Photograph of construction of Boulder Dam, showing work behind the dam, ca.1930. Wooden frames stand behind the wall of the dam on the left with piles of thin, wooden beams lying on the cement supports which stand beneath them. Thick wires extend from the top of the dam on the far left down to the busy construction site on the right. People resemble ants walking through the maze of buildings and parked automobiles as well as piles of supplies and a crane at center. Dirt is settled in a large pile in the foreground on the left while a tall, lightly-colored portion of the dam stands to the left of a rock wall in the background.