Until 1963, Glen Canyon was one of the most beautiful stretches of natural scenery in the American West. The canyon had been cut over thousands of years as the Colorado River flowed over sandstone that once formed the floor of an ancient sea. The colorful walls of Glen Canyon were often compared to those of the Grand Canyon, only about 50 mi (80 km) downstream.

Humans have long seen more than beauty in the canyon, however. They have envisioned the potential value of a water reservoir that could be created by damming the Colorado. In a region where water can be as valuable as gold, plans for the construction of a giant irrigation project with water from a Glen Canyon dam go back to at least 1850.

Flood control was a second argument for the construction of such a dam. Like most western rivers, the Colorado is wild...