Sonoran Desert

The Sonoran Desert, also called Desierto de Altar, is an arid region covering 120,000 sq mi (310,800 sq km). It is Mexico's hottest desert.

This North American desert covers large parts of northwestern Mexico in Sonora, Baja California and Baja California Sur. 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.

Sonoran Desert Ecoregion

The Sonoran Desert ecoregion is bounded 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 the 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 comprises plateaus and dunes reaching no more than 200 m (656 ft) above sea level.

The foothills of the western Sierra Madre Occidental dominate the south-central part of the Mexican state of Sonora. 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. The Arizona upland section climate is more mesic, with bi-seasonal rainfall between 100-300 mm annually.

The 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 a dry arid 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. The ecoregion generally is very dry, receiving less than 90 mm (3.5 in) of annual rainfall.

Flora and Fauna

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).

Mammals able to withstand the extreme desert climate of this ecoregion include California leaf-nosed bats (Macrotus californicus) and ring-tailed cats (Bassasiscus astutus).

Many plants survive and thrive in the harsh 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 worldwide. In addition, five hundred sixty plant species grow in the extremely harsh conditions of drought and heat and interact in various 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. In addition, Cholla (Cylindropuntia spp.), beavertail (Opuntia basilaris), hedgehog (Echinocereus spp.), fishhook (Ferocactus wislizeni), prickly pear (Opuntia spp.), night-blooming cereus (Peniocereus spp.), and organ pipe (Stenocereus thurberi) are other taxa of cacti found here.

Cactus provide 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.