Walnut Canyon National Monument

The Sinagua farmed the rim of this canyon before moving into its limestone walls, and they stayed from roughly 1100 to 1250 CE — then left, reasons still debated. The canyon floor sits 350 feet below the rim. The Island Trail, a one-mile loop, passes 25 cliff dwellings built into natural alcoves in the Kaibab Limestone. Proclaimed a national monument in 1915, it sits about 10 miles southeast of Flagstaff. Come for the dwellings; leave wondering what made people go.