Bandelier National Monument, New Mexico

These remarkable ancient cliff dwellings in Frijoles Canyon, next to Los Alamos National Lab, many accessed only by ladders, are eroding due to time and traffic. The cliff dwellings were occupied by as many as 800 Anasazi, who had departed by 1550. Adolph Bandelier began documenting the site in the late 1800s, and the site was transferred to the National Park Service in 1932, when most of the classic Civilian Conservation Corps (CCC) buildings, built in a local style, were constructed, as well as a road to the site. Now 300,000 visitors a year come. It was a controlled burn performed on the grounds by the Park Service that sparked the devastating fires that burned some of the National Lab and 400 homes in Los Alamos in 2000.