Warren T. Hannum, Director 
 Department of Natural Resources 
 May 4, 1948 
 
 (3) 
 
CONTENTS 
 
 Page 
 
 ABSTRACT 7 
 
 INTRODUCTION 7 
 
 Location and accessibility 7 
 
 Field Work 9 
 
 Acknowledgments 9 
 
 Previous work 10 
 
 GEOGRAPHY 11 
 
 Relief and topography 11 
 
 Climate and vegetation 11 
 
 Drainage and water supply 12 
 
 Hetch-Hetchy water supply 13 
 
 STRATIGRAPHY 14 
 
 General statement 14 
 
 Jurassic system 15 
 
 Franciscan formation and related igneous rocks 15 
 
 Cretaceous system 23 
 
 Horsetown formation 23 
 
 Panoche formation 24 
 
 Moreno Grande formation 31 
 
 Tertiary system 38 
 
 Eocene series 33 
 
 Tesla formation 33 
 
 Miocene series 38 
 
 Oursan? sandstone 38 
 
 Cierbo formation -- 40 
 
 Neroly formation 42 
 
 Tertiary-Quaternary system . 47 
 
 Pliocene-Pleistocene series . 47 
 
 Livermore gravels 47 
 
 Tulare formation . 48 
 
 Quaternary system 49 
 
 Terrace deposits and alluvium 49 
 
 STRUCTURE 49 
 
 Folds 49 
 
 Faults 52 
 
 Summary-analysis 56 
 
 OUTLINE OF THE GEOLOGIC HISTORY 58 
 
 MINERAL RESOURCES 59 
 
 Chromite 59 
 
 Clav 60 
 
 Coal 60 
 
 Glass and foundry sand 61 
 
 Gravel and rock 62 
 
 Lime rock . 62 
 
 Magnesite . 62 
 
 Manganese 62 
 
 Petroleum 66 
 
 Tuff 67 
 
 REGISTER OF FOSSIL LOCALITIES 68 
 
 BIBLIOGRAPHY 70 
 
 INDEX 73 
 
 (5) 
 
ILLUSTRATIONS 
 
 Page 
 Figure 1. Index map showing location of Tesla quadrangle 8 
 
 2. Generalized columnar section, Tesla quadrangle 16 
 
 3. Diagram showing regional structural trends, Tesla quadrangle 57 
 
 Plate 1. Geologic map of Tesla quadrangle In pocket 
 
 2. Economic mineral map of Tesla quadrangle In pocket 
 
 3. Geologic structure sections, Tesla quadrangle In pocket 
 
 4. Relief map of Tesla quadrangle, showing important place names 32-33 
 
 5. A, Bedded Franciscan chert in Arroyo Mocho. B, Pillow structure 
 
 in Franciscan basalt along Arroyo Mocho road 32-33 
 
 6. A, Outcrop of white sand of the Tesla formation in Corral Hollow. 
 
 B, Copy of old photograph showing Tesla mining camp, about 
 1910 32-33 
 
 7. A. Cross-bedded and pebbly white sand of Cierbo formation. B, 
 
 Angular unconformity between Cierbo formation and underlying 
 Panoche formation 32-33 
 
 8. A, Andesitic boulder conglomerate of Neroly formation. B, Basal 
 
 andesitic gravels of Neroly formation resting with angular uncon- 
 formity on sandstones and shales of Panoche formation 32-33 
 
 9. A. Slickensided fault-plane surface in GreenvUle fault zone. B, 
 
 Sharp fold in Neroly blue sandstone 32-33 
 
 10. Boulders from Panoche conglomerate on Rocky Ridge 32-33 
 
 11. Andesitic boulders from Neroly conglomerate 32-33 
 
 (6 ) 
 
GEOLOGY OF THE TESLA QUADRANGLE, CALIFORNIA* 
 
 By Arthur S. Huet ** 
 
 ABSTRACT 
 
 The Tesla quadrangle comprises an area of about 240 square miles in Alameda 
 and San Joaquin Counties, California. The area includes part of the Diablo Range 
 and small portions of the Livermore and San Joaquin Valleys. 
 
 The stratigraphic section is typical of the California Coast Ranges ; the rocks 
 range in age from Jurassic to Recent. The oldest rocks, the Jurassic Franciscan group, 
 consisting chiefly of sandstone, shale, and chert, occupy most of the southern half of 
 the quadrangle. Serpentine occurs in large irregular masses, and other rocks, such as 
 diabase, basalt, and glaucophane schist, are restricted in their occurrence. The Creta- 
 ceous rocks include the Horsetown, Panoche, and Moreno Grande formations. The 
 Moreno Grande is an enlargement of the original Moreno to include equivalents of the 
 Pachydiscus silt member, which were mapped as part of the Moreno north of Pacheco 
 Pass. The Tesla formation of middle Eocene age includes white and buff sands, car- 
 bonaceous shales, anauxitic clays, and a little coal. Sandstone formerly mapped as 
 Briones in Arroyo Valle is regarded as Oursan (?) sand.stone (middle Miocene). The 
 upper Miocene is represented by two members of the San Pablo group, the Cierbo 
 white pebbly sands, and the Neroly formation consisting of blue sandstones, andesitic 
 boulder conglomerates, and tuffaceous shales. Fringing the southeast margin of Liver- 
 more Valley are the Livermore gravels (Plio-Pleistocene) . The Tulare formation 
 (Plio-Pleistocene) is found only in the extreme northeast part of the area. Quaternary 
 terrace deposits, landslides, and alluvium complete the stratigraphic column. 
 
 The rocks are involved in a complex of folds and faults. The major faults are 
 classified into two groups : (1) the transverse faults which trend eastward, and (2) the 
 longitudinal faults which trend northwestward. The average trend of the regional fold- 
 ing is intermediate between the trends of the two fault groups. The principal time of 
 regional deformation was post-Neroly, possibly Pleistocene. 
 
 Economic resources include coal, clay, chromite, glass and foundry sand, gravel, 
 lime rock, magnesite, manganese, and tuff. Important contributions to the state's out- 
 put of manganese have been made by the many manganese properties in the area. About 
 25 wells have been drilled and abandoned in an unsuccessful search for a commercial 
 accumulation of petroleum. 
 
 INTRODUCTION 
 
 The geology of the Tesla quadrangle is typical of the Coast Ranges 
 of California. Rock formations ranging in age from Jurassic to Recent 
 are involved in a complex of folds and faults. Sedimentary rocks pre- 
 dominate ; igneous rocks are limited in occurrence. Economic interest in 
 the area is furnished by minor occurrences of such minerals as coal, clay, 
 chromite, magnesite, manganese, glass and foundry sand, and petroleum. 
 
 Location and Accessibility 
 
 The Tesla quadrangle comprises an area of about 240 square miles 
 covering parts of Alameda and San Joaquin Counties, California. 
 Its location with reference to neighboring towns and gas fields of central 
 California is shown on the accompanying index map (fig. 1). The area 
 includes a part of the Diablo Range and small portions of the Livermore 
 and San Joaquin Valleys. No towns are located within the area. Alta- 
 mont, Greenville, and Midway in the northern part of the area are rail- 
 road sidings and maintenance stations. The quadrangle takes its name 
 from the old abandoned mining camp of Tesla, which once had a popu- 
 lation of two thousand but today has only tailing dumps and foundation 
 scars to indicate a former site of development. 
 
 • Based upon a dissertation submitted in partial satisfaction of the requirements 
 for the degree of Doctor of Philosophy in Geology, in the Graduate Division of the 
 University of California, Berkeley, California, 1940. Manuscript submitted to the 
 Division of Mines for publication October 1947. 
 
 ** Geologist, The Hancock Oil Company, Long- Beach, California. 
 
 (7) 
 
GEOLOGY OF TESLA QUADRANGLE 
 
 Bull. 140 
 
 Figure 1. Index map, showing location of Tesla quadrangle. 
 
J -J i I I I : 
 I' J' K' L'Im'N' O' 
 
INTRODUTION V 
 
 The area is quite accessible. It is best reached from Oakland on the 
 west or from points in the San Joaquin Valley on the east by way of 
 U. S. Highway 50. This new four-lane highway replaces the old winding 
 Altamont Pass road as the main carrier of east-west traffic in the north- 
 ern part of the area. To the south, other roads which cross the range are 
 the Patterson Pass road and the Tesla road into Corral Hollow. A sur- 
 faced road in Arroyo Mocho crosses the area diagonally and leads from 
 Livermore Valley southeastward beyond the limits of the quadrangle 
 to Mt. Hamilton. The road into Arroyo Valle from Livermore is surfaced 
 in part and ends blindly where the canyon narrows in Franciscan rocks. 
 Other roads, generally in poor condition and private, reach to various 
 parts of the area. The only areas of difficult accessibility are in the 
 southern third of the quadrangle where the relief is greatest and the 
 country has not warranted development. 
 
 The Western Pacific and the Southern Pacific Railroads cross the 
 area in the northern part through Altamont Pass.' The branch railroad 
 shown on the original quadrangle map in Corral Hollow has long been 
 removed since the coal and clay development ceased. 
 
 Field Work 
 
 About 6 months were spent in the field during the summers of 1934, 
 1935, and 1936. Numerous week-end trips were made into the area from 
 1937-40 to complete the study. Supporting the field work were laboratory 
 and general research done principally at the University of California, 
 Berkeley, California. Geologic observations were plotted on the U. S. 
 Geological Survey topographic map, the Tesla 15-minute quadrangle, 
 contour interval 50 feet, scale 1 :62,500. The townships of this quadrangle 
 take survey reference from the Mt. Diablo baseline and meridian. 
 
 In 1940 the Agricultural Adjustment Administration of the U. S. 
 Department of Agriculture had the region photographed from the air 
 as a part of an extensive areal survey of agricultural and grazing areas 
 in California. Emergency measures during World War II made prints 
 of these aerial photographs unavailable to the general public. The writer 
 has not had an opportunity to review the geologic mapping in the field 
 with the aid of these photographs but has examined under the stereo- 
 scope photographs of parts of the area. The use of these photographs 
 would facilitate any future detailed investigations in the field. 
 
 Acknowledgments 
 
 This investigation was done under the direction of Dr. N. L. Talia- 
 ferro of the Department of Geological Sciences of the University of 
 California, Berkeley. Others of the University of California faculty who 
 gave helpful suggestions or criticism were Professors G. D. Louderback, 
 C. D. Hulin, C. A. Anderson, and the late B. L. Clark. Assistance with 
 the paleontology of the field collections was contributed by Dr. R. A. 
 Bramkamp, Dr. Arthur S. Campbell, Dr. R. A. Stirton, Mrs. P. Rossello 
 Nicholson, and the late Dr. F. M. Anderson. Paleobotanical identifica- 
 tions were contributed by Dr. R. W. Chancy and Dr. Carlton Condit. 
 Visitors in the field included Dr. Cordell Durrell of the University of 
 California, Los Angeles, and Dr. P. W. Reinhart, Shell Oil Company, 
 Incorporated. Mr. M. J. Bartell of the San Francisco Engineering 
 Department was very cooperative concerning data on the Hetch-Hetchy 
 
•v.. 
 
 S N 
 
 V, 
 
 MAPI 
 
 SAN FRANCIS 
 
INTRODUTION 9 
 
 The area is quite accessible. It is best reached from Oakland on the 
 west or from points in the San Joaquin Valley on the east by way of 
 U. S. Highway 50. This new four-lane highway replaces the old winding 
 Altamont Pass road as the main carrier of east-west traffic in the north- 
 ern part of the area. To the south, other roads which cross the range are 
 the Patterson Pass road and the Tesla road into Corral Hollow. A sur- 
 faced road in Arroyo Mocho crosses the area diagonally and leads from 
 Livermore Valley southeastward beyond the limits of the quadrangle 
 to Mt. Hamilton. The road into Arroyo Valle from Livermore is surfaced 
 in part and ends blindly where the canyon narrows in Franciscan rocks. 
 Other roads, generally in poor condition and private, reach to various 
 parts of the area. The only areas of difficult accessibility are in the 
 southern third of the quadrangle where the relief is greatest and the 
 country has not warranted development. 
 
 The Western Pacific and the Southern Pacific Railroads cross the 
 area in the northern part through Altamont Pass.' The branch railroad 
 shown on the original quadrangle map in Corral Hollow has long been 
 removed since the coal and clay development ceased. 
 
 Field Work 
 
 About 6 months were spent in the field during the summers of 1934, 
 1935, and 1936. Numerous week-end trips were made into the area from 
 1937-40 to complete the study. Supporting the field work were laboratory 
 and general research done principally at the University of California, 
 Berkeley, California. Geologic observations were plotted on the U. S. 
 Geological Survey topographic map, the Tesla 15-minute quadrangle, 
 contour interval 50 feet, scale 1 :62,500. The townships of this quadrangle 
 take survey reference from the Mt. Diablo baseline and meridian. 
 
 In 1940 the Agricultural Adjustment Administration of the U. S. 
 Department of Agriculture had the region photographed from the air 
 as a part of an extensive areal survey of agricultural and grazing areas 
 in California. Emergency measures during "World War II made prints 
 of these aerial photographs unavailable to the general public. The writer 
 has not had an opportunity to review the geologic mapping in the field 
 with the aid of these photographs but has examined under the stereo- 
 scope photographs of parts of the area. The use of these photographs 
 would facilitate any future detailed investigations in the field. 
 
 Acknowledgments 
 
 This investigation was done under the direction of Dr. N. L. Talia- 
 ferro of the Department of Geological Sciences of the University of 
 California, Berkeley. Others of the University of California faculty who 
 gave helpful suggestions or criticism were Professors G. D. Louderback, 
 C. D. Hulin, C. A. Anderson, and the late B. L. Clark. Assistance with 
 the paleontology of the field collections was contributed by Dr. R. A. 
 Bramkamp, Dr. Arthur S. Campbell, Dr. R. A. Stirton, Mrs. P. Rossello 
 Nicholson, and the late Dr. F. M. Anderson. Paleobotanical identifica- 
 tions were contributed by Dr. R. W. Chancy and Dr. Carlton Condit. 
 Visitors in the field included Dr. Cordell Durrell of the University of 
 California, Los Angeles, and Dr. P. W. Reinhart, Shell Oil Company, 
 Incorporated. Mr. M, J. Bartell of the San Francisco Engineering 
 Department was very cooperative concerning data on the Hetch-Hetchy 
 
10 GEOLOGY OP TESLA QUADRANGLE [Bull. 140 
 
 tunnel which crosses the Tesla quadrangle as a part of a development 
 for supplying water to the city of San Francisco. Others to whom the 
 author wishes to express appreciation are Dr. F. P. Vickery of the 
 Sacramento Junior College, Dr. Paul P. Goudkoff, and Mr. Alfred Vitt, 
 Seaboard Oil Corporation. The hospitality and courtesies of many of 
 the ranchers are also acknowledged. 
 
 Previous Work 
 
 No comprehensive report on the geology of the Tesla quadrangle 
 has so far been published, but many workers have made contributions 
 toward an understanding of the geologj^ of the area. Among the earliest 
 writings are some notes by Brewer ^ describing the occurrence of fossil 
 leaves in Corral Hollow and predicting economic failure for the Tesla 
 coal mines then in operation. Volume I of the Geological Survey of Cali- 
 fornia as edited by -Whitney (1865) included two short cross-sections 
 in Corral Hollow, an analysis of the Tesla coal, and a few notes by 
 W. M. Gabb on some brackish-water fossils (Eocene) in Corral Hollow. 
 The Pliocene tuffs and conglomerates containing andesite boulders whicli 
 occur north of Corral Hollow are given early reference in the writings 
 of Turner -. The ' ' San Pablo formation " as it occurs north of Corral 
 Hollow was briefly described by Weaver ^. The water-supply and mar- 
 ginal geology of Livermore Valley were discussed in separate papers 
 by Lawson * and Branner ^. The report by Anderson and Pack ^ on 
 the geology and oil resources of the west border of the San Joaquin 
 Valley includes a sketch map of the geology of the northern part of 
 the Tesla quadrangle based upon reconnaissance mapping by R. W. Pack 
 and E. L. Ickes. This report also describes the formations present and 
 gives a brief history of the early wells drilled for oil in the Tesla area. 
 
 For a number of successive summers around the early twenties, the 
 Stanford University Geological Survey was engaged in mapping the 
 Tesla and several neighboring quadrangles, including the Pleasanton, 
 San Jose, and Mt. Hamilton quadrangles. The maps and full results of 
 this work were never published, but Vickery '^ in a doctor 's thesis 
 analyzing the geologic structure of the Livermore region introduced 
 a generalized map of the above named quadrangles as surveyed by the 
 Stanford parties. The published form of this structural analysis by 
 Vickery ^ did not include the generalized map of the four quadrangles. 
 Clark ^ and Taif ^^, writing separately on the Mt. Diablo region, made 
 
 1 Brewer, W. H., Up and down California in 1860-64, Yale Univ. Press, 1930. 
 
 2 Turner, H. W., The geology of Mt. Diablo: Geol. Soc. America Bull., vol. 2, pp. 
 383-414, 1891. . . . Rocks of the Coast Ranges of California: Jour. Geology, vol. 6, 
 pp. 493-499, 1898. 
 
 3 Weaver, Charles E., Stratigraphy and paleontology of the San Pablo formation 
 in middle California: Univ. California, Dept. Geol. Sci. Bull., vol. 5, pp. 243-269, 1909. 
 
 * Lawson, Andrew C., Report on the geology and underground water supply of 
 Livermore Valley, in The future water supply of San Francisco, a report ... by the 
 Spring Valley Water Co., pp. 223-230, 1912. 
 
 5 Branner, J. C, Report on the geology of Livermore Valley, in The future water 
 supply of San Francisco, a report ... by the Spring Valley Water Co., pp. 203-222, 
 1912. 
 
 8 Anderson, R., and Pack, R. W., Geology and oil resources of the west border of 
 the San Joaquin Valley north of Coalinga : U. S. Geol. Survey Bull. 603, 1915. 
 
 T Vickery, P. P., The structural dynamics of the Livermore region, Ph.D. thesis, 
 Stanford Univ., 1925 (unpublished). 
 
 8 Vickery, F. P., The structural dynamics of the Livermore region : Jour. Geology, 
 vol. 33, pp. 608-628, 1925. 
 
 9 Clark, Bruce L., Tectonics of the Mt. Diablo and Coalinga areas, middle Coast 
 Ranges of California: Geol. Soc. America Bull., vol. 46, pp. 1025-1078, 1935. 
 
 i»Taff, J. A., Geology of Mt. Diablo and vicinity: Geol. Soc. America Bull., vol. 46, 
 pp. 1079-1100, 1935. 
 
GEOGRAPHY 11 
 
 brief references to the geology in parts of the Tesla quadrangle. The 
 stratigraphy of the Tesla quadrangle was discussed by Huey ^^. Allen ^^ 
 described the occurrence of Eocene anauxitic clays and sands in Corral 
 Hollow. The most recent paper is one by Campbell and Clark ^^ describ- 
 ing the Upper Cretaceous radiolarian fauna contained in a sample of 
 limestone concretion collected by this writer near Corral Hollow. 
 
 Besides the published works mentioned above, there are several 
 unpublished reports on the geology of parts of the area, such as the 
 geological reports on the Hetch-Hetchy project made by Bailey Willis 
 and G. L. Green for the San Francisco Engineering Department and 
 various private geological investigations made by oil company geologists. 
 
 GEOGRAPHY 
 Relief and Topography 
 
 The Tesla quadrangle contains portions of three topographic units : 
 Livermore Valley, San Joaquin Valley, and the Diablo Range. Liver- 
 more Vallej^ in the northwestern part of the area is a surface of low 
 relief; average elevation is 550 feet above sea-level. A part of the San 
 Joaquin Valley which cuts across tlie northeast corner of the quadrangle 
 contains the lowest elevation in the area, approximately 95 feet above 
 sea-level and is bounded approximately by the 250-foot contour line. 
 The relief of the main topographic unit, the Diablo Range, increases 
 in general toward the south. In the northern part of the area in rocks 
 of Cretaceous and Tertiary age, the hills are smooth and rounded, and 
 elevations range from about 500 feet to more than 2000 feet above sea- 
 level. South of Corral Hollow in rocks principally of the Franciscan 
 group, the topography is higher, more rugged, and characterized by 
 deep youthful canyons and long smooth-topped ridges. Two thousand 
 feet of relief is not uncommon from the bottoms of many of the arroyos 
 to the tops of the ridges. The highest recorded elevation, 3820 feet above 
 sea-level, is on Rose Flat near the southwestern corner of the quadrangle. 
 
 The relief of the area is well represented in plate 4, a photograph 
 of a portion of a plaster relief model of the San Francisco Bay region 
 on exhibit in the geological museum in Bacon Hall, University of Cali- 
 fornia, Berkeley. Elevations and important place names have been 
 added to aid the reader in his orientation of the area. 
 
 The physiographic state of development is late youth, and the 
 drainage pattern of the area is well developed. The approximate accor- 
 dant relationship of the summit levels along the ridges in the southern 
 high country is suggestive of an old erosional surface of low relief, 
 which in late geologic time was uplifted with a gentle northwesterly 
 tilt and later dissected by erosion. Prominent terraces in Arroyo Mocho 
 and Corral Hollow are indicative of recent uplift in at least three stages. 
 
 Climate and Vegetation 
 
 Semi-aridity characterizes the climate of the region. Summers are 
 dry and hot, and day temperatures often reach 100 degrees Fahrenheit. 
 Low morning fogs are often driven in from the west by the winds, and 
 late summer afternoons are occasional!}' marked by winds of consid- 
 
 uHuey, Arthur S., Stratigraphy of the Tesla quadrangle, California (abstract) : 
 Geo!. Soc. America Proc. 1936, pp. 335-336, 1937. 
 
 ^ Allen, V. T., Eocene anauxitic clays and sands in the Coast Range of California : 
 Geol. Soc. America Bull., vol. 52, pp. 271-294, 1941. 
 
 "Campbell, A. S., and Clark, B. L., Radiolaria from Upper Cretaceous of middle 
 California: Geol. Soc. America Special Paper 57, pp. 1-61, 1944. 
 
12 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 erable velocity. Spring and fall are quite comfortable and regionally 
 picturesque. The mean annual temperature is approximately 58 degrees 
 Fahrenheit, and temperatures below freezing are common in the winter. 
 Rainfall is concentrated chiefly in the winter months, and some snow 
 falls, principally at the higher elevations. The average seasonal rainfall 
 ranges from about 10 inches in the low northeastern part of the area 
 to about 26 inches in the high southwestern portion. 
 
 The vegetation cover varies with elevation, distribution of rainfall, 
 rock or soil type, directional slope, and local features, such as streams 
 and springs. Most of the area is covered by a short grass, chiefly natu- 
 ralized wild oat. Sage is sparsely distributed. Cottonwood, sycamore, 
 willow, pipestem, and oak occur along stream courses and at springs. 
 Trees are more plentiful in the southern higher portion of the region 
 and include several varieties of oak, cypress, buckeye, and juniper. A 
 dense cover of chaparral and manzanita is common over areas of serpen- 
 tinized rock. The California Experiment Station at the University of 
 California, Berkeley, has collected data on plant species occurring at 
 different elevations in the area, and such information is available at 
 the station. 
 
 As a whole the region is open and the vegetation cover does not 
 interfere with geological work. The best exposures are found along 
 stream courses and in highway and railroad cuts. Exposures over much 
 of the area are poor to absent, owing to a heavy soil mantle, and in these 
 soil mantled areas special features such as soil color, pebble content, or 
 vegetation contrast aid in the delineation of a formational contact. 
 
 Drainage and Water Supply 
 
 Although the drainage pattern of the area is well developed, the 
 streams are all intermittent. The smaller gullies and creek bottoms are 
 dry most of the year and contain water only during or for short periods 
 after a rain. The larger water-courses, including Arroyo Valle, Arroyo 
 Mocho, Corral Hollow Creek, and Mitchell Ravine are in the southern 
 half of the quadrangle. These streams drain the areas of greatest relief 
 and rainfall. They contain running water until the middle of summer, 
 after which the water sinks below the surface and reappears as water- 
 holes at intervals along the courses of the streams. The directional trend 
 of these major drainages is in general northwesterly in conformance 
 with the main structural trends in the southern part of the area. Arroyo 
 Valle and Arroyo Mocho drain into Livermore Valley and contribute 
 greatly to the subsurface water supply in the valley. For further infor- 
 mation on the water supply of Livermore Valley, the reader is referred 
 to the writings of Lawson,^^ Branner,^^ and M. B. Smith. ^^ Near its 
 source, Corral Hollow Creek flows northwestward, but makes a sharp 
 change of direction near Tesla and flows eastward toward the San 
 Joaquin Valley. The existence of what may be a wind-gap about 1000 
 feet north of the southwest corner of sec. 35, T. 3 S., R. 3 E., is sug- 
 gestive that Corral Hollow Creek once drained out through Arroyo Seco 
 into Livermore Valley but was captured and diverted toward the San 
 Joaquin Valley by subsequent drainage developing in Corral Hollow 
 in late geologic time. 
 
 " Op. cit. 
 ^ Op. cit. 
 
 i« Smith, M. B., Ground water in the Livermore Valley, California, Master's thesis, 
 Stanford University, 1934 (unpublished). 
 
GEOGRAPHY 13 
 
 Springs are common throughout the area, occurring principally at 
 stratigraphic boundaries and along fault traces. The represejitation of 
 many of these springs on the geologic map illustrates their geologic rela- 
 tionship. The waters of only a few of these springs are good for human 
 consumption; the others are alkaline, sulfurous, or otherwise miner- 
 alized. 
 
 Soil erosion is active in many parts of the area, where the grass 
 cover is thin. Hillsides and valleys are being deeply dissected, and unless 
 some restrictive measures are taken by the ranchers or proper authorities, 
 serious damage to grazing lands and roadways will result. 
 
 Hetch-Hetchy Water Supply 
 
 The city and county of San Francisco at a total cost of about $105,- 
 000,000 constructed the Hetch-Hetchy water system to carry water 
 from two impounding reservoirs in the Sierra Nevada to the San Fran- 
 cisco Bay region. The first bond issue to buy lands was authorized in 
 1908, and 26 years later, in October 1934, the Hetch-Hetchy water was 
 admitted to the system. The water is carried along a system of 81.9 
 miles of tunnels and 72.7 miles of pipeline. The Coast Eange division 
 of the aqueduct includes a main tunnel 25 miles in length, of which 
 about 14 miles is routed across the Tesla quadrangle. The finished tunnel 
 is 10.5 feet in diameter and has a concrete lining which ranges in thick- 
 ness from 6 inches to 3 feet. The tunnel is constructed on a grade of 
 about 3 feet per mile and has a capacity of about 250,000,000 gallons 
 of water daily. Five shafts were sunk to the tunnel grade. In the Tesla 
 quadrangle, shafts were located in Arroyo Valle, Arroyo Mocho, and 
 Mitchell Ravine. Another shaft, the Thomas, was located just east of 
 the edge of the quadrangle. From cross-cuts at the bases of the shafts, the 
 tunnel was driven both east and west until segments of the tunnel were 
 joined between shafts. The sinking of the shafts began in the spring of 
 1927, and the last section of the tunnel was bored through in January 
 of 1934. The cross-cuts at the bases of the shafts were so constructed that 
 a parallel tunnel can be made from these control stations sometime in 
 the future. 
 
 The route of the tunnel across the Tesla quadrangle is represented 
 along the line of section H-H' on plate 2. During the driving of the 
 tunnel some changes in route were made in an attempt to gain bet- 
 ter ground, as in the vicinity of Corral Hollow Creek where enormous 
 underground pressures were encountered in the core of a tightly over- 
 turned anticline. Through the courtesy of Mr. M. J. Bartell of the San 
 Francisco Engineering Department, the writer was privileged to read 
 the geological reports on the tunnel by Bailey "Willis and G. L. Green, 
 and in section H-H' their tunnel data have been combined with the 
 surface geology. The writer was also allowed to examine the wall-rock 
 samples which are kept in core-sheds in Livermore. The only unusual 
 rock type observed was some crushed granodiorite encountered about 
 a mile east of the Arroyo Valle shaft where it underlies the Livermore 
 gravels. 
 
 The character of the formations penetrated in the tunnel and spe- 
 cial geological features which were encountered will be brought out in 
 subsequent pages, but a few interesting general facts are presented 
 in this preliminary discussion. The progress in driving the tunnel 
 through the various geologic formations, expressed in terms of feet of 
 tunnel per month, is given in table 1. 
 
14 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 Talle 1. Rate of tininel progress through geologic formations * 
 
 Age or formation Lithology Feet per month of 
 
 tunnelling 
 
 Tulare Sands and blue clay 553 
 
 Livermore Gravels and sands 325 
 
 Clays and shales 130 to 196 
 
 Neroly (San Pablo) Sandstone 475 
 
 Upper Cretaceous Shale 443 
 
 Sandstone 360 
 
 Lower Cretaceous Shale 310 
 
 Franciscan Sandstone and shale 343 
 
 Sei-pentine and schist 217 
 
 Shattered zones 130 to 236 
 
 * After B. Willis. 
 
