Nature Bank

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 North America, with an area of 280,000 square kilometers. 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). 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 state of Sinaloa.  Source