Black and white image of two men standing in front of penstock tunnel piping at the site of Hoover Dam construction. Note: Boulder Dam was officially renamed Hoover Dam in 1947.

Black and white image of Hoover Dam construction, including work on the dam forms and intake towers. Note: Boulder Dam was officially renamed Hoover Dam in 1947.

Black and white image of equipment being lowered into Hoover Dam. People are watching from the lookout point on the Nevada side of the dam. Note: Boulder Dam was officially renamed Hoover Dam in 1947.

Black and white image of a man looking at Hoover Dam's downstream face and the outlet works in the walls of Black Canyon. Note: Boulder Dam was officially renamed Hoover Dam in 1947.

Black and white montage of a person sitting in a small boat near Hoover Dam's upstream side. The lake and canyon portion of the image look to be from a photograph, but the dam seems to be a drawing. Note: Boulder Dam was officially renamed Hoover Dam in 1947.

Black and white image of Hoover Dam's crest and a sailboat on Lake Mead, as seen from the Nevada upstream side of the dam. Note: Boulder Dam was officially renamed Hoover Dam in 1947.

Black and white image of a crowd of people gathered together for the Boulder Junction, a ceremony celebrating the beginning of work on Boulder Canyon Project and the beginning of construction on a Union Pacific Railroad from Boulder Junction (Bracken Junction) to the dam site. Note: Boulder Dam was officially renamed Hoover Dam in 1947.