 Mr. Bartell in a discussion with the writer presented some inter- 
 esting observations on ' ' working-ground, ' ' which hampered the driving 
 of the tunnel at numerous places. The squeezing-in process was some- 
 times slow, extending over 2 weeks, or even several months. Ground 
 moved in from the top or any part of the tunnel circumference, and 
 ground upwellings with sufficient pressure to crumple the concrete floor 
 of the tunnel were common. According to Bartell, there was a release 
 of static pressure as the tunnel face was extended. He estimated that 
 500 cubic feet of material at the surface would occupy about 499 cubic 
 feet at a depth of 1800 feet underground, and that everj'^ cubic foot 
 of material squeezed into the tunnel represented a release of pressure 
 of about 2000 pounds per square inch on about 500 cubic feet of material 
 adjacent to the tunnel. These figures were theoretical, and variations 
 occurred owing to heterogeneity of rock, parting planes, and other causes. 
 Zones of swelling-ground generate considerable heat by friction, and 
 Bartell, using a friction factor of 0.3, computed that working ground 
 should show a temperature rise of about 15 degrees Fahrenheit through 
 the loss of 2300 feet head in friction. Accordingly, during the driving 
 of the tunnel, temperature observations were made, and a rise of tem- 
 perature often served as a forewarning of working-ground in time to 
 reenforce the timbering in the tunnel. The temperature at the bottom 
 of the shafts averaged 64 degrees Fahrenheit, the average wall-rock 
 temperature was 70 to 76 degrees Fahrenheit, and that of working- 
 ground about 85 degrees Fahrenheit. The tunnel ventilating system, 
 which removed about 14,000 cubic feet of air per minute at 4 pounds 
 pressure per square inch, provided a means of measuring the heat 
 removed from the tunnels. About 6,000,000 B.t.u. of heat was taken 
 from the tunnel daily, and Bartell estimated that for every cubic foot 
 of ground squeezed into the tunnel there were generated 240,000 B.t.u. 
 of heat. 
 
 STRATIGRAPHY 
 
 General Statement 
 A variety of rock types and a stratigraphic section typical of the 
 California Coast Ranges are present in the Tesla quadrangle. Sedimen- 
 tary rocks predominate and include many interesting varieties, such as 
 radiolarian cherts, manganiferous cherts, white quartz sands, coal, tuff, 
 blue opaline-coated sands, and andesitic boulder conglomerates. Igneous 
 and metamorphic rocks are confined to areas of Franciscan rocks in the 
 southern part of the quadrangle. 
 
STRATIGRAPHY 15 
 
 The formations range in age from Jurassic to Recent. Some of the 
 formations that are present in one part of the area are absent in other 
 parts, and nowhere in the quadrangle do all of the formations occur in 
 a complete stratigraphic sequence. The accompanying chart (fig. 2) pre- 
 sents a composite columnar section. All of the formations, except the 
 Tesla and Moreno Grande, have been named by previous workers and 
 are briefly described in the Lexicon of Geologic Names of the United 
 States by Wilmarth.^" 
 
 Jurassic System 
 
 Franciscan Formation and Related Igneous Rocks 
 
 The oldest rocks in the Tesla quadrangle are comprised in the Fran- 
 ciscan formation of Jurassic age. Sedimentary rocks consisting of sand- 
 stone and some shale and chert constitute the bulk of the formation, and 
 limited occurrences of typical Franciscan metamorphic and volcanic 
 rocks complete the group. Associated with these rocks are intrusions of 
 diabase, basalt, and serpentinized gabbro and peridotite. 
 
 In mapping the Franciscan an attempt was made to differentiate 
 areally the occurrences of the several rock types, to interpret the gen- 
 eral regional structure and to zone or group the rocks stratigraphieally. 
 Those areas which consisted of a monotonous succession of beds of sand- 
 stone, shale, and chert were mapped in a rapid but detailed reconnais- 
 sance manner; more detailed observations were attempted in the more 
 interesting and critical areas, such as the borders of serpentinized intru- 
 sions, areas of glaucophane schist, and fault zones, and along contacts 
 with j^ounger formations. 
 
 Distrilyution and Thickness. The Franciscan formation and related 
 intrusive rocks comprise most of the southern half of the Tesla quad- 
 rangle and extend into adjacent quadrangles. A bottom to the formation 
 is not exposed, nor can a top be distinguished. Difficulty was experienced 
 in attempting to interpret a stratigraphic section across the folds and 
 faults which involve the Franciscan rocks because of the following con- 
 ditions : absence of marker beds of distinctive lithology or fossil content ; 
 lack of distinctive variation or grouping of the lithology vertically in the 
 section; and general discontinuity of outcrop. Consequently, an attempt 
 to measure a stratigraphic section in these rocks was abandoned. The 
 thickness of the sediments, as obtained graphically from cross-sections 
 E-E' and H-H' (pi. 3), is about 12,000 feet. Tolman^^ reported a section 
 of 15,000 feet of Franciscan sediments in this area, and divided the sec- 
 tion into three members. He took a dense bluish-gray arkosic sandstone 
 in Corral Hollow Creek as the lower part of the section, the "Corral 
 Hollow shales ' ' with folded and crumpled cherts as the middle member, 
 and the ' ' Oak Ridge sandstone ' ' as the upper member. As Oak Ridge is 
 a divide in the northwest corner of the Mt. Hamilton quadrangle, Tolman 
 probably extended his section into this area adjoining on the south. In 
 the Tesla area sandstone is the predominant rock type throughout the 
 section of Franciscan rocks; it is not characteristic only of the upper 
 and lower portions. Likewise, shales and cherts occur througliout the 
 section as interbeds in the sandstones, and although more numerous in 
 
 " Wilmarth, M. Grace, Lexicon of geologic names of the United States : U. S. Geol. 
 Survey Bull. 896, 1938. 
 
 1** Tolman, C. F., and others, Nature and science on the Pacific Coast, San Fran- 
 cisco, Paul Elder and Co., 1915. 
 
16 
 
 GEOLOGY OF TESLA QUADRANGLE 
 
 [Bull. 140 
 
 GENERALIZED COLUMNAR SECTION -TESLA QUADRANGLE 
 
 FORMATION 
 
 TH-CKNCSS 
 
 DESCOIPTION 
 
 QUATERNAgy 
 
 Ta.'-racg. da.posi•^s 
 
 PLIO- 
 PLEI5T0CENE 
 
 Tulare. 
 
 Livcrmor* 
 Gravels 
 
 UPPER. 
 
 MIOCENE 
 
 (5r«3l'e/5, sonds. 
 
 Corrf-inenial deposits oP qravais. 
 sands, clays. 
 
 3h3/Q,s, blue 33nds-f-onc, i'uffs. 
 
 Ciorbo 
 
 MIDDLE 
 MIOCENE 
 
 Oursan ? 
 
 X SO'-TCC' 
 9 
 
 Blue sands-hone., andcsi-hfc conqlomzra-hz-fl, 
 
 Granuli^<z.rou3 whihz sends, buff stands, 
 ^Ltffs, con<^lornz.rs-ha, coal. 
 
 Tan sands-toniz., fuffac<zous sh^.'^s- 
 
 MIDDLE 
 EOCENE 
 
 Tasla 
 
 ■^T+s-: 
 
 Buff sand, vvhi^t, sands, days, 
 {marina) 
 
 Suff sands, chocola^a ahaizs, coal, 
 (brackish - wahir) 
 
 Moreno Grande 
 
 =-'^§=^ 
 
 5 0-6S0 
 
 Buff sands-lone a-f -top locslly. 
 Sil/czous, araillace-ous, and sandy shala^, 
 lin^tzs-hon^ t^oncniz^ians, sandstontt, bzds. 
 
 
 UPPEt^ 
 CR.ETACEOUS 
 
 > ■■.•■<?.: 
 
 Panoche 
 
 4 10,000'* 
 
 Concr^-hionaru and massive sandstone, 
 argillact^ous and sil-hy shales, 
 conqlormra-ha. 
 
 LOWER. 
 CRETACEOUS 
 
 Horsa.+own 
 
 Dark shalas, sands4-on<z 
 
 Sands'hon<z,, shaizs, cheri" lenses, 
 conylomte.ra^e.. 
 
 Pillow basaH-s. 
 
 Glauaophane, schis-h 
 
 3erpenhne, diahase, diorihe-qabbro. 
 
 UPPER 
 JUR^ASSIC 
 
 Franciscan 
 
 and rc.l84«xd 
 infrusiv^, roccs 
 
 --.:Jf.^- 
 
 l5,0OO'? 
 
 
 Explana+ion 
 
 V4rf«,bra+* .fossils 
 
 Invar+abra+a fossils 
 
 (?.adiolaria 
 
 Foraminifcra 
 
 Laaves 
 
 Tuff 
 
 Figure 2 
 
 Figure 2. Generalized columnar section, Tesla quadrangle. 
 
STKATIGRAPHY 17 
 
 the middle portion of the section, they are subordinate and do not con- 
 stitute a special grouping. For these reasons, Tolman 's divisions are not 
 recognized in this report, and the section of Franciscan rocks is left 
 undivided. 
 
 Lithology. Sandstone is the principal sedimentary rock, comprising 
 approximately two-thirds of the Franciscan formation. In outcrop it is 
 characteristically massive, highly jointed and weathered. It is bluish to 
 greenish gray, weathering to greenish brown and buff, well indurated 
 and cemented, frequently cut by quartz veinlets and less commonly by 
 calcite veinlets. Medium grain-size is predominant over coarse or fine. 
 Angularity of grain, denseness of the rock, and an abundance of fresh 
 plagioclase feldspar are characteristic features. Quartz is the pre- 
 dominant mineral of the sandstones averaging about 50 percent of the 
 whole, orthoclase is common and constitutes 10 to 20 percent of the sand- 
 stone, fresh oligoclase and oligoclase-andesine are characteristic and may 
 total 20 percent or more of the mineral assemblage. Muscovite is common, 
 green or brown biotite is usually present, and hornblende and augite are 
 sparse or absent. Minor constituents are magnetite, zircon, pyrite, 
 titanite, and epidote. Calcite is prominent among the secondary min- 
 erals along with chlorite, zoisite, and sericite. Fragments of carbonized 
 wood are found rarely in the sandstone in this area. Davis ^^ and Talia- 
 ferro ^^ have presented chemical analyses of Franciscan sandstones which 
 indicate a relatively low percentage of silica and a high percentage of 
 soda and potash as compared with the analyses of other sandstones. The 
 high soda content was probably a contributive factor in the formation 
 of glaucophane schist from the sandstone by pneumatolytic meta- 
 morphism. Taliaferro points out that chemical analyses of Franciscan 
 sandstones correspond closely with that of granodiorite, which may have 
 been the main source rock for the sediments. 
 
 Shale, though inconspicuous in outcrop, probably comprises about 
 30 percent of the formation, judging from its abundance in the wall- 
 rock samples from the Hetch-Hetchy tunnel. It is generally dark in 
 color — gray, green, brown, or red^ — and hard, silty, locally argillaceous 
 or siliceous. A slate-like character, probably induced by depth of burial, 
 was possessed by many of the shale samples examined from the Hetch- 
 Hetchy tunnel. Rhythmic alternation of thin bands of shale and chert 
 is common and in such groupings the shale is generally quite siliceous. 
 Fragmentary carbonized plant remains are rare. Shales range through- 
 out the formation interbedded with sandstone and chert, and in no por- 
 tion of the section are they thick enough to allow stratigraphic grouping 
 or mapping as a unit. 
 
 Streamer-like lenses of chert are common throughout the formation 
 and may constitute as much as 5 percent of the formation. Some of these 
 lenses of chert have been represented diagrammatically on the geologic 
 map in order to illustrate the nature of their distribution. A few lenses 
 are traceable for more than a mile. Some are as much as 100 feet thick, 
 but few are thicker. Massive cherts, which are more common than the 
 bedded cherts, are light green, gray, or white in color. Most of the bedded 
 cherts are red, but some are gray in color. They are separated by thin 
 
 18 Davis, E. F., The Franciscan sandstone : Univ. California, Dept. Geol. Sci. Bull., 
 vol. 11, pp. 1-44, 1918. 
 
 -"Taliaferro, N. L., Franciscan-Knoxville problem: Am. Assoc. Petroleum Geol- 
 ogists Bull., vol. 27, pp. 109-219, 1943. 
 
 2—85413 
 
18 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 shale partings. Red cherts in proximity to pillow basalts are particu- 
 larly well developed in Arroyo Valle south to the Devil's Hole in sees. 
 3 and 10, T. 5 S., R. 3 E. Many of the bedding surfaces of the thin- 
 bedded red cherts show an intricate network of quartz veinlets. In 
 places some of the bedded cherts show a strong wavy contortion of the 
 bedding, probably caused by structural deformation prior to final con- 
 solidation of the cherts. In a thin-section of red chert, several radiolarian 
 tests were observed in the form of round specks of clear silica in a micro- 
 granular matrix of chalcedonic silica colored red by iron oxide. Davis ^' 
 pointed out that the term "radiolarian chert" is somewhat misleading, 
 as the contained radiolaria constitute only a fraction of the whole siliceous 
 rock, and that an additional source for the silica of the cherts must be 
 considered. In places the cherts are manganif erous, and locally low-grade 
 manganese deposits are present in intimate association with chert. Other 
 features shown by the cherts include veining, rhythmic banding, intricate 
 brecciation, and metamorphism into glaucophane schist. The cherts occur 
 in lenses throughout the formation and it is not possible to group them 
 into one or two divisions that might correlate with the Ingleside and 
 Sausalito cherts of Lawson 's ^- five divisions of the Franciscan rocks in 
 the San Francisco area. 
 
 Lenses of conglomerate are very restricted in occurrence, and 
 -^nowhere in the area did conglomerate constitute a mappable unit. Most 
 of the pebbles are less than an inch in diameter, but cobbles up to 4 inches 
 in diameter were seen in places. Most of the pebbles are of varicolored 
 cherts, sandstone, and shale, probably re-worked from other portions of 
 the formation, so that the conglomerates in this area are chiefly intra- 
 f ormational in type. Pebbles of granite, quartzite, and porphyritic rocks, 
 which have been noted elsewhere by Davis and Taliaferro and regarded 
 as possibly having been derived from older formations, were not observed. 
 Taliaferro ^^ reports that the Franciscan conglomerates are coarser and 
 more abundant in the western part of the central Coast Ranges, indicat- 
 ing a western source for the material. 
 
 A few thin lenses of limestone enclosed in shale and chert were 
 observed, but they are of very limited occurrence. 
 
 Sedimentary features observed in the Franciscan rocks as they occur 
 in the Tesla quadrangle seem to support the conditions of sedimentation 
 described by Taliaferro.^^ He pictures the deposition of the Franciscan 
 sediments in a shallow geosyncline that developed in a depressed area 
 west of the ancestral Sierra Nevada following the Nevadan orogeny in 
 upper Jurassic time. Reed ^^ held that this geosynclinal basin was divided 
 into two separate basins by a landmass called ' ' Salinia ' ', but Taliaferro -^ 
 presents evidence against the existence of "Salinia" until late in the 
 Cretaceous. In this sinking geosynclinal basin, a great thickness of shal- 
 low marine elastics, and chemical and organic sediments accumulated. 
 
 21 Davis, E. F., The radiolarian cherts of the Franciscan group : Univ. California, 
 Dept. Geol. Sci. Bull., vol. 11, pp. 235-432, 1918. 
 
 =^^ Law^son, Andrew C, U. S. Geol. Survey, Geol. Atlas, San Francisco folio (no. 
 193), 1914. 
 
 28 Op. cit., p. 140. 
 
 2* Taliaferro, N. L., Geologic history and structure of the central Coast Ranges 
 of California: California Div. Mines Bull. 118, pp. 119-162, 1941. . . . Geologic history 
 and correlation of the Jurassic of southwestern Oregon and California : Geol. See. 
 America Bull., vol. 53, pp. 71-112, 1942. . . . Franciscan-Knoxville problem: Am. 
 Assoc. Petroleum Geologists Bull. vol. 27, pp. 109-219, 1943. 
 
 2B Reed, Ralph D., The geology of California, Am. Assoc. Petroleum Geologists, 
 1933 
 
 ' 28 Op. cit, 1943, pp. 125-129. 
 
STRATIGRAPHY 19 
 
 No suggestion as to the probable direction of source for the detrital 
 material is obtained in the Tesla quadrangle, but in other areas Taliaferro 
 has observed a general westward coarsening of some of the Franciscan 
 sediments, indicating a principal western source. The source area is 
 pictured as a rugged highland composed of granodiorite, crystalline 
 schists, quartzites, recrystallized black cherts, and quartz and feldspar 
 porphyries. The lower slopes of the land area were probably well wooded, 
 and after forest fires detrital carbonized wood was supplied to the basin 
 of sedimentation. Rigorous climatic conditions, characterized by heavy 
 rainfall and cold temperatures in the highlands, supplied large swift- 
 fiowing rivers with great quantities of unaltered detritus to be trans- 
 ported to the basin. Interspersed with the clastic sediments thus accumu- 
 lating in the marine basin, were chemical and organic sediments in the 
 form of foraminiferal limestone and radiolarian cherts. Davis,^^ after 
 extensive studies of the cherts, favored the hypothesis that the cherts 
 were formed through the chemical precipitation of colloidal silica belched 
 from submarine volcanic springs. He regarded the radiolarian tests which 
 are sparsely disseminated through some of the cherts as merely entrapped 
 fossils, and not the primary source of the silica for the cherts. He also sug- 
 gested that the rhythmic bedding of the shales and cherts may have been 
 caused by a diagenetic segregation of silica and silt particles intermixed 
 in a colloidal ooze. Widespread vulcanism was active especially in the 
 later stages of Franciscan sedimentation, resulting in the outpouring of 
 pillow basalts and andesites and in the intrusion of dikes, sills, plugs, and 
 laccoliths. No record of the black shale deposition (Knoxville), which 
 according to Taliaferro followed the Franciscan sedimentation in the 
 same basin, was observed in the Tesla quadrangle. 
 
 Metamorphic rocks are of very restricted occurrence, and nowhere in 
 the area do they define a complete border around an igneous body. Glau- 
 cophane schist, the most characteristic type, is generally found as a nar- 
 row band along a portion of the upper contact of a serpentine mass. How- 
 ever, some isolated masses of glaucophane schist occur peculiarlj^ in locali- 
 ties where no igneous rocks are exposed but where there may be subjacent 
 igneous bodies. Glaucophane schist derived from sandstone, shale, or 
 chert is observable in the field, and the contact between schist and 
 unaltered sedimentary rock may be quite sharp. Microscopic examination 
 of a thin-section that was cut across such a boundary showed that the 
 sharpness was retained even under magnification. Although a variety 
 of metamorphic rocks was found, all of the types that were seen had been 
 described from the Franciscan by previous workers. Ten thin-sections 
 were made and examined, and the following types were recorded : glauco- 
 phane-muscovite schist, glaucophane-quartz-biotite schist, glaucophane- 
 quartz-epidote schist, glaucophane-antinolite-muscovite schist, antinolite 
 schist, tremolite schist, quartz-mica schist, and albite-glaucophane schist. 
 These schists were probably developed by local pneumatolytic meta- 
 morphism marginal to or near basic intrusions. Taliaferro ^^ reviews the 
 several theories on the mode of origin of these schists and presents evi- 
 dence to show that their formation probably required the introduction of 
 some soda, magnesia, alumina, lime, water, etc., into the rocks undergoing 
 alteration. 
 
 2^ Davis, E. F., The radiolarian cherts of the Franciscan group: Univ. California, 
 Dept. Geol. Sci. Bull., vol. 11, pp. 402-408, 1918. 
 =sOp. cit., 1943. 
 
20 GEOLOGY OF TESLA QUADRANGLE [BuU. 140 
 
 / Some of the igneous rocks were formed contemporaneously with the 
 /sediments and are to be considered as part of the formation. These include 
 the pillow-basalts, which were observed in the Arroyos Mocho and Valle. 
 The rocks are dark brownish green, dense, and aphanitic. Alteration is 
 generally well advanced, and in many of the thin-sections of these rocks 
 the groundmass cannot be resolved for study under the microscope. The 
 groundmass is commonly finely crystalline and composed of minute lath- 
 shaped basic feldspars and grains of augite and magnetite. Phenocrj-sts of 
 altered feldspar are uncommon. In outcrop the basalts are greatly jointed, 
 fractured, and cut by numerous veinlets of calcite and quartz. The pillow- 
 structure is poorlj^ developed ; the spheroids range from 1 to 3 feet in their 
 greatest axial dimension. Rocks of this type are generally regarded as 
 representing submarine lava flows. 
 
 Two small volcanic necks of basalt occur in the Arroyo Mocho in the 
 NW i sec. 32, T. 4 S., R. 4 E., and a large intrusive mass of basalt almost 
 half a mile in areal extent occurs on the north side of Lang canyon near 
 where it enters Arroyo Valle in sec. 29, T. 4 S., R. 3 B. Glaucophane schist 
 is developed locally around the border of the large basalt mass. 
 
 Numerous large and small intrusive masses of serpentinized rocks 
 occur in a southeastward-trending belt in the central southern part of 
 the quadrangle. In outline they range from relatively small kidney- 
 shaped or boat-shaped bodies, through a nearly circular mass measuring 
 about a mile in diameter on Cedar Mountain, to irregular elongate intru- 
 sions measuring from a quarter of a mile to a mile in width and up to 4 
 miles in length. The rocks are bluish black to light bluish green, massive 
 to nodular, internalh^ sheared, and possessed with greasy or dull earthy 
 lustre. Bastite and antigorite are the chief varieties and they are locally 
 cut by veinlets of fibrous chrysotile. The serpentine was derived from the 
 alteration of basic and ultrabasic rocks such as peridotite, pyroxenite, and 
 gabbro. One sample of parent rock, which was classified in the field as a 
 pyroxenite, under the microscope was seen to be composed chiefly of 
 hypersthene. Powdery brick-red soil and a dense brush cover characterize 
 large portions of the serpentinized areas. Some occurrences of silica- 
 carbonate rock were noted in the serpentine in fault zones. Some deposits 
 of good-grade magnesite and low-grade chrome ore, which are developed 
 locally in the marginal portions of the serpentine bodies, as at Cedar 
 Mountain, have been prospected and mined. 
 
 All of the structural relationships of the serpentine bodies are not 
 clear, but the intrusions seem to be rudely sill-like or laccolithic. In places, 
 however, the outlines of the serpentine masses cut irregularly and directly 
 across the strike of the sedimentary beds. In general the serpentine belt 
 parallels the axes of the folds in the Franciscan rocks, and in places the 
 serpentine is in fault contact with Cretaceous rocks. These basic intru- 
 sions were probably emplaced before the sediments in the basin of deposi- 
 tion were deformed into folded and faulted structures, for the serpentines 
 apparently are involved in these structures. The process of serpentiniza- 
 tion of the basic and ultrabasic rocks probably took place near the close 
 of or immediately following the magmatic intrusion. 
 
 The finding of what appeared to be hornblende-quartz diorite as 
 float in the Arroyo Valle greatly interested the writer during the map- 
 ping, for the rock was apparently being derived from an area of Fran- 
 ciscan rocks — yet it seemed unlike the rock types usually described from 
 the Franciscan. Tracing the float upstream led to the discovery of two 
 
STRATIGRAPHY 21 
 
 interesting intrusive bodies, one of which is located in the NE ^ sec. 32, T. 
 4 S., R. 3 E., and the other near the common north corner of sees. 3 and 4, 
 T. 5 S., R. 3 E. Instead of being parts of a plutonic body of coarse- 
 grained rock as anticipated, the intrusives are mainly composed of diabase 
 and include large blocks of coarse-grained hornblende-quartz gabbro 
 and hornblende-quartz diorite. Dr. Cordell Durrell, University of Cali- 
 fornia at Los Angeles, who made a field trip with the writer to observe 
 these rocks expressed the opinion that late in the stage of solidification of 
 the diorite-gabbro magma the rocks had become auto-brecciated into 
 blocks which were caught up in the still fluid phase of the magma as it 
 invaded the Franciscan rocks and solidified as diabase. A number of thin- 
 sections of these rocks were examined. A fine-grained, dark-gray rock, 
 which was microscopically determined as uralite diabase, is typical of the 
 main part of the intrusives. The rock is holocrystalline and consists of a 
 coarse diabasic intergrowth of laths of bytownite (50 percent) and uralite 
 (48 percent), a pale green amphibole with some of the crystals showing 
 wormy cores of diopside and included small basal sections of hornblende 
 crystals. Also found in the section were traces of interstitial quartz, iron 
 minerals, and chlorite. After microscopic examination one of the blocky 
 inclusions in the diabase was named hornblende-quartz gabbro. The rock 
 is hj^pidiomorphic granular, and the grains average 2 millimeters in size. 
 It consists of the following minerals: bytownite (55 percent), green 
 hornblende (40 percent), quartz (3 to 5 percent), titanite, iron minerals, 
 chlorite, and epidote. The bytownite has the following optical properties : 
 2V of 80 degrees, negative sign, symmetrical extinction angle of 40 
 degrees, average refractive index of 1.57, and twinning according to the 
 albite, pericline, and Carlsbad laws. Two other thin-sections of the 
 included phase were of coarse hornblende gabbro, consisting chiefly of 
 green hornblende (70 percent) and bytownite (30 percent). One par- 
 ticularly interesting section was that of a hornblende-quartz diorite. The 
 rock is hypidiomorphic granular ; average grain size is half a millimeter. 
 It consists of the following minerals: labradorite (45 percent), pale 
 green hornblende (50 percent), diopside (1 percent), hypersthene (less 
 than 1 percent) quartz (3 percent) , and some minor secondary and acces- 
 sory minerals. Some of the laboradorite crystals possess outer zonal rims 
 of orthoclase and oligoclase, suggesting an interruption of the process of 
 crystallization. Some of the hornblende crystals show poikilitic inclusions 
 of and indentations by plagioclase crystals. That there has been some 
 uralitization is suggested locally by amphibole rims around pyroxene 
 cores. A few minute veinlets of serpentine cut through the section. This 
 rock is also interesting because of dark-gray, fine-grained, autolithic 
 segregations about an inch in diameter. The boundary of these segrega- 
 tions is not sharp, and aside from a paler aspect to the hornblende and 
 a finer texture, their composition is identical with the enclosing phase. 
 Cutting the diabase-gabbro intrusions in numerous places are 3-inch to 
 1-foot veins of serpentine, quartz-albite rock, and quartz-calcite-barite 
 rock. Glaucophane schist is developed along the Avestern margin of the 
 southernmost diabase intrusive, and both of the intrusives are in fault 
 relationship with Cretaceous rocks along part of their borders. 
 
 In the driving of the Iletch-Hetchy tunnel about a mile east of the 
 Arroyo Valle shaft, a rock mass which Bailey Willis classified as shattered 
 granodiorite was penetrated (see section H-H', pi. 3). This rock is not 
 exposed at the surface, being covered by a thick mantle of gravels. 
 
22 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 Crushed grains from a crumbly sample of this rock were examined in 
 index oils under the microscope and the following minerals were recog- 
 nized : quartz, kaolinized and sericitized orthoclase, oligoclase-andesine, 
 and badly chloritized and altered hornblende (?). The proportion of 
 these minerals in the poor sample obtained by the writer was not deter- 
 minable, so that the classification of the rock as granodiorite could not be 
 confirmed. No such rock has ever been described from the Franciscan. 
 The rock mass occurs along a projection of the Valle fault and is probably 
 in fault-contact with Cretaceous rocks in depth. However, it is not known 
 whether the granodiorite is intrusive into or faulted into the Franciscan 
 rocks. If intrusive, this occurrence may be similar in type to the afore- 
 mentioned diabase-gabbro intrusions which occur about 3 to 4 miles to 
 the southeast ; that is, rather than representing the shattered cupola of a 
 granodiorite intrusive mass, it may be a large blocky inclusion in a dia- 
 basic intrusive. 
 
 Along the Tesla fault-zone in Corral Hollow and again near Car- 
 negie a dike rock of feldspar porphyry occurs. The rock is badly 
 weathered and fractured, and its structural relationship to other Fran- 
 ciscan rocks in the vicinity is not clear. In thin-section the matrix, which 
 cannot be clearly resolved under the microscope, consists of a fine granu- 
 lar aggregate of feldspar and altered pyroxene ( ?). Cloudy phenoerysts, 
 which are 2 to 3 millimeters in length, are of altered plagioclase showing 
 albite twinning. This rock is of interest, as somewhat similar porphyries 
 are found in some Franciscan conglomerates and in a prominent Cre- 
 taceous conglomerate on Rocky Ridge in the central western portion of 
 the the area; however, it is not suggested that this local occurrence of 
 dike rock served as a source for any of these conglomerates. 
 
 Structure. The dominant regional structures involving the Fran- 
 ciscan rocks are a series of long northwestward-trending folds that are 
 complicated by faulting and igneous intrusions. Underground in the 
 walls of the Hetch-Hetchy tunnel, countless faults and fracture planes 
 are observed that are not in evidence at the surface. In the vicinity of 
 Corral Hollow, the tunnel bored through a tight overturned anticline 
 which was so intricately fractured and compressed in its axial portion 
 that enormous pressures and moving ground greatly interfered with the 
 progress of the tunnel. The Franciscan rocks are separated from the 
 Cretaceous by three major faults, the Tesla, the Williams, and the Valle 
 faults. The only younger formation which is in depositional contact with 
 the Franciscan is the Plio-Pleistocene Livermore gravels. In Arroyo Valle 
 a do^vn-dropped fault-wedge of Cretaceous rocks occurs within the general 
 area of Franciscan rocks. A generalized interpretation of the structures 
 involving the Franciscan rocks is shown in the cross-sections E-E', F-F', 
 G-G', andH-H' (pi. 3). 
 
