TheColorado Desert is a part of the largerSonoran Desert located inCalifornia, United States, andBaja California, Mexico. It encompasses approximately 7 million acres (2,800,000 ha; 28,000 km2), including the heavilyirrigatedCoachella,Imperial andMexicali valleys. It is home to many unique flora and fauna.
The Colorado Desert is asubregion of the largerSonoran Desert,[1] covering about 7 million acres (2.8 million ha; 28,000 km2).[2] The desert occupiesImperial County, parts ofSan Diego andRiverside counties, and a small part ofSan Bernardino County inCalifornia, United States,[3] as well as the northern part ofMexicali Municipality inBaja California, Mexico.
Most of the Colorado Desert lies at a relatively low elevation, below 1,000 ft (305 m), with the lowest point of the desert floor at 275 ft (84 m)below sea level, at theSalton Sea. Although the highest peaks of thePeninsular Ranges reach elevations of nearly 10,000 ft (3,048 m), most of the region's mountains do not exceed 3,000 ft (914 m).
In this region, thegeology is dominated by the transition of thetectonic plate boundary fromrift tofault. The southernmost strands of theSan Andreas Fault connect to the northernmost extensions of theEast Pacific Rise. Consequently, the region is subject toearthquakes, and the crust is being stretched, which will result in a sinking of the terrain over time.
The Colorado Desert's climate distinguishes it from other deserts. The region experiences greater summer daytime temperatures than higher-elevation deserts and almost never experiences frost. In addition, the Colorado Desert experiences two rainy seasons per year (in the winter and late summer), especially toward the southern portion of the region; the more northerlyMojave Desert usually has only winter rains.[4][5]
The west coast Peninsular Ranges, or other west ranges, of Southern California–northernBaja California, block most eastern Pacific coastal air and rains, producing an arid climate.[4] Other short or longer-term weather events can move in from theGulf of California to the south, and are often active in the summermonsoons. These include remnants of Pacific hurricanes, storms from the southern tropicaljetstream, and the northernIntertropical Convergence Zone.
The region's terrestrial habitats includecreosote bush scrub; mixedscrub, includingyucca andcholla cactus; desertsaltbush; sandy soilgrasslands; and desertdunes. Higher elevations are dominated bypinyon pine andCalifornia juniper, with areas ofmanzanita andCoulter pine. In addition to hardyperennials, more than half of the desert's plant species are herbaceous annuals, and appropriately timed winter rains produce abundant early spring wildflowers. In the southern portion of the region, the additional moisture supplied by summer rainfall fosters the germination of summer annual plants and supportssmoketree,ironwood, andpalo verde trees.
Common desert wildlife includemule deer,bobcat, desertkangaroo rat,cactus mouse,black-tailed jackrabbit,Gambel's quail, andred-diamond rattlesnake. Among sensitive species areflat-tailed horned lizard, Coachella Valley fringe-toed lizard,desert tortoise,prairie falcon,Andrews' dune scarab beetle, peninsularbighorn sheep, andCalifornia leaf-nosed bat.[4] The best place to spot wildlife is at the wetland refuges along the Colorado River,Cibola National Wildlife Refuge andImperial National Wildlife Refuge.[6]
In the Colorado Desert's arid environment, aquatic andwetland habitats are limited in extent but are critically important to wildlife. Runoff from seasonal rains and groundwater springs forms desertarroyos, desert fan palmoases, freshwatermarshes, brine lakes, desert washes, ephemeral and perennial streams, anddesert riparian vegetation communities dominated bycottonwood,willow, and non-nativetamarisk. Two of the region's most significant aquatic systems are theSalton Sea and theColorado River. While most desert wildlife depend on aquatic habitats as water sources, a number of species, such as thearroyo toad,desert pupfish,Yuma rail, andsouthwestern willow flycatcher, are restricted to these habitats. In some places, summer rains produce short-lived seasonal pools that host uncommon species likeCouch's spadefoot toad.
Desert fan palm oases are rare ecological communities found only in the Colorado Desert. They occur only where permanent water sources are available, such as at springs or along fault lines, wheregroundwater is forced to the surface by the movement of hard impermeable rock, and can be found in the San Jacinto, Santa Rosa, and Little San Bernardino mountains, in the canyons ofAnza-Borrego Desert State Park, and along theSan Andreas Fault in theCoachella Valley.[4] The only palm native to California,Washingtonia filifera (desert fan palm), grows at the oases.[7]
Some sub-regions of the Colorado Desert containendemic flora. Along theLower Colorado River Valley, in-flow side canyons, flatlands, or low-to-higher level elevations, at least one such plants occur:Salvia greatae (Orocopia sage).
The Colorado Desert is one of the least-populous regions in California, but human activities have had substantial impacts on the region's habitats and wildlife. Many unique communities, particularly aquatic and dune systems, are limited in distribution and separated by vast expanses of inhospitable, arid desert terrain. Even limited human disturbances can have markedly deleterious effects on the endemic and sensitive species supported by these unique regional systems.[4]
Some of the greatest human-caused effects on the region have resulted from the water diversions and flood control measures along theColorado River. These measures have dramatically altered the region'shydrology by redistributing the region's water supply to large expanses of irrigatedagriculture and metropolitan coastal areas such asLos Angeles andSan Diego. The once-dynamicSalton Sea and Colorado River ecosystems are now controlled by human water management. Because of the scarcity of water resources in the desert environment, these alterations have had substantial impacts on regional wildlife and habitats. In addition, portions of the region are experiencing substantial growth and development pressures, most notably theCoachella Valley.[4]
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