U.S. Department of the Interior Open-File Report 2015−1041 U.S. Geological Survey Sheet 10 of 10 Pamphlet accompanies map 122°55' 122°50'

adf Tp Kgr Qmt Qls adf Qls? Qls Qf Qf Qa 123°20 123° Qmt Qf Tp Qmt Qed Qe Qed Tl Qa Tp Qe Tp Qf Qls? Qf Tp Qls Qa Qed Tp Qls Qf Tp Qds Tp Qa Qf Qbs Qls Qe CALIF. Qls adf Qmt Tm Qds Qe adf Tp Tp Qbs Qf Drakes Estero de Tp Qa Qbs Qa Qds MAP LOCATION Qed Tp Estero Limantour Qds Qbs Tl Qedaf Qds Qds Qds Qls Limit of California’s Qbs Tp Qbs Kfs Qf State Waters afem Tsm Tp Qds af Qls? Qed Qa Qms Qls? 38°20' Tp Qoc Qmsd Qmsd Bodega Qmsd Qa Bodega Qmsd Harbor Qmsd Qa Bay Tsc Qms Qmsd Qa Tp Tomales Bay Qmsd Qmsd Qmsc Tm Qmt Qls? San Andreas Fault Zone CORRELATION OF MAP UNITS Qmt Qls Qmsd 10 Qmsd [See Description of Map Units (chapter 8, in pamphlet) for precise unit ages] Qmsd Qf Kgr Inverness Ridge Qmt OFFSHORE GEOLOGIC AND GEOMORPHIC UNITS ONSHORE GEOLOGIC AND GEOMORPHIC UNITS Qmsd Qls Qmsd Tsm U-Ranch Tl Qsr Qms Qmsc Qmsf Qmsd Qmsw af afem adf Qbs Qls? af Qds Qe Qed Qf Qa Qls? Qf Holocene Point Reyes Qf Qls 38° Tsm QUATERNARY Tsc Qmt Qmt Qoc Drakes Bay 0 5 10 Qa Pleistocene Kilometers Nautical Miles Qmt Qoc 0 5 10 Area of Qmt Map Tsm Pliocene Qmt Tsm Tp Tp Qa Tsc Tsc Tsm Tp Tp Qls? Tm Tl Qa Qmt Tm Tu Miocene Qls? TERTIARY Tu Qmt Tsc Qls? Tu Qms Qls? Tpr Paleocene Tu Late 30 Qls? Qa Kgg Kgr Kfs Cretaceous Qmsc Tsm Early CRETACEOUS Tu Tu Qls? Cretaceous Tp Tsm

Qls? 38° Qmt 38° Tp Tu Tu Tsc LIST OF MAP UNITS Lobos (Greene and Clark, 1979; Clark and others, 1984; Dickinson and others, 2005). Greene, H.G., and Clark, J.C., 1979, Neogene paleogeography of the Monterey Bay area, Qmsc Qls? The Point Reyes Fault Zone marks the southern boundary of the Point Reyes peninsula. It runs Qms Tu California, in Armentrout, J.M., Cole, M.R., and Ter Best, H., Jr., eds., Cenozoic [See Description of Map Units (chapter 8, in pamphlet) for complete map-unit descriptions] through the offshore part of the map area as a curvilinear reverse fault zone (Hoskins and Griffiths, paleogeography of the western United States: Pacific Coast Paleogeography Symposium 3, p. Point Reyes Tsm 1971; McCulloch, 1987; Heck and others, 1990; Stozek, 2012) that likely connects with the west 277–296. OFFSHORE GEOLOGIC AND GEOMORPHIC UNITS strand of the San Gregorio Fault farther south (Ryan and others, 2008). The Point Reyes Fault Zone Grove, K., Colson, K., Binkin, M., Dull, R., and Garrison, C., 1995, Stratigraphy and structure of headland Tsm Qls? Qsr Marine shelf deposits, rough seafloor (late Holocene)—Irregular “lumps” on is characterized by a 5- to 11-km-wide zone that is associated with two main fault structures: the the Late Pleistocene Olema Creek formation, San Andreas fault zone north of San Francisco, Qmsc Qls seafloor; interpreted as marine debris; possibly related to either one or more Point Reyes Fault, and also a west strand mapped offshore of the Point Reyes peninsula (fig. 1). California, in Sangines, E., Andersen, D., and Buising, A., eds., Recent geologic studies in Qbs Qls Offshore of the Point Reyes headland, granitic basement rocks are offset vertically (north side Tm Qls? shipwrecks or biological “hardgrounds” the San Francisco Bay area: Society for Sedimentary Geology (SEPM), Pacific Section, Book Qmt up) about 1.4 km on the reverse-slip Point Reyes Fault Zone (McCulloch, 1987); this uplift, Qls? Qls? Qms Marine nearshore and shelf deposits (late Holocene)—Mostly sand; ripples common 76, p. 55–77. Tpr combined with west-side-up offset on the San Andreas Fault Zone (Grove and Niemi, 2005), has Grove, K., and Niemi, T.M., 2005, Late Quaternary deformation and slip rates in the northern San Qmsc Qls Qmsc Coarse-grained marine nearshore and shelf deposits (late Holocene)—Coarse sand, resulted in uplift of the Point Reyes peninsula and the adjacent shelf (both the Bodega Head– Andreas fault zone at Olema Valley, Marin County, California: Tectonophysics, v. 401, p. Tm gravel, and cobbles Tomales Point shelf, north of the map area, and the Bolinas shelf; see sheet 9). Late Pleistocene 231–250, doi:10.1016/j.tecto.2005.03.014. 