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Subsection M261Fd
Southern Granitic Foothills

This subsection comprises the lower slopes around the southern end of the Greenhorn Mountains and on the western sides of Breckenridge Mountain and the Tehachapi Mountains.  Hot Spring Valley along the Kern River and the lower part of South Fork Valley are included in 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 Mesozoic mafic plutonic and pre-batholith metamorphic rocks.  There is Quaternary alluvium in Linns, Hot Spring, and South Fork Valleys and a few other small valleys.

Geomorphology.  This subsection is mostly on moderately steep to steep mountains and hills.  Major valleys are aligned east-west or toward the south-south west parallel to the Breckenridge Fault.   Ridges at the northwestern end of the Tehachapi mountains curve from east-west around toward the west-northwest.  Alluvial fans, floodplains, and basin floors are important, but not extensive, parts of the subsection.  The subsection elevation range is about 1000 to 5000 feet.  Mass wasting and fluvial erosion are the main geomorphic processes.

Soils.  The soils are mostly Typic and Pachic Haploxerolls; shallow Typic Xerorthents; and Lithic and Typic Argixerolls.  Xerochrepts are common on metamorphic rocks.  Soil in the larger valleys are mostly Xeric Torripsamments and Xeralfic Haplargids.  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.  Soil temperature regimes are mostly thermic.  Soil moisture regimes are mostly xeric, but aridic in at least South Fork Valley and possibly in other valleys.

Vegetation.   The predominant natural plant community is Blue oak series.   Also, there are some Needlegrass grasslands, Chamise series on shallow and rocky soils, and Valley oak series in valleys.

Climate.  The mean annual precipitation is about 8 to 25 inches.  It is practically all rain.  Mean annual temperature is about 50 to 64  F.  The mean freeze-free period is about 200 to 300 days.

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

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