History of the National Park Service and multi purpose river basin development programs like the Tennessee Valley Authority which began in the 1930s and spread to river valleys in all parts of the country after World War II. Lake Mead was the first National Recreation Area. The Boulder Canyon Project Act, passed in 1928, authorized the Bureau of Reclamation to construct Hoover Dam on the Colorado River. Work began in 1931 and the dam, highest in the Western Hemisphere, was completed in 1935. The next year, under provisions of an agreement with the Bureau of Reclamation, the National Park Service assumed responsibility for all recreational activities
Transportation in Arizona large-scale reconstruction and expansion of I-10 was supported and completed in mid-2009. Yuma is served by I-8, while Casa Grande served by I-8 and I-10; Flagstaff is served by I-17 and I-40. US 95 parallels the Colorado River, from Las Vegas to the Mexico–United States border near Yuma. Historic US 66, a major route for Midwestern emigrants prior to the advent of the interstate highway system, traversed the northern part of the state, passing through Flagstaff and Kingman. US 66 in Arizona closely followed the route of what is now I-40 except for an stretch between Seligman and Kingman now