40 Qbs Tsm uplift of marine terraces on the southern Point Reyes peninsula suggests active deformation of Kgg Qmsd Tm Millers Point Qmsf Fine-grained marine shelf deposits (late Holocene)—Mostly mud to muddy sand Grove, K., Sklar, L.S., Scherer, A.M., Lee, G., and Davis, J., 2010, Accelerating and spatially- Qmt offshore structures west of the San Andreas Fault Zone (Grove and others, 2010). Offshore of varying crustal uplift and its geomorphic expression, San Andreas Fault zone north of San Qmsd Qmsf Double Point, the Point Reyes Fault is associated with the warping and folding of Neogene strata, Francisco, California: Tectonophysics, v. 495, p. 256–268, doi:10.1016/j.tecto.2010.09.034. Qmsw Qmsd Qmsd Marine shelf scour depressions (late Holocene)—Inferred to be coarse sand and Tsm gravel, in low-relief scours which is visible on high-resolution seismic-reflection data (see figs. 1, 2, 3, 4 on sheet 8). Although Hallenbeck, T.R., Kvitek, R.G., and Lindholm, J., 2012, Rippled scour depressions add Kgg Qmsd the post-Miocene slip rate on the Point Reyes Fault Zone in the map area is poorly constrained, it is ecologically significant heterogeneity to soft-bottom habitats on the continental shelf: Marine Tsm Qmsw Marine sediment wave deposits (late Holocene)—Predominantly sand; formed by Qmsd strong tidal currents that flow around Point Reyes headland and into Drakes Bay estimated to be 0.3 mm/yr on the basis of vertical offset of granitic basement rocks (McCulloch, Ecology Progress Series, v. 468, p. 119–133, doi:10.3354/meps09948. 1987; Wills and others, 2008). Qms Qmsd Tp Purisima Formation (Pliocene and late Miocene)—Siltstone interbedded with Heck, R.G., Edwards, E.B., Kronen, J.D., Jr., and Willingham, C.R., 1990, Petroleum potential of Kgg Qms Qmsd Tm mudstone and sandstone; locally contains diatomite Granitic basement rocks of the Salinian block are exposed onland along Inverness Ridge (unit the offshore outer Santa Cruz and Bodega basins, California, in Garrison, R.E., Greene, H.G., Kgr) and west of the map area on the Point Reyes headland (mapped as unit “Kgg” in the adjacent Hicks, K.R., Weber, G.E., and Wright, T.L., eds. Geology and tectonics of the central Qmsd Qmsd Tsc Santa Cruz Mudstone (late Miocene)—Thin- to thick-bedded siliceous mudstone that Qmsd Offshore of Point Reyes map area). Unit Kgg also is exposed offshore in the northwestern part of California coastal region, San Francisco to Monterey: American Association of Petroleum Qmsc Qmsd has carbonate concretions Tm Monterey Formation (late and middle Miocene)—Marine, thin-bedded chert, this (Drakes Bay and Vicinity) map area. The granitic rocks are mapped offshore on the basis of Geologists, Pacific Section, Bulletin GB67, p. 143–164. Kgg Qmsd Tsc their massive, bulbous texture and extensive fracturing seen in multibeam imagery (see sheet 2), as Hoskins, E.G., and Griffiths, J.R., 1971, Hydrocarbon potential of northern and central California Tm Qls porcelanite, shale, and sandstone Tm well as their high backscatter (see sheet 3). Much of the inner shelf is underlain by Neogene marine offshore: American Association of Petroleum Geologists Memoir 15, p. 212–228. Qmsd Tu Sedimentary rocks, undivided (late and middle Miocene)—May consist of the Santa 10 Qls Tsc sedimentary rocks that form the core of the Point Reyes Syncline (Weaver, 1949). These rocks McCulloch, D.S., 1987, Regional geology and hydrocarbon potential of offshore Central Qms Cruz Mudstone (unit ), the Santa Margarita Sandstone (mapped onland as unit 50 Tsm), and the Monterey Formation (unit Tm) include the upper Miocene Santa Margarita Formation (in the offshore, mapped as part of the California, in Scholl, D.W., Grantz, A., and Vedder, J.G., eds., Geology and resource potential Kgg undivided sedimentary rocks unit [Tu]); the middle and upper Miocene Monterey Formation (unit of the continental margin of western North America and adjacent ocean basins—Beaufort Sea Tu Kgg Point Reyes Granodiorite, porphyritic facies (Late Cretaceous)—Contains Tu Tu potassium-feldspar phenocrysts that average 2 to 3 cm