The Sonoran Desert is a North American desert which covers large parts of the Southwestern United States in Arizona and California and of Northwestern Mexico in Sonora, Baja California, and Baja California Sur. It is the hottest desert in Mexico. It has an area of 260,000 square kilometers (100,000 sq mi). The western portion of the United States–Mexico border passes through the Sonoran Desert.
In phytogeography, the Sonoran Desert is within the Sonoran Floristic Province of the Madrean Region in southwestern North America, part of the Holarctic Kingdom of the northern Western Hemisphere. The desert contains a variety of unique and endemic plants and animals, such as the saguaro (Carnegiea gigantea) and organ pipe cactus (Stenocereus thurberi).