Chapter 11: The Agricultural Core

San Francisco, Ca is considered to be part of the West Coast, because it is in the Western part of the United States.

The soil types as reported by USGS are:

Soil type A	Vs > 1500 m/sec	Includes unweathered intrusive igneous rock. Occurs infrequently in the bay area. We consider it with type B (both A and B are represented by the color blue on the map). Soil types A and B do not contribute greatly to shaking amplification.
Soil type B	1500 m/sec > Vs > 750 m/sec	Includes volcanics, most Mesozoic bedrock, and some Franciscan bedrock. (Mesozoic rocks are between 245 and 64 million years old. The Franciscan Complex is a Mesozoic unit that is common in the Bay Area.)
Soil Type C	750 m/sec > Vs > 350 m/sec	Includes some Quaternary (less than 1.8 million years old) sands, sandstones and mudstones, some Upper Tertiary (1.8 to 24 million years old) sandstones, mudstones and limestone, some Lower Tertiary (24 to 64 million years old) mudstones and sandstones, and Franciscan melange and serpentinite.
Soil Type D	350 m/sec > Vs > 200 m/sec	Includes some Quaternary muds, sands, gravels, silts and mud. Significant amplification of shaking by these soils is generally expected.
Soil Type E	200 m/sec > Vs	Includes water-saturated mud and artificial fill. The strongest amplification of shaking due is expected for this soil type.

The soils of the Agricultural Core is mollisols and alfisols.  Mollisols form in semi-arid and semi-humid areas, typically under a grassland cover.  Alfisols, like mollisols, also form in semi-arid and semi-humid areas, but under a hardwood forest cover.  The soil type in the Bay Area does not include these two types of soil.  The climate does not accomodate to help form them. There aren't any farms in SF because it is a densely populated city along the bay.