in length (maximum, 5 cm) Tm); the upper Miocene Santa Cruz Mudstone (unit Tsc); and the upper Miocene and Pliocene to Baja California: Circum-Pacific Council for Energy and Mineral Resources, Earth Science Purisima Formation (unit Tp). At Millers Point, the Monterey Formation, which is exposed both Series, v. 6, p. 353–401. Tu Qls Qsr ONSHORE GEOLOGIC AND GEOMORPHIC UNITS onshore and on the seafloor in the nearshore, is highly fractured, making bedding planes difficult to Murray, B., and Thieler, E.R., 2004, A new hypothesis and exploratory model for the formation of Qsr Tu identify. Seafloor exposures of the younger units (the Santa Cruz Mudstone [Tsc] and the Purisima large-scale inner-shelf sediment sorting and “rippled scour depressions”: Continental Shelf Qms Tu [Bedrock units compiled from Clark and Brabb (1997), Blake and others (2000), and Wagner and Formation [Tp]) are characterized by thin to very thick bedding that commonly is gently folded and Research, v. 24, no. 3, p. 295–315, doi:10.1016/j.csr.2003.11.001. Gutierrez (2010); unit ages, which are from these sources, reflect local stratigraphic relations. fractured, which is in contrast to the highly fractured rocks of the Monterey Formation that are National Park Service, 2012, Shipwrecks on the Point Reyes Peninsula 1849–1940, in Shipwrecks Qsr Tu Quaternary units compiled from Witter and others (2006) and Wagner and Gutierrez (2010), with visible in multibeam imagery offshore of Millers Point. Along the southeast coast of Drakes Bay, at Point Reyes: National Park Service Web site, available at http://www.nps.gov/pore/ Tsc Tsc Tsc some additional mapping by M.W. Manson (this report); in addition, some units modified by M.W. the Santa Margarita Sandstone consists of massive arkosic sandstone that rests unconformably on historyculture/upload/map_shipwrecks.pdf. Tsc Manson on basis of analysis of 2012 lidar imagery] the Monterey Formation; in the map area, this unit is not mapped in the offshore because it consists Noble, M.A., and Gelfenbaum, G., 1990, A pilot study of currents and suspended sediment in the Tsc Tsc Qbs of relatively thin (5 to 60 m thick) deposits that are difficult to identify in multibeam imagery. Strata af Artificial fill (late Holocene)—Engineered and (or) nonengineered Gulf of the Farallones: U.S. Geological Survey Open-File Report 90–476, 30 p. mapped as the Monterey Formation (Tm) may also include that of the Santa Margarita Sandstone, Page, B.M., 1982, Migration of Salinian composite block, California, and disappearance of Qls Tsc particularly just offshore of Millers Point where no multibeam imagery exists. Seafloor outcrops afem Artificial fill over estuarine mud (late Holocene)—Material deposited by humans fragments: American Journal of Science, v. 282, p. 1,694–1,734, doi:10.2475/ajs.282. Point Reyes Fault mapped as the undivided sedimentary rocks unit Tu may include rocks of the Monterey Formation over estuarine sediments 10.1694. Tsc (Tm), the Santa Margarita Sandstone (mapped onland as unit Tsm), and the Santa Cruz Mudstone adf Artificial-dam fill (late Holocene)—Earth- or rock-fill dams, embankments, and Reid, J.A., Reid, J.M., Jenkins, C.J., Zimmerman, M., Williams, S.J., and Field, M.E., 2006, (Tsc). In an oil test well at Double Point, the Santa Cruz Mudstone and the underlying Santa levees; constructed to impound land-locked water bodies usSEABED—Pacific Coast (California, Oregon, Washington) offshore surficial-sediment Tsc Margarita Sandstone are more than 450 m thick (Clark and Brabb, 1997), and these units form Tsc Qbs Beach-sand deposits (late Holocene)—Active beaches in coastal environment; may data release: U.S. Geological Survey Data Series 182, available at http://pubs.usgs.gov/ds/ coastal bluffs and tidal-zone exposures that extend offshore, onto the adjacent bedrock shelf. The form veneer over bedrock platform 2006/182/. Santa Cruz Mudstone thins markedly to the northwest, and it disappears from the section about 10 Qds Dune sand (Holocene)—Active dunes and recently stabilized dunes in coastal Ryan, H.F., Parsons, T., and