Pueblo Bonito, the largest and best known Great House in Chaco Culture National Historical Park was built by ancestral Pueblo people and occupied between AD 828 and 1126. Many Chacoan buildings may have been aligned to capture the solar and lunar cycles, requiring generations of astronomical observations and centuries of skillfully coordinated construction. Climate change is thought to have led to the emigration of Chacoans and the eventual abandonment of the canyon, beginning with a 50-year drought in 1130.

Source: Wikipedia