TN 24- C3 A3 ->wife7 WWXMM WI STATE OF CALIFOENm DEPARTMENT OF NATURAL RESOURCES >!^'ilH»«l GEOLOGY OF THE ORTIGALITA PEAK QUADRANGLE CALIFORNIA BULLETIN 167 1S53 DIVISION OF MINES FEsaT ^WLDma, san frakcsco ■HMMMOMMMHanWRHa THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA DAVIS STATE OF CALIFORNIA EARL WARREN, Governor DEPARTMENT OF NATURAL RESOURCES WARREN T. HANNUM, Director DIVISION OF MINES FERRY BUILDING, SAN FRANCISCO II OLAF P. JENKINS, Chief SAN FRANCISCO BULLETIN 167 lUNE 1953 GEOLOGY OF THE ORTIGALITA PEAK QUADRANGLE CALIFORNIA By LOUIS I. BRIGGS. JR. LIBRARY UNIVERSITY OF CALIFORNIA DAVIS LETTER OF TRANSMITTAL To His Excellency The Honorable Earl Warren Governor of the State of California Dear Sir : I have the honor to transmit herewith Bulletin 167, Geology of the Ortigalita Peak Quadrangle, California, prepared under the direc- tion of Olaf P. Jenkins, Chief of the Division of Mines, Department of Natural Resources. The report includes colored geologic and economic mineral maps, geologic sections, and many other illustrations. The area mapped lies on the west side of the San Joaquin Valley, largely within Merced County, although parts of it are in San Benito and Fresno Coun- ties. Since it describes a large number of important oil field formations, it is of particular interest to oil geologists. Economic minerals present in the area are magnesite, quicksilver, diatomite, gypsum, lime, sand, gravel, and bentonite. The author, Louis I. Briggs, Jr., prepared the map and report as a doc- torate thesis required by the University of California. The publication of the results of this project represents one of the cooperative undertakings of the Division of Mines with the University. Respectfully submitted, Warren T. Hannum, Director Department of Natural Resources February 26, 1953. (3) CONTENTS Page ABSTRACT 7 INTRODUCTION 7 Geography 9 STRATIGRAPHY 11 Jurassic sj-stem 11 Franciscan group 11 Cretaceous system 20 "Wisenor formation 20 Panoche formation 24 Moreno formation 32 Petrography of the Upper Cretaceous sediments 34 Tertiary-Quaternary system 36 Laguna Seca formation 37 Tesla (?) formation 39 Kreyenhagen formation 41 San Pablo formation 44 Oro Loma formation 46 Tulare formation 48 Stream terraces 49 Recent alluvium 50 Landslides ^ 50 GEOLOGIC STRUCTURE 50 Folding 50 Faulting 52 Structural history 53 GEOLOGIC HISTORY 53 ECONOMIC RESOURCES 58 Quicksilver 58 Magnesite 58 Diatomite 58 Gypsum 58 Lime 59 Bentonite 59 Sand and gravel 59 Petroleum 59 BIBLIOGRAPHY 60 (5) ILLUSTRATIONS Page Plate 1. Geologic map of the Ortigalita Peak quadrangle, California In pocket 2. Economic map of the Ortigalita Peak quadrangle, California In pocket 3. Geologic structure sections across Ortigalita Peak quadrangle, California In pocket 4. Geologic map of Tertiary formations in the Laguna Seca Hills, Merced County, California In pocket Figure 1. Index map showing location of Ortigalita Peak quadrangle 8 2. Columnar section of rock in Ortigalita Peak quadrangle 12 3. Photomicrograph of typical Franciscan graywacke from Ortigalita Peak area 13 4. Photomicrograph of Franciscan phyllonite from Ortigalita thrust zone 14 5. Photomicrograph of Franciscan pillow basalt from Miner Creek 15 6. Photomicrograph of Franciscan metagreenstone from east slope of Ortigalita Peak 16 7. Photomicrograph of pegmatoid vein in Franciscan quartz gabbro sill south of Ortigalita Peak 17 8. Photomicrograph of ex-solution patterns of magnetite-ilmenite altered to leucoxene and quartz 20 9. Photo showing quartz gabbro sill on north bank of Miner Creek 21 10. Photo showing slump bedding in silt strata 23 11. Photo showing gnarly bedding of Upper Cretaceous sandstone 25 12. Photo showing concretions in Upper Cretaceous rocks 26 13. Photo showing conglomerate series in north branch of Los Banos Creek 26 14. Photo showing sandstone penetrating overlying conglomerate 27 15. Photomicrograph of Upper Cretaceous subgraywacke 28 16. Histogram of rock types in coarse conglomerate at Ortigalita Creek and Los Banos Creek 29 17. Photo showing concretion in Panoche formation 30 18. Photo showing diatomaceous shale in Moreno formation 33 19. Photo showing formations in Rattlesnake Canyon 37 20. Photo showing outcrop of Kreyenhagen shale on Oro Loma Creek 40 21. Photomicrograph of jarosite and glauconite 42 22. Photomicrograph of jarosite crystals and clusters 43 23. Photo showing disconformity separating Tesla(?) shale and lower member of Kreyenhagen formation 44 24. Photo showing Kreyenhagen shale, San Pablo beds, and Oro Loma formation 45 25. Photo showing view north across Dog Leg Creek 46 26. Photomicrograph of sandstone from base of San Pablo formation 47 27. Photo showing Tulare formation underlain by Moreno shale in cliff on tributary to Ortigalita Creek 48 28. Photo showing Piedra Azul fault 51 29. Photo showing view down Ortigalita Creek in sec. 18, T. 12 S., R. 10 E. 54 30. Photo showing view north along crest of Laguna Seca Hills 54 31. Photo showing badland topography in Tulare beds 55 32. Photo showing Mercy quicksilver mine, southern workings 56 33. Photo showing remains of Scott furnace of Mercy quicksilver mine 57 (6) GEOLOGY OF THE ORTIGAUTA PEAK QUADRANGLE, CALIFORNIA* By Louis I. Briggs, Jr.** ABSTRACT Ortigalita Peak quadrangle is in the Coast Ranges bordering the San Joaquin Valley, approximately 5 miles south of Los Banos. The small part of Diablo Range in the southwestern portion of the mapped area is underlain by Franciscan (Upper Jurassic) graywacke, chert, and greenstone intruded by quartz gabbro and serpen- tine, and locally converted to glaucophane schists and phyllonites along the Ortigalita thrust, the major structural element of the area. Franciscan rocks have been thrust northeastward over Upper Cretaceous conglomerate, sandstone, and shale, and locally Wiseuor shale of Lower Cretaceous (Horse town) age is exposed beneath the fault surface. The thickest known section of Upper Cretaceous rocks in California (some 30,000 feet) underlies the foothill belt to the east of the thrust ; it consists of the Panoche formation (sandy shale, massive concretionary sandstone, and a coarse con- glomerate) overlain by the Moreno formation (purplish organic shale and sandstone). Relatively thin-bedded Tertiary sediments fringe the eastern edge of the foothills. They include Laguna Seca (Paleocene) concretionary sandstone, siltstone, and shale, Tesla(?) anauxitic sand and shale, Kreyenhagen diatomite and glauconitic sandstone of Eocene age, San Pablo (Miocene-Pliocene) bentonitic sandstone, shale, and con- glomerate, and Oro Loma (Pliocene) gravels, sands, and silts. Flat-lying Tulare (Plio- Pleistocene) reddish gravels and white-weathering silt and marl overlap the older formations and obscure much of the tilted bedrock series, especially near Little Panoche Creek. The major uplift of Diablo Range occurred during the upper Pliocene orogeny along the Ortigalita thrust which forms the eastern structural element of Diablo Range for some 130 miles. Dislocation in the thrust zone near the end of the Jurassic period, probably during the Diablan orogeny, is indicated by coeval development of glaucophane schists and phyllonites in apparent equilibrium, and was accompanied by intrusion of ultrabasic igneous masses. Subsequent to the Jurassic deformation, deforming forces have squeezed the serpentinous ultrabasic rocks into faults and fractures of the dis- rupted Franciscan rocks in the thrust zone during the upper Pliocene orogeny. Economic resources include magnesite, quicksilver, diatomite, gypsum, lime, sand, gravel, and bentonite ; however, sand, gravel, and gypsum are the products success- ■ fully exploited from this area to date. At least 7 holes have been drilled for petroleum but all have been