Sliter, R.W., 2008, Vertical tectonic deformation associated with the km to the northwest where the Purisima Formation unconformably overlies the Santa Margarita environments San Andreas fault zone offshore of San Francisco, California: Tectonophysics, v. 457, p. Sandstone. We infer that the offshore contact between the Santa Cruz Mudstone and the Purisima Qe Estuarine deposits (Holocene)—Heterogeneous mixture of coarse and fine estuarine 209–223, doi:10.1016/j.tecto.2008.06.011. Formation is an angular unconformity that is visible in seismic-reflection data just southeast of the sediment; deposited in Drakes Estero Stozek, B.A., 2012, Geophysical evidence for Quaternary deformation within the offshore San map area. This angular unconformity becomes a conformable contact to the northwest in the Drakes Tsc Qed Estuarine-delta deposits (Holocene)—Heterogeneous mixture of coarse and fine Andreas fault system, northern California: San Francisco, Calif., San Francisco State Tu Qls Bay and Vicinity map area; in addition, we suggest that this contact bends northward in the subsur- University, M.S. thesis, 141 p. Tsc estuarine sediment; deposited in delta at mouths of tidally influenced coastal Tsc face and comes onshore near U-Ranch (Galloway, 1977; Clark and Brabb, 1997). Given the lack of streams, where fresh water mixes with seawater Trembanis, A.C., and Hume, T.M., 2011, Sorted bedforms on the inner shelf off northeastern New Tsc Qbs lithological evidence for this contact offshore of Double Point, this interpretation is speculative; an Zealand—Spatiotemporal relationships and potential paleo-environmental implications: Qf Alluvial fan deposits (Holocene)—Sediment deposited by streams emanating from U alternative interpretation is that the angular unconformity is present within the Santa Cruz Geo-Marine Letters, v. 31, p. 203–214, doi:10.1007/s00367-010-0225-8. D mountain canyons onto alluvial valley floors or alluvial plains Mudstone. To indicate this uncertainty, we have queried unit Tp (the Purisima Formation) in the Wagner, D.L., and Gutierrez, C.I., 2010, Preliminary geologic map of the Napa 30′ × 60′ Qa Alluvial deposits, undivided (Holocene)—Alluvium deposited in fan, terrace, or basin offshore part of the map area. environments quadrangle, California: California Geological Survey, scale 1:100,000, available at http:// Tsm Tsc Modern nearshore sediments are mostly sand (unit Qms) and a mix of sand, gravel, and Double Qls Landslide deposits (Holocene and Pleistocene)—Weathered rocks and soil. Internal www.conservation.ca.gov/cgs/rghm/rgm/Pages/preliminary_geologic_maps_1page.aspx. Qms cobbles (units Qmsc and Qmsd). Coarser grained sands and gravels (units Qmsc and Qmsd) are Point contacts differentiate individual landslide bodies Weaver, C.E., 1949, Geology of the Coast Ranges immediately north of San Francisco Bay region, Qms Tsc recognized primarily on the basis of bathymetry and high backscatter (sheets 1, 2, 3). Both units California: Geological Society of America Memoir 35. Tsc Qmt Marine terrace deposits (late Pleistocene)—Sand, gravel, and cobbles; deposited on Tu Qmsc and Qmsd typically have abrupt landward contacts with bedrock, and they form irregular to Weber, K.M., List, J.H., and Morgan, K.L.M., 2005, An operational mean high water datum for Qms marine-abrasion platforms and later uplifted to present-day elevations along coast 10 lenticular exposures. Contacts between units Qmsc and Qms typically are gradational. Tsc Qoc Olema Creek Formation of Grove and others (1995) (late Pleistocene)—Alluvial determination of shoreline position from topographic lidar data: U.S. Geological Survey Tsm Unit Qmsd typically is mapped as erosional lags in scoured depressions (see, for example, Tsc and estuarine sediments; includes sand derived from granitic rocks; interbedded Open-File Report 2005–1027, available at http://pubs.usgs.gov/of/2005/1027/. Cacchione and others, 1984) that are bounded by relatively sharp or, less commonly, diffuse Tsc with organic mud and peat Wills, C.J., Weldon, R.J., II, and Bryant, W.A., 2008, Appendix