THE PURISIMA FORMATION AND RELATED ROCKS (UPPER MIOCENE - PLIOCENE), GREATER SAN FRANCISCO BAY AREA, CENTRAL CALIFORNIA Review of literature and USGS collection (now housed at the Museum of Paleontology, University of California, Berkeley) By Charles L. Powell, II 345 Middlefield Rd., M/S 975, Menlo Park, CA 94025 Open-File Report 98-594 U. S. DEPARTMENT OF THE INTERIOR U. S. GEOLOGICAL SURVEY U. S. DEPARTMENT OF THE INTERIOR U. S. GEOLOGICAL SURVEY THE PURISIMA FORMATION AND RELATED ROCKS (UPPER MIOCENE - PLIOCENE), GREATER SAN FRANCISCO BAY AREA, CENTRAL CALIFORNIA Review of literature and USGS collection (now housed at the Museum of Paleontology, University of California, Berkeley) By Charles L. Powell, II 1998 OPEN-FILE REPORT 98-594 To obtain this report, contact: USGS Information Service Box 25286 Denver Federal Center Denver, CO 80225 (303) 202-4700 (303) 202-4693 FAX This report is preliminary and has not been reviewed for conformity with U. S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purpose only and does not imply endorse- ment by the U. S. Government. CONTENTS Abstract...................................................................................................................................4 Introduction..............................................................................................................................5 Stratigraphy.............................................................................................................................5 Age..........................................................................................................................................8 Introduction..................................................................................................................8 Paleontologic age.........................................................................................................8 Radiometric dating.....................................................................................................11 Previous work on paleontology of the Purisima Formation.......................................... ........11 Paleontologic significance of Purisima Formation outcrops..................................................18 Point Reyes................................................................................................................18 La Honda Block..........................................................................................................19 Redondo Beach................................................................................................19 Purisima Creek................................................................................................20 Lobos Creek and Martins Beach......................................................................22 Tunitas Creek..................................................................................................24 Mussel Rock........................................................................................................24 San Gregorio and San Gregorio Creek...........................................................25 San Gregorio State Beach...............................................................................26 Pomponio State Beach....................................................................................26 Pescadero Creek..................................................................................................27 Pigeon Point Block.....................................................................................................27 Halfmoon Bay area...........................................................................................27 Moss Beach/Pillar Point........................................................................27 Año Nuevo area..............................................................................................30 Gazos Creek........................................................................................30 Cascade Creek.....................................................................................30 Año Nuevo Bay.....................................................................................31 Ben Lomond Block.....................................................................................................33 Santa Cruz area..............................................................................................33 Capitola City Beach..............................................................................33 New Brighton-Sea Cliff State Beaches.................................................36 Point Santa Cruz...................................................................................36 Santa Cruz Mountains/Scotts Valley...............................................................37 Mountain Charlie Road.........................................................................37 Scotts Valley.........................................................................................37 Chittenden Pass/Sargent Oil field......................................................................38 Chittenden Pass/Sargent oil field..........................................................38 San Francisco Block..................................................................................................42 Miscellaneous collections...........................................................................................42 Biostratigraphy......................................................................................................................42 Conclusions...........................................................................................................................43 Acknowledgments.................................................................................................................44 References.............................................................................................................................44 Appendix 1: Faunal notes.....................................................................................................60 Appendix 2: Fossil localities.................................................................................................97 USGS Open file Report 98-594, page 2 Figures 1.--Generalized locality map showing structural blocks in the San Francisco Bay region. Also shown are areas of finer coverage illustrated by other figures.....................................6 2.--Correlation chart showing age of outcrops within the La Honda Block as determined by paleontological and other methods..............................................................................8 3.--Correlation chart showing age of outcrops within the Pigeon Point Structural Block........9 4.--Corrleation chart showing age of outcrops within the Ben Lomond Structural Block as determined by paleontological and other methods.....................................................10 5.--Index map of Purisima Formation fossil occurrences discussed in the text. Map covers the coast from Moss Beach to Martins Beach in San Mateo County.........................23 6.--Index map of Purisima Formation fossil occurrences discussed in the text. Map covers the coast from Martins Beach to Pescadero Point in San Mateo County...................25 7.--Index map of Purisima Formation fossil occurrences discussed in the text. Map covers the coast from Franklin Point to Año Nuevo Bay in San Mateo and Santa Clara Counties....................................................................................................................30 8.--Generalized sea cliff geology on south of Punta del Año Nuevo, San Mateo Co....31 9.--Index map of Purisima Formation fossil occurrences discussed in the text. Map covers the Santa Cruz County occurrences...........................................................................34 Tables 1.--Molluscan taxa reported by Arnold (1908a) from his lower member of the Purisima Formation, now considered the Ladera Sandstone................................................12 2.--Molluscan taxa reported by Arnold (1908a) from his middle member of the Purisima Formation..................................................................................................................13 3.--Molluscan taxa reported by Arnold (1908a) from his upper member of the Purisima Formation..................................................................................................................14 4.--Mollusks from the Purisima Formation in the general area of Purisima [Creek?] from recent USGS collections and from the literature........................................................20 5.--Fossils reported from the Purisima Formation at San Gregorio by Ashley (1895a)........26 6.--Fossils from the Purisima Formation east of the Seal Cove fault at Moss Beach, San Mateo County, CA......................................................................................................29 7.--Mollusks from the Purisima Formation at Año Nuevo Creek...........................................32 8.--Mollusks reported from the Purisima Formation at Capitola City Beach.........................34 9.--Mollusks from Purisima Formation at New Brighton-Seacliff State Beaches..................36 10.--Marine fossils reported from the lower part of the Purisima Formation in the Sargent oil field area................................................................................................................39