abandoned. INTRODUCTION Ortigalita Peak quadrangle, delimited by meridians 120^45'-121°00' west and by parallels 36°45'-37°0U' north, lies largely within Merced County, although it extends into parts of San Benito and Fresno Coun- ties. There are no settlements within the quadrangle, but Los Banos is only 5 miles beyond the northern boundary, and Dos Palos, Firebaugh, and Mendota are within 20 miles of the eastern boundary. The area is approximately 50 miles west of Fresno and 100 miles southeast of San Francisco. Numerous roads enter the region ; one is oiled, and the others are well graded and passable except during and immediately after rains. The most convenient approach to the northern sector is by Ortigalita Road, past the oil-pumping station in the north-central map area ; but Mercy Springs Road (2 miles farther east) is a better access to the Laguna Seca area. Little Panoche Valley is best approached from Mendota. • Based upon a dissertation submitted in partial satisfaction of requirements for the degree of Doctor of Philosophy in Geology, in the Graduate Division of the Univer- sity of California, Berkeley, California, 19 50. Manuscript submitted for publica- tion January 1951. •• Instructor, Department of Geology, University of Michigan. (7) 8 ORTIGALITA PEAK QUADRANGLE [Bull. 167 Figure 1. Index map of part of central California showing location of the Ortigalita Peak quadrangle and of other quadrangles in the vicinity published as geologic maps by the Division of Mines. Mapping of Ortigalita Peak quadrangle was begun in the spring of 1948, continued during the summers of 1948 and 1949, and completed during the spring of 1950. Field data were plotted on aerial photographs (scale approximately 1:16,700) and later transferred in the field to the U. S. Geological Survey topographic map of the Ortigalita Peak quadrangle (scale 1:62,500). Acknoivledgments. I am particularly indebted to N. L. Taliaferro, C. M. Gilbert, F. J. Turner, and J. Verhoogen, of the University of California, for their help in this work. Invertebrate megaf ossils collected during the course of the investigation were identified by J. W. Durham and M. V. Kirk, also of the University of California. I am grateful also for the hospitality and courtesies shown me during the field seasons by Mr. Frank Arburua, Mr. and Mrs. S. Marsi, and Mr. P. Lindbloom. The Board of Research, University of California, Berkeley, furnished mate- rial aid to defray the major part of expenses incurred in the field. Previous Literature. One of the earliest and most comprehensive pa- pers covering geology of the Ortigalita Peak area is the report on the geology and oil resources of the eastern foothill belt of Diablo Range by Anderson and Pack (1915). Although their work was of a recon- naissance nature, considerable attention was given to description and distribution of lithologic units. 0. P. Jenkins (1931) in a detailed de- scription of the stratigraphic and economic significance of the Kreyen- hagen shale, mentions the occurrence of the Kreyenhagen in the 1953] INTRODUCTION 9 Ortigalita area, and includes a comprehensive bibliography up to the year 1930. A. P. Bennison mapped in detail the stratigraphy of late Upper Cretaceous strata both to the north and to the south of Pacheco Pass ; although the results of his work were never published, they were presented before the LeConte Club in April 1940. The Moreno shale in Panoche Hills was subdivided into lithologic units by M. B. Payne (1951) who described the continuation of the units as far north as Ortigalita Creek. N. L. Taliaferro (1941) published a structure section across Ortiga- lita Peak quadrangle in 1941, and in a later paper (1944) discussed Lower Cretaceous sediments to the east of Ortigalita thrust. Detailed stratigraphy of late Upper Cretaceous and Eocene sediments of Laguna Seca Hills was described by C. F. Green (1942) in an unpublished thesis, and several stratigraphic correlation sections from the same area by Stewart, Popenoe, and Suavely (1944) were published as a preliminary chart of the U. S. Geological Survey Oil and Gas Investigations. Radio- laria from the Kreyenhagen shale were described by B. L. Clark and A. S. Campbell (1945). S. N. Daviess (1946) attempted to establish a mineralogical basis for correlation of Upper Cretaceous, Paleocene, and Eocene sandstones from a study of outcrop samples from Laguna Seca, Oro Loma, and Rattle- snake Creeks and from well cores taken from the floor of the adjacent valley. Quien Sabe quadrangle to the west was mapped and the geology described by C. J. Leith (1949) the San Benito quadrangle to the south- west was mapped by I. F. "Wilson (1942). Geography Relief and Topography. The area of Ortigalita Peak quadrangle, as a part of the Diablo Range, the easternmost of the Coast Ranges, is typ- ical in many ways of the foothills at the western border of the San Joaquin Valley. Flat hills of low relief rise abruptly from the vaUey floor with slopes approaching the eastward dip of underlying Tertiary and Cretaceous beds. The maximum elevation in Laguna Seca Hills is only 1,320 feet, whereas the average elevation is 800 feet. Westward, the altitude slowly increases, except in the broad terraced flats of Carrisa- litos, Salt Creek, and Little Panoche Valley, Rugged and steep Fran- ciscan terrane of Diablo Range contrasts markedly with rolling foot- hills of softer Cretaceous and Tertiary rocks, culminating at 3,716 feet in an unnamed peak. Lower but better known Ortigalita Peak rises abruptly some 2,000 feet from the floor of Little Panoche Valley. The gently rolling summit areas of the Diablo Range are a striking topo- graphic feature, contrasting with precipitous slopes of lower altitudes. Climate and Vegetation. The western slopes of Diablo Range are characterized climatically by hot, dry summers, mild winters, and little rainfall. Average daily maximum temperatures during July and August are 99 to 101 degrees Fahrenheit, whereas average daily minimum tem- peratures during December and January are about 30 to 35 degrees. Summer rains are rare. A northwesterly breeze, at times reaching gale proportions, blows throughout much the year. The predominant vegetation of the foothills is range grass, principally foxtail and wild oat, but even these are absent over extensive areas. Soils derived from shale and silt are largely barren ; northern slopes and sandy 10 ORTIGALITA PEAK QUADRANGLE [BuU. 167 soils support a good grass cover; and cottonwood, sycamore, oak, and willow trees mark the course of major streams, in particular Los Banos, Ortigalita, Little Panoche, and Piedra Azul Creeks. In contrast, higher Franciscan terrane of Diablo Range supports a sparse but widespread flora including oak, juniper, cottonwood, sycamore, and pine, as well as a short brush cover largely of sage. Drainage and Water Supply. Drainage is toward the east except in a small part of Diablo Range near the southwestern margin of the area. Most of the stream valleys are dry except during rainstorms, but water flows sluggishly throughout much of the year through shallow ponds in the upper reaches of Los Banos Creek and Little Panoche Creek, seeping into alluvium before reaching the valley. Trellis drainage is well developed in Laguna Seca Hills and less per- fectly in the remainder of the foothill belt, whereas a dendritic pattern is carved into more homogeneous Franciscan rocks of Diablo Range. Extensive terrace mantle indicates that Los Banos, Little Panoche, and Salt Creeks follow Plio-Pleistocene drainage lines; however, Ortigalita Creek, Laguna Seca Creek, and others appear to have developed courses, in a large part dictated by relative resistance of underlying strata, in late Pleistocene or Recent time. Several minor terrace levels