High precipitation rates found in humid tropical environments provide a nearly constant influx of water, and all minerals except quartz are leached out. When ferrallitic soils develop in quartz-rich rocks, kaolinite forms in subsurface horizons. Poor drainage within this kaolinitic horizon produces red and white mottling. Watertable fluctuations promotes the development of a ferricrete crust. 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.