The Colorado River cut through the plateau, exposing 300-million-year-old rock. The canyon was once a complex space containing some 100 side canyons, natural bridges, arches, archaeological sites and wildlife habitat.
In the 1940s, the U.S. Bureau of Reclamation planned a series of dams on the Colorado Plateau. The Colorado River Storage Act passed Congress in 1956, providing power, flood control and water storage to much of the West.
The Sierra Club protested a proposed dam at Echo Park, Colorado, that would have flooded Dinosaur National Monument. It succeeded, but flooding Glen Canyon was the compromise.
In 1963, Glen Canyon was flooded by the Glen Canyon Dam, creating Lake Powell. Lake Powell has marinas and campgrounds. Houseboats, powerboats, jet skis, kayaking and fishing are popular.
The water in Lake Powell is dropping. More than 100 square miles of the canyon's original geography not seen since the dam was built were exposed in 2006.