are evident even in the smallest streams, and although most of the valleys are stepped by a single terrace, Molino, Piedra Azul, Los Banos, Ortigalita, and Little Panoche Creeks have well- preserved terraces at three levels. Leith (1949) and Wilson (1942) noted similar occurrences in adjacent regions. Paucity of water suitable for irrigation of crops, for watering of stock, and for human consumption is perhaps the major obstacle hinder- ing economic development of the fertile soil covering much of the area. In the San Joaquin Valley the problem has been partly solved by the drilling of deep wells into the valley alluvium and by a vast network of irrigation canals which bring water from the San Joaquin River drain- age system. The vast system of the Delta-Mendota Canal now brings water from the Sacramento River drainage to the Mendota area, aiding agricultural development of the semi-arid regions of the San Joaquin Valley. The remainder of the area has less available water. Shallow wells, bored into Tulare terrace mantle or in thin alluvium of larger streams, produce a meager supply of water. A considerable number of large steel water tanks are spotted throughout the central portion of the area to water sheep during the short spring grazing period. A few of these tanks are supplied from local sources, but the majority must be replenished with water trucked from the valley. Natural springs in the Diablo Range supply sufficient water for the few hundred head of cattle that remain there throughout most of the year. The spring in the NWl sec. 29, T. 13 S., R. 10 E. flows several hun- dred gallons an hour of clear water, but at present it is not utilized; neither is the sulfurous spring about half a mile to the south. However, Mercey Hot Springs, in Little Panoche Valley 3 miles beyond the southern quadrangle limits, is a popular summer spa. The structure sections (pi. 3) show the inadvisability of boring water wells into Cretaceous and Tertiary bedrock of the foothills, as the beds dip steeply toward the valley, even at a depth of 6,000 feet below sea 1953] STRATIGRAPHY 11 level. Most units of the Upper Cretaceous are lenticular, and probably do not carry much water ; furthermore, those waters that are present are charged with calcium sulfate, sodium chloride, and other soluble salts, as evinced by several horizons of salt water struck by borings for oil into the adjacent valley. Only some 8 inches of rain falls during the year, and much of this runs off into the alluvium of the valley. Of the little water that seeps into the tilted bedrock, much must return to the atmosphere by capillary action and evaporation ; therefore, the supply of water from the foothill belt is meager. The Tulare terrace mantle forms the only reservoir rock but it is very thin and patchy in distribution ; yet shallow wells obtain water from this formation in Little Panoche Valley, the north slopes of Wisenor Hills, Carrisalito Flat, the Gastonbide Ranch area, and the Laguna Seca Ranch area. Elsewhere water may be obtained from shallow wells in the alluvium of the major streams. STRATIGRAPHY The oldest rocks of the region are Franciscan graywaeke, siltstone, and shale, interbedded with chert and greenstone, and intruded by quartz gabbro and serpentine. Lower Cretaceous shale is sandwiched between Franciscan rocks and Upper Cretaceous conglomerate along Ortigalita thrust about a mile east of Ortigalita Peak, and the major part of the foothill belt to the east is underlain by Upper Cretaceous sandstone, shale, and conglomerate. Comparatively thin Tertiary and Quaternary beds border the San Joaquin Valley and include Paleocene Laguna Seca sandstone and shale, lower or middle Eocene Tesla ( ?) white quartzose sand, and upper Eocene Kreyenhagen diatomaceous shale. Miocene- Pliocene San Pablo bentonitic sandstone, conglomerate, and shale over- lain by Pliocene unconsolidated sand, silt, and gravel complete the bed- rock sequence. Pleistocene Tulare terrace deposits mantle much of the foothill belt. Jurassic System Franciscan Group Distribution and Thickness. Franciscan rocks underlie the southwest portion of the map area, and form a small part of the almost continuously exposed Franciscan core of Diablo Range covering an area of about 1,500 square miles. In the Ortigalita Peak quadrangle the Franciscan is exposed in the eastern limb of an asymmetrical anticline, overturned adjacent to Ortigalita thrust. Total thickness is difficult to estimate as faults are difficult to trace in the homogeneous graywaeke sediments, but erratic attitudes and some development of phyllonites indicate a zone of dislocation southwest of Sugarloaf. The layered sequence above this zone is 8,000 to 10,000 feet in thickness, and if repetition is absent or minor, the thickness (measured on section E-E' tbrough Ortigalita Peak) is at least 20,000 feet. Neither the bottom nor the top of the Fran- ciscan group is represented. Lithology. Graywaeke sandstone associated with black slaty shale and siltstone is the predominant rock type of the diversified Franciscan group and comprises an estimated 80 percent of the total volume. The graywaeke characteristically is massive, slate-blue to greenish gray when fresh and tan to buff on weathered surfaces. In the upper reaches of 12 ORTIGALITA PEAK QUADRANGLE [Bull. 167 AGE FORMATION COLUMN FEET DESCRIPTION Quoternary "'"Pho"-'"" Pleistocene a ferroces Tulore 0-500 Pliocene CrO LOmo 400 + Miocene Son Pablo 400 - Jravel, sand, and silt Gravel, sand, silt, azr.z marly beds St -'; . ar. J ^rave , sa:.. Eocene Kreyenhogen 700 ^' Tesia (?) Upper - '-liite and brown diatomaceous shale. Lower - glauconitic pebbly sand anJ browu radiolariau shale, locally tuffaceous Paleocene Loquno Seca 50-200 Anauxitic quartzose sands and kaolinitir clay, locally tuil'aceous 1.200 CoT-cretionary feldspathic sandstone, silts, and sf-ales 2,600 Purplish brown shale and concretionary feldscathic sandstone Upper Cretaceous Ponoche 23,000 to 29,000 Concretionary feldspathic ssindstone, coarse conglomerate, and sandy shale Lower Crefoceous 1,800 t Dark shale and thin hard carbonaceous sand- stone Upper Jurassic Franciscan 10,000 + Thin bedded and massive graywacke sandstone and siltstone, chert and greenstone. Intruded by quartz gabbro and serpentine, and locally metamorphosed to glaucophane schists and re- lated green schists Figure 2. Columnar section of rocks In the Ortigalita Peak quadrangle, California. 1953] STRATIGRAPHY 13 ^yf?^^:^ L^^S? ^^^r-^ Figure] 3. Photomicrograph of typical Franciscan graywacke, from the Ortiga- lita Peak area. Angular quartz and feldspar grains in micaceous matrix are poorly sorted and distinctly laminated. Magnification 20x, plane polarized light. Piedra Azul Creek and southward persistent strata 1 foot to 10 feet in thickness are separated by dark gray siltstone and slaty shale in con- tinuous layers a fraction of an inch to several inches in thickness. Hard platy red shale that is intimately bedded with chert and greenstone in the upper part of the sequence only is well exposed along the road be- tween Piedra Azul Spring and Wisenor Flat. Graywacke of the lower beds is typically fine-grained though angular grains of quartz, fresh feldspar, muscovite, and black pelitic fragments are recognizable with the use of the hand lens. A fresh sample will fracture across grains and matrix alike revealing a few clear quartz and feldspar grains. A faint lineation may be seen throughout Franciscan exposures and in some places, such as south of the Sugarloaf diabase-gabbro sill, strong shearing on two or more shear planes has produced pencil cleavage in finer-grained sediments. Lineation is pronounced near Ortigalita thrust. The fabric and the mineralogy were determined by metamorphic reorgan- ization