Arizona was one of the major pre-Columbian cultural centers of North America, and it is one of the best places to experience ancient history in the United States. Looking out from an airplane window, it’s hard to imagine that the vast grid of Phoenix streets below obscures a network of thousand-year-old canals. Much of Arizona’s Salt River Valley was once the center of the Hohokam people, canal builders who turned the desert green growing corn. The city’s prominent modern canals often sit atop their ancient counterparts.