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Subsection M261Fe
San Emigdio Mountains

This subsection comprises  the San Emigdio Mountains and the southwest end of the Tehachapi Mountains at the southern end of the Great Valley.  The San Andreas Fault is the southern boundary of this subsection.  It has a hot and semi-arid to subhumid climate.  MLRA 18e.

Lithology and Stratigraphy.  Mesozoic granitic rocks predominate in this subsection.  Also, there are some pre-batholith metamorphic rocks.  Adjacent to the Great Valley there are Eocene, Oligocene, and Miocene sedimentary rocks.  There is Quaternary alluvium in Castaic Valley and a few other small valleys.

Geomorphology.  This subsection is mostly on moderately steep to steep mountains and hills.  The east-northeast aligned Garlock Fault meets the west-northwest aligned San Andreas Fault on the southern margin of this subsection.  Ridges adjacent to these faults are aligned parallel to them.  Most other ridges point to the Great Valley, which is the direction that the larger streams flow.  Alluvial fans, floodplains, and basin floors are not extensive.  The subsection elevation range is from about 2000 feet up to 7495 feet on San Emigdio Mountain.  Mass wasting and fluvial erosion are the main geomorphic processes.

Soils.  The soils are mostly Typic and Dystric Xerochrepts; shallow Typic Xerorthents; Typic and Pachic Haploxerolls; Ultic Haploxerolls; and Pachic Argixerolls on granitic rocks.  They are mostly Calcic Haploxerolls and Typic Argixerolls on Tertiary sedimentary rocks, which happen to be at lower elevations than most of the granitic rocks.  The soils are well drained.  Bicarbonate weathering and leaching and accumulation of clay in subsoils are the main pedogenic processes.  Calcium carbonates accumulate in some soils on Tertiary sedimentary rocks.  Soil temperature regimes are thermic and mesic.  Soil moisture regimes are xeric.

Vegetation.   The predominant natural plant community is Blue oak series,  with Ponderosa pine series and Jeffrey pine series at higher elevations.  Also, there are some Needlegrass grasslands, Canyon live oak series on steep canyon slopes, Chamise series and Mixed chaparral shrublands on shallow and rocky soils, and Valley oak series in valleys.

Climate.  The mean annual precipitation is about 10 to 20 inches.  It is practically all rain.  Mean annual temperature is about 45 to 60  F.  The mean freeze-free period is about 150 to 250 days.

Surface Water.   Runoff is rapid from most of the subsection.  It flows to closed basins in the southern end of the Great Valley.  The streams are generally dry during the summer.  There are no natural lakes. 


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