Geology of San Nicolas Island California GEOLOGICAL SURVEY PROFESSIONAL PAPER 369 Prepared in cooperation with the U .S. Department of the Navy, Ofice of Naval Petroleum and Oil Shale Reserves £173 , {315“ / .’ 3', ,I EARTH SCIENCES LIBRARY Oblique aerial photograph of San Nicolas Island viewed from the southeast. Geology of San Nicolas Island California By J. G. VEDDER and ROBERT M. NORRIS GEOLOGICAL SURVEY PROFESSIONAL PAPER 369 Prepared in cooperation with the U. S. Department of the Navy, Ofllce of Naval Petroleum and Oil Slzale Reserv es UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1963 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U.S. Geological Survey Library catalog card for this publication appears after index. For sale by the Superintendent of Documents, U.S. Government Printing Office Washington ’25, D.C. CONTENTS Abstract ____________________________________________ Introduction _______________________________________ Purpose and scope of report ______________________ Location and accessibility ________________________ Fieldwork and methods __________________________ Acknowledgments _______________________________ History and culture _____________________________ Climate, vegetation, and wildlife __________________ Regional structure and stratigraphy ___________________ Geomorphology _____________________________________ Geomorphic setting of the island platform _________ General features of the island ____________________ Terraces _______________________________________ Drainage ______________________________________ Dunes _________________________________________ Landslides _ _ _ _ ; _ _ _- _____________________________ Beaches _______________________________________ Stratigraphy _______________________________________ Concealed rocks ________________________________ General features of the exposed rocks ______________ Tertiary system ________________________________ Eocene series _______________________________ General features of the Eocene rocks ______ Description of mapped units _____________ Laboratory analyses of Eocene sandstone samples ______________________________ Source rocks of the Eocene sandstones _____ Correlation ____________________________ Igneous rocks ______________________________ Quaternary system ______________________________ Pleistocene series ___________________________ Terrace deposits ________________________ "U .2 mxlxlmflkwlotOHr-‘Hv-‘o Hi—Ir—‘l—‘l-‘i—Ir—IHD—Il—Ir—A U‘WWWWNNMHr—i—‘m 22 25 25 27 29 29 29 QEVFP4 ‘ v ‘Q' 1‘ ' “ EARTH SCIENCES LIBRARY Stratigraphy~Continued Quaternary system—Continued Pleistocene and Recent series, undifferentiated" Windblown sand ________________________ Caliche deposits ________________________ Recent series _______________________________ Beach deposits and alluvium _____________ Offshore shelf and slope deposits __________ Structure __________________________________________ Faults _________________________________________ Folds __________________________________________ Offshore structure observed by divers _____________ Paleontology _______________________________________ Eocene Foraminifera ____________________________ Eocene megafossils ______________________________ Fossils from marine terrace deposits _______________ Annotated checklist _________________________ Paleoecologic inferences ______________________ Habitat _______________________________ Anomalous occurrence of restricted-depth forms _______________________________ Relative surface water paleotemperatures_- Causes and effects of surface water tempera- ture variation off southern California and northwestern Baja California ___________ Inadequacies of paleoecologic comparisons of terrace faunas ______________________ Age and fauna] correlation _______________ Kitchen middens __________________________________ ‘_ Economic geology ___________________________________ Petroleum possibilities ___________________________ Water‘ resources ________________________________ Supplementary data _________________________________ References cited ____________________________________ Index _____________________________________________ ILLUSTmIONS [Plates are in pocket] FRONTISPIECE. Oblique aerial photograph of San Nicolas Island viewed from the southeast. PLATE 1. UIQWNI 280 Index map of part of the continental borderland and coastal area of southern California. . Pleistocene fossil localities and traces of inferred inner margins of the terrace platforms. . Geologic map and sections of San Nicolas Island. . Bathymetry and geologic observations on the sea floor west of San Nicolas Island. . Stratigraphic sections of the Eocene strata exposed on San Nicolas Island. Page 30 30 32 32 32 33 34 34 35 35 36 36 36 37 38 38 38 38 39 51 51 52 54 57 57 57 58 59 63 VI' FIGURE TABLE 9"“‘99N‘r‘ 9° 9° 10. ll. 12. 13. 14. 15. 16. 17. 18. 19. CONTENTS Reconnaissance geologic map of the sea floor 011’ southern California ________________________________________ Conglomeratic mudstone of unit 2 exposed in a sea cliff near the west end of the island _______________________ Lenticular beds of conglomerate, breccia, and sandstone in unit 4 near the west end of the island ______________ . Clastic fragments of siltstone and mudstone embedded in a matrix of sandstone contained in unit 4 ____________ Slope-forming siltstone beds of unit 6 overlain by cliff-forming sandstone beds of unit 7 along the east wall of Sand Dune Canyon _____________________________________________________________________________________ Thick- bedded sandstone typical of the lower part of unit 7 exposed 1n a sea cliff about one-third of a mile southeast of the mouth of Sand Dune Canyon ___________________________________________________________________ Honeycomb weathering exhibited on the windward surfaces of sandstone beds in unit 7 near Dutch Harbor _____ Interbedded sandstone and siltstone in unit 8 exposed in a deep ravine southwest of Jackson Hill .............. Well-bedded siltstone and fine-grained sandstone in the lower part of unit 20 exposed in a sea cliff at the east end of the island ________________________________________________________________________________________ Histograms showing grain size in samples of Eocene sandstone ____________________________________________ Correlation chart of Eocene formatiohs in central and southern California ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Narrow igneous dike cutting a sandstone bed about three—quarters of a mile east of Dutch Harbor _____________ Generalized block diagram showing the relation of the terrace deposits to the terrace platform _________________ Well-preserved mollusks in a marine terrace deposit at an altitude of 725 feet near fossil locality SN—2 _________ A view southeast along the old sea cliff of the well-developed 100-foot terrace near Coast Guard Beach _________ Quaternary dune deposits and caliche at an altitude of about 825 feet on the western upland surface of the island_ A westward view of a normal fault exposed near the east end of the island __________________________________ Map showing distribution of selected fossil localities in terrace deposits of southern California and northwestern Baja California- 1 , ,' ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, Kitchen midden deposits and burial in partly cemented dune sand near Seal Beach ___________________________ TABLES . Designation, altitude, fossil localities, and description of terraces on San Nicolas Island __________________________ . Mineral composition, porosity, and permeability of Eocene sandstone outcrop samples from San Nicolas Island___ . Checklist of Eocene mollusks from San Nicolas Island _____________________________________________________ Checklist of fossils from terrace deposits of Pleistocene age on San Nicolas Island _____________________________ . Mollusks from selected low, intermediate, and high terrace deposits on San Nicolas Island that are known in the living faunas only as extralimital and near limital, or that are not known to be living ________________________ List of invertebrates observed in kitchen middens _________________________________________________________ . Observations by diving teams on operational dives ________________________________________________________ . Eocene mollusk fossil locality descriptions ________________________________________________________________ . Pleistocene fossil locality descriptions ____________________________________________________________________ Page 6 15 16 16 17 18 18 19 22 24 26 27 28 29 30 32' 34 54 56 Page 23 37 40 50 58 58 59 GEOLOGY OF SAN NICOLAS ISLAND, CALIFORNIA By J. G. VEDDER and ROBERT M. NORRIS ABSTRACT San Nicolas Island lies approximately 65 miles seaward from the nearest part of the southern California mainland and is the outermost of the Channel Island group. The island has an area of about 32 square miles and a maximum relief of 907 feet. The exposed Tertiary section on San Nicolas Island consists of nearly 3,500 feet of alternating marine sandstone and silt- stone beds that contain minor amounts of interbedded conglomerate and pebbly mudstone. This sedimentary rock sequence has been divided into 35 mappable units, all of Eocene age. The mineral content of the sandstone samples suggests a source area of plutonic igneous rocks of intermediate composition with lesser contributions from metamorphic rocks adjacent to the igneous bodies. Several small andesitic dikes of Miocene( ?) age intrude the Eocene sedimentary rocks near the southeast end of the island. Dune sand and fossiliferous marine terrace deposits of Quaternary age cover most of the central and western parts of the island. A brief reconnaissance of the extensive kitchen middens and the related dune deposits indicates not only an increase in aridity but also a diminishing of the aboriginal population in early Recent time. Structurally, San Nicolas Island is a broad, complexly faulted anticline that roughly parallels the long dimension of the island and plunges gently southeast, with its crest near the southwest shoreline. Two sets of intersecting faults, which trend approximately N. 30" W. and N. 80° E. and offset the fold axis, seem to be contemporaneous. Most of the faults are high-angle normal faults with a maximum throw of 800 feet on the north—trending set and 650 feet on the east-trending set. Underwater geologic investigations off the west end of the island indicate that the axis of the anticline extends northwest and that a fault pattern similar to that exposed on the island exists on the sea floor. The age of the main faulting episode may be pre-niiddle Miocene with continuing lesser movement through late Pleistocene time. Foraminiferal assemblages that best correlate with faunas of late Eocene age elsewhere in California occur in all the siltstone units. The only significant Tertiary molluscan fauna probably is middle to late Eocene in age. More than 250 species of marine invertebrates collected from 11 terrace platforms suggest a late Pleistocene age for the terrace deposits and indicate environmental conditions nearly the same as at present. These fossil assemblages seem to show slight surface-water temperature variation at difl’erent terrace levels. . Seven well-developed wave-cut platforms and seven addi- tional less distinct levels of marine planation are recognized on the island at altitudes from .25 to 900 feet. Several sub- merged terraces are present on the shelf adjacent to the island, the lowest being about 400 feet below sea level. The higher emergent terraces may represent wave-abraded plat— forms that were eroded during eustatic changes of sea level combined with tectonic uplift. The lowest emergent terrace and the submerged terraces may have been cut during eustatic sea-level changes followed by very slight regional seaward warping that did not appreciably affect any of the platforms on the island. Presumably all the terrace platforms on San Nicolas Island were cut later than the middle Pleistocene diastrophism recognized elsewhere in southern California. INTRODUCTION PURPOSE AND SCOPE OF REPORT Geologic investigations to evaluate the petroleum potential of San Nicolas Island were undertaken early in 1955 by the US. Geological Survey at the request of the Director, Naval Petroleum Reserves. The pur- pose of the present report is to make available the geologic information obtained for the Department of the Navy during the 11 inonths of fieldwork 0n the island and parts, of the adjacent continental shelf. Because little has been published concerning San Nicolas Island, brief introductory statements are in- cluded in this report to describe the climate, vegetation, wildlife, and history of the island. A part of the paper is devoted to a résumé of the regional structure and stratigraphy of the continental borderland ofl' southern California as an introduction to the geology of the island; a short section on the physiography of the island and surrounding shelf area follows. Descriptive geology of the Tertiary and Quaternary rocks and unconsolidated sediments exposed on and around the island composes the bulk of the report, with shorter sections on laboratory analyses, the fossil content and paleoecology of the sedimentary rocks, and the char- acter of the aboriginal shell mounds. LOCATION AND ACCESSIBILITY San Nicolas Island is the outermost of a group of eight islands off the coast of southern California and is a part of Ventura County (pl. 1). The San Nicolas Island quadrangle, of which more than half is ocean, lies between long 119°25’30” and 119°35’ “7., and lat 1 2 _ GEOLOGY OF SAN Niooms IKSIJAND 33°12’ and 33°18’ N. The island is located approxi- mately 80 statute miles south of Santa Barbara, about ‘90 miles southwest of Los Angeles, and almost 120 miles west of Oceanside. The total land area is about 32.2 square miles, and the maximum dimensions are 9.7 by 3.7 miles. At present the island and surrounding waters are under the jurisdiction of the Naval Air Missile Test Center at Point Mugu; consequently, authorization must be obtained from the Navy to visit the island. Transport to the island is provided by Navy cargo aircraft from the air station at Point Mugu or by the Navy Crash Boat Division at Port Hueneme. FIELDWORK AND METHODS Geologic mapping of San Nicolas Island was begun by R. L. Harbour and R. J. Burnside in March 1955. After May 1, 1955, J. G. Vedder directed the field party and was later joined by R. M. Norris and D. J. Milton. S. R. Dabney and T. M. Eisner were employed as field assistants and aqualung divers. The first field season was concluded September 29, 1955. On May 1, 1956, a preliminary geologic map of San Nicolas Is- land accompanied by a short text (Vedder and others, 1956) was released for public inspection with the ap- proval of the Director of Naval Petroleum Reserves. J. G. Vedder, R. M. Norris, and N. C. Privrasky re— sumed fieldwork on the island in June 1956 with G. P. Frymire assisting in the diving operations and with the photography. Fieldwork was completed in September 1956. Surface mapping of San Nicolas Island was done. on aerial photographs (approximate scales, 1:4,800; 1:8,000; 1:9,600). The geology was transferred from the photographs to the San Nicolas Island quadrangle map, (scale 1224,000, 1952), which was enlarged to a scale of 1:12,000 and extended westward, beyond the quadrangle boundary, to include the area where un— derwater geologic work was done. Seventeen strati— graphic sections were measured and systematically sampled for foraminiferal study. Samples obtained by a jeep~mounted auger aided in determining. the thick- ness and lithology of the Quaternary deposits. Diving operations were undertaken on the shelf area off the west end of San Nicolas Island to supplement the geologic mapping on shore and to further evaluate the nature and extent of the structural features. More than 100 dives were made during the summer of 1955, and approximately 50 additional dives were made in the summer of 1956. Geologic information was ob- tained on 98 dives at depths ranging from 30 to 120 feet. Rock samples, strike and dip determinations, and photographs were taken in conjunction with the un- derwater geologic studies. The methods of geologic diving outlined by Dill and Shumway (1954) and by Menard and others (1954) were employed with a few modifications. Self-contained underwater—breathing apparatus was used by the divers. The lack of a harbor on San Nicolas Island during 1955 and 1956 required the use of a 122- foot landing craft (LCU) to move the diving crews on and off the island. A 26-foot motor whaleboat was used as a diver’s tender. Reference points for offshore position location were erected at six locations along the western shore of the island. Two temporary auxiliary marker buoys were set to augment the shore reference points during the second-season’s operation. All of the reference points were located from known triangulation stations by planetable and alidade surveys. Horizontal sextant angles to the shore stations and to the marker buoys were used for offshore position location. Because of operational difficulties the position of the outer offshore stations probably is accurate only to within 100 to 150 feet. Stations nearer shore are presumably accurate to within 50 feet or less. ACKNOWLEDGMENTS The provision of transportation, boats and boat crews, and other equipment and supplies by the Island Facilities Oflicer and the Oflicer-in-Charge, San Nicolas Island, is gratefully acknowledged. New aerial photo- graphs promptly furnished by Composite Squadron VC—61, Naval Air Station, Miramar, expedited the geologic mapping. The assistance extended by Mr. R. E. Jones of the Naval Civil Engineering Research Lab- oratory, Port Hueneme, in supplying crews and equip- ment to set marker buoys is appreciated. H. W. Men- ard, E. L. Hamilton, and R. F. Dill of the Naval Elec‘ tronics Laboratory at Point Loma kindly ofl’ered ad— vice concerning diving equipment and geologic diving techniques. Instructors from Scripps Institution of Oceanography trained the divers in the use of self- contained underwater-breathing apparatus before the first season of diving. Leo G. Hertlein and Allyn G. Smith of the Califor- nia Academy of Sciences kindly assisted in the iden- tification of some of the Pleistocene mollusks and made available for study the collections at that institution. A. Myra Keen of Stanford University gave helpful advice on the taxonomy of several Pleistocene mollusks and provided access to the collections at Stanford University. J. E. Schoellhamer visited the island each field sea- son to help measure and sample stratigraphic sections, aided in the compilation of the regional geology, and made valuable contributions to other parts of the re— port. R. L. Harbour began the geologic mapping and INTRODUCTION 3 supplied the basic data for differentiation of the stratigraphic units in the Eocene rocks. R. F. Yerkes provided the petrographic data on the igneous rocks, and Robert M. Norris did the petrographic studies, mechanical analyses, and heavy-mineral separations of the Eocene sandstone samples. A. O. “'oodford re- viewed the results of the laboratory studies of the rock samples and offered pertinent suggestions on their mineralogy. M. C. Israelsky furnished the de- scription of the methods used for possible zonation of the Eocene Foraminifera and determined their probable age and correlation. HISTORY AND CULTURE San Nicolas Island probably was first sighted by Europeans in 1542 or 1543 during the exploration of the California coast by Juan Rodriquez Cabrillo, al— though the records of the voyage contain no specific mention of the island (Henshaw, 1879, p. 312; David- son, 1889, p. 76). Sixty years later, on December 6, 1602, Sebastian Vizcaino’s launch Tres Beg/es anchored off the island on the feast day of Saint Nicholas of Myra, patron of sailors, travelers, and merchants. The crew gave the island the name in common usage today (Gudde, 1949, p. 311) but erroneously charted its size and position (Davidson, 1889, p. 76). The early Spanish explorers found a relatively cul- turally advanced group of Indians living on the island. The many extensive kitchen middens indicate that a fairly large aboriginal population inhabited the island for many centuries before the arrival of the Spaniards. According to Kroeber (1953, p. 623—635), the San Nicolefio who dwelled on the island were a division of the coastal Gabrielino tribe, derived from Shoshonean stock. The island was known as Gha-las—hat by the Indians, but the meaning of the name has been lost. In 1811 a group of Kodiak Indians from Sitka was landed on the island by Captain VVhittemore, from the Boston fur-trading firm of Boardman and Pope, for the purpose of sea otter hunting. During their 2- year stay the Kodiaks killed most of the male in— habitants of the island. The remaining San Nicolefio lived undisturbed until 1836 when Captain Isaac Wil- liams, collector of the port of San Pedro, at the re- quest of the Spanish mission authorities, removed all but one native to the mainland (Schumacher, 1877 , p. 2). The one exception, the famous “lost woman of San Nicolas,” lived 1n complete isolation on the island for 18 years before she was found by Captain George Nidever and taken to Santa Barbara (Hardacre, 1880, p. 657—664). During the 2 centuries following Vizcaino’s voyage of exploration little is recorded of the history of San Nicolas Island; but many white men, chiefly sealers and sea otter hunters from American and Russian fur—trading ships, doubtless disembarked on the island early in the 19th century. French, English, Russian, and American exploring and survey parties that sailed past the coast of southern California during the period 1787 to 1849 may have sighted San Nicolas Island, but Davidson (1889, p. 68) made the following remark regarding the lack of knowledge of the island region prior to 1851 : Until the Coast Survey first examined in detail the islands lying off the main. nothing accurate was known of their number. peculiarities, extent, or position. Upon all maps, as of recent date as 1850. an island called San Juan was laid down, and upon a map of the Republic of Mexico, compiled in the Ifnited States. and dated 1847. we find no less than twelve large islands. the positions and extent of which are most grotesquely erroneous. Occasional visits, most of them before 1900, were made by several archeologists and naturalists (Schu- macher, 1877; Cessac, 1882; Yates, 1896; Hemphill, 1901; Lowe, 1903; Comstock, 1946, p. 95—96, 97—98; Meighan and Eberhart, 1953). As early as the 1870's, Chinese abalone fishermen used the island as a source of supply of the large mollusks for export to China (Schumacher, 1877, p. 48). The island reportedly was laid out in lots by an enterprising and optimistic real— tor in 1886 (Holder, 1910, p. 283), but the Ventura County records contain no mention of the subdivision. San Nicolas Island was acquired from the govern- ment by the U.S. Navy in 1933 for use as a gunnery range; in 1940, the U.S. Army assumed control of the government-owned land. Jurisdiction of the island was transferred back to the U.S. Navy in 1946. The earliest geologic description of San Nicolas Island appears in a brief report by J. G. Cooper of the Geologic Survey of California (Cooper in Whit- ney, 1865, p. 184). In a discussion of the southern California island group, Cooper mentions the un- fossiliferous sandstone that dips 25° on the north side of San Nicolas Island, and he describes the terrace deposits and their fossil content, the Indian shell mounds, and the lack of vegetation. Both Paul Schumacher, an archeologist (1877, p 4) and George Davidson, of the U.S. Coast Survey (1889, p. 75—78), note the sandstone bedrock, the dune- .covered areas 011 the west end of the island, and the sparse vegetation that resulted from over-stocking of sheep. Stephen Bowers, in another early geologic report (1890, p. 57—59) describes the flat upper surface of San Nicolas Island, the underlying sandstone and its apparent structure, the molluscan fauna from the low- est terrace, and the dune sands. 4 GEOLOGY OF SAN NICOLAS ISLAND Only two reports, both unpublished, describe the geology of San Nicolas Island in detail. L. E. Kem- nitzer1 gives a generalized account of the structure, stratigraphy, and age correlation of the sedimentary rocks on the island. R. M. Norris 2 presents a detailed oceanographic study of the shelf areas around San Nicolas Island and a brief discussion of the island geology. Both reports contain reconnaissance geologic maps. A short description of the underwater geology off the north coast of the island, together with a re‘ production of Norris’ geologic map, is contained in a paper on geologic diving techniques by Menard and others (1954). CLIMATE, VEGETATION, AND WILDLIFE Under average meteorological conditions a layer of cool, moist marine air envelopes San Nicolas Island from sea level to an altitude of about 2,500 feet, re- sulting in the formation of low clouds or fog in all but the coolest winter months. Fog occurs during all months of the year but is more frequent and more dense during the spring-and summer. The prevailing westerly winds frequently reach velocities of 35 to 55 miles per hour during the winter and attain periodic velocities of 45 miles per hour during the summer. The Navy has maintained detailed weather records for the island since 1948, and their temperature and rainfall data for an 8—year period from 1948 'to 1956 are summarized below. Monthly mean temperatures (in degrees Fahrenheit) : January ________________ 53 July- , _________________ 60 February _______________ 52 August _________________ 61 March _________________ 54 September ______________ 63 April __________________ 55 October ________________ 61 May ___________________ 56 November____i,,___,____ 59 June ___________________ 58 December ______________ 54 Maximum temperature observed: 105° F. Minimum temperature observed: 33° F. Average annual rainfall: 6.61 inches. The vegetation on the island is limited to low grasses and shrubs, some of which were identified by K. S. Norris (Department of Zoology, University of California, Los Angeles, 1950) and R. M. Norris as salt grass (Distiohlis spicata); bur—weed (F mnseria chamissonis) ; coast goldenbush (H aplopappus oenetus oernoniodes); Australian salt bush (Atriplew semi- baccata); coyote brush (Baccham's pilulam's consan- 1 Kemnitzer, L. E., 1933, Geology of San Nicolas and Santa Barbara Islands, southern California: California Inst. Technology, unpublished M.S. thesis, 45 p. ’Norris, R. M., 1951, Marine geology of the San Nicolas Island region, California: California Univ., Los Angeles, unpublished I’h.D. thesis, 124 p. gm'nes), the largest native plant now growing on the island; seascale. (Atriplem leucophylla); rabbitfoot (Polypogon monspeliemis); silver lupine (Lupinus albifrons); and giant coreopsis (Uoreopsz's gigantea). Cattail (Typha sp.) grows along some of the water- courses in which seepage occurs throughout the year. Cockerell (1938, p. 19) lists two forms of plants (Lotus ornithopsiss and Convol’vulus macmstegz'us) found on the island that presumably do not occur on the main- land. Holder (1910, p. 322) states that Mrs. Blanche Trask collected about one hundred species of plants on the island, many of which were new; and Bowers (1890, p. 60) makes reference to a statement'by Cap- tain George Nidever of Santa Barbara that a part of the island was covered by trees and brush before 1850. ' Resistant White calcareous sandstone casts of roots of large shrubs or trees as well as numerous shells of land snails, now rarely found living, indicate that Recent vegetation was at one time dense over much of the island. The only land vertebrates now living on the island are the San Nicolas Island fox (Uri-ocyon littoralz's diekeyi), the San Nicolas deer mouse (Peromyscus maniculatus extents), and the island night lizard (Xantusia m'oersiana). The subspecies of mouse live only on San Nicolas Island, but other subspecies, lives on Santa Catalina, San Clemente, and Santa Bar- bara Islands (Cockerell, 1938, p. 12). The same species of lizard also lives on San Clemente and Santa Bar- bara Islands (Cockerell, 1938, p. 14). Both the mouse and lizard may have reached San Nicolas Island on floating debris, in Indian canoes, or perhaps were even carried by large birds. The fox, however, is a variant of a group of foxes which inhabit the other islands, and like the mouse, shows some evidence of evolu- tionary change subsequent to its arrival on San Nicolas Island. Presumably the foxes were introduced by the Indians at an early date, for their remains often are present in the kitchen middens. Large Wild dogs, un- doubtedly imported by the Indians, were numerous on the island as late as 1850 (Schumacher, 1877, p. 48; Hardacre, 1880 [1950, p. 11])but were last re— ported to be present only 3 years later (Bowers, 1890, p. 59). Large herds of the California sea lion (Zalophns caliform'anns) inhabit the southwest shore between Vizcaino Point and Seal Beach. The elephant seal (Mironnga angustimstm's), harbor seal (Phoca witn- lina) , and the Steller sea lion (Eumetopias jubata) occa— sionally appear on the beaches in the same area. The rare Guadalupe fur seal (Arctocephalus towmendi) has recently been observed on the island (Ingles, 1954, REGIONAL STRUCTURE AND STRATIGRAPHY 5 p. 137). Sea otters (Enhydm Zutn's) were plentiful around the island before 1800, but they are now ex- tinct locally. ' Many species of sea birds and several species of land birds, including ravens and bald eagles, were observed on and around San Nicolas Island, but no attempt was made to identify individual forms. In about 1900, Professor Joseph Grinnell found more than 20 species of birds on the island during a short visit (Holder, 1910, p. 249). REGIONAL STRUCTURE AND STRATIGRAPHY The eight islands off the coast of southern Califor- nia afford the only surface exposures of the rocks that may lie beneath the sea over an area of about 31,000 square miles between the mainland and the continental slope. The following excerpt from Emery (1954, p. 107) describes the limitations and the precau— tions necessary for study of this predominantly sub— marine area: ‘ * * here the unknown geology far exceeds the known. Because of the relative inaccessibility of the submarine area, each new fact gained is expensive in terms of both time and effort, and thus it receives more attention and interpretation than an equivalent new fact of land geology. Care must con- stantly be exerted to avoid over-exploitation of the facts, and this can be done mainly by judging what is reasonable in terms of knowledge borrowed from the geology of the adjacent land. Any correlation, other than age, of the rocks on San Nicolas Island with those of the mainland and other nearby islands should be made with reservations, for inadequately known geologic structures of great magnitude certainly are present on the sea floor be- tween the island the the southern California coast. Inasmuch as San Nicolas Island is the most seaward of the island group, a correct interpretation of the rocks exposed there is important in further under- standing the structural features and stratigraphic cor— relation of the rocks lying on the floor of the con— tinental borderland off southern California. About 55 miles north and northwest of San Nicolas Island are four northern Channel Islands. These are, from west to east, San Miguel, Santa Rosa, Santa Cruz, and the Anacapa Islands (pl. 1). Marine sedi- mentary rocks of Cretaceous, Paleocene, Eocene, and Miocene age crop out on San Miguel Island where they attain a total thickness of approximately 20,000 feet (Kennett in Redwine, and others, 1952). Intrusive igneous rocks of Miocene age cut the older sedimentary rocks, and volcanic breccias and flows are interbedded with the Miocene sedimentary rocks on San Miguel Island. Both Santa Rosa and Santa Cruz Islands have exposures of marine sedimentary rocks of Paleocene, EOCene, and Miocene age together with volcanic rocks of Miocene age (Bremner, 1932, p. 14; Kew, 1927; T. L. Bailey, 1954). Sedimentary rocks of Cretaceous age occur in the subsurface on Santa Cruz Island, and it is on this island that the only metamorphic rocks in the northern group are exposed. Pre—Cretaceous chlor- ite phyllites and sericite schists intruded by quartz diorite occur in the central part of Santa Cruz Island (Rand, 1931, p. 215; Bremner, 1932, p. 13—16). The Anacapa Islands are composed of volcanic rocks of Miocene age as mapped by T. L. Bailey (1954), but in— terbedded schist breccia has recently been reported from the volcanic sequence (Scholl, 1959). This northern group of islands has east-trending structures and is the partially submerged continuation of the Santa Monica Mountains onthe mainland to the east. The Santa Monica Mountains and the“north- ern Channel Islands form the southwest margin/of the structural and geomorphic Transverse Ranges Province (Reed, 1933, p. 9—11). Shepard and Emery (1941, p. 47) and Corey (1954, p. 74) suggest that Santa Cruz Island is bounded on the south by a fault scarp, indicating that the island has been elevated and the submarine area to the south down-dropped. This inferred fault is presumably the seaward continuation of the major zone of faulting along the south side of the Santa Monica Mountains. South of the northern group of Channel Islands and the Santa Monica Mountains the gross structural fea— tures trend northwest, and this area may be considered the partially submerged part of the structural and geomorphic Peninsular Range Province (J ahns, 1954, p. 29). The index map (pl. 1) shows the orientation of the islands and the numerous northwest-trending submarine escarpments that presumably indicate the general structural pattern of this part of the offshore area. The reconnaissance geologic map (fig. 1) also illustrates this general trend by the distribution of the Cenozoic igneous and sedimentary rocks and the Mesozoic( '9) metamorphic rocks dredged or cored from the sea floor off southern California. Large-scale faults about which little is known also are present in this seaward extension of the Peninsular Range Province (Shepard and Emery, 1941, fig. 18, p. 47; Norris, p. 59—69;3 and Corey, 1954, p. 74). Santa Barbara and San Clemente Islands are com— posed almost entirely of volcanic rocks of middle Mio- cene age (Smith, 1898; Olmsted, 1958; and Kemnitz— er) .4 Small outcrops of marine sedimentary rocks of middle Miocene age are interbedded with the volcanic rocks on San Clemente Island. The type and age of the rocks beneath these islands are unknown. 