 Age. The Franciscan is a difficult group of rocks to which to assign 
 an age, because of: (1) the general absence of megafossils; (2) the 
 unidentifiable character of contained radiolaria, foraminifera, and car- 
 bonized plant and wood fragments; (3) the lack of a discovered base to 
 the formation ; and (4) a generally faulted relationship to younger for- 
 mations. No important contribution to the problem of the age of the 
 Franciscan was found in the Tesla quadrangle. However, if a conclusion 
 were drawn from the general stratigraphic relation of the rocks and 
 their degree of induration, alteration, and deformation as compared with 
 the formations of established age, it could be said that the rocks appear 
 
STRATIGRAPHY 23 
 
 to be definitelj^ older than Upper Cretaceous and at least as old as and 
 probably older than Lower Cretaceous. 
 
 Taliaferro -^ has concluded that the Franciscan is confined to a com- 
 paratively short space of geolojric time, probably Tithonian, Upper 
 Jurassic. He reported the findinor in 1936 of an ichthyosaur snout in a 
 boulder of red radiolarian chert in the Carbona quadrangle (adjoining 
 Tesla on the east) by Neil Smith, then a graduate student at the Uni- 
 versity of California. Although the boulder was found in a Tertiary 
 conglomerate, the petrography of the chert and the associated radiolaria 
 were interpreted by Taliaferro as Franciscan in type. In 1940 a second 
 ichthyosaur snout was found in a similar boulder in Recent stream 
 gravels in El Puerto Creek west of Patterson, California. The two 
 ichthyosaur snouts were described by C. L. Camp,^^ who concluded that 
 they were practically identical with Tithonian TTpper Jurassic ichthyo- 
 saurs of Europe and with certain questionably Lower Cretaceous forms 
 from Australia. Although the evidence of the age of the Franciscan as 
 probably Tithonian Upper Jurassic from the ichthj^osaur snouts is 
 indirect, it constitutes the best fossil evidence to date. 
 
 Cretaceous System 
 Horsetown Formation 
 
 Rocks of the Horsetown formation (Lower Cretaceous) occur in two 
 fault-wedge blocks along the Tesla fault zone on the south side of Corral 
 Hollow. The larger wedge, which is narrow and lenticular in outline, is 
 traceable for about 2 miles east and west across the northern parts of 
 sees. 34 and 35, T. 3 S., R. 3 E. In this occurrence the rocks reach their 
 maximum thickness of about 500 feet. The smaller wedge occurs near the 
 east quarter corner of sec. 36, T. 3 S., R. 3 E. Other small masses of these 
 rocks may occur along the fault zone, but unless fossils are found the 
 lithology is not readily distinguishable from that of the Franciscan rocks. 
 
 Lithology. Dark-gray to almost black, hard, nodular, and concre- 
 tionary shales are the dominant lithologic type in the Horsetown forma- 
 tion. Fossils are occasionally found in the limestone or sandstone con- 
 cretions. Buff, fossiliferous, fine-grained sandstone characterizes the 
 easternmost occurrence. 
 
 =»Op. cit, 1943, pp. 190-195. 
 
 30 Camp, C. L., Ichthyosaur rostra from central California : Jour. Paleontology, vol. 
 16, pp. 362-372, 1942. 
 
 Table 2. Checklist of Ilorsetoicn fox/tils. 
 
 
 Localities 
 
 
 
 Corral Hollow 
 
 12 
 
 Pelecj'poda 
 
 
 
 Pecten operculiformis Gabb 
 
 X 
 
 X 
 
 Pecten sp. 
 
 
 X 
 
 Cephalopoda 
 
 
 
 Desmoceras (Holodiscus) cf. theoboldiencis Stoliczka 
 
 X 
 
 
 " " lecontei Anderson 
 
 X 
 
 
 " " papillatus Stoliczka 
 
 X 
 
 
 Phylloceras shastalense Anderson 
 
 X 
 
 
 Sonneratia rogersi Hall and Ambrose 
 
 X 
 
 c 
 
 Scaphopoda 
 
 
 
 Dentalium 
 
 X 
 
 
 X = present 
 
 
 
 C = common 
 
 
 
24 GEOLOGY OF TESLA QUADRANGLE [Bllll. 140 
 
 Fauna and Correlation. Fossils of Horsetown age were found in 
 Corral Hollow by the Stanford Geological Survey, and a list of the fossils 
 is included in table 2. The writer found only two poor specimens in 
 Corral Hollow; but at locality No. 12, at the side of a road in the NE^ 
 sec. 36, T. 3 S., K. 3 E., several well-preserved specimens of a small 
 distinctive ammonite, Sonneratia rogersi, were found along with some 
 pectens. 
 
 Dr. F. M. Anderson, who identified the fossils from locality 12, 
 regarded them as a cool- water fauna and classified them as upper Horse- 
 town (Lower Cretaceous) in age. 
 
 Relation to Adjacent Formations. The small eastern mass of Horse- 
 town rocks appears to be a fault-wedge between the Franciscan and 
 Panoche formations along the Tesla fault. In Corral Hollow the shales 
 have a vertical attitude and are separated from the Franciscan by the 
 Tesla fault zone. The upper contact with the Panoche formation of Upper 
 Cretaceous age is not exposed but is characterized by a spring and a 
 hummocky furrow on the west side of the canyon. This contact is inter- 
 preted as a fault, Avhich is possibly related to the Tesla fault. 
 
 Panoche Formation 
 
 The Panoche formation (Upper Cretaceous) was first mapped across 
 the northern part of the Tesla quadrangle by Robert Anderson and 
 R. W. Pack ^^ assisted by E. L. Ickes. They recognized that the forma- 
 tion as they mapped it locally included strata of Lower Cretaceous age 
 (Horsetown formation of this report), which by more detailed mapping 
 could be differentiated from the Panoche proper. In recent years there 
 has been some tendency to divide the Panoche into different formations or 
 establish new limits for the formation, but there is at the present time 
 no agreement on this problem among stratigraphers. Except for the 
 differentiation of the Horsetown beds, the sense in which the Panoche 
 was originally mapped in this area is retained in this report. 
 
 Distribution and TJiicl'ness. Strata of Upper Cretaceous age occur 
 in the northern and western parts of the quadrangle. South of Corral 
 Hollow an east-west band is traceable for about 7 miles, the outcrop 
 being from a quarter to more than half a mile wide. These rocks consist 
 principally of massive and concretionary sandstone and minor amounts 
 of shale, attain a maximum thickness of about 2000 feet, and dip steeply 
 northward. 
 
 North of Corral Hollow, the axial portions of several anticlines are 
 comprised of Upper Cretaceous rocks. On one of these, the Patterson Pass 
 anticline, the Seaboard Oil Company "Johnston" 1 well was drilled to 
 a depth of 5925 feet and abandoned. The well started in sands of the 
 Cierbo formation (upper Miocene) and penetrated Panoche strata from 
 an approximate depth of 95 feet to bottom. 
 
 No correlative of the hard conglomerate, which occurred between the 
 depths of 1882 and 1933 feet, is kno"\ATi in the outcrop. However, the 
 hard blue shales in the lower part of the hole are believed to be correlative 
 with some argillaceous shales in the Altaniont anticline about 3^ miles 
 to the north. 
 
 In the broad Altamont anticline in the northern part of the area 
 a thickness of approximately 7500 feet of Panoche rock is exposed. The 
 
 "Op. cit. 
 
STRATIGEAPHY 25 
 
 Summary of log of "Johnston'^ 1 well " 
 
 0—95' sand and shale 
 95-504' hard sand, shale streaks 
 504—1405' hard shale, streaks of hard sand 
 1405-1455' fault gouge and sheared rocks (Patterson Pass fault zone) 
 1455-1850' hard blue shale, streaks of hard sand (brecciated zones at 
 
 1534 to 1548', and at 1618-1638') 
 1850-1882' hard coarse gray sandstone "^VtY-^f^ 
 
 1882-1933' hard conglomerate and sandstone I '■'■.^^■\ 
 
 1933-5925' hard dark blue silty claystone and shale, minor streaks of 
 hard sandstone ; average dip, about 23' ; fragments of 
 Inoceramus and Baciilites found at intervals from 1965 to 
 3160' 
 new highway, U. S. 50, which crosses the anticline, has numerous road- 
 cuts which give good exposures of these Cretaceous rocks. Section A-A' 
 (pi. 3), which represents a transverse section across the Altamont 
 anticline, shows the following Cretaceous section : 
 
 3500' buff, massive and concretionary sandstone, minor shale 
 
 3000' argillaceous shales, interbeds of sandstone 
 
 1000' (plus) massive tan sandstone, becoming pebbly at base 
 
 The approximate boundaries of the above lithologic groupings are rep- 
 resented on the geologic map (pi. 1) . The top of the section is overlapped 
 on the west limb of the anticline by the Cierbo formation (upper Miocene) 
 and on the east limb by the Neroly formation (upper Miocene), and at 
 the base of the section is not exposed. Since the anticline is plunging 
 southeastward, additional Upper Cretaceous section occurs to the north- 
 west in the adjoining Byron quadrangle. In 1941, Shell Oil Company, 
 Incorporated, "Nissen" 1 well was drilled in sec. 7, T. 2 S., K 3 E. 
 (Byron quadrangle) to a depth of 6563 feet and abandoned in hard 
 dense siltstone believed to be Upper Cretaceous. The well was located on 
 the axis of the Altamont anticline about 2 miles north of tlie Tesla 
 quadrangle, and the entire Upper Cretaceous section penetrated by it 
 underlies and supplements the Altamont outcrop-section described 
 above. Hard, dense siltstone characterizes roughly 75 percent of the 
 section encountered in the well and the balance consists of interbeds of 
 hard, impermeable, fine-grained sandstone ranging in thickness from 
 thin streaks up to a maximum of 250 feet. 
 
 In Arroyo Valle and along Rocky Ridge in the central western 
 part of the area, an incomplete thickness of more than 9000 feet of 
 Cretaceous rocks occurs dipping about 50° NE. These strata are over- 
 lapped by Tertiary strata and the base of the section is cut out by 
 faulting. An approximate section of the Cretaceous rocks on Rocky 
 Ridge is as follows : 
 
 4000-5000' buff, massive to bedded, concretionary sandstone, minor shale 
 and conglomerate 
 10-50' conglomerate containing polished, well-rounded pebbles and 
 cobbles 
 2500' buff, massive sandstone, minor shale 
 2000' shales, sandstone interbeds 
 
 The conglomerate in the middle of the section is traceable for more than 
 2 miles along Rocky Ridge and it continues to the northwest onto the 
 Pleasanton quadrangle. This conglomerate is believed to be intra forma- 
 tional, as the lithology and attitudes of the sediments above and below it 
 are quite uniform. 
 
 " Published with permission of Seaboard Oil Company. 
 
26 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 To the southeast alono- thf east side of Arroyo Valle a fault-wedge 
 block of Cretaceous rocks is completely enclosed by the Franciscan 
 complex. It is estimated that several thousand feet of sandstone and 
 shale are present, but no measurement of the section was attempted. 
 A conglomerate containing some fossiliferous sandstone boulders was 
 found beside the road on the east bank of Arroyo Valle in the SE| sec. 
 29, T. 4 S., R. 3 E. 
 
 Lithology. Sand and sandstone probably characterize more than 
 60 percent of the Panoche sediments in this area. The sandstones are 
 gray, weathering to tan or buff, fine to medium grained, missive to 
 bedded, and often concretionary^. The concretions are dark reddish 
 brown, hard, cemented with iron oxide, ellipsoidal or spheroidal in shape, 
 and range in size from a few inches up to 6 feet or more in diameter. 
 Several heavy-mineral separations were made of representative samples 
 of the sand and examined under the miseroscope. The mineral content 
 of these samples was found to be similar, and their average composition 
 as follows: the light minerals were identified as quartz (30 percent), 
 altered orthoclase (60 percent), oligoelase-andesine (5 percent), biotite 
 (5 percent), and muscovite (trace). The grains are angular, and the 
 sorting is only fair. The heaw minerals, which comprise about one- 
 tenth of one percent of a separation, consist of the following : magnetite, 
 (abundant), ilmenite (common), zircon, brown tourmaline, green horn- 
 blende, rutile, zoisite, colorless garnet, and hematite. All but the first 
 two heavj^" minerals are present in very small amounts. The general 
 mineral assemblage suggests derivation from a source area of granitic 
 rocks. 
 
 The shales are typically blue gray, weathering to browTi, argilla- 
 ceous to silty, thinly bedded, and locally concretionary. They weather to 
 a deep soil-cover and are expressed by a smooth, subdued relief. Any 
 organic content of the shales is inevident, and no foraminifera-bearing 
 shales were found, although the hand lens was freely employed at shale 
 outcrops and a number of trial washed samples were examined under 
 the microscope. 
 
 Conglomerates are very uncommon among the Upper Cretaceous 
 rocks in the area, and the only prominent bed of conglomerate occursi 
 on Rocky Ridge in the central western part of the area. The Rocky 
 Ridge conglomerate contains well-rounded highly polished pebbles and 
 cobbles set in a plentiful matrix of buff sandstone. The cobbles range 
 from about 2 to 5 inches in diameter. Some of the cobbles, such as those 
 consisting of limestone, shale, and dark-brown concretionary sand- 
 stone, are sub-rounded, lack the high polish of the other cobbles, and 
 probably represent the re-working of someAvhat earlier Upper Cretaceous 
 rocks. The polished and well-rounded cobbles apparently were derived 
 from a distant and older source rock. They consist of dark-gray sand- 
 stone and quartzite, quartz and feldspar porphyries, black chert, quartz, 
 and aplite. About a dozen thin-sections were made of this second group 
 of cobbles, and a brief description of the petrography follows. The sand- 
 stone making up a majority of the cobbles is gray to dark gray, fine 
 to coarse grained, poorly sorted, angular grained, well indurated and 
 cemented. In thin-section the average mineral assemblage of the sand- 
 stone cobbles consists of quartz (60 percent), altered orthoclase (25 
 percent), oligoclase (10 percent), biotite (less than 3 percent), augite 
 (trace), and hornblende (trace). Minor accessory minerals include 
 
STRATIGRAPHY 27 
 
 titanite, zircon, magnetite, and apatite ; secondary minerals inchide eal- 
 cite, zoisite, epidote, chalcedony, kaolin minerals, sericite, and chlorite. 
 The sandstones are noticeably more quartzose and less feldspathic than 
 the average Upper Cretaceous or Franciscan sandstone. Examination 
 of a thin-section of a quartz porphyry cobble showed that the phenocrysts 
 make up about 10 percent of the field, reach a maximum of 2^ milli- 
 meters, and consist chiefly of euhedral basal sections of quartz and a 
 few prisms of orthoclase and oligoclase. The groundmass is a finely 
 crystalline aggregate of quartz and orthoclase clouded by alteration. 
 There is some accessory magnetite, and the secondary minerals include 
 chlorite after biotite, iron minerals and kaolin. The rock is evidently 
 hypabyssal in origin. Another rock variety determined is a feldspar 
 porphyry in which small phenocrysts make up 10 percent of the rock and 
 include orthoclase, oligoclase, and microperthite. The ground mass is a 
 microcrystalline aggregate of quartz and feldspar, accessory rutile, 
 and secondary mica, zoisite, and iron minerals. One unusual type is a 
 pitchstone porphyry, which in hand specimen is black in color and 
 has a resinous lustre. The phenocrysts make up 15 percent of the 
 rock, reach a maximum size of 4 millimeters, and consist of embayed 
 euhedral crystals of quartz (30 percent), cloudy orthoclase (25 percent), 
 altered oligoclase (40 percent), and microperthite (5 percent). The 
 goundmass is irresolvable but appears to be devitrified glass with an 
 index of refraction of less than 1.54. In this groundmass there are a few 
 tiny shreds of biotite, specks of magnetite, and a few vesicles that are 
 lined and infilled with chalcedony, tridymite, and finely crystalline 
 quartz. A thin-section of black chert was seen under the microscope 
 to be a minutely brecciated and receraented aggregate of microscopic 
 colorless and black chert particles. Fine quartz veinlets cut across the 
 section. 
 
 A heavy conglomerate containing a cobble assemblage similar to that 
 of Rocky Ridge was examined near the axis of the Altamont anticline in 
 sec. 7, T. 2 S., R. 3 E., Byron quadrangle. This locality is about 1^ miles 
 north of the northern edge of the Tesla quadrangle. In addition to the 
 types of cobbles already described, rare quartz-diorite cobbles were found. 
 An unusual feature of this conglomerate was the occurrence of numerous 
 large boulders of hard red-brown sandstone concretions, some of which 
 measured 2^ feet in diameter. As this horizon was traced from the west 
 limb of the anticline around to the east flank, the heavy boulder con- 
 glomerate graded into a granuliferous and pebbly gritstone, suggesting 
 a probable western source for the material. 
 
 The conglomerate which was penetrated in the Seaboard Oil Com- 
 pany ''Johnston" 1 well (sec. 13, T, 3 S., R. 3 E.) between the depths 
 1882 and 1933 feet was very well indurated and cemented, had a sand- 
 stone matrix, and carried rounded pebbles and cobbles (up to 4 inches in 
 diameter) of limestone, shale, sandstone, and quartz. 
 
 Conditions of Sedimentation. The Panoche sediments are believed 
 to have accumulated in a shallow marine basin. The flnding of a few 
 marine fossils in the rocks supports the concept of a marine environment. 
 The general uniformity of the lithology from the lower part to the top 
 of the formation indicates a probable maintenance of the same source for 
 a period long enough for the deposition of many thousands of feet of beds, 
 and may indicate a balance between a slowly subsiding basin of deposition 
 and a slowly rising source area. The laying down of boulder eonglom- 
 
28 ' GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 erates marks the interruptions of this balance. The types of cobbles in the 
 conglomerates suggest a re-working of other similar Cretaceous rocks and 
 the introduction of rounded and polished boulders derived from a distant 
 and probably older source rock. A general absence of rock types that are 
 found in the Franciscan and Sur series is to be noted. Turner ^^ in writing 
 of Cretaceous conglomerates at Mt. Diablo noted that some of the cobbles 
 were a variety of quartz porphyry which is indistinguishable from a type 
 that is common in the foothills of Calaveras County in the Sierra Nevada. 
 The petrography of the sands and sandstones suggests a source area of 
 granitic rocks. Thus, certain features of the sediments suggest that the 
 Sierra Nevada may have served as the principal source; however, a 
 Avestern source for a least part of the material is suggested by the west- 
 ward coarsening of the conglomerate of the Altamont anticline in the 
 Bj-ron quadrangle. 
 
 Fauna and Correlation. Fossils were found in the Upper Cre- 
 taceous rocks in only a few places. The late Dr. F. M. Anderson of the 
 California Academy of Sciences contributed the fossil lists given below. 
 Tnlle 3. Checklist of some Zipper- Cretaceous fossils 
 