A—California fault parameters for Qmsd Qms contacts with the horizontal sand sheets of unit Qms. These depressions typically are a few tens of the National Seismic Hazard Maps and Working Group on California Earthquake Qms Tp Purisima Formation (Pliocene and late Miocene)—Siltstone interbedded with centimeters deep and range in size from a few tens of meters to more than 1 km2. Such scour Probabilities 2007, in The Uniform California Earthquake Rupture Forecast, version 2 Qmsd mudstone and sandstone; locally contains diatomite Tsc depressions are common along this stretch of the California coast (see, for example, Cacchione and (UCERF 2): U.S. Geological Survey Open-File Report 2007–1437A and California Tu Tsc Santa Cruz Mudstone (late Miocene)—Thin- to thick-bedded siliceous mudstone that Tsc others, 1984; Hallenbeck and others, 2012; Davis and others, 2013) where offshore sandy sediment Qms has carbonate concretions Geological Survey Special Report 203A, 48 p., available at http://pubs.usgs.gov/of/2007/ Tsc can be relatively thin (and, thus, is unable to fill the depressions) owing to lack of sediment supply Tsm Santa Margarita Sandstone (late Miocene)—Massive arkosic sandstone 1437/a/. Qms Qms from rivers and also to significant erosion and offshore transport of sediment during large northwest Witter, R.C., Knudsen, K.L., Sowers, J.M., Wentworth, C.M., Koehler, R.D., Randolph, C.E., Qms winter swells. Such features have been referred to as “rippled scour depressions” (see, for example, Brooks, S.K., and Gans, K.D., 2006, Maps of Quaternary deposits and liquefaction Qms Tm Monterey Formation (late and middle Miocene)—Thin-bedded siliceous shale, Tsc Tu Tu Cacchione and others, 1984) or “sorted bedforms” (see, for example, Murray and Thieler, 2004; susceptibility in the central San Francisco Bay region, California: U.S. Geological Survey 10 interbedded with arkosic sandstone Qms Tu Goff and others, 2005; Trembanis and Hume, 2011). Although the general areas in which both unit Open-File Report 2006–1037, scale 1:24,000, available at http://pubs.usgs.gov/of/2006/ Qms Tl Laird Sandstone of Clark and others (1984) (late and middle Miocene)—Arkosic Qms 10 Qmsd scour depressions and surrounding Qms sand sheets are found are not likely to change sandstone that contains basal granitic-boulder conglomerate 1037/. substantially, the boundaries of the unit(s) likely are ephemeral, changing seasonally and during Tpr Point Reyes Conglomerate (Paleocene)—Sandy conglomerate, interbedded with Qmsd Tsc significant storm events. arkosic sand Two areas of high-backscatter (see sheet 3) and rough seafloor (unit Qsr) are notable in that Tu Granodiorite and granite of Inverness Ridge (Late Cretaceous)—Granodiorite and Kgr each includes several small (less than about 20,000 m2), irregular “lumps” that have as much as 1 m granite; commonly includes aplite and alaskite dikes Qms of positive relief above the surrounding seafloor. Southeast of the Point Reyes headland, unit Qsr is Tsc Sandstone and shale of San Bruno Mountain terrane (Cretaceous)—Sandstone and Qms Qmsd Kfs mapped in water depths of between 50 and 60 m, and the orientation of the individual lumps ranges Tsc shale; part of Franciscan Complex Qmsd from randomly distributed to west trending. Southeast of Double Point, unit Qsr is mapped in water Tsc depths of between 30 and 40 m, and individual lumps have a more northwestward trend. Seismic- 123°20' 123° 122°40' Qmsd EXPLANATION OF MAP SYMBOLS reflection data (see, for example, fig. 4 on sheet 8) reveal that this lumpy material rests on several Qms 0 105Kilometers

