The Sonoran Desert is a North American desert and ecoregion which covers large parts of the southwestern United States and of northwestern Mexico. With an area of 260,000 square kilometers (100,000 sq mi), it is the hottest desert in Mexico. The western portion of the Mexico–United States border passes through the Sonoran Desert. The Sonoran Desert region includes the Sonoran Desert and some surrounding areas. All of Sonora, the Baja California Peninsula, and the islands of the Gulf of California are included. Also included are parts of Sinaloa and Chihuahua, some Pacific islands off the coast of Baja California (excluding Guadalupe Island), and southern Arizona and southern California in the United States.