of the rock ; therefore, in the thrust zone phyllonites have formed from graywacke by partial recrystallization along planes of shear. In the typical graywacke incipient crystallization of the matrix is the only alteration revealed by the microscope. Sorting is poor, both of grain size and of grain composition. The largest grains and rock fragments are 0.5 to 1.0 millimeter in diameter but the average grain is much smaller ; furthermore, there is a complete gradation in grain size down to that not resolvable under the highest magnification (x350). Packing is moderately close although the matrix occupies about half the tOtal volume. Feldspar and quartz appear to be equally abundant. The quartz 14 ORTIGALITA PEAK QUADRANGLE [Bull. 167 Figure 4. Photomicrograph of Franciscan phyllonite from the Ortigalita thrust zone north of Wisenor Flat. Deformation lamellae in quartz grrains (resembling polysynthetic twinning of plagioclase) are aligned with pelitic streaks and lawsonite prisms. Glaucophane is common. Magnification 20x, crossed nicols. grains show strain shadows, fritted edges, and inclusions of minute needles of a colorless prismatic amphibole ( ?), and of the feldspar grains, plagioclase, invariably calcic oligoclase or sodic andesine, is much more abundant than orthoclase and perthite. Present also are chlorite, mus- covite, sericite, epidote, clinozoisite, sphene, magnetite, and carbonate minerals. Lithic fragments constitute about 5 percent of the grains, including volcanic rock, chert, and pelitic schist. A greater proportion of matrix (70 to 80 percent), smaller average grain size, and paucity of composite grains distinguish graywacke siltstone from sandstone. The striking similarity in mineral composition of sandstone, siltstone, and shale of the Franciscan graywacke sediments is their characteristic microscopic property. Crystalline chert comprises the remainder of the sedimentary rock types and is characteristic of the late volcanic sequence. The chert is typically white or pale yellowish, less commonly red or green, and bedded in lenticular layers a few feet to several tens of feet thick that form discontinuous outcrops one eighth to one half mile in length. Continuous outcrops of 2 or 3 miles occur locally as along the spur south of Ortigalita Peak. Countless thin lenticles, a fraction of an inch to several inches in thickness, separated by papery-thin argillaceous or tuffaceous material, compose a single chert bed, which is characteristically contorted, frac- tured, and intricately quartz-veined. Rhythmic banding typifies aU varieties except the strongly sheared and completely recrystallized massive chert. Quartz, both cryptocrystalline and coarsely granulose, stilpnomelane, and small acicular prisms of clinozoisite ( ?) make up the 1953] STRATIGRAPHY 15 minerals of these rocks, over 90 percent of which is quartz. Colored patches of red chert contain acicular clinozoisite( ?) and cryptocrystalline quartz, the latter exhibiting strong preferred orientation, in contrast to the coarse granulose patches which show undulatory extinction of doubly polarized light. Partially or completely altered pillow basalt, andesite, intrusive basalt and diabase, tuff, and agglomerate are conveniently grouped as green- stone, which is most profuse in the upper part of the sequence adjacent to Ortigalita thrust. Northwesterly continuation of these rocks in a similar stratigraphic position is recorded by Leith (1949, p. 15) who correlates them with El Puerto volcanic rocks of the eastern portion of Diablo Range. FiGUKD 5. I'hotomicrograph of Franciscan pillow basalt from Miner Creek showing variolitic texture of flamboyant sheaths of feldspar micro- liths (saussuritized). Euhedral grains are quartz and calcite, pseudo- morphs after olivine and feldspar and amygdules. Magnification 9 Ox, plane polarized light. Thickness of greenstone strata ranges from a few inches to several hundred feet. A broad zone of schistose igneous rock east of Ortigalita Peak attains an apparent thickness of at least 3,000 feet (measured on structure sections), although extreme shearing and faulting prevent an exact measurement. Some of the rock may be intrusive, indeed abundant coarse augite grains in a specimen from this area may be evidence of intrusion. However, prevalence of fine-grained meta-igneous rock makes it doubtful that all greenstone in the thrust zone east of Ortigalita Peak is intrusive ; moreover, complete disruption of the entire sequence in this area nullifies any attempt to establish the intrusive or extrusive character of the greater part of these rocks. Thin sheets of greenstone occur sporadi- 16 ORTIGALITA PEAK QUADRANGLE [Bull. 167 Ir Figure 6. Photomicrograph of Franciscan metagreenstone from the eastern slope of Ortigalita Peak with relict augite (lower right), flamboyant glauco- phane (feathery tinted grains), and acicular lawsonite (small prismatic grains in groundmass). Magnification 25x, plane polarized light. cally in the lower graywacke beds. Many of the thinner layers, some only 2 to 4 inches in thickness, are certainly altered tuffs, whereas a few layers several feet in thickness are certainly volcanic flows. Pillow structure is clearly shown by a flow in Miner Creek a mile east of Sugarloaf, com- posed largely of altered volcanic glass containing microscopic bundles of radiating flamboyant saussuritized feldspar microliths. Most of the greenstone is very fine-grained, thoroughly chloritized and oxidized, making fresh fracture surfaces a rarity. Much greenstone has an ophitic or diabasic texture; some carries clear colorless phenocrysts of augite rimmed by colorless or green uralite, and minor amounts of leucoxene and granular sphene. Greenstone, quartz diabase-gabbro, and serpentine intrude the Fran- ciscan sediments. A small body of greenstone is located 1^ miles west of Ortigalita Peak, and a half mile northwest an elliptical basaltic plug with steeply dipping curved joint planes forms a craggy prominence visible from Wisenor Flat and adjacent ridges to the north. Serpentinous ultrabasic rock, highly sheared and locally altered to silica-carbonate rock, occurs only along the Ortigalita thrust zone. There is no thermal contact zone along the serpentine, rather the contacts are marked by shearing in both the intrusive serpentine and the invaded rock. Small irregular patches of glaucophane schist are common along the contact zones. Thin stringers and sheets of serpentine in the disrupted rock of the thrust zone and a single thin sheet, only 20 to 50 feet in thickness, marking the sinuous trace of Ortigalita thrust east of Orti- 1953] STRATIGRAPHY 17 galita Peak, are evidence of * * cold ' ' intrusion during a period of deforma- tion later than that accompanying the original intrusion of ultrabasic rock. Hornblende-quartz gabbro forms the sill passing through Sugarloaf and Ortigalita Peak. The sheet swells and pinches within short distances along the strike, attaining a maximum thickness of approximately 1,350 feet in Miner Creek, and dips steeply to the east at angles greater than 70 degrees except immediately south of Ortigalita Peak where the incli- nation flattens to about 45 degrees. Although the intrusive body is not continuously exposed between Ortigalita Peak and Sugarloaf, the rela- tive stratigraphic position of the exposures suggests continuity of the sill at depth. Specimens from a section across the sill in Miner Creek contain the following minerals : augite, hornblende — including colorless, green, brown, and blue varieties — chlorite, saussuritized feldspar, quartz, magnetite, ilmenite, leucoxene, chromite, chalcopyrite, and calcite. Epidote and sphene are sparse in some of the specimens. Apatite com- monly forms euhedral grains in quartz, and in one specimen large euhedral grains up to 4 millimeters in length compose several percent of the rock. Augite ranges in composition from diopsidic at the top of the sill to subcalcic near the base where the grains have an optic angle of about 40 degrees. Diallage parting is common and most of the grains are rimmed with secondary hornblende or partially replaced by a felted mass of 0A1: Figure 7. Photomicrograph of pegmatoid vein in Franciscan quartz gabbro sill south of Ortigalita Peak, showing intergrowth pattern of quartz (white) and saussuritized feldspar (dark). Magnification 18x, plane polarized light. 