Contact—Solid where location is certain, long-dashed where location is approximate meters of uppermost Pleistocene to Holocene sediment and, thus, is not bedrock outcrop. We PRF interpret it as marine debris, possibly derived from the more than 60 shipwrecks that occurred Qmsd U Fault—Solid where location is certain, long-dashed where location is approximate, offshore of the Point Reyes peninsula between 1849 and 1940 (National Park Service, 2012). It also D U dotted where location is concealed. U, upthrown block; D, downthrown block. is conceivable that this lumpy terrain consists of biological “hardgrounds” (that is, groups of fauna D Arrows show direction of relative movement on the seafloor that have rigid, often calcareous, shells that exhibit high reflectivity, similar to SAFZ PRP Tp? Tsc Folds—Solid where location is certain, long-dashed where location is approximate, lithified rock). Note that the video ground-truthing data that crosses unit Qsr near the Point Reyes Qms short-dashed where location is inferred, dotted where location is concealed, queried headland (see Box A on sheet 6) was of insufficient quality to distinguish between these two where uncertain alternatives. 37°55' PRH 37°55' Tp? Anticline A transition to finer grained marine sediments (unit Qmsf) is seen south of the Point Reyes DB 38° headland and west of Double Point at depths of about 50 to 60 m; however, directly south and east U Tp? D Syncline of Drakes Estero, both backscatter data and seafloor-sediment samples (Chin and others, 1997) WPRF U PRF suggest that fine-grained sediments extend into water depths as shallow as 30 m. Unit Qmsf, which BODEGA BASIN DP Tp? D Tp? Significant inflection (change in dip) within limb of fold commonly is extensively bioturbated, primarily consists of mud and muddy sand. These fine-grained sediments are inferred to have been derived either locally from Drakes Estero and Area of UPRF Map D Approximate modern shoreline—Defined as Mean High Water (MHW) (+1.46 m), Estero de Limantour or from the San Francisco Bay to the south (about 30 km south of the map Farallon High Tp? Tp? North American Vertical Datum of 1988 (NAVD 88) area) via the predominantly northwestward flow (Noble and Gelfenbaum, 1990). 3-nautical-mile limit of California’s State Waters Tp? REFERENCES CITED Area of “no data”—Areas beyond 3-nautical-mile limit of California’s State Waters WSGF Blake, M.C., Jr., Graymer, R.W., and Jones, D.L., 2000, Geologic map and map database of parts of Farallon Is. Qsr were not mapped as part of California Seafloor Mapping Program Tp? Tp? Marin, San Francisco, Alameda, Contra Costa, and Sonoma Counties, California: U.S. 30 Qms Qms Geological Survey Miscellaneous Field Studies Map 2337, scale 1:62,500, available at Figure 1. Map showing important structures of Point Reyes Fault Zone Qsr Tp? offshore of Point Reyes peninsula. Fault structures are based on DISCUSSION http://pubs.usgs.gov/mf/2000/2337/. Qsr Cacchione, D.A., Drake, D.E., Grant, W.D., and Tate, G.B., 1984, Rippled scour depressions of the interpretation of both deep-penetration multichannel and USGS Marine geology and geomorphology were mapped in the Drakes Bay and Vicinity map area shallow minisparker seismic-reflection data. Faults are shown by thick 30 inner continental shelf off central California: Journal of Sedimentary Petrology, v. 54, p. Qsr from approximate Mean High Water (MHW) to the 3-nautical-mile limit of California’s State 1,280–1,291. black lines: solid lines show buried faults that are imaged in shallow Waters. MHW is defined at an elevation of 1.46 m above the North American Vertical Datum of minisparker data; dashed lines indicate buried faults that show no Qsr 30 California Geological Survey, 1974, Alquist-Priolo earthquake fault zone map of Inverness 1988 (NAVD 88) (Weber and others, 2005). Offshore geologic units were delineated on the basis of quadrangle: California Geological Survey, State of California Special Studies Zone Map, scale visible offset in shallow minisparker data; U, upthrown block; D, Tp? integrated analyses of adjacent onshore geology with multibeam bathymetry and backscatter 1:24,000, available at http://www.quake.ca.gov/gmaps/WH/regulatorymaps.htm. downthrown block; paired arrows indicate relative motion on strike- imagery (sheets 1, 2, 3), seafloor-sediment and rock samples (Reid and others, 2006), digital Chin, J.L., Karl, H.A., and Maher, N.M., 1997, Shallow subsurface geology of the continental shelf, slip faults. Dashed magenta line shows axis of Point Reyes Syncline. camera and video imagery (sheet 