Ancestral Puebloan cliff dwellings in southwestern Colorado, occupied 600-1300 CE. Inscribed 1978 (founding-12 site).
From Wikipedia
Mesa Verde National Park is a national park of the United States and UNESCO World Heritage Site located in Montezuma County, Colorado, and the only World Heritage Site in Colorado. The park protects some of the best-preserved Ancestral Puebloan ancestral sites in the United States.