Hoover Dam

OK, this is not a park, but it's a must-see landmark for anyone traveling between Nevada and Arizona. Hoover Dam – originally known as Boulder Dam – was built from 1931-36 as part of President Franklin D. Roosevelt's infrastructure projects. Engineers had to divert the Colorado River away from the construction site to clear the way for the dam's massive 726-foot high, 1,244-foot long concrete arch. In recent years the hydroelectric power it generates has declined as the levels of Lake Mead have receded, but the dam still supplies electricity to Arizona, Nevada and California. Run by the Bureau of Reclamation, Hoover Dam draws around 7 million tourists a year to marvel at its Art Deco design and staggering scale.