Subsection M262Ba
San Rafael - Topatopa Mountains

Lithology and Stratigraphy.  This subsection contains mainly Cretaceous, Eocene, Oligocene, Miocene, and Pliocene marine sedimentary rocks.  Mesozoic rocks of the Franciscan Complex predominate southwest of the Camuesa fault, between it and the Little Pine fault.

Geomorphology.  This is a subsection of steep mountains with narrow to rounded summits and narrow canyons.  Mountains northwest of the Big Pine fault trend northwest, which is the common trend in the southern California Coast Ranges.  Mountains south of the Santa Ynez fault trend east-west, which is the common trend in the Transverse Ranges.  Mountains between the Big Pine and the Santa Ynez faults curve from a northwest trend on the north to an east-west trend on the south.  The subsection elevation range is from about 1000 feet up to 7510 feet on Reyes Peak on Pine Mountain.  Mass wasting and fluvial erosion are the main geomorphic processes.

Soils.  The soils are mostly Typic and Lithic Xerorthents and Lithic Haploxerolls on rocks of the Franciscan formation; Typic and Lithic Xerochrepts, Lithic Haploxerolls, and Lithic, Mollic, and Ultic Haploxerolls on Cretaceous, Eocene, Oligocene, and some Miocene sedimentary rocks; and Calcixerollic Xerochrepts and Calcic Pachic Haploxerolls on Pliocene and some Miocene marine sedimentary rocks.   Most, but not all, of the soils are leached free of carbonates.  The soils are well drained.  The soil temperature regimes are thermic at lower elevation and mesic at higher elevation. Soil moisture regimes are xeric.

Vegetation.  The predominant natural plant communities include Chamise series on shallow and very stony soils, Scrub oak series, and Mixed chaparral shrublands; some Coast live oak series, California sagebrush series, and Purple sage series at lower elevations; and small areas of Bigcone Douglas-fir series and Bigcone Douglas-fir - canyon live oak series on north-facing slopes and in canyons.   Mixed conifer series and Ponderosa pine series occur at higher elevations.

Characteristic series by lifeform include:
Grasslands: Beaked sedge series, Bur-reed series, California annual grassland series, Tufted hairgrass series.
Shrublands: Black sage series,  California sagebrush series, California sagebrush - purple sage series, Bigberry manzanita series, California buckwheat series, California sagebrush - black sage series, Chamise series, Chamise - bigberry manzanita series, Chamise - black sage series, Chamise - Eastwood manzanita series, Chamise - wedgeleaf ceanothus series, Deebrush series, Eastwood manzanita series, Hairyleaf ceanothus series, Hoaryleaf ceanothus series, Hollyleaf cherry series, Interior live oak - canyon live oak series, Interior live oak - scrub oak shrub series, Mixed scrub oak series, Mountain-mahogany - hollyleaf cherry series, Scrub oak - birchleaf mountain-mahogany series, Parry rabbitbrush series, Purple sage series, Scrub oak series, Sumac series, Toyon - hollyleaf cherry series, Tucker’s oak series, Wedgeleaf ceanothus series, White sage series.
Forests and woodlands: Bigcone Douglas-fir series, Bigcone Douglas-fir - canyon live oak series, Black oak series, Black cottonwood series, Canyon live oak series, Coast live oak series, Coulter pine series, Coulter pine - canyon live oak series, Incense-cedar series, Interior live oak series, Jeffrey pine series, Mixed conifer series, Ponderosa pine series, White fir series.

Surface Water.  Runoff is rapid.  All but the larger streams and those that drain from the higher watersheds are dry through the summer.  Natural lakes are absent.