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This part of DS 781 presents data for the bathymetry and shaded-relief maps of the Offshore of Fort Ross map area, California. Raster data file is included in "Bathymetry_OffshoreFortRoss.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreFortRoss/data_catalog_OffshoreFortRoss.html. The bathymetry and shaded-relief maps of the Offshore of Fort Ross Map Area, California, were generated from bathymetry data collected by California State University, Monterey Bay (CSUMB), and by Fugro Pelagos. Mapping was completed between 2007 and 2010, using a combination of 200-kHz and 400-kHz Reson 7125, and 244-kHz Reson 8101 multibeam echosounders, as well as 468-kHz SEA SWATHPlus interferometric system. These mapping missions combined to collect bathymetry from about the 10-m isobath to beyond the 3-nautical-mile limit of California's State Waters.

This part of DS 781 presents data for the geologic and geomorphic map of the Offshore of Bodega Head map area, California. The vector data file is included in "Geology_OffshoreBodegaHead.zip," which is accessible from https://pubs.usgs.gov/ds/781/OffshoreBodegaHead/data_catalog_OffshoreBodegaHead.html. The morphology and the geology of the Offshore of Bodega Head map area result from the interplay between tectonics, sea-level rise, local sedimentary processes, and oceanography. The Offshore of Bodega Head map area is cut by the northwest-trending San Andreas Fault, the right-lateral transform boundary between the North American and Pacific tectonic plates. From southeast to northwest, this fault extends through Bodega Bay and Bodega Harbor, crosses the Bodega Head isthmus at the mouth of Salmon Creek, and extends in the offshore for about 20 km before passing onland at Fort Ross, about 12 km north of the Offshore of Bodega Head map area. The San Andreas Fault juxtaposes Cretaceous granitic rock on the southwest with the Jurassic, Cretaceous, and early Tertiary Franciscan Complex on the northeast. Uplift of the granitic rock (unit Kg) on the west side of the San Andreas Fault has created extensive, rugged, rocky seafloor, centered offshore Bodega Head and extending northwest for about 15 km, from the western flank of Bodega Bay to the shelf offshore of the mouth of Salmon Creek. At its south and north ends this rocky seafloor extends to water depths of about 40 m and 50 m, respectively where it is onlapped by young sediment (see below); offshore of Bodega Head, the rocky seafloor extends to water depths of 80 m. Northeast of the San Andreas Fault, offshore rocky outcrops of the Franciscan complex (units Kfs, Kjfss, fsr) occur only in the nearshore (water depths less than 15 m). Sediment-covered areas of the offshore part of the map occur in gently sloping (less than about 1 degree) nearshore, inner-, and mid-shelf environments. Sediment supply to the shelf north and west of Bodega Head is predominantly from coastal watersheds including the Russian River (4.5 km north of the map area) and Salmon Creek. Sediment supply to Bodega Bay and the shelf in the southern part of the map area is from small coastal watersheds and estuaries such as Estero Americano and Estero de San Antonio, and most likely from sediment flux out of the mouth of Tomales Bay, located two kilometers south of the map area. Shelf morphology and evolution largely reflects eustacy; sea level has risen about 125 to 130 m over about the last 21,000 years (for example, Lambeck and Chappell, 2001; Peltier and Fairbanks, 2005), leading to broadening of the continental shelf, progressive eastward migration of the shoreline and wave-cut platform, and associated transgressive erosion and deposition. Given present exposure to high wave energy, modern nearshore to inner-shelf sediments are mostly sand (unit Qms) and a mix of sand, gravel, and cobbles (units Qmsc and Qmsd). The more coarse-grained sands and gravels (units Qmsc and Qmsd) are primarily recognized on the basis of bathymetry and high backscatter. Unit Qmsc occurs in two areas: (1) as a linear nearshore bar (water depth less than 10 m) offshore of Salmon Creek - the eastern contact of this unit