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
Course of the Colorado River Colorado. Although the dams have mostly been erased by erosion, a small portion remains as Lava Falls, generally considered the most difficult and dangerous rapids for boaters on the Colorado River. The Colorado then swings sharply south and turns northwest north of Peach Springs, emerging from the Grand Canyon at the Grand Wash Cliffs, where it widens into the upper reaches of Lake Mead. The area also marks the general boundary between the Colorado Plateau and the Mojave Desert. Shortly west of that point it begins to form the border of Nevada to the north/west and Arizona to the south/east.