The lowermost paleosol comprises four distinct beds and is best exposed in the northernn part of the field area. All units contain quartz in a kaolinitic matrix. Hematite staining of the kaolinite matrix produces red to lavender mottles. Paleosol 1 grades laterally to the south into a saprolite. Mono- and polycrystalline quartz grains are partially dissolved, etched, and angular.
Potassium feldspars are highly dissolved and are altering to kaolinite.
We have identified two distinct paleosols exposed in the middle part of the Paleogene Silverado Formation in the San Joaquin Hills. These paleosols, which were originally mapped as a single clay bed, occur in texturally immature arkoses and lithic arenites. Recent mapping of the lowermost paleosol has extended this unit an additional 1.5 miles to the south from the previously mapped location. In all units, dissolved, etched and pitted monocrystalline quartz grains float in a kaolinitic matrix. Disaggregation of polycrystalline quartz along crystal boundaries is evident.