is queried because of the lack of data in the surf zone; and (2) as a west-trending bar at the north end of Bodega Bay. Unit Qmsd forms erosional lags in scoured depressions that are bounded by relatively sharp contacts with bedrock or sharp to diffuse contacts with unit Qms. These scoured depressions are typically a few tens of centimeters deep and range in size from a few 10's of sq m to more than one sq km. Similar unit Qmsd scour depressions are common along this stretch of the California coast (see, for example, Cacchione and others, 1984; Hallenbeck and others, 2012) where surficial offshore sandy sediment is relatively thin (thus unable to fill the depressions) due to both lack of sediment supply and to erosion and transport of sediment during large northwest winter swells. Such features have been referred to as "rippled-scour depressions" (see, for example, Cacchione and others, 1984) or "sorted bedforms" (see, for example, Goff and others, 2005; Trembanis and Hume, 2011). Although the general areas in which both unit Qmsd scour depressions and surrounding mobile sand sheets occur are not likely to change substantially, the boundaries of the individual Qmsd depressions are likely ephemeral, changing seasonally and during significant storm events. Unit Qmsf lies offshore of unit Qms, consists primarily of mud and muddy sand and is commonly extensively bioturbated. The water depth of the transition from sand-dominated marine sediment (unit Qms) to mud-dominated marine sediment (Qmsf) occurs at depths of about 45 to 50 m except offshore of Bodega Head where seafloor bedrock outcrops extend to depths of 80 m at the outer limit of California's State Waters. The smooth seafloor in the northern part of the map area between water depths of 40 m and 70 m notably includes an about 3-km-wide field of elongate, shore-normal, paired sediment lobes and chutes (unit Qmsl). Individual lobes within the field are as much as 1,000-m long and 150-m wide, and have as much as 2 m of relief above the surrounding smooth seafloor. This sediment-lobe field lies just one kilometer west of the San Andreas Fault and we infer that large earthquakes on this structure generated strong ground motions and slope failures, mobilizing small sediment flows that moved down the gentle slope and were deposited as lobes. Unit Qmsl also occurs as a 250-m-wide field of four discrete lobes and paired arcuate, low-relief scours on the south flank of a west-trending bar in northern Bodega Bay. Map unit polygons were digitized over underlying 2-meter base layers developed from multibeam bathymetry and backscatter data (see Bathymetry--Offshore Bodega Head, California and Backscattter A to C--Offshore Bodega Head, California, DS 781, for more information). The bathymetry and backscatter data were collected between 2007 and 2010. References Cited Cacchione, D.A., Drake, D.E., Grant, W.D., and Tate, G.B., 1984, Rippled scour depressions of the inner continental shelf off central California: Journal of Sedimentary Petrology, v. 54, p. 1,280-1,291. Goff, J.A., Mayer, L.A., Traykovski, P., Buynevich, I., Wilkens, R., Raymond, R., Glang, G., Evans, R.L., Olson, H., and Jenkins, C., 2005, Detailed investigations of sorted bedforms or "rippled scour depressions", within the Martha’s Vineyard Coastal Observatory, Massachusetts: Continental Shelf Research, v. 25, p. 461-484. Hallenbeck, T.R., Kvitek, R.G., and Lindholm, J., 2012, Rippled scour depressions add ecologically significant heterogeneity to soft-bottom habitats on the continental shelf: Marine Ecology Progress Series, v. 468, p. 119-133. Lambeck, K., and Chappell, J., 2001, Sea level change through the last glacial cycle: Science, v. 292, p. 679-686, doi: 10.1126/science.1059549. Peltier, W.R., and Fairbanks, R.G., 2006, Global glacial ice volume and Last Glacial Maximum duration from an extended Barbados sea level record: Quaternary Science Reviews, v. 25, p. 3,322-3,337. Trembanis, A.C., and Hume, T.M., 2011, Sorted bedforms on the inner shelf off northeastern New Zealand-Spatiotemporal relationships and potential paleo-environmental implications: Geo-Marine Letters, v. 31, p. 203-214.

