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
Agriculture in the Southwestern United States Agriculture in the Southwestern United States Agriculture in the Southwest United States is very important economically in that region. The three main watersheds of the southwest United States are the Colorado River Basin, the Great Basin, and the Rio Grande Basin. The Colorado River Basin includes parts of California, Utah, Arizona, New Mexico, Colorado, and Wyoming. The Colorado River is the largest river in the Southwest United States. The Great Basin watershed includes parts of southern California, most of Utah, the northwest half of Nevada, and parts of Oregon and Idaho. The Rio Grande Basin includes most of New Mexico,