 Localities 
 
 ~~~ X XI XIII 
 
 Pelecypoda 
 
 Aplirodina nitida (Gabb) X 
 
 Cucullaea sp. X 
 
 Glycimeris sp. X 
 
 Inoceramus cf. vancouverensis Shumard X 
 
 Mactra ashburneri Gabb X 
 
 Gastropoda 
 
 Anchura californica (Gabb) X 
 
 Gyrodes cf. expansus Gabb X 
 
 Turritella petersoni Anderson X 
 
 Cephalopoda 
 
 Baculitus chicoensis Trask X 
 
 Baculites inoratus Meek X 
 
 Baculites cf. vagina Forbes X/ 
 
 Desmoceras colusaense (Anderson) X/ 
 
 Desmoceras cf. selwynianum Whiteaves X 
 
 Lytoceras alamedense Smith X 
 
 Lytoceras cf. cala (Forbes) X 
 
 Metaplacenticeras pacificum (Smith) X 
 
 Metaplacenticeras californicum (Anderson) X 
 
 Parapachydiscus suciaensis Meek X 
 
 Parapachydiscus cf. arbucklensis nov X 
 
 Parapachydiscus canadoceras sp. X 
 
 Fossil wood containing boring shells {Turnus Gabb) X. 
 
 Locality X on the old Jordan ranch is on a small flat on the east side 
 of Arroyo Valle in the SE^ sec. 11, T. 4 S., R. 3 E. A few fossils were also 
 found on the west side of the creek at approximately the same horizon. 
 J. P. Smith in 1900 published two lists of fossils said to have been found 
 there prior to 1895 by L. G. Yates, a Livermore dentist. Anderson in a 
 personal communication dated February 21, 1939, wrote that some of 
 Yates ' fossils must have come from Shasta County and that the lists pub- 
 lished by Smith included forms not found at the Jordan ranch locality. 
 Anderson's revised list of fossils from the locality is given in the pre- 
 ceding checklist, and he determined them as lower Senonian in age and 
 representative of the Panoche formation. These fossils occur about 2500 
 feet above the Rocky Ridge conglomerate. 
 
 " Op. cit., 1891. 
 
STRATIGRAPHY 29 
 
 At locality XI in the SE-i sec. 29, T. 4 S., R. 3 E., two fossiliferous 
 sandstone boulders yielded a fauna distinctly different and older than 
 the assemblage from the Jordan ranch locality. Anderson classified them 
 as Cenomanian and probably correlative with faunas in the lower part of 
 the Chico (his Pioneer group). Anderson (written communication, Feb- 
 ruary 21, 1939) regarded the conglomerate at locality XI and the Rocky 
 Ridge conglomerate as marking the base of restricted Panoche resting 
 unconformably on an older Pioneer group (lower Chico). 
 
 Locality XIII is in a railroad cut on the Altamont anticline near the 
 east quarter-corner of sec. 27, T. 2 S., R. 3 E. The large ammonite Para- 
 pachydisciis canadoceras sp., which was found there in a shale concretion, 
 is indicative of the upper Panoche (upper Senonian), according to 
 Anderson. 
 
 ProMem of Dividing the Panoche. A division of the Panoche (as 
 originally described by Anderson and Pack ^^) into two component for- 
 mations, restricted Panoche and Chico, was suggested by F. M. Anderson 
 and G. D. Hanna ^^' and by Taff.^*" Later F. M. Anderson ^"^ proposed the 
 Chico series to replace the Chico group of Anderson and Pack and divided 
 the series into three groups, the Moreno, Panoche, and Pioneer. The latter 
 two groups coincide approximately with the original Panoche formation ; 
 the base of the Panoche group was taken at the horizon of some con- 
 glomerates containing sandstone boulders with Turonian or older Cre- 
 taceous fossils. Talif erro ^^ proposed that the Upper Cretaceous strata of 
 the California Coast Ranges be divided into the Asuncion and Pacheco 
 groups separated by an unconformity marking the Santa Lucian orogeny. 
 Under this terminology the upper part of the original Panoche formation 
 was included in the upper or Asuncion group and the lower part relegated 
 to the Pacheco group, excluding any Lower Cretaceous or older strata. 
 In contrast with a pronounced angular unconformity separating the two 
 groups in the Santa Lucia Range, Taliaferro referred to a generally dis- 
 conf ormable relationship along the east side of the Diablo Range. The base 
 of the Asuncion group (like the base of Anderson's Panoche group) was 
 taken at some conglomerates containing boulders with Turonian fossils. 
 Taliaferro ^^ elaborates further on the occurrence of these conglomerates, 
 stating : 
 
 "It is doubtful that these heavy conglomerates all occur at the same 
 horizon ; they are lenses and cannot be traced continuously. They do not 
 represent an unconformity locally, but they definitely reflect an uplift, or 
 uplifts, on the west and the exposure of the early Upper Cretaceous sedi- 
 ments." 
 
 Kirby,^'' in writing of the Upper Cretaceous stratigraphy of the 
 west side of the Sacramento Valley, reports that the Chico series there 
 represents both the Pioneer and Panoche groups of F. M. Anderson or 
 the Pacheco and lower Asuncion groups of Taliaferro. However, he was 
 unable to recognize a boundary for such groupings or point to any 
 
 " Op. cit. 
 
 "> Anderson, F. M., and Hanna, G. D., Cretaceous geology of Lower California: 
 California Acad. Sci. Proc, 4th ser., vol. 23, no. 1, pp. 1-34, 1935. 
 
 88 Op. cit. 
 
 "Anderson, F. M., Synopsis of the later Mesozoic in California: California Div. 
 Mines Bull. 118, pp. 183-186, 1941. 
 
 ssQp. cit., 1941. 
 
 '» Taliaferro, N. L., Cretaceous and Paleocene of Santa Lucia Range : Am. Assoc. 
 Petroleum Geologists Bull., vol. 28, p. 485, 1944. 
 
 *" Kirby, James M., Upper Cretaceous stratigraphy of west side of Sacramento 
 Valley south of Willows, Glenn County, California: Am. Assoc. Petroleum Geologists 
 Bull., vol. 27, pp. 279-306, 1943. 
 
30 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 significant indication of the Santa Lucian orogeny there. Goudkoff,^^ 
 describing the stratigraphic relations of the Upper Cretaceous in the 
 Great Valley of California on the basis of the microfauna from wells 
 and outcrop sections, shows on a correlation chart that the separation of 
 Anderson 's Panoche and Pioneer groups would fall between his G-2 and 
 H zones ; but he does not refer to any unconformity, disconformity, or 
 missing foraminiferal zone at this boundary. 
 
 The problem of the suggested division of the Panoche requires a 
 proper interpretation of the conglomerates that contain the fossiliferous 
 boulders with Turonian or older fossils. It is evident that more research is 
 needed in both the field and laboratory for a clear understanding of these 
 conglomerates and their stratigraphic relations to the sediments above 
 and below. The problem is not simple, for if there were a prominent 
 conglomerate horizon, traceable throughout most of the Diablo Range 
 and containing fossils reworked from the underlying sediments, Ander- 
 son and Pack would have recognized such an important feature and 
 set up their Upper Cretaceous stratigraphy to conform with this break. 
 Instead, they found these conglomerates at no less than three different 
 horizons and they were impressed with the rapid lateral disappearance, 
 in a few thousand feet, of great conglomerate lenses aggregating almost 
 a thousand feet in thickness. Their description of these conglomerates ^- 
 reflects how interested they were in finding a correct stratigraphic 
 interpretation, and they concluded finally that the conglomerates were 
 intraformational. Although numerous references have been made to the 
 finding of Turonian fossils in boulders in the Panoche conglomerates, 
 very few lists of the fossils have been published. Stewart-*^ recently 
 published the faunas found in several such fossiliferous boulders from 
 five localities in the Reef Ridge area of the southern part of the Diablo 
 Range, where several beds of conglomerate occur in the upper 2000 
 feet of the Panoche formation. He reports that the Upper Cretaceous 
 fossils found in the boulders represent a fauna that has not been recog- 
 nized in any section in the Reef Ridge area. To this writer's knowledge, 
 no one has yet reported finding a Turonian fauna from Panoche sedi- 
 ments in place and clearly underlying a conglomerate horizon containing 
 the fossiliferous boulders. Thus the possibility remains that the fossil- 
 iferous boulders were not derived from the strata underlying the con- 
 glomerates, but from early Upper Cretaceous rocks that became exposed 
 on the margin of the basin of deposition. Several geologists, among them 
 Anderson and Pack, and N. L. Taliaferro, have expressed the opinion 
 that there is no indication of a break in deposition between the con- 
 glomerate lenses and the underlying sediments. Finally, no one has 
 yet reported that he has mapped a contact along the east flank of the 
 Diablo Range that would divide what was originally defined and mapped 
 as Panoche into two separate stratigraphic units. For these reasons this 
 writer believes that the proposed division of the Panoche into separate 
 formations or groups needs further supporting evidence. 
 
 As the problem applies to the Tesla quadrangle, the Panoche forma- 
 tion is left undivided, and the several conglomerates, such as the one on 
 Rocky Ridge, are regarded as intraformational for want of evidence to 
 the contrary. 
 
 ^ Goudkoff, P. P., Stratigraphic relations of Upper Cretaceous in Great Valley, 
 California: Am. Assoc. Petroleum Geologists Bull., vol. 29, pp. 9-56-1008, 1945. 
 
 «Op. cit, pp. 43-44. 
 
 " Stewart, Ralph, Geology of Reef Ridge, Coalinga district, California : U. S. Geol. 
 Survey Prof. Paper 205-C, pp. 88-89, 1946. 
 
STRATIGRAPHY 31 
 
 Belation to Adjacent Formations. The Panoclie formation shows 
 several types of relationship to the adjacent formations. It is in fault 
 contact with the Franciscan and Horsetown formations; it is overlain 
 gradationally by the Moreno Grande formation ; and it is overlain uncon- 
 f ormably by the Oursan ( ? ) , Cierbo, and Neroly formations, and the 
 Livermore gravels. 
 
 Moreno Grande Formation 
 
 Along the south side of Corral Hollow, Anderson and Pack,^^ assisted 
 by Ickes, first mapped and set apart from the Panoche formation a 
 narrow east-trending belt of shale, which they called tlie Moreno forma- 
 tion because of its resemblance in character and general stratigraphic 
 position to that formation as it exists farther south in the Diablo Range. 
 They postulated that these shales with their organic content were prob- 
 ably the source beds for the oil which occurs in seepages and which was 
 produced on a minor scale from a few wells on the old Hamilton ranch 
 in sec. 15, T. 3 S., R. 3 E. The present writer in 1936^^ and again in 
 1940^^ followed Anderson and Pack in calling these beds Moreno. Since 
 that time his work in other parts of the Diablo Range along the west 
 border of the San Joaquin Valley and the contributions of other geol- 
 ogists, indicate clearly that the Moreno as originally mapped is more 
 inclusive than the Moreno as originally defined, and that some clarifica- 
 tion of the stratigraphic relationships of the Upper Cretaceous in this 
 region is needed. The term Moreno Grande, signifying greater or enlarged 
 Moreno, was first proposed by Huey and Daly in a joint paper read before || 
 the Pacific Section of the American Association of Petroleum Geologists 
 meeting at Los Angeles in November 1941.^^ North of Pacheco Pass the 
 Moreno Grande comprises what Anderson and Pack mapped as Moreno 
 and the maximum section is developed at Garzas Creek. Southward to 
 the Coalinga region the Moreno Grande includes the restricted Moreno,^^ 
 the Brown Mountain sandstone, and the Pachydiscus silt^^ as members.^ 
 The top of the underlying Joaquin Ridge sandstone member of the 
 Panoche in this southern area correlates approximately with the top of 
 the Panoche as mapped by Anderson and Pack in the area north of 
 Pacheco Pass. A separate publication is planned to describe more fully 
 the Moreno Grande and to present the basis for tlie correlations outlined 
 above. That the mapped Moreno north of Pacheco Pass includes equiva-■^ 
 lents of Upper Cretaceous beds down to the top of the Joaquin Ridge 
 sandstone in the Coalinga region was shown by Goudkoff ^^ in a correki- 
 tion chart based on microfaunal studies. Taliaferro^'' has stated that the > 
 proposed Moreno Grande is ' ' the best approach toward the solution of 
 the Moreno problem" that has been presented. ■' 
 
 Distribution and Thickness. Only the lower part of the ]\Ioreno 
 Grande formation is present in the Tesla quadrangle. It occurs as a 
 narrow east-trending band for about 5 miles along the south side of 
 Corral Hollow. The subdued topographic expression of the formation 
 
 " Op. cit. 
 
 *' Huey, A. S., op. cit. 
 
 *"Huey, A. S., The geology of the Tesla quadrangle of middle California, Ph.D. 
 thesis, Univ. California, Berkeley, 1940. 
 
 *' Huey, Arthur S., and Daly, J. W., A discussion of part of the Upper Cretaceous 
 along the west border of the San Joaquin Valley. (Unpublished paper read before the 
 Pacific Section, Am. Assoc. Petroleum Geologists, Oct. Ifi, 1941.) 
 
 *» Also called Ragged Valley shale. 
 
 " Op. cit., fig. 2. 
 
 «>Op. cit, 1944, p. 472. 
 
32 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 and the dark red-brown soil containing platy shale fragments aid in the 
 delineation of the upper and lower contacts which are generally not 
 exposed. North of Corral Hollow in anticlines which bring Cretaceous 
 rocks to the surface, the Panoche is overlain by sands of the Cierbo 
 formation (upper Miocene) and the Moreno Grande is absent, except for 
 one occurrence in the central western part of sec. 24, T. 3 S., K.. 3 E. 
 
 The generally poor exposures of the formation were unsuited for 
 the measurement of a section, but the thickness here is estimated to 
 reach a maximum of about 650 feet. 
 
 LitJiology. The Moreno Grande in this area consists of shale 
 and minor amounts of sandstone. The shales are dark gray to brown, 
 weathering in places to purplish brown and generally supporting the 
 development of a dark brown soil cover. Much of the shale is argilla- 
 ceous, some is sandj^, and thin partings of fine sand are common. In 
 places the shale is carbonaceous and very dark in color. A thin platy 
 variety containing abundant foraminifera is common as platy frag- 
 ments in the derived soil cover, but few good outcrops are found. Buff- 
 colored limestone concretions occur sparsely in the shales. From one 
 of these concretions a rich radiolarian fauna and an ammonite were 
 obtained. Although the organic content of the shales is probably low, 
 it is judged to be distinctly greater than that of any other shales in 
 the area, as evidenced by the presence of foraminifera, diatoms, radio- 
 laria, fish remains, megafossils, and carbonaceous matter. These shales 
 were probably the source beds for the small amount of oil that was found 
 on the old Hamilton ranch in the S| sec. 15, T. 3 S., R. 3 E. 
 
 At Tesla and westward for about a mile a massive and concretionary 
 sandstone occurs at the top of the Moreno Grande. The sand is light 
 gray weathering to buff; it is fine grained, massive to concretionary, 
 and locally carries considerable coarse biotite. The exposures of this 
 sand are poor and limited, but it is estimated that a thickness of about 
 150 feet is developed. This sand is probably older than the Garzas sand. 
 
 Fauna and Correlation. The poor exposures of the Moreno Grande 
 were unsuited for the detailed sampling of a section for microfaunal 
 study, but foraminifera were observed in the shales in a number of 
 places. Foraminifera from a shale sample at a locality about 100 feet 
 east of the Tesla road near the center of sec. 27, T. 35 S., K. 3 E. were 
 identified by Dr. A. S. Campbell as follows : 
 
 Bulimina obtusa d'Orbigny 
 
 Bulimina spinata n. sp. Cushman and Campbell 
 
 Eponides umbonella (Reuss) 
 
 Gaudryina navarroana Cushmau var. 
 
 Globigerina cf. triloba Reuss 
 
 Globotruncana area (Cushman) 
 
 Gyroidiua depressa (Alth) 
 
 Nodogenerina lepidula (Schwager) 
 
 Nodosaria monile v. Hagenon 
 
 Nodosaria spinifera Cushman and Campbell 
 
 Nodosaria sp. (smooth) 
 
 A few radiolaria were also present in the sample. The above fauna 
 would appear to fall in Goudkoff 's D-2 zone ^^ and be correlative with 
 the Pachydiscus silt of the Coalinga region. 
 
 " Op. cit, range chart, pp. 968, 969. 
 
DIVISION OF MINKS 
 
 BULLETIN 14U I'LATE 4 
 
 RELIEF MAP OF TESLA QUADRANGLE 
 
 Showing iiiiijortant place names. Photograph of a plaster relief niudt-l in the 
 
 Geological Museuni of the University of California, Berkeley. 
 
i>]\isit)N ()K :\nxEs 
 
 Bl'LLETIX 1 ill ri.ATI-: 
 
 
 
 A. BEDDED FRAXCISCAX L'HEKT IX ARROYO MOCHO 
 
 
 JS, PILLOW STRUCTURE IN FRANCISCAN BASALT 
 Along Arroyo Mocho road in sec. 13, T. 4 S., R. 3 E., M.D. 
 
DIVISION OF MINES 
 
 BULLETIN 140 PLATE fi 
 
 41^ 
 
 
 
 A. OUTCROP OF WHITE SAND OF TESLA FORMATION IN CORRAL HOLLOW 
 Leaves are piesent in the carbonaceous shales to the left of the white sand. Note 
 the truncation of the overturned beds l)v a terrace. Looking west, in northern part of 
 sec. Zn, T. 3 S., R. .1 E., M.D. 
 
 7;. C(»I'V ol' < il.l > l'HOT( KlK.AI'll SUdWl.VC, TKSL.A .MLXl.XC I'.V.MI', .M^.olT DM (i. 
 
DIVISION- OF MINES 
 
 BUI^LETIN 140 PLATE 1 
 
 
 V.^1»^' 
 
 ■*• '^"^^r^ 
 
 
 I "v 
 
 A, CROSS-BEDDED AND PEBBLY WHITE SAND OF CIERBO FORMATION 
 In a roadcut near the center of sec. 26, T. 2 S., R. 2 E., M.D. 
 
 
 
 l: 
 
 .\\ 
 
 -<•*, 
 
 .^' 
 
 
 B. ANGULAR I'NCOxXFORxMIT V 
 
 Between Cierbo formation and underlying Panoclie formation in a 
 
 railroad rut in sec. ;!(i, T. 2 S., R. 3 E., M.D. 
 
DIVISION OF MIXES 
 
 BULLETIN' 140 PLATE S 
 
 ^^i 
 
 A, ANDESITIC BOULDER CONGLOMERATE OF NEROLY FORMATION 
 In SE^ sec. fi, T. 3 S., R. 4 E., M.D 
 
 B. BASAL ANDESITIC GRAVELS OF NEROLY FORMATION" 
 Resting with angular unconformity on sandstones and shales of I'annche forma- 
 tion. View of north side of roadcut along U.S. Highway 50 in SEJ sec. :;4, T. i; S., 
 U. :i E.. M.D. 
 
DIVISION OF ^rrxKs 
 
 BUT.T>RT1X 140 PI.ATK :i 
 
 ...-.-^4^^. 
 
 A, SLICKENSIDED FAULT-PLANE SURFACE 
 In Greenville fault zone in cut of Western Pacific Railroad near tlie soutfiwest 
 corner of sec. 30, T. 2 S., R. 3 E., M.D. The fault plane has a dip of about 70 degrees, 
 and striations on the surface are nearly horizontal. 
 
 "jij**il . . ."•5*^'? 
 
 B. SHARI' FOLD IX XEltoLV RMK SAXDSTONE 
 
 Smooth surface to left is in upper Nernly shales, and Cierl)0 formation lunlerlies blue 
 
 sandstone, uppei- risht. View east, in southern part of sec 4, T. 3 S.. R. 4 JO., M.D. 
 
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STRATIGRAPHY 33 
 
 At locality XIV on the east bank of Mitchell Eavine a small ammo- 
 nite and minute specks thought to be foraminifera and radiolaria were 
 found in a yellow-buff colored limestone concretion when it was broken 
 open with a hammer. A thin-section of the sample was shown to Dr. 
 Campbell who observed the outlines of foraminifera, some diatoms, and 
 an abundance of well preserved radiolarian tests. These latter forms 
 greatly intrigued Campbell and he asked for the remainder of the con- 
 cretion which by then consisted of a few cubic inches of limestone, 
 including a small ammonite. From this small limestone sample Campbell 
 and Clark ^^ recovered after treatment of the material in acid, the 
 most extensive Cretaceous radiolarian fauna that has been recorded 
 from North America. The fauna includes nine families, 25 genera and 
 approximately 100 species. According to the above authors the fauna 
 may be referred to as a Saturnalis or Dictyomitra fauna. The associa- 
 tion of certain of the fossil species with recent Arctic forms indicated 
 that the fauna lived in very cold water. The ammonite found with the 
 radiolaria was identified by the late Dr. F. M. Anderson as Lyfoceras 
 (Tragonites) aff. epigonus (Kossmat), an Upper Cretaceous species 
 found elsewhere in the Pacliydiscus silt. The term Corral Hollow shale 
 mentioned from Huey in the paper by Campbell and Clark ^^ is replaced 
 by the term Lloreno Grande used in this report. 
 
 The sandstone in the upper part of the Moreno Grande from Tesla 
 westward contained some Upper Cretaceous megafossils. A sample of 
 sandstone float near Tesla contained Acila (trxincata) demessa Finlay 
 and two cephalopods, an ammonite and a Nautilus sp. At locality IX, 
 a little northwest of the center of see. 26, T. 3 S., R. 3 E., Parallelodon 
 (Xano)iovis) brewer ianus Gabb and an ammonite were found. 
 
 Structure and Relation to Adjacent Formations. The Moreno 
 Grande along the south side of Corral Hollow dips steeply northward 
 at angles of 60 to 80 degrees into a syncline. The formation is over- 
 lapped by the Cierbo formation (upper Miocene) to the north. The 
 contact with the underlying Panoche is nowhere well exposed but it 
 appears to be conformable and gradational. The contact with overlying 
 Tesla formation (middle Eocene) is unconformable. Angular discord- 
 ance is slight, but there is progressive overlap to the east. The upper 
 sand which is present west of Tesla is absent to the east at Mitchell 
 Ravine and still farther east near Carnegie the Moreno Grande is com- 
 pletely lapped out by the Tesla formation. This unconformity marks an 
 interval of time in which the cold-water marine conditions under which 
 the Moreno Grande was deposited were replaced by the warm brackish- 
 water conditions under which the lower part of the Tesla was formed. 
 
 Tertiary System 
 Eocene Series 
 
 Tesla Formation 
 
 The name Tesla formation was proposed by Huey ^^ for a group 
 of brackish-water and marine sediments of middle Eocene age that are 
 typically and most completely exposed near the former mining camp 
 of Tesla. The occurrence of coal, pottery clays, and quartz sand in the 
 formation makes it one of economic interest. 
 
 « Op. cit. 
 " Op. cit. 
 " Op. cit., 1936. 
 
 4—85413 
 
34 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 Distrihuiion and Thickness. The Tesla can be traced as a band 
 for about 5 miles along Corral Hollow from Carnegie westward toward 
 Livermore Valley. To the north no Eocene rocks occur on the flanks 
 of the anticlines, having been completely overlapped by the Cierbo 
 formation (upper Miocene) which in turn rests directly on the Panoche. 
 This relationship means that either an old high in the northern part 
 of the area prevented the deposition of the Eocene sediments or that 
 they were deposited and later stripped off prior to the transgression of 
 the Cierbo formation. This condition may be related to the buried arch 
 in the vicinity of Manteca over which Miocene strata rest on Upper 
 Cretaceous beds with the lapped-out Eocene strata preserved in the Sacra- 
 mento basin to the north and in the San Joaquin basin to the south. 
 
 A maximum thickness of about 2000 feet of section is developed 
 in the vicinity of Tesla. East of Tesla the Corral Hollow fault cuts out 
 about 700 feet of the upper part of the formation, and west of Tesla the 
 upper" part of the formation is progressively overlapped by the Cierbo 
 formation. 
 
 Lithology. The Tesla formation is characterized by a variety of 
 sedimentary rocks including white quartz sand, buff sand, iron- and 
 manganese-stained concretionary sand, dark carbonaceous shales, lignite 
 seams, and white to light blue clays. The sediments show considerable 
 variation both vertically and laterally. Brackish- water sediments, in gen- 
 eral, characterize the lower part of the formation, and marine sediments 
 predominate in the upper part. The occurrence of the white quartz sand 
 at several horizons in the section serves to bind the variable group of 
 sediments into a whole unit. 
 
 A paced section along the Tesla road in the center of sec. 25, T. 3 S., 
 R. 3 E., illustrates the variable lithology. The top of the section is locally 
 in fault contact with the Cierbo formation and about a quarter of a mile 
 to the west, 100 feet of additional section underlies a basal gravel of tlie 
 Cierbo. From top to bottom, the section along Tesla road is as follows : 
 
 40' Fine white quartzose sand, some shale. 
 700' Buff sand, fine grained,, concretionary, massive. 
 
 (Marine fossils including Turritella merriami Dickerson occur near 
 the top and base of this unit.) 
 SO' White sand and claj-s, some gray shales. 
 2.50' Buff sand, finely micaceous, massive, concretionary, and gypsiferous. 
 60' White to light gray sandy shales and clays with limonitic staining. 
 20' White quartz sand. 
 10' Dark carbonaceous shales. 
 
 .50' Buff sandstone, fine grained, locally manganese-stained concretions. 
 160' Gray to chocolate carbonaceous shales, minor sandstone. A thin lig- 
 nite seam occurs about 40' down in this unit. 
 150' Buff massive to crossbedded and concretionary sandstone, minor 
 amount of shale. 
 10' Gray shales. 
 100' Buff sandstone. Brackish-water fossils (Anomia and Diodus) occur 
 
 about 60' down in this unit. 
 125' Carbonaceous shales, streaks of micaceous sands. Fossil leaves occur 
 about 10' down and brackish-water fo.ssils including Corhicula sp. 
 occur about 85' down in this unit. 
 200' Light gray to buff massive sandstone, some shales. 
 
 1955' Total thickness of section. 
 
 At Mitchell Ravine to the east, the zone of brackish-water fossils con- 
 taining Corhicula sp. occurs in the basal part of the section about 30 feet 
 above the Tesla-Moreno Grande contact so that more than 200 feet of the 
 
STRATIGRAPHY 35 
 
 lower part of the formation which is present at Tesla is missing. Also at 
 Mitchell Ravine the upper 700 feet of the Tesla section is cut out by the 
 Corral Hollow fault. 
 
 The white sands are fine to medium grained, well sorted, massive to 
 finely cross-bedded, friable, locally gypsiferous, and generally finely 
 streaked with limonitic staining. Heavy mineral separations from three 
 samples of white sand were studied. Angular quartz averages about 75 
 percent of the total light minerals. However in one sample taken from the 
 upper white sand, quartz comprised 95 percent of the minerals present, 
 Orthoclase, much of which is kalonized and occurs in clay aggregates, 
 constitutes from 10 to 22 percent of the light minerals. Microcline and 
 oligoclase-andesine are present, each ranging from a trace up to 3 percent 
 of a separation. Grains of black and lavender chert generally constitute 
 from 1 to 2 percent of the light minerals. The micas are present in less 
 than 1 percent proportion and most of the biotite is pale. Anauxite is 
 present up to a percent or more. The heavy minerals comprise only about 
 one-half of one percent of a separation but include an interesting list of 
 minerals, mostly chemically resistant. Ilmenite and magnetite are abun- 
 dant, ilmenite being predominant. Andalusite and euhedral zircon are 
 very common, greenish-brown tourmaline is common, some barite is 
 present, staurolite and pink to colorless garnet are present in small quan- 
 tities. The sparse to very rare minerals include rutile, epidote, anatase, 
 corundum, basaltic and green hornblende, brookite, sillimanite, and 
 titanite. 
 
 Allen ^^ has made a more comprehensive study of the Tesla sands and 
 clays, and for additional petrographic details and discussion the reader is 
 referred to his report. Allen in examining a number of white sands found 
 anauxite ranging as high as 24 percent of the mineral assemblage. 
 
 The similarity of the mineral assemblage of the Tesla white sands 
 with that described from the lone sands by Allen ^^ is striking. Allen sug- 
 gested a Sierran source for the constituents of the lone sands. A Sierran 
 source for the Tesla white sands was suggested by Huey ^"^ (1936, 1940). 
 Andalusite which is present in these sands occurs in the schists in the 
 Sierras but has not been reported from the older rocks of the Coast 
 Ranges. Tourmaline, zircon, magnetite, ilmenite, epidote, garnet, stauro- 
 lite, in fact, about all of the heavy minerals from the Tesla white sands 
 occur in the Sierran province. The low feldspar content, the presence of 
 anauxite, the occurrence of minerals resistant to chemical weathering, and 
 the absence or sparsitj^ of such minerals as pyroxenes, amphiboles, and 
 micas suggest a derivation of the minerals from an area undergoing 
 intense chemical weathering. Allen ^^ suggested a Sierran source for the 
 material in the white anauxitic sands and clays at Tesla but postulated a 
 second contemporaneous source probably in the Coast Ranges, for the 
 mineral constituents such as fresh biotite, sparse glaucophane and albite, 
 which he found in some of the micaceous sands alternating with the white 
 sands and clays. 
 
 Petrographic examination of a sample from the upper buff sands 
 showed 35 percent quartz, 60 percent feldspar much of which was kaolini- 
 
 " Op. cit. 
 
 ""Allen, V. T., The lone formation of California: Univ. California. Dent Geol 
 Sci. Bull., vol. 18, pp. 347-448, 1929. 
 6- Op. cit., 1936, 1940. 
 "Op. cit., 1941. 
 
36 GEOLOGY OF TESLA QUADKANGLE [Bull. 140 
 
 zed, 4 percent altered biotite, and a heavy mineral assemblage essentially 
 the same as that of the white sands. Allen ^^ notes the occurrence of glau- 
 cophane, a characteristic Franciscan mineral, in a sample of the bufE sand 
 that he examined. 
 
 Associated with some of the chocolate-colored carbonaceous shales 
 are streaks of black, very micaceous sand. This sand containing an abun- 
 dance of what appeared to be fresh to slightly altered biotite seemed 
 inconsistent with a source area that was undergoing intense chemical 
 weathering. A petrographic examination of this sand showed quartz 10 
 percent, muscovite about 5 percent, and phlogopite with a sagenite web- 
 structure as rare. It was surprising that 85 percent of the sample was com- 
 posed of altered biotite and an alteration product of biotite, believed to 
 be the mineral, jefferisite. The optical properties of this vermiculite were 
