History of the Grand Canyon area stretched along a 278-mile (447 km) segment of the Colorado River from the southern border of Glen Canyon National Recreation Area to the eastern boundary of Lake Mead National Recreation Area. Grand Canyon National Park was designated a World Heritage Site on October 24, 1979. In 1935, Hoover Dam started to impound Lake Mead south of the canyon. Conservationists lost a battle to save upstream Glen Canyon from becoming a reservoir. The Glen Canyon Dam was completed in 1966 to control flooding and to provide water and hydroelectric power. Seasonal variations of high flow and flooding in the spring and
Risks to the Glen Canyon Dam Risks to the Glen Canyon Dam Glen Canyon Dam, a concrete arch dam on the Colorado River in the American state of Arizona, has been associated with a large amount of risk, most notably the risk of its siltation and failure. Because of high silt content carried in by the Colorado and San Juan rivers, Lake Powell is gradually filling with sediment, decreasing its capacity; eventually the sediment will build up against the dam and affect its safe operation. The dam, anchored in unstable Navajo sandstone (sometimes said to be "solidified sand dunes"), nearly failed in 1983 as the result