Canyon de Chelly National Monument, a unit of the National Park System in northeastern Arizona. The monument lies in the middle of a Navajo Indian Reservation and covers 83,840 acres (33,955 hectares). There are three canyons in the monument. The largest, De Chelly, has red sandstone walls that rise up to 1,000 feet (305 m) from the canyon floor. One of the monument's main attractions are 1,800-year-old ruins of cliff dwellings built by the Anasazi people. The area was made a national monument in 1931.