3 See footnote 2, p. 4. 4 See footnote 2, p. 4. 120° GEOLOGY OF SAN NIGOLAS ISLAND 118° 117° // // Z é , 7<7 fi-SASI "" f \/ 4///- ../._./_/-$a.d1aCrUZ.'S'9"d¥ ”V 34.. L7. / /,"y“;,75-'/:""' " /:.//// a; / {Santa R6537V1M~Wbii / i I ///// /QLSMM7¢2 . ‘ _X— w ‘ ///// /a. \ 1 ' x ’- ‘ //// / /////‘ (P // / ‘/ // //// ///// ///// //// /// \(/ /// /// /// O // a /‘ / a? / I 1., ‘5} / 31¢ / " 0 _ v 33 :*-I%?4’fi’é , :1"! /"" $9. 9'.H 0' I” / ,7.‘ // 7., /// . //// / we; , //" // 00 / ‘om/ / / ‘\ V‘Q O t“ 3? — . / i // // 10 5 O 10 20 30 40 MILES \ CONTOUR INTERVAL 3000 FEET WITH SUPPLEMENTAL CONTOURS AT 75 AND 600 FEET l 121 120° FIGURE 1,—Reconnaissance geologic map of the sea floor off southern California. Cortes and Tanner Banks (pl. 1), with reported minimum water depths of 2 and 9 fathoms, respec— tively, presumably were islands during part of late Pleistocene time, or perhaps even in Recent time. The shallow—water areas on both banks are underlain by basaltic rocks of Miocene(?) age, and the shelf areas are composed of calcareous sedimentary rocks of probable middle Miocene age (Holzman, 1952, p. 100, 103, and 105—106). Santa Catalina Island, 52 miles east of San Nicolas Island, has extensive outcrops of volcanic rocks inter- bedded with small exposures of elastic limestone of Mio- cene age in the central part of the island (E. H. Bailey, 119° EXPLANATION Rocks of post—Miocene age Rocks of Miocene age Dashed pattern where probable _ 34 a Includes igneous and sedlmentary rocks Rocks of pre-Miocene age Basement rocks of pre-Late Cretaceous age Includes metamorphic rocks 33° 43// 0 Roy / ///_‘» .- _- //////»: ’//////".'Ii "’/////- ’////’ 117° (After Emery, 1954, fig. 1, p. 108.) 1954). The southeast end of the island is composed of quartz diorite porphyry that may be of Tertiary age (ibid., map explanation). Most of the western part of the Santa Catalina Island contains outcrops of glau- cophane schist and related metamorphic rocks not found in the basement rocks on Santa Cruz Island. Woodford (1924) called these metamorphic rocks the Catalina metamorphic facies of the Franciscan series. Reed (1933, p. 31) suggested that the metamorphic rocks underlying the San Nicolas Island area are of the Fran- ciscan type. Along the southwest margin of the Los Angeles basin and in the Palos Verdes Hills, sediment- ary rocks of Miocene age rest directly on Catalina schist GEOMORPHOLOGY 7 basement (Woodring and others, 1946, p. 12—13; Schoellhamer and Woodford, 1951). Emery and Shep- ard (1945, p. 435) report the presence of “unfossilifer- ous sandstone and chert similar to Franciscan (Juras- sic?) rocks of the mainland” from a submerged area 30 miles southwest of San Nicolas Island, west of Tanner Basin, but no glaucophane-bearing rocks are reported from this area. Holzman (1952, p. 117) found no evi- dence of sodium-amphibole rock debris in the sediment— ary rocks bordering Cortes and Tanner Banks. Areas of crystalline rock similar to the Catalina schist that are further removed from San Nicolas Island are shown on the regional geologic map south and east of San Clemente Island (fig. 1). The part that the structural highs of supposed pre- Cretaceous rocks at Catalina Island, Santa Cruz Is- land, and west of Tanner Basin may have played in the depositional history of the younger sedimentary rocks in the region of San Nicolas Island is unknown. Dredging and coring of the sea floor in the vicinity of San Nicolas Island have yielded no elastic fragments derived from basement rocks similar to those found on Catalina Island; however, small tabular fragments of glaucophane schist occur in the older terrace de- posits of Pleistocene age, suggesting a nearby source area for this rock type. Whether these schist frag— ments were derived from a sedimentary formation resembling the San Onofre breccia of middle Miocene age (Woodford, 1925) that now may be concealed on the sea floor near the island or from old structural highs of sodium-amphibole schists is conjectural. Begg Rock, 8 miles northwest of San Nicolas Island, is presumably the remnant of a rhyolite‘ dike or flow (Kemnitzer, p. 6) 5 that may correlate with rliyolite flows and agglomerates of Miocene age exposed on the south side of Santa Cruz Island (Bremner, 1932, p. 22—24) and on San Clemente Island (Olmsted, 1958, p. 62). An elongate shoal about 2 miles long lying 33/4 statute miles northeast of Army Camp Beach on the north coast of San Nicolas Island is composed of diabase (Norris, p. 37—39).6 The structural and stratigraphic relations of these nearby offshore igneous bodies to the sedimentary rocks on the island shelf area are not known, but they may represent extensive intrusions along large faults. GEOMORPHOLOGY GEOMORPHIC SETTING OF THE ISLAND PLATFORM San Nicolas Island is on the south edge of a broad, relatively flat salient submarine ridge that protrudes east from the main trend of Santa Rosa-Cortes sub- 5 See’footnote 1, p. 4. ' See footnote 2, p. 4. marine ridge (fig. 1). Santa Rosa-Cortes Ridge ex- tends southeast from Santa Rosa Island to Cortes Bank, a distance of approximately 130 statute miles. The ridge rises to 907 feet above sea level on the San Nicolas Island salient and to within 15 feet of the surface at Bishop Rock (fig. 1) on Cortes Bank. Most of the crest of the ridge lies less than 600 feet below sea level. Santa Cruz Basin, with depths in excess of 6,000 feet, lie directly north of San Nicolas Island and is one of the deepest closed basins in the continental borderland off southern California. South of the island, depths of about 3,900 feet occur in the westernmost part of San Nicolas Basin, which deepens to 6,000 feet to the southeast toward San Clemente Island. Westward from San Nicolas Island, the island platform joins Santa Rosa-Cortes Ridge at a depth of less than 600 feet. Eastward, the island salient ends abruptly at the edge of a trough more than 3,000 feet deep which connects Santa Cruz and San Nicolas Basins. San Nicolas Island is surrounded by a sloping shelf, the outer edge of which has an average depth of 350 feet. South of the island the edge of the shelf is no- where more than a mile from shore, but the northern shelf is, in marked contrast, more than 6 miles wide. As a consequence, the southern shelf has an average gradient of about 350 feet per mile (3°50’) and the northern shelf a gradient of only 60 feet per mile (0°40’). The slopes beyond the shelves also differ in steepness; on the south side of the island the gradient is about 1,000 feet per mile (11°) and on the north side about 600 feet per mile (61/2°). The gradients of the shelf and slope on the south side of the island presumably indicate the presence of an eroded fault scarp relatively near the insular shelf. Earthquake epicenters located in this area support the hydro— graphic evidence for a large fault (Clements and Emery, 1947). i The surface of the shallow shelf adjacent to San Nicolas Island is reasonably flat when considered as a unit, but when examined in detail, as was done by the diving teams during 1955 and 1956, much local irregularity is observed that is not apparent from the bathymetric contour pattern. Nearly vertical clifi's 40 feet or more high were found on a few dives, as well as many overhanging ledges formed by differential ero- sion of soft siltstone interbedded with resistant sand- stone. Although some faults were observed by the diving teams, they account for only a small part of the local irregularity of the sea floor. Most of the re- lief presumably is due to differential erosion by stream and wind at a eustatic lower stand of sea level. A prominent bench at a depth of 330 feet has been re- 8 GEOLOGY or SAN corded on echo-sounding profiles made across the deeper part of the shelf area. Other less prominent. benches occur at depths of 55 to 65 feet, 110 to 130 feet, 160 to 180 feet, and at 230 feet (Norris, p. 39— 40). 7 Additional submerged terraces at intervening depths and down to nearly 400 feet are plotted by Emery (1958, p. 54, fig. 11). Furthermore, a relatively steep break in slope is present at the shelf edge, start- ing at about 60 fathoms (Uchupi;8 Emery, 1958, p. 54, fig. 11) and may demark the lowest stand of sea level in late Pleistocene time. US. Coast and Geodetic Survey chart 5101 and chart I in Shepard and Emery (1941) show many small submarine canyons cutting the slope on the north side of the island and at least two canyons cross— ing the south slope. All these canyons are concentrated at the east end of the island platform. Echo-sounding profiles (Norris, p. 40) 9 show numerous small gullies not indicated on any existing charts. These small fea- tures are common to many submarine slopes and are not unique at San Nicolas Island. These gullies ap- parently do not cut into the bedrock surface and may be due to erosion of the slope sediments by turbidity currents. GENERAL FEATURES OF THE ISLAND From the south and southwest, San Nicolas Island appears as a bold, highly dissected escarpment that attains an altitude of 600 to 900 feet for a distance of approximately 6 miles. The elongate ridge that forms the crest of the escarpment lies % to 11/4 miles from the shoreline on the south side of the island. The highest point on the island is only slightly more than 1 mile from the south coast. From the north and northeast, the island presents an entirely different aspect. A sequence of wave—cut terraces that ranges in altitude from near sea level to the high part of the island lends a steplike appearance to the broad, relatively gentle north slope. The ridge that forms the crest of the island lies slightly more than 2 miles from the north shoreline. A relatively steep slope 400 to 500 feet high forms the east face of the island, but the west end is characterized by a rather gentle slope from sea level to an altitude of 600 feet over a distance ranging from 1% to nearly 21/2 miles. TERRACES The most striking physiographic feature on the north slope of San Nicolas Island is the nearly con- tinuous sequence of marine terraces. A brief descrip— 7 See footnote 2, p. 4. HUchupi, Elazar, 1954, Submarine geology of the Santa Rosa-Cortes Ridge: Southern California Univ. unpublished M.S. thesis, p. 9. 9 See footnote 2. p. 4. NICOLAS ISLAND tion of the terraces by Upson (1951, p. 442) lists altitudes for several prominent platforms. Both Kem— nitzer (1936) 1° and Norris (p. 15—18) 11 include state- ments about the main terrace platforms and their estimated altitudes, which roughly match those given in this report. Seven fairly well defined terraces were recognized on the north and east parts of the island during the fieldwork for the present report. (See table 1). In addition to the well—defined terraces, seven other poorly defined platforms are present on the higher central upland surface of the island north of Jackson Hill. Except for the two lowest terraces, which extend discontinuously along much of the southern coast, only a few remnants appear either along the steep stream- dissected southern escarpment or in the sand-covered western part of the island. The higher terraces are difficult to trace for more than half a mile owing to destruction by extensive gullying, to burial of the platforms by deposits of aeolian sand or slope wash, and to the merging of the ancient sea cliffs where terrace cutting on later levels destroyed parts of the shorelines of preceding levels. Below the 400—foot contour on the north side of the island the slope is steep and scarred by extensive landslides, and the terrace platforms that may have been cut in this area cannot be definitely recognized. A few additional minor benches may exist on the north side, but they are impossible to follow because of slope-wash cover. The terrace platforms Vary considerably in width; the 100-foot terrace is a few' hundred feet to nearly 1/4 mile wide. VVave-abraded platforms between the 400- and 800—foot contours attain their greatest widths in the northeastern part of the island where several prominent benches (including some intervening poor- ly developed benches) underlie gently sloping non- marine terrace surfaces 14 to 34 mile in width and 5 miles in length. Vertical distances between successive terrace platforms also vary considerably; the most abrupt and prominent ancient sea cliff between plat- forms is displayed along the northeast side of the island between the 120- and 400-foot contours. Pre— sumably the cutting of the 100-foot terrace in this area destroyed the intervening levels by shoreward erosion of the sea cliff. The other ancient sea cliffs on the island exceed a height of 50 feet at only a few places. It is evident that the terraces represent surfaces of marine planation because all the principal platforms locally are covered at their eroded outer edges by thin deposits of fossiliferous calcareous sand and gravel 6 inches to 10 feet thick that are very similar to de- 10 See footnote 1, p. 4. 1‘ See footnote 2. p. 4. GEOMORPHOLOGY 9 TABLE 1.—Designation, altitude, fossil localities, and description of terraces on San Nicolas Island [See pl. 2] Pleistocene fossil localities Inferred altitude Terrace 1 (feet) of inner Collections made Observed Remarks margin of terrace platform 3 Locality Altitude Number of Altitude (feet) localities (feet) 1 3 ____________ 25-30 SN—15 20;}: 6 20—25 Not well defined. May be remnants of terrace 2. 2 ______________ 100 SN—l 45—60 7 40—95 Well defined except on south side of island. SN—12 65—70 SN—4 85 j: SN—13 80-85 3 ______________ 225—230 ____________________ 5 190—230 Poorly represented on north side of island. 4 ______________ 310—320 ____________________ 1 310 Poorly represented except on extreme northwest side of island. 5 ______________ 385 SN—lO 375i _________________ Found only on northeast side of island. One indis- tinct intermediate level may be present. 6 ______________ 450 SN—14 425:]: _________________ Represented only on northeast side of island. 7 ______________ 500 SN—l6 4701 4 450~500 Well defined on north and northeast side. Not represented on south side. One indistinct inter- mediate level may be present. 8 ______________ 600 M—2 565—575 10 520-595 Well defined on north side of island and represented M—l 575 by several fossil localities on south side. One SN—l 1 590+ . indistinct intermediate level may be present. 9 ______________ 700 SN—7 665 j; 7 620—685 Fairly well defined on north side of island; represented by three fossil localities on south side. 10 _____________ 775 SN—2 730i 2 740—765 Possibly one indistinct intermediate level. SN-3 735d: 11 _____________ 820 SN—6 815i 7 785—815 Not well defined. Possibly two indistinct inter— mediate levels. 12 _____________ 865 SN—5 840:}: 1 850 Poorly defined because of slope wash and dune-sand cover. 13 _____________ 890—900 SN—8 885i 1 880—885 Poorly defined because of slope wash and dune-sand cover. 14 _____________ Sea cliff SN—9 900+ _________________ Island presumably completely submerged. not pres- ent. l Does not include indistinct or minor levels. ' Base of sea cliff or shoreline angle. ' Moot bench not included. posits now accumulating on the shallow sea floor north and west of the island. The fossiliferous deposits char- acteristically grade shoreward into beach and dune remnants that originated at the time of the terrace cutting. The great thickness of the shallow marine, beach, and coastal dune deposits on many of the plat- forms suggests that these shorelines may have been cut by a retreating sea (Davis, 1933, p. 1055—1056). Similar wave-cut terraces are prominent features at many places along the coast of southern California and on the other islands. These marine terraces are described in numerous reports dealing with various areas throughout the coastal region (Lawson, 1893; Smith, 1900; Davis, 1933; Putnam, 1942, p. 739—748; Hertlein and Grant, 1944, p. 17—22; Woodring and others, 1946, p. 113-116; Upson, 1949, 1951; Putnam, 1954; Emery, 1958, p. 39—60). Supposed wave—abraded platforms that now lie below sea level on the shelf area around San Nicolas Island are described by Nor- ris (p. 39—40) 1’ and Emery (1958, p. 54, fig. 11) 1’ See footnote 2, p. 4. and are referred to in the section of this report titled “Geomorphic setting of the island platform.” These submerged platforms are cut into the island shelf to depths of 400 feet. Comparison of the altitudes reported for the ter- raced areas elsewhere in southern California with those of San Nicolas Island show only general agree- ment for the lower levels and very little agreement with the higher levels. Errors in measurement of ter- race altitudes are common and can be attributed to several causes: variable seaward gradients of the wave- cut platform, cover of marine and nonmarine sedi- ments, differential erosion of the seaward margins of higher terraces by successively lower stands of sea level, warped or faulted platforms, and lateral changes in altitude due to variation in resistance to erosion of the bedrock. Because all these factors were not considered by some of the earlier workers on San Nicolas Island and elsewhere in California and as reliable reference points other than shoreline angle (which itself varies in altitude) are ordinarily absent, terrace correlation often is erroneous. 10 GEOLOGY or SAN The general lack of correlation between the higher emergent terrace levels from area to area and the great altitude of the higher platforms demonstrate that the cutting of these terrace levels in southern California cannot be ascribed entirely to eustatic change of sea level but must be attributed in part to local differential uplift of individual terraced blocks. It is probable that eustatic changes of sea level took place during some such local uplifts with the result that wave-abraded platforms cut during various eusta- tic sea levels may have been superimposed on platforms eroded into emerging or submerging fault blocks. Rela- tive sea-level changes of this nature possibly would result in terraces that are not synchronous but that lie at the same altitude in widely separated areas and would also account for the partial lack of correlation of terrace altitudes in different terraced areas along the mainland coast. However, the apparent regional correlation in the depth of shallow submerged terraces ofl' southern California (Emery, 1958, p. 42—44), the relatively good correlation of the altitudes of the lowest emergent terraces at some localities along the coast (Davis, 1933, p. 1066—1070; Upson, 1951, p. 427— 434; Hoskins 13) and the relation of both to worldwide levels (Shepard and Wrath, 1937, p. 45; Zeuner, 1945, p. 252), all indicate that the abrading of these plat- forms may have occurred during eustatic changes in sea level, followed by slight deformation. Even though the low emergent platforms along the mainland coast of southern California are locally tilted a few degrees in the Ventura area (Davis, 1933, p. 1052—1053; Put- nam, 1954, p. 45) and near Newport Beach, and up to 26° in the Palos Verdes Hills (Woodring and others, 1946, p. 109), and though there is evidence for slight regional seaward warp of the submerged shelf edge at the rate of 160 feet per 100 miles (Emery, 1958, p. 44—46) , tilting of the emergent terrace platforms of San Nicolas Island cannot be demonstrated. Two minor faults noted in the terrace deposits at altitudes of 650 and 840 feet have no pronounced effect on the gradient of the underlying platforms. However, the terraced areas on the island may not be of sufficient extent to measure a slight regional warp such as that discussed by Emery. Conclusive evidence is lacking for the existence of a land bridge that may have connected San Nicolas Island to the late Pleistocene peninsula now occupied by the northern Channel Islands. Bathymetric data indicate that the lowest definite submerged terrace ‘3 Hoskins, C. W., 1957. Paleoecology and correlation of the lowest emergent California marine terrace, from San Clemente to Halfmoon Bay: Stanford Univ., unpublished Ph.D. thesis. NICOLAS ISLAND platform (shelf edge) was cut at depths of less than 430 feet on Santa Rosa—Cortes Ridge between Begg Rock and Santa. Rosa Island (Emery, 1958, p. 44). However, a 13-mile span of ocean floor that lies at depths greater than 430 feet transects this ridge half- way between Santa Rosa Island and San Nicolas Island. The maximum recorded depth in this saddle is 245 fathoms (1,470 feet) (Uchupi, p. 10),“ which is far deeper than any supposed submerged terrace platforms of late Pleistocene age. The presence of the diminutive fox of San Nicolas Island often is cited as evidence for a land bridge, but it is more probable that the animal was imported by the aborigines as part of their food supply long after the fox had evolved to its dwarfed form on the northern Channel Islands. Both the white-footed mouse and night lizard could have been transported to San Nicolas Island on floating debris derived from mainland floods, in Indian canoes, or on the ships of otter hunters. The presence of fossil terrestrial snails in the 100—foot terrace de- posit at locality SN—l presumably can be attributed to the rafting of these forms to the island on flood debris from the mainland. Neither floral nor faunal evidence can be cited for the presence of a land bridge before the cutting of the supposed oldest terraces on San Nicolas Island because the highest points on the island are mantled by marine deposits that indicate complete submergence in late Pleistocene time. The well-preserved third upper molar of a normal- size mammoth reported to have been collected by Mrs. Blanche Trask on San Nicolas Island is in the verte- ' brate collection of the Paleontology Department at the University of California, Berkeley. Examination of the fossil tooth revealed uncemented sand grains and Recent( Z) shell fragments in the tooth crevices, sug- gesting that it was found in a kitchen midden on a coastal dune rather than in a shallow marine terrace deposit. As Mrs. Trask did considerable artifact col— lecting from the kitchen middens on San Nicolas Island sometime before 1910 (Meighan and Eberhart, 1953, p. 112, table 3), it is possible that she found the tooth in such a deposit. The size of the tooth also implies that the mammoth .could not have been a migrant dwarf from the northern Channel Islands. All vertebrate material collected from the terrace deposits at San Nicolas Island is poorly preserved, worn, caliche encrusted, and contains only aquatic-bird and marine-mammal bones. Presumably the lone occur- rence of a single elephant tooth can be attributed to its transport to the island by the aborigines as a curio or ceremonial object. 14 See footnote 8t p. 8. GEIOMORPHOLOGY 1 1 DRAINAGE No permanent streams are present on San Nicolas Island and the intermittent streams contain running water only for a short period after moderately heavy rains which occur infrequently during the winter. Dur— ing heavy rainstorms the larger steep ravines may contain rapidly flowing water to a depth of l to 3 feet. Much of the mud- and silt—laden water is dis- charged into the ocean, which remains discolored to more than a mile offshore for several days. Springs flow throughout the year in a number of the deeper canyons where the stream bed intersects large faults, but the runoff from the springs is negligible. Else- where springs appear along the contact between the bedrock and Quaternary deposits in a few drainage systems. The steep south side of the island is highly dissected by stream channels that have a dendritic drainage pattern. Badland topography has been developed at a number of places on this slope but is best displayed in exposures of the thick siltstone unit one-half mile south of Jackson Hill. The drainage system is poorly devel— oped on the north side of the island, and on the west end most of the stream channels in the dune-covered areas do not reach the coast. The mouths of all the stream channels are accordant with sea level, and there is no evidence of alluviation due to drowning or of incising resulting from a relative drop in sea level. ' DUNES Active and partly stabilized longitudinal dunes ori— ented parallel to the direction of the prevailing west— erly winds blanket much of the western third of San Nicolas Island. Most of the large active dunes are concentrated in the arcuate area between Vizcaino Point and the 200-foot contour between Seal Beach and Thousand Springs. Several large active dunes extend to the vicinity of hill 905 and upper Tule Creek (pl. 3). The prevailing westerly and northwesterly winds transport sand from the western coastal area onto and across the higher upland surfaces of the island where roughly parallel fingerlike projections of active and partly stabilized sand protrude east and southeast as far as upper Mineral Creek. A few older stabilized longitudinal dunes reach southeast on the high terrace platforms beyond Jackson Hill and Celery Creek. A strip of small isolated active dunes derived in part from adjacent beaches extends the length of the north and south shorelines along the outer margin of the lowest emergent terrace. On the steep parts of the south side of the island the progress of the migrat- 654890 0 - 63 — 2 ing sand is impeded by the deep canyons that dissect the slope. The dimensions of individual dunes are difficult to record because of the rapid shifting of the active dunes and the lack of definite separation between stabilized or partly stabilized dunes. Many of the large Recent dunes on the west end of‘ the island are 50 feet or more high and may attain a length of 1,600 feet. Extremely long dunes are present on the higher terrace platforms but few are more than 10 feet high. Sand Dune Canyon contains an extensive isolated dune, more than 100 feet high and approximately 600 feet long, composed of sand that was transported across the high upper surface of the island. Wind-scoured troughs several feet deep and ex- humed soil surfaces formed on older dune deposits are common features in many partly destroyed dune areas. Study of aerial photographs of the island taken in 1943 and 1955 indicate that the dunes on the higher terrace platforms are periodically stabilized and re- activated and that the area covered by dunes is gradu- ally diminishing in size. LANDSLIDES Several extensive landslides up to a mile in width occur along the steep slope on the north side of San Nicolas Island. Only one slide of comparable size is present on the south side of Jackson Hill. The east- ernmost large landslide, northwest of Coast Guard Beach, is about three-quarters of a mile wide and con- sists of relatively unbroken strata derived from a sandstone unit and a siltstone unit. A part of this large broken block has moved downslope a distance of approximately 100 yards, forming a sizeable rubble— filled crevice between its rearward margin and the stable bedrock. Eolian sand has completely filled this opening at the western extremity of the slide and forms a surface continuous with the nonmarine cover on the 385-foot terrace, indicating that the slide took place before much of the terrace cover was deposited. Most of the other large slides along the north coast show the same features along their inner margins. Along the north side of the island, the bedrock dips seaward about 10° to 15°. When relative sea level was about 100 feet higher, during a part of late Pleistocene time, waves undercut the base of the slope; thus, only a slight triggering action is necessary to set the land- slide blocks in motion downdip on siltstone bedding planes. Because of the relatively unbroken nature of the slide debris some of the landslides are difficult to recognize. 