 quite variable and the refractive indices of beta and gamma ranged from 
 1.455 to 1.560. The mineral was pseudouniaxial, negative in sign, and 
 retained the basal cleavage of biotite. Among the heavy minerals zircon 
 and hypersthene were common ; andalusite, ilmenite, and magnetite 
 rather common; and titanite, rutile, staurolite, brown tourmaline, and 
 anatase sparse to rare. This was the only sample of the micaceous sands 
 that was examined, but a question arises whether some of the other mica- 
 ceous sand streaks may also be mostly composed of altered biotite and 
 vermiculite rather than fresh biotite. Such sands would be consistent with 
 a source area undergoing chemical weathering. 
 
 The white clays of the Tesla formation were not examined petro- 
 graphicallj^, but Allen ^^ reports that the clays have similar chemical 
 composition, optical properties, and X-ray patterns to the anauxitic clays 
 near lone. 
 
 Fauna and Flora. The fauna and flora found in the Tesla forma- 
 tion afford clues to the conditions of sedimentation and help fix the age 
 and stratigraphic position of the formation. In general the fossils from 
 the lower part of the formation (localities I to III inclusive) indicate 
 a brackish-water environment, whereas those from the upper part (local- 
 ities IV to VI inclusive) suggest marine conditions. Dr. R. A. Bramkamp 
 kindly identified the fossils listed below. 
 
 5»Op. cit, 1941. 
 ""Op. cit., 1941. 
 
 Checklist of fossils from the Tesla formation 
 
 Localities 
 
 Pelecypoda I II III IV Y VI 
 
 Acila gabbiana (Dickerson) R 
 
 Anomia inornata (Gabb) A C 
 
 Brachidontes cowlitzensis (Weaver & Palmer) R 
 
 Corbicula n. sp.? A 
 
 Diodus tenuis (Gabb) C A 
 
 Glycimeris cf. meganoseusis Clark & Woodford X 
 
 Nuculana cf. gabbi (Gabb) A 
 
 Pitar sp X 
 
 Plagiocardium cf. brewerii (Gabb) R R 
 
 Spisula sp. X 
 
 Tellina cf. lajollaensis Dickerson X 
 
 Gastropoda 
 
 Turritella buwaldana Dickerson (mold) R 
 
 Turritella merriami Dickerson C X 
 
 A = abundant R = rare 
 
 C ^= common X = preseni 
 
STRATIGRAPHY 
 
 37 
 
 Some of the fossil assemblages seem to constitute zones as they are 
 found in several successive canyons in about the same stratigraphic 
 position. The lowermost zone carries the brackish-water form, CorMcula. 
 At Mitchell Ravine (locality III) this zone is about 80 feet above the top 
 of the Moreno Grande and about 75 feet below the Anomia-Diodus zone. 
 Nuculana gdhhi occurs consistently about 30 feet above the base of the 
 upper 700-foot unit of massive buff sand; and generally at a horizon 
 about 10 feet above the Nuculana zone a group of marine fossils including 
 Turritella merriami occurs. No fossils were found in the white sands, 
 and although the sands looked like clean beach sands, it was not deter- 
 mined whether they were deposited under marine or brackish-water 
 conditions. The white sands occur at several horizons in the formation 
 and in association with sediments that appear to have been deposited 
 under contrasting conditions. The late Dr. B. L. Clark informed the 
 writer of his finding in the Eocene white sands near Mt. Diablo a gas- 
 tropod, Spiroglyphus tejonensis (Arnold), and orbitoid foraminifera, 
 Discocylina cf. psilla, which forms would suggest a marine environment 
 of deposition for these sands. 
 
 In a south-facing bank at the foot of the Tesla grade (U. C. locality 
 No. P-3718) in the SE^ sec. 25, T. 3 S., R. 3 E., fossil leaves were found 
 in chocolate-colored shales. Professor R. W. Chancy of the University 
 of California, Berkeley, kindly supplied the following list of leaf species 
 and suggestions as to their time range. 
 
 Leaf species from University of California localiiy P-371S. 
 
 Floral list 
 
 Suggested time range 
 
 Ciiinamomum dilleri 
 Cordia cf. rotunda 
 Cupania cf. oregona 
 Glyptostrobus europeus 
 Laurus princeps 
 Magnolia californica 
 Nectandra presanguinea 
 Octotea ovoidea 
 Persea pseudocaroliniaua 
 Polyalthea chaneyi 
 Rhamnus cf. cleburni 
 Sabalites sp. (palm frond) 
 Trochodendroides sp. 
 
 Middle to upper Eocene 
 
 Upper Eocene to lower Oligocene 
 
 Middle Eocene to lower Oligocene 
 
 Paleocene to upper Eocene ' 
 
 Middle to upper Eocene 
 
 Middle to upper Eocene 
 
 Upper Eocene to lower Oligocene 
 
 Upper Eocene to lower Oligocene 
 
 Middle Eocene to lower Oligocene 
 
 Upper Eocene 
 
 Paleocene to lower Eocene 
 
 Eocene 
 
 Eocene 
 
 Concerning the above leaf specimens. Dr. Chancy ^^ writes : 
 
 "... the flora is probably of middle Eocene age. All of the species 
 are typically of Eocene age, and the details of migration are not sufficiently 
 well known to make possible a final age reference. 
 
 "All of the species fall in genera whose modern distribution is in lati- 
 tudes 15 to 20 degrees south of the Tesla region. The representation of the 
 Lauracea and the present-day occurrence of the modern equivalent of most 
 of the Tertiary species, suggest an environment without frost and with 
 abundant rainfall." 
 
 Age and Correlation. The occurrence of the index fossil Turritella 
 merriami in the upper half of the formation indicates that the Tesla 
 formation is middle Eocene in age and probably falls in what is cur- 
 rently called the Capay stage, which was proposed by Merriam and 
 Turner ^2. According to Dr. Chancy, the flora listed from the lower part 
 
 "* Written communication dated May 8, 1947. 
 
 «2 Merriam, C. W., and Turner, P. E., The Capay middle Eocene of California: 
 Univ. California, Dept. Geol. Sci. Bull., vol. 24, pp. 91-141, 1937. 
 
38 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 of the formation also indicates middle Eocene age, but the brackish-water 
 fossils in this lower part do not lend themselves to definite age assign- 
 ment since a few of the forms have been noted in beds purported to be 
 Paleocene or older. 
 
 The Tesla formation in this area, as herein mapped, was earlier 
 called Tejon by Anderson and Pack ®^. They mapped "Tejon" beds 
 for a considerable distance along the west border of the San Joaquin 
 Valley north of Coalinga. Part of what they mapped as Tejon is now 
 differentiated as Domengine, some of it has been referred to the Lodo 
 and Martinez ( ?) formations, and part of it is correlative with the Tesla 
 formation. Stewart, Popenoe, and Snavely ^^ have described a number 
 of columnar sections and the involved faunas from the Panoche Hills 
 northward into the Orestimba area. They described in the Orestimba 
 area a section of 1800 feet of iron-oxide streaked white sands with fer- 
 ruginous ledges and siltstones containing much carbonaceous material 
 in portions. A brackish-water fauna, which occurred in the lower part 
 of these beds, included Diodus tenuis, " Placunanomia" cf. inornata, and 
 "Psammo})ia" cylindrica, the latter a Paleocene species. "With some 
 uncertainty they assigned these beds to the Martinez ( ? ) formation and 
 indicated their probable age as Paleocene. They noted both the lithologic 
 and faunal similarity of these beds to some in Corral Hollow and postu- 
 lated that both might belong to the same formation. This writer concurs 
 in the suggested correlation of these two sets of beds, having previously 
 used the formational name Tesla for the beds in the Orestimba area, 
 where he directed some private unpublished mapping. 
 
 Structure and Relation to Adjacent Formations. The Tesla for- 
 mation in Corral Hollow dips steeply northward and locally the beds 
 are overturned in proximity to the Corral Hollow fault. In several 
 cross-sections (pi. 3) the Tesla is represented in the subsurface as dipping 
 down into a syncline and being overlapped to the north by the Cierbo 
 formation (upper Miocene) without emerging on the north limb of 
 the syncline. 
 
 The relation of the Tesla to the underlying Moreno Grande has 
 already been described. The Tesla is overlain unconformably by the 
 Cierbo formation. In places a gravel bed in the base of the Cierbo facil- 
 itates the mapping of the contact between the two formations. In Corral 
 Hollow the Tesla formation is in fault contact with the Cierbo and the 
 upper part of the Tesla is cut out along the Corral Hollow fault. 
 
 Miocene Series 
 
 Oursan? Sandstone 
 
 The Oursan sandstone was named by Lawson ^^ for its occurrence 
 at Oursan Ridge in the Concord quadrangle. In Arroyo Valle near the 
 central western margin of the Tesla quadrangle, some massive buff 
 sandstones, locally pebbly and reef-forming with minor interbedded 
 shale, are herein assigned with some uncertainty to the Oursan sand- 
 stone. These beds had previously been mapped as Briones by the Stan- 
 ford Geological Survey, but an invertebrate fauna found by the writer 
 indicates that the beds are probably older than Briones. 
 
 83 Op. cit. 
 
 8* Stewart, R., Popenoe, W. P., and Snavely, P. D., Jr., Correlation and subdivisions 
 of Tertiary and late Upper Cretaceous rocks in Panoche Hills, Laguna Seca area, and 
 Orestimba area, Fresno, Merced, and Stanislaus Counties, California : U. S. Geol. 
 Survey, Oil and Gas Investigations Prelim. Chart 6, 1944. 
 
 «»Op. cit., 1914. 
 
STRATIGRAPHY 39 
 
 The principal occurrence of the sandstone in the Tesla quadrangle 
 is limited to the N^ sec. 3, T. 4 S., R. 2 E. It extends northwestward 
 into the Pleasanton quadrang:le. To the southeast the formation is com- 
 pletely overlapped by the Livermore gravels. 
 
 Lifhology. Massive buff sandstone characterizes the bulk of the 
 formation, which locally attains a thickness of about 700 feet. At the 
 entrance of Arroyo Valle south of Livermore the road takes a sharp 
 turn around a strike ridge of the sandstone which locally is pebbly and 
 carries an abundance of shell fragments. 
 
 A heaw mineral separation of a sample of light gray weathering 
 to buff, fine-grained sandstone from locality VIII in sec. 3. T. 4 S., 
 R. 2 E., was examined petrographically. Quartz constitutes 40 percent 
 of the light minerals. Shards of clear and brown glass with a refractive 
 index of 1.50± make up 25 percent of the separation. Chert grains 
 constitute 15 percent, and kaolinized feldspars make up 20 percent 
 of the sample. Among the hea^^^ minerals pale green hornblende is very 
 common; magnetite, basaltic hornblende, bro^ATi biotite, and hypersthene 
 are common ; glaucophane, titanite, epidote. and ilmenite are scarce. 
 The presence of glaucophane suggests a probable Franciscan source for 
 the detrital material of the sediments, and the shards of glass attest 
 to A^olcanic activity during the middle Miocene. 
 
 A few beds of light gray punky, tuffaceous and diatomaceous shale 
 are interbedded with the buff sandstones. 
 
 Fauna and Correlation. At locality VIII in sec. 3, T. 4 S., R. 2 E., 
 abundant but poorly preserved marine fossils were found in friable buff 
 sandstone. Fossils from this locality were identified by Mrs. P. Rossello 
 Nicholson of the Museum of Paleontology, University of California, 
 Berkeley. 
 
 Checklist of fo.tails from the Oursau? satidstone (lor. YIIJ) 
 
 Pelecypoda 
 
 Cardium sp. X 
 
 Chione n. sp. X 
 
 Chione sp. (cf. C panzena Anderson & Martin) X 
 
 Chione sp. (cf. C templorensis Anderson) X 
 
 Cryptomya sp. X 
 
 Dosinia merrianii Clark X 
 
 Mytilus sp. (cf. M. perrini Clark) X 
 
 Nitidella sp. X 
 
 Ostrea n. sp. X 
 
 Pecten (Equipecten) andersoni Arnold RC 
 
 Schizothaerus sp X 
 
 Siliqua sp. (?) RC 
 
 Tagelus n. sp. X 
 
 Thracia ( ?) n. sp. X 
 
 Gastropoda 
 
 Bullaria n. sp. (?) RC 
 
 Calyptraea inornata Conrad RC 
 
 Polinices (Neverita) reclnziana var. andersoni Clark X 
 
 Trophon sp. 
 
 Arthropoda 
 
 Balanus sp. X 
 
 X = present 
 RC = rather common 
 
 The above faunal assemblage was regarded by the late Professor 
 B. L. Clark ^^ as middle Miocene (Temblor) and older than Briones. 
 
 *° Oral communication. 
 
40 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 Certainly, index fossils for the Briones, sncli as Astrodapsis trewerianus 
 and Pecten raymondi, are conspicuous by their absence. However, the 
 fauna bears some resemblance to one listed by Trask ^"^ from the lower 
 sandstone member of the Briones in the San Pablo Bay region. 
 
 Vanderhoof ^^ has described the fossil material from a sea cow, 
 Desmo stylus, which was found in these beds at the mouth of Arroyo 
 Valle. Vanderhoof referred to the beds as Briones, following general 
 usage in the area. 
 
 There is practically no chance to clarify the stratigraphic relations 
 of this formation from the limited occurrence in the Tesla quadrangle ; 
 however, in the adjoining Pleasanton quadrangle to the west the key 
 to this stratigraphic problem may lie in some work done towards a 
 Master's degree by Harding.^^ He mapped a section of about 3000 feet 
 of Briones formation carrying Feet en raymondi and Ostrea tourgeoisii 
 in the Maguire Peaks area east of the Sunol fault. He found underlying 
 the Briones with slight angular unconformity a middle Miocene forma- 
 tion comprised mostly of a tan sandstone resembling the Oursan sand- 
 stone that he had mapped west of the Sunol fault. Fossils found in this 
 sandstone included Pecten andersoni, Dosinia merriami, Tivela gahti, 
 and Cancellaria daUinna? The lithologic and faunal similarity of this 
 unit to the beds in question in Arroyo Valle is striking, and the strati- 
 graphic position underlying definite Briones is clearly demonstrated. 
 Although Harding noted a resemblance of these beds to the Oursan 
 sandstone, he was not certain as to the assignment. The Tice and Clare- 
 mont shales, which respectively overlie and underlie the Oursan sand- 
 stone in the area west of the Sunol fault, are not recognized east of that 
 fault so that the assignment as Oursan had to be based largely on litho- 
 logic appearance and general stratigraphic position. 
 
 Structure and Relation to Adjacent Formations. The Oursan? 
 sandstone formation rests with an angular discordance of about 15 
 degrees upon the Panoche formation (Upper Cretaceous) and is overlain 
 unconformably by the Livennore gravels (Plio-Pleistocene). The beds 
 dip 35 degrees homoclinally to the northeast. These structural and 
 stratigraphic relations are represented in section B-B (pi. 3). 
 
 Cierbo Formation 
 
 The Cierbo formation was named by Clark '^^ who classified it as 
 the middle member of the San Pablo group of upper Miocene age. The 
 formation, herein called Cierbo, was mapped and described as '' undif- 
 ferentiated Miocene" by Anderson and Pack.''^^ 
 
 The Cierbo is a transgressive formation of widespread occurrence 
 over the northern part of the area. Exposures of the Cierbo formation 
 are limited and poor; but the occurrence of rounded quartz and black 
 chert pebbles in the soil and the widespread occurrence of the large 
 oj^ster, Ostrea hourgeoisii, aid in the recognition of the formation. 
 
 «^ Trask, Parker D., The Briones formation of middle California: Univ. California, 
 Dept Geol. Sci. Bull., vol. 13, p. 140, 1922. 
 
 "« Vanderhoof, V. L., A Study of the Miocene Sirenian Desmostylus : Univ. Cali- 
 fornia, Dept. Geol. Sci. Bull., vol. 24, pp. 169-262, 1937. 
 
 «» Harding, John "W. Jr., The geology of the southern part of the Pleasanton quad- 
 rangle, California, Master's thesis, University of California, 1940 (unpublished). 
 
 '° Clark, B. Li., The marine Tertiary of the west coast of the United States ; its 
 sequence, paleogeography, and problems of correlations : Jour. Geology, vol. 29, pp. 
 583-614, 1921. 
 
 ■^ Op. cit. 
 
STRATIGRAPHY 41 
 
 Nowhere in the area is a good section of Cierbo sediments exposed, and no 
 accurate measurement of the formation can be made. However, it is 
 estimated that the maximum thickness is about 500 feet. 
 
 Lithology. Several different types of lithology are found in the 
 Cierbo sediments. Beds of white quartzose sands resembling those of 
 the Tesla formation are common. The sands are poorly sorted, coarse 
 grained, massive to cross-bedded, friable, streaked with limonite, and 
 carry rounded pebbles of quartz and black chert. Yellow or buff sands 
 are also common. A conglomerate carrying rounded pebbles and cobbles 
 of quartz, vari-colored cherts, lavender quartzite, and sandstone occurs 
 locally in the SE i sec. 24, T. 2 S., R. 2 E. Northwest of Tesla a conglom- 
 erate carrying angular pebbles and cobbles of Franciscan chert and sand- 
 stone characterizes the base of the Cierbo. Tuffs and carbonaceous brown 
 shale are locally present. A bed of white tuff has been mined at the K-ola 
 mine in sec. 27, T. 3 S., E. 3 E. The tuff is made up of 97 percent clear 
 glass with a refractive index of 1.50, quartz (2 percent), kaolinized feld- 
 spar (1 percent) and traces of pale biotite and magnetite. Also in the 
 tunnel of the K-ola mine several lignite seams, locally 2 feet thick, are 
 associated with brown carbonaceous shales. 
 
 A sample of the white granuliferous sandstone was examined petro- 
 graphically. Quartz makes up 70 percent of the sample. Kaolinized feld- 
 spar, chiefly orthoclase and a little microcline, constitute 10 percent of 
 , the sample. Black, gray, and green chert particles make up most of the 
 remaining 20 percent. HeaYj minerals represent only a small fraction of 
 a percent of the sandstone, but they comprise a large number of mineral 
 species. Of these magnetite andilmenite are very common ; zircon is fairly 
 common ; garnet, basaltic and green hornblende, andalusite, hypersthene, 
 zoisite, and broAvn biotite are sparse ; and titanite, brown tourmaline, 
 staurolite, actinolite, and glaucophane are rare. There is some similarity 
 between the above mineral assemblage and that described for the Eocene 
 white sands, and it would appear that the Cierbo white sands may have 
 derived the bulk of their constituent minerals from the same hypothetical 
 source area, the Sierra Nevada. However, the presence of grains of 
 actinolite, glaucophane, and chert suggests that areas of Franciscan rocks 
 in the Coast Ranges were also suppljdng some of the detritus for the 
 sediments. 
 
 Fauna and Correlation. The numerous fossil symbols indicated in 
 the areas of Cierbo rocks on the geologic map mark the occurrence of the 
 large oyster, Ostrea hourgcoisii, generally as fragments in the soil. A zone 
 of this oyster characteristically occurs from 50 feet to 150 feet above the 
 base of the formation. The parallelism of the oyster zone with the basal 
 contact of the formation is well demonstrated on the southwestern flank 
 of the Altamont anticline. Other marine fossils are generally limited in 
 occurrence and poorly preserved, but at locality No. VII near the south- 
 ern boundary of sec. 3, T. 3 S., R. 3 E., a fair collection was obtained. 
 Mrs. P. Rossello Nicholson contributed the identifications which are listed 
 below. 
 
 The occurrence of Ostrea lourgeoisii and Pecten raymondi in the 
 formation is indicative of upper Miocene age, and the formation is con- 
 sidered as correlative with the Cierbo formation at Mt. Diablo. 
 
 Fragments of petrified wood are frequently found in soil of the 
 Cierbo formation, and a few leaf impressions were noted in a tuff that 
 outcrops at the K-ola mine. 
 
42 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 Checklist of some Cierho fossils 
 
 Localities 
 VII Kola mine 
 
 Gastropoda 
 
 Acteon sp. X 
 
 Calyptraea sp. C 
 
 Littorina n. sp. X 
 
 Polynices kerkerensis Clark X 
 
 Pelecypoda 
 
 Cardium sp. X 
 
 Cryptomya sp. X 
 
 Macoma andersoni Clark X 
 
 Mulinia gabbi X 
 
 Ostrea bourgeoisii Remond C 
 
 Panope generosa Gould — X 
 
 Pecten raymondi Clark X 
 
 Pecten tolmani C 
 
 Solen perrini Clark X 
 
 Tellinia salmonea Carpenter X 
 
 X = present C = common 
 
 Relation to Adjacent Formations. The Cierbo, a transgressive for- 
 mation, is structurally involved in the regional folding and faulting. 
 Over most of the area it rests with angular unconformity upon Panoche 
 rocks; this relationship suggests that there were some conditions of 
 folding and erosion prior to the transgression of the Cierbo. In the vicin- 
 ity of Tesla the Cierbo has both faulted and unconformable relationships 
 with the Tesla formation. Nowhere in the area is the Cierbo found in 
 conjunction with the Oursan ? sandstone. The Cierbo is overlain conform- 
 ably to unconformably by the Neroly formation, which is the upper mem- 
 ber of the San Pablo group. Apparently there are slight angular dis- 
 cordances between the attitudes of bedding in the Cierbo and Neroly 
 formations in several places, but the vagueness of the bedding in the 
 Cierbo makes the interpretation uncertain. Over most of the area a basal 
 reef bed of the Neroly consisting of blue sandstone and tuffaceous shale 
 rests sharply on the incoherent coarse white sands of the Cierbo. In the 
 vicinity of Kock Cut in the SE i sec. 25, T. 2 S., R. 3 E., and northward, 
 the Cierbo is lapped out by the Neroly, which there rests unconformably 
 upon the Panoche. This unconformity between basal Neroly gravels and 
 Panoche sandstone is well exposed in a road cut at the east end of the 
 new U. S. Highway 50. 
 
 Neroly Formation 
 
 The Neroly formation was named by Clark and Woodford "^^ as the 
 upper formation of the San Pablo group, which was defined originally to 
 include only the Cierbo and Neroly formations. Anderson and Pack '^^ 
 described what is herein called Neroly as the San Pablo formation. 
 
 Distribution and Thickness. The Neroly was probably once a con- 
 tinuous sheet of sediments over the northern part of the area, but much 
 of the formation was stripped off by eroison following a post-Neroly 
 period or periods of deformation, and today the rocks are preserved 
 chiefly in synclinal areas. The northeastern part of the area is well 
 blanketed by blue sandstones, conglomerates, and shales of the formation. 
 
 '= Clark, B. L., and Woodford, A. O., The geology and paleontology of the type 
 section of the Meganos formation of California: Univ. California, Dept. Geol. Sci. Bull., 
 vol. 17, p. 69, 1927. 
 
 "Op. cit., pp. 96-100. 
 
STRATIGRAPHY 43 
 
 To the northwest the Neroly extends into the Byron and Mt. Diablo quad- 
 rangles, and to the southeast it continues across the Carbona quadrangle 
 and along the west border of the San Joaquin Valley. 
 
 In the Tesla area the Neroly is conveniently divided into two parts, 
 as follows : a lower part consisting mainly of blue sandstone, some ande- 
 sitic boulder conglomerates, and interbeds of tuffaceous clay shales ; and 
 an upper part consisting mainly of poorly exposed clays, and minor 
 interbeds of soft brownish sands, gravels, and some blue sandstone. The 
 lower blue sandstone unit ranges in thickness from about 100 to 700 feet, 
 and the maximum thickness is developed along the north side of Corral 
 Hollow. The upper shales reach a thickness of at least 2000 feet, but a 
 measurement of their complete thickness could nowhere be obtained as 
 the top of the formation is masked by the alluvium of the San Joaquin 
 Valley. This division of the Neroly is an arbitrary one ; and the contact, 
 which is represented on the geologic map (pi. 1), does not everywhere 
 occur at the same stratigraphic horizon. 
 
 LitJiology. The most distinctive rock type in the Neroly is blue 
 sandstone, which resembles the so-called "vivianitic" sandstones of the 
 Etchegoin formation near Coalinga. The blue color of the sands is caused 
 by opalescence from a dull opaline coating on the grains. This coating- 
 can be removed by boiling a sample of the sand in a solution of potassium 
 hydroxide. Heavy mineral separations were made of two samples of the 
 blue sands. The light minerals constitute about 87 percent of the sample. 
 Quartz, oligoclase, and labradorite are sparsely present. Black micro- 
 crystalline to glassy lava particles containing microlites make up a large 
 part of the light material, and these particles resemble the groundmass 
 of many of the cobbles of andesite porphyry found in the Neroly con- 
 glomerates. The bulk of the light grains are opaque, somewhat magnetic, 
 and angular in shape. The heavy minerals literally rain down during a 
 separation and make up about 13 percent of a sample. Among the heavy 
 minerals, augite is abundant ; brown basaltic hornblende and hypersthene 
 are very common ; green hornblende, magnetite, and andesitic ground- 
 mass particles are rather common ; titanite and epidote are sparse. The 
 mineral assemblage suggests a source area of andesitic rocks. The absence 
 of typical Franciscan minerals and the dissimilarity of the heavy mineral 
 assemblage with that of the Tesla formation are noteworthy. 
 
 The Neroly conglomerates consist of rounded andesitic pebbles and 
 cobbles set in a matrix of blue sandstone. The cobbles range from 2 to 5 
 inches in diameter. Seventeen thin-sections Avere studied of representa- 
 tive cobbles. Of these, six are augite-plagioclase andesite porphyry, five 
 are hornblende-plagioclase andesite porphyry, three are hypersthene- 
 augite-plagioclase andesite porphyry, and three are hornblende-pyroxene- 
 plagioclase andesite porphyry. All of the andesite porphyries have many 
 features in common, and differences in classification are based upon the 
 characterizing phenocrysts of the rocks. It is convenient, therefore, to 
 describe the rocks as a group, noting any special features. The pheno- 
 crysts constitute about 55 percent of a porphyry in thin-section and 
 range in length from ^ to 3 millimeters. Labradorite and andesine- 
 labradorite (Ab45Anr,5 to AbsoAnjo) make up from 65 to 90 percent of 
 the phenocrysts. The feldspars show such features as albite and pericHne 
 twinning, delicate zoning, strong dispersion, "dust-charged" cores, and 
 partial to complete resorption of some of their outlines. Augite is very 
 common as a phenocryst, ranging to as much as 20 percent of the total 
 
44 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 phenocrysts. Some of the augite is present in euhedral basal sections 
 having good cleavages. Twinning is common, and dispersion in the augite 
 phenocrysts is strong. Hypersthene, which is present as a phenocryst in 
 six of the thin-sections, constitutes a maximum of 30 percent of the 
 phenocrysts in one sample. Hypersthene shows good pleochroism and 
 well-developed pyramidal terminations of the prisms. Brown basaltic 
 hornblende is another principal phenocryst in some of the porphyries, 
 constituting from 1 to 10 percent of the phenocrysts. It appears in pris- 
 matic and euhedral basal sections having good cleavages, and shows 
 resorption rims of magnetite dust. Some of the hornblende crystals are 
 completely resorbed, and the magnetite dust retains the distinctive out- 
 line of the parent mineral. The hornblende is pleochroic from yellow to 
 red-brown and frequently contains small feldspar inclusions. Pale biotite 
 is very rare as a phenocryst. 
 
 The groundmass textures of the porphyries are dominantly pilo- 
 taxitic, some show a fluidal or trachytic tendency, and a few are hyalo- 
 pilitic. The groundmass is dark to black in color. Under the microscope 
 with the nicols crossed and a low power objective, the darkness of the 
 groundmass suggests the presence of glass, but in most cases under high 
 power the groundmass is seen to be microcrystalline to cryptocrystalline. 
 However, three of the sections do appear to have a glassy base. In one 
 of the sections examined, the groundmass is thoroughly oxidized and 
 very red in color. Microlites of oligoclase-andesine are very common. 
 Some fine augite is present, and magnetite is abundant as small specks in 
 the groundmass. Vesicles are present in more than half of the sections. 
 Many of the vesicles are lined with opal, which under the microscope is 
 pale brown in color but which in hand specimen appears dull bluish. 
 A few secondary minerals, such as epidote, sericite, calcite, and limonite 
 are also present. 
 
 A few samples of tuff were examined petrographically and found 
 to be composed of fine andesitic detritus. 
 
 Source Area for the Neroly Sediments. Turner '^* has described 
 and illustrated from the Sierra Nevada some andesite porphyries which 
 petrographically seem to be identical with the andesite porphyry cobbles 
 herein described from the Neroly. In 1924 Louderback ''^^ pointed out 
 the following: 
 
 "The distribution and character of the andesitic conglomerates of the 
 
 San Pablo correspond well with a derivation from the Sierra Nevada during 
 
 the period of andesitic eruption." 
 
 In the Tesla quadrangle the Neroly conglomerates are most promi- 
 nent in the eastern part of the area, so that their distribution is con- 
 sistent with a Sierra Nevada source as suggested by Louderback. The 
 tuffs and blue sandstones also carry andesitic detritus. All evidence seems 
 to point to the Sierra Nevada as the probable source area for the detrital 
 material in the Neroly sediments. 
 
 Fauna and Flora. No marine fossils were found in the Neroly in 
 the Tesla quadrangle, but marine fossils are known from the Neroly in 
 the Mt. Diablo area. The only fossils found were leaves, horse teeth, and 
 petrified wood. 
 
 '* Turner, H. W., The rocks of the Sierra Nevada : U. S. Geo!. Survey Ann. Bept. 
 14, pp. 487-490, 1894. 
 
 '= Louderback, G. D., Period of scarp production in the Great Basin : Univ. Cali- 
 fornia, Dept. Geol. Sci. Bull., vol. 15, p. 16, 1924. 
 
STRATIGRAPHY . 45 
 
 Teeth fragments and foot bones of a horse were found by Dr. P. "W. 
 Reinhart of the Shell Oil Inc. in a 10-foot gravel bed in the middle of 
 the lower blue sandstone unit. The locality (University of California 
 locality V-3620) is on a small ridge near a point where a fence crosses 
