D. ruins of an ancient civilization
The ancient civilization that was centered in the Chaco Canyon and Mesa Verde region was that of the Anasazi. The name "Anasazi" means "ancient outsiders." Later explorers of the regions also referred to them as "Cliff Dwellers." Around 1500 BC, the Anasazi arose as a thriving civilization in what is now the American southwest. The Anasazi built dwellings underneath cliffs so that they'd be sheltered. They used sandstone blocks and mortar made from mud to build lasting structures. The Pueblo Indian tribes are descended from the Anasazi civilization.