Lithology and Stratigraphy
This subsection contains recent alluvium of stream channel, stream overflow, and alluvial fan deposits. The alluvium is from granitic, volcanic, sedimentary, and metamorphic[ rock sources in mountains around the Sacramento Valley.
This subsection is on nearly level to very gently sloping stream channels, levees, overflow basins, and alluvial fans. The subsection elevation range is from about 10 to about 40 feet. Fluvial erosion and deposition are the main geomorphic processes.
The soils are mostly Aquic Xerofluvents; Aeric Haplaquepts; and Cumulic and Vertic Haplaquolls. Pelloxererts and Chromoxererts are common on alluvial fans. The soils are moderately well drained to poorly drained. Soil temperature regimes are thermic, and soil moisture regimes are aquic and xeric.
The predominant natural plant communities are Emergent aquatic communities and Needlegrass grasslands.
Characteristic series by lifeform include:
- Wetlands: Bulrush series, Bulrush - cattail series, Cattail series, Sedge series.
Forests and woodlands: California sycamore series, Fremont cottonwood series, Mixed willow series.
The mean annual precipitation is about 14 to 18 inches. It is practically all rain. Mean annual temperature is about 60° to 62° F. The mean freeze-free period is about 250 to 275 days.
The Sacramento River overflows onto parts of this area and overflowed onto most of the area when it flooded before being controlled by dams, artificial levees, and diversions. Streams drain toward the Sacramento River on alluvial fans and parallel to it in overflow basins. All but the larger streams are generally dry during the summer. There are no lakes, but there is temporary ponding in overflow basins.