On 15 October 1956 President Dwight D. Eisenhower pushed a button at his White House desk, initiating the blast that started construction of the Glen Canyon Dam in Arizona, eight miles below the Utah border. Not only did this put in motion a mammoth building project by the Bureau of Reclamation, it also was one more effort to end the free-rolling life of the Colorado River, a knowledge of whose history is essential in understanding the West.

The dammed water of Lake Powell backed up the flows of the Colorado and San Juan rivers 186 miles and 72 miles respectively, creating 1,960 miles of shoreline (more than that along the New England coast). It also rendered unserviceable prehistoric, historic, and religious sites of value. The Navajo lost at least two sacred places. The confluence of the San Juan and the Colorado was a meeting place where two Navajo deities, embodied in theses rivers, met to create water children of the cloud and rain people. Nearby stood Rainbow Bridge, an arch with a span of 278 feet. Said to be male and female holy beings who created clouds, rainbows, and moisture, this site, like the confluence, is no longer used for worship. The waters of Lake Powell are eroding the foot of the rainbow while crowds of pleasure seekers land at the dock facilities nearby, making public this place of privacy.

Historic sites have disappeared including the Crossing of the Fathers, used by Escalante and Dominquez in 1776; the fording place on the Hole-in-the-Rock Trail created by the Mormons in 1880; gold mining sites of the 1880s, 1890s, and early 1900s; and rock art panels and homes of the Anasazi. Even the glen in which John Wesley Powell stood in awe and for which the canyon and dam took its name, is covered beneath 500 feet of water.