12 GEOLOGY or SAN BEACHES Short sandy pocket beaches separated by broad headlands of thick-bedded sandstone occur along much of the coastline of San Nicolas Island. Relatively wide sand beaches up to 1 mile in length break the con- tinuity of the pocket beaches and intervening head- lands at Dutch Harbor, 1 mile east" of Dutch Harbor, along the spit, at Army Camp Beach, and at 2 places between Thousand Springs and Vizcaino Point. Along the extreme western part of the south coast and near BM—21 on the northwest coast, metamorphic cobble or sandstone-boulder beaches, rather than the usual sandy beaches, are present. Elsewhere along the shoreline only thick-bedded sandstone is continuously exposed, locally for distances of half a mile or more; Where the sandstone is jointed or rests on easily eroded rocks, wave erosion has excavated deep, narrow channels and caverns, and in other places has created an inclined rocky shelf by eroding the rock along bedding planes that dip seaward. A sea clifl’ 5 to 30 feet high borders the inner margins of the beaches and the seaward edges of the rocky headlands along most of the island coast. . The most prominent beach feature on the island is the roughly triangular sandspit that in 1955 extended about 1 mile beyond the east end of the island proper: a submerged bar continued eastward beyond the ex- posed portion of the spit for about an additional mile. Sand has been deposited on the spit by waves and winds to about 16 feet above mean sea level. A study of the spit (Norris, 1952, p. 224—228) indicates that it is subject to considerable change both in outline and position from year to year as the result of the vari- ability of wave force. The sand comprising the spit seems to have been transported in part by strong longshore currents that move southeast along the north side of the island; waves and currents on the south side, on the other hand, move mainly west and erode the spit. Winds from the northwest blow obliquely across the spit and carry much sand from the north side to the south. The outline of the sand spit in 1955 showed no marked change in shape or size from the 1943 survey, but its position was slightly different; the spit had shifted south, possibly because of the construction of the breakwater at Coast Guard Beach in 1951—52. STRATIGRAPHY CONCEALED ROCKS The thickness and lithology of the rocks underlying San Nicolas Island are not known. The principal difli— culty in predicting the subsurface stratigraphy on San Nicolas Island is the lack of detailed geologic NICOLAS ISLAND data in the adjacent submerged or island areas that can be directly correlated with the geologic features on San Nicolas Island: Such a lack of information is quite unlike geologic studies on the mainland, where surface and subsurface information in adjoining areas can be used to evaluate the structural and sedimenta— tional picture of the region under observation. How- ever, rocks exposed on other islands, seismic data obtained offshore, and rock samples collected from the sea floor in the San Nicolas Island area provide some evidence as to the lithology and thickness of sedi— mentary rocks that may lie beneath the rocks of Eocene age exposed on the island. Approximately 15,000 feet of sedimentary rocks of Cretaceous, Paleocene, and Eocene age is exposed on San Miguel Island (Kennett in Redwine and others, 1952). Most of this thick sedimentary sequence is older than that exposed on San Nicolas Island, but some of the rock types are remarkably similar, sug- gesting the same source area for the sediments. Seismic data obtained by Raitt (1949, p. 1915) indi- cate that approximately 3 kilometers (9,840 feet) of sedimentary rock rests on the basement rocks in Santa Cruz basin between San Nicolas Island and Santa Cruz Island. The sedimentary rocks exposed on the sea floor in Santa Cruz Basin are probably of Miocene age or younger, as shown on the reconnaissance geo— logic. map of the sea floor (fig. 1). About 21/2 miles northeast of Begg Rock (pl. 1 and fig. 1), which lies 8 miles northwest of San Nicolas Island, a northwest- trending seismic profile indicates an approximate sedi- ment thickness of 1.7 kilometers (5,600 feet) and a gentle northwest dip in the bedrock (Raitt, oral com- munication, 1955). Norris (p. 46-47) describes 15 sedi— mentary-rock samples of probable Eocene age dredged from the ocean bottom in the vicinity of the southeast end of seismic profile and between Begg Rock and the island. Emery’s map (fig. 1) shows rocks of ques- tionable Miocene age on the sea floor in the seismic- profile area. Samples of shale from the sea floor along the Santa Rosa-Cortes Ridge between Begg Rock and the saddle in the ridge 12 miles to the north have yielded foraminiferal faunas that range in age from early to late Miocene (Uchupi p. 22—27 ).16 Norris also notes the presence of sedimentary rocks resembling the Monterey shale of Miocene age along the 50-fathom contour north of San Nicolas Island. Unfortunately, it is not known whether sedimentary strata older than the Eocene crop out on the shelf area northwest of the island, nor is the location and nature of the Eocene— Miocene contact known. 15 See footnote 2, p. 4. 1“ See footnote 8, p. 8. STRATIGRAPHY 13 In June 1955 the US. Geological Survey conducted an aeromagnetic survey of San Nicolas Island and vicinity. The flight consisted of a traverse from the Palos Verdes Hills across Santa Barbara Island to San Nicolas Island, 11 traverses across San Nicolas Island, and a return traverse across Santa Catalina Island to the Palos Verdes Hills. Concerning this sur- vey, R. W. Bromery (written communication, 1956) states: The magnetic pattern over San Nicolas Island shows only the regional gradient and suggests that there is little igneous rock in the general area. There is no significant anomaly from which a depth to basement can be calculated. The total thickness of sedimentary rocks exposed on and beneath San Nicolas Island is estimated to be about 5,000 feet, based mainly on Raitt’s preliminary seismic work north and east of Begg Rock. However, the lithology and age of sedimentary rocks that may lie beneath the oldest unit exposed on the island are not known, and any correlation with the Cretaceous and early Tertiary sedimentary rocks exposed on the northern Channel Islands would be misleading. The nature of the basement rock on which these unknown sedimentary rocks rest is even more obscure. On the basis of the inferred regional geology, it is possible that the basement rocks are a correlative of the Cata- lina schist. GENERAL FEATURES OF THE EXPOSED ROCKS The stratigraphic section of sedimentary rock ex— posed on San Nicolas Island consists primarily of alternating sandstone and siltstone beds that attain a thickness of approximately 3,500 feet. Fossils indicate that the sedimentary bedrock, of which neither the base nor top is exposed, is of middle to late Eocene age. Several small igneous dikes of Miocene(?) age in- trude the sedimentary rocks near the southeast end of the island. Unconformably overlying the rocks of Eocene age are unconsolidated marine terrace deposits and windblown sand of Pleistocene age. Large areas of Recent dune deposits and lesser amounts of beach sand and alluvium obscure the older sedimentary rocks over much of the island. Thirty stratigraphic units have been differentiated in the rocks of middle to late Eocene age. These units have not been named formally because the section is incomplete. They are numbered consecutively, with unit 1 the oldest; the relative position and gross lith- ology of each unit is shown on the map explanation (pl. 3) and on the stratigraphic sections (pl. 5). Each unit is differentiated primarily on the basis of its 'pre- dominant lithology, relative strategraphic position, na- ture of the upper and lower contacts, and thickness. The description of grain size and sorting is based on field determination and not on the results of laboratory analyses. It is difficult to distinguish any single sand- stone or siltstone unit from another on the basis of lithology alone, because there is no apparent change in the mineral content from unit to unit and dis- tinctive marker beds are lacking throughout the sec- tion. A few siltstone units isolated by faults are differentiated on the basis of foraminiferal faunas. In addition to the numbered units, five informal rock units of middle to late Eocene age are indicated by the letters A, B, C, D, and E on the geologic map. The lettered zones either contain individual mappable lithologic units of unknown stratigraphic position that have been isolated by Quaternary deposits or faults, or they are composed of strata that have not been differentiated with respect to the known stratigraphic sequence. Detailed subdivision of the stratigraphic section on San Nicolas Island was necessary to determine the amount and direction of displacement on numerous intersecting faults and to correlate the lithologic units in adjoining fault blocks. The sedimentary rocks of Quaternary age have been subdivided into terrace deposits, dune sand, and allu- vium on the geologic map (pl. 3). The deposits on the terrace platforms include shallow marine sediments, old beach sands and dune deposits, and a cover of slope wash and dune remnants. Partly cemented eolian sands of Pleistocene and Recent age are not differen— tiated from active dunes on the geologic map, and aboriginal shell mounds are included with these dune deposits. Limited exposures of stream outwash com- posed of silt, sand, and rubble and Recent beach deposits that consist of sand, gravel, and rubble are combined and are shown as Quaternary alluvium on the geologic map. TERTIARY SYSTEM EOCENE SERIES GENERAL FEATURES OF THE EOCENE BOOKS The rock sequence of middle to late Eocene age ex- posed on San Nicolas Island is composed of four principal rock types that are the lithologic basis for the subdivision of the stratigraphic section into mappable units. These rock types are thick—bedded sandstone, thin-bedded siltstone, thinly interbedded sandstone and siltstone, and conglomerate or conglom- eratic mudstone. Sandstone units are the most numerous in the Eocene sequence and have a combined thickness nearly equal to that of the other lithologic units. In general, the sandstone units consist of light—gray thick-bedded fine- 14 GEOLOGY or SAN NICOLAS ISLAND to medium-grained micacous arkosic sandstone (arko‘ sic sandstone as defined by Williams, Turner, and Gilbert, 1954, p. 310—315). The clastic fragments are predominantly angular and poorly sorted to moder- ately well sorted, and the grain size ranges from very fine to very coarse within a single bed. Scattered tabular fragments of siltstone frequently occur in thin, nonpersistent beds in many of the sandstone units, and many are twisted or curved, suggesting that the siltstone was only semiconsolidated during transportation and deposition. . A few of the sand- stone beds exhibit cross-lamination, current ripple marks, or a variety of small-scale sedimentary struc- tures, but well-defined graded bedding is rare. Exam— ination of a few current-bedding structures in several sandstone units indicates current movement from north to south. Large calcareous concretions that lie in individual beds or in a sequence of beds are commonly present within the sandstone units. Many sandstone beds are separated by sandy siltstone partings or by very thin siltstone beds that commonly contain car- bonaceous material. Mollusk(?) borings and tracks and worm(?) trails and tubes frequently mark the upper surfaces of some sandstone beds. When weath- ered, the thick sandstone beds form prominent yellow- ish-gray outcrops; many are cavernous or honey— combed. Nearly vertical joints that intersect at about 90° occur in most of the thick—bedded sandstone units. Secondary calcite fills many small joints or faults in the sandstone units, and most exposures show varying degrees of discoloration from ferruginous stain. Some of the sandstone units vary markedly in thickness. and several lens out completely. Several distinct mappable units composed pre- dominantly of blue—gray siltstone with minor amounts of mudstone and claystone occur in the stratigraphic sequence. Interbedded with the siltstone are very thin beds of limy fine-grained sandstone a few inches thick that weather yellowish gray or reddish brown and that emphasize the bedded appearance of the siltstone units. Ordinarily the siltstone exhibits a hackly or conchoidal fracture and may contain thin streaks of concentrated carbonaceous material and scattered small pyritiferous concretions. Gypsum fills many small joints and fractures in the rock. The siltstones weather olive gray and usually form gentle slopes be- neath the cliff-forming sandstone units. Another distinct set of units composed of inter- bedded sandstone and siltstone is made up of a se- quence of alternating beds that individually are too thin to be delineated on the geologic map. The per— centage of sandstone and siltstone in these units is approximately equal The light-gray sandstone is gen- erally fine to medium grained, weathers to yellowish gray, and much of it displays small-scale structures and current ripple marks. The siltstone contained in the interbedded sandstone and siltstone units is somewhat sandy and weathers to light gray or olive gray. In places, claystone and mudstone are interbedded with the siltstone. Many units composed of interbedded sandstone and siltstone are lenticular, and the ratio of sandstone to siltstone and the thickness of the bed- ding may vary. The thin-bedded sandstone and silt- stone units are deeply eroded where they occur between thick-bedded sandstone units, but they form relatively prominent outcrops where locally present within silt- stone units. The only unit on San Nicolas Island containing massive conglomerate is composed primarily of lenti- cular beds ,of pebbles and cobbles interbedded with sandstone and breccia.. Two conglomeratic mudstone and sandstone units that commonly display slump structures occur at widely separated places in the straitgraphic sequence. These two units are not ex- tensively exposed but are easily eroded to relatively gentle slopes strewn with pebbles and cobbles. The same rock types that occur on San Nicolas Island are present on the submarine shelf adjacent to the northwest end of the island and are tentatively correlated with the exposed sequence on the basis of general lithology and Foraminifera content. Brief notes on the rock types observed or collected on the submarine shelf are shown in table 7. In the areas where submarine ridges rise above the general level of the sea floor and where rocky shoals project close to or above the surface of the water, the bedrock generally is thick-bedded sandstone that usual- ly supports a heavy kelp growth. Areas in water less than 100 feet deep that form depressions or broad troughs on the sea floor and that support little or no kelp growth usually indicate siltstone bedrock. Kelp apparently cannot maintain holdfasts in the softer, finer grained rocks, and only‘the smaller varieties of algae grow over the submarine outcrops of siltstone and mudstone. Conglomerate beds and interbedded sandstone and siltstone beds usually have a variable amount of kelp cover, depending on the amount of current action and the induration of the rocks. The combined thickness of the stratigraphic sections measured in the middle to late Eocene rocks exposed on San Nicolas Island is slightly less than 3,500 feet (see pl. 5), but lateral variation in the thickness of individual units undoubtedly alters this figure in dif- ferent areas. Sea-floor outcrops of Eocene sedimentary STRATIGRAPHY 15 rocks extend several miles northWest and east of the island (Norris, p. 46, 48),“ but the structure and areal extent of these rocks are not definitely known. The probable repetition of this sea-floor section by faulting and folding leads the authors to postulate a minimum outcrop thickness of 5,000 feet for the Eocene rocks exposed on San Nicolas Island and the surrounding shelf area. DESCRIPTION or MAPPED UNITS UNIT 1 The oldest stratigraphic unit in the unnamed sand- stone, siltstone, and conglomerate sequence is known only from exposures on a wave-cut bench at the south- west edge of an up—faulted block near Vizcaino Point. Thick-bedded medium-grained arkosic sandstone con— stitutes most of the unit. Thin, 2- to 4-inch beds of fine-grained sandstone occur at intervals in the middle part of the outcrop, and a lenticular bed of cobble conglomerate approximately 1 foot in maximum thick— ness is exposed near sea level at the west edge of the outcrop. Curved and twisted siltstone fragments 2 to 6 inches in length are also scattered through a few feet of sandstone near the extreme western part of the outcrop. Large elongate calcareous concretions occur in a few of the thick-bedded sandstone strata near the top of the unit. As the base of unit 1 is not exposed above the low-tide line, a minimum thick- ness of about 30 feet is estimated (pl. 5). No fossils were found in the unit, but because the lithology is similar to that of overlying units and because there is no unconformity at the top of the unit, it is considered to be Eocene in age. UNIT 2 Unit 1 is overlain by a cobble-bearing mudstone and sandy siltstone unit which is designated unit 2 and which is found only in the up-faulted block on the southwest side of Vizcaino Point. The well-rounded pebbles and cobbles contained in the mudstone are not sufficiently abundant to warrant usage of the term “conglomerate.” Massive olive-gray mudstone is the predominant lithology, but it grades into sandy silt- stone and fine—grained sandstone. The pebbles and cobbles range in maximum diameter from about 1/2 inch to approximately 8 inches, with an average diam- eter of about 3 inches, and are composed mainly of hard, dense dark-gray, greenish‘gray, and brownish- gray metavolcanic and metasedimentary rocks. Scat- tered angular and tabular fragments of sandstone and siltstone, with maximum dimensions of about 2 feet, occur in the unit. Bedding in unit 2 is either indistinct 17 See footnote 2, p. 4. FIGURE 2.—Conglomeratic mudstone of unit 2 exposed in a sea cliff near the west end of the island. The large sandstone block at the right center is a elastic fragment. The pebbles and cobbles are predominantly metamorphic rocks derived from an unknown source. or absent, and there is no apparent preferred orienta— tion of the cobbles (fig. 2). Exposures in the wave- cut bench and sea cliff indicate a minimum thickness of 25 feet for the unit. Because faults bound units 1 and 2 on the northwest and southeast, their lateral variation in lithology and thickness is unknown. The base of unit 2 is sharply defined and shows no evidence of channeling; Quaternary deposits cover the upper contact of the unit. Widely scattered oyster-shell frag- ments and a few worn and incomplete gastropods are the only fossils in unit 2. Several incomplete specimens comparable to Turm'tella lawsom' indicate an Eocene age for the unit. An extensive cobble—bearing siltstone that resembles unit 2, and that may correlate with it, occurs on the sea floor at offshore stations 51, 84, 86, 87 and 89 (pl. 4; table 7). The wellvrounded cobbles of unit 2 may possibly represent material reworked from older conglomerates, or they may have been transported a great distance before deposition. Conglomerates of Cretaceous and Paleocene age exposed on San Miguel Island, 63 miles to the northwest, contain similar rock types that show the same degree of roundness. UNIT 3 A thick—bedded sandstone sequence that crops out a short distance southeast of Vizcaino Point and that presumably overlies unit 2 in the same area, is desig— nated unit 3. It consists primarily of yellowish—gray 16 GEOLOGY OF SAN NICOLAS medium-grained micaceous, arkosic sandstone that contains scattered coarse-grained rock fragments. In- dividual beds within unit 3 are separated by thin silt- stone or fine-grained sandstone beds a few inches thick. Small lenticular beds of metavolcanic cobbles occur at two places in the upper part of the unit. Large elongate to nearly spherical resistant calcareous con- cretions, 1 to 10 feet in the long dimension, are com- mon in some of the thick beds. The base of unit 3 is either covered by dune sand or occurs below low tide, but a minimum thickness of 115 feet is estimated for unit 3. Its lateral variation in thickness and lithology is unknown. UNIT 4 Unit 4 contains the only massive conglomerate exposed on San Nicolas Island Eight-tenths of a mile southeast of Vizcaino Point, this unit consists of three rock types: conglomerate, fine— to coarse-grained sand— stone, and breccia (fig. 3). The conglomerate contains a silty sandstone matrix with well-rounded pebbles and cobbles that range in maximum diameter from 14 inch to 10 inches, with an average diameter of about 21/2 inches. The cobbles and pebbles are pre- dominantly hard, dense gray, greenish-gray, and, brownish-gray metavolcanic and metasedimentary rocks that are unlike any basement rocks exposed on the other islands or the nearest parts of the mainland. Scattered among the metamorphic pebbles are small subangular elastic. fragments of siltstone and fine- grained sandstone that were probably locally derived. Imbrication of the cobbles in some beds suggests a FIGURE :$.~—Lenticu1ar beds of conglomerate, breccia, and sandstone in' unit 4 near the west end of the island. Imbricatlon of the cobbles In the lowest bed, although not apparent in this photograph, 8115‘ gests current movement from left to right. ISLAND FIGURE 4.—C1astic fragments of siltstone and mudstone embedded in \ a matrix of sandstone contained in unit 4. Presumably the tabular fragments in the breccia were locally derived. south—moving current at the time of deposition, and the roundness of the metamorphic cobbles may indicate reworking from older conglomerates. The irregular lenticular conglomerate beds range in thickness from a few inches to 5 feet. The interbedded sandstone is medium to coarse grained and poorly sorted to moder— ately well sorted. It resembles the sandstone of unit 3 in general appearance, but contains poorly defined graded beds of pebble conglomerate and coarse—grained sandstone near the top of the unit. Associated with the massive conglomerate beds are intraformational breccia beds 1 to 3 feet thick. Angular slabs of silt~ ] stone, mudstone, and fine—grained sandstone constitute ' most of the larger elastic fragments within a coarse- grained sandy matrix (fig. 4). A few blocks and boulders of coarse-grained sandstone and cobble-bear— ing mudstone are distributed through the breccia. All the constituents in the breccia closely resemble the older Eocene sedimentary rocks exposed elsewhere on the island and were probably locally derived. The maximum thickness of unit 4 is approximately 20 feet (fig. 35). The conglomeratic parts of the unit thin northwest from the thickest exposed section in the sea clifl' west of hill 192, but the thickness of the entire unit seems to remain constant. The upper con- tact of unit 4 is gradational. Fragments of oyster shells are commonly found in the breccia sequences of unit 4 and are the only fossils recovered from the unit. A sandy conglomerate observed by divers at station 25, is lithologically similar to unit 4. The conglomeratic parts of unit 4 bear a striking resemblance to conglomerates of Cretaceous and Paleo- cene age observed on the west coast of San Miguel STRATIGRAPHY ' 17 Island. Possibly the source area for the conglomerates in unit 4 was the same, or perhaps the well—rounded pebbles and cobbles of unit 4 were reworked from older conglomerates like those exposed on San Miguel Island. UNIT 5 Unit 5 is one of two exceptionally thick sections of sandstone in the unnamed sandstone and siltstone se— quence on San Nicolas Island. The best exposures are found along the wave-cut bench about 114 miles south- east of Vizcaino Point and at the tip of the point. The narrow submarine ridge that extends northwest from Vizcaino Point probably is formed in part by strata correlative with unit 5. In general, unit 5 is composed of thick—bedded, poorly sorted to moderately well sorted medium—grained arkosic sandstone. The grain size of the sandstone ranges from fine to coarse Within a single bed without apparent graded bedding. Thin beds of intercalated sandstone and siltstone occur in unit 5 near the base and top and are as much as 10 feet thick. Concentrations of mica flakes and car- bonaceous material appear in some beds and delineate the bedding. Large elongate to nearly spherical cal— careous concretions like those present in unit 3 occur in some of the thick beds. Fresh outcrops are light gray but weather to yellowish gray. The estimated maxi- mum thickness of unit 5 is approximately 445 feet. The upper contact is gradational. UNIT 6 Unit 6 is not only the thickest siltstone unit in the sedimentary sequence but also is the thickest individual unit exposed on the island. The one completely ex— posed section of unit 6 occurs along a tidal bench about 11/2 miles southeast of Vizcaino Point where it can be examined only during low tide. The pre- dominant lithology in unit 6 is thin—bedded blue-gray clayey to sandy siltstone that breaks with a hackly or conchoidal fracture. Some claystone and mudstone are interbedded with the siltstone. Beds of light-gray, very fine grained micaceous sandstone a few inches thick are commonly interbedded with the siltstone near the base of the unit but become less numerous near the middle and top. The thin lime—cemented sandstone beds weather to yellowish-gray or brownish-gray re- sistant bands that emphasize the bedding in the unit. Small amounts of carbonaceous material are concen- trated in a few thin beds throughout the unit, and: secondary gypsum and calcite fill many small joints as well as fractures along bedding planes. Small dark- gray pyritiferous concretions 1 to 3 inches in diameter occur sporadically throughout the siltstone. Unit 6 weathers to olive—gray slopes beneath the cliff-forming beds of unit 7 (fig. 5). The single complete exposure of unit 6, measured along the tidal bench southeast of Vizcaino Point, has a stratigraphic thickness of 596 feet (pl. 5). A local minor unconformity exists at the top of the unit in the Sand Dune Canyon area. F ora— minifera are common throughout the unit, but no megafossils were found. The broad semicircular trough that lies between the offshore rocky shoals and the west end of the island has a bedrock floor composed primarily of siltstone that has yielded Foraminifera that correlate with those of unit 6. The thickness and lithology of this belt of siltstone on the sea floor also indicates that it is cor— relative with unit 6. Lenticular beds composed mainly of thick-bedded sandstone are locally present within unit 6 in upper Sand Dune Canyon, in several fault blocks south of Jackson Hill, and in the area north of Dutch Harbor. These discontinuous sandstone lenses appear at about the middle of unit 6 and are collectively designated unit 6a on the geologic map and structure sections. The lenses consist of a sequence of sandstone beds 6 inches to 15 feet thick interbedded with thin alternat- ing lenticular beds of sandstone and siltstone. The lithologic character and bedding of the sandstone in this unit compare closely with those of the upper part of unit 7. A maximum thickness of 150 feet is esti— mated for the lenticular sandstone bodies in unit 6 southwest of Jackson Hill and north of Dutch Har- bor. One specimen of Acila decisa. a small pelecypod restricted to strata of Eocene age in California, was found in the lenticular sandstone beds at locality E—3. FIGURE 5.—Slope—formlng siltstone beds of unit 6 overlain by cliff- formlng sandstone beds of unit 7 along the east wall of Sand Dune Canyon. The canyon wall at this point Is approximately 460 feet high. 18 GEOLOGY OF SAN NICOLAS ISLAND Foraminifera are present in the interbedded siltstone beds. UNIT 7 The cliff-forming thick—bedded sandstone sequence that everywhere overlies the siltstone of unit 6 on San Nicolas Island is designated unit 7. The unit is best exposed on the east side of Sand Dune Canyon, in the area immediately southeast of Jackson Hill, and in the cliffs three-quarters of a mile north of Dutch Harbor. The predominant rock type is light-gray medium- to coarse—grained arkosic sandstone containing varying amounts of biotite and muscovite. Carbonaceous ma- terial is scattered through a few beds and often serves to delimit the bedding. Individual grains in the sand— stone are angular and may range in size from very fine to very coarse. Large elongate calcareous concre- tions averaging 2 to 4 feet in diameter are common throughout the unit and occur in distinct beds. The , unit is usually thicker bedded near the base, where some beds attain a thickness of 20 feet (fig. 6) ; toward the top, the sandstone is thinner bedded and contains increasing amounts of interbedded siltstone. A silt- stone marker bed that attains a thickness of 15 feet (pl. 5) is present close to the base of unit 7 in the fault block across which section 4 was measured and immediately northwest of Dutch Harbor. Unit 7 nor— mally forms prominent yellowish-gray outcrops that display cavernous or honeycomb weathering (fig. 7). Slump bedding is a common sedimentary feature throughout the unit and usually occurs in beds 6 inches FIGURE 6.——Thick~beddcd sandstone typical of the lower part of unit 7 exposed in a sea cliiT about one—third of a mile southeast of the mouth of Sand Dune Canyon. FIGURE 7.~Honeycomb weathering exhibited on the windward sur-‘ faces of sandstone beds in unit 7 near Dutch Harbor. The resistant network contains a higher percentage of calcium carbonate cement than the surrounding hollow surfaces. to 3 feet thick. Calcite fills some narrow joints in the sandstone, and ferruginous stain colors much of the weathered rock reddish brown. Between Sand Dune Canyon and Dutch Harbor, unit 7 maintains a rela— tively constant thickness of 125 to 150 feet. In the small fault blocks about three-quarters of a mile northwest of Seal Beach the unit thins to approximately 80 feet but thickens again to the west and north. Locally a minor unconformity separates unit 7 from unit 6. Exposures on the east side of upper Sand Dune Can- yon exhibit progressive truncation of unit 6. To the east the lower contact is sharply defined and appears to be conformable. The upper contact of unit 7 is gradational. Oyster fragments were found in the thick sandstone beds, and Foraminifera were collected from the thin siltstone beds near the top of the unit. Many of the resistant thick-bedded sandstone beds found by the divers near the exposed rocky shoals 1% miles west of Vizcaino Point may be repeated fault blocks of unit 7. UNIT 8 Unit 8 is a sequence of alternating sandstone and siltstone beds (fig. 8) that individually are too thin to be shown on the geologic map. Unit 8 is best ex- posed near the coast south of Jackson Hill and in the fault blocks north of Dutch Harbor. Sandstone and siltstone beds are distributed approximately equally throughout the unit, although the ratio of sandstone beds to siltstone beds may vary at different localities or in different parts of the unit. The sandstone is predominantly fine to medium grained, micaceous, fairly well sorted, and commonly concretlonary. A STRATIGRAPHY 19 few sandstone beds contain less mica than is ordi- narily present in the thick—bedded sandstone units. Individual sandstone beds in unit 8 attain a maximum thickness of 20 feet but usually range in thickness from a few inches to several feet. Cross—lamination occurs in some sandstone beds, and small amounts of carbonaceous material are usually present in both the sandstone and siltstone. Much of the gray siltstone that is interbedded with the sandstone is sandy or clayey and forms gentle olive—gray slopes between the resistant yellowish-gray sandstone beds. Thin beds of limy fine-grained sandstone usually are present in the FIGURE 8,—Interhedded sandstone and siltstone in unit 8 exposed in a deep ravine southwest of Jackson Hill. The thick-bedded sand- stone in the upper part of the photograph is included in unit 8. siltstone strata. Individual beds are commonly lenticu— lar and some thin beds lens out Within a distance of a few feet. In several fault blocks northeast of Dutch Harbor the upper part of unit 8 is interbedded with the overlying unit. Unit 8 generally maintains a relatively constant thickness of 125 to 155 feet. UNIT 9 Unit 9 is best exposed north of Dutch Harbor in the fault block across which stratigraphic section 6 was measured. Unit 9 is a thick-bedded concretionary sandstone sequence that, in general lithologic char- acter, resembles unit 7. The sandstone is usually micaceous, indistinctly bedded, and poorly sorted. Thin siltstone beds occur near the top of the unit but are subordinate to the sandstone beds. Ordinarily, unit 9 weathers to prominent yellowish-gray outcrops. Mark— ed lateral variation in lithology and thickness is typical of unit 9; a quarter of a mile northeast of Dutch Harbor it grades laterally into, and inter- tongues with, units 8 and 10 and is not present in some fault blocks in this area. In stratigraphic section 6 (pl. 5), unit 9 attains a maximum thickness of 72 feet and grades upward into the overlying unit. UNIT 10 Unit 10 is a conglomeratic mudstone and sandstone sequence that is lithologically similar to unit 2. How— ever, the cobbles are generally widely dispersed, and only in the type area, about a quarter of a mile north- east of Dutch 'Harbor, are they as abundant as the cobbles in the pebbly mudstone of unit 2. Nowhere in unit 10 are the larger clastic fragments as closely packed as in the masswe conglomerate of unit 4. The cobbles are well rounded and range from less than 1 inch to about 8 inches in maximum diameter in the type area. No cobbles have been found in several fault blocks in the area between Seal Beach and J ack- son Hill; here a correlative unit is designated 10a on the geologic map. The predominant rock types are gray, greenish—gray, and brownish—gray dense meta- volcanic and metasedimentary rocks. The matrix ranges from mudstone to poorly sorted medium-grained sandstone that is ordinarily olive gray in fresh ex- posures and locally contains large angular fragments of sandstone and siltstone. Bedding in the conglomer- atic parts of unit 10 is usually indistinct or absent, but many large-scale slump structures are present. The unit is not resistant to erosion and forms rounded slopes or subdued outcrops between unit 9 and the overlying unit. Northeast of Dutch Harbor, unit 10 reaches a maximum thickness of approximately 50 feet; elsewhere the unit is 10 to 20 feet thick. It grades laterally and vertically into thin-bedded sandstone and 20 GEOLOGY or SAN siltstone or into sandstone. Interbedded