The Sonoran Desert covers over 120,000 square miles across two countries and several Native American Nations. It lies between the Mohave Desert to the north and west and the Chihuahuan Desert to the south and east. It is bounded by the Mogollon Rim on the northeast, the Chiricahua and Pinaleño Mountains in the east, and the Sierra Madre Occidental in the southeast. The geographical boundaries reach from the southeastern part of southern California, across the western two thirds of southern Arizona, into northwest Sonora, Mexico, and the eastern shore of the Baja California peninsula, including the islands of the Sea of Cortez. The elevation of the Sonoran Desert ranges from approximately 200 feet to nearly 4,000 feet above sea level.
Biomes, or major ecological community types, do not have strictly defined borders. Rather they have transition zones from one biome to another, called ecotones. These