This part of DS 781 presents data for the acoustic-backscatter map of the Offshore of Bolinas map area, California. Backscatter data are provided as separate grids depending on mapping system or processing method. The raster data files is included in "BackscatterE_Swath_OffshoreBolinas.zip", which are accessible from https://pubs.usgs.gov/ds/781/OffshoreBolinas/data_catalog_OffshoreBolinas.html. The acoustic-backscatter map of the Offshore of Bolinas map area, California, was generated from backscatter collected by California State University, Monterey Bay (CSUMB), by Fugro Pelagos, and by Moss Landing Marine Laboratory (MLML). Mapping was completed between 2004 and 2010, using a combination of 200-kHz and 400-kHz Reson 7125, and 244-kHz Reson 8101 multibeam echosounders, as well as 468-kHz SEA SWATHPlus and 250-kHz GeoSwath interferometric systems. Moss Landing Marine Laboratory mapped the nearshore region north of Bolinas in 2004 prior to the California Seafloor Mapping Program (CSMP). The nearshore region from south of Bolinas Lagoon to Stinson Beach was mapped by Fugro Pelagos in 2009 for a project outside of the CSMP and only bathymetry data were collected. Therefore, note that the shaded relief map coverage (see Bathymetry Hillshade--Offshore of Bolinas, California, DS 781) does not match the acoustic-backscatter map coverage (see Backscatter A-E--Offshore of Bolinas, California, DS 781). Within the acoustic-backscatter imagery, brighter tones indicate higher backscatter intensity, and darker tones indicate lower backscatter intensity. The intensity represents a complex interaction between the acoustic pulse and the seafloor, as well as characteristics within the shallow subsurface, providing a general indication of seafloor texture and sediment type. Backscatter intensity depends on the acoustic source level; the frequency used to image the seafloor; the grazing angle; the composition and character of the seafloor, including grain size, water content, bulk density, and seafloor roughness; and some biological cover. Harder and rougher bottom types such as rocky outcrops or coarse sediment typically return stronger intensities (high backscatter, lighter tones), whereas softer bottom types such as fine sediment return weaker intensities (low backscatter, darker tones). These data are not intended for navigational purposes.

This part of SIM 3306 presents data for the seafloor-character map (see sheet 5, SIM 3306) of the Offshore of San Gregorio map area, California. The raster data file is included in "SeafloorCharacter_OffshoreSanGregorio.zip," which is accessible from https://pubs.usgs.gov/ds/781/OffshoreSanGregorio/data_catalog_OffshoreSanGregorio.html. This raster-format seafloor-character map shows four substrate classes in the Offshore of San Gregorio map area. The substrate classes mapped in this area have been colored to indicate which of the following California Marine Life Protection Act depth zones and slope classes they belong: Depth Zone 2 (intertidal to 30 m), Depth Zone 3 (30 to 100 m), and Slope Class 1 (0 degrees - 5 degrees). Depth Zones 1 (intertidal) and 4 to 5 (greater than 100 m), as well as Slopes Classes 2 to 4 (greater than 5 degrees), are not present in this map area. The map is created using a supervised classification method described by Cochrane (2008), available at http://doc.nprb.org/web/research/research%20pubs/615_habitat_mapping_workshop/Individual%20Chapters%20High-Res/Ch13%20Cochrane.pdf. References Cited: California Department of Fish and Game, 2008, California Marine Life Protection Act master plan for marine protected areas--Revised draft: California Department of Fish and Game, accessed April 5 2011, at http://www.dfg.ca.gov/mlpa/masterplan.asp. Cochrane, G.R., 2008, Video-supervised classification of sonar data for mapping seafloor habitat, in Reynolds, J.R., and Greene, H.G., eds., Marine habitat mapping technology for Alaska: Fairbanks, University of Alaska, Alaska Sea Grant College Program, p. 185-194, accessed April 5, 2011, at http://doc.nprb.org/web/research/research%20pubs/615_habitat_mapping_workshop/Individual%20Chapters%20High-Res/Ch13%20Cochrane.pdf. Sappington, J.M., Longshore, K.M., and Thompson, D.B., 2007, Quantifying landscape ruggedness for animal habitat analysis--A case study using bighorn sheep in the Mojave Desert: Journal of Wildlife Management, v. 71, p. 1419-1426.

