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This
subsection is a narrow strip of predominantly ultramafic and associated
rocks of an ophiolite sequence that is between the Coast Range Thrust on
the west and the Stony Creek Fault on the east. It has a hot, subhumid
climate. MLRAs 15d and 15e.
Lithology and Stratigraphy. This subsection contains mostly Jurassic ophiolitic rocks, including peridotite, gabbro, sheeted dikes, and pillow basalt that have been altered to a melange of basalt, gabbro, and diabase in a serpentinized peridotite matrix. There are relatively small areas of Quaternary alluvium along Stony Creek and in Bear Valley.
Geomorphology. This subsection is along the steep north-trending east edge of the Northern Coast Range mountains. Most of the mountains are elongated in north-northwest to northwest directions. The elevation range is about 1200 feet to 3700 feet. Mass wasting and fluvial erosion are the main geomorphic processes.
Soils. The soils are mostly Lithic Argixerolls in serpentinitic families. Dystric Lithic Xerochrepts and Lithic Mollic Haploxeralfs are common nonserpentinitic soils. There are some Pachic Ultic Argixerolls in colluvium. Typic Pelloxererts predominate in Bear Valley. The mountain soils (excluding Bear Valley) are generally leached free of carbonates. The soil temperature regimes are predominantly thermic, but some are mesic at higher elevation and on north-facing slopes. Soil moisture regimes are almost exclusively xeric.
Vegetation. The predominant natural plant communities are Leather oak series on serpentinitic soils and Chamise series on others. In Bear Valley, the presumed potential natural plant communities are Needlegrass grasslands.
Surface Water. Runoff is rapid and all but the larger streams
are dry through most of the summer. Natural lakes are absent.
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