http://www.fs.fed.us/r5/projects/ecoregions/m261ca.htm

Subsection M261Ca
Western Foothills
This subsection includes Blue Ridge in the northern California Coast Ranges and steep hills east of Blue Ridge and east of the Stony Creek fault. It extends north to the Klamath Mountains. The climate is hot and subhumid. MLRAs 15d and 15e.
Lithology and Stratigraphy. This subsection contains Jurassic and Cretaceous marine sedimentary rocks of the Great Valley Sequence. They are mostly sandstone, shale, and conglomerate that are tilted monoclinally eastward toward the center of the Great Valley.

Geomorphology. Blue Ridge, in the southeast margin of the northern California Coast Ranges mountains, trends north-northwest. The steep hills east of the mountains are elongated parallel to the edge of the Great Valley. They resemble hogbacks along the west edge of the Valley, but do not have such distinct forms at the north end of the Valley. The elevation range is from about 300 feet up to 3057 feet on Berryessa Peak. Mass wasting and fluvial erosion are the main geomorphic processes.

Soils. The soils are mostly Lithic Xerochrepts, Typic Haploxeralfs, Xerolls, and Chromoxererts. The soils are generally, but not all, leached free of carbonates. Few surfaces are old enough, because of active erosion, to have Palexeralfs. Soil temperature regimes are predominantly thermic. Soil moisture regimes are xeric.

Vegetation. The predominant natural plant communities include Chamise series and Blue oak series. Chamise series is most prevalent on steep slopes with shallow or rocky soils. Needlegrass grasslands predominate on some Vertisols.

Characteristic series by lifeform include:
Grasslands: California annual grassland series.
Shrublands: Chamise series, Chamise - wedgeleaf ceanothus series, Scrub oak series, Wedgeleaf ceanothus series, Whiteleaf manzanita series.
Forests and woodlands: Birchleaf mountain-mahogany series, Blue oak series, California buckeye series, Foothill pine series, Interior live oak series.
Climate. The mean annual precipitation is about 25 to 40 inches; most of it is rain. Mean annual temperature is about 55� to 62� F. The mean freeze-free period is from 150 to 250 days.
Surface Water. Runoff is rapid and all but the larger streams are dry through most of the summer. There are no natural lakes, but there are a few reservoirs

Subsection M261Cb
Tehama Terraces
This subsection is a dissected plain between the hills to the west and the western margin of the Great Valley. It extends from Stony Creek north to the Klamath Mountains. The climate is hot and subhumid. MLRAs 15d and 17d.
Lithology and Stratigraphy. This subsection contains nonmarine Pliocene sandstones and conglomerates that are only slightly consolidated rocks, and unconsolidated Quaternary alluvium.

Geomorphology. This subsection is on a plain of Pliocene and Quaternary fluvial surfaces that are highly dissected by streams draining toward the Sacramento River. The drainage patterns are dendritic, branching from streams that drain toward the Sacramento river. Slopes range from nearly level to very gentle on remnants of depositional surfaces to moderately steep to steep in ravines. The elevation is about 200 to 1000 feet. Fluvial erosion is the main geomorphic process; mass wasting is active on steep ravine slopes.

Soils. The soils are mostly Typic, Mollic, and Ultic Palexeralfs on remnants of alluvial plain surfaces and Typic and Ultic Haploxeralfs on erosional slopes below the older surfaces. The soils are generally, but not all, leached free of carbonates. Some of the older soils have claypan (Palexeralfs) or duripan (Durixeralfs) subsoils. Soil temperature regimes are thermic and soil moisture regimes are xeric.

Vegetation. The predominant natural plant community is Blue oak series. Needlegrass grasslands predominate on some fine-textured Alfisols, and Northern claypan vernal pools are common.

Characteristic series by lifeform include:
Grasslands: California annual grassland series.
Vernal pools: Northern claypan and hardpan vernal pools.
Shrublands: Chamise series, Chamise - wedgeleaf ceanothus series.
Forests and woodlands: Blue oak series, Foothill pine series.
Climate. The mean annual precipitation is about 20 to 40 inches; most of the precipitation is rain. Mean annual temperature is about 60� to 62� F. The mean freeze-free period is from 175 to 250 days.
Surface Water. Runoff is rapid and all but the larger streams are dry through most of the summer. Vernal pools are common in areas with claypans or duripans. There are no natural lakes in the area.

Subsection M261Cc
Dunnigan Hills
This subsection comprises Dunnigan Hills and the low hills that extend northerly along the western edge of the Sacramento Valley to just north of Nye Creek. MLRAs 15e and 17e.
Lithology and Stratigraphy. This subsection contains predominantly nonmarine Pliocene mudstones, sandstones and conglomerates that are only slightly consolidated rocks. There are small areas of Pleistocene nonmarine deposits.

Geomorphology. Pliocene and Quaternary fluvial surfaces are highly dissected by streams draining toward the Sacramento River. Drainage patterns are dendritic, branching from streams that drain toward the Sacramento River. The Dunnigan Hills are almost completely dissected, leaving very little of the Pliocene depositional surface. They are well rounded hills with moderately steep to steep sides. The elevation range is about 200 to 1500 feet. Fluvial erosion is the main geomorphic process; mass wasting is important on moderately steep slopes with Vertisols and on steep slopes.

Soils. The soils are mostly Entic and Typic Chromoxererts. Palexeralfs predominate on undissected terrace surfaces. Other common soils are Lithic and Calcixerollic Xerochrepts, Haploxeralfs, and Argixerolls. Calcium carbonate accumulations are common in subsoils. Soil temperature regimes are thermic and soil moisture regimes are xeric.

Vegetation. The predominant natural plant communities are Needlegrass grasslands. Blue oak series is present, but not common, on soils other than Vertisols.

Characteristic series by lifeform include:
Grasslands: California annual grassland series.
Forests and woodlands: Blue oak series.
Climate. The mean annual precipitation is about 15 to 25 inches; most of it is rain. Mean annual temperature is about 60� to 62� F. The mean freeze-free period is from 200 to 250 days.
Surface Water. Runoff is rapid and all but the larger streams are dry through most of the summer. There are no natural lakes in the area.