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This
subsection includes the Sierra Pelona and a relatively low, but still mountainous,
part of the north-northeastern Transverse Ranges between the Sierra Pelona
and the San Gabriel Mountains. It is between the San Andreas fault
on the east, the Santa Susana Mountains on the southwest, the Bee Canyon
and Francisquito faults on the north, and Soledad Canyon on the south.
The San Gabriel fault runs along the southwest border of the subsection.
The climate is hot to temperate, and subhumid. MLRA 20e.
Lithology and Stratigraphy. This subsection has relatively large areas of Pre-Mesozoic plutonic rocks and gneisses, Mesozoic granitic rocks, Pre-Cretaceous Pelona schist, Oligocene volcanic rocks, Oligocene nonmarine and Miocene marine sedimentary rocks, Plio-Pleistocene sediments, and Quaternary alluvium.
Geomorphology.
This is a subsection of steep mountains with narrow to rounded summits
and narrow canyons, although there are a few broad valleys with Quaternary
to Recent alluvial plains. The mountains trend east-west, but hills
along the San Andreas fault trend west-northwest. The subsection
elevation range is from about 1000 feet up to 5187 feet on Mount McDill
in the Sierra Pelona. Mass wasting and fluvial erosion and deposition
are the main geomorphic processes.
Soils. The soils are mostly Lithic and shallow Typic Xerorthents, shallow Entic Haploxerolls, and Mollic Haploxeralfs. Also, Lithic Haploxerolls are common on Pelona schist. Typic and Mollic Xerofluvents and Fluventic, Pachic, and Calcic Pachic Haploxerolls are common on Recent alluvial fans and floodplains. Most of the soils are leached free of carbonates. The soils are well drained. Soil temperature regimes are mostly thermic, with some mesic on north-facing slopes at higher elevations. Soil moisture regimes are xeric.
Vegetation. The predominant natural plant communities are Chamise series on shallow and very stony soils, Mixed chaparral shrublands, and Coast live oak series. Purple sage series and Mixed sage series occur at lower elevations, Birchleaf mountain-mahogany - California buckwheat series occurs on south facing slopes, and Bigcone Douglas-fir series and Bigcone Douglas-fir - canyon live oak series occur on north-facing slopes at higher elevations. California juniper series is common on the interior side of the mountains.
Surface Water. Runoff is rapid. All but the larger streams are dry through the summer. Most of the streams drain through the Santa Clara river to the ocean, but those near the San Andreas fault drain into closed drainage basins. Natural lakes are absent, except along the San Andreas fault. There are numerous sag ponds along the San Andreas fault.
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