 the ridge about 500 feet due west of the southeast corner of sec. 21, T. 
 3 S., R. 4 E. Dr. R. A. Stirton, formerly of the University of California, 
 examined the teeth and classified them as belonging to Nannipus sp. 
 From four other localities in the adjoining Carbona quadrangle teeth 
 fragments found in the Neroly by Reinhart were identified by Stirton 
 as Nannipus cf. tehonense and Pliohippus sp. Stirton,'^^ on the basis of 
 the teeth, regards the age of the Neroly as probably upper lower Pliocene, 
 approximately equivalent to the Chanac beds of the lower San Joaquin 
 Valley and older than the * ' vertebrate Jacalitos. ' ' 
 
 In the Tesla quadrangle a fairly regular zone of fossil leaves occurs 
 from 10 to 30 feet above the base of the Neroly. Condit'^'^ has published 
 on the fossil flora of the San Pablo, and two of his localities are in the 
 Tesla quadrangle. Leaf collections made by the writer were presented to 
 Condit for study and inclusion with the material he collected. 
 
 Partial list of the San Pablo (Neroly) flora, after Gondii 
 
 University of California Localities 
 
 P 361 199 
 
 (Corral Hollow) (Altamont Pass) 
 
 Flora : 
 
 Alnus corrallina Lesquereaux X A 
 
 Betula multineruis Jennings X A 
 
 Cyperacites sp. X 
 
 Equisetum sp. R 
 
 Juglans oregoniana A 
 
 Magnolia californica Lesquereaux R 
 
 Nyssa knowltoni Berry R 
 
 Persea princeps Heer C R 
 
 Platanus dissecta Lesquereaux R R 
 
 Populus alexanderi Dorf X X 
 
 Populus balsamoides Goepp C R 
 
 Prunus chaneyi n. sp R C 
 
 Salix sp. X C 
 
 A = abundant C = common X = present B = rare 
 
 Some of the conclusions reached by Condit '^^ are as follows : 
 
 1. The flora is most similar to the present swampy coastal plain forest of 
 the southeastern United States. 
 
 2. The climatic conditions were abundant rainfall evenly distributed 
 throughout the year and a warm average temperature. 
 
 3. The age of the leaf-bearing beds of the Neroly is probalily upper Miocene 
 on the basis of the flora and indicated climate. 
 
 However, Condit entertained the possibility that the beds were transi- 
 tional Mio-Pliocene. Chancy, Condit, and Axelrod ''^ in a recent book 
 on the Pliocene floras of California and Oregon now regard the age 
 of the Neroly flora as probably transitional Mio-Pliocene and correlate 
 the flora with those from Remington Hill and Table Mountain on the 
 lower slopes of the Sierra Nevada. 
 
 " stirton, R. A., Cenozoic mammal remains from the San Francisco bay region : 
 Univ. California, Dept. Geol. Sci. Bull., vol. 24, pp. 339-410, 1939. 
 
 " Condit, Carlton, The San Pablo flora of west central California : Carnegie Inst. 
 Washington, Contr. Paleontology 476, pp. 217-268, 1938. 
 
 "Op. cit, p. 250. 
 
 '* Chaney, R. W., Condit, C, and Axelrod, D. I., Pliocene floras of California and 
 Oregon: Carnegie Inst. Washington Pub. 553, 1944. 
 
46 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 Fragments of petrified wood are common in the Neroly sediments. 
 Mr. Dougherty, formerly of the University of California, identified one 
 specimen as a dicot and another as larch (Larix) or Douglas fir (Pseu- 
 dotsuga). 
 
 Age of the Neroly. The problem of whether the Neroly is upper 
 Miocene, lower Pliocene, or transitional Mio-Pliocene has long been a 
 matter of disagreement among geologists. In 1915 Clark gave a summary 
 of the opinions of previous workers and assigned what was later called 
 Neroly to the upper Miocene on the basis of the percentage of recent 
 species in the invertebrate fauna. In 1924 Louderback reviewed the 
 published opinions concerning the age of the San Pablo and postulated 
 the probable derivation of the andesitic material in the San Pablo sedi- 
 ments from the Sierra Nevada during the period of andesitic eruptions. 
 Condit in his study of the San Pablo flora originally favored an upper 
 Miocene age, but later joined with Chancy and Axelrod in regarding the 
 Neroly flora as probablj' transitional Mio-Pliocene. Stirton proposed a 
 lower Pliocene age on the basis of the vertebrate remains. 
 
 In this report the Neroly is conveniently left assigned to the upper 
 Miocene. However it is recognized that the more recent trend in strati- 
 graphic assignment is to regard the formation as Mio-Pliocene transi- 
 tional or as lower Pliocene. It seems appropriate to merely report the 
 organic and physical evidence found in the Tesla quadrangle that may 
 have a bearing on the age problem and therewith leave the problem to 
 stratigraphers to settle from evidence more widely gained. 
 
 In the Tesla quadrangle no marine invertebrate fossils were found 
 in the Neroly and the organic evidence is limited to the flora and verte- 
 brate remains, for which respective age indications have already been 
 mentioned. The sediments, the flora, and the vertebrate fauna all seem to 
 indicate a broad coastal plain as a site of deposition. It is conceivable that 
 this coastal plain may have been marginal to a marine environment of 
 deposition in the Mt. Diablo area, from which Clark has described an 
 invertebrate fauna. In support of this geographic setting, Axelrod ^° 
 mentions plant species from the Neroly in the Mt. Diablo area that appear 
 to have lived closer to a coast line than the species found in the Tesla area. 
 
 Leaving aside the conflict in age assignment based upon the different 
 types of fossil remains, geological observations in the Tesla quadrangle 
 seem to indicate a time interval of some extent between the periods of 
 deposition of the Cierbo and Neroly. In the northeastern part of the area 
 the Neroly laps out the Cierbo and rests with angular unconformity 
 on the Panoche. In most places the Neroly overlies the Cierbo with sharp 
 disconformity and in some places a slight angular discordance between 
 the two formations is observed. This boundary marks a change from a 
 marine environment of deposition for the Cierbo sediments to a broad 
 flood plain or coastal plain as a local site of deposition for the Neroly. 
 This distinct change in character of the sediments from the white 
 quartzose pebbly sands of the Cierbo to the tj^pically blue Neroly sedi- 
 ments composed of andesitic detritus must indicate a time interval 
 sufficient to allow for at least a local withdrawal of the seas, a slight 
 uplift of the lands, and the introduction of andesitic volcanic activity 
 in the Sierra Nevada which is believed to have served as a source area for 
 both sets of sediments. Whether this time interval represents the bound- 
 
 «•> Chaney, Condit, and Axelrod, op. cit. 
 
STRATIGRAPHY 47 
 
 ary between the Miocene and Pliocene or an interformational uncon- 
 formity within the upper Miocene is problematical. It is significant 
 however, to point out the physical eAddence here for a break between the 
 Cierbo and Neroly formations, which are classified as the upper two mem- 
 bers of the tripartite San Pablo group. 
 
 Relation to Adjacent Formations. The contact between the Neroly 
 and Cierbo formations and the unconformable relation between the 
 Neroly and the Panoche in the northeast part of the area have already 
 been described. On the east side of Livermore Valley the Neroly sediments 
 are overlapped by the Livermore gravels, presently to be described. In 
 the northeast part of the quadrangle the Neroly is overlain by the Tulare 
 formation composed mostly of Franciscan detritus, but the contact is 
 not exposed. 
 
 Tertiary-Quaternary System 
 Pliocene-Pleistocene Series 
 Livermore Gravels 
 
 The name, Livermore gravels, was applied in 1925 by Vickery ^^ 
 to a group of fresh-water gravels, sands, and clays bordering on the 
 southern part of Livermore Valley. 
 
 Distrihution and Thickness. These beds occupy an area of about 14 
 square miles in the central western part of the Tesla quadrangle. The 
 deposits have a nearly plane surface gently inclined toward Livermore 
 Valley, and topographically this surface averages from 250 to 500 feet of 
 elevation above the general level of the valley. The tableland has been 
 considerabl}^ dissected, but exposures are poor. The total thickness of the 
 gravels was estimated by Branner ^- to be about 4000 feet. 
 
 Several odd occurrences of the gravels were found. One of these is 
 in the lap of the syncline north of Corral Hollow. From this point the 
 gravels can be traced westward to join the main extent of the gravels on 
 the south side of the Livermore Valley. High on Rocky Ridge along the 
 common boundary of sees. 23 and 24, T. 4 S., R. 2 E., a small outlier was 
 found in which the gravels are dipping 20° NE. and resting with angular 
 discordance on the Panoche sandstones on the north side of the Williams 
 fault zone. Involvement of the gravels in the faulting is further evidenced 
 by an occurrence of gravels noted by Bailey Willis ^^ in a phase of the 
 Williams fault zone in the Hetch-Hetchy tunnel. 
 
 Lithology. Massive buff gravels composed chieflj^ of Franciscan 
 detritus are characteristic of the formation. Light gray to buff sands are 
 common, and sandy clays make up a minor part of the formation. One 
 ledge-forming tuff layer, which averages 10 feet in thickness, occurs 
 prominently in the upper part of the formation in sec. 18, T. 4 S., R. 3 E. 
 
 A heavy mineral separation of a sample of light gray, fine sand from 
 the NW:^ sec. 6, T. 4 S., R. 3 E., was examined petrographically. The 
 light minerals consist of kaolinized feldspar (55 percent), quartz (30 
 percent), oligoclase-andesine (10 percent), chert particles (1 to 2 per- 
 cent), chlorite (2 to 3 percent), and pale biotite (trace). Heavy minerals 
 comprise 1.26 percent of the whole sample. Of these, basaltic hornblende 
 is abundant; magnetite, chromite (?), and glaucophane are very com- 
 
 *" Vickery, F. P., The structural dynamics of the Livermore region, Doctor's thesis, 
 Stanford University; 1925 (unpublished). 
 
 "-Op. cit. 
 
 ''Unpublished geologic report on the Hetch-Hetchy tunnel for the San Francisco 
 Engineering Department. 
 
48 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 mon ; zircon and green hornblende are rather common ; titanite, epidote, 
 actinolite and garnet are sparse. The general assemblage suggests a 
 source area of Franciscan rocks, but the presence of basaltic hornblende 
 may indicate a derivation of some of the detritus from another source, 
 perhaps an area of Neroly rocks. 
 
 The tuff, which was mentioned above, contains the following light 
 minerals : pale brown glass (10 percent ; refractive index = 1.460) , devit- 
 rified glass (80 percent), kaolin minerals (3 percent), quartz (2 per- 
 cent), sericitized and kaolinized feldspar (4 percent) , plagioclase (trace) , 
 chlorite (trace), and muscovite (trace). Among the heavy minerals, 
 magnetite is abundant; glaucophane, basaltic hornblende, and epidote 
 are very common ; green hornblende and chromite ( ? ) are sparsely 
 present. Mineralogically this tuff does not appear correlative with the 
 Pinole tuff east of San Francisco Bay. 
 
 The Livermore gravels are primarily fluviatile deposits laid down 
 over a broad flood plain but may include lacustrine sediments under the 
 alluvium of Livermore Valley. 
 
 Correlation. No fossils were found by the writer, but Branner ^^^ 
 reports finding fresh-water fossils within 340 feet of the base of the forma- 
 tion at Cuesta Blanca on Arroyo del Valle. 
 
 The age and correlation of this formation are uncertain. Branner 
 referred these beds to the Orinda formation, but the Orinda is now 
 regarded as probably older. Vickery ^^ postulated a correlation of the 
 Livermore gravels with the Santa Clara formation (Plio-Pleistocene). 
 Hannibal ^"^ also regarded these beds as correlative with the Santa Clara 
 formation, from which he described some leaves. The late B. L. Clark ^'^ 
 informed the wi'iter that the Livermore gravels are probably correlative 
 with the Tassajero formation, which he named some beds on the north 
 side of Livermore Valley. 
 
 Relation to Adjacent Formations. Structurally the formation dips 
 at angles of 10 to 30 degrees northward towards Livermore Valley. At 
 different places it rests unconformably on the following formations: 
 Neroly, Cierbo, Oursan ?, Panoche, and Franciscan. The formation 
 extends out under the alluvium of Livermore Valley and was regarded 
 by Branner ^^ as an important conductor of water for the valley. 
 
 Tulare Formation 
 
 The Tulare formation is of very limited extent in the northeastern 
 part of the area. Anderson and Pack ^^ have described and mapped this 
 formation as a narrow strip along the west border of the San Joaquin 
 Valley from the Coalinga area northward to the eastern boundary of 
 the Tesla quadrangle. The formation is poorly exposed locally, and 
 characterized by a surface containing Franciscan detritus weathered 
 from the gravels. This formation may be seen to better advantage in 
 the Carbona and other quadrangles to the southeast. The deposits are 
 fluviatile in origin and consist mainly of brown ill-sorted sands, gravels, 
 and clays. Areas of Franciscan rocks have apparently supplied most of 
 the detritus. No estimate of the thickness is made. 
 
 s'' Op. cit, p. 216. 
 *" Op. clt., Jour. Geology. 
 
 8« Hannibal, Harold, A Pliocene flora from the Coast Ranges of California : Torrey 
 Botanical Club Bull., vol. 38, pp. 329-342, 1911. 
 " Oral communication, 1937. 
 88 Op. cit., pp. 209-222. 
 8»Op. cit., pp. 101-105. 
 
STRATIGRAPHY 49 
 
 Fauna and Age of the Tulare. No fossils were found locally in tlie 
 Tulare. However, Vanderhoof ^° reports fossil remains of a camel, Came- 
 lops hesternus, and a ground sloth, Mylodon harlani, from the upper 
 part of the formation in the Carbona quadrangle. The locality is near 
 the Tesla portal of the Hetch-Hetchy tunnel in the NEi sec. 33, T. 3 S., 
 R. 5 E. Vanderhoof regards the fauna as correlative with that of Rancho 
 La Brea, or late Pleistocene in age. 
 
 Vanderhoof also reports that some camel bones were found by P. W. 
 Reinhart at a locality near the base of the Tulare formation in the 
 Carbona quadrangle and that these are tentatively regarded as Pliocene 
 in age. From the evidence of vertebrate faunas from near the top and 
 base of the formation, it may be said that the Tulare ranges in age from 
 Pliocene to late Pleistocene. 
 
 Quaternary System 
 Terrace Deposits and Alluvium 
 
 Terraces were mapped in a few of the stream valleys. In Arroyo 
 Mocho there are some well-defined terraces which suggest several stages 
 of regional uplift during the Quaternar}-. Two levels and in places three 
 levels of terraces are cut into the Livermore gravels. A veneer of gravels 
 is discontinuous over the shelves, which are mainly erosional in origin. 
 In Corral Hollow mapping of the terraces was done locally, except where 
 the scale of the map and complexity of the geolog}^ interfered. On the 
 south side of Corral Hollow between Tesla and Mitchell Ravine a terrace 
 has been cut into the Moreno and Eocene rocks about 200 feet above 
 the creek level. Another prominent terrace level is about 50 feet above 
 the creek and carries a capping of about 15 feet of gravels. 
 
 Alluvial deposits complete the stratigraphic column. Portions of 
 the Livermore and San Joaquin Valleys which are included within the 
 Tesla quadrangle are alluviated. In Corral Hollow Creek near Carnegie, 
 alluvial gravels consisting of andesitic pebbles from the Neroly and rock 
 particles from older formations, have been excavated and graded for use 
 as railroad ballast and in concrete. 
 
 STRUCTURE 
 
 For about 75 miles along the west border of the San Joaquin Valley 
 from Panoche Creek northward to Hospital Creek, a rather simple 
 homoclinal section of Cretaceous and Tertiary rocks dip valleyward 
 under the alluvium. In contrast, northwest of Hospital Creek across the 
 Carbona, Tesla, Byron, and Mt. Diablo quadrangles, the geologic struc- 
 ture is complex and characterized by numerous folds and faults. 
 
 Many of the structural features, including those within the areas 
 of Franciscan rocks, have already been described or mentioned in the 
 description of the stratigraphy. The main structural lines and axes, and 
 the attitude and succession of the strata are represented areally on 
 the geologic map (pi. 1). The interpretation of the subsurface struc- 
 ture is presented in the sections (pi, 3). 
 
 Folds 
 Altamont Anticline. The largest fold in the area is the broad 
 Altamont anticline in the central northern part of the quadrangle. The 
 limbs and axis of this fold, which was named by Anderson and Pack,^^ 
 
 •"Oral communication, 1937. 
 " Op. cit., p. 191. 
 5—85413 
 
50 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 are well exposed in road cuts along the old Altamont Pass highway 
 and along the new TJ. S. Highway 50. The axis of this fold trends about 
 42 degrees west of north and can be traced for 4^ miles in the Tesla 
 quadrangle and about 3 miles to the northwest in the Byron quadrangle. 
 The plunge of the fold is to the southeast. Section A- A' (pi. 3), which 
 is a transverse section through the fold, illustrates the general sym- 
 metry of the fold. Dips on the east flank average 16 degrees; those 
 on the west flank range from 12 to 36 degrees, making the west flank 
 slightly steeper. Down-flank on both the west and east limbs, high- 
 angle faults parallel the axial trend of the fold. 
 
 The northwest extension of the Altamont anticline in the Byron 
 quadrangle is represented by Taff ^^ on a geologic map of the Mt. Diablo 
 area as abruptly but simply dissolving into a northwest-dipping homo- 
 clinal section of Cretaceous and post-Cretaceous rocks. However, a 
 reconnaissance inspection of this area of structural change indicates a 
 zone of faulting truncating the anticline and separating it from the 
 homoclinal section to the northwest. This fault zone, which trends north- 
 eastward, is marked by numerous springs. 
 
 The Altamont fold involves principally rocks of the Panoche forma- 
 tion and to a minor extent Cierbo and Neroly formations. In section 
 A-A' a marked angular unconformity is represented between the Cierbo 
 and Panoche formations on the west flank of the fold. This uncon- 
 formity is interpreted as indicating that the inception of folding on 
 this anticline was pre-Cierbo in age. It further allows for the possibility 
 that Moreno Grande and Eocene sediments may have been deposited 
 above the Panoche formation and then folded and eroded away prior to 
 the transgression of the Cierbo formation. However, the absence of sedi- 
 ments of an age between tliat of the Panoche and Cierbo formations in 
 the Altamont area may mean that a post-Panoche folded high, locally 
 denied their deposition. Instead of a folded high, a positive fault block, 
 the Altamont block, as postulated by Clark ^^ would also have denied 
 deposition of the missing sediments. However, the fault-block concept 
 seems less applicable than either of the two preceding explanations men- 
 tioned, since there is evidence of pre-Cierbo folding but no direct evidence 
 of pre-Cierbo faulting. 
 
 It is also significant that on the west flank of the anticline the Cierbo 
 formation rests on the Panoche, while on the east flank the Neroly over- 
 lies the Panoche, and the Cierbo is lapped out. It is possible that the 
 Cierbo was not deposited locally on the east flank of the Altamont fold. 
 It is equally (if not more) possible that its deposition there was fol- 
 lowed first i)y an accentuation of the ancestral Altamont fold and then 
 by a stripping off of the Cierbo sediments prior to the deposition of the 
 Neroly sediments. The significance of the Neroty-Cierbo overlap ha^ 
 already been discussed. The closing stages of the folding of the Alta- 
 mont anticline were post-Neroly. 
 
 Small Faulted AnticU7ie. A small faulted fold in the S^ sec. 8, 
 T. 3 S., R. 4 E., is probably a continuation of the Altamont line of 
 folding. The axis is not well defined in the smooth hills of Cretaceous 
 rocks which make up the core, but it trends approximately S. 80° E. 
 
 »2 Op. cit. 
 
 «' Clark, Bruce L., Tectonics of the Valle Grande of California : Am. Assoc. Petro- 
 leum Geologists Bull., vol. 13, p. 228, 1929. . . . Tectonics of the Coast Ranges of middle 
 California: Geol. Soc. America Bull., vol. 41, p. 776, 1930. 
 
STRUCTURE 
 
 51 
 
 The Cretaceous rocks are overlain by Cierbo and Neroly beds on the 
 flanks. The north limb of the fold towards the east is a sharp flexure 
 which passes westward into a thrust fault that cuts out the Cierbo, 
 bringing Cretaceous rocks in contact with overturned Neroly blue 
 sandstone. Section E-E' (pi. 3) is drawn through this structural com- 
 plication. 
 
 Patterson Pass Anticline. The Patterson Pass anticline, which 
 can be traced for about 7^ miles across the north-central portion of 
 the area, is interesting because more than a dozen wells have been 
 drilled along its flanks and axis in an attempt to find a commercial 
 accumulation of petroleum. The fold plunges at both east and west 
 ends. The west end of the fold is truncated diagonally by the Carnegie 
 fault. The axial trend is about S. 80° E. in the western part, turning 
 slightly to S. 70° E. in the east half. The central portion of the axis 
 is cut diagonally by the Patterson Pass fault at the locality of the 
 Seaboard Oil Company- Johnston No. 1 well (sec. 13, T. 3 S., R. 3 E.) 
 and by a lesser fault about a third of a mile to the east. 
 
 Panoche rocks are exposed in the core of the anticline which is 
 flanked by Cierbo and Neroly beds. Locally down flank on the south 
 side poorly exposed Moreno Grande shale occurs in the NW^ sec. 24, 
 T. 3 S., R. 3 W. The occurrence of the Moreno Grande on the south side 
 of the fold is significant for two reasons : first, it may be related with 
 the showings of petroleum which were encountered principally in wells 
 drilled on the south flank ; and second, the occurrence strengthens the 
 concept that Moreno Grande was deposited to the north of Corral Hollow 
 and later almost entirely stripped off following a period of pre-Cierbo 
 folding. 
 
 The age of the folding is post-Neroly and earlier than the several 
 faults which cut the fold. 
 
 Patterson Pass Syncline. North of the Patterson Pass anticline and 
 paralleling it roughly there is a broad synclinal area, the Patterson Pass 
 syncline. The axis, which is discontinuous and interrupted by faulting, 
 can be traced for about 6 miles. The axial trend is S. 65° E. in the west- 
 ern portion, turning to about S. 82° E. in the eastern portion. Rocks of 
 the Neroly formation occur in the lap of the syncline, and rocks of the 
 Cierbo and Panoche formations are exposed on the upturned flanks and 
 in faulted areas. 
 
 The age of the fold is post-Neroly. 
 
 Midway Anticline. A small anticline, herein given the name of Mid- 
 way anticline, extends southeastward (S. 35° E.) across sees. 10 and 14 
 in T. 3 S., R. 4 E. Panoche rocks are exposed in the core in two isolated 
 patches, and Cierbo and Neroly beds occur on the flanks. The plunge at 
 the northwest end is well exposed in the field. At the other end of the fold 
 where the beds appear to lap around, a plunge to the southeast is implied, 
 but the exposures are poor and the apparent closure may be a topographic 
 rather than structural effect. 
 
 The age of the fold is post-Neroly. 
 
 Synclinal Area North of Corral Hollow. North of Corral Hollow the 
 San Pablo rocks are involved in a discontinuous synclinal structure that 
 trends eastward for about 3 i miles. The Corral Hollow fault cuts the axis 
 diagonally in the western portion, a tear-fault offsets the axis just north 
 of Tesla, and the Carnegie fault cuts diagonally across the syncline at the 
 east end. 
 
52 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 In the Si sec. 24, T. 3 S., R. 3 E., the north limb of the syncline 
 becomes the south limb of a small anticline, which in turn is cut on its 
 north flank by the Carnegie fault. 
 
 The age of this fold is probably post-Li vermore gravels (Plio-Pleisto- 
 cene) , as gravels which are believed to be a part of the Livermore gravels 
 are folded and preserved in the lap of syncline. The fold is regarded as 
 earlier than the several faults which cut it. 
 
 Faults 
 
 Greenville Fault. In the northwest portion of the quadrangle there 
 is a fault which has been previously referred to as the Riggs Canyon fault 
 by Vickery ^^ and by Clark.^° The writer prefers to give this fault a local 
 name in the Tesla quadrangle to avoid involvement in a problem concern- 
 ing the delineation, and even the existence, of the Riggs Canyon fault in 
 the Mt. Diablo quadrangle. 
 
 The trace of the fault, which is herein designated as the Greenville 
 fault, trends approximately S. 40° E. The fault zone is best seen in a rail- 
 road cut of the Southern Pacific Railway Company near Greenville, just 
 north of the trestle across the old Altamont highway. Numerous gouged 
 and slickensided surfaces occur defining a zone of disturbance nearly 500 
 feet wide. The slickensided surfaces possess characteristically a steep to 
 vertical attitude with essentially horizontal striations. Near this locality, 
 on the west side of the fault, beds of the Cierbo and Neroly formations dip 
 northeastward into the fault; whereas east of the fault Panoche and 
 Cierbo strata dip southwestward toward the fault. Northwest and south- 
 east of Greenville the fault is traced principally with physiographic con- 
 trol. A sag pond occurs along the apparent trace about a mile northwest 
 of Greenville. The southeast trace of the fault is lost in the NB^- sec. 8, 
 T. 3 S., R. 3 E. ; and no structural connection to the southeast is observed 
 in the field between the Greenville fault and the Carnegie fault which 
 Clark ^^ regarded as a continuation of the "Riggs Canyon" (Greenville) 
 fault. 
 
 In addition to horizontal displacement, which was indicated from 
 examination of the striations on the fault surfaces, vertical displacement 
 has probably also taken place, and the area east of the fault is interpreted 
 as upthrown. An estimated order of magnitude for the vertical displace- 
 ment is 100 to 300 feet, but the estimate is questionable, as the base of the 
 Cierbo formation in the west side of the fault is not exposed. The age of 
 the Greenville fault is regarded as post-Neroly. 
 
 Midivay Fault. The Midway fault, which was named by Vickery ^"^ 
 cuts across the northeastern part of the area. From the vicinity of the 
 junction of the old and new highways, the fault is vaguely traceable for 
 about 3 miles to the southeast, and the northwestward extension of the 
 fault in the Byron quadrangle was not surveyed. The trend of the fault 
 is S. 40° E. The best evidence for the fault is seen on a small hill near the 
 southeast corner of see. 24, T. 2 S., R. 3 E. There the Cretaceous rocks 
 appear to be upthrown approximately 100 feet on the northeast side ; how- 
 
 0* Op. cit. 
 
 °'Op. cit., 1935. 
 
 "^Op. cit., 1935, p. 1038. 
 
 »' Op. cit, Jour. Geology, p. 614. 
 
STRUCTURE 53 
 
 ever, this apparent vertical throw may have resulted from horizontal dis- 
 placement along the fault. Nowhere is the fault exposed, and southeast of 
 the locality just mentioned its trace is indirectly suggested by such phy- 
 siographic features as furrows, sag ponds, and springs. Southeastward the 
 fault may dissolve into the Midway anticline, since its trace is lost in the 
 vicinity of the north end of that fold. 
 
 The age of the fault cannot be assigned more definitely than post- 
 Neroly. 
 
 Blach Butte Fault. The Black Butte fault is an important fault in 
 the Carbona quadrangle, but its northwest extension onto the Tesla quad- 
 rangle is weakly expressed in the physiography. This fault was named by 
 Keirihart ^^ from its occurrence at the east base of Black Butte near Corral 
 Hollow Creek in the Carbona quadrangle. Anderson and Pack^^ have 
 mapped the trace of this fault across the Carbona quadrangle. From 
 evidence in wells and in the Hetch-Hetchy tunnel in the Carbona quad- 
 rangle, the fault is known to be reverse in type and to dip about 45 degrees 
 to the southwest. In that area Upper Cretaceous strata are thrust over 
 Neroly (San Pablo) and locally over Tulare beds. 
 
 The age of the fault appears to be post-Tulare. 
 
 Patterson Pass Fault. An important fault, which is herein desig- 
 nated the Patterson Pass fault, was not recognized in previous published 
 geological reports on the area. It cuts diagonally across the central part 
 of the area in a cur\ang southeasterly trace. The maximum vertical dis- 
 placement on this fault is probably in the northern part of sec. 10, T. 3 S., 
 R. 3 E., where a remnant patch of Neroly blue sandstone occurs on the 
 northern downthrow side of the fault. The throw at this place is estimated 
 at 500 feet (see section C-C, pi. 3) , but a throw of 100 to 200 feet appears 
 to be more characteristic of other parts. Where the fault crosses the Pat- 
 terson Pass anticline, the Seaboard Oil Corporation Johnston No. 1 well 
 encountered it at the depth of 1400 feet. Other sympathetic fault zones 
 were encountered at greater depths in the well. In core samples from the 
 weU, the fault plane dips about 80 degrees, and the slickensiding indicates 
 shear displacement at an angle of 25 to 30 degrees from the horizontal. 
 The Patterson Pass fault is classified as a diagonal oblique-slip fault. 
 
 To the northwest the fault apparently joins the Greenville fault. 
 The two have some characteristics in common, such as strong horizontal 
 components of displacement and high angularity, but differ in having 
 their upthrow on opposite sides. To the southeast the Patterson Pass fault 
