April 30, 1947
The Boulder Canyon Act was passed in 1921 authorizing a dam be built on the Colorado River in Boulder Canyon. By 1928 the site had been moved to Black Canyon. Two years later many people started referring to it as Hoover Dam after President Hoover. Over the next 17 years, the name switched back anf forth many times. Finally, in 1947, the House and the Senate passed a resolution, which President Harry Truman signed on April 30, 1947, restoring the name to Hoover Dam.