Long before there were people dinosaurs roamed Arizona. In fact some of the oldest dinosaur bones ever found were in the Grand Canyon. The oldest bone ever found in Arizona dates back to two hundred twenty-five years ago. Ancient Indians roamed the Grand Canyon for at least twelve thousand years. These Indians hunted Mastodons that lived among the rocks. Mastodons are extinct but they looked much like the elephants that we have today. Before the Grand Canyon was formed it was flat marshy lands.