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This
subsection comprises the alluvial plain in McCoy Wash and Palo Verde Valley,
which are between the McCoy Mountains, Chuckawalla Valley, Mule Mountains,
and Palo Verde Mountains on the west and the Colorado River on the east.
It has a very hot arid climate. MLRAs 30g and 31g.
Lithology and Stratigraphy. Quaternary alluvial deposits predominate in this subsection.
Geomorphology. This subsection is on very gently to moderately sloping alluvial fans and nearly level floodplain. The elevation ranges about 250 to 800 feet. Fluvial erosion and deposition and are the main geomorphic processes.
Soils.
The soils are mostly Typic Torrifluvents, Typic Torripsamments, and Typic
Torriorthents on younger fans and on floodplain of the Colorado River and
mostly Typic Calciorthids, Typic Haplargids, and shallow Typic Durorthids
on older fans. The soils are well drained. Soil temperature
regimes are hyperthermic; and soil moisture regimes are aridic.
Vegetation. The predominant natural plant community on alluvial fans is Creosote bush - white bursage series. Mesquite series occurs in riparian areas along the Colorado River and Tamarisk series has invaded some riparian areas.
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 70° to 75° F. The mean freeze-free period is about 300 to 325 days.
Grasslands: Big galleta series, Indian ricegrass series.
Shrublands: Allscale series, Bush seepweed series, Brittlebush series, Brittlebush - white bursage series, Catclaw acacia series, Creosote bush series, Creosote bush - white bursage series, Desert-holly series, Fourwing saltbush series, Iodine bush series, Mixed saltbush series, Ocotillo series, Teddy-bear cholla series, White bursage series.
Forests and woodlands: Blue palo verde - ironwood - smoke tree series, Mesquite series.
Surface Water. Runoff is rapid from alluvial fans and slow from floodplain. Drainage is to the Colorado River. Streams, other than the Colorado River, have no water in some years and are dry most of each year in other years.
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