18 ORTIGALITA PEAK QUADRANGLE [Bull. 167 chlorite and colorless amphibole. Hornblende is believed to be secondary although that which is darker colored, pleochroic, and rimmed by slender prisms of colorless amphibole might well be primary. Acicular needles of glaucophane line cleavage traces of some of the hornblende and occur in irregular patches in others. Quartz abounds in specimens taken near the top of the sill, is rare in those from the base, and averages about 5 percent of the bulk of the minerals. It is commonly intergranular, and micrographic intergrowths with saussuritized feldspar constitute 25 percent or more of pegmatoid rocks near the top of the sill. Veins of coarse granular quartz are profuse throughout the intrusive rock and in the adjacent contact graywacke wliereas minute granulose quartz occurs wdthin saussuritized feldspar laths. Chlorite — both pale green and yellow varieties — makes up the greater part of most specimens, and appears to have formed from augite and perhaps from amphibole. Abundance of chlorite and actinolite may be ascribed to dynamic meta- morphism in the shear zone bordering Ortigalita thrust ; incipient glau- cophane may be attributed to metasomatic solutions permeating the frac- tures of this zone. Differentiation of the sill is indicated by decrease in optic angle of augite from top to bottom of the intrusion and by concentration of quartz at the top. The texture is diabasic near the top and clotty or gabbroic near the base although a subophitic texture is common throughout the sill. Intrusion at high temperature is indicated by a hornfelsic zone border- ing the top and the bottom of the sill. No high-temperature metamorphic minerals were detected in the contact sediments ; the matrix is coarsely crystalline chlorite and sericite with lawsonite( ?) and epidote, and the rock is traversed by a myriad of quartz veins. The hornfels zone border- ing the top of the sill in Miner Creek is about 400 feet in thickness but elsewhere it rarely exceeds 50 feet. Greater breadth of both sill and con- tact zone along Miner Creek indicates that the sill originated in this vicinity and spread southward between the bedded grayvvacke. Hornblende-quartz gabbro of the Franciscan group has been described only from the Tesla area by Huey (1948, pp. 20-21), thus the outcrops in Diablo Range may hold an important — though presently unkno^vn — sig- nificance in the history of the Franciscan series. Glaucophane schist is restricted largely to the Ortigalita thrust zone which reaches a width of 1^ miles east of Ortigalita Peak and maintains a width of about 1 mile elsewhere to the northwest. The Ortigalita Peak- Sugarloaf sill apparently formed a bulwark against which the overlying rock was sheared, as the metamorphic zone is wider adjacent to the sill and the rocks forming the uppermost part of the intrusive are metamor- phosed. The zone of metamorphism, marked by sheared graywacke at the southern border of the map area, doubtless extends at least as far as Glaucophane Ridge, 5 miles beyond the southern border of the quad- rangle. Some of the rocks, for example the sheared graywacke or phyllonite, owe their metamorphic recrystallization largely to stress and dislocation, whereas in others, such as the glaucophane schists of Piedra Azul Spring, metasomatic solutions appear to have played the dominating role. For most rocks it is difficult or impossible to conclude whether shearing stress or metasomatism has been the primary factor producing metamorphism, but both have had an influence. All of the previously described Fran- 1953] STRATIGRAPHY 19 ciscan rock varieties have their metamorphic derivatives in the thrust zone, and in most of them metamorpliism has not progressed to the deforce that the original rock type cannot be recognized as there is a complete graduation from practically unaltered sedimentary rock and greenstone to that which is completely recrystallized. For reasons of cartographic continuity those slightly altered rocks whose parentage was certain w^ere mapped wdth unaltered rocks of the same group. Glaucophane schist occurs in a small area about Piedra Azul Spring surrounded by serpentine and silica-carbonate rock. Glaucophane, mus- covite, actinolite, and quartz are the prominent minerals. The schist ap- pears to be embedded in the serpentine, suggesting that the metamorphic rock was carried up from depth within the serpentine body, and the min- eralogy and distinctive appearance leave little doubt that metasomatism has played a dominant role in metamorphism. Phyllonites of the thrust zone southeast of Piedra Azul Spring owe their recrystallization to shearing stress although the glaucophane ap- pears to be in stable equilibrium. The microscope reveals a mixture of very coarse schistose and clastic texture with elongate streaks of pelitic material, incipient glaucophane, and rotation of grains. Quartz showing deformation lamellae, andesine plagioclase, chert, and basic igneous lithic fragments occur as relict clastic grains whereas glaucophane, lawsonite, chlorite, sericite, stilpnomelane, and actinolite are metamorphic minerals, and granular spene, clinozoisite, magnetite, and carbonate minerals may be either relict or metamorphic. Fabric and structure of these meta-gray- wackes may be correlated with the Subzone Chlorite 2 described by F. J. Turner (1948, p. 38) for the graywackes of southern New Zealand. In this and other schists of the metamorphic zone along Ortigalita thrust lawsonite takes the place of albite generally present in rocks of corre- sponding composition in the green schist facies [See G. A. Joplin (1937, pp. 424-430) for similar occurrences in New Caledonia] . Most metagreenstone is very fine-grained and contains abundant glau- cophane (or crossite) and lawsonite. It is widespread in the shear zone east of Ortigalita Peak where the eastern slope of the peak is composed largely of alternating greenstone and glaucophane schist, fractured into small splintery fragments. Some rare occurrences of quartz-sericite schist appear to have developed from chert by metamorphism. Sericite in very thin partings between massive layers of coarse-grained quartz suggests thin argillaceous partings of rhythmically banded chert. Diahlan Orogeny. Franciscan rocks in the Ortigalita Peak area are in fault contact with Lower Cretaceous and Upper Cretaceous sediments, thus precluding any possibility that an unconformity may have been preserved between Franciscan and Lower Cretaceous rocks ; consequently evidence of a Jurassic-Cretaceous orogeny must be sought in the lithology and fabric of the Franciscan rocks. Common field association of glaucophane schist with serpentine has led Taliaferro (1943) to the opinion that glaucophane schist of the Cali- fornia Coast Ranges is a product of pneumatolytic or metasomatic emanations from ultrabasic intrusives. There are numerous localities where devlopment of glaucophane schist can be explained in no other plausible manner; however, there are other occurrences where miner- alogy and fabric of the schist are clearly the result of dislocation, and metasomatism— although it may be instrumental in