 is represented as joining other faults, which are believed to be north- 
 westerly diverging branches of the Tesla fault. 
 
 The fault is post-Neroly in age. It also appears to be post-folding 
 since it cuts diagonally across the Patterson Pass anticline. 
 
 Carnegie Fault. The Carnegie fault, which was named by Vickery,^°° 
 is a high-angle reverse fault striking N. 60° to 70° W. for more than 7 
 miles through the central portion of the quadrangle. It is nowhere well 
 exposed. However, its trace can be mapped over the central hill in sec. 23, 
 T. 3 S., R. 3 E., where the fault dips to the northeast and brings Cierbo 
 sediments over Neroly beds. The fault cuts through the old Hamilton 
 ranch on the south flank of the Patterson Pass anticline. Northwestward 
 it truncates diagonally the west plunge of the Patterson Pass anticline 
 and continues out under the alluvium of Livermore Valley. 
 
 »" Personal communication, 1936. 
 
 "Op. cit. 
 
 "»Op. cit.. Jour. Geology, p. 614, 
 
54 GEOLOGY OF TESLA QUADRANGLE [BuU. 140 
 
 The age of the fault is post-Neroly. However, Clark ^°^ believed that 
 the fault was existent in "pre-Briones (lower upper Miocene) time" 
 and he represented it as a continuation of his Riggs Canyon fault. In fact 
 he referred to the Carnegie fault as the "Riggs Canyon fault" in both 
 text and illustration. Not only is no connection observed in the field 
 between the Carnegie and Greenville (or Riggs Canyon) fault, but the 
 characteristics of the faults are quite different. The Carnegie fault is a 
 relatively high-angle reverse fault striking in general eastward; the 
 Greenville fault is essentially a vertical fault having horizontal and 
 some vertical components of displacement and a southeasterly strike. 
 Clark, in assigning the inception of movement along the Carnegie fault 
 to the pre-Briones, was impressed with the difference in stratigraphic 
 sequence north and south of the fault. 
 
 Corral Hollow Fault. Paralleling the Carnegie fault on the south 
 but having an opposing dip and opposite relation of upthrow, is the Cor- 
 ral Hollow fault, which was named by Vickery.^'^^ This fault branches 
 off at its east end from the Tesla fault, trends N. 80° W. up the north side 
 of Corral Hollow, curves or shifts northward in the vicinity of Tesla, and 
 then continues in the direction of N. 70° W. towards Livermore Valley. 
 It is best seen just west of where it crosses the Tesla road in the NW ^ sec. 
 25, T. 3 S., R. 3 E. There the dip of the fault plane is about 80° S., and 
 the upthrow is on the south, defining a high-angle reverse fault. The 
 throw at this place is roughly 300 to 500 feet, and the fault cuts out the 
 upper part of the Tesla formation and more than the basal half of the 
 Cierbo formation. East of this locality'" in Corral Hollow more of the 
 upper part of the Tesla formation is cut out, and the throw on the fault 
 is estimated to attain a maximum of at least 1500 feet. The change in 
 throw along the trace of this fault from west to east is illustrated in the 
 successive structure sections C-C, D-D', E-E', and F-F', on plate 3. 
 
 Clark ^^^ apparently regarded the Corral Hollow fault as also a part 
 of the Riggs Canyon fault zone with a "sliver block" existing between 
 the Corral Hollow fault and the local trace of his "Riggs Canyon fault", 
 which is herein designated as tlie Carnegie fault. No field observations 
 which were made by the writer could be interpreted as indicating any 
 connection between the Corral Hollow fault and Clark's Riggs Canyon 
 fault, other than that displacements along both faults may have taken 
 place during the same period or periods of diastrophism and that both 
 faults may have been formed in answer to the same set of forces acting 
 on the region. 
 
 The age of the fault is believed to be post-Neroly and subsequent to 
 the regional folding. However, Clark regarded this fault as related to his 
 Riggs Canyon fault and as having been active in pre-Briones time. 
 
 The basis for Clark's reasoning, which was briefly mentioned in the 
 preceding discussion of the Carnegie fault, is the difference in the strati- 
 graphic sequence north and south of a fault zone that separated a positive 
 northern block from a sinking basin on the south that received most of 
 the sediments. For example, south of the Corral Hollow fault Panoche 
 beds are overlain by a sequence of beds which include Moreno Grande, 
 
 "iQp. cit, 1935, pp. 1038-1039. 
 ^"^ Op. cit., Jour. Geology. 
 "^Op. cit, 1935, p. 1038. 
 
STRUCTURE 55 
 
 Tesla, and Cierbo formations ; whereas immediately north of the Carnegie 
 fault, the northernmost of the two faults in Clark 's fault zone, Panoche 
 strata are overlain by Cierbo beds and the Moreno Grande and Tesla 
 sediments are characteristically missing. This change in sequence cannot 
 be demonstrated as taking place abruptly, for a minimum distance of 
 three-quarters of a mile separates the contrasting columnar sections in 
 the outcrop. Then, too, this distance is necessarily foreshortened by fold- 
 ing and faulting ; therefore, if the folds were unravelled and fault dis- 
 placements allowed for, the distance separating the two sequences would 
 comprise roughly 1^ miles or more. Such a distance is sufficiently great to 
 allow for the wedging out of beds by overlap and thinning. It should be 
 noted also that the present distribution of the formations with respect to 
 the Corral Hollow fault indicates that the beds on the south side of the 
 fault are upthrown, which is opposite to the position they are supposed 
 to have occupied in a sinking fault-basin during their deposition, accord- 
 ing to Clark 's concept. 
 
 In summary, the MTiter favors the concept that originally the 
 Moreno Grande and Tesla sediments extended north of the line now 
 marked by the Carnegie fault ; that they were removed in a pre-Cierbo 
 period of folding and erosion that was followed by the Cierbo transgres- 
 sion upon the exposed Panoche rocks. The faulting did not take place until 
 after the deposition of the Neroly sediments and may have been contem- 
 poraneous with or subsequent to the last regional folding. 
 
 Tesla Fault. The most prominent fault in the area is the Tesla 
 fault, which was named by Vickery.^^^ South of Corral Hollow this fault 
 forms the northern boundary of the area of Franciscan rocks. It can be 
 traced for about 9 miles across the central part of the quadrangle ; to the 
 west it disappears under the terrace and alluvial fill of Livermore Valley, 
 and east of the limits of the quadrangle it continues southeastward across 
 the Carbona quadrangle. Locally, its average strike is N. 80° W. The 
 plane of the fault zone is essentially vertical where the fault crosses Corral 
 Hollow, but at Mitchell Ravine the fault plane dips steeply northward, 
 which with the upthrow on the south makes it appear as a normal fault. 
 However, the fault is believed to be dominantly reverse in type. In the 
 walls of the Hetch-Hetchy tunnel near the Thomas shaft, the fault was 
 observed by Willis ^^"^ to be a high-angle reverse fault dipping about 65 '- 
 SW. Exposures of the fault are rather poor, but the fault zone can be 
 easily traced because of such features as springs, notchings of ridges, 
 wide zones of disturbance, fault wedges of Horsetown rocks, and the 
 lithologic distinction between Franciscan rocks on the south side and 
 younger rocks on the north side of the fault. 
 
 Assuming a minimum thickness of 10,000 feet of Cretaceous strata, 
 the throw on this fault is at least 14,000 feet near the east boundary of 
 the quadrangle where Franciscan rocks are faulted into contact with 
 upper Neroly sediments, cutting out the Horsetown, Panoche, Moreno 
 Grande, Tesla, and Cierbo formations, and parts of the Franciscan and 
 NerolJ^ The throw of the fault diminishes to the west, but it is probably 
 measurable in thousands of feet throughout the trace of the fault. Near 
 Carnegie several faults appear to branch off from the Tesla fault to the 
 northwest. 
 
 "" Op. cit., Jour. Geology, p. 614. 
 
 305 Private report for the San Francisco Engineering Department on the geology 
 of the Hetch-Hetchy tunnel. 
 
56 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 The age of the fault is post-Neroly. 
 
 Valle Fault. Another fault boundinsr the area of Franciscan rocks 
 is the Valle fault in the vicinity of Arroyo Valle in the western part of the 
 area. This fault, striking about N. 60° W, bounds one side of an interest- 
 ing fault wedge of Cretaceous rocks enclosed within the general area of 
 Franciscan rocks. Northward its trace changes in direction to about N. 
 20° W., separating the Franciscan on the eastern and upthrown side 
 from the Cretaceous on the west. It finally disappears into or under the 
 Livermore gravels; its trace could not be established across the soft, 
 poorly exposed sediments of the Livermore gravels. However, the fault 
 was observed under the cover of the gravels in the Hetch-Hetchy tunnel. 
 Section H-H' (pi. 3), which combines surface data with subsurface 
 information in the Iletch-Hetchy tunnel shows a mass of " granodiorite " 
 on the east upthrown side and gravels overlying Cretaceous rocks on the 
 downthrown side. The fault in the tunnel dips about 50 degrees to the 
 west, or downthrown side, indicating a normal fault. 
 
 The fault is certainly post-Cretaceous, and it may have been active 
 within or after the period of deposition of the Livermore gravels (Plio- 
 Pleistocene) ; but its age cannot be established very closely. 
 
 Williams Fault. The Williams fault was so named by Willis ^^^ 
 from its occurrence in the vicinity of Williams Creek. Vickery ^^"^ called 
 it the Del Valle fault, but Willis' assignment seems preferable. 
 
 This fault also bounds the Cretaceous wedge-block mentioned above. 
 To the northwest it strikes about N. 70° W. and is a high-angle reverse 
 fault with serpentine and Franciscan sedimentary rocks upthrown on the 
 south side against Cretaceous rocks. It is traced with some difficulty, but 
 physiographic features and formational contrasts aid in its delineation. 
 It is represented in sections B-B', E-E', F-F', and H-H', plate 3. In the 
 Hetch-Hetchy tunnel, the fault is a high-angle reverse fault, according to 
 Willis. 
 
 The fault is post-Cretaceous ; that it may be younger that the Liver- 
 more gravels (Plio-Pleistocene) is surmised on the basis of some gravels 
 observed in the Hetch-Hetchy tunnel in a phase of the fault. 
 
 Summary -Analysis 
 
 The structural dynamics of the Livermore region, which includes the 
 Tesla area, have been discussed by Vickery.^"^ He classified the faults into 
 two groups in accordance with their general directional trend. After 
 plotting the fault trends and average direction of fold axes in several 
 diagrams, he arrived at the conclusion that the region had been deformed 
 by rotational forces, that is, a north-south force couple with the ' ' great- 
 est force from the south. ' ' 
 
 It is convenient to follow Vickery 's general method of analysis in 
 summarizing the structure of the Tesla area. 
 
 The major faults are classified into two groups: (1) the transverse 
 faults, which trend eastward, and (2) the longitudinal^"^ faults, which 
 
 100 "wriUis, Bailey, in private report on Hetch-Hetchy tunnel for San Francisco 
 Engineering- Department. 
 
 '<" Op. cit., Jour. Geology, p. 614. 
 
 "8 Op. cit.. Jour. Geology, pp. 608-628. 
 
 109 rpj^ig terminology differs from that of Vickery, who classified the first group as 
 "branch faults" and the second group as "dominant faults." 
 
STRUCTURE 
 
 57 
 
 Longifudinal 
 faupf trends 
 
 Hypol-ha+ical force 
 
 Transvarsa, 
 fauH" trends 
 
 V 
 
 \ 
 
 Hqpo+h«.+ical force 
 
 Figure 3. Diagram showing regional structural trends, Tesla quadrangle. 
 
 trend northwestward. The transverse faults, which comprise the most 
 prominent faults, include - the Tesla, Carnegie, Corral Hollow, and 
 Williams. They are high-angle reverse faults having an average trend of 
 approximately N. 73° W. "With the exception of the Carnegie fault, they 
 have the uptlirown side on the south and dip at high angles principally 
 to the south. The longitudinal faults include the Greenville, Midway, 
 Patterson Pass, Valle, and Black Butte. The average trend of these 
 faults is about N. 41° W., roughly parallel with the trend of the Diablo 
 Eange. The first three of this second group of faults are essentially 
 vertical in attitude and exhibit strong components of shear-type dis- 
 placement. The Valle and Black Butte faults dip at moderately high 
 angles to the southwest and have opposite sides of upthrow. 
 
 The average strike of the regional folds is approximately N. 55° W. 
 or intermediate to the trends of the two fault groups. The direction of 
 greatest regional shortening is interpreted as normal to the axial direction 
 of the folding or about N. 35° E. 
 
 The foregoing structural relationships are plotted in figure 3. 
 
 Any analysis of the forces causing the general pattern of folds and 
 faults is extremely hypothetical and, perhaps, should be avoided. How- 
 ever, the presentation of a few conjectural interpretations can do no 
 harm. The region may have been deformed by a set of rotational forces 
 (N and S in the diagram), comprising a north-south force couple. These 
 opposing forces were necessarily equal, although the release of stress by 
 deformation may have been greater in certain directions because of differ- 
 ences in the thickness distribution of the rocks and other causes. Imag- 
 
58 GEOLOGY OP TESLA QUADRANGLE [Bull. 140 
 
 inaiy minor-force-components, such as s and n, may have operated 
 opposingly in the direction of greatest shortening to form the folds, and 
 minor force components, such as s' and w', may have caused some shear 
 type of displacement along the longitudinal faults. It is noteworthy that 
 in this area no major fault broke with a northeasterly trend. However, in 
 the B.yron quadrangle to the north, a fault zone which truncates the Alta- 
 mont anticline, trends northeastward and is seemingly a tear fault. 
 
 The principal time of regional deformation is believed to have been 
 post-Neroly, possibly Pleistocene. Indications of earlier or pre-Cierbo 
 folding were cited, but pre-Cierbo faulting as postulated by Clark 
 cannot definitely be established. The folding, in general, is probably 
 earlier than the faulting, or in part contemporaneous with some of the 
 faulting. 
 
 OUTLINE OF THE GEOLOGIC HISTORY"" 
 
 I. Upper Jurassic 
 
 A. Deposition of about 15,000 feet of Franciscan sandstones, shales, and cherts 
 
 under marine conditions. 
 
 1. Few intraformational outpourings of basaltic lava on the sea floor. 
 
 2. Belchings of submarine silicious springs depositing colloidal silica and 
 entrapping minute marine organisms. 
 
 B. Regional deformation accompanied by intrusion of basic plutonic rocks as 
 sills and laccoliths. 
 
 1. Extensive serpentinization in the late stage of intrusion. 
 
 2. Some metamorphism marginal to the intrusive rocks. 
 
 -Diablan orogeny- 
 
 II. Lower Cretaceous 
 
 A. Deposition of more than 500 feet of dark shales and sands (Horsetown) 
 under shallow, cool-water, marine conditions. 
 
 Unrecorded interval 
 
 (Slight regional deformation) 
 III. Upper Cretaceous 
 
 A. Deposition of 10,000 feet or more of sands and argillaceous shales in a shallow 
 
 marine environment. 
 
 1. Site of deposition was slowl.v sinking in pace with a slowly rising source 
 area. 
 
 2. Intraformational conglomerates represent times of oscillation of shoreline 
 which may be related to the Santa Lncian orogeny. 
 
 B. Close of period marked by deposition of about 650 feet of shales and sands 
 under cool-water, marine conditions. 
 
 1. Minute marine organisms common in the shales. 
 
 -T^nrecorded interval- 
 
 IV. Middle Eocene 
 
 A. Early deposition of dark shales, gray sands, and a few coal beds. 
 
 1. Brackish water to swampy conditions. 
 
 2. Warm temperature to sub-tropical climate. 
 
 B. Later marine deposition of white and gray sands, clays, and shales. 
 
 1. Principal source area, the Sierra Nevada, was undergoing deep chemical 
 weathering. 
 
 — I'nrecorded interval 
 
 no rpj^g main events in the geologic history of the area as interpreted from the 
 rocks are outlined herein. An attempt is made to inter-relate the local history with that 
 of a larger area now comprising central California. Many of the topical sentences in 
 the outline constitute in themselves generalizations, the basis for which is described 
 elsewhere In the paper. 
 
MINERAL RESOURCES 59 
 
 V. Middle and upper Miocene 
 
 A. Marine deiwsition of 700 feet or more of sands, shales, and tuffaceous days 
 
 in the western part of the area. 
 
 1. Evidence of Franciscan detritus in the sediments. 
 
 2. Indirect evidence of vulcanism during the middle Miocene. 
 
 (Note: Before the transgression of the Cierbo seas — folding and stripping of 
 some of the earlier sediments pos.sibly occurred in northern high areas.) 
 
 B. Transgression of Cierbo seas. 
 
 1. Deposition of coarse sands, shales, tuffs, and a trace of coal. 
 
 2. General marine conditions, local swamps. 
 
 3. Sierra Nevada source area for the sediments. 
 
 4. Indirect evidence of volcanic activity in surrounding area. 
 
 -Slight folding and erosion locally- 
 
 C. Neroly deposition 
 
 1. Spreading of coarse andesitic gravels and sands over a broad coastal plain. 
 
 a. Abundant rainfall, warm average temperature. 
 
 b. Coastal swamps. 
 
 c. Horses roaming over coastal plains. 
 
 d. Andesitic outpourings in source area (Sierra Nevada). 
 
 2. Closing deposition of tuffs and shales. 
 
 -Unrecorded interval- 
 
 VI. Plio-Pleistocene 
 
 A. Spreading of about 4000 feet of coarse gravels, sands, and clays over Liver- 
 more Valley area. 
 
 1. Broad river flood plains and lakes. 
 
 2. Source area : Franciscan rocks. 
 
 3. Indirect evidence of some regional volcanic activity. 
 
 B. Broad flood-plain deposits of gravels and sands along the border of the San 
 Joaquin Valley. 
 
 1. Source area : Franciscan rocks. 
 
 2. Existence of camels and ground sloths in the area. 
 
 Unrecorded interval — 
 
 (Main regional deformation — folding and faulting. 
 Stream terraces recording stages of uplift.) 
 VII. Recent 
 
 A. Erosion of hills and valleys. 
 
 B. Alluviation of stream courses and major valleys. 
 
 MINERAL RESOURCES 
 
 The Tesla quadrangle contains a variety of mineral deposits, includ- 
 ing some notable potential reserves. Although none of its mines would 
 be regarded as a major development, a number of small mines and work- 
 ings have probably operated with profit, and collectively some mines, 
 such as the manganese properties, have made important contributions 
 to strategic needs during time of war. The accompanying economic 
 mineral map (pi. 2) shows the location of the mines and prospects, and 
 also the location of the abandoned wells that have been drilled for oil 
 or gas. 
 
 Chromite 
 
 Chromite has been mined at the Newman mine on Cedar Mountain 
 near the west quarter-corner of sec. 26, T. 4 S., K. 3 E. The chromite 
 occurs in irregular segregations and as disseminated grains in a serpen- 
 tine gangue near the margin of a large body of serpentine. When the 
 writer visited the mine in 1936, the workings were abandoned but some 
 sacks of ore were still at the mine. 
 
60 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 Clay 
 
 The old Tesla coal mine was operated in its late history as a clay- 
 mine. ^^^ The clay is of good quality and occurs above the coal seam in 
 association with the white sands in the Tesla formation. Exposures of 
 the white to light-colored clays are poor at the surface, but good samples 
 may be obtained from road-cuts, or recent workings, or by digging test 
 pits. The clay from the old Tesla mine was transported on a branch of 
 the Western Pacific Railway a few miles down Corral Hollow to brick 
 and pottery plants at Pottery and Carnegie. This development was in 
 full operation in 1911 when Anderson and Pack ^^^ were working in 
 the area. It is said that a large brick company later bought out the mines 
 and brick works. For many years following the shutdown the clays in 
 this area were not worked, and time has erased much of the evidence of 
 the old brick and pottery works. 
 
 During a revival of clay mining in 1928, the Livermore Clay and 
 Sand Company operated a mine on the north side of the Tesla road in 
 the NWi sec. 26, T. 3 S., R. 3 E. Again clay mining lapsed for a number 
 of years until in 1939 the Tesla Clay Company operated a clay devel- 
 opment south of the Tesla road in the northwest quarter of the same 
 section. The clay is smooth textured, compact, white to light blue gray 
 in color. V. T. Allen ^^^ studied petrographically samples of the white 
 Tesla clay and found the clay to be anauxitic and possessing a refrac- 
 tive index gamma close to 1.566. He also listed some chemical analyses 
 made of the clay, which is reportedly suitable for the manufacture of 
 pottery and has been used successfully by a number of companies in 
 the Bay region, including the Technical Porcelain and Chinaware Com- 
 pany, El Cerrito. 
 
 Coal 
 
 The history of the development of the mineral resources in the Tesla 
 area really began with the Tesla coal mine in sec. 25, T. 3 S., R. 3 E. 
 "When Brewer visited Corral Hollow in October of 1861 the coal mines 
 were already in operation. He^^^ predicted that coal mining there would 
 not prove profitable. In later years clay mining replaced the coal develop- 
 ment. 
 
 The coal seam occurs in the lower brackish-water portion of the 
 Tesla formation below the lower white sand and in association with sand 
 and chocolate-colored carbonaceous shales. The seam, which is only about 
 6 inches thick at the surface, is lenticular. The writer was unable to gain 
 access to the old underground workings, but Whitney^^^ reported a 
 maximum thickness of 66 inches for the coal seam in the mines. He 
 reports that by October 1861 from 200 to 400 tons of low-grade coal had 
 been mined. Whitney gives an analysis of the coal as follows : 
 
 H2O 20.53 percent 
 
 Bituminous substance 35.62 percent 
 
 Fixed carbon 36.55 percent 
 
 Ash 3.94 percent 
 
 •" Dietrich, Waldemar Fenn, The clay resources and ceramic industry of Cali- 
 fornia : California Min. Bur. Bull. 99, pp. 38, 42-45, 207-208, 263, 1928. 
 "2 Op. cit., p. 211. 
 113 Op. cit., 1941, pp. 274-277. 
 
 11^ Brewer, W. H., Up and down California in 1860-64, Yale Univ. Press, 1930. 
 "'Whitney, J. D., Geological survey of California, vol. 1, p. 498, 1865. 
 
MINERAL RESOURCES 61 
 
 Along the general strike of the Tesla coal horizon are evidences today 
 of a number of old abandoned prospect diggings for coal. These prospects 
 and their general location are as follows : 
 
 1. Sec. 32, T. 3 S., R. 4 E., near north quarter-corner. (Note: This 
 prospect may also have been worked for glass sand.) 
 
 2. Sec. 30, T. 3 S., R. 4 E., near south quarter-corner in west bank 
 of Mitchell Ravine. 
 
 3. Sec. 26, T. 3 S., R. 3 E., near the west line and in the northwest 
 quarter of the section (Livermore Coal Mine Company) . 
 
 4. Sec. 27, T. 3 S., R. 3 E., in the northeast quarter a few hundred 
 feet west of the coal prospect in section 26 {Livermore Coal Mine Company). 
 
 Thin lenticular seams of low-grade coal occur locally in the Cierbo 
 formation. One such occurrence is noted in the tunnel of the K-ola mine 
 in the NW:^ sec. 27, T. 3 S., K. 3 E. Coal fragments are common in the 
 dump at the caved entrance of a prospect adit on the south side of the 
 Tesla road near the center of the same section 27. 
 
 Glass and Foundry Sand 
 
 The white sands of the Tesla formation are high in their content of 
 quartz and low in ferromagnesian mineral content, hence they have been 
 prospected and mined to some extent for use in the manufacture of glass. 
 The petrography of the white sands was described earlier in the report, 
 and for additional petrographic description of these sands, the reader 
 is referred to V. T. Allen's paper.^^*^ Abandoned glass sand prospects 
 are located near the north quarter-corner of sec. 32, T. 3 S., R. 4 E., in 
 the NWi sec. 26, T. 3 S., R. 3 E., and near the center of the NWi sec. 25, 
 T. 3 S., R, 3 E, The mining of glass sand in the Tesla area has been held 
 back by the more ready accessibility and higher quality of the white 
 sands near Mt. Diablo. The importation of high quality glass sand as 
 ship ballast from Holland is also said to have competed in years past 
 with the local development. 
 
 A current demand for good quality molding or foundry sand has 
 revived the mining of sand, called "Livermore ganister, " in the area. 
 The Tesla Clay and Sand Company has a new development near the old 
 Tesla coal mine in the western part of sec. 25, T. 3 S., R. 3 E. Mr. Lauren 
 Wright, Associate Geologist with the California State Division of Mines, 
 recently visited these workings and has kindly submitted the following 
 information for inclusion in this report : 
 
 "The current operations of the Tesla Clay and Sand Company are 
 confined to a single stratigraphic unit, apparently the same as that described 
 by Dr. Huey as the 'lower white sand'. Both nodular clay and the so-called 
 'ganister' are mined by underground methods and marketed in the San 
 Francisco Bay area. 
 
 "The term 'ganister' when strictly applied refers to a quartzite or 
 silica rock. This rock, when crushed or mixed with fire clay, is used in 
 foundry practice as a ladle-patching and furnace-lining material. The Liver- 
 more 'ganister', a natural mixture of siilca sand and clay, is used similarly 
 and is also marketed as a naturally bonded molding sand. 
 
 "The physical properties and adaptability of Livermore 'ganister' 
 have been briefly described by Donaldson^" and by Wright." "* 
 
 "»Op. cit., 1941, pp. 274-277. 
 
 n^ Donaldson, Harris M., and others, Foundry sands and mold materials : Am. 
 Foundrymens Assoc, Northern California Chapt., Rept 2, p. 119, 1945. 
 
 118 "Wright, Lauren A., California foundry sands : California Jour. Mines and Geol- 
 ogy, vol. 44, pp. 37-72, 1948. 
 
62 GEOLOGY OF TESLA QUADKANGLE [Bull. 140 
 
 Gravel and Rock 
 
 In Corral Hollow east of Carnegie, loose gravels of the creek bottom 
 have been excavated, graded, and piled into large gravel piles. The 
 gravels are constituted principally of rounded andesite pebbles and 
 cobbles from the Neroly formation admixed with standstone pebbles 
 from older formations. For several years the gravels were used for rail- 
 road ballast by the Western Pacific Railway Company and in the early 
 1930 's the gravel was used in concrete for the Hetch-Hetchy project. 
 
 A rock quarry in red Franciscan chert, located in the NW^ sec. 14. 
 T. 4 S., R. 3 E., is known as the McLean red shale deposit. The material 
 has been used for roofing granules. 
 
 Lime Rock 
 
 Old lime rock workings are located in the southwest corner of sec. 
 32, T. 3 S., R. 4 E., and in the southeast quarter of the adjoining section 
 33 {California Lime and Cement Company). The rock consists of spar 
 and travertine which was probably deposited by hot springs along the 
 Tesla fault zone. The rock was mined for use in the brick and pottery 
 works at Carnegie and Pottery, which were in operation around 1911. 
 
 An unimportant travertine prospect is located just north of the 
 Patterson Pass road in the center of sec. 10, T. 3 S., R. 3 E. It is appar- 
 ently an old hot-spring deposit along a minor fault. 
 
 Another lime rock prospect is located in the southwest corner of 
 sec. 32, T. 3 S., R. 4 E., developed in Franciscan rocks about a quarter 
 of a mile south of the Tesla fault. 
 
 Magnesite 
 
 Good quality magnesite ore was mined during World War I from 
 two surface workings of the Cedar Mountain magnesite mine in the NE^ 
 sec. 27, T. 4 S., R. 3 E. The rock is white, porcellaneous, massive to mam- 
 millarj^; fracture is conchoidal. It occurs in large irregular masses in 
 the outer margin of a serpentine body on Cedar Mountain. When last 
 visited in 1936 by the writer, the deposit still contained considerable 
 available ore. 
 
 Two other magnesite prospects occur in a serpentinized mass on the 
 Hayes Ranch just south of the Williams fault in the southern part of 
 sec. 24, T. 4 S., R. 2 E. 
 
 Manganese 
 
 For an excellent reference on the mineralogy, occurrence, genesis, 
 history and utilization of manganese ore in California, the reader is 
 referred to Bulletin 125 of the California Division of Mines (1943). 
 In giving some of the highlights of the occurrence of manganese in 
 the Tesla area, the writer has drawn freely from this bulletin. 
 
 The largest manganese mine in California, the Ladd mine, is 
 located in the SE^ sec. 2, T. 4 S., R. 4 E., just east of the boundary 
 of the Tesla quadrangle in San Joaquin County. The mine was first 
 operated in 1867 and in the first 7 years produced more than 5000 
 tons, most of which was shipped around Cape Horn to England to be 
 used in the manufacture of chlorine. After 1875 the shipments to Eng- 
 land were discontinued but the mine was operated until about 1902 
 and much of the production was used in the manufacture of batteries. 
 
MINERAL RESOURCES 63 
 
 The mine was reopened during World War I and according to Trask, 
 Wilson and Simons ^^^ about 10,000 tons of ore containing 44 percent 
 manganese and 12 percent silica was mined for its last operation. Trask 
 estimates on the basis of the size of the dump and underground workings 
 that the Ladd mine has produced a total of about 30,000 tons of ore. 
