The Sonoran Desert (sometimes called the Gila Desert after the Gila River or the Low Desert in opposition to the higher Mojave Desert) is a North American desert which straddles part of the United States-Mexico border and covers large parts of the U.S. states of Arizona and California and the Mexican states of Sonora and Baja California. It is one of the largest and hottest deserts in North America, with an area of 311,000 km² (120,000 mi² ). The desert contains a variety of unique plants and animals, such as the saguaro cactus. On January 17, 2001, 2,008 km² (496,337 acres) of the Sonoran Desert was set aside as the Sonoran Desert National Monument for the purpose of enhancing resource protection.
The desert's sub-regions include the Colorado Desert and Yuma Desert. In the 1951 publication, Vegetation of the Sonoran Desert, Forrest Shreve divided the Sonoran Desert into seven regions according to characteristic vegetation: Lower Colorado Valley, Arizona Upland, Plains of Sonora, Foothills of Sonora, Central Gulf Coast, Vizcaino Region, and Magdalena Region. (see An Overview of the Sonoran Desert, external link below). Many ecologists now consider Shreve's Vizcaino and Magdalena regions, which lie on the western side of the Baja California Peninsula, to be a separate ecoregion, the Baja California desert. The PBS series Reading Rainbow shot its sixty-second episode Desert Giant: The World of the Saguaro Cactus here on March 27,1990. This book by Barbara Bash was narrated by Philip Bosco.
The largest city in the Sonoran Desert is Phoenix, Arizona, U.S.A. This metropolitan area in central Arizona is one of the fastest-growing metropolitan area in the United States, with a population of 4 million. In the North Phoenix area, desert is losing ground to development at a rate of approximately 4,000 m2 (1 acre ) per hour. The next largest cities are Tucson, in southern Arizona, U.S.A., with a metro area population of around 900,000, and Mexicali, Baja California, Mexico, whose municipality also has a population of around 900,000. The municipality of Hermosillo, Sonora, Mexico has a population of around 700,000.