This photograph has three images. The first one, (0272_0035) shows people high scaling Boulder Dam. The handwritten inscription reads, "The Blackbirds drilling holes for blasting. High scalers, tough job. No chance to sleep here unless you want a long nap. 'Blackie', the graveyard shifter, tells me when he was working the drill from a bo'sn chair. He caught a man who had fallen out of his chair. Had a little too much of on the rocks. Some did fall without any help." The second image (0272_0036) shows the last big blast at Boulder Dam. (Provided by U.S. Bureau of Reclamation) It reads, "Blasting walls of canyon for keyway." The third one (0272_0037) is a picture of Coffer dam at Boulder Dam. The inscription reads, "Steel beams pile driven, rock filled and covered with reinforced concrete. Note size of trucks (at this time, largest in the world) in front of largest 'drilling jumbo' in the world also. There's six working levels on each side for men to work from, and is forty ft. long. About fifty men, each with a tender, works on this jumbo."

Machinery for construction of Boulder Dam, 1931-1936