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Ecological Sections: Southern California Mountains and Valleys

Subsection M262Bp
Desert Slopes

This subsection comprises the dry interior side of the Peninsular Ranges, from San Gorgonio Pass to the Mexican border.  It includes the lower slopes of the San Jacinto Mountains and all but the highest parts of the Santa Rosa Mountains.  The climate is hot and semi-arid to subhumid.  MLRAs 20e, 20f, 29f.

Lithology and Stratigraphy.  This subsection contains mostly Mesozoic granitic and Pre-Cenozoic metamorphic rocks.  There is some Pleistocene sediment and Recent alluvium and small areas of Miocene volcanic rocks and Miocene and Pliocene nonmarine sediments.

Geomorphology.  This is a subsection of moderately steep to steep mountains with narrow to rounded summits and both narrow canyons and broad valleys.  There are small areas of rolling plateau.  The valleys are occupied by Pleistocene to Recent alluvial fans.  The subsection elevation range is from about 300 feet up to 5261 feet on Asbestos Mountain.  Mass wasting and  fluvial erosion and deposition are the main geomorphic processes.

Soils.  The soils are mostly Lithic and shallow Typic Xerorthents, Lithic Xerochrepts, Haploxerolls, and Mollic Haploxeralfs.  In badland areas at lower elevations, they are mostly shallow Typic Torriorthents and Typic Camborthids.  The soils on alluvial fans are mostly Typic Torrifluvents, Torripsamments, Typic Toriorthents, and Typic Haplargids.  Carbonates accumulate in the soils.  They are well drained.  The soil temperature regimes are mostly thermic.  Soil moisture regimes are xeric (nearly aridic) and aridic.

Vegetation.  The natural plant communities are mostly Creosote bush series and Creosote bush - white bursage series, Chamise series and Red shank - chamise series, Mixed chaparral shrublands, Singleleaf pinyon series,  and California juniper series.

    Characteristic series by lifeform include:

    Grasslands:  Foothill needlgrass series, Nodding needlegrass series, Purple needlegrass series.

    Shrublands: Big sagebrush series, Bitterbrush series, Brittlebush series, Brittlebush - white sage  series, California buckwheat - white sage series, Creosote bush series, Creosote bush - white bursage series, Chamise series, Chamise cupleaf ceanothus series, Cupleaf ceanothus - fremontia - oak series, Fourwing saltbush series, Mixed salbush series, Mulefat series, Nolina series, Red shank - birchleaf mountain-mahogany series, Red shank - chamise series, Scalebroom series, Shadscale series, White sage series.

    Forests and woodlands: Birchleaf mountain-mahogany series, California juniper series, Canyon live oak series, Coast live oak series, Parry pine series, Singleleaf pinyon series.
Climate.  The mean annual precipitation is about 4 to 20 inches.  Most of it is rain.  Mean annual temperature is about 55 to 70  F.  The mean freeze-free period is about 200 to 275 days.

Surface Water.  Runoff is rapid.  The streams are dry through the summer.  They drain to the Salton Trough or sink into the ground before reaching the Salton Trough.  There are no lakes in the subsection. 

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