Lithology and Stratigraphy
This subsection contains late Quaternary alluvium. The alluvium is predominantly from sedimentary rocks sources in the Coast Ranges.
This subsection is on nearly level to gently sloping alluvial fans and basins. There are small areas of floodplain along streams that cross from mountains of the Coast Ranges to reach basins in the San Joaquin Valley. The subsection elevation range is from 170 to about 600 feet. Fluvial erosion and deposition are the main geomorphic processes.
The soils are mostly Typic and Vertic Torrifluvents and Typic Torriorthents, and, on basin floors, Typic Natrargids. The soils are well drained. Leaching and accumulation of clay and calcium carbonates in subsoils are the main pedogenic processes. Sodium accumulates in soils on the basin floors. Soil temperature regimes are thermic, and soil moisture regimes are aridic.
The predominant natural plant communities are Needlegrass grasslands, with Greasewood series on floodplains and basin floors.
Characteristic series by lifeform include:
- Grasslands: California annual grassland series, Purple needlegrass series.
Shrublands: Bladderpod - California ephedra - narrowleaf goldenbush series.
The mean annual precipitation is about 6 to 8 inches; it is all rain. Mean annual temperature is about 59° to 62° F. The mean freeze-free period is about 250 to 275 days.
The main streams from the Coast Ranges are Panoche Creek, Cantua Creek, and Warthan and Zapato Creeks. Warthan and Zapato Creeks converge to Arroyo Pasajero. Thus, there are three major fans — those of Panoche Creek, Cantua Creek, and Arroyo Pasajero. Streams in this subsection drain to basins at the toes of the alluvial fans. Drainage in the basins is parallel to the axis of Central Valley. It is to the San Joaquin River north of the Arroyo Pasajero fan and to the Tulare Basin south of the Arroyo Pasajero fan. The streams dry during the summer. There are no permanent lakes.