What we refer to as "Copper Canyon" is really a series of canyons which drain the western side of the Sierra Tarahumara. The entire Copper Canyon region comprises almost a third of the state of Chihuahua, which is Mexico's largest state. The principal canyon is Urique Canyon, which is the one which is traversed by the Chihuahua al Pacifico Railroad. Eventually, all of the rivers which formed the Copper Canyons merge into the Rio Fuerte which continues across the adjacent state of Sinaloa, emerging near the City of Los Mochis on the Sea of Cortez.