Description: This part of DS 781 presents data for the bathymetric contours for several seafloor maps of the Offshore of Salt Point map area, California. The vector data file is included in "Contours_OffshoreSaltPoint.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html. 10-m interval contours of the Offshore of Salt Point 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 State Waters. Bathymetric contours at 10-m intervals were generated from a modified 2-m bathymetric surface. The original surface was smoothed using the Focal Mean tool in ArcGIS and a circular neighborhood with a radius of 20 to 30 meters (depending on the area). The contours were generated from this smoothed surface using the ArcGIS Spatial Analyst Contour tool. The most continuous contour segments were preserved while smaller segments and isolated island polygons were excluded from the final output. The contours were then clipped to the boundary of the map area.These data are not intended for navigational purposes.
Description: This part of DS 781 presents data for faults for the geologic and geomorphic map of the Offshore of Salt Point map area, California. The vector data file is included in "Faults_OffshoreSaltPoint.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html. The onshore part of the Offshore of Salt Point map area is cut by the northwest-trending San Andreas Fault, the right-lateral transform boundary between the North American and Pacific tectonic plates. The San Andreas extends extends into the offshore about 5 km south of the map area near Fort Ross, and about 50 km north of the map area on the east flank of Point Arena. The coast between Fort Ross and Point Arena, the northwesternmost exposed section west of the San Andreas Fault, is known as the "Gualala Block" on the basis of its distinctive geology, which has been widely used to develop paleogeographic reconstructions of coastal California that restore as much as 150 to 180 km of right-lateral slip on the combined San Andreas and San Gregorio Fault systems. The Gualala Block is underlain by a thick (as much as 9 to 11 km, in aggregate), discontinuous Upper Cretaceous to Miocene stratigraphic section, however only the Eocene and Paleocene German Rancho Formation (unit Tgr) is exposed onshore and is inferred to form seafloor bedrock outcrops in the Offshore of Salt Point map area. The German Rancho Formation consists of sandstone, mudstone, and conglomerate interpreted as deep-water, submarine-fan deposits. The western boundary of the Gualala Block lies offshore. Using seismic-reflection data, McCulloch (1987; his fig. 14) mapped a shore-parallel fault about 3 to 5 km offshore, which Dickinson and others (2005) subsequently named the Gualala Fault. Jachens and others (1998) evaluated aeromagnetic and gravity data across this zone and modeled this structure as a steep fault within the Salinian basement block, characterized by 3 to 5 km of right-lateral offset. In contrast, Dickinson and others (2005) consider the Gualala fault a Late Miocene strand of the San Andreas fault, separating Salinian and Franciscan basement rocks, with minimum right-lateral slip of 70 km. Our analysis of deeper industry seismic-reflection data within California State Waters shows the Gualala fault as a steep, northeast-dipping structure. Shallower seismic-reflection crossing the Gualala fault reveal a thick late Pleistocene section characterized by recent faulting and gentle asymmetric folding. Hence, the Gualala fault appears to be a recently active "blind" structure that has deformed young sediments. Our mapping also documents a more nearshore zone of deformation that we refer to as the "east Gualala deformation zone." This zone extends through the central and southern parts of the Offshore of Salt Point map area and is similarly charcterized by steep faults and gentle folds that deform inferred late Pleistocene strata. This section of the San Andreas Fault onland has an estimated slip rate of about 17 to 25 mm/yr. The devastating Great 1906 California earthquake (M 7.8) is thought to have nucleated on the San Andreas Fault about 100 kilometers south of this map area offshore of San Francisco, with the rupture extending northward through the onshore part of the Offshore of Salt Point map area to the south flank of Cape Mendocino. Emergent marine terraces along the coast in the Offshore of Salt Point map area record recent contractional deformation associated with the San Andreas Fault system. Prentice and Kelson (2006) reported uplift rates of 0.3 to 0.6 mm/yr for a nearby late Pleistocene terrace (exposed at Fort Ross, about 5 km south of the map area) and this recent uplift must also have affected the nearshore and inner shelf, at least as far west as the Gualala fault. Faults were primarily mapped by interpretation of seismic reflection profile data (see field activity S-8-09-NC). The seismic reflection profiles were collected between 2007 and 2010.
