The Sonoran Desert is a North American desert and ecoregion that covers large parts of the southwestern United States of Arizona and California, as well as the northwestern Mexican states of Sonora, Baja California, and Baja California Sur. It is the hottest desert in both Mexico and the United States.

In the geographical distribution of plants (phytogeography), the Sonoran Desert is within the Sonoran Floristic province of the Madrean Region of southwestern North America, part of the Holarctic realm of the northern Western Hemisphere. This desert contains a variety of unique endemic plants and animals, notably, the saguaro (Carnegiea gigantea) and organ pipe cactus (Stenocereus thurberi).

The Sonoran Desert is clearly distinct from nearby deserts including: the Great Basin, Mojave, and Chihuahuan deserts because the Sonoran provides subtropical warmth in winter and two seasons of rainfall in contrast, for example, to the dry summers and cold winters of the Mojave desert. Thus, in the Sonoran desert, there is an extreme contrast between aridity and moisture.

The Sonoran desert 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 coniferous Arizona Mountains forests are to the northeast. The Chihuahuan Desert and Sierra Madre Occidental pine–oak forests are at higher elevations to the east. 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.

100,000 square miles

Colorado river

Salt river, Gila river, Rillito river

Nearctic deserts and xeric shublands

The Sonoran desert occupies a large area in the southwestern area of Arizona.