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Subsection 322Bb
Palen - Riverside Mountains

This subsection includes six small mountain ranges, each surrounded by alluvial plain,  that are close together.  They are between Ward and Rice Valleys on the north,  the Colorado River on the east, Chuckawalla and Palo Verde valleys on the south, and Palen valley on the west.  The subsection has a hot to very hot arid climate.  MLRA 30g.

Lithology and Stratigraphy.  The bedrock in this subsection is mainly Mesozoic granitic, Pre-Cretaceous metavolcanic, Paleozoic marine sedimentary, and Precambrian igneous and metamorphic rocks.

Geomorphology.   This subsection is on steep mountains.  The mountain ranges are somewhat elongated, with trends ranging from north-south to northwest.  The elevation ranges from about 400 feet adjacent to the Colorado River up to 2252 feet in the East Riverside and 2667 feet in the West Riverside Mountains, 2870 feet in the Big Maria Mountains, 2835 feet in the McCoy Mountains, 3043 in the Little Maria Mountains, 3623 feet in the Palen Mountains, and 4353 feet in the Granite Mountains.   Mass wasting and fluvial erosion are the main geomorphic processes.

Soils.  The soils are mostly Lithic Torriorthents and Lithic Camborthids.  Soils on alluvial fans surrounding the mountains are mostly Typic subgroups of Torriorthents, Calciorthids, and Haplargids.  Soil temperature regimes are mostly thermic, and some  hyperthermic; and soil moisture regimes are aridic.

Vegetation.   The predominant natural plant community is Creosote bush - white bursage series.  Blue paloverde - ironwood - smoke tree series occurs in washes.

Characteristic series by lifeform include:
Grasslands: Big galleta series.
Shrublands: Brittlebush series, Brittlebush - white bursage series, Catclaw acacia series, Creosote bush series, Creosote bush - white bursage series, Desert-holly series, Ocotillo series, Teddy-bear cholla series, White bursage series.
Forests and woodlands: Blue palo verde - ironwood - smoketree series.
Climate.  The mean annual precipitation is about 3 to 5 inches.  It is all rain.  Mean annual temperature is about 60 to 75 F.  The mean freeze-free period is about 250 to 300 days.

Surface Water.  Runoff is rapid.  Streams are dry most of each year, and dry throughout some years. 


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