Description: This part of DS 781 presents data for folds for the geologic and geomorphic map of the Offshore of Salt Point map area, California. The vector data file is included in "Folds_OffshoreSaltPoint.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html. The onshore part of the Offshore of Salt Point map area is cut by the northwest-trending San Andreas Fault, the right-lateral transform boundary between the North American and Pacific tectonic plates. The San Andreas extends extends into the offshore about 5 km south of the map area near Fort Ross, and about 50 km north of the map area on the east flank of Point Arena. The coast between Fort Ross and Point Arena, the northwesternmost exposed section west of the San Andreas Fault, is known as the "Gualala Block" (fig. 1) on the basis of its distinctive geology, which has been widely used to develop paleogeographic reconstructions of coastal California that restore as much as 150 to 180 km of right-lateral slip on the combined San Andreas and San Gregorio Fault systems. The Gualala Block is underlain by a thick (as much as 9 to 11 km, in aggregate), discontinuous Upper Cretaceous to Miocene stratigraphic section, however only the Eocene and Paleocene German Rancho Formation (unit Tgr) is exposed onshore and is inferred to form seafloor bedrock outcrops in the Offshore of Salt Point map area. The German Rancho Formation consists of sandstone, mudstone, and conglomerate interpreted as deep-water, submarine-fan deposits. The western boundary of the Gualala Block lies offshore. Using seismic-reflection data, McCulloch (1987; his fig. 14) mapped a shore-parallel fault about 3 to 5 km offshore, which Dickinson and others (2005) subsequently named the Gualala Fault. Jachens and others (1998) evaluated aeromagnetic and gravity data across this zone and modeled this structure as a steep fault within the Salinian basement block, characterized by 3 to 5 km of right-lateral offset. In contrast, Dickinson and others (2005) consider the Gualala fault a Late Miocene strand of the San Andreas fault, separating Salinian and Franciscan basement rocks, with minimum right-lateral slip of 70 km. Our analysis of deeper industry seismic-reflection data within California State Waters shows the Gualala fault as a steep, northeast-dipping structure. Shallower seismic-reflection crossing the Gualala fault reveal a thick late(?) Pleistocene section characterized by recent faulting and gentle asymmetric folding. Hence, the Gualala fault appears to be a recently active "blind" structure that has deformed young sediments. Our mapping also documents a more nearshore zone of deformation that we refer to as the "east Gualala deformation zone." This zone extends through the central and southern parts of the Offshore of Salt Point map area and is similarly charcterized by steep faults and gentle folds that deform inferred late Pleistocene strata. This section of the San Andreas Fault onland has an estimated slip rate of about 17 to 25 mm/yr. The devastating Great 1906 California earthquake (M 7.8) is thought to have nucleated on the San Andreas Fault about 100 kilometers south of this map area offshore of San Francisco, with the rupture extending northward through the onshore part of the Offshore of Salt Point map area to the south flank of Cape Mendocino. Emergent marine terraces along the coast in the Offshore of Salt Point map area record recent contractional deformation associated with the San Andreas Fault system. Prentice and Kelson (2006) reported uplift rates of 0.3 to 0.6 mm/yr for a nearby late Pleistocene terrace (exposed at Fort Ross, about 5 km south of the map area) and this recent uplift must also have affected the nearshore and inner shelf, at least as far west as the Gualala fault. Folds were primarily mapped by interpretation of seismic reflection profile data (see field activity S-8-09-NC). The seismic reflection profiles were collected between 2007 and 2010.
Description: This part of DS 781 presents data for the geologic and geomorphic map of the Offshore of Salt Point map area, California. The vector data file is included in "Geology_OffshoreSaltPoint.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html. The morphology and the geology of the Offshore of Salt Point map area result from the interplay between local sea-level rise, sedimentary processes, oceanography, and tectonics. The offshore part of the map area extends from the shoreline to water depths of about 90 to 100 m on the mid-continental shelf; the shelfbreak occurs about 20 km farther offshore at water depths of about 200 m. The nearshore and inner shelf (to water depths of about 50 to 60 m) typically dips seaward about 1.0 to 1.5 degrees; the mid to outer shelf dips more gently, generally less than 0.5 degrees. Sea level has risen about 125 to 130 m over about the last 21,000 years, leading to broadening of the continental shelf, progressive eastward migration of the shoreline and wave-cut platform, and associated transgressive erosion and deposition. Land-derived sediment was carried into this dynamic setting, then subjected to full Pacific Ocean wave energy and strong currents before deposition or offshore transport. Tectonic influences impacting shelf morphology and geology are related to local faulting, folding, uplift, and subsidence. Bedrock of the Eocene and Paleocene German Rancho Formation (unit Tgr) underlies much of the inner shelf, extending to water depths of as much as 60 m. Although onshore coastal outcrops of this unit are well bedded, seafloor outcrops imaged on high-resolution bathymetry have a hackly surface texture and abundant fractures. Embayments in the outer margin of the seafloor bedrock outcrops are commonly paired with the mouths of coastal watersheds and are inferred to have formed by fluvial erosion during the last sealevel lowstand. One of the more prominent embayments occurs about one kilometer north of Salt Point at the mouth of Miller Creek. These coastal watersheds are relatively small and steep, extending to a drainage divide just 2 to 3 km east of the shoreline, and are inferred sources of coarse-grained sediments. Immediately east of this onshore topographic divide, drainage along this part of the coast is captured by the northwest-flowing South Fork of the Gualala River, which runs parallel to the coast along the trace of the San Andreas fault. Given relatively shallow water depths (0 to about 50 m) and exposure to high wave energy, modern nearshore to mid-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. Both Qmsc and Qmsd typically have abrupt landward contacts with bedrock (unit Tgr) and form irregular to lenticular exposures that are commonly elongate in the shore-normal direction. Contacts between units Qmsc and Qms are typically gradational. Unit Qmsd forms erosional lags in scoured depressions that are bounded by relatively sharp and less commonly diffuse contacts with unit Qms horizontal sand sheets. These 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 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" or "sorted bedforms". 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. The offshore decrease in slope at mid-shelf water depths (about 60 m) approximately coincides with a transition to more fine-grained marine sediments (unit Qmsf), which extends to the outer (3-nautical-mile) limit of California's State Waters. Unit Qmsf consists primarily of mud and muddy sand and is commonly extensively bioturbated. These fine-grained sediments are inferred to have been derived from from the Russian River, which has its mouth about 15 km south of the map area. Both Drake and Cacchione (1985) and Sherwood and others (1994) have documented seasonal, mid-shelf, northwest-directed, bottom currens capable of transporting fine-grained, suspended sediment from the Russian River to the Offshore of Salt Point map area. Map unit polygons were digitized over underlying 2-meter base layers developed from multibeam bathymetry and backscatter data (see Bathymetry--Offshore Salt Point, California and Backscattter--Offshore Salt Point, California, DS 781, for more information). The bathymetry and backscatter data were collected between 2006 and 2010.