development of glau- 20 ORTIGALITA PEAK QUADRANGLE [Bull. 167 ^ 4 < ■1 Figure S. Photomicrograph of ex-solution patterns of magnetite-ilmenlte altered to leucoxene and quartz in Franciscan quartz gabbro sill. Magnification 18x, plane polarized light. cophane — could not have formed the dominant metamorphic fabric and mineralogy of the schist. In meta-graywacke of the Ortigalita thrust zone, granulation and rotation of grains, deformation lamellae in quartz, and large discoidal pelitic streaks are the product of shearing stress during dislocation coeval with crystallization of lawsonite, glaucophane, chlorite, sericite, and stilpnomelane. Lawsonite and glaucophane occur in schists derived from various Franciscan rock types — graywacke, sand- stone and shale, but most abundantlv in metagreenstone — and if em- anations from ultrabasic magma are necessary for development of these minerals in the thrust zone, then shearing and fracturing, intrusion of ultrabasic magma, and metasomatism must have taken place concurrently. Since serpentine and schist are restricted to Franciscan-Knoxville rocks, it follows that dislocation in the Ortigalita thrust zone occurred during the period of metamorphism, that is, during the Diablan orogeny near the close of the Jurassic period. Wisenor Formation Cretaceous System Name and Occurrence. East of Ortigalita Peak Lower Cretaceous shale and thin sandstone beds extend for 2 miles northward from Little Panoche Valley between the Ortigalita thrust and the basal conglomerate of the Panoche formation. They were originally included in the Panoche formation by Anderson and Pack (1915) but Taliaferro (1943a) distin- guished them and placed them in the Shasta group on the basis of lith- ology and stratigraphic position. Later (Taliaferro, oral communication, 1953] STRATIGRAPHY 21 Figure 9. Exposure of quartz gabbro sill on north bank of Miner Creek. Intricate quartz veining and strongly developed sheet jointing roughly paral- lel boundary of sill. 22 ORTIGALITA PEAK QUADRANGLE [BuU. 167 1950) fossils indicating the Horsetown stage as defined by F, M. Ander- son (1936) were collected from these beds, indicating that they are to be correlated with similar strata along the east side of Diablo Range in Hospital Creek and Corral Hollow. Because of their exposure in the Wisenor Hills, the name Wisenor formation is suggested for these strata of Horsetown age. That an angular discordance exists between the Wisenor formation and the Panoche formation is seen in several localities where the strikes of the two formations differ. But everywhere the angle of dip of the two formations is steep and approximately the same, so that the observed unconformity might be explained by gentle warping of the Wisenor strata before the Panoche was laid down. If this is correct the uncon- formity may be only local and elsewhere the same formations might ap- pear conformable, as they do north of Ortigalita Creek where the lowest conglomerate beds occur about 3,000 feet stratigraphically above the lowest exposed Cretaceous strata. The shale and thin sandstone beds at the base of this section, however, are lithologically similar to those inter- bedded vidth Panoche conglomerate, and the presence of very coarse Pan- oche conglomerate at the base of the section in Ortigalita Creek indicates that if Lower Cretaceous beds are to be found farther north their ex- posure must be very limited. A single thin section of the fine-grained flaggy sandstone typical of the Wisenor formation has approximately the following composition : Mineral constituent Percentage Quartz 20 Feldspar 15 Matrix 35 Caleite 20 Lithic fragments 4 Carbonaceous material . 2 Chlorite, biotite, epidote . 4 100 Carbonate cement consists of coarse to fine crystalline interstitial cal- eite and veins. Much of the feldspar is twinned and some is sericitized or kaolinized ; both quartz and feldspar grains are fractured and angular. Matrix material consists of recognizable crystallized clay(?), granular quartz, chlorite, and serieite ; the chlorite listed separately appears to be altered biotite. Lithic fragments include quartzite, chert, schist, and other rock types. The sandstone is a graywacke (Tallman, 1949; Petti- john, 1950) although the texture and proportion of argillaceous matrix are intermediate between Franciscan graywacke and Upper Cretaceous subgraywacke. Sandstone of the Wisenor formation resembles micro- scopically sandstone of the Shasta group from Lake County, California (Brice, 1953). Origin. There is some evidence that Lower Cretaceous sediments were deposited in a continuous geosyncline extending throughout the central and northern Coast Ranges within the approximate limits of the previous Franciscan basin (Taliaferro, 1944). Preponderance of black shale and abundant carbonaceous fragments suggest that deposition was in quiet waters under anaerobic conditions. Interbeds of sandstone are indicative of occasional currents competent to transport sediment of sand size. 1953] STRATIGRAPHY 23 OS a;" 24 ORTIGALITA PEAK QUADRAXGLE [Bull. 167 Panoche Formation Anderson and Pack (1915) subdivided Upper Cretaceous sediments (previously called the Chico formation) on the east side of Diablo Range north of Coalinga into two formations, namely the Panoche formation below and the Moreno shale above. Taliaferro (1943a) and F. M. Ander- son (1941) have proposed divisions of the Panoche formation wherein Anderson's Pioneer group is approximately the equivalent of Talia- ferro's Pacheco group and Anderson's Panoche and Moreno groups are inclusive of Taliaferro 's Asuncion group. Taliaferro made his divisions in the Santa Lucia Range where Upper Cretaceous strata are separated by a strong unconformity that represents the Santa Lucian orogeny. He correlated conglomerate strata bearing reworked Turonian * fauna along the eastern slopes of Diablo Range with the disturbance. Anderson's sub- division is based on the same fossiliferous conglomerate beds, thus the close correspondence in their Upper Cretaceous grouping. That lithologic units in the Upper Cretaceous can be separated within limited areas was recognized by Anderson and Pack who subdivided the Panoche and Moreno formations along the 130-mile strip north of Coa- linga ; but because they also realized that the units could not be extended with any degree of certainty beyond local areas, they did not attempt to subdivide Upper Cretaceous sediments along Diablo Range into units more refined than the Panoche and Moreno formations. Because Cre- taceous rocks are not continuously exposed along the east side of Diablo Range, owing to considerable overlapping of Quaternary terrace deposits and alluvium and to extreme lenticularity of the Upper Cretaceous lith- ologic units, exact correlation between isolated areas is not possible. Stratigraphic terminology of the Upper Cretaceous of Diablo Range is not satisfactory. Fossils are relatively sparse throughout great thick- nesses of sedimentary strata and where preserved they are frequently long-range forms. Distribution and Relations. The Panoche formation is the most wide- spread formation unit of the map area ; it underlies approximately 100 square miles of the area covered by Ortigalita Peak quadrangle. The outcrops in this region comprise but a small part of the very extensive belt of early Upper Cretaceous rocks along the west side of the San Joaquin Valley that includes the type section in Panoche Hills, which extend into the southeastern part of the mapped area. The greatest thickness accurately measured on cross-sections where both the base and top of the formation are exposed is shown on structure sec- tion C-C (pi. 3) where there are 30,000 feet of beds mapped as Panoche • European names applied to stages of the Cretaceous System. Series Stages * I Danian 1 Maestrichtian Upper ) ( Campanlan Cretaceous \Senonian •< Santonian Turonian , Cenomanian [ Albian Coniacian . tower Cretaceous .jAptian /Barremian I -KT^^ „:„- jHauterivian (Neocomian Ticlinal deposition and mid-Cretaceous folding, uplift, and regression of the sea which exposed the tilted Lower Cretaceous sediments to erosion. "^W^ -x-'.