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Western Sonoran Basins

Ecoregion in Sonoran Desert, CA

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The Western Sonoran Basins ecoregion includes the alluvial plains, fans, and bajadas that occur between the higher relief mountain ranges of Ecoregions 81a and 81b. The region of rolling terrain and some badlands of the Anza Borrego and Yuha Desert areas slopes to the east toward the Salton Sea and Imperial Valley. These basins have some similarities to Ecoregion 81j to the east, although this western ecoregion receives less summer precipitation. Much of this area is underlain by Late Miocene to Latest Pleistocene marine and non-marine sandstones and mudstones of the Palm Springs Formation. Alluvium, colluvium, and lacustrine deposits are thicker in the eastern, gently sloping part of the ecoregion and thinner in the western part where tectonic forces have uplifted Palm Springs Formation deposits to the surface where they form incised badland topography. Soils typically are sandy to gravelly loam in texture and highly permeable, with high potential for wind erosion. Sonoran creosotebush scrub covers large areas of the ecoregion. On alluvial fans and coarse soils, ocotillo, brittlebush, and cholla occur. Shrub density varies from low to moderate, with shrub spacing from several feet to tens of feet. Some desert saltbush scrub occurs on fine-textured, poorly drained soils with high alkalinity and salinity. In the washes and ephemeral streams, mesquite and nonnative tamarisk are mixed with creosotebush. Microphyll woodland habitat is found along some dry-wash channels. In these washes, blue paloverde, ironwood, smoke tree, or desert willow occur, and these additional vegetation species support a diversity of wildlife. Fauna of the ecoregion include reptiles such as the desert flat-tailed horned lizard, side-blotched lizard, desert iguana, zebra-tailed lizard, and Colorado Desert sidewinder, and mammals such as the black-tailed jackrabbit, desert cottontail, California ground squirrel, coyote, and desert kit fox.

— EPA

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