Subsection M262Af
Gabilan Range

Lithology and Stratigraphy.  This subsection has a core of Salinian block Mesozoic granitic rock and older metamorphic rocks, mainly the Sur Series, that dominate the northwestern part of the subsection.  This core of pre-Cenozoic rocks is covered by Pliocene marine, Miocene nonmarine, and upper  Miocene marine sediments toward the southeast.  Remnants of nonmarine Plio-Pleistocene sediments are scattered across the southeastern part of the subsection.  Miocene rhyolite flow and pyroclastic rocks are exposed on a down-faulted block at the Pinnacles, near the center of the subsection.

Geomorphology.  This is a subsection of steep to very steep mountains on the northwest that grade to steep to moderately steep hills on the southeast.  The mountain range is much steeper on the northeast, adjacent to the San Andreas fault, than on the southwest.  Therefore, the longer and larger streams drain southwest, and the have more alluvium in their valleys.  Only a few streams run parallel to the San Andreas fault and the axis of the Gabilan Range.  The elevation range is from about 200 feet up to about 3450 feet in the northwestern part of the range.  Mass wasting and fluvial erosion are the main geomorphic processes.

Soils.  The soils of granitic terrain are shallow Typic Xerorthents, Pachic Haploxerolls, Pachic Argixerolls, and Typic Haploxeralfs.  Those on Miocene and Pliocene marine sediments are predominantly  Calcic Haploxerolls, Typic Xerorthents and Typic  Argixerolls.  Chromic Pelloxererts and Pachic and Calcic Pachic Haploxerolls are common on Miocene and Plio-Pleistocene nonmarine sediments.  Rock outcrop and Lithic Xerorthents dominate the Miocene volcanic terrain.  The soils are generally leached free of carbonates in areas with more precipitation and mesic soil temperature regimes, but subsoils are commonly calcareous in areas of less precipitation and thermic soil temperature regimes.  The soil temperature regimes are predominantly thermic, but mesic on north-facing slopes at higher elevation.  Soil moisture regimes are xeric.

Vegetation.   The predominant natural plant community is Blue oak series, with Coast live oak series on north-facing slopes in at least the northwestern part of the subsection. There is some Black oak series and Mixed conifer series on north-facing slopes at higher elevations.  Chamise series is common on shallow soils.  Needlgrass grasslands prevail on Vertisols.

Characteristic series by lifeform include:
Grasslands: California annual grassland series, Purple needlegrass series.
Shrublands: Bigberry manzanita series, California sagebrush series, Chamise series, Chamise - bigberry manzanita series, Deer brush series, Scrub oak series, Wedgeleaf ceanothus series.
Forests and woodlands: Black oak  series, Birchleaf mountain-mahogany series, Blue oak series, California sycamore series, Coast live oak series, Coulter pine series, Coulter pine - canyon live oak series, Foothill pine series, Interior live oak series, Valley oak series.

Surface Water.  Runoff is rapid and all but the larger streams are dry through most of the summer.   Natural lakes are absent.