Oxnard Plain - Santa Paula Valley

http://www.fs.fed.us/r5/projects/ecoregions/261bd.htm

This subsection includes valleys of the Santa Clara River and Calleguas Creek (which is an extension of Arroyo Simi that drains Simi Valley) and a plain at the mouths of these streams. The climate is hot and subhumid; it is modified greatly by marine air. MLRA 19d.
Lithology and Stratigraphy. This subsection contains mainly late Quaternary alluvium and lesser amounts of Plio-Pleistocene nonmarine sediments. Dune sand is present along the coast.

Geomorphology. This subsection is mostly on nearly level floodplains and very gently to gently sloping alluvial fans and terraces. There are small areas of dissected Plio-Pleistocene sediments. Dunes are present in a narrow strip adjacent to the coast. The subsection elevation range is from sea-level up to about 800 feet. Fluvial erosion and deposition are the main geomorphic processes. Wind is an important geomorphic agent along the coast, along with coastal marine processes.

Soils. The soils are mostly Fluventic, Cumulic, and Calcic Haploxerolls, and, near the coast, some Aquic Xerofluvents and Fluvaquentic Haploxerolls. Typic Argixerolls, Mollic Haploxeralfs, and Abruptic Durixeralfs are common on alluvial fans and terraces. On dissected Plio-Pleistocene sediments there are shallow Typic Xerorthents, Calcixerollic Xerochrepts, and Calcic Pachic Haploxerolls. Typic Xeropsamments are common on stabilized dunes. The soils are well to somewhat poorly drained. Calcium carbonates accumulate in some of the soils. Soil temperature regimes are thermic; and soil moisture regimes are xeric.

Vegetation. The predominant natural plant communities include California sagebrush series and Purple sage series. There are small areas of Pickleweed series.

Characteristic series by lifeform include:
Saltmarshs: Cordgrass series, Ditch-grass series, Pickleweed series.
Grasslands: California annual grassland series.
Shrublands: Black sage series, California buckwheat series, California sagebrush series, California sagebrush - black sage series, California sagebrush series - California buckwheat series, Coyote brush series, Mixed sage series, Purple sage series.
Forests and woodlands: California sycamore series, Coast live oak series.
Climate. The mean annual precipitation is about 12 to 18 inches; it is practically all rain. Summer fog is common. Mean annual temperature is about 56� to 60� F. The mean freeze-free period is about 300 to 350 days.
Surface Water. The Santa Clara River drains much of the northern part of the Transverse Ranges. It is perennial, but Calleguas Creek, which is the next largest stream that runs through the subsection, is not perennial. There are no lakes or ponds, other than temporary ponding behind dunes.