Description: This part of DS 781 presents data for the habitat map of the seafloor of the Offshore of Salt Point map area, California. The vector data file is included in "Habitat_OffshoreSaltPoint.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html. Using multibeam echosounder (MBES) bathymetry and backscatter data, potential marine benthic habitat maps were constructed. The habitats were based on substrate types and documented or "ground truthed" using underwater video images and seafloor samples obtained by the USGS. These maps display various habitat types that range from flat, soft, unconsolidated sediment-covered seafloor to hard, deformed (folded), or highly rugose and differentially eroded bedrock exposures. Rugged, high-relief, rocky outcrops that have been eroded to form ledges and small caves are ideal habitat for rockfish (Sebastes spp.) and other bottom fish such as lingcod (Ophiodon elongatus). Habitat map is presented in a map format generated in a GIS (ArcMap), and both digital and hard-copy versions will be produced. Please refer to Greene and others (2007) for more information regarding the Benthic Marine Potential Habitat Classification Scheme and the codes used to represent various seafloor features.
Description: This part of DS 781 presents the seafloor-character map Offshore of Salt Point, California (raster data file is included in "SeafloorCharacter_SaltPoint.zip," which is accessible from http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html). This raster-format seafloor-character map shows four substrate classes offshore of Salt Point, California. The substrate classes mapped in this area have been further divided into the following California Marine Life Protection Act depth zones and slope classes: Depth Zone 2 (intertidal to 30 m), Depth Zone 3 (30 to 100 m), Slope Class 1 (0 degrees - 5 degrees), and Slope Class 2 (5 degrees - 30 degrees). Depth Zone 1 (intertidal), Depth Zone 4 (100 to 200 m), Depth Zone 5 (greater than 200 m), and Slopes Classes 3-4 (greater than 30 degrees) are not present in the region covered by this block. 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.
Description: This part of DS 781 presents data for the bathymetry and shaded-relief maps of the Offshore of Salt Point map area, California. Raster data file is included in "BathymetryHS_OffshoreSaltPoint.zip", which is accessible from http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html. The bathymetry and shaded-relief maps of the Offshore of Salt Point 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. These data are not intended for navigational purposes.
Description: This part of DS 781 presents data for the acoustic-backscatter map of the Offshore of Salt Point map area, California. Backscatter data are provided as separate grids depending on mapping system or processing method. The raster data files are included in "BackscatterA_8101_OffshoreSaltPoint.zip", which are accessible from http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html. The acoustic-backscatter map of the Offshore of Salt Point map area, California, was generated from backscatter 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 backscatter data from about the 10-m isobath to beyond the 3-nautical-mile limit of California State Waters. 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 composition. 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.
Description: This part of DS 781 presents data for the acoustic-backscatter map of the Offshore of Salt Point map area, California. Backscatter data are provided as separate grids depending on mapping system or processing method. The raster data files are included in "BackscatterB_Swath_OffshoreSaltPoint.zip", which are accessible from http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html. The acoustic-backscatter map of the Offshore of Salt Point map area, California, was generated from backscatter 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 backscatter data from about the 10-m isobath to beyond the 3-nautical-mile limit of California State Waters. 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 composition. 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.
Description: This part of DS 781 presents data for the acoustic-backscatter map of the Offshore of Salt Point map area, California. Backscatter data are provided as separate grids depending on mapping system or processing method. The raster data files are included in "BackscatterC_7125_SaltPoint.zip", which are accessible from http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html. The acoustic-backscatter map of the Offshore of Salt Point map area, California, was generated from backscatter 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 backscatter data from about the 10-m isobath to beyond the 3-nautical-mile limit of California State Waters. 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 composition. 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.
Description: This part of DS 781 presents data for the bathymetry and shaded-relief maps of the Offshore of Salt Point map area, California. Raster data file is included in "Bathymetry_OffshoreSaltPoint.zip", which is accessible from http://pubs.usgs.gov/ds/781/OffshoreSaltPoint/data_catalog_OffshoreSaltPoint.html. The bathymetry and shaded-relief maps of the Offshore of Salt Point 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. These data are not intended for navigational purposes.