sandstone and siltstone at the base grade upward into the character- istic cobble mudstone. Locally the mudstone appears to have channeled the underlying sandstone and silt- stone beds, and at several places northeast of Dutch Harbor the lower part is intertongued with unit 9 or directly overlies unit 8. The upper contact is sharply defined in the type area. Unit 10 has yielded the only significant molluscan fauna from the entire Eocene sequence exposed on San Nicolas Island (loc. E—2). Turm'tella Zawsom' and T urritella uvasana ethem'ngtom' are the most common forms; both presumably are restricted to strata of middle and late Eocene age in California. Large-scale slump structures are common in unit 10 and suggest that deformationwithin the unit was nearly contemporaneous with sedimentation, as the overlying and underlying units are not tightly folded. Locally derived clastic fragments of sandstone and siltstone within the mudstone and sandstone support this interpretation. The primary structures and sedi- mentary features suggest an origin of the contorted strata by submarine slumping possibly associated with turbidity currents as described by Crowell (1957, p. 1003—1005). The metamorphic pebbles and cobbles contained in unit 10 may have been reworked from older conglomerates such as those in unit 4 or from older conglomeratic strata not exposed on the island. UNIT 1 1 Unit 11 is well developed half a mile north of Dutch Harbor, in the fault block across which stratigraphic section 6 was measured. This unit is much like unit 7 lithologically. In general, unit 11 is thick-bedded, poorly sorted micaceous arkosic sandstone that is pre- dominantly medium to coarse grained. Elongate re- sistant calcareous concretions occur in some beds. The unit varies markedly in thickness and attains a maxi- mum thickness of approximately 70 feet northeast of Dutch Harbor, but it may be only 10 feet thick in some fault blocks (pl. 5, stratigraphic section 4). The upper contact is conformable with the overlying unit. UNIT 1 2 Unit 12 is a sequence of thin—bedded sandstone and siltstone that is best exposed north of Dutch Harbor in the fault block across which stratigraphic section 6 was measured. Fresh exposures of the fine- to medium- grained arkosic sandstone, which generally occurs in beds less than 1 foot thick, are light gray but weather to yellowish gray. The siltstone is blue gray, weathers to olive gray, and much of it is clayey or sandy. Alter- nating beds of sandstone and siltstone 2 to 8 inches thick occur in approximately equal amounts in the NICOLAS ISLAND lower part of the unit, but siltstone is predominant near the top. Bedding in unit 12 is relatively well de- fined by the thin resistant sandstone beds, but the unit as a whole forms slopes between the enclosing cliff-forming sandstone units 11 and 13. Unit 12 ranges in thickness from 50 feet to approximately 100 feet. The upper contact with unit 13 is sharply defined but irregular, indicating a local minor unconformity. UNIT 13 Unit 13 is a thick-bedded cliff-forming sandstone sequence closely resembling the lower part of unit 7 in lithology and bedding. Typical exposures of unit 13 are in the fault block across which stratigraphic sec- tion 6 was measured. Angular, very coarse grained arkosic sandstone and granule sandstone form very thin lenticular bodies within several of the sandstone beds, and nonpersistent siltstone and fine grained sandstone beds a few inches thick are present at irregularly spaced intervals throughout the unit. The angular granules are composed primarily of quartz and dense greenish-gray metamorphic-rock fragments. Cross-lamination and large tabular calcareous concre- tions occur in a few of the sandstone beds. Unit 13 maintains a relatively uniform thickness of 45 to 65 feet where measured. The lower part of the unit locally contains small tabular fragments and pellets of mudstone. The upper contact is relatively sharply defined. UNIT 14 Unit 14 is a thin—bedded siltstone and sandstone unit similar in lithology to unit 12. It is best exposed in the fault block across which stratigraphic section 6 was measured northeast of Dutch Harbor. Interbedded sandstone and siltstone in the lower part of unit 14 grade upward into siltstone that contains a few thin lenticular sandstone beds near the top. The amount of siltstone in proportion to sandstone varies from place to place, as does the thickness of the individual beds. Tabular fragments of siltstone several inches in length appear sporadically in some of the sand- stone beds. The thickness of unit 14 is variable; in stratigraphic section 2 it is 28 feet thick and in strati- graphic section 6 it is 63 feet thick (pl. 5). The upper contact of unit 14 is gradational. Foraminfera are common in the siltstone beds throughout the unit. UNIT 15 Unit 15 is a thick-bedded concretionary sandstone sequence resembling unit 7 in lithology and thickness. Typical exposures are in the large unfaulted area between structure sections D—1)’ and E—E’ (pl. 3). The sandstone is arkosic and commonly medium grained but ranges from fine to very coarse. A 5- to STRATIGRAPHY 21 15-foot siltstone bed containing «thin layers of fine- grained sandstone usually is present in the middle part of the unit. Thin lenticular siltstone and fine- grained sandstone beds a few inches thick occur between the medium— to coarse-grained sandstone beds. Slump bedding and cross-lamination are commonly associated with normal bedding in the sandstone. The unit ranges in thickness from about 100 to approxi— mately 140 feet and forms cliffs. Locally the top of unit 15 grades upward into interbedded sandstone and siltstone of unit 16, but at most places the contact is fairly well defined. UNIT 1"» Unit 16 is the second thickest siltstone unit in the Eocene sequence exposed on San Nicolas Island, and in gross lithology it is similar to unit 6. The best exposures are about 1 mile northeast of Dutch Har- bor, adjacent to stratigraphic section 7. The pre— dominant rock type is blue-gray sandy siltstone inter— bedded with a few thin beds of calcareous fine-grained sandstone. Unit 16 differs from unit 6 in that several thin-bedded lenticular bodies of intercalated sandstone and siltstone occur locally within the unit. These sandy lenses, shown on plates 3 and 5 as units 16a, 16b, and 160, are not as thick bedded as those in unit 6a and contain proportionally more interbedded siltstone. The sandstone lenses form relatively resistant outcrops in the slope—forming siltstone and vary in thickness, dis-- tribution, and stratigraphic position. Unit 16 is 247 feet thick near Dutch Harbor and seems to be about 300 feet thick in the faulted area east of Celery Creek on the north side of the island. The upper contact of unit 16 is gradational. Foraminifera are common in the siltstone strata. UNIT 17 Unit 17 is a sandstone sequence that is best exposed at the top of the cliff—forming outcrops along structure section [Ll—IL" (pl. 3). Most of the sandstone in the unit is medium grained but ranges from fine to very coarse grained. A few lenticular pebbly sandstone beds as much as 2 feet thick occur near the middle of unit 17. Angular granules and small pebbles of quartz are common in these lenticular beds, which contain lesser amounts of greenish-gray, gray, and yellowish-brown metamorphic-rock fragments. Occasional oyster—shell fragments occur with the rock fragments. Concentra~ tions of mudstone balls and tabular fragments of silt- stone in the unit indicate almost contemporaneous erosion and deposition and local minor unconformities. The sandstone is thin to thick bedded, relatively well bedded, and forms prominent cavernous-weathering outcrops. Thin siltstone and fine-grained sandstone beds a few inches thick separate many of the thick sandstone beds. Unit 17 is 114 feet thick in strati- graphic section 8 (pl. 5) and appears to vary only slightly in thickness. The upper contact is gradational. The angularity of the granules in the coarser clastic sediments of unit 17 suggests a nearby source for the metamorphic-rock fragments during the deposition of the unit. UNIT 18 Blue-gray siltstone unit 18 is similar in appearance to units 6 and 16, but it is not as thick as either. Unit 18 is well exposed just south of hill 606, near the southeast end of the island. Approximately 50 feet of siltstone and thin-bedded calcareous sandstone is present slightly above the base of the unit. Siltstone is predominant in this basal interbedded interval, and a few thin beds of lime-cemented fine-grained sandstone occur in the middle part of the siltstone unit. Unit 18 is .163 feet thick in stratigraphic section 9 (pl. 5). The upper contact of the unit is conformable and usually sharply defined. UNIT 19 ' Unit 19 is the thickest sandstone section in the sedi- mentary sequence of Eocene age exposed on San Nico- las Island. Cliff-forming outcrops that closely resemble unit 7 in lithology occur over most of the southeast end of the island. Unit 19 is primarily thick-bedded sandstone that locally contains relatively thin-bedded sandstone slightly above the base and near the middle of the unit. Generally the sandstone is highly arkosic, micaceous, and fine to medium grained. Thin beds of siltstone and fine-grained sandstone are present throughout the unit and tend to be thicker than other sandstone units. Slump bedding and current bedding are common in parts of the unit, and many small tabular fragments of siltstone are present in some of the thin sandstone beds. Unit 19 is 520 feet thick in stratigraphic section 10 (pl. 5). The upper contact is gradational. UNIT 20 TO 30 The sequence of units 20 to 30 was mapped at the southeast end of the island and is discussed under a single heading because of its small outcrop area, similarity of rock types, and the lack of evidence for the determination of lateral variation in thickness and lithology. All these units are exposed in a small down— faulted block near Jehemy Beach. Stratigraphic sec— tions 11 and 12 on plate 5 indicate the thickness and lithology of each unit. Units 21. 23, 25, 27, and 29 are relatively thin cliff—forming sandstone units'much like unit 7 in lithology. Units 22, 24, 26, and 28 are thin interbedded sandstone and siltstone units that resemble unit 8 or the lower part of unit 12. Units GEOLOGY OF SAN FIGURE 9.——Well-bedded siltstone and fine~gra1ned sandstone in the lower part of unit 20 exposed in a sea cliff at the east end of the island. Siltstone beds predominate in unit 20 both above and below the pictured sequence of beds. 20 and 30 are siltstone units that have the same general appearance and lithology as unit 6 (fig. 9). The top of unit 30 is not exposed owing to faulting. The combined thickness of units 20 through 30 is approximately 450 feet; unit 20, the thickest individual unit, is 108 feet thick. Foraminifera are present throughout the silt- stone units and in the interbedded sandstone and silt- stone units. ZONE A Two fault blocks in the sea cliff west of Jehemy Beach contain beds of siltstone and interbedded sand- stone and siltstone that have not been differentiated stratigraphically because they are poorly exposed. This faulted outcrop is designated zone A on plate 3 and , probably represents parts of units 26, 27, and 28. ZONE B Outcrops of siltstone beds of uncertain stratigraphic position that are isolated by Quaternary deposits or faults of unknown displacement are assigned to zone B on plate 3. All siltstone outcrops designated as zone B occur in the stratigraphic sequence somewhere be- tween units 5 and 17. ZONE C Included in zone C are isolated outcrops of thick— bedded sandstone of unknown stratigraphic position, or sandstone units that occur in an undifl'erentiated se— quence of beds. All sandstone beds designated zone C on plate 3 occupy a stratigraphic position somewhere between units 6 and 18. NICOLAS ISLAND ZONE D Intercalated thin-bedded sandstone and siltstone beds that individually cannot be assigned to numbered- units either because they are isolated from known units or occur in an unknown sequence of units are placed in zone D. All units assigned to zone D lie at unknown stratigraphic positions between units 7 and 18. ZONE E Due to the intense weathering of the rocks, dune- sand cover, or the indefinite nature of the contacts, a sequence of beds lying between units 8 and 12 has not been differentiated northwest of Seal Beach and west of Sand Dune Canyon. These beds are shown as zone E on plate 3. LABORATORY ANALYSES 0F EOCENE SANDSTONE SAMPLES Laboratory study of 15 sandstone samples selected at random from the sedimentary section of middle to late Eocene age on San Nicolas Island was undertaken to determine the physical character of the sandstone beds and to ascertain whether the mineralogic com- positions suggest possible source areas for the sedi- ments. The sandstone samples were collected at irregular intervals, the lowest near the top of unit 3 and the highest at the top of unit 19. Thus, the samples span about 2,500 feet of the exposed section. In addition to thin-section studies of the samples, mechanical-analysis, heavy-mineral, and porosity and permeability deter- minations were made. The results of the laboratory analyses are listed in table 2 and in figure 10. Thin—section studies indicate that quartz is the most abundant mineral and constitutes 40 to 60 percent of the grains in nearly all the thin sections. Most of the quartz grains are clear, angular, generally without in- clusions, and exhibit sharp extinction. The sandstone samples from San Nicolas Island average 48 percent feldspar, most of which is oligoclase with lesser amounts of andesine, orthoclase, and microcline. Deter— minations of 5 to 10 grains of plagioclase selected at random in each thin section show that oligoclase is the predominant plagioclase and that andesine and other varieties are relatively rare. Potassium feldspar is present in all the samples, and about one—third or less of the potassium feldspar is microcline. A few grains of perthite are present in about half the slides. The most abundant accessory mineral in the sandstone samples is biotite. Muscovite is less common than bio- tite, and hornblende is rare. Fine-grained dark—colored rock fragments, chiefly of metavolcanic origin, com— prise 8 to 20 percent of the total grains. The majority of the slides also contain discrete calcite grains that may be detrital rather than secondary grains. 23 STRATIGRAPHY .23 E :05 wwmhmuwmwu :3? was .283 2:88 we EH?» :5: weEEker a .Sfingfi 2:8 $32: :32 m 5228;: ES .mSBEQEa .338 3353.5 2:3: ”A585 :2 . .23“ 23508ch >3 28 :A somaawwumuamww .534 a .EheoEoE :A coumhaaww a Amman .xoo Aim 32:59 @232: mEESm >3 Uaflfihfiofl : .onA MA NAA w.AA v -- A -- a -- -- A NN -- n N -- m -- -- NV -..- -- -- w. w «M mm ................ m in: Ac no? .oQ n4“ a.AN ad N -- A -- mA -- -- 5 mA .-. A. N -.- c -- -- an --. -- -- h. N. mm «m --------- n fin: A: AEQ :oBc‘A .AuothAAQQBQD «A «.2 A KN VA -- A ll n mA 0A A m -- -- m -- -- NN .-.- -- -- m. wA mm NA. ---------------- h 2:: A0 mmwm 45:95:00 A . o.wA mdm A -- A .-- v c @N -- h -- -- .mA -- -- cm -- --. -- MN m. pm on -------- w find Ac GEE 9:532 damn???» NSAAMAAw o.m NA: A .NA A. -- m .-.. N w mN A n A -.-. -..- Nn -.-. .-- -- AIA ., wA Am on ........ m 3:: Ac tag 33:: 60.53%?» Eva-ESSA? 9mm A .AN w .m c m N --. A -- -- om AA .-- A. N -- -- Am -- -- -- m. nA Nm mm ---------------- m flan we 908 60:23:32» 93 o.AN AAA A MA A -- A -- -.- AWN NA II N :2 -- A m -.- mA -- .-.- -... N. c an mm --------------- AA HE: E mwamA .oQ odN mfNN NA» NA -- A -- A -- -- N m. -- m --. A m N -- E. -- -- --. m. 2 Nm mm. ------- mA i=5 Ac tan 2:32 .onA owe NZMN A.NA m -- A --. A -- -- nA «A -- nN -- -- m. A .-.- -- um .-- A N. nA vw Aw .mA .2550 “.59 263:: SEGA .835“; 2:8: 3E. 92. g H m N S a m ma. m N a 3 m m. m mm 8 ........ 2 :Eco :8 .533 .8553?» Z 92 a: N m h a. a a n m m S A. a mm m... ........ 2 25:0 :8 E5: day—Saw? zany—Am o .w w NA N .3 MA -- AA AA @A -- n 3 MA 3 -- .-- N v I: -- ww -- 1! o .A «A «m Nm. .9 fi:: .0 aha ESE: amBowA .onA o.oAN a SA A .m w A 3A --. «.A ll CN AA .-- NA --. .-- A m .1. MA Am A -.-. N. A. 3» cv .oA “Esme fan 23:8 SEAS 60.5533 o.m.A mdN A .3 N -.- A -- «A -.-. .7. NA NA -- AA -- A N A ll -.- wA I: 1-. AiA n mm «m .......... NA :5: .8 no» .502 .Avvhunuawa hsnwzm koN CNN oNA MA --. VA -- w m A N. N -- m -- -- m AV -- MA we -- {I -- N. .A wA Aum av --------------- oA fin: Ac norA. .d .d d m L l L L S H W W X H H H D H O O O H 8 V V V .d 0 a ”0 m 1m s0: 1 )o )o o n. m. n e A I A o .m. m .- 1. n u 9 Ian pu- wm n mm Mam-mmmmumm m m m .U. “mm... m m pm m m m ....m.m mwmmwwfig "He 6U dOu u mmom Z N 0 a o a ”4.0.1.1 .01.. w... W M u... m4 H m4 9 0 BAU9_9m m- P8 d1 103 (B we 6 H A. m. 0 Km. w.- e a 1 a 1 m4 m H mKW 29:3 we 55:50.0 m m.. m aw fix aw .m1. (.m1. 9 m. M m. w B U- u H v H. fl. m. d m m :oEmoQ 295% mm m a mé a a , m u m w. 9 a a N 1.9 3_Aan._w5m:m 8a::woaa< WA “w W n. 9 8w w. : 3:883 m. A m m 552.: m n 3:855 H8523 A823: NEWS-A .sl 3.558.3qu 5:88: A :5: £2 .E figsAwA. 29332 :sm .wfiaficm aetuze 233ng geoefi \c SANAegztmoA ~23 $32:an .ggfiwofitou NESSEIN H.228 24 PERCENT PERCENT PERCENT FIGURE 10.—Hisitograms showing grain size in the samples of Eocene Sandstone. sand (Wentworth, 1922) with the exception of sample P9. 1932‘). 40- 30— 20- 10— 0... 40— 30- 20— 10- O- 40— 30- 20- 10- 0.. 1 1 1 P1 1/2 W 1/a 1/160 M 0.21 80 1.61 V2 1% 1/8 %60 M017 801.43 P11 1/2 V4 1/8 1/15 0 MO.21 So 1.56 SIZE, IN MILLIMETERS GEOLOGY P2 40- 30- 20-— 10- 1 1/2 1/4 1/3 V15 0 M 0.16 30 2.11 40- 1 1/2 % 1/8 1160 MO.16 50 1.80 P12 40— 30— 20- 10- o- 1 1,; 1./4 ‘/s I/1/r3 O M 0.19 80 1.52 SIZE, IN MILLIMETERS OF SAN NICOLAS ISLAND P3 40- 3o— 20— 19— 1 1/2 1/4 vs 1/150 MO.21 $01.41 P8 50- 4o- P13 40— 30.. 20— 10- O... 1 1/2 1/4 ‘/s ‘4 M0.17 301.77 SIZE, IN MILLIMETERS P4 40-.- 30- 20- 10- 11/2 1/4 ‘/a ‘150 M019 50 1.48 P9 50-— P14 40— 30— 20— 10- °11/;1A1/81/.so M 0.15 80 1.63 SIZE, IN MILLIMETERS P5 40— 30- 20- ' 10- O— 1 1/2 V1 1/3 1/16 0 M019 $01.61 P10 40- M 020 So 1.71 P15 40—— 30— 20- 10— O.— 1 1/2 1A 1/3 1160 M 0.13 So 1.83 SIZE, IN MILLIMETERS Median diameter in all the samples is within the limits of fine Explanation of symbol: M, median diameter; S0, sorting coefficient (Trask, STRATIGRAPHY ‘ 25 Calcite is the common cementing agent in the sand- stone, but it may be a secondary replacement of a clay matrix. Some ferruginous clayey material that may also act as a cementing agent was observed in several thin sections. The mineralogic character of the sandstones from San Nicolas Island resembles that of other Eocene sandstones from the California Coast Ranges. Reed (1928) reports that the average feldspar content is nearly 50 percent for Mesozoic and Tertiary sandstones in the Coast Ranges. Woodford (1925, p. 174—177) studied six samples of “Tejon” Eocene sandstones from the southeastern part of the Los Angeles basin and found that their feldspar content ranged from 12 to 60 percent. These “Tejon” sandstones, however, are not as consistently rich in oligoclase as are those from San Nicolas Island. An Eocene sandstone sample from San Diego analyzed by G. A. Macdonald for L. G. Hertlein and U. S. Grant, IV, (1944a, p. 44) has a composition similar to the “Tejon” samples except that it lacks biotite. SOURCE ROCKS OF THE EOCENE SANDSTONES The composition of the samples from the sandstone beds of Eocene age on San Nicolas Island suggests a source area of plutonic rocks of intermediate composi— tion with lesser contributions from metamorphic rocks adjacent to igneous bodies. The nearest known occur— rence of basement rocks of this type is on Santa Cruz Island, where hornblende diorite and quartz diorite intrude schists, phyllites, and greenstones of pre— Cretaceous age (Bremner, 1932, p. 13—16). However, similar basement—rock types, possibly now buried by middle and late Tertiary sedimentary rocks on the sea floor, may have provided a source for the Eocene sedimentary rocks on San Nicolas Island. Many of the rock fragments in the sandstone samples resemble the metamorphic rocks that occur in the Eocene con- glomerate beds on the island. N0 source area is known for rocks of this type although similar clastic frag- ments are common in conglomerates of Cretaceous and Paleocene age exposed on San Miguel Island. The metamorphic and plutonic rocks on Santa Cata- lina Island presumably were not the source rocks for the San Nicolas Island Eocene sandstone. Not one of the glaucophane schist minerals of the Catalina meta- morphic facies of the Franciscan series (\Voodford, 1924) has been found in the sandstones of San Nicolas Island. The intrusive quartz diorite porphyry on Santa Catalina Island has a fine-grained groundmass (VVood- ford, oral communication, 1957). Fine-grained rock fragments of this type were not seen in the sandstone samples from San Nicolas Island. The distribution of quartz, sodium-calcium feldspar, and potassium feldspar suggests that the sandstones were derived chiefly from an igneous rock of inter— mediate composition, possibly a granodiorite or quartz diorite. The percentage distribution of the three essen— tial minerals, with allowance for some decrease in the relative abundance of quartz during transport, shows a fairly good correlation with a typical granodiorite or quartz diorite, although the anorthite content of the plagioclase is somewhat low. Nearly all the mineral grains are angular, and most of the quartz grains have sharp extinction. The marked angularity of zircon, garnet, and titanite grains further suggests that the sandstones were derived from igneous and metamorphic source rocks rather than having been reworked from sedimentary rocks (Pettijohn, 1957, p. 512—514). CORRELATION Marine strata of Eocene age are widely distributed over much of southern California, but many local areas of outcrop have been inadequately studied. The best known stratigraphic sections of marine Eocene sedi- mentary recks in southern California occur at the south end of the San Joaquin Valley, in the Santa Ynez Mountains, and near La Jolla. For comparison with the exposed section on San Nicolas Island, the formations at the above-named localities are breiefly described. The correlation chart (fig. 11) indicates the relative ages of well—known formations of Eocene age in central and southern California. Included on the chart are the little-known rocks of the same age on Santa Cruz and San Nicolas Islands. The type area of the Tejon formation lies at the south end of the San Joaquin Valley, about 35 miles south of Bakersfield. The formation consists of ap- proximately 3,500 feet of sedimentary rocks and has been subdivided into four members (Marks, 1943, p. 534—538; Beck, 1952). In ascending order, these are the Uvas sandstone and conglomerate member (110 feet thick), the Liveoak member composed predomi- nantly of interbedded sandstone and siltstone (1,970 feet thick), the Metralla sandstone member (1,300 feet thick), and the Reed Canyon siltstone member (160 feet thick). Much of the section is highly fossiliferous and is considered to range in age from late middle to late Eocene. An exceptionally thick section of Eocene sedimen- tary rocks is present in the Santa Ynez Mountains, which trend parallel to the coast in the vicinity of Santa Barbara. About 8,000 feet of marine strata aSSIgned to the upper Eocene was penetrated by the Tecolote Tunnel 12 miles northwest of Santa Barbara. GEOLOGY OF SAN NICOLAS ISLAND 26 , .553 3 5.8: Sou“ .898 Banduwoow 5 wowndhd 45—38 :33 5 9.2: ms $3.8m 525.3 35° 33 59G and Avg: 935° and $533 Scum @2552 4:53—30 955:3 was 35:8 5 3056.53 wnaeofl go «.35 nozfivuucoléa 552% xuzzm .nuiofiao .m .3 3 2.30m um‘aEmcooN 39 .o 7mg: :mEBI 3.3.53 363 mm 3.9.5.9 mass m. ABEwEoficS EmSEemcou _E_m 7 777 Cu . E 2235 Isms“ may? 7 7 7 .357. u it? w :o «£33525 :oznzzo. . ,1 1 .77‘. ,. . _ 7 7 7 7 23m 3750 M 7 9.88.3 9.25ch 73:79.... 73.67 «75 7 7 7 7.0. 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I I I I I H Iwcloaamm I 7 7 7 7 7 Mawnmmw\ \sosz78 Conant”: 23:5 cam / />wE3. 7 \ £0.50 / I w ,\/\/\/\/\/\< /\/\/\/\/\r\A\/\/\/\/\/\/\/\/\/\/\/\/\ u 7 $33. m 7 o 3 N 3 7 7 $me wocwnoa ANmmC mmmmecEx u—E .wEm: AmmmG Ang :35: :82 2.: 95 $758; 29% can :3: 6mm: :53: £83 63 778:8 7&8: 63 .355 2275 $920 9.5 B>~w>> 025m. w<._0.0_z Zmw>> wz_uj<> _S:w NmZ> (7.2% I>u;_1_<> Z_DOm23h _mD_w me>> 4 mmmz O :mmOdhw: ‘zsos <, present as named; ct, similar form, inadequate material for comparison; afi., close affinity but with known difference in detail; ?, identification of species doubtful; ?cf., identification of genus doubtful; generic name in quotes, used in a broad or probably incorrect sense] E—l E—2 E—3 E—4 E—5 USGS USGS USGS USGS Field 21648 21649 21650 21651 identi- fication G astropoda: Turritella cf. T. buwaldana Dickerson__ ________ Turritella luwsom‘ Dickerson __________ cf. Tum‘tella lawaom' secondaria Merriam.. ? Turritella ummma etheringloni Mer- riam ________________________________________ Turritella uvasana Conrad, n. subsp.? cl. T. uvasana hendom‘ Merriam ______________ “ Tubulaslium” tejonenaix (Arnold) _-_. ________ Architectonica cf. A. cognate Gabb _____________ Architectonica cf. A. ullreyana Dick- erson ________________________________________ Lozotrema tum'tum Gabb ............. X Potamz'des of. P. carbonicola Cooper__ Neven'm of. N. recto Gabb ....... Euspira cf. E. nuciformis (Gabb Amaurellina clarki Stewart? ..... Amaurellina maragai Stewart? ..... ._ Globularia? of. G. hannabali (Dicker- son) _________________________________________ “Phos”? cf. “P.” blakianus Anderson and Hanna __________________________________ Latirus? cf. L. nightingalei M. A. Hanna ______________________________________ Fusinua aft. F. mem‘ami Dickerson._.. ........ “Volulocristuta” cf. “V.” lajollaemz‘s (M. A. Hanna) _____________________________ Lyric aff. L. andersom‘ Waring ................. “Agaronia” of. “A.” mathewaonii (Gabb) ...................................... Cryptoconus? of. C. cooperi (Dickerson). ........ Surculites cf. 8. mathewsonii (Gabb)... ________ Pleurofusia afi. P. lindaviataemis M. A. Hanna _______________________________ X ________________ “Surcula” cf. “S ” pracatten‘uata Gabb _______________________________________ X ________________ Scaphopoda: Dentalium cooperi Gabb? ______________________ X ________________ Pelecypoda: Acila (Truncacila) decisa (Conrad)____ ________________ >< ________ Oslrea afi. 0. stewarli (M. A. Hanna)._ ________ >< ________ X ties during the fieldwork for this report (table 3). The largest assemblage of Eocene megafossils was found in the matrix of pebbly mudstone in unit 10 at locality 14 ; it yielded 27 identifiable mollusk forms and 1 coral. Although most of the specimens are incomplete, the sculpture on the shells usually is well preserved. Elsewhere only 1 to 3 species were found at each of the other 4 localities. Descriptions of the Eocene fossil localities are given in table 8. The, bulk of the specific determinations suggest an age assignment of middle to late Eocene on the basis of forms presumed to be conspecific with those com— monly found in the Domengine formation, the upper part of the Llajas formation, the Rose Canyon shale member of the La J 011a formation, and the Tejon formation, all of which are considered by most pale- ontologists to represent the upper half of the Eocene in California. FOSSILS FROM MARINE TERRACE DEPOSITS More than 250 identified species and subspecies of marine mollusks and other invertebrates were collected from 16 localities distributed over 11 of the 14 terrace platforms evident on San Nicolas Island (table 4). The platforms range in altitude from 20 to 900 feet above sea level (pl. 2). These 16 collections represent the most complete sequence of fossil assemblages from succes- sive terrace levels in southern California and contain the largest faunas reported from terrace levels higher than 500 feet. The overall vertical range, however, does not rival that found in the Palos Verdes Hills, where terrace fossils have been found at an altitude of 1,215 feet (Woodring and others, 1946, p. 93—95). Descriptions of the Pleistocene fossil localities are given in table 9. Foraminifera, Bryozoa, and calcareous algae are abundant constituents of some of the fossil assemb- lages but have not been identified. Provisional de- terminations by the senior author have been made for brachiopods, echinoids, corals, and barnacles, but no attempt has been made to identify the less common decapod crustacean fragments. Vertebrate material including bird, sea lion and seal, walrus (?), and sea otter (?) was collected at four localities, one of which has been described by Howard (1955, p. 135—143) in a paper on a new species of diving goose. Specific determination of the poorly preserved and fragmen— tary fossil vertebrates has not been made for this report. Several early records mention fossil marine in- vertebrate faunas from the terrace deposits of San Nicolas Island, but little has been published since Cooper’s short list of 1894 (Cooper, 1894, p. 24—32). A brief chronological summary of the published and unpublished data on Pleistocene fossils from San Nicolas Island is as follows: 1865. Cooper, J. G., in Whitney, J. D., Islands off the coast of southern California: California Geol. Survey, Geology, v. 1, chap. 6, sec. 5, p. 182—186. Describes raised beaches on which were found “* * ‘ shells of existing species. * * * all of a rather northern type." 1888. Cooper, J. G.. Catalogue of Californian fossils: California State Mining Bur. 7th Ann. Report of the State Mineral- ogist for the year 1887, p. 223—308. Includes six forms from the “Quaternary (post- Pliocene)” on San Nicolas Island. Listed are 5 marine gastropods and 1 land snail, but the collector and locality are not given. 1890. Bowers, Stephen, San Nicolas Island: California State Mining Bur., 9th Ann. Report of the State Mineralogist for the year 1889, p. 57—61. The author lists 39 invertebrate forms at a locality presumed to be the same as SN—l of this report. The list includes 27 marine gastropods, 8 pelecypods, 1 chiton, 1 echinoid, and 2 land snails. 1894. Cooper, J. G., Catalogue of Californian fossils: California State Mining Bur. Bull. 4, 65 p. A distributional list including seven additional inver- tebrate forms from the “Quaternary” of San Nicolas Island. Listed are 5 marine gastropods, 1 chiton, and 1 echinoid collected by Stephen Bowers at an unde- scribed locality. 38 pre—1900( '3). A previously unreported collection by Henry Hemphill containing 25 marine mollusks presumably was found in the vicinity of SN—12 of this report. The collection was made available for study by Leo G. Hertlein of the California Academy of Sciences. 1938. Cockerell, T. D. A., Studies of island life: Colorado (Univ.) Studies, v. 26, no. 1, p. 3—20. A list of 13 molluscan species from an altitude of be- tween 400 and 500 feet is recorded, which includes 11 marine gastropods and 2 pelecypods. Identifications were made by Myra Keen. 1940. Cockerell, T. D. A., The marine invertebrate fauna of the Californian islands: Pacific Sci. Cong. 6th, Berkeley, Palo Alto, and San Francisco, Calif., 1939, Proc., v. 3, p. 501. A supplemental list to the report of 1938 includes 11 species of gastropods and 3 pelecypods identified by Myra Keen. . 1950. Thirty-one species of marine invertebrates are listed in an unpublished report by George Kanakoff of the Los Angeles County Museum. The fossils were referred to the museum for identification by R. M. Norris. This locality is the same as SN—14 of this report. 1955. Howard, Hildegarde, New records and a new species of Ghendytes, an extinct genus of diving geese: The Condor, v. 57, no. 3, p. 135—143. Describes bird bones and records marine mammal and fish remains originally collected by R. M. Norris and K. S. Norris from a marine mollusk locality that is the same as SN—14 of this report. GEOLOGY OF SAN ANNOTA'I'I‘B) CHECKLIST A checklist of fossils from terrace deposits of Pleis- tocene age on San Nicolas Island (table 4) has been prepared for each locality at which fossils were col— lected on San Nicolas Island. Included with the iden— tifications are the approximate altitude of the localities, new records of species not previously reported from sediments of Pleistocene age, notes on variation of certain species from the typical form, and forms not known to be living. The recorded geographic ranges of living forms that presumably are distributed only north or south of the latitude of the island, together with forms that now live close to their northern or southern limits in the latitude of the island, also are noted.28 The recorded bathymetric ranges of forms that now presumably inhabit only depths from 10 to 100 fathoms or more than 100 fathoms off southern California also are included on this list, but the depth ranges of mollusks that now are widely dispersed from littoral through sublittoral depths (Hedgpeth, 1957, p. 94, fig. 1) are not shown. Some of the species that are cited as living in 10 to 100 fathoms ofl' southern California live in shallower water northward and are found in a littoral environment in- the colder surface waters from northern California to Alaska (for ex- ample, Pupz'llam'a papilla, Ceratostoma foliatum). 