Soils & Geology
Five soil series dominate. Four, usually intermingled, are developed from basic metavolcanic rocks: Auburn, the most extensive, is loam in texture, 1-2 feet deep, well drained and slightly acid; Sobrante, similar to Auburn but 1.5-3 feet deep with slightly more clay in the subsoil; Las Posas and Argonaut, 1.5-3.5 feet deep with clayey subsoils. The fifth series is Wyman, 4-5 feet deep, loam with clay-loam subsoil, formed in alluvium from the four series previously described.