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Lithology and Stratigraphy. Quaternary alluvial, lacustrine, and eolian deposits predominate in this subsection.
Geomorphology. This subsection is mainly on very gently to moderately sloping alluvial fans and nearly level basin floors and dry lake beds. Also, there are some Pliocene and Pleistocene nonmarine sediments that have been eroded and dissected to form “badlands”, as in the Mecca Hills. The Coachella Valley is aligned toward northwest, but it curves around to the west along the Banning Fault; the Banning Fault being the southern branch of the San Andreas Fault, which splits in the Coachella Valley along two paths at the southern edge of the San Bernardino Mountains. The elevation range is from about -230 feet on the shore of the Salton Sea up to 1837 feet in the Mecca Hills and over 2000 feet in San Gorgonio Pass. Fluvial erosion and deposition and eolian deflation and deposition are the main geomorphic processes.
Soils. The soils are mostly Typic Torrifluvents, Typic Torripsamments, and Typic Torriorthents. Coarse-loamy and coarse-silty Typic Torrifluvents predominate in lacustrine sediments and Typic Torripsamments in eolian sand. There are shallow Typic Torriorthents and Typic Calcior-thids in Pliocene and Pleistocene sediments that have been eroded to form “badlands”. The soils are well drained, except on poorly drained playas. The soil temperature regimes are hyperthermic within the subsection, but they are thermic at San Gorgonio Pass. Soil moisture regimes are aridic.
Vegetation. The predominant natural plant communities are Creosote bush - white bursage series and, around the Salton Sea, Allscale series. Fan palm series occurs in many small riparian areas throughout the subsection. Mixed saltbush series and Mesquite series are common on basin floors, and Iodine bush series and Saltgrass series are present on wet basin-fill and lacustrine deposits.
Characteristic series by lifeform include:Climate. The mean annual precipitation is about 3 to 4 inches. It is all rain. Mean annual temperature is about 68° to 75° F. The mean freeze-free period is about 300 to 350 days.
Surface Water. Runoff is rapid from alluvial fans and slow from basin floor. Drainage is to the Salton Sea through the Whitewater River. Streams have no water in some years and are dry most of each year in other years. There is temporary ponding on playas, or dry lake beds, in some years.Colorado Desert - next >