3' New fossil records, notes on forms not known to be living, and geographic and bathymetric range data are based on reports published before November 1959. NICOLAS ISLAND A serious limitation in using published bathymetric data is that the reported findings are inadequate (for conclusive evidence of depth range, as further dredg- ing and collecting by divers may extend the depth ranges of many mollusks, particularly the small forms. An additional shortcoming of the geographic and bathymetric ranges given on the checklist is that the Recent fauna around San Nicolas Island is relatively unknown, and future collecting in the area may reveal some range extensions. Furthermore, the geographic position of the island is such that the composition of the living fauna probably does not exactly correlate with mainland coast faunas at the same latitude be- cause of upwelling cold water in the vicinity of the island (Sverdrup, Johnson, and Fleming, 1942, p. 724— 725; Orr and others, 1958, p. 929). PALEOECOLOGIC INFERENCES HABITAT The bulk of the molluscan species from each terrace platform can be assigned to the rock-cliif and tide-pool facies (Woodring, 1935, p. 297; Woodring and others, 1946, p. 93) or, less specifically, to the intertidal open- coast and protected outer-coast habitats (Ricketts and Calvin, 1952, p. 6-7). Associated with the rock-cliff and tide-pool forms are many sublittoral species that now live below low tide on a rocky substrate, several species that exist in widely varied habitats, and a few ofl’shore forms. The same depositional environ— ments, which are indicated by the composition of the fossil assemblages, occur along the coast of San Nico— las Island at the present time. Because bedrock types similar to those now being out were being eroded by the Pleistocene seas, it is reasonable to assume that the character of the coastline and the gradient of the wave-cut benches around the island were essentially the same as now. Shoreline features including short sandy beaches separated by broad, but not projecting, headlands and a sea floor with a rather steep slope can be inferred from the configuration of the ancient sea cliffs, the gradient of the terrace platforms, and the composition of the terrace faunas. ANOMALOUS OCCURRENCE OF RESTRICTED-DEPTH FORMS The presence at several fossil localities of one or more forms that are now most commonly found at a depth of 10 to 100 fathoms off coastal southern Cali- fornia (for example, Puncturella cooper/‘2', Bursa, cali— form'ca. Barbarofusus kobelti) or that sometimes range into depths greater than 100 fathoms (for example. Boreotrophon stumti. “Progabbe'a” coopem’. Cyclo- cardia. longim') can be attributed to several causes or to a combination of causes. Collections at SN—l, SN—2, and SN—3, were made on steeply sloping terrace platforms at some distance from the associated sea PALEONTOLOGY 39 cliff, suggesting that these deposits may have accumu- lated at depths of as much as 10 fathoms. Arbitrary platform gradients adopted by Davis (1933, p. 1057) for the offshore area of the Santa Monica Mountains indicate that the platform depth below sea level ranges from 50 feet 1/4 mile offshore to 85 feet at a distance of 1/2 mile, except in the area east of Point Dume where the gradient increases 25 to 33 percent. Off the south coast of San Nicolas Island the gradient is even greater; 14 mile south of Seal Beach the depth is 60 feet, and at 1/2 mile, 150 feet. Forms common in the deeper parts of the inner sublittoral zone thus might be expected in terrace deposits at the outer edge of platforms with steep gradients. In addition, a combination of storm waves and unusually strong tidal current occasionally carries outer sublittoral forms into littoral zones. Uprooted kelp holdfasts often transport inner sublittoral forms to shore. A11— other remote possibility for transport of minute spe- cies is provided by bottom-feeding fish which may deposit fecal pellets containing deep-water shells in areas of shallow water. Furthermore, it is possible that some of the organisms now living only in the deeper sublittoral zone may have been able to tolerate more adverse conditions in Pleistocene time, such as greater wave impact, coarser substrate, or the greater temperature differential of shallow water. Perhaps, during different episodes of terrace cutting, regional wave action was diminished and surface-water tem- peratures were locally less variable, allowing some delicate forms to move into shallow water. Bay and estuarine or mudflat habitats are not represented in the faunal composition of any terrace deposit on San Nicolas Island, although a few indi- viduals commonly associated With these environments are present at some localities (for example, Panope generosa, Samidomus nuttalli, Schizothaerus nuttalli). A few occurrences of forms usually considered indi- cative of a protected sandy—beach or offshore sandy— bottom habitat (for example, Spisula planulata, Trigo— niocardz'a biangulata, Tellina salmonea) may be at- tributed to the existence of extensive sandspits such as the one now present at the east end of the island, or to the fact that a few forms generally regarded as indicators of a restricted habitat sometimes live in other seemingly adverse environments. RELATIVE SURFACE WATER PALEOTEMPERATURES Conclusions regarding the relative paleotempera- tures of the surface sea water during the cutting of individual terraces must be drawn with reservations when based on faunal compositions. It is well estab- lished that both northern and southern shallow-water species occur in the same beds in Pleistocene strata at a number of localities in southern California and northwestern Baja California (Woodring and others, 1946, p. 95—96; Brufi', 1946, p. 221—222; Valentine, 1955, p. 465; Emerson, 1956a, p. 326—327; Emerson, 1956b, p. 396—397). To relate temperatures inferred from faunal compositions t0 definite glacial or inter— glacial stages, with their resulting isothermal shifts, is problematical even where local Pleistocene and Recent marine mollusks and their ecology are well known (Woodring and others, 1946, p. 100—103). However, Valentine and Meade (1958, p. 57) suggest that a good correlation exists between oxygen isotope esti- mates of paleotemperatures and those inferred from zoogeographic methods applied to well-known Pleisto- cene localities in California. Therefore, it is reason- able to assume that the composition of the large terrace faunas on San Nicolas Island is a fairly accurate indicator of relative surface water paleo- temperatures. The constituents of the faunal assemblages (collec- tions of more than 65 molluscan species) from selected terrace platforms that suggest relatively cooler surface water at the time of high—terrace cutting and rela- tively warmer surface water at the time of low—terrace cutting based on present geographic ranges are listed in table 5. Three fossil localities (SN-1, SN—12, SN— 13) from the lOO-foot terrace yielded a total of 150 molluscan species (excluding terrestrial gastropods, chitons, scaphopods, and pyramidellids), of which 6 now live south of San Nicolas Island on the mainland coast (lat 33° 14’30” N) and 11 now occur only near the northern limit of their recorded geographic ranges at this latitude. The same collections contain 6 forms that now range entirely north (on the mainland coast) of the latitude of the island and 15 forms that now live near the southern, extreme (on the mainland coast) of their recorded geographic ranges in the latitude of the island. Two localities (SN—2, SN—3) that yielded large assemblages (more than 140 mol- luscan forms excluding terrestrial gastropods, chitons, scaphopods, and pyramidellids) from the 775-foot terrace contain only 3 small forms that supposedly now live south of the latitude of the island and 5 forms that now are reported to live near their north— ern limits at lat 33° N. From the same collections, 11 forms were obtained that are reported to live en- tirely north (on the mainland coast) of the latitude of San Nicolas Island and 15 forms that now are recorded as living near their southern limit (on the mainland coast) in this latitude. None of the inter- mediate terrace deposits contain large enough faunas for significant paleotemperature estimates, although two of the larger assemblages are listed in table 5 for comparison. 40 GEOLOGY OF SAN NICHOLAS ISLAND Table4.——Checklist of fossils from terrace [Identified by J. G. Vedder; land snails from locality SN-l and chitons from localities SN-l and SN—3 identified by A. G. Smith, but with known difference indetail;?,identification of species doubtful; ?cf. or ?sp., identification of genus doubtful; unidentified; *, collected by Henry Hemphill; X”), probable locality of Hemphill's collection; (?), end point of geographic Locality number and altitude in feet above sea level Spemes SN-is SN-l SN-IZ SN<13 SN~4 SN-lO SN-14 SN-lé SN-ll SNJ sN-2 SN-3 SN-6 SN-S SN-8 smo 20t 45-60 65-70 80-85 85! 375? 425t 470* 590‘ 665't 730t 7351 815* 8401 3851 900’ Gastropoda: Acmaea asmi Middendorff -------------------------------- --.- ---_ _--- ............... ,__- __-_ ____ A. pelta Eschscholtz ----------------------------------- ? —--- X ----- X ..... X -—-- 7 A. digitalis Eschscholtz ------------------------------- X -'--- X X X X ----- .--- ---— A. funiculata Carpenter -------------------------------- ---- ---- .--- ----- X .......... -.-- ---- A. insessa (Hinds) ------------------------------------ X '2 _--_ ____________________ -_-_ ____ A. instabilis (Gould) ---------------------------------- X ---- ----- __-. .................... --..-.--- .......... -__- -.-. .-_- A. limatula Carpenter"--------------? ------------ Z7 X ? cf. ---- X X X 7 cf. ---- X 7 X cf. no A. scutum Eschscholtz ---------------------------------- ---- ---- ----.---- X ---------- ---- X X x ..... --__ _.._ _.-- A. mitra Eschscholtz ----------------------------------- X X ---— X X X X X X X X X X ———— X A. scabra (Gould) --------------------------------- x x x )< x x ----- X x cf. cf. >< ————— x 7 cf Acmaea n. sp.? ----------------------------------------- ---- —--— ----- ----~-—-— X ---------- ---— X X X X 7 .--- Lottia gigantea (Sowerby) ------------------------- X ---- X X X -------------------- X ——————————————— --—_ —-—- .——- Haliotis cracherodii Leach ----------------------------- X X X cf, r"-— .......... Cf, cf. X X ..... 5p, 5p, ---- H. rufescens Swainson ---------------------------------- X cf. X an 7 ---------- 7 —--— cf, X ..... --.- .... .... Haliatis of. H. sorenseni Bartsch --------------------------- ---- ————— ———— ———————————————————— ..-- ..... X .......... -.-- ..._ Haliotis kamtschatkana Jonas --------------------------- ---- ---- ----- _-__ -------------------- ---— ----- X _____ -.-_ --._ --.- Fissurella volcano Reeve -------------------------- X X X X X X X X X X --------------- ~-—- ---- .—-- Dindora aspera (Eschscholtz) ---------------------- X X ---- X ?sp. X ----- ----- X X X X X cf. ---- ---- Lucapinella Ci. L. callomarginata Dall ----------------- —-—— ---— ..... __-- --------------- -—-— —-—— ----- X ..... .-.- --—- ---- Megatebennus bimaculatus D311 .......................... .-.. -.-- ..... --.. X .......... X ---. ..... h.-- ..... ---. .... MEgathura crenulata (Sowerby) .......................... _-.. X X ---. .................... -——- ——————————————— -..-..-.. ———— PunCtlH‘Ella cf. P. Cooperi Carpenter ------------------- —--- ---- ------------------------ 7 ---- ----- X L—--—-——— ———— -.—— Norrisia norrisii (Sowerby) ----------------------- ---- ---- -------------------- ---- --------------- ---- —--- --—- Halistylus pupoideus (Carpenter) ------------------ ---- ----- -—--| X --------------- ---- ----- X ----- ---— -—-- ——-- Tegula funebralis (Adams) ------------------------- 7 X ---- ---------- X X X X X X X ? of T. brunnea (Philippi) ----------------------------- X ---- --------------- X ---- X X X ~--- ? cf, T. brunnea fluctuosa (Dall) ---------------------------- ---- ----- ----~ ---------- ---— ————— X X _____ __-- _--- T. gallina multifilosa (Stearns) ----------- ---- --------------- X --~- --------------- -—.—— ——-- —-_- Tegula cf. T. aureotincta (Forbes) ---------------- X .--. .................... _.._. ____________________ ____ ____ Tegula pulligo (Gmelin) -------------------- ,. ---------------- ---- --------- ----- --------------- ---- ----- X ---------- ---- ---- "Tegula"montereyi (Fischer) ---------------------------- X cf. ---- ---- -------------------- ---- --------------- '? ---- _--- Calliostoma ligatum (Gould) ---------------------------- X ---- X ---- ? --------------- -—-- ————— cf. cf, ..... ---- ---- Pupillaria cf. P. optabilis (Carpenter) ---------------- X ? X —--- X X —----( X ---- X X X ————— _—_- _-—- Pupillaria pupilla (Gould) ---------------------------------- ---- ----- ——-— X --_.--—-1 ..... "Ur.--“ ..... .---- ..... ---- -_-- Pup_illaria cf. P. parcipicta (Carpenter) -------------------- ---- ----- ---- -------------------- ——.—. X ..... h--. ..... --.. ---- Papillaria cf. P. succincta (Carpenter) --------------------- ---- ----------------------------- ——-— ..... X -.-- Vitrinella cf. V. oldroydi Bartsch ------ -- X X 7 ---- ----- X ----- X 7 sp. X ---- Vitrinella stearnsii Bartsch? --------- X -'------------------- ---------------’ --—- Teinostoma sapravallatum (Ca1penter)-- --—- Liotia fenestrata (Carpenter) --------- ---- Arena acuticastata Carpenter ---------------------- .--- A. acuticostata radiata (Ball) [A. acuticostata -_-- bristolae (Baker)]. Astraea cf. A. undosa Wood ------------------------ ..-- ‘Astraea gibberosa (Dillwyn)-- - X Homalopoma carpenteri (Pilsbry)~ X H. paucicostatam (Dall) ............... ____ Homalopoma cf. H. baculum (Carpenter) ------------- ---. Tricolia of. T. pulloides (Carpenter) ————————————— ____ Tricolia cf. T. rubrilineata (Strong)- "'— Littorina ptanaxis Philippi ----------------------- ---- L. Scutulata Gould ------------- ' ------------------- __-.. Lacuna unifasciata Carpenter- 7 Lacuna cf. L. Carinata Gould ---------------------- -_-_ Rissoina cf. R. coronadoensis Bartsch ----------------------- ---- ---------- ----- ----- P'" ————— —-—— ————— X --—.——--. .--- -_.. Rissoina aff. R. dalli Bartsch ------------------------- -------- ------—--»---- ............... _-_- X X .......... _-__ _--_ Rissoina cf. R. hannai Smith and Gordon ----------- ---- ---- ----.---- --------------- -.—_ X .......... --.- -._. Rissoina of. R. bakeri Bartsch-- ---- ---- ______-__ --------------- -——- ————— X .......... __-- .__- "Rissoina"aequisculpta (Keep)-- X ---- cf, ---- ----- cf. ----- X --—- ----- cf_ .......... _-- -___ Alvania purpurea Dall-n‘ ------- X 7 X <--- X ----- '? X X X X X ---- cf. 4‘ almo Bartsch?---——--------------7 ------------------- X *--- ---- -------—_ ---------- X ---- ................... ---. _--_ See footnote at end of table. PALEONTOLOGY deposits of Pleistocene age on San Nicolas Island 41 California Academy of Sciences.)<, present as named; cf., similar form, inadequate material for comparison; aff., close affinity quotation marks around generic name indicate the designation is used in a broad or probably incorrect sense; sp., spectes range doubtful;>((2) number of unidentified species presenq Remarks Forms not known to be living, new fossil records1 , and variant forms Recorded geographic ranges only for forms now living north or south of latitude of San Nicolas Island or close to their northern or southern limits. Depth ranges only for forms restricted to deep sublittoral zones off southern California2 previously reported as fossilh Includes a form with a narrow shoulder and faint oblique axial ribs at SN-l. Smaller than typical form .......................................... Shows an inflated whorl profile similar to that of R. keenae Smith and Gordon and R. bakeri Bartsch but is larger and thicker shelled. Larger and more inflate than typical form. Sculpture similar to that of R. hannai Smith and Gordon. Not previously reported as fossiU ------------------------------------------- Not previously reported as fossil ------------------------------------------- Fragments show a well-developed double peripheral keel ----------------------- Coarsely sculptured form with heavy axial ribs, operculum typical ............ L ............................................................................. r ---------------------------------------------------------------------------- Kodiak Island, Alaska, to Cayucos, Calif.; San Diego(?L Includes Dall’s A. limatula morchii at SN-l. SN-3 and SN-10 .................. ------------------------------------------------------------------------------ Rare south of Santa Barbarm F --------------------------------------------------------------------------- Only in areas of intense upwelling south of San Pedro. This form may be a variant of A. scabra (Gould) .............................. Thicker spired than typical form. Not previously reported as fossiU ------ Thicker shelled and more coarsely sculptured than typical form. Not Sitka, Alaska, to Redondo Beach, Calif.; rare south of Monterey. Off Redondo Beach, Calif., to San Diego. in 25—75 fathoms. Alaska Crescent City, Calif. Crescent City, Calif., to San Nicolas Island. San Pedro, Calif., to Guadalupe Island, Baja Calif Santa Barbara Islands, Calif. Island, Baja Calif. to Santa Barbara Islands. to Santa Margarita Bolinas Bay, Calif., to Santa Barbara Islands Kodiak Island to San Diego; Luis Obispo. rare south of Port San Nunivak Island to San Pedro. Off Redondo Beach in 50 fathoms. Monterey to Coronado Islands, Daja Calif. San Pedro, Calif., to the Gulf of California Mugu Lagoon, Calif., to Cedros Island, Baja Califl Vancouver to San Diego. Bering Sea(?) to San Diego(?); rare south of Cayucos. Calif. Catalina Island to San Martin Island, Baja Calif. Known only from Carmel Bay, Calif., in 25 fathoms Catalina Island to Todos Santos Bay, Baja Calif. 42 GEOLOGY OF SAN NICOLAS ISLAND Table4.—-Checklist of fossils from terrace Locality number and altitude in feet above sea level SPECIES SN-IS SN-l SN-12 SN-ls SN-4 SN—ln SN.14SN-1esN-11 sN-7 SN-2 SN-3 SN-é sN-s SN-B SN-9 303 45-60 65-70 30-85 R51 3752* 4'251 4701 500‘ 6651 730* 7351 8152 3401 885i 900‘ Gastropoda—Cantinued Alvania cf. acutelirata (Carpenter) -------------------- X --—- ---- —--- X ----- ----~——--.-.._ X X -------------- -_--- Alvania aff. A. dinora Bartsc'n ----------------------------- ---- —--- ~--- ............................. X ................... Alvania of. A. aldroydae Bartsch ----------------------- X ---- --—- —- -. -——_ X n... X --—_,---_ X _-.-.--_- ..... ,.--.. Alvania of. A. lirata (Carpenter) -------------------------- ---- —--— ---- ---------- --—- ---- ‘---r---- X ------------------- Alvania n‘ sp.? -------------------------------------------- ---- --.. -..- ............... .--_ --.- ’? .......... Amphithalamus inclusus Carpenter-- X —--— —-—_ ——-— X X ---- X ................... A. tenuis Bartsch -------------------------------------- X X ---- —-—- X X --—- cf. cf‘ -H- .......... Barleeia cf. 13. oldroydi Bartsch ------------------ ? X ---- X —--- ----- X ? X ..... X ..... Sp, Barleeia subtenuis Carpenter? ----- ? 7 X cf. X cf. X -—--. cf ---------- Assiminea translucens (Carpenter) ---------------------- X .--- ———- -.—- ---------- an un ................... Hipponiz tumens Carpenter ------------------------------ X X X -—-- ---------- ---- —--- -~—- ----- X X ---- cf. ----- ”- antiquatus (Linnaeus) ------------------------------- X X X X X X ---- X X X X X -—-- ..... X Crucibulum spinosum (Sowerby) ------------------------------ L-.-— ————— -~-~ .......... --_- -... X .......... _.-...-._ __________ Crepidula princeps Conrad, large form ------------------ ---_ ----- ---< ---- ---------- -—-- ---- __-- ..... X --_- ---- .......... C. onyx Sowerby ---------------------------------------- --—-+---- ---- ---- X ? X X X X X X cf. .......... Crepidula cf. C. excavata (Broderip)- —--- -~-- ---------- 7 —-.- ._.. ..... X .-._ ..._ .......... Crepidula aculeata (Gmelin) ---------------------------- X ---- _--— --——r X .......... ---- X .......... ---- ---- .......... C. adunca Sowerby ...................................... X X --.- X X .--_. X X X X X ---_ ..... 7 C. perforans (Valenciennes) ------- X .-_- Cf. .--_ X ........................ X ..... ___- .......... Crepipatella lingulata (Gould) ------------------------- ——-- ----- X X .......... .-.- X --_- ..... X ..... _--_ .......... *Calyptraea cf. C. mammllaris Rroderip ----------------- -----X(?) ---- ---- ---------- .-__ ........................ ._._ .......... Elachisina grippi Dall --------------------------------- ---- ---- ---- CryptonatiCa Cf. C- clausa (Broderip and Sowerby)- ----- ---- —--- -—-- Lunatia cf. L. lewisii (Gould) ------------------------- 70f. X X Turritella cooperi Carpenter --------------------------- —--- X ---- ---- --------------- —--— ---- .......... Caecum dalli Bartsch -------- X ---- X ---- ---------- ---— X _._- .......... C. californicum Dall ----------------------------------- X X X cf. ---------- ---- X 'X __._ cf, Fartulum occidentale Bartsch --------------------------- X X X 7 ..... X _-.-.‘-.-- _-_- ..... _-... Fartulum cf. F. orcutti Da]1-- -----« X X ---- ---- ..... X ? X ---_.-.-.,---. Aletes squamigerus Carpenter—- _---- X X X -—-~ ----- ---—----- X X -——-)---—- Petaloconchus anellum (MBrch)—- -------------- ? X ----- ---~ ---- X .......... ---- X -..- ..... P. complicatus Dall-uv ---------------------------- ---- X ---- X ---- X ----- -——— X ------ ........ Spiroglyphus lituellus (M'drch) ------------- - cf. X X X ---- cf. X X ?cf. ——-— cf. "Diala" cf. YID.” marmorea Carpenter ------- ~ X X ——-- ---— ---- ---------- ? --—- X —-—- ----- Bittium eschrichtii montereyense Bartsch" — ————— X ---- ---- ---- X cf, ..... ---- X _--- X B. armillatum Carpenter-u: ------------------------ ’? X ---- cf. 75p, cf, '? .-_- X —-—- ..... ? B. attenuatum Carpenter --------------------------- 7 X ---- cf. ---- ----- X ---- X cf. ---- ----- Seila montereyensis Bartsch--- - ----- -_.....-.- X X ---- ---------- ---- ---- ---------- Cerithiopsis Cl", C. grippi Bartsch--- ---------- ---- ---- ---— ---- --------------- ---- ---- ---------- Cerithiopsis, unidentified forms ---------- X(l) X(2 ---- X(2) —-—- X(2) ----- ---- XQ) X(l) ---- ----- Mataxia of. M. diadema Bartsch -------------------- --—— ---- ----- ---- ---- --------------- --4- ~--- ---------- Triphoru cf. T. pedroanu (Bartsch) --------------------- X sp. 7 ? —--~ ---------- ---- -~-- ---------- Lamellaria rhdmbica D311 ------------------------------ ---- ----- ---- -—-- ---------- L---<---- ---—— _-— X --—— -—-—--——-——--- Velutina aff. V. laevlgata (Linnaeus) ------------------ ---- ---- ---- ---- ---------- L--~--~-- ---- ----- X ----- ---- ---------- Zonaria spadicea (Swainson) ---------------------------- ---- cf X ---- ---------- L—------- ---~ --------------- ---- ---------- Pusula californiana (Gray) ----------------------------- ---- X X ---- ---------- ~--- X -~-- --------------- ---- ---- ----- Bursa californica Hinds -------------------------------- ---- X ---- ---- --------------- ---- ----)----- ------------------------ Balcis cf. B. prefalcata (Bartsch) --------------------- X ---- ---- ---- ---------- L---—---- ---- sp. - Sp. -----‘---- ----- sp. BalCiS cf. B. arnbldi (Bartseh) ------------------- ----~---- ---- ____ ---- X ----- .--..---- —--- ---------- ----4—--- ---------- Balcis thersites (Carpenter) ---------------------- ---- X ---- ---- ---- ----- Cf. ----- ---- ---------- Turbonilla cf. T. rqymondi Ball and Bartsch ------- ---- X ----- sp. ---- --------------- ---- ---------- Turbonilla tenuicula (Gould)? -------------- X ---- ---- ---- ---------- ---- ---- ----- ""4 Turbonilla cf. T. valdezi Ball and Bartsch ------------- 7 -—-- ---- ---- ----- X ----- ---- -------- OdOStomia cf. 0- oldroydi Dall and Bartsch -------- --—- 7 ---- 7 ---- ----- X 7 ‘--- ----- X Odostomia aff. 0- americana Ball and Bartsch —————— -_—— ---_ ————— ---- ---- ..... ----4 ..... ____ .......... Odostomia phanella D311 and Bartsch ---------- ---- ----- ---- ---- ---------------- ---- --------- X ----- "-- """"" Odostomia cf. 0_ tenuisculpta Carpenter- -------- ---- X ---- ----- ----‘ ----- ---- --------- Odostomia terricula Ball and Bartsch ------- --—- X ---- ---- ---- ----- ""‘ """ -___ """"" Odastomia cf. 0. virginalis D311 and Bartsch-— - -—-- 7 —--- ___- ..... X ..... ____._-_-_--_~_ Odostomia cf. 0. eugena Ball and Bartsch ---------- ---- X --—— ---- --—- ---------- h-—-<---- _--- _______________ .—-- .......... Odostomia altina Ball and Bartsch? ---------------- ---- ---- ---- ---- ___- """"""""""" "" """"" Odostamia cf. 0. i0 Ball and Bartsch -------------- ---- X ---- ---- ---— ..... X ..... --_. ..... .-_-- See footnote at end of table. PALEONTOLOGY deposits of Pleistocene age on San Nicolas Island~—Continued 43 Remarks Forms not known to be living, new fossil records 1, and variant forms Larger and thicker shelled than typical form. Sculpture similar to that of A. dalli Bartsch. Not previously reported as fossil. Smaller and more elongate than typical form .................................. Lacks the prominent nodes below the suture shown on the typical form --------- Resembles A. dalli Bartsch but has fewer spiral cords ------------------------ Includes the variant H. antiquatus craniodes Carpenter with typical form at SN-l, SN-2, SN-S. Bare in strata of late Pleistocene age ------------- Not known to be living 1. Larger and thicker shelled than C. fostigiata Gould or C. contorta Carpentem Not previously reported as fossill ----------------------------- Elogate strongly noded forms with a strong cord above the suture from SN-l may be B. catalinense Bartsch This shell may be a northern variant of M. convexa (Carpenter) --------------- Outer lip more flaring than typical; sculpture subdued ——————————————————————— A variable species. Not known to be living1 ---------------------------------- Resembles B. berryi (Bartsch) but has heavier callus and lacks doubly reflexed spire. Not known to be living1 ...a _________________________________________________________________________ Smaller than typical form. Not previously reported as fossill ---------------- Larger and less inflate than typical form .................................... Coarser sculpture than typical. Not previously reported as fossiU ---------- More elongate and with more prominent spiral lines than typical. Not previously reported as fossilh Smaller than typical form ......................................... ThiCkEr shelled and slightly more inflate than typical form —————————————————— Thick-shelled variants with coarse Sculpture at SN.3 ............. L---.-.,...- Smaller than typical form .................................................... Smaller than typical form. Not previously reported as fossil‘ ................ Recorded geographic ranges only for forms now living north or south of latitude of San Nicolas Island or close to their northern or southern limits. Depth ranges only forforms restricted to deep sublittoral zones off southern California2 Forrester Island, Alaska Guadalupe Island, Baja Calif.(?), to the Gulf of California. San Pedro to the Gulf of California. Rare north of southern California; ranges south to Tome, Chile. San Pedro(?) to Panama. Magdalena Hay, Baja Calif., to Peru. Known only from San Diego in 16—20 fathoms. Duncan Bay, British Columbia, to Todos Santos Ray, Baja Calif. Off southern California in 10-50 fathoms. Off Coronado Islands, Baja Calif., in 14 fathmns San Pedro to Mazatlan. Found off California only in moderate dethS (20—25 fathomsL Forrester Island, Alaska, to San Diego. Redondo Beach, Calif., Baja Calif. to San Geronimo Island, lcy Cape, Arctic Ocean, to Cayucos, Calif. Off Catalina Island and Redondo Beach in 15-55 fathoms. Monterey to Coronado Islands, Baja Calif. Redondo Beach, Calif., to POint Abreojos, Baja CaliL Monterey and Pacific Grove. Monterey to Coronado Islands. Redondo Beach, Calif., to Point Abreojos; Baja Calif Redondo Beach, Calif., to San ”iPOIitO Point, Baja Calif. Known only off San Diego in deep wateL 654890 0 - 63 - 4 44 GEOLOGY OF SAN NICOLAS ISLAND Table 4.——Checklist of fossils from terrace Locality number and altitude in feet above sea level SPSCIes SN-lS SN-l SN-IZ SN-l3 SN—4 SN-lo SN-Uo SN- l6 SN-ll SN-7 SN-2 SN-3 SN-G SN-S SN-B SN-9 20* 45-60 65-70 80-85 851 3752 4352 470* 500* 665* 730* 735* 815* 840* 8852 900+ Gastropoda-Continued Odostamia cf. 0. sapia Ball and Bartsch -------------------------- ""4"-— ..... --——.———- ——_. X "—-.-... ...... --.— Odostomia cf. 0. sanctorum Ball and Bartsch ----------------- ...— .............. ..——4-——— —_.- X ..... .--_ ..... 4—--- Epitonium cf. 0. indianorum (Carpenter) ————— X —--— ..... .-.- ? .......... _ .-._ .......... ...- .......... Opal“! cf. 0. evicta de Boury -------------------------- x -——— ----- ---— ————— --~- ----- ---- ---------- ---- ----- ——-- Opalia wroblewskyi chacei Strong ....................... X .... ..... ..-. X ___- __________ _._- -___ _____ ____ ___. _____ ____ Ceratostoma foliatum (Gmelin) ——————————————————————————————— -—-- ..... -_-- ..... ---- .......... ---- Cf. X ..... -__- ..... ---- C. nuttalli (Conrad)? ........................................ X ..... .._. ..... ._-. .......... .... ............... -_._ ...... --.— Jaton cf. J. festivus (Hinds) ------------------------------- X -------------- -_-- .......... --.- ---...- _ ..... ---- ..... ...— Maxwellia? of. M. gemma (Broderip) ............... __-_. ..... -..- ---- X ..... ---- .......... --_- -.--l.-.-. ..... --.- ..... ---- Ocenebra cf. 0. lurida (Middendorrf)-- ---------------------- 7 ---- X ----- 7 ---------- --—— x x 7 Sp ......... Ocenebra lurida munda (Ball in Williamson)? ———————————— X -—-- ..... ---. X -——— .......... ---_ ..... h--. .................... Ocenebra cf. 0. foveolata (Hinds) ...................... X .... ..... ---- ..... .... ..... ? ...- ..... 7 ................... Ocenebra interfossa (Carpenter) ........................ X .... ..... -.-. x _.. --_.]cf_ .... cf. ___________________ h.-- 0. interfossa clathrata (Dall) ------------------------- X ———— ————————— X ? —_-- ..... -_-- cf, cf. ?cf. ---- ..... _-_- 0. subangulata (Stearns) ------------------------------- x ..____. cf. ——_. _____ .-.- .......... -.-- ..-. .................... ..-— 0. circumtexta (Stearns) ------------------------------- X —————————— ._-. .................... ---- ---- ..... 7 -__- ..... ---- 0. beta (Dall) ----------------------------------------- cf, X ..... ---_ .................... ...-.-.-- .............. .--_ --._ Boreotraphon stuarti (Smith) --------------------------- x .--- -_-_:-.-- ? ............... --.-t-.-- .......... --.- ...... -_-_ Acanthina spirata (Blainville) ------------------------------ X ——-- ---- .................... -_-- ............... .-_- ...... _.__ A. spirata punctulata (Sowerby) ........................ x u—. ....e..... X .......... cf. --.- .......... t .............. ---_ Acanthtna cf. A. lugubris (Sowerby) --------------- Thais emarginata (Gould)? ————————————————————————— Morula? cf. M. lugubris (Adams) ................... Amphissa versicolor Dall .......................... A. columbiuna Dall--—-—----———------~-------—-——4— Mitrella tuberasa (Carpenter) ..................... M. carinata (Hinds) ............................... M. carinata gausapata (Gould) .................... q *Kelletia kelletii (Forbes) --------------------------------- (7) --------- —---a----a —————————— --—— —_.. ------------------- —_-. Calicantharus fortis (Carpenter) ---------- \ ------------------ ""l --------- X x x X cf. X X X X —_.. cf. "Searlesia" dira (Reeve) ------------------------------------ ---- ----- ---- --------------- —--- cf. X X X ——-- ficf. Macron lividus (Adams) --------------------------------- ---_--——— ----- ---- ............... cf X -_-_ ................... ---- Nassarius mendicus cooperi (Forbes) -------------------- X ——-— ..... ._.. .................... -... .