USGS 50 Years in Menlo Park

Bay Area’s Geology Is Remapped

The San Francisco region’s underground geology--its gravity, its radioactivity and its earthquake faults--have been mapped with new geophysical tools by the United States Geological Survey.

The result is a set of detailed maps that shed new light on the complex land masses of Northern California areas.

Releases yesterday was an extremely large-scale map covering the underground geology of the South San Francisco area, showing a maze of fine features.

Artificially-filled sections, landslides, bay muds, marine terraces, silt debris and depostis of sand, silt, gravel and clay.

The map shows the age and types of underlying bedrock, and details the network of faults that radiate outward from the famed San Andreas Fault--the major rock fracture that cleaves the coastal region of California.

Another Geological Survey map, prepared with sensitve airborne instruments that measure the tug of gravity, shows gravitational variations in a 1600-square-mile region of the northern Bay Area.

The map covers the territory from Pt. Reyes to Vallejo and from Sausalito to Sonoma.

The variations in gravity, superimposed on data about underground geological features, offer new information on the nature of the earth’s hidden structure.

Still another new map covers 21,625 square miles of Central California around the Bay Area, and details variations in the natural radioactivity of underground rock formations.

Prepared by sensitive radiation counters aboard low-flying planes, the map provides valuable clues to the types of the rocks beneath the surface.

It covers a 19-county area around San Francisco--from the Pacific coast eastward to the Sierra foothills, and from Watsonville 170 miles north to Clear Lake.

All the maps are available for examination and copying at the Survey’s Menlo Park Office, 345 Middlefield Road, and its map library in the Custom House here, 555 Battery Street.

San Francisco Chronicle
October 7, 1965

Back to index