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Geomorphology. Narrow ranges and broad fault blocks; alluviated lowlands, and dissected westward sloping granitic uplands. Transverse and Peninsular Ranges geomorphic provinces.
Lithology. Cenozoic marine and nonmarine sedimentary rocks and alluvial deposits, and Mesozoic granitic rocks.
Soil Taxa. Alfisols, Aridisols, Entisols, Inceptisols and Mollisols in combination with thermic, mesic or frigid soil temperature regimes and xeric or aridic soil moisture regimes.
Vegetation. Predominant potential natural communities includes Mixed chaparral shrublands, Chamise series, Canyon live oak series, Coast live oak series, Ponderosa pine series, Jeffrey pine series, White fir series and Lodgepole pine series.
The following series are found throughout the section and are not restricted to or extensive in any subsection. Series dominated by exotic plants are not listed under subsections unless they are extensive and stable.
Elevation. 300 to 11,500 feet.
Precipitation. 6 to 40 inches.
Temperature. 40° to 70°F.
Growing Season. 150 to 300 days.
Surface Water Characteristics. Common rivers and streams, but most do not flow throughout the year. Rivers and streams flow in alluvial and weak bedrock channels westward to the Pacific Ocean, or eastward to basins in the Mojave Desert or Colorado Desert sections. Many reservoirs for municipal water supply and flood control occur below steep mountains throughout the section.
Cultural Ecology. Humans have been utilizing the area for some 10,000 years; the early San Dieguito Paleoindian hunting assemblage is well documented at sites along the San Dieguito River. After the end of the Pleistocene, prehistoric assemblages reflect extensive practice of seasonal rounds for resource gathering. Late in the 1700’s the Spanish established colonies and missions, and converted the economy of the entire area to ranching and farming; the later citrus industry became a major agricultural influence. Contemporary attitudes and beliefs are varied; lifestyle is urban. The international border and large Hispanic populations contribute to cultural diversity. The economy is varied and urban oriented; tourism and recreation are important industries.
Subsections. The Southern California Mountains and Valleys
section is divided into 16 subsections.
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