 Hoover Dam , once known as Boulder 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 . It was constructed between 1931 and 1936 during the Great Depression and 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 one hundred lives . The dam was controversially named after President Herbert Hoover . 
