Parker Dam is a concrete arch-gravity dam that crosses the Colorado River 155 miles (249 km) downstream of Hoover Dam. Built between 1934 and 1938 by the Bureau of Reclamation, it is 320 feet (98 m) high, 235 feet (72 m) of which are below the riverbed (the deep excavation was necessary in order to reach the bedrock on which the foundation of the dam was built), making it the deepest dam in the world. The portion of the dam above the foundation stands 85 feet (25.9 m) tall, making it the only dam in the world that stands more underground than above ground. The dam's primary functions are to create a reservoir, and to generate hydroelectric power. The reservoir behind the dam is called Lake Havasu and can store 647,000 acre⋅ft (798,000,000 m3; 2.11×1011 US gal; 1.76×1011 imp gal). The dam straddles the Arizona-California state border at the narrows the river passes through between the Whipple Mountains in San Bernardino County, California and the Buckskin Mountains in La Paz County, Arizona.

Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U.S. states of Nevada and Arizona. Constructed between 1931 and 1936, during the Great Depression, it was dedicated on September 30, 1935, by President Franklin D. Roosevelt. Its construction was the result of a massive effort involving thousands of workers, and cost over 100 lives. In bills passed by Congress during its construction, it was referred to as the Hoover Dam, after President Herbert Hoover, but was named the Boulder Dam by the Roosevelt administration. In 1947, the name Hoover Dam was restored by Congress.