^J »A. Figure 30. View north along crest of Laguna Seca Hills across Laguna Seca Creek. Subsequent drainage pattern well developed in the alternating hard and soft strata of the massive concretionary sandstone unit that underlies greater part of the summit area. 1958] GEOLOGIC HISTORY 55 Figure 31. Badland topography eroded into Tulare beds in westward-facing bluffs in sec. 36, T. 13 S., R. 10 E. The upper light-colored beds are white, red, and bluish cross- bedded gravel, sand, and silt underlain by deep bluish green and deep red unconsoli- dated silt. Subsequent sinking allowed ingress of the broad shallow Upper Cre- taceous sea that lapped against a deeply eroded Sierra Nevada of low relief near the eastern border of the present Great Valley. A vast thick- ness (over 30,000 feet in the Ortigalita Peak region) of shallow-water marine sediment was deposited in this basin during Upper Cretaceous time. The sea persisted until middle Eocene when local uplift allowed shallow scoring of the previously deposited sediments. In middle Eocene .the long-lived western landmass contributed little or no detritus to the basin ; deeply weathered crystalline rock of the Sierra Nevada supplied quartz sands and refractory kaolinitic clay. The climate was tropical, warm and moist, and chemical weathering deeply altered exposed rock masses. Near the close of the Eocene epoch the sea returned, teeming with plankton, and siliceous tests accumulated on the sea floor to a thickness of several hundred feet to form the Kreyenhagen shale. Silica derived from volcanic ejecta showered into the sea from distant volcanos possibly at- tracted these organisms. Renewed epeirogenic uplift drained the narrow upper Eocene seaway and laid bare to erosion the freshly formed siliceous shale in lower Miocene time. Denudation was followed by ingress of a shallow sea and deposition of a thin stratum of quartpse sand close ashore or in brackish water. Local uplift at the close of the Miocene epoch flooded the area with coarse detritus coeval with deposition of great thicknesses of wind- blown tuffaceous silt and sand. Volcanism ceased in lower Pliocene but deposition of detritus derived largely from nearby Franciscan rocks continued. The material spread as broad alluvial fans from the embryo Diablo Range onto vast flood plains to the east. Deposition was interrupted in upper Pliocene by upbowing of the sediments into the broad anticlinal Diablo Range while other ranges of the Coast Ranges were folded and thrust into much their present topo- graphic form. Rupture of the rocks along the Ortigalita thrust displaced Franciscan over Cretaceous and disjointed the eastern limb of the anti- clinal structure. The bordering foothills were eroded and imperfectly 56 ORTIGALITA PEAK QUADRANGLE [Bull. 167 Figure 32. Mercy quicksilver mine, southern workings. 1953] GEOLOGIC HISTORY 57 * •r .■-•«- ^ ' V %* % \-~ V ^ t ^-^'•««->*^;^ • «l ?.-^:' -3^-- ■ vK »5te °*'*^l^%^ im. -*■ :?s- .v»»^, . Figure 33. Remains of Scott furnace of Mercy quicksilver mine. 58 ORTIGALITA PEAK QUADRANGLE [Bull. 167 planed in early Pleistocene and a thin mantle— the Tulare formation — was spread over the surface. The mid-Pleistocene orogeny locally folded and fractured the rocks, and the invigorated streams cut rapidly into soft sediments to form the present drainage pattern. Several more recent elevations temporarily renewed the activity of streams which cut into previously graded channels to form local terraces along their valleys. The geologic history recorded in the Ortigalita Peak area is much the same as that elsewhere along the eastern border of Diablo Range. This area was a central basin for accumulation of Upper Cretaceous sediment, and perhaps for Franciscan sediment as well ; however, the Tertiary rec- ord throughout the Coast Ranges varies greatly from area to area, even where they are adjacent, as the Tertiary seas were narrow and much of the rocks were land-laid. ECONOMIC RESOURCES Quicksilver There is no recorded production of quicksilver from the Ortigalita Peak area ; however, the Mercy mine lying only a quarter mile bej^ond the southern boundary of the area is a large producer. According to Yates and Hilpert (1945, p. 25) ''It is the leading producer in the dis- trict with a total recorded production of 1,682 flasks of quicksilver. Mexicans started mining cinnabar about 1860, but it is reported that the property had been explored earlier for silver. In 1911 the Pacific Quick- silver Company took over the mine, enlarged the operations, and installed a 24-ton Scott furnace, which was operated until about the end of 1914. Since then operation has been intermittent. ' ' The mining claims extend northward into sees. 32 and 33, T. 13 S., R. 10 E. in the area covered by the Ortigalita Peak quadrangle and ore of economic value may exist along the kaolinized zone extending north of Mercy mine. Deeply colored green clay of this zone is similar to the deeply colored beds at the base of the Tulare formation in the adjacent area to the east, indicative that a vast amount of quicksilver ore was stripped from this zone during lower Pleistocene time. Magnesite Associated with Franciscan serpentine are small thin veins of mag- nesite that have been worked on a small scale, as that north of Wisenor Flat. However, no production has been recorded. Fracturing and shear- ing of the serpentine bodies and the irregularity and small size of the veins makes it doubtful that these deposits are economically valuable. Diatomite The Kreyenhagen shale is an almost inexhaustable supply of pure diatomite in the Ortigalita Peak area. Argillaceous diatomite, almost as pure, is in the Moreno formation of Wildcat Can^'on. Neither of these sources has been exploited. Gypsum Vein gypsum, most too disperse to be of economic value, occurs abun- dantly in the Kreyenhagen and Moreno shales. Efflorescent surface de- posits are in the same formations and are especially abundant on the 1953] ECONOMIC RESOURCES 59 flattish summits of the ridge-forming Kreyenhagen shale. North of Oro Loma Creek such material was being cleared of top soil in the spring of 1950 for marketing by the Agriculture Minerals and Fertilizer Company of Los Banos, California. Mr. A. D. Sousa of this company prospected and prepared the deposits, which contain highly concentrated gypsite that demands little processing, and is of easy access for the local users of agricultural gypsum. Lime Lime is locally mined and processed for agricultural use from Tulare marl at the summit of Panoche Hills in the adjacent Panoche Valley area. Anderson and Pack (1915, p. 210) listed partial analyses of two samples taken in Ni sec. 30, T. 14 S., R. 11 E. : Partial analyses of calcareous beds in fhe terrace capping the Panoche Hills in sec. 30, T. 14 S., H. 11 E. (Analyst, George Steiger) 1 2 SiOo 19.84 9.74 AI2O3 4.97 2.76 Fe203 1.95 1.65 Sample 1 was considered a fair average MgO 5.28 1.85 of the marl ; sample 2 was taken from CaO 34.06 45.48 a thin hard limestone intercalated with CO2 29.85 35.34 clay. SO3 0.0 0.0 95.95 97.42 The white Kreyenhagen shale locally contains a notable proportion of lime and much of the shale will effervesce freely with acid. Several samples taken from NW^ sec. 2, T. 12 S., R. 10 E. were analyzed by means of the standard alkalimeter tests following sedimentary laboratory pro- cedure giving a range of CaCOs for