The Sonoran Desert (sometimes calle 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.