 The following description of the mine is from Trask, Wilson, and 
 Simons.^^" 
 
 "The mine was worked on three levels about 75 feet apart, and the ore 
 was mined mainly from one bed, which lies in the white chert. This bed is 800 
 feet in length and 35 feet in maximum thickness. The pai-t that was mined 
 was from 1 foot to 16 feet thick. It consisted of high grade oxide ore which 
 contained between 40 and 45 percent manganese and was generally richest near 
 the base of the bed. The part that was not mined consists of stockwork oxide ore 
 containing 15 to 20 percent manganese. It is estimated that there are 170,000 
 tons of such ore, averaging 18 percent manganese, the cut-off being placed at 
 10 percent. The maximum depth of oxidation is about 250 feet. Some 10,000 
 tons of carbonate and bementite ore containing about 20 percent manganese 
 is inferred to be present below the zone of oxidation." 
 
 The manganese ore in this mine is a typical Franciscan sedimentary 
 deposit laid down contemporaneously with the cherts with which the ore 
 is interbedded. For a discussion of the genesis of Coast Range manganese 
 deposits, the reader is referred to a discussion by Taliaferro and Hud- 
 son.^^^ At the Ladd mine the chert beds associated with the ore are 
 dipping about 50° NE., and black manganiferous rocks show along the 
 strike, N. 50° W., for about a mile. To the northwest along the strike 
 is the Fahian mine also in section 2. The Fabian mine may have pro- 
 duced as much as 2000 tons, but its workings are now flooded and no 
 reliable estimate can be made. In 1917 the Fabian mine was taken 
 over by the operators of the Ladd mine and its production combined 
 with that of the Ladd mine. 
 
 The U. S. Bureau of Mines, in cooperation with the U. S. Geological 
 Survey, explored the Ladd mine during 1940-41 by diamond drilling, 
 drifting, cross-cutting, and trenching. This exploration program proved 
 ore reserves of 232,000 tons having an average grade of 17.8 percent 
 manganese. 
 
 The U. S. Bureau of Mines tested the Ladd mine ore at the pilot- 
 plant of the government-owned Manganese Ore Company, Boulder City, 
 Nevada. The process produced manganese metal by electrolytic deposi- 
 tion. A flow-sheet was drawn for a commercial electrolytic manganese 
 plant to be built at Oakland adjoining an idle power-generating plant. 
 In 1942 American Alloys and Chemicals Corporation made application 
 to the War Production Board for a loan of $1,400,000 to purchase the 
 mine, mining equipment, the power plant; to finance construction of 
 the electrolytic plant; and to provide working capital. This loan was 
 not granted. 
 
 The general area drained by Arroyo Mocho in the south-central 
 part of the Tesla quadrangle is an important source of manganese, having 
 yielded 4,600 tons from 16 properties. The principal mines have been 
 the Camp 9, the Man Ridge, the Section 14, the Graves, and the Bladk 
 Jack. 
 
 "» Trask, P. D., W^ilson, I. F., and Simons, F. S., Manganese depo.sits of California 
 a summary report: California Div. Mines Bull. 125, p. 85, 1943. 
 
 '-'»Op. cit., pp. 85-86. 
 
 ^ Taliaferro, N. L., and Hud.son, F. S., Genesis of the manganese deposits of the 
 Coast Ranges: California Div. Mines Bull. 125, pp. 217-275, 1943. 
 
64 
 
 GEOLOGY OF TESLA QUADRANGLE 
 
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66 GEOLOGY OF TESLA QUADRANGLE [BuU. 140 
 
 The manganese mines and prospects in the Tesla quadrangle are 
 tabulated below, arranged by counties according to location by section, 
 township, and range. These mines are all typical Franciscan deposits. 
 The production is classified in one column by letters following the 
 scheme used in Bulletin 125. The letters have the following signification : 
 
 A. Production 1000 tons or more 
 
 B. Production 150 to 999 tons 
 C Production 1 to 149 tons 
 D. No production 
 
 All but two of the mines named below are listed in Bulletin 125 with 
 citations to state and other publications giving special information on 
 individual properties. The Dragi and Foscilina mines were reported by 
 Mr. Charles Scott. 
 
 List of manganese properties in the Tesla quadrangle. 
 
 Class 
 Name of claim Owner Sec. T. R. (production) 
 
 Alameda County 
 
 Kelly prospect Mrs. Kelly NW 5 
 
 Camp 9 Crocker Estate NW 9 
 
 Nelson mines (2) Holm Bros. NW 10 
 
 Chaney Frank J. Rodriguez NE 12 
 
 Jumbo prospect .1. M. Beraudiere NE NE 14 
 
 Black Jack H. T. Beraudiere NE 14 
 
 Beraudiere J. M. Beraudiere NW14 
 
 Newman Mabel Newman SW 22 
 
 Dewhirst Mrs. Amanda Dewhirst 22 
 
 Gallagher Dan Gallagher NW 19 
 
 Section 14 Lee Ogier NE 14 
 
 Winegar H. V. Winegar SW 4 
 
 Phil Winegar & 
 
 Man Ridge Arthur Most 7 
 
 Graves J. B. Graves 7 
 
 Foscilina SW 8 
 
 Dragi 18 
 
 San Joaauin County 
 
 Ladd* Connelly Ranch SE 2 
 
 Fabian Mack C. Lake 2 
 
 Scott Charles Scott 34 
 
 * In Carbona quadrangle. 
 
 Petroleum 
 
 A few oil seeps, a small amount of produced medium gravity oil, and 
 about 25 abandoned exploratory wells make a short story of the unsuccess- 
 ful search for an economic accumulation of oil or gas in the Tesla quad- 
 rangle. Almost half of these ventures were shallow cable-tool holes drilled 
 prior to 1912. The largest concentration of wells is near some old seeps on 
 the Hamilton ranch in sec. 15, T. 3 S., R. 3 E. 
 
 4S 
 
 3E 
 
 D 
 
 4S 
 
 3E 
 
 A 
 
 4S 
 
 3E 
 
 B 
 
 4S 
 
 3E 
 
 C 
 
 4S 
 
 3E 
 
 D 
 
 4S 
 
 3E 
 
 B 
 
 4S 
 
 3E 
 
 C 
 
 4S 
 
 3E 
 
 C 
 
 4S 
 
 3E 
 
 C 
 
 4S 
 
 4E 
 
 C 
 
 5S 
 
 3E 
 
 B 
 
 5S 
 
 4E 
 
 D 
 
 5S 
 
 4E 
 
 B 
 
 5S 
 
 4E 
 
 B 
 
 5S 
 
 4E 
 
 C 
 
 5S 
 
 4E 
 
 C 
 
 4S 
 
 4E 
 
 A 
 
 4S 
 
 4E 
 
 A 
 
 4S 
 
 4E 
 
 D 
 
MINERAL RESOURCES 67 
 
 Oil Seeps. Anderson and Pack ^^- have described in detail some oil 
 seeps located in two gulches in the southern part of sec. 15, T. 3 S., R. 3 E. 
 The seeps occur in the coarse sands of the Cierbo formation just north of 
 the Carnegie fault. Oil-stained sand can still be seen in the tunnel about 
 500 feet below the Alisal well in the southwest quarter of the section. The 
 other tunnel mentioned by Anderson and Pack, which is located about 
 200 yards above the old Hamilton ranch house, is caved and the seep could 
 not be seen. The dry oil sand reported as outcropping in the creek bottom 
 a few yards below the tunnel was not found. 
 
 In 1944 a well being drilled for water on the Heifner ranch in the 
 SWi sec. 7, T. 3 S., R. 3 E., encountered a sand at depth 241 feet from 
 which a heavy oil-water emulsion was bailed. The writer interprets this 
 occurrence as seepage oil from the Carnegie fault working laterally into 
 the shallow sands of the Livermore gravels. This oil showing led Bradford 
 and Guardino in 1945 to drill a shallow well adjacent to the abandoned 
 water well to a depth of about 500 feet. The well was abandoned and pre- 
 sumably they obtained comparable showings. In the spring of 1947 a 
 water well drilled on the ranch of the JVIingoia Bros, near the north quar- 
 ter-corner of the same section 7 was abandoned because of oil showings. 
 A successful water well was then drilled about 1000 feet southwest of the 
 abandoned well. These near-surface seepage indications are about 3 
 miles northwest of the seeps which also occur along the Carnegie fault 
 in section 15. 
 
 Wells Drilled for Petroleum. Of the 25 wells drilled for oil or gas in 
 the Tesla quadrangle about half have reported some minor oil or gas 
 shows, but only one or two wells actually produced a few barrels of oil 
 with water. The oil found on the Hamilton ranch occurs both in basal 
 Cierbo sands and in upper Panoche sands. A reasonable speculation on 
 the probable source of this oil would favor the shales of the Moreno 
 Grande, which appear to have the highest organic content of any in the 
 area. These shales crop out along the south side of Corral Hollow. 
 
 The wells drilled for oil and gas are shown on the economic mineral 
 map (pi. 2) and are tabulated (see pp. 64-65) with supporting data as to 
 location, date drilled, depth reached, log summary, and remarks. 
 
 Tuff 
 
 A white tuff bed in the Cierbo formation outcrops in the NW^ sec. 27, 
 T. 3 S., R. 3 E. The material is a compact fine white tuff. It was not mined 
 at the surface, but from an adit several hundred feet long which was 
 driven into the hiU. A large mill was erected, which has since been 
 removed, and the name of the mine "K-ola" was spelled out in large white 
 letters in the rock, so that it could be read from an automobile on the Tesla 
 road or from an airplane overhead. 
 
 A sample of the material was examined in oil under the microscope. 
 The tuff is made up of 97 percent clear glass, refractive index 1.50 ; 
 quartz (2 percent), kaolinized feldspar (1 percent), and traces of pale 
 biotite and magnetite. Mr. T. T. Copeland, the owner of the property 
 when the writer visited there in 1936, indicated that he had trouble find- 
 ing a market for the material. There has been no activity at the site for 
 3'-ears, and the inner portion of the tunnel has caved. 
 
 •"Op. cit., pp. 136-137. 
 
68 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 REGISTER OF FOSSIL LOCALITIES 
 
 Invertebrate localities 
 
 Loc. I (U. C. loc. A-3083) In creek bottom in north central part of sec. 32, T. 
 3 S., R. 4 E., about 500 feet south of mouth of creek 
 Stratigraphy : Basal part of Tesla formation 
 Lithology: Fine-grained sandstone 
 Fauna: Brackish-water pelecypods 
 Collector: A. S. Huey 
 
 Loc. II (U. C. loc. A-3082) In west bank of Mitchell Ravine near north quarter- 
 corner of sec. 31, T. 3 S., R. 4 E. 
 
 Stratigraphy: Same horizon as loc. I, about 100 feet above base of Tesla 
 formation 
 
 Lithology: Massive tan fine sand 
 Fauna: Brackish-water pelecypods 
 Collector: A. S. Huey 
 
 Loc. Ill (U. C. loc. A-3080) In east bank of Mitchell Ravine near north quarter- 
 corner of sec. 31, T. 3 S., R. 4 E. 
 
 Stratigraphy: 30 feet above Tesla-Moreno Grande contact and 70 feet below 
 horizon of loc. II 
 
 Lithology: Gray bedded sandstone 
 Fauna: Brackish -water pelecypods 
 Collector: A. S. Huey 
 
 Loc. IV (U. C. loc. A-3084) About 200 feet west of and above the Tesla road, 
 near center of sec. 25, T. 3 S., R. 3 E. 
 
 Stratigraphy: About 700 feet below the upper white sand in the Tesla for- 
 mation 
 
 Lithology: Buff fine-grained sandstone 
 Fauna: Marine pelecypods (middle Eocene) 
 Collector: A. S. Huey 
 
 Loc. V (U. C. loc. A-3081) Near center of sec. 25, T. 3 S., R. 3 E., east of Tesla 
 road and beside a post on east bank of creek 
 
 Stratigraphy: About 690 feet below upper white sand in Tesla formation 
 Lithology: Soft tan sand 
 
 Fauna: Poorly preserved marine pelecypods and gastropods 
 Collector: A. S. Huey 
 
 Loc. VI (U. C. loc. A-3085) On side of ridge in western part of NWi sec. 25, 
 T. 3 S., R. 3 E. 
 
 Stratigraphy : As float in upper portion of Tesla formation 
 Lithology: Hard light brown sandstone 
 Fauna: Marine pelecypods and gastropods (middle Eocene) 
 Collector: A. S. Huey 
 
 Loc. VII North bank, near bottom of creek at south quarter-corner of sec. 3, T. 
 3 S., R. 3 E. 
 
 Stratigraphy: About 300 feet above oyster zone which occurs near base of 
 Cierbo formation 
 Lithology: Tan sandstone 
 
 Fauna: Marine gastropods and pelecypods (upper Miocene) 
 Collector: A. S. Huey 
 
 Loc. VIII In Arroyo Valle near center of NWi sec. 3, T. 4 S., B. 2 E. 
 
 Stratigraphy: About 50 feet above base of Oursan( ?) sandstone 
 
 Lithology: Tan sand 
 
 Fauna: Abundant but rather poorly preserved marine gastropods and 
 
 pelecypods 
 
 Collector: A. S. Huey 
 
 Loc. IX In south-facing bank along dirt road in central western part of sec. 26, 
 T. 3 S., R. 3 E. 
 
 Stratigraphy : Not far bdow top of Cretaceous 
 
 Lithology: Massive tan sandstone 
 
 Fauna: Marine cephalopods and pelecypods (Upper Cretaceous) 
 
 Collector: A. S. Huey 
 
REGISTER OF FOSSIL LOCALITIES 69 
 
 Loc. X Old Jordan Ranch locality. On small flat on the east side of and above 
 creek level of Arroyo Valle in the SE^ sec. 11, T. 4 S., R. 3 E. ; also on west 
 side of creek 
 
 Stratigraphy : About 2500 feet above conglomerate on Rocky Ridge 
 Lithology: Tan sandstone 
 
 Fauna: Marine invertebrate (Upper Cretaceous) 
 Collectors: Lorenzo G. Yates and F. M. Anderson 
 
 Loc. XI Near road in bottom of Arroyo Valle in SE^ sec. 29, T. 4 S., R. 3 E. 
 Stratigraphy: Reworked Upper Cretaceous fossils 
 Lithology: Fossiliferous sandstone boulders in conglomerate 
 Fauna: Marine invertebrates (Upper Cretaceous) 
 Collector: A. S. Huey 
 
 Loc. XII Beside road near east quarter-comer of sec. 36, T. 3 S., R. 3 E. 
 Stratigraphy : Horsetown formation (Lower Cretaceous) 
 Lithology: Light brown sandstone 
 Fauna: Marine cephalopoda and pelecypods 
 Collector: A. S. Huey 
 
 Loc. XIII In cut of Western Pacific Railroad, near east quarter-corner of sec. 27, 
 T. 2 S., R. 3 E. 
 
 Stratigraphy: Panoche formation (Upper Cretaceous) 
 Lithology: Concretion in argillaceous shale 
 
 Fauna: Large cephalopod ; donated to California Academy of Science 
 Collector: A. S. Huey 
 
 Loc. XIV (U. C. loc. A-2615) In east bank of Mitchell Ravine in north central 
 part of sec. 31, T. 3 S., R. 4 E. 
 
 Stratigraphy : About 250 feet below Eocene-Cretaceous contact in Moreno 
 Grande formation 
 
 Lithology: Yellow-brown limestone concretion weathering out of shale 
 Fauna: Abundant well preserved radiolaria. Also foraminifera and an 
 ammonite 
 Collector: A. S. Huey 
 
 Vertebrate locality 
 
 TJ. C. loc. V-S620 About 500 feet due west of southeast corner of sec. 21, T. 3 S., 
 R. 4 E., on small ridge near fence 
 
 Stratigraphy: In middle of lower blue sandstone member of Neroly for- 
 mation 
 
 Lithology: Gravel bed 
 Fauna: Teeth and foot bones of horse 
 Collector: P. W. Reinhart 
 
 Leaf localities 
 
 U. C. loc. 199 In cut of Western Pacific Railway right-of-way near Greenville in 
 west center of sec. 31, T. 2 S., R. 3 E. 
 Stratigraphy : Neroly formation 
 Lithology: Interbedded sand and tuffaceous clay 
 Flora: Fossil leaves of coastal plain type 
 Collectors: Carlton Condit and A. S. Huey 
 
 U. C. loc. P-361 In NEi NWi sec. 29, T. 3 S., R. 4 E., in creek bottom about 1 
 mile north of Corral Hollow road 
 Stratigraphy: At base of Neroly formation 
 
 Lithology: Gray tuffaceous clay stone beneath a blue sandstone bed 
 Collectors: Carlton Condit and A. S. Huey 
 
 U. C. loc. P-371S In south-facing bank at foot of Tesla grade in the SEi aec. 25, 
 T. 2 S., R. 3 E. 
 
 Stratigraphy: Lower part of Tesla formation 
 Lithology: Chocolate colored shales 
 Flora: Abundant leaves (middle Eocene) 
 Collectors: A. S. Huey and others 
 
70 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 BIBLIOGRAPHY 
 Allen, Victor T. 
 
 The lone formation of California : Univ. California, Dept. Geol. Sci. Bull., vol. 
 18, pp. 347-448, 1929. 
 
 Eocene anauxitic clays and sands in the Coast Range of California : Geol. Soc. 
 America Bull., vol. 52, pp. 271-294, 1941. 
 
 Anderson, Frank Marion 
 
 Synopsis of the later Mesozoic in California : California Div. Mines Bull. 118, 
 pp. 183-186, 1941. 
 
 (and Hanna, G. Dallas) Cretaceous geology of Lower California: California 
 Acad. Sci. Proc, 4th ser., vol. 23, no. 1, pp. 1-34, 1935. 
 
 Anderson, Robert 
 
 (and Pack, R. W.) Geology and oil resources of the west border of the San Joa- 
 quin Valley north of Coalinga, California : U. S. Geol. Survey Bull. 603, 1915. 
 
 Branner, J. C. 
 
 Report on the geology of Livermore Valley, in The future water supply of San 
 Francisco, a report ... by the Spring Valley Water Co., pp. 203-222, 1912. 
 
 Brewer, W. H. 
 
 Up and down California in 1860-64, Tale Univ. Press, 1930. 
 
 Camp, C. L. 
 
 Icthyosaur rostra from central California : Jour. Paleontology, vol. 16, no. 3, 
 pp. 362-372, 1942. 
 
 Campbell, A. S. 
 
 (and Clark, B. L.) Radiolaria from Upper Cretaceous of middle California: 
 Geol. Soc. America Special Paper 57, pp. 1-61, 1944. 
 
 Chaney, Ralph W. 
 
 (Condit, C, and Axelrod, D. I.) Pliocene floras of California and Oregon: Car- 
 negie Inst. Washington Pub. 553, 1944. 
 
 Clark, Bruce L. 
 
 Fauna of the San Pablo group of middle California : Univ. California, Dept. 
 Geol. Sci. Bull., vol. 8, pp. 385-572, 1915. 
 
 The marine Tertiary of the west coast of the United States ; its sequence, paleo- 
 geography, and problems of correlation : Jour. Geology, vol. 29, no. 7, pp. 583-614, 1921. 
 
 Tectonics of the Valle Grande of California : Am. Assoc. Petroleum Geologists 
 BuU., vol. 13, no. 3, 1929. 
 
 Tectonics of the Coast Ranges of middle California : Geol. Soc. America Bull., 
 vol. 41, pp. 747-828, 1930. 
 
 Tectonics of the Mount Diablo and Coalinga areas, middle Coast Ranges of Cali- 
 fornia : Geol. Soc. America Bull., vol. 46, pp. 1025-1078, 1935. 
 
 (and Woodford, A. O.) The geology and paleontology of the type section of the 
 Meganos formation of California : Univ. California, Dept. Geol. Sci. Bull., vol. 17, 
 pp. 63-142, 1927. 
 
 Condit, Carlton 
 
 The San Pablo flora of west central California : Carnegie Inst. Washington, 
 Contr. Paleontology 476, pp. 217-268, 1938. 
 
 Crook, T.H. 
 
 (and Kirby, J. M.) Capay formation (abstract) : Geol. Soc. America Proc. 1934, 
 pp. 334-335, 1935. 
 
 Pavis, E. F. 
 
 The Franciscan sandstone : Univ. California, Dept. Geol. Sci. Bull., vol. 11, pp. 
 1-44, 1918. 
 
 The radiolarian cherts of the Franciscan group : Univ. California, Dept. Geol. 
 Sci. Bull., vol. 11, pp. 235-432, 1918. 
 
BIBLIOGRAPHY 71 
 
 Goudkoff, Paul P. 
 
 Stratigraphic relations of Upper Cretaceous in Great Valley, California : Am. 
 Assoc. Petroleum Geologists Bull., vol. 29, pp. 956-1008, 1945. 
 
 Hannibal, Harold 
 
 A Pliocene flora from the Coast Ranges of California : Torrey Botanical Club 
 Bull. 38, pp. 329-342, 1911. 
 
 Harding, John W., Jr. 
 
 The geology of the southern part of the Pleasanton quadrangle, California, Mas- 
 ter's thesis, unpub., Univ. California, 1940. 
 
 Huey, Arthurs. 
 
 Stratigraphv of the Tesla quadrangle, California (abstract) : Geol. Soc. America, 
 Proc. 1936. pp. 335-336, 1937. 
 
 The geology of the Tesla quadrangle of middle California, Doctor's thesis, unpub., 
 Univ. California,' 1940. 
 
 (and Daly, J. W.) A discussion of part of the Upper Cretaceous along the west 
 border of the San Joaquin Valley, paper read before Pacific Section, Am. Assoc. Petro- 
 leum Geologists at Los Angeles, Oct. 16, 1941. 
 
 Kirby, James M. 
 
 Upper Cretaceous stratigraphy of west side of Sacramento Valley south of Wil- 
 lows, Glenn County, California : Am. Assoc. Petroleum Geologists Bull., vol. 27, pp. 
 279-306, 1943. 
 
 Lawson, Andrew C. 
 
 Report on the geology and underground water supply of Livermore Valley, in 
 The future water supply of San Francisco, a report ... by Spring Valley Water 
 Company, pp. 223-230, 1912. 
 
 U. S. Geol. Survey Geol. Atlas, San Francisco folio (no. 193), 1914. 
 
 Louderback, George D. 
 
 Period of scarp production in the Great Basin : Univ. California, Dept. Geol. 
 Sci. Bull., vol. 15, pp. 1-44, 1924. 
 
 Merriam, C. W. 
 
 (and Turner, F. E.) The Capay middle Eocene of California : Univ. California, 
 Dept. Geol. Sci. Bull., vol. 24, pp. 91-141, 1937. 
 
 Reed, Ralph D. 
 
 The geology of California, Am. Assoc. Petroleum Geologists, 1933. 
 
 Smith, James Perrin 
 
 The development and phylogeny of PlacenUceras: California Acad. Sci. Proc, 
 3d ser., vol. 1, pp. 181-240, 1900. 
 
 Smith, M. B. 
 
 Ground water in the Livermore Valley, California, Master's thesis, unpub., 
 Stanford Univ., 1934. 
 
 Stewart, Ralph 
 
 Geology of Reef Ridge, Coalinga district, California : U. S. Geol. Survey Prof. 
 Paper 205-C, pp. 81-115, 1946. 
 
 (Popenoe, W. P., and Snavely, P. D., Jr.) Correlation and subdivisions of Ter- 
 tiary and late Upper Cretaceous rocks in Panoche Hills, Laguna Seca area, and 
 Orestimba area, Fresno, Merced, and Stanislaus Counties, California : U. S. Geol. Sur- 
 vey, Oil and Gas Investigations, Preliminary Chart 6, 1944. 
 
 Stirton, R.A. 
 
 Cenozoic mammal remains from the San Francisco Bay region : Univ. Califor- 
 nia, Dept. Geol. Sci. BuU., vol. 24, pp. 339-410, 1939. 
 
 Taff, J. A. 
 
 Geology of Mount Diablo and vicinity : Geol. Soc. America Bull., vol. 46, pp. 
 1079-1100, 1935. 
 
72 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 Taliaferro, N. L. 
 
 Geologic history and structure of the central Coast Ranges of California : Cali- 
 fornia Div. Mines Bull. 118, pp. 119-162, 1941. 
 
 Geologic history and correlation of the Jurassic of southwestern Oregon and 
 California : Geol. Soc. America Bull., vol. 53, pp. 71-112, 1942. 
 
 Franciscan-Knoxville problem : Am. Assoc. Petroleum Geologists Bull., vol. 27, 
 pp. 109-219, 1943. 
 
 Cretaceous and Paleocene of Santa Lucia Range : Am. Assoc. Petroleum Geolo- 
 gists Bull., vol. 28, pp. 449-521, 1944. 
 
 (and Hudson, F. S.) Genesis of the manganese deposits of the Coast Ranges: 
 California Div. Mines Bull. 125, pp. 217-275, 1943. 
 
 Tolman, C. F. 
 
 (et al.) Nature and science on the Pacific Coast, San Francisco, Paul Elder & 
 Co., 1915. 
 
 Trask, Parker Davies 
 
 The Briones formation of middle California : Univ. California, Dept. Geol. Sci. 
 Bull., vol. 13, pp. 133-174, 1922. 
 
 (Wilson, I. F., and Simons, F. S.) Manganese deposits of California, a sum- 
 mary report : California Div. Mines Bull. 125, pp. 51-217, 1943. 
 
 Turner, H. W. 
 
 The geology of Mount Diablo : Geol. Soc. America Bull., vol. 2, pp. 383-414, 1891. 
 
 The rocks of the Sierra Nevada : U. S. Geol. Survey, 14th Ann. Rept., pp. 487- 
 490, 1894. 
 
 Rocks of the Coast Ranges of California : Jour. Geology, vol. 6, pp. 493-499, 1898. 
 
 Vanderhoof, V. L. 
 
 A study of the Miocene sirenian Desmostylus: Univ. California Dept. Geol. Sci. 
 Bull., vol. 24, pp. 169-262, 1937. 
 
 Vickery, F. P. 
 
 The structural dynamics of the Livermore region. Doctor's thesis, unpub., Stan- 
 ford Univ., 1925. 
 
 The structural dynamics of the Livermore region : Jour. Geology, vol. 33, pp. 
 608-628, 1925. 
 
 Weaver, Charles E. 
 
 Stratigraphy and paleontology of the San Pablo formation in middle California : 
 Univ. California, Dept. Geol. Sci. Bull., vol. 5, pp. 243-269, 1909. 
 
 Whitney, J. D. 
 
 Geological survey of California, vol. 1, 1865. 
 
 Wilmarth, M. Grace 
 
 Lexicon of geologic names of the United States : U. S. Geol. Survey Bull. 896, 
 1938. 
 
INDEX 
 
 Alameda County, index map showing location of Tesla quadrangle in, 8 
 
 Oil Co. of San Francisco, well in Tesla quadrangle, 64 
 Alisal OU Co. weU No. 1, 65 
 Alluvium, 49 
 
 Altamont anticline, 24-25, 27, 28, 41, 49-51 
 Arroyo Mocho, Franciscan chert from, pi. 5, 11, 20 
 Quaternary in, 49 
 
 VaUe, geology of, 18, 25-26, 38, 40, 48 
 Asuncion group, 29 
 
 Atlantic & "Western Oil Co., French No. 1 well, 65 ; well No. 2, 64 
 Beraudiere manganese mine, 66 
 Bibliography, 70-72 
 Black Butte fault, 53 
 
 Jack manganese mine, 63, 66 
 Bradford & Guardino "B&G" No. 1 weU, 64 
 Byron quadrangle. Cretaceous in, 25, 27, 28 ; Tertiary in, 43 
 California Lime and Cement Co., 62 
 Capay stage, 37 
 Carbona quadrangle. Black Butte fault in, 53 ; Neroly formation in, 43 ; Tesla fault in, 
 
 55 ; Tulare formation in, 48, 49 
 Carnegie fault, 51, 52, 53-54, 67 
 Cedar Mountain, Newton chromite mine on, 59 
 
 magnesite mine, 62 
 Camp 9 manganese mine, 63, 66 
 Cephalopoda, checklist of Upper Cretaceous, 28 
 Chaney manganese mine, 66 
 Chico group, 29 
 Chromite, 59 
 
 Cierbo formation, 16, 24, 25, 32, 33, 34, 38, 40-42, 46, 59, 61, 67 ; photo showing white 
 sand, pi. 7A ; photo showing unconformity between Panoche and, 
 pi. 7B 
 Clay, 16, 60 
 Climate, 11-12 
 Coal, 60-61 
 Coast Exploration Co., well "T.F." No. 1, 65 
 
 Ranges, California, stratigraphy, 14, 29, 35 
 Conglomerates, Neroly, 43 ; Upper Cretaceous, 26, 27 
 Coniff, J. E., "Calhoma" No. 1 well, 64 
 Connelly Ranch, owner, Ladd maganese mine, 66 
 Copeland, T. T., owner, K-ola tuff mine, 67 
 Corral Hollow, svnclinal area north of, 51-52 ; white sand of Tesla formation in, 11, 
 
 32-33, 62, pi. 6 
 Craig, George L., well No. lA, 64 
 Cretaceous system, 11, 14, 16, 20, 21, 22, 23-33, 58 
 
 fossils, checklist of, 28 
 Crocker Estate, owner, Camp 9 manganese mine, 66 
 Dewhirst manganese mine, 66 
 Diablo Range, 11, 30, 41, 43, 44, 46, 52 
 Doane ( ?) wee No. 1, 65 
 Dragi manganese mine, 66 
 Drainage, 12-13 
 Eocene series, 16. 33-38, 58-59 
 Etchegoin formation, 43 
 Fabian manganese mine, 63, 66 
 Faults, 22, 52-56. 57-58 
 
 Fifteen-Three Oil Co. "Hamilton Ranch" well No. 1, 65 ; well No. 2, 65 
 Folds, 49-52 
 
 FoscUina manganese mine, 66 
 Fossil localities, invertebrate, 68-69 ; leaf, 69 ; register of, 68-69 ; vertebrate, 69 
 
 7—85413 ( 73 ) 
 
74 GEOLOGY OF TESLA QUADRANGLE [Bull. 140 
 
 Fossils, checklist of Cierbo, 42 ; checklist of Horsetown, 23 ; checklist of Tesla forma- 
 tion, 36 
 Foster & Hammil well No. 2, 65 
 Franciscan group, 11, 14, 15-23, 58, 62, 63, 66 
 
 basalt, photo showing pillow structure in, pi. 5B 
 
 chert, photo showing bedded, pi. 5A ; rock quarry in, 62 
 Gallagher manganese mine, 66 
 Gastropoda, checklists of, 28, 36, 42 
 Geography of Tesla quadrangle, 11 
 Geologic history, in Tesla quadrangle, 58-59 
 Gilstrap, A. M., well No. 1, 64 
 Gravel and rock deposits, 62 
 Graves manganese mine, 63, 66 
 Great Valley, Cretaceous in the, 30 
 
 Greenville fault, 52, 54 ; photo showing slickensided surface in, 32-33 
 Hayes Ranch magnesite prospects, 62 
 Hetch-Hetchy water supply, 13-14 
 Holm Bros., owners. Nelson manganese mines, 66 
 Horsetown formation, 16, 23-24 
 Johnston No. 1 well, 25, 27, 51, 53, 64 
 Jumbo manganese prospect, 66 
 Jurassic system, 15-23, 58 
 K-ola tuff mine, 41, 61, 67 
 Kelly manganese prospect, 66 
 Ladd manganese mine, 62-63, 66 
 Lake, Mack C., owner, Fabian manganese mine, 66 
 Lime rock, 62 
 Livermore Clay and Sand Co., clay production, 60 
 
 gravels, 14, 16, 31, 39, 40, 47-48, 49, 51, 56, 67 
 
 Oil Co. "Hamilton" No. 1 well, 65 
 
 region, structural dynamics of the, 56-58 
 
 Talley, Livermore gravels in, 47-48 ; Quaternary alluvium in, 49 ; topographic 
 unit, 11 
 Magnesite, 62 
 Manganese, 62-63, 66 
 
 properties, table showing, 66 
 Man Ridge manganese mine, 63, 66 
 
 Map, index, showing location of Tesla quadrangle, 8; relief, showing important place 
 names, Tesla quadrangle, pi. 4 ; economic mineral, pi. 2 ; geologic, 
 pl.l 
 McLean red shale deposit, 62 
 Midway anticline, 51, 53 
 
 fault, 52-53 
 Mineral resources, 60-67 
 Miocene series, 16, 38-47, 59 
 Mitchell Ravine, geology, 33, 34-35, 37, 49 
 Moreno Grande formation, 16, 31-33, 51, 54, 55 
 Most, Arthur, owner Man Ridge manganese mine, 66 
 Mt. Piablo, Cretaceous conglomerates near, 28 
 
 quadrangle, 43 
 Nelson manganese mines, 66 
 Neroly formation, 14, 16, 25, 42-47, 59, 62 ; photo showing andesitic sediments of, 
 
 pis. 8, 11 ; photo showing sharp fold in, pi. 9B 
 Newman chromite mine, 59 
 
 manganese mine, 66 
 Oak Ridge divide, Mt. Hamilton quadrangle, 55 
 Ogier, Lee, owner Section 14 manganese mine, 66 
 Oil and gas, table showing wells drilled in Tesla quadrange for, 64 
 
 seeps, 67 
 Oursan (?) sandstone, 38-40 
 Facheco group, 29 
 
 Panoche formation, 16, 24-31 ; photos showing sediments of, pis. 8, 10 
 Patterson Pass anticline, 24, 51, 53 
 
 fault, 51, 53 
 syncline, 51 
 Pelecypoda, check lists of, 28, 36, 42 
 
INDEX 75 
 
 Petroleum, 66-67 ; wells drilled for, 67 
 Pioneer group, 29-30 
 Pliocene-Pleistocene series, 16, 47-49, 59 
 Quaternary system, 49 
 Reef Ridge area, geology, 30 
 Riggs Canyon fault. 52, 54 
 
 Rocky Ridge, Cretaceous conglomerate on, 22, 25-26, 28, 29, 30 ; photo showing, pi. 10 
 Rodriguez, Frank J., owner Chaney manganese mine, 66 
 Sacramento Valley, west side, Upper Cretaceous stratigraphy, 29-30 
 San Joaquin Valley, Moreno Grande in, 31 ; Quaternary alluvium in, 49 ; topographic 
 unit, 7 11 
 
 Pablo group. 42, 46 ; partial list of flora from, 45 
 Sand, glass and foundry, 16, 61 ; white, of Cierbo formation, pi. 7 ; white, of Tesla 
 
 formation, pi. 6 
 Sandstone, Franciscan, 16, 17, 26, 27, 28 
 Santa Lucian orogeny, 29, 30, 58 
 Scott manganese mine, 66 
 
 Seaboard Oil Co., Johnston No. 1 well, 25, 27, 51, 53, 64 
 Section 14 manganese mine, 63, 66 
 
 Sedimentary rocks, predominance of in Tesla quadrangle, 14, 17, 18-19 
 Sediments, Neroly, 44 ; Panoche, 27-28 
 Serpentinized intrusions, 15 
 Shasta County, Yates fossils from, 28 
 Shell Oil Co., Inc., "Nissen" No. 1 well, 25 
 
 Sierra Nevada, source of sediments in Tesla quadrangle, 28, 35, 41. 44, 46 
 Standard Oil Co., "Egan" No. 1 well, 64 ; "Leonardo" No. 1 well, 64 
 Stratigraphy, 14-19 
 Structure, 49-58 
 
 Structure sections, geologic, pi. 3 
 Structural trends, diagram showing regional, 57 
 Talbot Oil Co. well No. 1, 65 
 
 Technical Porcelain and Chinaware Co., clay consumers, 60 
 Tejon formation, 38 
 Terrace deposits, 49 
 Tertiary system, 11, 33-47 
 
 -Quaternary system, 47-49 
 Tesla Clay Co., description of deposit, 60 
 
 and Sand Co., sand production, 61 
 
 coal mine, clav production, 60 ; coal production and analysis, 60-61 
 
 fault, 23, 24, 53, 55-56, 62 
 
 formation, 16, 33-38, 60, 61 
 
 mining camp about 1910, photo showing, pi. 6 
 Thomas & Hammil well No. 1, 65 
 Tithonian age of Franciscan, 23 
 Topography of Tesla quadrangle, 11 
 Tracy Oil Co. well No. 1, 65 
 Tulare formation, 14, 16, 48-49 
 Tunnel, progress of Hetch-Hetchy, 14 
 Turonian fossils, 30 
 Valle fault, 56 
 
 Vegetation of Tesla quadrangle, 11-12 
 Volcanic rocks, 15 
 
 W. M. & S. Co. "Hamilton Ranch" No. 1 well, 65 ; No. 2 well, 65 
 Water supply, Tesla quadrangle, 12-13, 13-14 
 Williams fault, 56 
 Winegar manganese mine, 66 
 
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