-.- .._. .............. .--- Nassarius cf. N. perpinguis (Hinds) ------------------------- X ————— -_—— ——————————————— __.. ()cf, --.. .——— —————————————— _—_. Barbarofusus kobelti (Dall) ---------------------------- cf. x ..... ---. ’_> ............... --_. 7 X .............. .--— B. arnoldi (Cossmann) ---------------------------------- 13- harfordi (Stearns) ---------------------------- ----fi B. monksae (Dall)? ------------------------------------- Mitra idae Melvill ------------------------------------- Gibberulina pyriformis (Carpenter) --------------------- Cysticus jewettii (Carpenter) .......................... Cysticus cf. C. regularis (Carpenter) ------------------ Olivella biplicata (Sewer-by) --------------------- -! ----- Olivella cf. 0. pedroana (Com-ad) ...................... HProgabbia"cf."P." cooperi (Gabb) ....................... Conus californicus Hinds ------------------------------- X X X X ---- ..... .-.m X X cf X X of ..... ---— Ophiodermella ophioderma(Da11)? ............................. ---- - -_---— .................... ---- X -——-——------- ----- —--- Psuedomelatnma grippi (D311)._.---—-------------.-- X ..... .-.- ----- -.-- -------------------- ---- ---- -—-- ----- »--- ----- -—-- P. torosa (Carpenter) ---------------------------- . ----- of. X ? ---- X ----A ---------- cf ---- Mangelia interfossa Carpenter -------------------------- 7 —.—- X ---- x ----- ----- ? Mangeliu cf. M. nitens Carpenter ---------------------------- ---- ----- --—- --------------- ? Mangelia variegata Carpenter -------------------- --- cf ---- X ——-— X cf. ----- cf. Mangelia aff. M. rhyssa Dall -------------------- -- X ___,. ----- ---- '? X .- --------- ---— ----- Daphnella fuscoligata Dall ------------------------ ---—-¢----« ---------- ---- ----- X ---------- )( cf. Mitromorpha of. M. filasa Carpenter ------------------------- ---- ----- —--- X ----- ----< ----- ---- 7 Mitromarpha gracilior (Hemphill in Tryon) -------------- cf. ---- X ---- cf. ----- (:1 cf ---- ----- M. aspera (Carpenter) ---------------------------------- cf. ---- ------------------- -----l ----- --------- X ----- ---- ----- ---- Glyphostoma n. sp.? -------------------------------- a ------------------ ---- X --------------- ---- ----- ---- ----- ---- ----- ---- Cytharella? sp..— --------------------------------- ~ ---------- ---- ----- -—------- ---------- X ---- --~— ---- X —--- ----- ---- Terebra (Striaterebrum) aff. T. lucana Dall ----------------- X ----- ---- ----- ----« ---------- ---- ---- ---- -----—-- ----- ---- Acteacina culcitella (Gould) --------------------------- X ---------- ---- -------------------- ---- ---- ---- ---—---- ----- ---- Coleophysis harpa (Dall) ------------------------------------ ---- ----- ---- ----- -----1---- ? ---- ---- X r-------- ----- ---- See footnote at end of table. PALEIONTOLOGY deposits of Pleistocene age on San Nicolas Island——Continued 45 Remarks Forms not known to be living, new fossil records 1, and variant forms ’ Recorded geographic ranges only for forms now living north or south of latitude of San Nicolas Island or close to their northern or southern limits. Depth ranges only for forms restricted to deep sublittoral zones off southern California2 NOt previously reported as fossil1 ------------------------ . ............. Not previously reported as fossil1 .......................................... An innomplete shell from SN—7 may be E. tinctum (Carpenter) ................. Not previously reported as fossil?I .......................................... Thicker shelled and with more varices than typical form --------------------- Round-shouldered short-spired small form that may be T. emarginata ostrina Could “ore elongate than typical form; sculpture subdued .......................... Small individuals from SN-l may be A. versicolor incisa Dall ................ Not known to be living’u A strongly sculptured form occurs at SN-2, SN-3, SN-S, SN-lO, SN-ll. Bare in late Pleistocene Large individuals at SN-3 are very close to ”Fusus” portolanesis Arnold ----- Not previously reported as fossifl ------------------------------------------ A short-spired-round whorled form (M. the typical at SN-l A very short spired form occurs with the typical at SN-11 ................... Incomplete shells from SN-lO may be 0. baetica Marrat in Sowerby ............ idae montereyi Berry) occurs with Extremely variable in shape and ornamentation ------------ i ................... Longer apertureand body whorl than typical form ............................ . More robust and slightly coarser sculptured than typical form ............... Shells from SN-ll and SN-l4 may be intergrades between M. filosa and M. gracilior Thicker shelled, shorter spired, and slightly larger than typical form; fewer spiral cords Known only from San Diego. La Jolla, Calif., to Magdalena Bay, Baja Califl Depoe Bay, Oregon, to Catalina Island in 50 fathoms San Diego(?). Sitka, Alaska,to San Pedro in 20—35 fathoms. San Diego(7). Point Conception, Calif., Calif. Monterey(7). Santa Barbara, Calif., to San Ignacio Lagoon, Baja Calif. to Magdalena Bay, Baja Forrester Island, Alaska, to Catalina Island in 30 fathoms. Middleton Island, Alaska, to San Diego, Calif. Monterey to Catalina Island. Half Moon Bay, Califuto Coronado Islands, Baja,CaliL Shumagin Islands, Alaska,to San Diego in deep water San Diego(?), Todos Santos Bay, Baja Calif, toPanamm Redondo Beach, Calif., to Panama. Chiachi Islands, Alaska, to San Pedro. Chirikof Island, Alaska Bare north of San Pedro, Baja Calif. Puget Sound to Todos Santos Bay, Baja Calif. to Monterey. south to Point Abreojos, Monterey(?) to San Diego; off Catalina Island in 30-60 fathoms. Coast of Mendocino County. Farallon Islands to San Diego. Monterey to Coronado Islands. Off Redondo Beach in 35 fathoms and San Pedro in 123 fathoms. Forrester Island, Alaska, to Catalina Island. La Jolla, Calif., to Gulf of California. Santa Margarita Island to Cape San Lucus, Baja Calif. 46 GEOLOGY OF SAN NICOLAS ISLAND Table4.——Checklist of fossils from terrace Locality number and altitude in feet above sea level Specles SN~15 SN.1 SNA12 SN-13 SN'4 SN-10 SN-14 SN-16 SN-ll SN-7 SN-2 SN-3 SN-6 5N.5 SN-8 SN-9 202 45-60 65-70 80-85 851 375* 425* 470* 590* 555* 730* 735* 815’ 540* 885* 900* Gas_tropoda—Cantinued Trimusculus reticulatus (Sowerby) ...................... X X X ___- _____ ---—-A ..... X X X X ___- -_-_ _-_- ..... “SiphonariaHbrannani (Stearns) ------------------ -- X ___- ___- ___-—_— ............. X ___- ___- X ___- ___- ___. _____ Terrestrial Gastropoda: Micrarionta sadalis (Hemphill) ————————————————————————— X ——_- ___- ___- .................... ___- -.-.).---.--.- ___- ---- ..... Quickella cf. Q. rehderi Pilsbry ----------------------- X --—- ---- —-—- .................... ---_ ----h-.-.---- -.-- .-n ..... Scaphopoda: Dentalium semipolitum Broderip and Sowetby? ------------ - X ---- ——-— >—-— X __________ X ___. ....;..-.-.-.- ___. -_-_l._-.._ Pelecypoda: Glycymeris subobsoleta (Carpenter) ---------------- ---—J X X -—-— —-—— X cf. .......... .--_ X X ___-“.-- ___- ..... Arca sisquocensis Reinhart, large form ---------------------- ---- ——-- ~--- 7 --——. .......... ___- ___. ..... *Anadara multlcostata (Sowerby) ——————————————————— ___- ..... Mytilus californianus Conrad ---------------------- ._._ Cf_ Septifer bifurcutus (Carpenter) ------------------- ---- --.. Modiolus farnlcutus (Carpenter)———- ————————————— ___- ___- Pecten diegensis Dal]? ------------------------- ---. ___- P. vogdesi Arnold —————————————————————————————— ___- _--_ Chlamys hastatus (Sowerby) ------------------------ ———> —.>. Aequipecten cf. A. circularis aequisulcatus-nv-v ----- ___- X ..... ___- .................... ___- ___. __________ ___- ___- ___. (Carpenter) Hinnites giganteus (Gray) ------------------------- X ----- X X X ———————————————————— X X X .......... ---- ___- Ostrea luridu Carpenter -------------------------------- X of. ----- --—- ____________________ ___. ___. ___. __________ ___. ___. Bernardina bakerl Dall --------------------------------- X ———— ————— ———— X _____ X X X .... ___. 7 ___. .-,. ___- Miodontiscus prolongatus Carpenter -------------------------- ———— ————— ———— X X __________ ___- ___. ___. ..... .-.- .-.- .... Clans subquadrata (Carpenter) -------------------------- X X X ‘X X ————— cf, X X X X X —-_- X __-. Cyclocardia cf. C. langini (Baily) -------------------------- --—- ----- ---. X _____ ____-_‘_-----_ -_-- ____r___.____ ___. ___- Milneria minima Dall ........................................ ___- _____ .-._ ____________________ ___- ___. X __________ ____ ___. Parvilucina tenuisculpta (Carpenter) ------------------------ _-_— ————— —_—— ____________________ ___- ___- ___- _____ -_-- ___- X Epilucina californica (Conrad) .................... X Diplodonta orbella (Gould)-- ___. Lusaea cf. L. cistula Keen ------------------------ ___. Turtonia cf. T. minuta (Fabricius) ---------------- ___- K611ia7 cf. K. laperausii (Deshayes) -------------- ___. Tellina salmonea (Carpenter) ...................... ____ Cumingia californica Conrad" 7 Spisula planulata (Conrad) ---------------------------------- X _____ ___- _-.- .................... -.-- -u- __________ ‘___ --__ Schizathaerus nuttalli (Conrad) ............................. X _____ ___- ___. X __________ .-.- ___. Ventricularta fordii (Yates) ——————————————————————————— —-—.———.—.1 X ___- -.-_ X __________ _--- -_-- [lumilaria perlaminosa (Conrad) ---------------------------------------- ___- ___- ............... ___- cf. X .......... __-- ___- Protothaca staminea (Conrad) ...................... .‘_._ X .......... ___- cf. .......... X ___- CL X __________ ___. ,___ Saxidomus nuttalli Conrad ----------------------------------- X X —..- X ? —————————— --—— X X ,__--._.-._-_- ‘___ Irus lamellifer (Conrad) ------------------------------- X X cf. ----,—---- ---------- cf, cf. X X __________ ___. __.. Transennella tantilla (Gould) -------------------------- X X X ___. X _____ X x IX X X X X ___- X Petricola carditoides (Conrad) ------------------------- X --—- X —-—— cf. ............... ——-— X X .......... __-- ___. Trachycardium quadragenarium (Conrad)? ———————————— F——-— ----- X ————— ‘n‘F-U' ............... —-—— 5p. -... _____ ___-“.-- ___- Clinocardium nuttallii (Conrad)? .................. X _____ X ___- ___. Triganiacardia biangulata (Sowerby) --------------- .......- _____ ___. ___. Chama pellucida Broderipu X __________ ___- X Gari californica (Conrad)- X .......... ____ ___- Panope generosa (Gould) --------------------------- cf. .......... ___. ___- Hiatella arctica (Linnaeus)- --------------------------- cf, .......... ——.— X .................... _.-_ cf. __________ ___. 76f Parapholas californica (Conrad) ------------------- ___- cf‘ .......... ___- ___- Penitella penita (Conrad) ------------------------- osp_ x __________ ___. ___- Thracia curta Conrad ------------------------------ X ___- ___- _____ ___- ___- Amphineura: Tonicella lineata (Wood) -------------------------- ---_ X ___- cf, ___- _________________________ --_- Cf‘ ___--‘__d____ ____ Cyanoplux cf. C. dentiens (Gould) ------------------ ..-. X .......... ___. _____ ___- ............... ___. ___. ..._ ..... ___. ____ ISOhnochiton (Lepidozona) cf. I. californiensis-.. _..._ X .......... ___. ......................... ___- ..-. .-.- _____ ___. .... Berry > Ischnochiton (Lepidozona) sp. ---------------------- ___. X —————————— --_- ......................... ___. ...- ___. _____ -_._ ___. Ischnochiton (Stenoplax) cf.I.canspicuus (Carpenter) ——-— X ---------- --—- cf. —--- --------------- ---- ---- --—— ————— ___— -—-- Ischnochiron (Stenoplax) sp. ----------------------- ___. x —————————— .—-_ ......................... ___. X ___. _____ .___ ___. Dendrochiton of. D. thamnopora Berry---— --- —--- x ---------- --_- ..... ___. .......... .-.-.-._. -.._ __________ ___. _-__ Callistochiton crassicostatus Pilsbry -------------- ---— X ---------- ---- ----- ___. _____ X ___.“... ___- .......... ___- -_.- Mopalia cf. M. Ciliata (Sowerby) ------------------- ---- X ---------- ---- --~- .................... ___- ___. ___. ..... ____ ____ See footnote at. end of table. PALEONTOLOGY deposits of Pleistocene age on San Nicolas Island——Continued 47 Remarks Forms not known to be living, new fossil records 1, and variant forms Recorded geographic ranges only for forms now living north or south of latitude of San Nicolas Island or close to their northern or southern limits. Depth ranges only forforms restricted to deep sublittoral zones off southern California2 Small shells assignable to C. carteziana Dall [?=G. migueliana Dalq are present at SN-l, SN'3, SN-IO, SN-lL Not known to be living. Length from 3.0 to 65-5 mm;'type measures 15.4 mm and may be an immature individuaL The northern form C. hastatus hericius (Gould) occurs with the typical form at SN-3_ Not previously reported as fossill .......................................... More ribs than typical form. Fewer ribs and higher shell than C. barbarensis (Stearns). Not previously reported as fossilh Not previously reported as fossil ------------------------------------------ Not known to be living}. Pleistocene age. Not previously reported from strata of Pleistocene age in Californid ------- Newport Beach, Calif.(7), to Panama. Trinidad, Calif., to San Pedro and Cortes Bank. Punta Eugenia, Baja Calif., to Paita, Peru. Monterey to San Diego; off Redondo Beach in 25~50 fathoms and 123 fathoms off San Pedro. Point Loma, Calif., to Magdalena Bay, Baja CaliL Middleton Island, Alaska, to San Diego. Off Catalina Island in 50-300 fathoms. Nunivak Island, Alaska, Baja Calif. to Coronado Islands, Baja Calif. Aleutian Islands to Coronado Islands, Off southern California in 20—68 fathoms Monterey to San Diego. Bering Sea to San Diego. Redondo Beach, Calif., to Guayaquil, Ecuadon to San Diego. Alaska, to San Diego. Coos Bay, Oregon, Chirikof Islands Aleutian Islands to San Luis Obispn County and San Diego(7). Forrester Island, Alaska, to San Diego. 48 GEOLOGY OF SAN NICOLAS ISLAND Table4.——Checklist of fOSsils from terrace Locality number and altitude in feet above sea level S ecies p SN-IS SN-l SN-l? SN-13 SN-‘l SN~10 SN-ltl- SN-léSN-ll SN-7 >N-2 SN-3 SN-G SN-S SN-8 SN-9 202 45-60 65.70 30.35 85* 37st 4251 470* 590+ 665* 730i 7351 815i 840i 885’ 900* Amphineura-Continued Mopalia muscosa (Gould) .......................... +-—-- X ..— cf. cf. >< ——-- cf. -.-. cf. X X X .......... M. hindsii (Reeve) ------------------------------------------------- ———- ---- cf, __.. X .................... Placiphorella cf. P, velata (Carpenter) --------------- X -------- ---- ---- —--- .--— ......................... HCryptmflliton" stelleri (Hiddendorff) ................. X H. X x -... __-- __-. .................... ___..1 Coelenterata: Balanophyllia elegans Verrill ------------------------- X -_. X X X X ..... X X X .......... X ..... -.._. Annelida: Dadecaceria flstnlacola Ehlers? [Serpula ---------- —--—- ..... —--- ---- ——-- .--- ..... -__- -.-. X --.-.--.-.1 ..... _-.-- octoforis Dallj Echinodermata; Strongylocentrotus purpuratus (Stimpson) --------- L--—- ° V X -—-- 7 ---- ----- 7 ---— ----- X --------- 7 ----- Strangylocentratus cf. 8. franciscanus (Agassiz)— ————— 1—”.— ........ ———. 7 ..._ .......... 7 X ..... ? '> _____ 7 Dendrflster cf. D. excentrlcus (Eschscholtz) ---------------- X _____ ..._ ._-- ..-_ _-.- ..... ._.- .___ _________________________ Brachiopoda: Terebratulina ungulcula Carpenter --------------------- X ""“'1"”‘ _... ........ ..... ._.. _... ................... .__._ Terebrata'lia cf. T. transversa Sowerby ------------------------ ”UT.” ——-_ .---—-_-. ..... ---- —--- X _---._.-- .......... Cirripedia: Tetraclita Squamosa rubescens Darwin ————————————— --.- X 9 9 -_.- X 7 _-_- ..... ’2 j Balanus cf. 8. nubilis Darwin -------------------- .--- .......... --._ X X ..... X _____ __.- Balanus cf. 8. tintinnubulum californicus Pilsbry ---------- X ——-- ————— --.— X ----- —-—- ---— __________ ---_ .......... Balanus spr -------------------------------------------------------- ——-- —--- -..—.——-- ..... --—_ .—-— X —---—..-. __________ 1These records compiled from reports issued before November 1959. 2Sources of geographic and bathymetric range data: (1957), bathymetric ranges supplementary to Burch (1944—46); Ball (1921) Bormann (1946), geographic range of some species of Ocenebra; Burch geographic ranges of Amphineura; Ball and Bartsch Keen (1937), range data not included in Burch (1944-46); Smith and Gordon (1948), range data supplementary to Burch (1944-46M PALE ONTOLOGY deposits of Pleistocene age on San Nicolas Island—Continued 49 Remarks Farms not known to be living, new fossil recordsl , and variant forms Recorded geographic ranges only for forms now living north or south of latitude of San Nicolas Island or close to their northern or southern limits. Depth ranges only for forms restricted to deep sublittoral zones off southern California2 Aleutian Islands to Monterey County and San Nicolas Island(?). British Columbia to the Channel Islands. Off Monterey in 10-40 fathoms. (1944-46), primary reference for geographic and bathymetric distribution of Gastropoda and Pelecypoda; Clark in Natland (100”), geographic and bathymetric ranges of selected Pyramidellidae; Ilertlein and Grant (1944b), range data on Brachiopoda; and \\'norlring and others (1°46). range data supplementary to Burch (1944-46)- 50 GEOLOGY OF SAN NICOLAS ISLAND TABLE 5.—Mollusks from selected low, intermediate, and high terrace deposits on San Nicolas Island that are known in the living faunas only as extralimital and near limital, or that are not known to be living [Amphineura, Scaphopoda, and Pyramidellidae not included] Locality No., altitude (feet), Forms now living only south of the latitude of Forms now living at or near their northern limit in the lati- Forms now living only north of the latitude of Forms now living at or near their southern limit in the lati- Forins not known to be living numberoftorms San Nicolas Island tude of San Nicolas Island San Nicolas Island tude of San Nicolas Island Low terraces Gastropoda: Gastropoda: Gastropoda: Gastropoda: Gastropoda: Calyptraea cf. 0. mam- Tegulacf. T.aureotincta(Forbes) Acmaea instabilis (Gould) Calliostoma ligatum (Gould) Balcia cf. B. prefalcata milaris Boderip Arene acuticostata radiata Tegula brnnnea (Philippi) Astraea gibberosa (Dillwyn) (Bartsch) Mangelia afi. (Dall) “Tegula” montereyi (Fischer) Spiroglgphus litnellus (Mérch) rhgasa Dall “Risaoina” of. “R.” aequis- Ocenebra lurida (Midden- Opulia wroblewakyi chacei Terebra (strioterebrum) culpta (Keep) dorfl)? Strong afl. T. (8.) lucana Amphithalamus inclusus Car- Ocenebra interfoua clathrata Ocenebra lurida mnnda (Dall Dall penter (Dall) in Williamson)? Pelecypods: Crepz'dula cf. 0. elacavata Bareotrophon stuarti (Smith) SN—l, SN—l2, Anadara mnlticostata (Broderip) var. SN—13 (Sowerby) Fartulnm occldentale Bartsch Barbarofuaus kobelti (Dall) 45-85 Pecten nogdesi Arnold Fartulum of. F. orcutti Dall Mitra idae Melvill 150 Bernardina bakeri Dall Ceratostoma nattalli (Conrad)? “Progabbia” cf. “P.” cooperi Jaton of. J. festivns (Hinds) (Gabb) Morula? cf. M. lugubris (C. B. Mangelia interfossa Carpenter Adams) Pelecypoda: Pelecypod: Chlamys cf. 0. hastatus (Sowet- Trigoniocardia biananlata (Sow— by erby) Irus lamellifer (Conrad) Gari californica (Conrad) Parapholas californica (Con- rad) Penitella penita (Conrad) Intermediate terraces Pelecypoda: Gastropoda: Gastropoda: Gastropoda: Gastropoda: Bernardina bakeri Dall Amphitahlamus inclnaus Car- Papillaria papilla (Gould) Acmaea mitra Eschscholtz Calicantharns fortis penter Ocenebra interfossa clathrata Calliostoma ligatum (Gould)? (Carpenter) Morale? cf. M. lugubris (C. B. (Dall) Lacuna cf. L. carinata Gould Balcis cf. B. arnoldi Adams) Amphisaa columbiana Dall Spiraglyphus lituellns (Morch) (Bartsch) Opalia wroblewskyi chacei Pelecypod: Strong Arca sisqnocemis Rein- Ocenebra lnrida munda (Dall hart? in Williamson)? SN—IO Boreotrophon stuarti (Smith)? 375 Barbara/um: kobelti (Dall)? 74 Manqelia interfoasa Carpenter Pelecypoda: Chlamy: haatatus (Sowerby)? Miodantiacua pralonaatus Car- penter Tellina aalmonea (Carpenter) Clinocardium nuttallii (Con- rad)? Gastropoda: Gastropoda: Gastropoda: Gastropoda: Gastropoda: Acanthina of. A. lugu- Tegula gallina multifilosa Tegula brunnea (Philippi) Acmaea mltra Eschseholtz Calicantharus fortis bris (Sowerby) (Stearns) Puncturella cooperi Carpenter? (Carpenter) “Rissoina” aequiscnlpta Astraea cf. A. gibberosa (Dill- (Keep) . Wynn) SN—ll Amphithalamns melnsus Car- Spiroglgphus litnellus (Merch) 590—595 penter Mitra idae Melvill 70 Fartnlnm cf. F. orcutti Dall Pelecypoda: Matron cf. M. lividus A.Adams Modiolns cf. M. fornicatus (Carpenter) Iras of. I. lamellifer (Conrad) High terraces Gastropoda: Gastropoda: Gastropoda: Gastropoda: Gastropoda: Alvania cf. A. lirata Arene acuticostata radiata Haliotis kamtschatkana Jonas Acmaea mitra Eschscholtz Crepidnla princeps (Carpenter) (Dall) Tegnla brunnea (Philippi) Puncturella of. P. cooperi Car- Conrad, large form Elachisina grippi Dall Rissoina of. R. coronadoensis Rissoina cf. R. hannai Smith penter Calicantharusform Mangelia all. M. rhyssa Bartsoh and Gordon Tegula hrunnea fluctnosa Carpenter Dall Amphithalamus inclusus Car- Alvania all. A. dinora Bartsch (Dall) Pelecypoda: . . penter Velutina afl. V. laem’gata Calliostoma of. C. ligatum Arca sisquocemu Rein- Crepidula cf. 0. euavata (Brod- (Linnaeus) (Gould) at . ‘ erip Ceratostomafoliatum (Gmelin) Astraea gibberosa (Dillwyn) Humilana perlammosa Fartulum occidentale Bartsch Ocenebra cf. 0. lurida (Mid- Lacuna cf. L. carinata Gould (Conrad) SN-Z, SN—3 dendorfi) Spiroglgphus litnellus (March) 730-735 Onenebra cf. 0. interfossa clath- Barbarofusus kobelti (Dall) 140 rata (Dall) Mitra idae Melvill “Searlesia” dim (Reeve) Barbarofusns harfordi (Stearns) Pelecypoda: Chlamya hastatus hericius (Gould) » Peleeypoda: Modiolus fornicatus (Carpen- er Chlamys haatatus (Sowerby) Irus lamelli’fer (Conrad) Clinocgrdium nuttallii (Con- Parapholaa califomica (Con- ra Penitella penita (Conrad) PALEONTOLOGY 51 CAUSES AND EEEECTS or SUREACE WATER TEMPERATURE VARIATION OF]? SOUTHERN CALIFORNIA AND NORTHWESTERN BAJA CALIEORNIA Causes other than the advance and retreat of polar icecaps and changes in worldwide oceanic circulation may have brought about. temperature changes of the California coastal surface waters during various ter- race-cutting episodes. The prevailing westerly winds have a pronounced seasonal effect on the surface water temperatures along the southern California and Baja California coasts at the present time (Sverdrup, J ohn- son, and Fleming, 1942, p. 724—725; Kuenen, 1950, p. 31). Changes in the direction or force of the prevail- ing winds, even for a short period, may result in a temperature differential of several degrees in the surface water. Extraordinarily warm surface water, temperatures recorded ofl' southern California in the period 1850—1870, in 1926, 1931, 1941, 1947 (Hubbs, 1948, p. 469—474), and again in 1957 and 1958, pre- sumably were due to abnormalities in atmospheric cir- culation with a resulting decrease in intensity of the prevailing westerly winds (Namais, 1959). During the summer of 1957 surface water temperatures averaged 2 to 3 degrees Fahrenheit higher than usual at coastal gaging stations and averaged slightly more than 5° above normal in some areas 150 miles off the coast. In Santa Monica Bay, the water temperature was 53° F. above the mean during February 1958. Cooler-than- normal surface water temperatures would be expected to result from increased intensity of the prevailing winds. Another possible cause of cold upwelling is that the southeast-flowing California Current may produce a drag effect on the surface water above Santa Rosa—Cortes Ridge to force this water seaward, and the replacement of the surface water, in part, by subsurface water from the deep basins may result in cooler surface water temperatures (Orr, Emery, and Grady, 1958, p. 929). Deep indentations in the coastline in the form of shallow embayments warmed by solar radiation adja— cent to open coast waters cooled by upwelling create habitats and depositional environments that might easily result in an anomalous association of dead shells after a short distance of transport. There is a striking change in surface water temperature from the northeast to the southwest side of Punta Banda, which forms the southern extremity of Bahia Todos Santos in Baja California. Here the seasonal temper— ature differential from the protected shallow bay to the windy outer coast may be as high as 21°F. (Wal- ton, 1955, p. 966). High coastal mountain ranges produce a dampening effect on the prevailing winds along parts of the coast of southern California with the result that near-shore surface waters in some areas remain relatively warm. The Santa Ynez Mountains along the Santa Barbara coast and the Santa Monica Mountains to the south- east tend to deflect prevailing winds. During part of late Pleistocene time the Santa Monica Mountains presumably extended west approximately 85 miles and included the area that is now occupied by the northwestern group of Channel Islands. This topo- graphic barrier undoubtedly diverted coastal currents and resulted in a local pronounced temperature differ- ential (Grant and Gale, 1931, p. 39, 64; Woodring and others, 1946, p. 102). However, this peninsula may have existed only during low eustatic stands of sea level. Although large-scale topographic barriers to wind and oceanic currents and expansive coastal indentations almost certainly affected water tempera- ture locally along the mainland coast, these features probably did not significantly alter surface condi- tions around ancestral San Nicolas Island except at the time of the cutting of the lower submerged terraces. The composition and distribution of the Pleistocene and Recent floral and faunal assemblages along the coast of southern California and northwestern Baja California apparently is governed to a large degree by surface water temperature (Dawson, 1951, p. 39— 58; Valentine, 1955, p. 466—468; Emerson, 1956a, p. 334—335). From the preceding discussion it can be ascertained that both cool and warm surface water probably existed in adjacent areas and that local cold upwellings or protected areas of warm surface water may have caused faunal and floral gaps or displace- ments and the resultant seemingly anomalous mixing of molluscan faunas in places along the coast of Cali- fornia and Baja California in Pleistocene time. Rapid distribution of hardy forms of mollusk larvae from the north by a cold ancestral California Current and from the south by warm countercurrents or warm surface water resulting from diminished prevailing winds could account for an influx of both cool and warm water forms into close proximity in California coastal areas. Protected shallow bays and areas of local intense upwelling would then provide suitable temperatures for the existence of migrant cool-water and warm-water adult forms, for at least one, or at most a few, generations. INADEQUACIES or PALEOECOLOGIC COMPARISONS or TERRACE FAUNAS The chief difficulty in making paleoecologic infer- ences from the composition of the terrace faunas at San Nicolas Island is the lack of complete faunal and ecologic data concerning the Recent forms that now live around the island. The insufficient collected living material, even from the intertidal zone, results 52 GEOLOGY OF SAN NICOLAS ISLAND in a poor correlation with the mainland coast, a defi- ciency which, in turn, hampers comparisons with the Pleistocene faunas both on the island and along the mainland coast. The dominant rock—cliff and tide-pool facies of the ancient outer coast indicated by constituents in the fossil collections is not particularly significant when employed to infer isothermal shifts in Pleistocene time because most of the abundant forms found in this facies are geographically widely dispersed in both the fossil and living faunas. Fossil assemblages from re— stricted environment or mixed habitats are more likely to yield mollusks that reflect changes in surface-water temperature. The recorded geographic and bathymetric ranges of living species are far from complete, especially along the coast of northwestern Baja California. Some early reports of geographic ranges in southern Cali- fornia are undoubtedly based on detrital fossil shells reworked into Recent sediments. As a result erroneous conclusions are likely to be derived from strict ad- herence to these data. A further complication of the distributional pattern results from apparent gaps with- in the geographic ranges that presumably are caused by local areas of intense upwelling of cold water such as that found off Punta Santo Tomas, Baja Califor- nia (Emerson, 1956b, p. 394—395), or by embayments of abnormally warm water such as those that occur in Scammon Lagoon and Magdalena Bay in Baja California. There is little doubt that faunal breaks of the same nature or dislocations in molluscan dis- tribution occurred in Pleistocene time along the Cali- fornia coast. F aunal discontinuities and extra-limital occurrences are reflected in deposits of Pleistocene age at Palos Verdes Hills (Woodring and others, 1946, p. 87—89), Newport Lagoon (Brufi, 1946, p. 222), San Diego (Hertlein and Grant, 1944, p. 71—72), and at (several localities in northwestern Baja California (Addicott and Emerson, 1959, p. 21; Emerson, 1956a, p. 325; Valentine, 1955, p. 465, 1957, p. 302). Large shallow embayments of warm water probably did not exist along the coast of San Nicolas Island during late Pleistocene time, but extended periods of inactive upwelling may have produced the warm surface water temperatures necessary to support the growth of south— ern molluscan forms. Another factor to be considered when drawing paleoecologic conclusions, although it may not be significant when applied to late Pleistocene faunas, is the possibility that the physiology or status of evolu— tion of certain organisms may have enabled them to tolerate more diverse environmental conditions in the past. The chemical composition and the nutrient content of the sea water also may have affected the compo- nents within localized molluscan faunas in Pleistocene time just as these factors control assemblage constitu- ents at the present time. Furthermore, anomalous or mixed assemblages us- ‘ ually are present in large accumulations of dead shells resulting from the transport of different environ- ment indicators into the same deposit or from the reworking of individuals from older deposits into younger sediments. Also, the common practice of se- lective collecting rather than collecting bulk assem- blages may lead to errors in paleoecologic interpreta- tion. AGE AND FAUNAL CORRELATION The age of the entire sequence of terrace-deposit faunas on San Nicolas Island is presumed to be Pleistocene and possibly is restricted to the last third of the epoch. No species considered to be restricted to strata of Pliocene age were found on the older high terraces, and a large percentage of the molluscan forms found in each of the terrace deposits is now ‘ living off the California coast. Species considered extinct were not collected on the low terraces, and only 3 percent of the species found on the high platforms are not known to be living. This low percentage of presumably extinct mollusks is generally considered to be sufficient evidence for dating the terrace assemblages as Pleistocene, but it is unlikely that early Pleistocene terrace deposits can be differentiated from late Pleistocene terrace de- posits on a faunalbasis (Woodring and others, 1946, p. 99). Locality SN—3 has yielded forms usually con- sidered to be early Pleistocene guides, or forms that rarely are found in late Pleistocene terrace deposits (large form of Orepidula pm’nceps, Calicanthams for- tis, Humilam'a perlaminosa, and Area sz'squocemz's). The presence of these species is attributed to the survival at San Nicolas Island of a relict fauna not known to occur in the higher