Photograph of construction of Boulder Dam, showing a concrete base, ca.1930. What resembles a large, concrete building stands at center against the canyon wall on the right with a large, concrete platform supporting it from below. The platform extends out of sight to the left while the building is incomplete further down. It consists of nothing more than a thin, wooden frame on the left with people walking through a maze of piled supplies around it. Jagged rocks form a small hill in the foreground while the tall, lightly-colored dam can be seen in the background on the far left.