Although Chihuahua is primarily identified with the Chihuahuan Desert for namesake, it has more forests than any other state in Mexico, with the exception of Durango. Due to its variant climate, the state has a large variety of fauna and flora. The state is mostly characterized by rugged mountainous terrain and wide river valleys. The Sierra Madre Occidental mountain range, an extension of the Rocky Mountains, dominates the state's terrain and is home to the state's greatest attraction, Las Barrancas del Cobre, or Copper Canyon, a canyon system larger and deeper than the Grand Canyon. On the slope of the Sierra Madre Occidental mountains (around the regions of Casas Grandes, Cuauhtémoc and Parral), there are vast prairies of short yellow grass, the source of the bulk of the state's agricultural production. Most of the inhabitants live along the Rio Grande Valley and the Conchos River Valley.