terrace deposits along the mainland coast rather than to the deposition of . strata equivalent to the early Pleistocene Santa Bar— bara formation, Lomita marl, Timms Point silt, or San Pedro sand. The apparent lack of tilting even on the highest terrace platforms on San Nicolas Island suggests a late Pleistocene age, although the areal extent of the higher platforms is not sufficient to demonstrate slight regional tilting. Elsewhere in coastal southern Cali- fornia fossiliferous sedimentary rocks designated as early Pleistocene in age are folded and faulted. Mar- ine sediments assignable to the middle Pleistocene are PALEONTOLOG’Y 53 not certainly known in southern California but may be present in the central parts of the Los Angeles and Ventura Basins, where deposition was continuous (Woodring, 1952, p. 402). Late Pleistocene terrace deposits are locally deformed along the margins of the Los Angeles and Ventura Basins. Because no trunc- ated sedimentary rocks of definite early Pleistocene or Pliocene age exist on the island, stratigraphic evi- dence for the age of the terrace deposits is lacking. The absence of Pliocene guide fossils and the low percentage of extinct forms in the terrace deposits on the island are the only available paleontologic evidence that the faunas are Pleistocene in age. The upper age limit for cutting of the lowest emer- gent terraces along the coast of California has been fairly well established at greater than 30,000 years. Selected samples taken at several low terrace localities from Santa Cruz to San Diego, including the marine strata and the associated nonmarine cover, have pro- vided radiocarbon dates that range from greater than 30,000 years to greater than 39,000 years (Kulp and others, 1952; Rubin and Suess, 1955; Rubin and Suess, 1956; Bradley, 1956; Broecker and Kulp, 1957; Carter, 1957, p. 6—7; Hoskins).29 Radiocarbon dates on cal- careous red algae cored from the shelf edge below the supposed deepest submerged terrace off the Palos Verdes Hills at water depths of 334 to 387 feet showed a range in age from 17,000 to 24,500 years (Emery, 1958, p. 56), suggesting that the lowest emergent ter- races are older than the submerged terraces off the California coast. Presumably the lowest well-developed 100-foot terrace on San Nicolas Island is older than 30,000 years, if a physiographic correlation is made from the mainland coast to the island, and if the warm—water constituents of the late Pleistocene Palos Verdes sand and its equivalents correlate with the few warm-water forms from SN—l, SN—12, and SN—13 (see table 5). Definite faunal correlations, terrace by terrace, with other nearby islands and the mainland coast cannot be made with confidence because of the lack of mol- luscan guide species restricted to any single terrace level, the great variety in environments represented by the well—known terrace assemblages, and the scarc- ity of large fossil assemblages on the higher terraces of the mainland. The supposed warm-water elements found in the low terraces on San Nicolas Island strongly suggest a faunal correlation with the fossil assemblages of warm—water aspect that are present on the four lower emergent terraces of the Palos Verdes Hills (Woodring and others, 1946, p. 95) and on the ’9 See footnote 13, p. 10. lowest emergent terrace elsewhere in southern California. Large molluscan assemblages collected by Valentine (1958) from the lowest emergent terrace at Cayucos, which are referred to a central California late Pleistocene faunal province, are strikingly similar to the San Nicolas Island terrace assemblages. Other large faunas composed primarily of the rock-cliff and tide-pool facies that resemble those from San Nicolas Island are known from several localities on the lowest emergent terrace in southern California and Baja California; collections numbering more than 90 species of mollusks are known from the following places: Laguna Beach-Dana Point area (more than 275 forms, Vedder and others, 1957, [localities only]), Point 'Loma (97 forms, Webb, 1947), Punta Descanso area (230 forms, Valentine, 1957), Punta China (96 forms, Emerson, 1956), and Punta Cabras area (99 forms, Addicott and Emerson, 1959) (fig. 18).30 Most of the other large well-known assemblages (more than 100 forms) from the well-developed low terrace in south- ern California represent mixed ecologic facies of bay and estuarine facies such as those reported from Pot— rero Canyon near Santa Monica (Woodring in Hoots, 1931, p. 121—122; Valentine, 1956), Playa del Rey (Willett, 1937a), Palos Verdes Hills (Woodring and others, 1946, p. 95—96), Newport Beach area (Brufl', 1946), and San Diego area (Arnold, 1903, p. 58—64; Hertlein and Grant, 1944a, p. 66—72). Exceptionally large mixed faunas also occur on the next highest well-developed terrace at several localities along the coast; the best known are at Palos Verdes Hills (Woodring and others, 1946, p. 93—95) and perhaps at Capistrano Beach (Willett, 1937b). There is no justification for direct faunal correla— tions between the high terraces on San Nicolas Island and those found elsewhere in southern California and northwestern Baja California even though many of the individual platforms may have been cut con- temporaneously in different areas. Only meager fossil assemblages have been obtained from terrace deposits above 400 feet along the California coast with the notable exceptions of the Palos Verdes Hills, where several collections have yielded faunas of the rock- cliif and tide-pool facies up to an altitude of 1,215 feet (Woodring and others, 1946, p. 93-95), and in the Ventura area, where a mixed ecologic facies is represented at altitudes of 500 and 700 feet (Putnam, 1942, p. 699—700). Many of the species from these localities are the same as those found in the terrace deposits above 400 feet on San Nicolas Island. 3° These records are compiled from reports published before November 1959. 54 35-00' L ) Point Sal 1 0 Santa Maria CAL Pom! Conception San Miguel Island Santa Cruz Island I <5: 34'00' W N ac Fotrero Canyon GEOLOGY OF SAN NICOLAS ISLAND EXPLANATION x19 Selected locality where fossil collections have been made LOS ANGELES | 7 121”” Santa Rdsa Blank/J1 w Anacapa Islands Playa del kw Long geagch Palos Verdes Hills X9 Newport Beach (1) Santa Barbara Island a O San Nicolas Is a d x C " 120 00 x 33‘00’ 4 SantaI Catalina Island Laguna Beach ‘ Q Dana Pomi ’ 15 : Capis‘rnno Beach 6 Oceanside m \:&m1 Clemente lsland 17819\ n Diego P int Lolmaa 20 TES mrED 5'”— mace “9‘00 40 MlLES Coronado Island“: :23\ ‘9'? '7 Punta Descanso Ensenadag 0 a «1, ‘A :7 118'00' Punta Cabras 25 117‘00’ FIGURE 18,—Map showing distribution of selected fossil localities in terrace deposits of southern California and northwestern Baja California (Santa Maria to Punta Ca- bras) that have yielded 40 or more molluscan forms. Only a few localities in the Ventura area and in the Palos Verdes Hills contain fossils on wave-cut platforms that are higher than the lowest emergent terrace. Santa Maria area, 10c. 263 (Woodring and Bramlette, 1950, p. 53—54) Loc. H56—64 (Hoskins,1 p. 59) Goleta (Oldroyd and Grant, 1931; Hoskins,l p. 58—59) Santa Barbara, loc. H56—21 (Hoskins,1 p. 57) Carpinteria (Grant and Strong, 1934) Ventura area, loo. 1 (Putnam, 1942, p. 699—700) Potrero Canyon (Woodring in Hoots, 1931, p. 121-122; Valentine, 1956) Playa del Rey (Willett, 1937a) Palos Verdes Hills area (Arnold, 1903, p. 22—47; Woodring and others, 1946 p. 54-106; Hoskins,l p. 53—54) 1 Signal Hill area (DeLong, 1941) 11. Huntington Beach (Hoskins,1 p. 49—50) 12. Newport Beach area (Brufi, 1946; Hoskins,l p. 46—48) 13. Laguna Beach area (Vedder and others, 1957 [localities only]; Hoskins,1 p. 45) 14. Dana Point (Vedder and others, 1957\[locality only]) PWFP’?‘*S‘7.‘°E‘ .0 KITCHEN MIDDENS The term “kitchen midden,” an anglicized Danish word, is applied to any occupational debris that de- marks areas of prehistoric settlement. Extensive refuse dumps and habitation sites of the former Indian popu- lation on San Nicolas Island are concentrated in the dune areas on the western part of the island near the coast but also occur sporadically on the upper terrace 15. Capistrano Beach (Willett, 1937b) 16. San Clemente (Vedder and others, 1957 [localities only]; Hoskins, 1 p. 43) 17. Pacific Beach (Arnold, 1903, p. 58, 60—64) 18. Point Loma (Webb, 1937) 19. Spanish Bight (Arnold, 1903, p, 59, 60—64; Hertlein and Grant, 1944, p. 67—70) 20. Indian Point (Arnold, 1903, p. 59, 60—64 [foot of 26th street]) 21. Border locality (Emerson and Addicott, 1953) . UCLA Ice. 3161 and 3160 (Valentine, 1957) . Punta Descanso area (Valentine, 1957) 22 23 .24. Punta China area (Emerson, 19568) 25 . Punta Cabras area (Addicott and Emerson, 1959) l Hoskins, C. W., 1957, Paleoecology and correlation of the lowest emergent California marine terrace, from San Clemente to Halfmoon Bay: Stanford Univ., unpublished Ph. D. thesis. platforms near the center of the island. The only places that appear to be entirely free of discarded shell material are the higher marine terrace levels at the east end of the island and the steeper parts of the south side some distance from the shore. Description of the middens and their content is included in this report not only as evidence for the length of prehistoric habitation of San Nicolas Island KITCHEN MIDDENS 55 but also as a means of inferring climatic conditions and surface sea-water temperature during early Re- cent time. Near the west coast of the island several of the larger middens cover dunes that measure from 1,200 to 1,600 feet in length and from 300 to 500 feet in width. The highest of the midden-covered dunes is 50 to 70 feet above the surrounding areas. Few of the concentrations of- shells marking the occupational levels are more than 1 or 2 feet thick on the tops of the dunes, but some shell accumulations on the margins attain a thickness of 5 feet. Ordinarily the eroded sides of the dunes are strewn with midden debris de- rived by wind deflation from the relatively thin oc— cupational levels, giving the false impression of a thick sequence of levels. However, the deepest ob— served shell layers are but 5 feet below the present dune surface. Most of the shell heaps in the high central portion of the island and along the central south coast are much smaller than the large mounds on the west end of the island. A map showing the location of 68 archeological sites was compiled by Meighan and Eberhart (1953, p. 110, fig. 33), but these authors do not include several fairly extensive middens on the south side of the island in the areas northwest and southwest of Seal Beach. A few additional sites are present on the upper surface of the island and near the coast between Dutch Harbor and Jehemy Beach. The same authors postu- late an aboriginal population-of between 600 and 1,200 individuals at the time of maximum development just prior to European contact (Meighan and Eberhart, 1953, p. 119, p. 123). The most abundant constituent in the kitchen mid— dens is mollusk shells, followed in diminishing order by rock fragments, mammal, fish, and bird bones, and a variety of artifacts. The lists of mollusk (see table 6) and associated marine invertebrate species observed in the shell mounds indicates the wide variety of forms used by the early islanders for food, ornaments, and artifacts. Several species that probably do not now live on San Nicolas Island suggest that some were imported by the natives from nearby coastal areas (for example, Traehycardium datum, PachydeSma crassatelloides) or are locally extinct (for example, “Org/ptochiton” stelleri). In addition to the mollusks, the bones of fish, birds, sea lions, seals, sea otters, whales, porpoises, dogs, and foxes are present in vary- ing abundance. A diversified assemblage of artifacts is briefly described by Meighan and Eberhart (195), p. 111~112, p. 119—123). The list of artifacts includes tools made of ground stone, chipped stone, shell, and bone; ornaments and burial offerings of shell, bone, and stone; textiles and cordage; and “foreign” arti— facts such as pottery and worked stone of exotic origin. TABLE 6.—List of invertebrates observed in kitchen middens IA, abundant; 0, common: U, uncommon; R, rare] Gastropoda: Acmaetr limatula Carpenter ___________________________ C Acmaea, mitra Eschscholtz ____________________________ R Lottia, gigantea (Sowerby) ____________________________ A Acmaea pelta nacelloides Dall 1--. ______________________ Haliotis corrugata Gray 1 Haliotis cracherodii Leach ____________________________ A Haliotis rufescens Swainson ___________________________ A M egathura crenulata (Sowerby) ................. ’ ...... U Diodora aspera (Eschscholtz)1 Norrisia riorrisi (Sowerby) ___________________________ C Tegula. brunnea (Philippi) ____________________________ A Tegula funebralis (Adams) ___________________________ A “Tegula” montereyi (Fischer) ......................... R Astraea gibberosa (Dillwyn)1 Astraea undosa (Wood) ______________________________ C Lunatic lewisii (Gould) ______________________________ U Zonaria spadicea (Swainson) _________________________ U Pusula califorrtiana (Gray___-_- _______________________ R Pusula solandri (Sowerby)1 Bursa californica Hinds ______________________________ R Ocenebra. circumtezta (Stearns)1 Acanthina spirata punctulata (Sowerby)1 Barbarofusus arrtoldi (Cossmann) _____________________ R Mitra idae Melvill ___________ y _______________________ U Erato vitellirta Hinds 1 Oliuella baetica Marrat in Sowerby 1 Olivella biplicata (Sowerby) ___________________________ C “Progabbia” cooperi (Gabb) __________________________ R Trimusculus reticulatus (Sowerby)1 Land snails, unidentified _____________________________ A Pelecypoda: M ytilus californianus Conrad _________________________ A Septifer bifurcatus (Carpenter) ________________________ C Aequipecten cf. A. circularis (Sowerby) ________________ R Hirmites giganteus (Gray) ____________________________ C Epilucina califomica (Conrad) ________________________ R I rus lamellifer (Conrad)1 Pachydesma crassatelloides (Conrad) [Tivela stultorum (Mawe)] _________________________________________ R Protothaca staminea (Oonrad) _________________________ R Ventricolaria fordii (Yates)1 Trachycarium quadragenarium (Conrad) _______________ R Trigoniocardia biangulata (Sowerby)1 Laevicardium elatum (Sowerby) _______________________ U Amphineura: Ischnochiton conspicuus Pilsbry 1 “Cryptochitort” stelleri (Middendorfi) __________________ C Small chitons, unidentified ___________________________ C Echinoidea: Strongylocentrotus framiscanus (Stimpson) .............. C Strongylocentrotus purpuratus (A. Agassiz) .............. C Cirripedia: Corarmla? of. C. diadema (Linnaeus) ___________________ R lReported by H. N. Lowe (1903), but not found by the authors. 56 GEOLOGY or SAN NICOLAS ISLAND Observations of a number of the kitchen middens suggest the presence of several successive occupational levels that could be differentiated by a thorough archeologic investigation. A hasty survey revealed two cultural levels connected by transitional sites. The earliest stratigraphic levels seem to be limited to the northwest and west parts of the island from the coast to the upland surface in the vicinity of hill 616. These early levels lie a few feet below the extensive surface midden deposits and are characterized by an abund— ance of large red abalone shells (Haliotis mfescens), localized heaps of large sea urchins (Strongylocentro- tus francz'scanus), and small piles of large turban shells (Astraea undosa). Plates from the giant chiton (“Urgptochz'ton” stellem') commonly are concentrated in small mounds throughout the older sites. Black abalone shells (H aliotis cmcherodii) seldom are pres- ent. Many of the lower occupational sites are in dune sand partly cemented by caliche and others contain well—cemented calcareous root casts but none occur in the reddish—brown deposits. Artifacts are rare and often seem to be entirely lacking in red abalone hori- zons, suggesting that occupation of the sites was seasonal. A number of transitional cultural levels may exist _on San Nicolas Island, but the lack of a complete stratigraphic sequence of levels within one dune or even within a restricted area and the usual occurrence of but one occupation site within a single dune makes it difficult to demonstrate the presence of more than one transitional culture on the basis of a hasty examin— FIGURE 19.—Kltehen-midden deposits overlying a flexed human burial exposed in a wind~scoured trough near Seal Beach. The partly cemented old dune in which the midden and burial ‘occur is over- lain by an active dune in the upper background. This midden represents a time of aboriginal occupation when large mussels were the predominant food. ation. Several of the large middens midway between Vizcaino Point and Thousand Springs exhibit at least three definite shell beds that may be interpreted as transitional culture levels. These transitional sites ordinarily contain mixed small red abalone and large black abalone shells, a great abundance of large mussel shells (Mytilus califomianus), and some land snail shells, but they yield relatively few artifacts when compared to the later occupational sites (fig. 19). Partly decomposed fish bones are abundant but mam- mal bones are rare. No evidence of cementation or the presence of calcareous root casts was observed. The uppermost midden levels that occur on the sur- face of many dunes generally contain an abundance of small black abalone shells, scattered small mussel shells, assorted small turbans and limpets, and numer- ous land-snail shells. Artifacts are relatively common on the surface and usually in good condition. The most striking feature of the upper levels is the black soot- like composition of the sand matrix and the slightly greasy texture of the midden material. The refuse heaps of the later sites are uncemented and contain many well-preserved mammal, bird, and fish bones. Relatively long aboriginal occupation of San Nicolas Island is indicated by the definite change in the pre- dominating invertebrate types used for food from the time of early habitation to 1836, when the last remain- ing group of Indians was removed to the mainland. The dwindling of the molluscan food supply and the gradual disappearance of the large forms probably was caused by excessive exploitation of the marine life by the Indians, but not from the warming of the sur- face waters and the resulting local extinction of the red abalone as implied by Carter (1957, p. 132). The common presence of the south-ranging, predominantly subtidal large turban (Astraea undosa) in the same deposits as the large Sea urchins (Strongg/locentrotus francisoanus), the red abalone (Haliotz's mfuscem), and giant chiton plates (Um/ptochz'ton” stellem') seems to disprove the implication that surface waters colder than at present persisted around the island well after the world—wide post-Wisconsin temperature rise. Fur- thermore, the red abalone and the large sea urchin now live in a few areas of shallow subtidal water (less than 3 fathoms) as well as in deeper water around San Nicolas Island. Thus, it seems likely that the early aborigines obtained part of their food supply by div- ing in shallow water for the above-noted forms, which are most commonly found below the intertidal zone. The transitional occupational levels, which seem to have existed for a long period of time, show a decrease in preferable seafood types. The red abalone shells are usually small and the medium-size black abalone shells ECONOMIC GEOLOGY 57 are more abunda t. One of the chief constituents of the transitional (evels is the mussel, but the large turbans and gian' sea urchins are uncommon. Apparently th available molluscan food supply diminished rapi 1y during the later stages of the transitional occu ation. The youngest archeological sites contain nu erous land-snail shells, but the red abalone shells ar almost entirely replaced by small black abalone shells. Mussel shells are smaller and less abundant, and small heaps containing hundreds of tegulas .(Tegula fumbmlis, Tegula bmmnea) with broken apices tog ther with numerous limpets (Lottia gigantea) occur i the uppermost occupational debris. This assemblage resumably indicates that the avail— able supply of Lrge mollusks had been almost com- pletely exhausted by the time the few remaining inhab- itants were removed from the island, or that the art of diving for the large subtidal forms had been lost. The depletion of the easily acquired food supply may partly account fcr the fact that only a few Indians remained on the island at the time the mission authori— ties sent a schooner to take the natives to the mainland. Further careful analysis of the molluscan and per— haps the mammalian content of the kitchen middens may result in a better and more complete zonation of the deposits than has been done by earlier workers. The antiquity f the cultural levels on San Nicolas Island is highly conjectural.all Meighan and Eberhart (1953, p. 115—118) suggest that the occupation of the island was relatively recent as compared to that of the mainland; that is‘ less than 2,000 years and most of it after AD. 1000. Orr (1951, p. 224) implies that the habitation of Sa Nicolas Island extended much fur- ther into the pas . A red abalone shell contained in a mass human buri. 1 found by Orr at Santa Cruz Island was dated at 7050:300 years by Broecker and Kulp (1957, p. 1328). ‘ comparable age may apply to the oldest red abalo e mounds on San Nicolas Island (Carter, 1957, p. 32). CONOMIC GEOLOGY PETROLEUM POSSIBILITIES The surface geology on San Nicolas Island indicates the presence of subsurface structures suitable for small accumulati us of Oil and gas. However, the com- plete lack of info mation concerning the thickness and lithology of [the concealed rocks prevents adequate l 31A radiocarbon date of 5,070i250 B.P. was obtained in 1961 from red abalone shells collected from a midden 1,675 feet N. 60° E. from BM—GIG (Meyer Rubin. written communication, 1961, sample W—981). These shells were taken from the middle of a layer 8 to 18 inches thick and 4 t 41/2 feet below the surface of the youngest midden layer. Although this site represents the oldest cultural type on San Nicolas Islano, similar middens may be as old as the mass burial on Santa Cruz Island. evaluation Of their petroleum potential. Until addi- tional geophysical and stratigraphic core-hole data are available, the presence or absence of source rocks and reservoir rocks in the subsurface section of the island will remain conjectural. Oil and tar seeps were not observed on the island, but small irregular masses of tar are concentrated on the rocks and beaches along the west and northwest shores. Possibly the tar emanates from unknown submarine seeps adjacent to the west end of the island, but it is more probable that the tar drifts ashore from known submarine seeps off the west end of San Miguel Island. Even if a thick section of sedimentary rocks of Late Cretaceous and Eocene age is present beneath San Nicolas Island, is is not likely that such a sequence would produce commercial quantities of oil, for rocks of the same age yield only a small percentage of the petroleum produced in California. Two wells drilled by Richfield Oil Corporation on Santa Cruz Island in 1955 penetrated Upper Cretaceous sedimentary rocks that might be assumed to be similar to the unknown section beneath San Nicolas Island. Neither well reported showings Of oil or gas. The nearest known accumulations of petroleum in rocks of Eocene age are in the Ventura basin, where only a very small amount of Oil is produced from Eocene rocks in a few fields. The closest commercial production of oil from Upper Cretaceous rocks is in the San Joaquin Valley approximately 200 miles north of San Nicolas Island. WATER RESOURCES Three shallow wells (60 to 72 feet deep) in the upper drainage basin’ of Tule Creek together with catchment basins beneath a line of springs in the deep canyon cut by Tule Creek provided the fresh-water supply for San Nicolas Island during the time field- work was in progress. These sources were capable of supplying approximately 60,000 gallons of water per day in 1956. Before the wells were drilled in 1952, fresh water was collected from small springs along the contact between Eocene rocks and dune deposits exposed in the sea cliff at Thousand Springs. Small springs of brackish water occur sporadically along several large faults on the south side of the island in the area between Seal Beach and Dutch Harbor. A spring of potable water flows from the contact between Eocene siltstone beds and Pleistocene dune deposits in the small gully about 2,000 feet north- west of hill 723 on the high western dune area. Fresh water also flows from several springs along the large sandy beach 1,500 feet east of hill 170 on Vizcaino Point. 58 A supplementary water supply could be obtained by the construction of catchment basins in the large drain- age systems where considerable runofi' follows heavy rains. Diversion of additional gullies into the upper Tule Creek basin presumably would recharge the wells now in operation. Another source of water might be found in dune deposits that fill depressions in the Eocene bedrock surface in the dune-covered area southeast of Vizcaino Point. A deep water well was drilled at an altitude of about 560 feet on the flat terrace platform between Celery Creek and the main road intersection sometime during the period 1950—54. This well was drilled to a depth of about 600 feet but did not yield enough water to sufficiently increase the total water supply of the island. SUPPLEMENTARY DATA TABLE 7.——Observations by diving teams on operational dives [See pl. 4] Station gent? Strike Dip Gross lithology (diver’s observation) ee N. 55° W. 20° NE Interbedded sandstone and siltstone. N. 50° W. 17+° NE no. N. 27° W. 21° NE Do. N. 58° W. 8° NE. Not recorded. N. 52° W. 18° NE 0. N. 65" W. 9° N. Interhedded sandstone and siltstone. N. 33° W. 8° NE. Do. N. 38° W. 14° NE. Not recorded. N. 10° W. 3,—I:° E. Sandstone. N. 52° E. 5° NW. Siltstone. N. 15° W. 12° NE Siltstone under high sandstone cliff. E.—W. 17° S. Thin-bedded sandstone and siltstone in sandstone cliff. N. 30° W 20° SW. Siltstone. N. 10° E 5° W. Do. N. 68° E 18° S Thin-bedded sandstone. N. 60° E 13° S Fine-grained thin-bedded sandstone. N. 65° E 12° S Thin—bedded sandstone and silt- 5 one. N. 30° E 15° SE Sandstone. N. 72° E 12° S. Siltstone. N. 25° E 10° SE Sandstone and siltstone. N. 27° E 11° SE. Siltstone. N. 35° E 9° SE. Thin-bedded sandstone and silt— stone. N. 10" W. 15° E. Sandstone. N. 50° E. 101° NE. Thin-bedded sandstone and silt- stone. N. 70° W 10:l:° N. Conglomeratic sandstone. N. 66° W 10:1:° N. Thin-bedded sandstone. N. 73° E 6° N. Siltstone. ____________ Horizontal Do. N. 20° E ° SE. Siltstone and thin-bedded sandstone. N. 63° E 16" S. Thin-bedded siltstone with some fine-grained sandstone. N. 66° E. 12° S. Do. N. 38° E. 15° SE Do. N. 79° E. 10° S. Siltstone. N. 53° W. 8° SW Siltstone and shale. N. 82° W. 4° N. o. N. 64° W 4° N. Thin-bedded siltstone and fine- grained sandstone. N. 38° E. 18° SE Interbedded siltstone and sandstone. N. 83° E. 8° S Siltstone and shale. E.—W. 13° S Siltstone and thin-bedded sandstone. N. 45° E 12° SE Siltstone and thin-bedded finc- 2rained sandstone. N 27° W 17° SW. Siltstone and thin-bedded fine- grained sandstone. N. 80° E 6" S. Interbedded siltstone and sandstone, faulted. N. 60° W. 9" S. Interbedded sandstone and siltstone. N. 58° E. 14° SE. Siltstone and shale. / N. 78° E. 15° S. Siltstone, shale, and some thin- bedded sandstone. N. 40° E 9° SE. Siltstone with some thin-bedded sandstone. N. 48° E 13" SE. Sandstone. N. 42° W 14° NE. Siltstone and shale. N. 50° W. 14" NE. Interbedded sandstone and siltstone. N. 75° E. 5° N. Do. N. 35° W. 6° NE.(?) Massive conglomerate. N. 17° E. 4° NW. Siltstone and shale, loose pebbles. N. 70° E. 6° S. Siltstone and shale. N. 17° W. 19° NE. Do. N. 51° W 7° NE. Sandstone with thin—bedded silt- stone. GEOLOGY OF SAN NICOLAS ISLAND TABLE 7 .—0bservatzons by diving teams on operational dives— Continued [See p]. 4] Station Déptl; Strike Dip Gross lithology (diver‘s observation) eet 28 1.. N. 55° E. 11° SE lnterbedded sandstone and siltstone. 45 N. 40° W. 4° SW Siltstone and shale. 60 . N. 46° E. 7° SE. Do. 55 i N. 30° W. 27° NE Interbedded sandstone and siltstone. 50 . N.—S. 21° E. Siltstone and thin-bedded sandstone. 45 l N. 5° E. 10° E, DO. 36 4 N. 55° W. 22° SW Siltstone and thin-bedded sandstone, . faulted. 60 ‘i N. 35° W. 6° NE Thin-bedded sandstone. 60 N. 63° W. 12° NE Siltstone and thin-bedded sandstone. 54 E N. 55° w. 15° NE Do. 62 I. N. 60° W. 18° NE Do. 65 W N. 30° W. 26° NE Interbedded sandstone and siltstone. 48 ' N. 26° W. 16° NE Siltstone. 62 , N. 22° E. 8° NW Siltstone and shale. 66 ____________ llori- Interhedded sandstone and siltstone, zontal faulted. 70 ____________ 3° W Siltstone and shale with some thin- bedded sandstone. 70 N. 56° W 8" W. Siltstone and thin—bedded sandstone. 68 N. 21° W 11° SW Siltstone with some thin-bedded sandstone. 40 N. 10° E. 22° E. Sandstone. 46 N. 42° W. 7° NE D0. 42 N. 30° W. 6° NE. D0. 51 N. 5° E. 7° E. Do. 60 N. 45" W 7° NE. Siltstone and thin-bedded sandstone. 66—80 N. 38° W 7° NE. Interbedded sandstone and siltstone. 42—50 N. 60° W 13° N. D0. 60 N. 60° E 5° N. Thin siltstone bed in thick—bedded sandstone. 66 N. 47° E 4° NW Siltstone. 60 N. 15° E 5° NW Do. ________________________ Conglomeratic siltstone, slump struc- tures, contorted. N. 80° W 3° N. Siltstone. ........................ Conglomerate, not bedded. 1 N. 37° W 6° NE. Interbedded sandstone and siltstone \ and conglomerate, faulted. N. 53° W 11° SW. Siltstone under thick-bedded sand- stone. N. 5° E. 3° E. Interbedded sandstone and siltstone under conglomeratic siltstone. 90 ........ 60—85 N. 17° E 17° SE. Siltstone 91 ________ 70 ____________ Horizon- Do. tal. 92 ........ 75 ____________ Horizon- Do. tal. 93 ________ 78—95 ____________ ngizon- Do. a . N. 12° E 6° W. Thick-bedded sandstone with thin siltstone beds. N. 14° W. 10° W. Siltstone. N. 78° W. 13° S. Do. N. 12° E. 9° W. Thin-bedded siltstone and sandstone. N. 26° E. 3° W. Siltstone. TABLE 8.-—Eoeene mollusk fossil locality descriptions [See pl. 3] Per- No. used manent . in this U.S. Altitude Description of locality Collections made report Geo]. (feet) by- Survey no. Evl ______ 21648 3103: Halfway up south side of J. G. Vedder and island north of Dutch Har- others in 1955. bor, 5,725 feet south and 4,525 feet west of lat 33°14’30”N., long 119°28’00" W. E42 ...... 21649 230—240 On first main ridge northeast J. G. Vedder and of Dutch Harbor, 7,425 feet others in 1955 and south and 2,775 feet west of 1956. lat 33°14'30“ N., long 119°28’00” W. . E53 ______ 21650 420:4: On steep slope southeast of J. G. Vedder in 1955. Jackson Hill, 3,825 feet south and 1,950 feet east of lat 33°14’30” N., long 119°30'30” W. ‘ _ E—4 ,,,,,, 21651 15—20 Southwest of Vizcaino Point, R. M. Norris, J. G. 9,675 feet north and 6,875 Vedder, and others feet west oflat 33°14’30” N., in 1955 and 1956. long 119°33’00” W. ‘ E~5 ______ 21652 10~15 Vizcaino Point, 12,500 feet No collectlon. north and 7,975 feet west of lat 33°14’30” N., long 119°33’00” W. REFERENCES CITED TABLE 9.—Pleistocene fossil locality descriptions No. used in this report Per- manent U.S. Geol. Survey N o. Altitude (feet) Description of locality Collections made by~ SN-1-_-_ SN—2-_.- SN-3---. SNv4..-. SN—5...- SN—6---_ SN-7. . .- SN—8. ..- SN—9.-._ SN-lO..-. SN—11.-._ SN—12..-_ SN—13_-.- SN—14..._ SN—l5.... SN—16.... 