Hoover Dam, once known as Boulder Dam, is a concrete arch-gravity dam

Arch-gravity dam

An arch-gravity dam, curved-gravity dam or arched dam is a dam with the characteristics of both an arch dam and a gravity dam. It is a dam that curves upstream in a narrowing curve that directs most of the water against the canyon rock walls, providing the force to compress the dam...

 in the Black Canyon

Black Canyon of the Colorado

The Black Canyon of the Colorado is the canyon on the Colorado River where Hoover Dam was built. The canyon is located on the Colorado River at the state line between Nevada and Arizona. The western wall of the gorge is in the El Dorado Mountains, and the eastern wall is in the Black Mountains of...

 of the Colorado River, on the border between the US states of Arizona

Arizona

Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...

 and Nevada

Nevada

Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...

. It was constructed between 1931 and 1936 during the Great Depression

Great Depression

The Great Depression was a severe worldwide economic depression in the decade preceding World War II. The timing of the Great Depression varied across nations, but in most countries it started in about 1929 and lasted until the late 1930s or early 1940s...

 and was dedicated on September 30, 1935, by President Franklin Roosevelt. Its construction was the result of a massive effort involving thousands of workers, and cost over one hundred lives.