Geology and geomorphology--Offshore of Point Reyes Map Area, California

Map unit polygons were digitized over underlying 2-meter base layers developed from multibeam bathymetry and backscatter data. Derivatives such as slope and curvature were generated from source rasters. Interpreted rasters include amplitude, hillshaded bathymetry (using various illumination angles and vertical exaggeration), slope, and curvature. Curvature was decomposed into profile and plan curvature for analysis purposes.

The mapped area was extended to the shoreline by using digital orthophotos to interpret the region between the inner edge of the multibeam bathymetry and the approximate shoreline. The approximate shoreline was generated at the NAVD88 +1.46 m contour, defined as the operational MHW shoreline by Weber and others (2005). The resulting boundary was transformed to WGS 84 UTM Zone 10 North in ArcGIS 10 using the NAD83 to WGS84 (ITRF00) transformation algorithm. This boundary was then used to extend and trim both onshore and offshore geology in the print and PDF product. The transformed boundary is contained within the WGS84 "contours" feature class and identified as a water boundary in the associated representation rules.
Only data for offshore map units are released digitally in this publication. For onshore geology, see Blake and others (2000), California Geological Survey (1974), Galloway (1976), and Witter and others (2006).
References Cited:
Blake, M.C., Jr., Graymer, R.W., and Jones, D.L., 2000, Geologic map and map database of parts of Marin, San Francisco, Alameda, Contra Costa, and Sonoma counties, California: U.S. Geological Survey Miscellaneous Field Studies Map 2337, scale 1:62,500.
California Geological Survey, 1974, Alquist-Priolo Earthquake Fault Zone Maps of Inverness quadrangle, scale 1:24,000.
Clark, J.C., and Brabb, E.E., 1997, Geology of the Point Reyes National Seashore and vicinity: U.S. Geological Survey Open-File Report 97 456, scale 1:48,000.
Galloway, A.J., 1976, Geology of the Point Reyes Peninsula Marin County, California: California Geological Survey Bulletin 202, scale 1:24,000.
Weber, K.M., List, J.H., and Morgan, K.L., 2005, An operational Mean High Water datum for determination of shoreline position from topographic lidar data: U.S. Geological Survey Open-File Report 2005-1027, available at http://pubs.usgs.gov/of/2005/1027/.
Witter, R.C., Knudsen, K.L., Sowers, J.M., Wentworth, C.M., Koehler, R.D., Randolph, C.E., Brooks, S.K., and Gans, K.D., 2006, Maps of Quaternary Deposits and Liquefaction Susceptibility in the Central San Francisco Bay Region, California, U.S. Geological Survey Open-File Report 06 1037, scale 1:24,000.

Added Distribution_Information section to metadata to facilitate data download.

Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog.

Added keywords from Coastal and Marine Ecological Classification Standard (CMECS) to metadata.

Edited metadata to add keywords section with USGS persistent identifier as theme keyword. No data were changed.

Metadata was modified to bring up to current USGS PCMSC standards. USGS Thesaurus and keywords were added, information for accompanying Open-File Report added to Abstract and Cross Reference sections, Point of Contact and Metadata Contact information was updated, and Process Steps were refined. Information about the data available for download and different Network Resource Name links and details were given in the Standard Order Process section. Minor typos were corrected. No data information was changed. The metadata available from a harvester may supersede metadata bundled within a download file. Users are advised to compare the metadata dates to determine which metadata file is most recent.