The Sonoran Desert, also called Desierto de Altar, is an arid region covering 120,000 sq mi. This North American desert ecoregion covers large parts of northwestern Mexico in Sonora, Baja California and Baja California Sur, as well as parts of the southwestern U.S. It is Mexico's hottest desert.
The Sonoran Desert, also called Desierto de Altar, is an arid region covering 120,000 sq mi (310,800 sq km). This North American desert covers large parts of northwestern Mexico in Sonora, Baja California and Baja California Sur; it is Mexico's hottest desert. It also covers southwestern Arizona and southeastern California in the United States.
The Sonoran desert wraps around the northern end of the Gulf of California, from Baja California Sur, north through much of Baja California, excluding the central northwest mountains and Pacific west coast, through southeastern California and southwestern and southern Arizona to western and central parts of Sonora.
It is bounded on the west by the Peninsular Ranges, which separate it from the California chaparral and woodlands (northwest) and Baja California Desert (Vizcaino subregion, central and southeast) ecoregions of the Pacific slope. To the north in California and northwest Arizona, the Sonoran Desert transitions to the colder-winter, higher-elevation Mojave, Great Basin, and Colorado Plateau deserts.
To the east and southeast, the deserts transition to the coniferous Arizona Mountains forests and Sierra Madre and Sierra Madre Occidental pine–oak forests at higher elevations. To the south the Sonoran–Sinaloan transition subtropical dry forest is the transition zone from the Sonoran Desert to the tropical dry forests of the Mexican state of Sinaloa.
The highest area in the western part of the ecoregion, which reaches 1,206 m (3,956 ft) in elevation, was formed when intense volcanic activity adjacent to a portion of the Gulf of California formed a lava spill and a variety of cinder cones surrounding the Pinacate area. The rest of the western section is composed of plateaus and sand dunes reaching no more than 200 m (656 ft) above sea level.
The south-central part of the Mexican state of Sonora is dominated by the foothills of the western Sierra Madre Occidental. These mountains reach elevations between 1,000 and 2,000 m (3,280 and 6,560 ft), resulting from a system of faults and generalized volcanic activity during the Cenozoic era. Soils are sandy and alkaline in the dunes, but toward the Pinacate and mountainous regions they are made of igneous or metamorphic material.
The climate of the Sonoran Desert ecoregion varies slightly due to its large size. In the Arizona upland section climate is more mesic, with bi-seasonal rainfall between 100-300 mm annually. Climate is subtropical dry near the Gulf of California. Near the Colorado River Valley and all remaining parts of the ecoregion temperatures are high year round with infrequent, irregular rainfall creating an arid dry climate. The Desierto de Altar, in the western Sonoran ecoregion, is one of the driest areas in North America, with periods of drought that can last for 30 months. In general, the ecoregion is very dry receiving less than 90 mm (3.5 in) of annual rainfall.
Many wildlife species, such as Sonoran pronghorn antelopes (Antilocapra sonoriensis), desert bighorn sheep (Ovis canadensis) and the endemic Bailey's pocket mouse (Perognathus baileyi) use ironwood, cacti species and other vegetation as both shelters from the harsh climate and a water source. Other mammals include predators such as mountain lions (Felis concolor), coyotes (Canis latrans) and prey such as black-tailed jackrabbits (Lepus californicus), and round-tailed ground squirrels (Spermophilus tereticaudus). Other mammals able to withstand the extreme desert climate of this ecoregion include California leaf-nosed bat (Macrotus californicus) and ring-tailed cat (Bassasiscus astutus).
Many plants not only survive, but thrive in the harsh conditions of the Sonoran Desert. Many have evolved to have specialized adaptations to the desert climate.The Sonoran Desert has the greatest diversity of vegetative growth of any desert in the world. 560 plant species grow in the extremely harsh conditions of drought and heat, and interact in a variety of ecological relationships that add to the complexity of the community. More than 160 plant species, including six threatened succulents, depend upon legumes such as ironwood and mesquite for their regeneration in the Sonoran Desert.
The Sonoran is the only place in the world where the famous saguaro cactus (Carnegiea gigantea) grows in the wild. Cholla (Cylindropuntia spp.), beavertail (Opuntia basilaris), hedgehog (Echinocereus spp.), fishhook (Ferocactus wislizeni), prickly pear (Opuntia spp.), nightblooming cereus (Peniocereus spp.), and organ pipe (Stenocereus thurberi) are other taxa of cacti found here. Cactus provides food and homes to many desert mammals and birds, with showy flowers in reds, pinks, yellows, and whites, blooming most commonly from late March through June, depending on the species and seasonal temperatures.
Creosote bush (Larrea tridentata) and bur sage (Ambrosia dumosa) dominate valley floors. Indigo bush (Psorothamnus fremontii) and Mormon tea are other shrubs that may be found. Wildflowers of the Sonoran Desert include desert sand verbena (Abronia villosa), desert sunflower (Geraea canescens), and evening primroses.