Copper Canyon is a system of six distinct canyons in the Sierra Madre Occidental in the southwestern part of the state of Chihuahua in northwestern Mexico that is 65,000 square kilometres (25,000 sq mi) in size. The canyons were formed by six rivers that drain the western side of the Sierra Tarahumara. All six rivers merge into the Rio Fuerte and empty into the Gulf of California. The walls of the canyon are a copper/green color, which is the origin of the name.