21653 21654 21655 21656 21657 21658 21659 21660 21661 21662 21663 21664 21665 21666 21667 21668 45—60 730:1: 735i 85:1: 815:1: 665:1: 885:1: 900+ 375:1: 590+ 65—70 470:1: Near Army Camp Beach, 8,400 feet north and 3,650 feet east of lat 33°14’30” N., long 119°30’30" E. On main ridge east of bill 818, 4,075 feet south and 600 feet west of lat 33°14’30” N ., long 119°28’00” E. On main ridge east of hill 818, 3,300 feet south and 1,875 feet west of lat 33°14'30” N., long 119°28’00” E. Near Seal Beach, 2,950 feet south and 5,225 feet east of lat 33°14’30" N., long 119°33’00” E. At the head of the first main canyon west of Sand Dune Canyon, 1,850 feet north and 5,775 feet east of lat 33°14’30” N., long 119°33’00” E. Near the head of the first main canyon west of Jackson Hill, 175 feet south and 600 feet west of lat 33°14’30” N ., long 119°30’30” E. East of hill 818, 2,850 feet south and 875 feet west of lat 33°14’30” N., 119°28’00” E. Northwest of Jackson Hill, 450 feet north and 1,200 feet west of lat 33°14’30” N ., long 119°30'30" E. long ‘West of hill 905, 2,075 feet north and 5,050 feet west of lat 33°14’30” N., 119°30’30” E. On the edge of the first deep canyon east of Celery Creek 5,925 feet north and 6,350 feet east of lat 33°14’30” N., long 19°30’30” E. East of upper Celery Creek, 1,450 feet north and 5,775 feet east of lat 33°14’30” N ., long 119°30’30” E. At east end of the island, 5,000 feet south and 9,375 feet east of lat 33°14’30” N ., long 119°28'00” E. East of Dutch Harbor, 8,675 feet south and 2,525 west of lat 33°14’30" N., long 119°28’00” E. West side of tributary to Min- eral Creek, 5,775 feet north and 3,500 feet east of lat 893°14’30" N ., long 119°30’30” 0n northwest coast, 13,950 feet north and 50 feet east of lat 33°14’30” N., long 119°33’00” E. On bluff southwest of Army Camp Beach, 8,075 feet north and 725 feet east of lat 83°14’30” N ., long 119°30’30” long J. G. Vedder, S. R. Dabney, and D. J . Milton in 1955. .l . G. Vedder in 1955. 5. G. Vedder in 1955 and 1956. .I'. G. Vedder in 1955. Do. R. M. Norris and J. G. Vedder in 1956. J. G. Vedder, N. C. Privrasky, and G. P. Frymire in 1956. J. G. Vedder and N. C. Privrasky in 1956. Do. J. G. Vedder in 1956. R. M. Norris in 1955. Do. REFERENCES CITED Addlcott, W. 0., and Emerson, W. K., 1959, Pleistocene inver- tebrates from P nta Cabras, Baja California, Mexico: Am. Mus. Novita es, no. 1925, 33 p. Arnold, Ralph, 1903,. The paleontology and stratigraphy of the marine Pliocene and Pleistocene of San Pedro, Cali- fornia: Californi Bailey, E. H., 1954. America field tr p, 1954, 15 p. Bailey, T. L., 1954, Geology of the western Ventura Basin, Santa Barbara, Ventura, and Los Angeles Counties: California Div. 654890 0 - 63 - 5 Acad. Sci. 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A Page Acanthina luaubris ............................ ‘44, 5o spirata ............................ _ ........ 44 punctulatu . 44, 55 Accessibility. 1—2 Acilo decisa.-.. 37 Acknowledgments ............................ 2—3 Acmaea asmi ................................. 40 40 40 40 imtabilia .................................. 40, 50 limatula .................................. 40, 55 pelta ...................................... 40 nacelloidae ....... acabra _______________ acutum . . n. sp ...................................... 40 Acteocina culcitella ............................ 44 Aeguipecten circularis._.. ____________ 55 circularis aaquisulcatus 46 Aaaro'm'a mathewsonii._ 37 Alum squamiaerus ............................ 42 Algae, red, radio carbon dates ________________ 53 Alluvium .................. Alvam'c acutelirata. alma __________ bakeri ..................................... 41 dalli ______________________________________ 43 dinora .......... harmai ......... keenae _________ lirata ................... oldroydae ________________ purpurea ...... n. sp ..................................... Amaurellina clarkz‘ ____________________________ 37 moragai .............. 37 Amphimorphina califomica ____________________ 36 Amphineura ............. Amphissa columbiarm ......................... 44, 50 oem'color ................................. 44 incisa __________________ 45 Amphithalamus inclusus. __________ 42,50 tenuis ______________________ 42 Anacapa Islands ................... , ........... 30 Anadara multicostata .......................... 46, 50 Analyses, Eocene sandstone. .......... 22—25 Anita shale ................ 27 Annelida _____________________________________ 48-49 Anomalous occurrence of restricted-depth forms ............................. 38—39 Arca sisquocemis.-. _________ 46, 50,52 Archeological sites. ............ 55 Architectom‘ca cognate. - ____________ 37 ullreyana ................................. 37 Arena acuticostata _____________________________ 40 acuticostatu bristolae-. ._ 40 radiate ................................ 40, 50 Araiminea translucens _________________________ 42 Astruea yibberosa... ......... 40, 50, 55 undosa ................................. 40, 55, 56 B Balcnophyllia elegam ......................... 48 Balance nubiliau .. 48 tintin'nclmlum calrformcus ........... 48 sp ........................................ 48 INDEX Page Balcis amoldi ................................. 42, 50 barn/i ........... prefalcota ....... thersitea ................................... 42 Barbarofusus amoldi .......................... 44, 55 harfordi .................. 44,50 .__- 38,44, 50 ..... 44 Barleeia haliotiphila ........................... 43 oldroudi ___________________________________ 42 subtcnuis _________ 42 Bathymetric ranges __________________________ 52 Beaches ______________________________________ 12 Beach deposits ............................... 32-33 Begg Rock _________________________________ 7, 12, 29 Bernardina bukeri ............ 46,50 Bifarina nuttalli .............................. 36 Bittium crmillatum ........................... 42 attenuatum ............................... 42 catalinense ________________________________ 43 eschrichtii momereyme.. 42 Boreotraphon sluarti ........................ 38, 44, 50 Brachiopoda .................................. 48—49 Bromery, R. W .............. 13 Bursa caliform'ca ___________________________ 38,42, 55 C Caecum dalli .................................. 42 califomicum ______________________________ 42 Caliccntharus fortis ....................... 44, 50, 52 Caliche deposits _____________ 32 Calliostoma ligatum .............. 40, 50 Callistochiton crusicostatus.. ....... 46 Calyptruea contorta ____________________________ 43 fastigiata .................................. 42, 50 mammilaris ______________ 43 Ceratoatoma foliatum.. _..- 38, 44. 50 nuttalli __________________ 44,50 Cerithiopais grippi ............................ 42 unidentified ,Iorms ........................ 42 Chama pellucida _____________ 46 Channel Islands ................. 5 Chlamys hastotua .............. 46, 50 hastatus hericius ........................... 47, 50 C‘Ibicidea sp ................................... 36 ' .. 48—49, 55 ___________ 4—5 Clinocardium nuttallii.-._ . _ . . . . . Coelenterata .................................. 48-49 Coleophyais harpa ............................. 44 Conus califomim ...... 44 Coronula diadema ............................. 55 Correlation, age and faunal ................... 52—53 Cortes Bank .................. 6—7 Cozy Dell formation ________ 27 C‘repidula aculeata. _ . _ . 42 performs ............ princeps ______________ C‘rcpipatella lingulata ......................... 42 Crucibulum spinosum ......................... 42 C‘rypwchiton stelleri... ._ 48, 55, 56 C‘ryptoconus cooperi ..... ._ 37 Cryptonatica clausa ..... .. 42 Culture ...................................... 3—4 Cumingiu califomica __________________________ 46 Cyanopla: dentiem ............................ 46 Page Cydocardla barbaremis ........................ 47 longini .................................... 38, 46 Cysticus jewem. 44 regularia .................................. 44 Cytharellu sp .................................. 44 D Daphnella fuaooliaata .......................... 44 Davidson, George, cited ....... 3 Dmdmster ezcentricus .......... 48 Dmdrochittm thamnopom. . 46 Dmtalium cooperi...._...--..._ - . -_ . .- _ _ .. - 37 aemipolitum .............................. 46 Diala acute ____________________ _ 43 murmorea" . 42 Diodora aspera. . 40, 55 Diplodomc orbella ............................. 46 Dodecaceria fiatulacolc ......................... 48 Drainage .................... 11 Dunes ........................................ 11 E Echinodermata ............................... 48-49 Echinoidea __________ _ . 55 Economic geology. . . . . .. 57-58 E'Iachisina arippi ....... .... 42,50 Emery, K. 0., cited .......................... 5 Eocene Foraminlfera ......................... 36 Eocene megafossils. . . . ...... 36-37 Eocene series analyses--. ...... 22-25 correlation ............... _._- 25—27 description of mapped units .............. 15—22 general features ........................... 13-15 source rocks ......... . . .. 25 Eolian sand _____________ . 13,30-32 Epilucina califomica ..... .... 46, 55 Epitom'um indianorum ........................ 44 tindum ................................... 45 Erato m‘tellina.... 55 Empire uuci/ormia __________ 37 F Fartulum occidentale .......................... 42, 50 orcum' .................................... 42, 50 Faults ....................................... 5, 7, 34 Features of island. . 8 Fieldwork _____ 2 F‘issurella volcano. 40 Folds .................................. 35 Foraminifera ................................. 36 Fossil localities .................... ._. 36—38, 58—59 Fossils from marine terrace deposits, age and fauna] correlation ................. 52—53 annotated checklist .......... . 38, 40—49 Fusinus merricmi .................. . 37 Fusm portolaenaia ............................ 45 G G'an' califomica ............................... 46, 50 Gastropoda __________________________ 37, 40—47, 50, 55 Geographic ranges. ..._ 52 Geomorphology _____________ _. 7—12 Gibberulina pyriformia ....... - 44 Glam subquadrata ............................ 46 Glaucophane .......................... _ ...... 30 Globularia hannabali. 37 Glycymeris corteziana. '17 miweliana.--. 47 subobsoleta ................................ 46 63 64 Page Glyphoatomo conrodiana ....................... 45 n. Sp .................. 44 H Habitat ...................................... 38 Hah‘olia corrugato ................ 55 cracherodii ................ 40, 55, 56 kamtachofkono ........... 40, 50 rufeace‘ns ............................... 40, 55, 56 sorensmi .................................. 40 Hausa/Ina pupoideus ............... 40 Hiatello erotica ..................... 46 H innitcs aiga‘nteus ........... 46,55 Hipponiz antiquatus .......................... 42 antiquatus craniodea ....................... 43 tumm: .............. - . - . 42 History .................... .... 3—4 Homalopoma baculum. .. ...- 40 carpemm' ................................. 40 paucicostatum ............................. 40 Humilan'a perlaminosa ..................... 46, 50, 52 I Igneous rocks .......... _. 5—7, 27—29 1m: lamellifer- .......... . __ 46,50, 55 lechnochz'ton compicuus ................ 55 Isclmochito'n (Lepidozona) califomiemia ........ 46 Sp ______________________________ 46 Ischnochiton (Stmoplaz) conspicuus.. 46 Sp ........................................ 46 J Jown factions ................................. 44, 50 K Kelletto kelletii ................................ 44 Kellie laperousii .............................. 46 Kitchen middens ............................. 54—57 L La Joila, Ca1if., Eocene rocks near ............ 25, 27 La J 011a formation ............................ 27 Lacuna carinata. - - ........ 40. 50 unifasciata ....... 40 Loevicordium elatum-.. ________ 55 Lamelleria rhombica __________________________ 42 Land bridge .................................. 10 Landslides .......... 11 Lemon cistulu _________________________________ 46 Latirus nightingalei ........................... 37 Liotio fenestrato ............................... 40 Littorina plamm's ............................. 40 scutulota-.._._.-. 40 Liveoak member _____________________________ 25 Llajas formation ______________________________ 27 Location .................... 1—2 Lottie gigantea ____________ 40, 55,57 Loxotrema turritum ______________ 37 Lucopinella callomarginato ____________________ 40 Dunatia lewz’sz‘i ________________________________ 42, 55 Lyrio andersoni _______________________________ 37 M Macnm lioidus ................................ 44,50 Mangelia interfossa ___________________________ 44,50 nitens __________ rhyssa _________ variegata _______ Matilija formation ............................ 27 Maxwellia gamma _____________________________ 44 Megafossils, Eocene _________________ 36—37 Megatebmnus bimaculatus ____________________ 40 Megathura crenulata __________________________ 40, 55 Metazia conveza ........................... . 43 diadema ............................... 42 Methods ............... 2 Metralla sandstone member .................. 25 Micrarionta aodalis ____________________________ 46 Milnm'a mim’ma ............................. 46 INDEX Page Miocene rocks, regional distribution .......... 12 Santa Barbara, San Clemente, and Santa Cruz Islands ..................... 29 Mindomiscus prolongatus" .. ..- 46,50 Mitre idae ................ 44, 50, 55 Mac montcreyz. .......... . . 45 Mitrella tuberosa ...................... r ....... 44 corinata ................................... 44 aausapata.-. . 44 Mitromorpha ospera. . 44 filosa ....... . 44 arucilior... 44 Modiolus fornicatus ........................... 46, 50 Monterey shale, rocks resembling Mopalia ciliata 46 hindsii--... 48 muscosa . . . 48 Momla luaubria .............................. 44, 50 Mutilua califomia‘nm ...................... 46, 55, 56 N Nauan‘us mendicua coopm‘ .................... 44 perpinquia ................ _ 44 Lemma recto- . ........ 37 Norrisia norriair ............................... 40, 55 Observations by diving teams..l4, 18, 30, 33, 35—36, 58 Ocembra beta ................... . 44 circumteua ............................... 44, 55 foveolata ................................ . . 44 interfoaaa. . clathrata . Iurida ...... mundo ............................... 44, 50 aubangulato ............................... 44 Odoatomia ultina. . 42 42 42 42 oldroydi ..................... 42 phamlla. - 42 aancforum ................................ 43 sepia ..................................... 44 tmuiaculpta. 42 terriwla. 42 virginalis ................. 42 Offshore shelf and slope deposits .............. 33—34 Offshore structure observed by divers ________ 35—36 Olirella baetica ...................... ... 45, 55 ..- 44, 55 . 44 Opalia ericta" 44 wroblewskyi chacei ........................ 44, 50 Ophiodermellu ophioderma... . 44 Ostrea lurida .................................. 46 stewam' ................................... 37 P Pachydesma crassatelloides ..................... 55 Paleoecology, inferences .......... ... 38—52 Paleontology, age and iaunal correlation. -.. 36—37, 52—53 Eocene Foraminifera ..................... 36 Eocene megafossils ....................... 36—37 fossils from marine terrace deposits. .. . 37—51 Paleotemperatures ___________________________ 39, 51 Panope generosa .............................. 39, 46 Parapholas califomica ......................... 46, 50 Parvilucina tenuisculpta ...................... 46 Pectm diegensis ......... 46 ooadesi .................................... 46,50 Pelecypoda __________________________ 37, 46—47, 50, 55 Penitclla penile __________________ 46, 50 Petaloconchus anellum. . ....... 42 complicatus ................ 42 Petricola carditoides ___________________________ 46 Petroleum possibilities ....................... 57 PM: blakianua ................................ 37 Page Placiphorella oelafa ........................... 48 Pleclina garzomi: ...... 36 Pleistocene and Recent series, caliche deposits. 32 windblown sand ....................... 13, 30-32 Pleistocene series, terrace deposits _____ . 29—30 Pleurofusia lindariataensis .............. - 37 Potomides carbonicola ......................... 37 Poway conglomerate ......................... 27 Proaabbio coopm‘..-. ....... 38, 44, 50, 55 Protothoca stominea" ............. 46, 55 Pseudomelatoma arippL _ 44 torosa ..................................... 44 Puncturello coopm' ........................ 38, 40, 50 Pupillaria optabilis. parcipz’cla.-- papilla . . . .mccinda __________________________________ Purpose ...................................... Puwla califomiana- solandri ....... Q Quaternary system, Pleistocene and Recent series, undifferentiated ........... 30—32 Pleistocene series ......................... 29—30 Recent series ...... . 32—34 Ouickello rehderi .............................. 46 R Radiocarbon date, kitchen midden ........... 57 red algae ........ 53 terrace localities ................... 53 Recent series, beach deposits and alluvium-.. 32- 33 ofl‘shore shelf and slope deposits .......... 33—34 Reed Canyon siitstone member.... . 25 Riaaoinu aequisculpta. .... _. 40,50 bakeri ........... . ... 40 coronadoemi: ............................. 40, 50 dalli ...................................... 40 hannai.. Robulus welch .... Rose Canyon shale ........................... S San Clemente Island ....................... 5 29, 35 San Joaquin Valley, Eocene rocks in 25 San Miguel Island .................... 5,12,15,25, 32 San Nicolas Basin ............................ 7, 35 San Onofre breccia ........................... 30 Sand Dune Canyon area- _. 17,18 Santa Barbara Island ....................... 5, 29, 35 Santa Catalina Island .................... 6, 7, 25, 30 Santa Cruz Basin ____________________ 7,12, 35 Santa Cruz Island .................. 5, 7, 25, 29, 30, 57 Santa Monica Mountains ..... Santa Rosa-Cortes Ridge ............. 7,10, 12, 30, 35 ,Santa Rosa Island ___________________ .... 5 Santa Susana formation ........... 27 Santa Ynez Mountains, Eocene rocks in 25 Santiago formation .................. 27 Saridomus nuttalli ............................ 39, 46 Scaphopoda ............................... 37, 48—49 Schizothaerm nuttalli. .. 39, 46 Scope ........... 1 Searleaia dim ................ .. 44,50 Sedimentary rocks, Eocene ................... 13—27 Septifer bi furcatua ............................. 46, 55 Scrzmlu octoforis ...................... 48 Setting, geomorphic, of island platform. 7-8 Seila montereyemia ................... 42 Siphonaria brummni .......................... 46 Spiroqluphus lituellua ......................... 42, 50 Spisula planulatu .............. Stratigraphy, concealed rocks ................. 12—13 general features of the exposed rocks ...... 13 Quaternary system ................. .. 29-34 regional ........................... 5—7 Tertiary system .......................... 13-29 Page Strongylocentrotus franciscanus ............. 48, 55, 56 purpuratus _______________________________ 48, 55 Structure, faults._ ......... 34—35 Structure, folds ........................... 35 Structure, ofi'shore structure observed by divers ............................ 35—36 Structure, regional ____________________________ 5—7 Surcula pracattenuata. 37 Surculites mathewsa'm‘i ________________________ 37 Surface-water paleotemperatures ______________ 39, 51 T Tanner Bank ................................. 6—7 Tegula aureotincta ____________________________ 40, 50 brunnea ____________________________ 40, 50, 55, 57 fiuctuosa _________________ 40, 50 funebrulis ............. _-._ 40, 55, 57 gaillina multifilosa.___ ..... 40, 5O montereyi ______________________________ 40, 50, 55 pulligo ____________________________________ 4O Teinostoma supravallatum. . _ _ _ 40 Tejon Eocene sandstones... 25 Tellina salmonea ______________ 39, 46,50 Temperature, monthly mean _________________ 4 Terebra (Striaterebrum) lacuna ................ 44, 50 Terebratalia transverse ........ . 48 Terebratulina unguicula ....... _ 48 Terrace deposits, fossils ....... . 37—38 vicinity of Celery Creek .................. 28 INDEX Page Terrace faunas, paleoecologic comparisons. .-- 51—52 Terraces, age limit ............................ 53 geomorphology .......... _.._ 8-10 Tertiary system, Eocene series .-__ 13-27 igneous rocks .............. .._- 27—29 Tetraclita squamosa rubexcens. .- ,_ ............. 48 Thais emarginata ............................. 44 emarginata ostrina ..... 45 Thrucia outta .............. 46 Tonicella lineata. 46 Torrey sand .................................. 27 Trachycardium elatum ........................ 55 quadragenariumnn 46, 55 Transennella tantilla ........... 46 Tricolia pulloides. - _ . 4O rubrilineata _______________________________ 40 Trigoniocardia bianaulata ................... 39, 46,55 Trimmculus reticulutus- .. _ Triphora pedroana ____________________________ 42 Tubulostz'um tejonmxis ________________________ 37 Turbom'lla mymondi .......................... 42 tmuicula- 42 valdezz' ________ 42 Turritella buwaldrma __________________________ 37 cooperi .................................... 42 lawsoui _____________________ 15, 20, 37 secondaria. _ _ _ uvasana etheringtom hendom' ............................... 37 65 Page Turto'm'a minute .............................. 46 U Uvas member, Tejon formation ............... 25 V Vegetation .................................... 4—5 Velutina laem'aata ............................ 42, 5O Ventricolaria fordii ............................ 46, 55 Vitrinella oldroydi ............................. 40 ateamsii ......... 40 Volutocristata Zajollaensis ______________________ 37 W Water paleotemperatures _____________________ 39, 51 Water resources ______________________________ 57-59 Water temperature variation ofl southern California and northwestern Baja California ________________________ 51 Wildlife ...................................... 4—5 Windblown sand ............................. 30—32 Z Zonan'a apadicca .............................. 42, 55 The U.S. Geological Survey Library has cataloged this publication as follows: Vedder, John Graham, 1926— Geology of San Nicolas Island, California, by J. G. Vedder and Robert M. Norris. Washington, U.S. Govt. Print. Off, 1963. vi, 65 p. i11us., maps, diagrs., tables. 29 cm. (U.S. Geological Survey. Professional paper 369) Part of illustrative matter folded in pocket. Prepared in cooperation with the US Department of the Navy, Office of Naval Petroleum and Oil Shale Reserves. Bibliography: p. 59-62. (Continued on next card) Vedder, John Graham, 1926— Geology of San Nicolas Island, California. 1963. (Card 2) 1. Geology—California—San Nicolas Island. 2. Paleontology—Cali- fornia—San Nicolas Island. I. Norris, Robert Matheson, 1921—, joint author. II. US Oflice of Naval Petroleum and Oil Shale Reserves. III. Title: San Nicolas Island, California. (Series) U.S. GOVERNMENT PRINTING OFFICE:1963 0‘654890 .-_._._. mmfljr“ ,fim UNITED STATES DEPARTMENT OF THE INTERIOR??? ' PROFESSIONAL PAPER 569 * ' GEOLOGICAL SURVEY ‘ _ t; PLATE 1 . 120°OO’ :fimfifijfi: €291 Base map by U. S. Geotogical Survey in co- INTERIOR#GEOLOGICAL SURVEY, WASHINGTON, D. C #10341 operation with the State of Caiiforma INDEX MAP OF PART OF THE CONTINENTAL BORDERLAND AND COASTAL AREA OF SOUTHERN CALIFORNIA SCA_E 1:1000 000 20 3) 4O 50 6O 7O 80 MILES }————* l————-—I i————-‘{ 1 CONTOUR INTERVAL 100 FATHOMS DATUM IS MEAN SEA LEVEL =»_. M..L UNITED STATES DEPARTMENT OF THE INTERIOR . PROFESSIONAL PAPER 569 GEOLOGICAL SURVEY PLATE 2 ' ”9'4. 2. 3.1.“. , . EXPLANATION >—- CONTOUR INTERVAL 25 FEET DATUM IS MEAN SEA LEVEL AP-‘woxiMAW MFAN IJECLINAIION‘ 19m UNITED STATES DEPARTMENT OF THE INTERIOR . . PROFESSIFCDDINAAFI}.E PéAPER 569 GEOLOGICAL SURVEY 119°33'00" 119°30’30” 119°28’00” l r‘ . L): EXPLANATION {is f . {a "”3 § . . . I i . C s AlluVIum and beach sand; unconsolldated Sllt, sand, Unit 20 TI”)... ea,” 'Y‘m‘ini/s \ ' and gravel Gray siltstone containing afew very thin beds . .r. .tu .. I .x , of limy fine—grained sandstone _ >- _ . I it \ 21 ' 0 i H i . _ Gray thin-bedded alternating beds of sandstone and . g: siltstone in approximately equal amounts; thickness Unlt 26 < variable :: m Light—gray thin-bedded alternating beds of sandstone I: § and siltstone in approximately equal amounts 0: ‘ . a LLl ‘ 13 7 is ,_ . , . \ g . Light—gray thick-bedded concretionary medium- to Unlt 25 coarse—grained sandstone containing a few very thin Light—gray thick-bedded medium—grained sandstone siltstone beds i containing a few very thin siltstone beds 24 , ' i Unit 12 . E . _ ,, ~ Unit 24 Gray thin-bedded alternating beds of sandstone and ...... ' 5' Light-gray thin-bedded alternating beds of sandstone siltstone in approximately equal amounts; Wilding-93 and siltstone in approximately equal amounts , variable Unit 23 Unit 11 Light-gray thick—bedded medium- to coarse—grained LightAgray thick-bedded concretionary medium- to sandstone containing a few very thin siltstone beds coarse-grained sandstone; thickness variable . l ‘ . . . Unit 10 3 Unlt 22 , . . . ,‘ , _ , , Gray siltstone and fine—grained sandstone that contains Gray thin-bedded'siltstone containing afew very scattered pebbles and cobbles; thickness variable; 10a, thm beds of limy fine—grained sandstone grades laterally into interbedded sandstone and silt- stone Unit 21 ' Light-gray thick-bedded medium-grained sandstone Unlt 9 containing afew 7167‘?! thin siltstone b9d3 Light-gray thick-bedded concretionary fine- to coarse- § grained sandstone; silty near top; locally grades 8 laterally into interbedded sandstone and siltstone of LS units 8 and 10 >. 3 CC 1 19°25'30” § 3 b 8 l— 1 D: *3 Unit 8 E E 7% Gray thin-bedded alternating beds of sandstone and w » J S siltstone in approximately equal amounts l" Ti r Unit 7 Light-gray thick-bedded concretionary medium- to coarse-grained sandstone containing a few very thin siltstone beds; siltstone beds increase in thickness and abundance near top 9 I?) A Unit 6 l - ‘ ~ ' Blue-gray thin-bedded siltstone containing afew very \ ” u thin interbedded limy fine-grained sandstone; 6a, l ~ locally contains thick-bedded lenticular medium- jr grained sandstone with thin interbedded siltstone l *7 , a 5 \ ’1’ ‘ It . . . 0 Unit 5 "b { Light-.9704] WT?! thick-bedded concretionary medium- ! grained sandstone containing a few thin beds of I" _ :_ , ‘ \ \ 3301430" intercalated sandstone and siltstone ". ‘ 339‘.l4l~30” *— . i ' ,4. / ‘. P Unit 4 b J Massive cobble conglomerate and siltstone breccia; y‘ lenticular; intertongued sandstone l h . ‘ . it Unlt 3 ’ Light—gray thick-bedded concretionary medium-grained sandstone; locally contains thin lenticular conglom- erate beds . , _ 2 v > ' Unit 2 "f .< f Light—gray fine-grained sandstone and mudstone containing numerous cobbles and pebbles . 9 ' l v I‘. r w k . Unit 1 ' l, i ..-,: Light-gray thick—bedded medium-grained sandstone \y p t with afew very thin beds offine-grained sandstone; Ii l » . . ' locally contains thin lenticular beds of conglomerate i «0 ll ' 9» V i I 1 i i .1 V ‘ and breccia g, j ' ‘ - .,‘ ' _ 119°33'00" ,___ . _ bal:Survey; San Nicolas ’ i ' ,. ' Tnia, (1956) A? V a . Zone A ‘ Siltstone and alternating beds of sandstone and silt- ' r 5 stone, undifferentiated; presumably represents parts i . . INDEX TO GEOLOGIC MAPPlNG ofunits 26, 27, and 28 Y ‘ 1 J. G. Vedder /. 2 R. L. Harbour ‘ f 3 RM. Norris g I . 4 R. L. Burnside, N. C. Privrasky, and R. M. Norris '5 j. P 5 N.C. Privrasky,R. L. Burnside,and D.J.Milton IS Zone B 6 R. M. Norris and D. J. Milton CL . . . . . h' w 7 R. M. Norris and J. G. Vedder '2 Siltstone, undifferentiated, unknown stratigrap ic 8 R. L. Burnside and D. J. Milton ,3 position between units 5. and 17 a I s g L9." 0 O 2 :6 i 2 33 s s ‘ .3 5 3 Zone C . L 5 E Sandstone, undifferentiated; unknown stratigraphic ‘ ,_ 7 Geologic contacts maybe slightly offset from their true position E a: position between units 6 and 18 .« in respect to topography and drainage % ’ E. l “’ e , ll 'V (I) a.) . APPROXlMATE MEAN g Z0119 D DECL‘NAT‘ONr 1962 N Sandstone and siltstone, interbedded, undifferentiated; * unknown stratigraphic position between units 7 and 18 LL .1 z E Z 9 o 9 ._ . 5 z 5 , , m Qs g UUJ) H'LL Zone E m // Sandstone and interbedded sandstone and siltstone, ///' undifferentiated; unknown stratigraphic position J / ’_______h between units 8 and 12 /// Dashed where determined by scattered exposures and float; short dashed where inferred u i D __ ............... Fault o ' H Trace offault and dip offault surface; dashed where 119 30 3’0 poorly exposed; dotted where concealed. U, upthrown side; D, downthrown side (7 _J_ B. Strike and dip of beds B L, 2 z , 1000" I 59 '5 F 1000 63 IL 2 5 Horizontal beds z m III 9 CD 0) Qs a 3 ,L ,_ o ‘ . A i f b ds 500 {L}; PRESUMED BURIED FAULTS OF 500 pparentd p 0 e 05 UNKNOWN DISPLACEMENT " 7 9 ,. SEA LEVEL 6 SEA LEVEL . Landslide - Arrows indicate direction of movement ______~ INTERIORHGEOLOGICAL sum/EV. WASHINGTON. D C ”10341 0 , ,, “—“\\‘ 119°28’00” 119 25 30 _500._ I .500 Geology mapped in 1955 and 1956 by J. G. Vedder, R. L. Harbour, P2 ‘ // R. M. Norris, R. L. BUFDSide. N. C. Privrasky, and D. J. Milton. Sandstone sample locality i/l/ V3 . 4000' 4000' ‘ , Dike-rock sample locality ' E4 Fossil locality, Eocene mollusks LL SN—3 Z Z C, D D, E A E/ Fossil locality, Pleistocene invertebrates C ‘ 9 t Z , 1000. g 5 t 1000' n‘ 1000L 9 1000 M52 . _ LL] [.1 6 Q 05 L z 5 Fossil locality, Pleistocene birds and LL m m 9 3i HILL 606 marine mammals ,1 5 18 . z . l” . 500' . _ 500 o 500 ~ 1 2 500 O |————~| E 6 D TCH HA RB COAST GUARD fl 6 /._/ l LANDSL'DE U ' OR aI BEACH Line of measured stratigraphic section /H-—— / 6 // Qal SEA LEVEL and section number SEA LEVEL /~'~-~—-/ ‘( 5 /,,'l/ - ._ SEA LEVEL SEA LEVEL \ 2 7 . i ‘ “/V/A /// \\l I i '3, 4 ' ‘ 75d t ' 500. ' I - . . ‘ ¢//T"’/ \ \\ l ; . L500 L500'— —500' Str1ke and dlpan s atlon number ’ . ‘ 6 f , // l N \ I 7 Station at intersection of strike and dip lines . . / \ \ / ‘ ‘ l / i ll I l / / I] // i l 1000' -1000' l l —1000' —1000’ L m. L LLl / F ~ 9 Z F m o . . . g A 1000 1000 7 m 0 6 E Z .l ; f3 HILL 606 . 2: 9 U 0 5 w Qt it 5 z z 6 1m” 1 16 16a _ 500' 500.- g g g 9 E 1 3W 1 > . 3 _ 5- . -L 29 or 29 F Q5 6 d t 28 A“ _ 28 JEHEMY BEACH 8 6 in m . " 2726 Qt 2524 Q I -—-——_.__ 2 a SEA LEVEL— ‘QS m I , . . ‘7-3-—-:.—VmH—m—_— —SEA LEVEL \\\\ 5 I ‘ ‘ 1 22 \\ 5 H-HLLLLE‘,____ 4r ~~~H~ —500'— \\\\\\ I — 7500' T“ ll \ I \ _ , —1000' 1000 GEOLOGIC MAP AND SECTIONS OF SAN NICOLAS ISLAND, CALIFORNIA SCALE 1:12 000 1000 0 1000 2000 3000 4000 5000 FEET H H H H H t————————l CONTOUR lNTERVAL 25 FEET DATUM IS MEAN SEA LEVEL UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 369 GEOLOGICAL SURVEY 119°35’30” PLATE 4 119°33’00“ Vizcaino Point \\\\\\\\ \ \_/ \ /”‘\ Sat/m \J _/ EXPLANATION 39 Ta Strike and dip and station number Station at intersection of strike and dip lines ,/\ \\ 28 6 /\ Horizontal beds and station number \\ ///\ §\ \ Station at center of symbol \ V /// /\ \ 71 3<— __ Apparent dip and station number \ Station at point of arrow X86 Station at which no attitude was measured \ Reef, bare at half tide \ \ ' ' \ 'zéiil“. L l / / l/ + Submerged reef, waves break in moderate swell 119° 35/30” 119°33’00” BATHYMETRY AND GEOLOGIC OBSERVATIONS ON THE SEA FLOOR WEST OF 2522:2232?:.b:'s:::2:,2y.azigzsszrsn . ~. ; Submarine contours are based on unpublished soundings taken by the U. 8. Coast and Offshore locations by R. M. No rrrrrr d J. . e er Submarine contours by J. G. Vedder Geodetic Survey in 1932 SAN NICOLAS ISLAND, CALIFORNIA SCALE 1:12 000 1/2 O 1 MILE [ CONTOUR INTERVAL 25 FEET DATUM IS MEAN SEA LEVEL DEPTH CURVE INTERVAL 1 FATHOM DEPTHS SHOWN RANGE FROM 5 TO 20 FATHOMS 654890 0 - 63 (In pocket) . UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 369 GEOLOGICAL SURVEY PLATE 5 6,7 Northeast of Dutch Harbor 8, 9,10 Nearly east of Dutch Harbor + v 2 . I, East of Seal Beach 1 mile southeast of . 1 T 3 5 Vizcaino Point 1‘/z miles southeast of 5 Sand Dune North of Dutch Vizcaino Point Canyon Harbor U7 \\ EXPLANATION , , 12,11 ,4 3 .' .. \ Interbedded sandstone )5- \ West OI Jehemy and conglomerate ’_ 4 Beach > .- \ Fault - ~ Conglomeratic siltstone T? Thick-bedded sandstone 4 I Southwest of i f / Jackson Hill i L Concretionary sandstone — E19 Sandstone with thin stltstone beds 14 ; Contact proiected /40 feet southwest , \ 7 \ \ i E I Section repeated by fault\ \ \\ _100 Thick-bedde and thin— adlusted to true \ \ A bedded sandstone thickness \ ,, ET.- Thinebedded sandstone and Siltstone . 6a ' Predominantly sandstone ‘\ beds \ —-ISO \ 11 10\a 10a N0 conglomeratic No conglomeratic Siltstone ~ \ 0299921683 beds \ Interbedded siltstone and Base not exposed. ‘ . I T - T . . . ' ‘ ' \ ‘ - v , i ' ' ' claystone ‘— 250 Correlation line, dashed where inferred 8 Designation of section on geologic map 28 * Unit number referred to In text and shown on geoe logic map Thicknesses of numbered sections measured by planetable With the exv ception of 1, which was taped; unnumbered secr tion (units 1 through 5) estimated from geologic map Base not exposed STRATIGRAPHIC SECTIONS OF THE EOCENE STRATA EXPOSED ON SAN NICOLAS ISLAND, CALIFORNIA 654890 0 — 63 (In pocket)