Bandelier National Monument - Geography and Geology

Geography and Geology

In October 1976, roughly seventy percent of the monument, 23,267 acres (9,416 ha), became part of the National Wilderness Preservation System. The park's elevations range from about 5,000 feet (1,500 m) at the Rio Grande to over 10,200 feet (3,100 m) at the summit of Cerro Grande. The Valles Caldera National Preserve adjoins the monument on the north and west, extending into the Jemez Mountains.

Much of the area was covered with volcanic ash (the Bandelier tuff) from an eruption of the Valles Caldera volcano 1.14 million years ago. The tuff overlies shales and sandstones deposited during the Permian period and limestone of Pennsylvanian age. The volcanic outflow varied in hardness; the firmer materials would be used by the Ancestral Pueblo People as bricks, while the softer material was carved into homes.