From the Morgan Sweeney Photograph Collection (PH-00228). Unit A-4 turbine at the Hoover Dam, the boring mill in operation boring for lower stationary seal on September 17, 1951.
There are two pictures together: the first one is titled, "Pouring the first concrete in Boulder Dam June 1933" and the second image is titled, "Spreading the first concrete in Boulder Dam June 6, 1933." Site Name: Hoover Dam (dam)