What is the main idea presented in this passage? Ancestral Puebloans lived in the cliff dwellings (of Mesa Verde] for less than 100 years. By about... 1300, Mesa Verde was deserted. Several theories offer reasons for their migration. We know that the last quarter of the ... 1200s saw drought and crop failures, but these people had survived earlier droughts. Maybe after hundreds of years of (overuse), the land and its resources-soils, forests, and animals-were (used up). Perhaps there were social and political problems, and the people simply looked for new opportunities elsewhere.​