6), and high-resolution seismic-reflection profiles (sheet 8). Aerial Gulf of the Farallones, California, and its relationship to surficial seafloor characteristics: Gray shading shows late Tertiary Bodega Basin (modified from 30 photographs taken in multiple years were used to map the nearshore area (0 to 10 m water depth) Marine Geology, v. 137, p. 251–269, doi:10.1016/S0025-3227(96)00091-6. McCulloch,1987). Red box shows Drakes Bay and Vicinity map area. and to link the offshore and onshore geology. Clark, J.C., and Brabb, E.E., 1997, Geology of the Point Reyes National Seashore and vicinity, Yellow line shows limit of California’s State Waters. Abbreviations: DB, Onshore bedrock mapping is compiled from Clark and Brabb (1997), Blake and others (2000), California—A digital database: U.S. Geological Survey Open-File Report 97–456, scale Drakes Bay; DP, Double Point; PRF, Point Reyes Fault; PRH, Point Reyes and Wagner and Gutierrez (2010). Onshore Quaternary mapping is compiled from Witter and others 1:48,000, available at http://pubs.usgs.gov/of/1997/of97-456/. headland; PRP, Point Reyes peninsula; SAFZ, San Andreas Fault Zone; Qsr (2006) and Wagner and Gutierrez (2010), with some additional mapping by M.W. Manson (this Clark, J.C., Brabb, E.E., Greene, H.G., and Ross, D.C., 1984, Geology of Point Reyes Peninsula WPRF, west strand of Point Reyes Fault Zone; WSGF, west strand of report); in addition, some units are modified by M.W. Manson on the basis of analysis of 2012 lidar and implications for San Gregorio fault history, in Crouch, J.K. and Bachman, S.B., eds., San Gregorio Fault Zone. imagery. Traces of San Andreas Fault are compiled from California Geological Survey (1974) and Tectonics and sedimentation along the California margin: Pacific Section, Society for Wagner and Gutierrez (2010). Sedimentary Geology, v. 38, p. 67–85. The offshore part of the map area, which includes the large embayment known as Drakes Bay, Davis, A.C.D., Kvitek, R.G., Mueller, C.B.A., Young, M.A., Storlazzi, C.D., and Phillips, E.L., extends from the shoreline to water depths of about 40 to 60 m. The continental shelf is quite wide 2013, Distribution and abundance of rippled scour depressions along the California coast: in this area; the shelf break is located west of the Farallon High (fig. 1), about 35 km offshore. The Continental Shelf Research, v. 69, p. 88–100, doi:10.1016/j.csr.2013.09.010. map area is characterized largely by a relatively flat (less than 0.8° offshore dip) bedrock platform Dickinson, W.R., Ducea, M., Rosenberg, L.I., Greene, H.G., Graham, S.A., Clark, J.C., Weber, that is overlain locally by a thin veneer of Holocene sediment. Shelf morphology and geology are G.E., Kidder, S., Ernst, W.G., and Brabb, E.E., 2005, Net dextral slip, Neogene San Gregorio– the result of local faulting, folding, uplift, and subsidence. Hosgri fault zone, coastal California—Geologic evidence and tectonic implications: The onshore part of the Drakes Bay and Vicinity map area contains part of the Point Reyes Geological Society of America Special Paper 391, 43 p. peninsula, which is located entirely west of the San Andreas Fault, the transform boundary between Galloway, A.J., 1977, Geology of the Point Reyes Peninsula, Marin County, California: California the Pacific and North American plates. The Point Reyes peninsula is composed of Late Cretaceous Geological Survey Bulletin 202, scale 1:24,000. granitic rocks of the Salinian block that are overlain by Tertiary marine sedimentary rocks (Page, Goff, J.A., Mayer, L.A., Traykovski, P., Buynevich, I., Wilkens, R., Raymond, R., Glang, G., 1982). Since late Miocene time, the Point Reyes peninsula has been offset about 155 km along the Evans, R.L., Olson, H., and Jenkins, C., 2005, Detailed investigations of sorted bedforms, or San Gregorio and San Andreas Faults from the Monterey peninsula, where it was adjacent to Point “rippled scour depressions,” within the Martha’s Vineyard Coastal Observatory, 122°55' 122°50' Massachusetts: Continental Shelf Research, v. 25, p. 461–484, doi:10.1016/j.csr.2004.09.019.

