<P> An area of almost 310 square miles (800 km2) adjacent to the park was designated as a second Grand Canyon National Monument on December 22, 1932 . Marble Canyon National Monument was established on January 20, 1969, and covered about 41 square miles (105 km2). An act signed by President Gerald Ford on January 3, 1975, doubled the size of Grand Canyon National Park by merging these adjacent national monuments and other federal land into it . That same act gave Havasu Canyon back to the Havasupai tribe . From that point, the park 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 . </P> <P> 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 Seasonal variations of high flow and flooding in the spring and low flow in summer have been replaced by a much more regulated system . The much more controlled Colorado has a dramatically reduced sediment load, which starves beaches and sand bars . In addition, clearer water allows significant algae growth to occur on the riverbed, giving the river a green color . </P> <P> With the advent of commercial flights, the Grand Canyon has been a popular site for aircraft overflights . However, a series of accidents resulted in the Overflights Act of 1987 by the United States Congress, which banned flights below the rim and created flight - free zones . The tourist flights over the canyon have also created a noise problem, so the number of flights over the park has been restricted . </P>

Where did the grand canyon get its name