Western Earth Surface Processes

U.S. Geological Survey
Scientific Investigations Map 2956

Geologic Map and Map Database of Eastern Sonoma and Western Napa Counties, California

By R.W. Graymer, E.E. Brabb, D.L. Jones, J. Barnes, R.S. Nicholson, and R.E. Stamski



This report contains a new 1:100,000-scale geologic map, derived from a set of geologic map databases (Arc-Info coverages) containing information at 1:62,500-scale resolution, and a new description of the geologic map units and structural relations in the map area. Prepared as part of the San Francisco Bay Region Mapping Project, the study area includes the north-central part of the San Francisco Bay region, and forms the final piece of the effort to generate new, digital geologic maps and map databases for an area which includes Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano, and Sonoma Counties. Geologic mapping in Lake County in the north-central part of the map extent was not within the scope of the Project. The map and map database integrates both previously published reports and new geologic mapping and field checking by the authors (see Sources of Data index map on the map sheet or the Arc-Info coverage eswn-so and the textfile eswn-so.txt). This report contains new ideas about the geologic structures in the map area, including the active San Andreas Fault system, as well as the geologic units and their relations.

Together, the map (or map database) and the unit descriptions in this report describe the composition, distribution, and orientation of geologic materials and structures within the study area at regional scale. Regional geologic information is important for analysis of earthquake shaking, liquifaction susceptibility, landslide susceptibility, engineering materials properties, mineral resources and hazards, as well as groundwater resources and hazards. These data also assist in answering questions about the geologic history and development of the California Coast Ranges.

Files for Viewing and Plotting

Map at standard resolution as a 34.5" x 50" PDF file (sim2956f.pdf; 6.8 MB).

map at tabloid size for quick viewing as a 1035- x 1500-pixel JPG file (sim2956h.jpg; 1.2 MB).

map at high resolution as a 34.5" x 50" PDF file (sim2956i.pdf; 26.1 MB).

Pamphlet as a 30-page PDF file (sim2956j.pdf; 1.3 MB).


ReadMe.txt as an ASCII text file (ReadMe.txt; 80 kB).


PostScript Plotfile Package which consists of PostScript plot files of a geologic map, explanation sheet, and geologic description. This is a tarred and zipped compressed file (sim2956a.tgz; 17.9 MB compressed, 147 MB when opened).

PDF Plotfile Package contains the same plotfiles as the first package, but in Portable Document Format (PDF). This is a tarred and zipped compressed file (sim2956b.tgz; 26.9 MB compressed, 27.4 MB when opened).

Digital Database Package contains the geologic map database itself and the supporting data, including base maps, map explanation, geologic description, and references. This is a tarred and zipped compressed file (sim2956c.tgz; 57.7 MB compressed, 84.1 MB when opened).

Metadata as an ASCII text file (sim2956d.met.txt; 136 kB).

Version history as an ASCII text file (sim2956e.rev; 56 kB).

For more about the geology of the San Francisco Bay region, visit the San Francisco Bay Region Geology website

For questions about the content of this report, contact Russ Graymer

Suggested citation and version history

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Page Last Modified: November 1, 2007