Onshore elevation data from California Coastal Conservancy 14° SCALE 1:24 000 Offshore geology and geomorphology mapped by Janet T. Watt, (available at http://www.csc.noaa.gov/digitalcoast/data/coastallidar) 1 1/2 0 1 MILE 2012−2013. Onshore geology and geomorphology compiled by

and from U.S. Geological Survey’s National Elevation Dataset RTH Michael W. Manson, 2012–2013, from California Geological Survey

(available at http://ned.usgs.gov/). Offshore shaded-relief bathymetry NO 1000 0 1000 2000 3000 4000 5000 6000 7000 FEET (1974), Clark and Brabb (1997), Blake and others (2000), Witter and from map on sheet 2, this report. California's State Waters limit from others (2006), and Wagner and Gutierrez (2010). Bathymetric 1 .5 0 1 KILOMETER TRUE NORT H contours by Mercedes D. Erdey, 2012 NOAA Office of Coast Survey AGNETIC

M Universal Transverse Mercator projection, Zone 10N GIS database and digital cartography by Janet T. Watt, Stephen R. APPROXIMATE MEAN BATHYMETRIC CONTOUR INTERVAL 10 METERS DECLINATION, 2015 Hartwell, Charlie A. Endris, Bryan E. Dieter, and Peter Dartnell NOT INTENDED FOR NAVIGATIONAL USE ONE MILE = 0.869 NAUTICAL MILES Manuscript approved for publication March 3, 2015

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government This map was printed on an electronic plotter directly from digital files. Dimensional calibration may vary between electronic plotters and Offshore and Onshore Geology and Geomorphology, Drakes Bay and Vicinity Map Area, California between X and Y directions on the same plotter, and paper may change size due to atmospheric conditions; therefore, scale and proportions may not be true on plots of this map. For sale by U.S. Geological Survey, Information Services, Box 25286, Federal Center, Denver, CO 80225, 1–888–ASK–USGS By Digital files available at http://dx.doi.org/10.3133/ofr20151041 or http://pubs.usgs.gov/of/2015/1041/ Suggested Citation: Watt, J.T., Manson, M.W., and Greene, H.G., 2015, Offshore and onshore geology and geomorphology, Drakes Bay and 1 2 3 1 Vicinity map area, California, sheet 10 in Watt, J.T., Dartnell, P., Golden, N.E., Greene, H.G., Erdey, M.D., Cochrane, G.R., Johnson, S.Y., Janet T. Watt, Michael W. Manson, and H. Gary Greene U.S. Geological Survey; 2 Hartwell, S.R., Kvitek, R.G., Manson, M.W., Endris, C.A., Dieter, B.E., Sliter, R.W., Krigsman, L.M., Lowe, E.N., and Chin, J.L. (J.T. Watt and S.A. California Geological Survey; ISSN 2331-1258 (online) Cochran, eds.), California State Waters Map Series—Drakes Bay and Vicinity, California: U.S. Geological Survey Open-File Report 2015–1041, 2015 3 Moss Landing Marine Laboratories, Center for Habitat Studies http://dx.doi.org/10.3133/ofr20151041 pamphlet 36 p., 10 sheets, scale 1:24,000, http://dx.doi.org/10.3133/ofr20151041.