Three bedrock knobs (Arch, Harding, and Shag rocks) rise above the unconsolidated sediment of central San Francisco Bay to a water depth of less than -12 m (

The Gulf of the Farallones is located on a continental margin that is tectonically active and has experienced eustatic fluctuations of sea level throughout the Quaternary. Bathymetry of the Gulf suggests that it is different from the average continental shelf off California in that instead of a seafloor that slopes gently seaward from the shoreline to the shelf edge (dominantly west to southwest), much of the Gulf shelf slopes to the northwest, a direction that is subparallel to that of the adjacent mainland shoreline. Isobaths are oblique to shore-normal for much of the Gulf shelf as opposed to the more typical shore-parallel isobaths. This northwest trend is parallel to that of the offshore granitic outcrops, the Farallon Island ridge and Cordell Bank. 3.5 kHz shallow subsurface profiles show a regional unconformity (basal unconformity of this study) that truncates bedrock and typically is overlain by a very thin veneer (1–2 m or less) of acoustically transparent unconsolidated sediment. In places, the basal unconformity appears to be coincident with the seafloor. Where the basal unconformity is within 1–2 m of the seafloor, side-scan sonar reveals that either bedrock pierces the seafloor or numerous linear depressions dissect the shelf seafloor. Side-scan sonar shows that the central part of the study area is characterized by numerous linear depressions that are on the order of 1–3 m deep, several meters to 5 km in length, and from 250 m to 2 km in width. The only Holocene unconsolidated sediment in excess of 1–2 m that has accumulated on the Gulf shelf is located where the bedrock surface is topographically depressed. The topographic lows are situated south of the Point Reyes headland and southwest of the Golden Gate. The sediment deposits that overlie these lows attain thicknesses up to 15–20 m; however, their average thickness is less than 10 m. Structure contours on the basal unconformity surface, essentially the top of the bedrock platform, also show that it is topographically high at its southern end and low at its northern end; the slope of the platform is therefore to the northwest. The seafloor mimics the attitude of the bedrock platform owing to the lack of appreciable sediment cover and hence also slopes northwest. This accounts for the oblique to shore-normal orientation of isobaths in the Gulf and the northwestward slope of the seafloor. The results of this investigation suggest that eustatic sea level fluctuations in conjunction with local tectonics had a profound effect on the deposition, erosion, and preservation of sediment on the Gulf shelf throughout the Quaternary and that the shallow subsurface greatly influences many aspects of the present surficial morphology.

Point based visual observations of benthic habitat from a samples obtained with a video sled.

The south-central Monterey Bay shelf is a high-energy, wave-dominated, tectonically active coastal region on the central California continental margin. A prominent feature of this shelf is a sediment lobe off the mouth of the Salinas River that has surface expression. High-resolution seismic-reflection profiles reveal that an angular unconformity (Quaternary?) underlies the entire shelf and separates undeformed strata above it from deformed strata below it. The Salinas River lobe is a convex bulge on the shelf covering an area of approximately 72 km 2 in water depths from 10 to 90 m. It reaches a maximum thickness of 35 m about 2.5 km seaward of the river mouth and thins in all directions away from this point. Adjacent shelf areas are characterized by only a thin (2 to 5 m thick) and uniform veneer of sediment. Acoustic stratigraphy of the lobe is complex and is characterized by at least three unconformity-bounded depositional sequences. Acoustically, these sequences are relatively well bedded. Acoustic foresets occur within the intermediate sequence and dip seaward at 0.7° to 2.0°. Comparison with sedimentary sequences in uplifted onshore Pleistocene marine-terrace deposits of the Monterey Bay area, which were presumably formed in a similar setting under similar processes, suggests that a general interpretation can be formulated for seismic stratigraphic patterns. Depositional sequences are interpreted to represent shallowing-upwards progradational sequences of marine to nonmarine coastal deposits formed during interglacial highstands and/or during early stages of falling sea level. Acoustic foresets within the intermediate sequence are evidence of seaward progradation. Acoustic unconformities that separate depositional sequences are interpreted as having formed largely by shoreface planation and may be the only record of the intervening transgressions. The internal stratigraphy of the Salinas River lobe thus suggests that at least several late Quaternary regressions and transgressions may be recorded under the present shelf. This record may represent the last major eustatic cycle of sea level, an interval not observed in uplifted onshore Pleistocene marine terraces.

Pleistocene Shoreline and Shelf Deposits at Fort Funston and Their Relations to Sea-Level Changes–Latest Cretaceous Eartly Tertiary Systems of the Northern Diablo Range, California Depositional Facies of Sedimentary Serpentinite: Selected Examples from the Coast Ranges, California