white diatomite of 10.0 — 13.2 percent (four tests) and for brown diatomite of 1.5 — 5.0 percent (two tests). Bentonite Bentonitic shale, sandstone, and conglomerate occur abundantly throughout the San Pablo formation along the eastern front of the Laguna Seca Hills. It is doubtful that the deposits are of economic im- portance at the present time as the bentonite is commonly intermixed with silt, sand and gravel arid in most localities it forms the cementing medium for these clastic sediments. Somewhat pure bentonite of limited extent does occur within the San Pablo sequence offering a possible future supply of this material for local consumption. Sand and Gravel Sand and gravel from Los Banos Creek is being worked in sees. 32 and 33, T. 10 S., R. 10 E. for aggregate and road metal. Fresno County operates a small gravel pit at the mouth of Little Panoche Creek in sec. 15 T. 13 S., R. 11 E. which is worked intermittently for use on local county roads. There is almost an unlimited supply of such materials. Petroleum At least 7 holes have been drilled within the area covered by Ortigalita Peak quadrangle in search of oil and gas ; however, all have been aban- 60 ORTIGALITA PEAK QUADRANGLE [Bull. 167 doned. The highly organic shales of the Kreyenhagen and Moreno formations have been long considered the source beds for much of the petroleum found in the San Joaquin Valley and bordering areas, and the presence of the same formations in the Ortigalita area suggests the possibility of economic accumulations of oil in the bordering valley. However, the attitude of outcropping strata in the foothills offers no clue to a favorable structure in the San Joaquin Valley. BIBLIOGRAPHY Allen, Victor T. (1929) The lone formation of California: Univ. California. Dept. Geol. Sci. Bull., vol. 18, pp. 347-448. Allen, Victor T. (1941) Eocene anauxitic clays and sands in the Coast Ranges of California : Geol. Soc. America Bull., vol. 52, pp. 271-294. Anderson, Frank M. (1938) Faunal and chronological aspects of the Upper Cre- taceous in the Great Valley of California (abstract) : Geol. Soc. America, 37th Annual Meeting, April 1, 1938. Anderson, Frank M. (1941) Subdivisions of the Chico scries (abstract) : Geol, Soc. America Bull., vol. 52, p. 1943. Anderson, J. Q. (1941) Talk given before the Pacific Section, Soc. Econ. Paleon. and Min. at Bakersfield, June 6, 1941. Anderson, Robert, and Pack, R. W. (1915) Geology and oil resources of the west border of the San Joaquin Valley north of Coalinga, California : U. S. Geol. Survey Bull. 603. Bennison, A. P. (1940) Late Cretaceous of the Diablo Range: paper read at the meeting of the LeConte Club, Stanford University, March 2, 1940, Bennison, A. P. (1941) Unpublished geological map of late Upper Cretaceous de- posits south of San Luis Creek, Merced and Fresno Counties, California, dated 1941. Brice, James (1953) Geology of Lower Laka quadrangle, California: California Div. Mines Bull. 166. Chaney, Ralph W., Condit, "C, and Axelrod, D. I. (1944) Pliocene floras of California and Oregon : Carnegie Inst. Washington Pub. 553. Clark, Bruce L. (1943) Notes on California Tertiary correlation: California Div. Mines Bull. 118, pp. 187-191. Clark, Bruce L., and Campbell, A. S. (1945) Radiolaria from the Kreyenhagen formation near Los Banos, California : Geol. Soc. America Mem. 10. Daviess, S. N. (1946) Mineralogy of late Upper Cretaceous, Paleocene, and Eocene sandstones of Los Banos district, west border of the San Joaquin Valley, California : Am. Assoc. Petroleum Geologists Bull., vol. 30, pp. 63-83. Goudkoff, Paul P. (1943) Stratigraphic relations of Upper Cretaceous in the Great Valley, California : Am. Assoc. Petroleum Geologists Bull., vol. 29, pp. 956-1007. Green, Charles F. (1942) Eocene and Cretaceous stratigraphy of the Laguna Seca Hills, Merced County, California : unpublished master's thesis, Stanford Uni- versity, California. Huey, Arthur S. (1948) Geology of the Tesla quadrangle, California: California Div. Mines Bull. 140. Jenkins, Olaf P. (1931) Stratigraphic significance of the Kreyenhagen shale: California Div. Mines Rept. 27, pp. 141-186. Joplin, G. A. (1937) An interesting occurrence of lawsonite in glaucophane bear- ing rocks from New Caledonia : Mineral. Mag., vol. 24, pp. 534-537. Kuenen, Ph. H. and Migliorini, C. I. (1950) Turbidity currents as a cause of graded bedding : Jour. Geology, vol. 58, pp. 91-127. Leith, Carlton J. (1949) Geology of the Quien Sabe quadrangle, California: California Div. Mines Bull. 147. Mackin, Jo.seph H. (1948) Concept of the graded river: Geol. Soc. America Bull., vol. 59, pp. 463-511. Payne, Max B. (1941) Moreno shale, Panoche Hills, Fresno County, California (abstract) : Geol. Soc. America Bull., vol. 52, pp. 1953-1954 (1951) Type Moreno formation and overlying Eocene strata on the west side of the San Joaquin Valley, Fresno and Merced Counties, California : California Div. Mines Special Rept. 9. Pettijohn, F. .T. (1949) Sedimentary rocks: Harper and Bros., New York (1950) Turbidity currents and graywacke : a discussion ; Jour. Geology vol. 58, pp. 169-171. 1953] BIBLIOGRAPHY 61 Popenop, W. P. (1942) Tapper Cretaceous formations and faunas of southern Cali- fornia : Am. Assoc. Petroleum Geologists Bull., vol. 20, pp. 1(52-187. Stewart, Ralph, Popenoe, \V. P., and Snavely, P. D., Jr. (1944) Tertiary and late I'pper Cretaceous stratigraphy of the west horder of San Joaquin Valley north of Panoche Creek, Fresno, Merced, and Stanislaus Counties, California : U. S. Geol. Survey Oil and (?as Investigations, Preliminary Chart 6. Stirton, R. A. (1989) Cenozoic mammal remains from the San Francisco Bay region : Univ. California Dept. Geol. Sci. Bull. vol. 24, pp. 339-410. Taliaferro, Nicolas L. (1943) Franciscan-Knoxville problem: Am. Assoc. Petro- leum Geologists Bull., vol. 27, pp. 109-219. Taliaferro, Nicolas L. (1943a) Geologic history and structure of the central Coast Ranges of California : California Div. Mines Bull. 118, pp. 119-163. Taliaferro, Nicolas L. (1944) Cretaceous and Paleocene of Santa Lucia Range, California : Am. Assoc. Petroleum Geologists Bull., vol. 28, pp. 449-591. Tallman, S. L. (1949) Sandstone types: their abundance and cementing agents: Jour. Geology vol. 57, pp. 582-591. Turner, Francis J. (1948) Mineralogical and structural evolution of the meta- morphic rocks : Geol. Soc. America Memoir 30. Wilson, Ivan F. (1942) Geology of the San Benito quadrangle, California: Cali- fornia Div. Mines Rept. 39, pp. 183-270. Yates, R. G., and Hilpert, L. S. (1945) Quicksilver deposits of central San Benito and northwestern Fresno Counties, California : California Jour. Mines and Geology, vol. 41, pp. 11-36. printed in California state printing office 71529 12-52 BM ^r^? 1 1 s 1 1 £ 2 3 3 s 1 i s 1 1 If « s -e s 3 g i 1 1 i 1 ! ] 1 O 1 1 . < < 1 > j_ 1 1 ■1 1 1 I I ! S" ',-1 S /' DIVISION OF MINES OLAF P. JENKINS, CHIEF STATE OF CALIFORNIA DEPARTMENT OF NATURAL RESOURCES BULLETIN 167 <^S PLATE 3 « LOS BANDS HILLS EXPLANATION Ool - olluvium, T0l,T0tg,TQ1m - Tulare I Tol - Oro Loma fm ; Tsp - San Pablo fm , Tk- Kreyenhogen fm , TI - Teslo (?) fm , Tls-Loguno Seco fm; Km- Moreno f m , Kp- Ponoctie fm , Kw - Wisenor fm JSP- serpentine, Jdg- diobose- gobbro, Jgr- greenslone. J fs - sondstone, jfsch- schists, ch- chert GEOLOGIC STRUCTURE SECTIONS ACROSS ORTIGALITA PEAK QUADRANGLE, CALIFORNIA VERTICAL AND HORIZONTAL SCALE .HIS BOOK IS DUE ON THE L/. STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO SO CENTS ON THE FOURTH DAY AND TO $1.00 ON THE SEVENTH DAY OVERDUE. AOgj s «? APR 2 i90fB" Jf\H 5 3B$ JUNU 1973 liOV 1 5 1930 J4lttl9l9Sl GEO' '- I m 1 4 ^381 SEP 24 1:3 J RECEIVED NOV 1 1981 PHYS SCI LIBRARY NOV 1 1 mi 00= oi 0= CDs co= PHYS £iCi t-lt^'"^^>>^o"*' BookSlip-25m-7,'53(A899884)458 106766