Boulder Dam, later renamed Hoover Dam, rises out of the Colorado River across four reels of Department of the Interior footage shot during construction. Part one surveys the arid stretch of the Nevada-Arizona border, follows bulldozers cutting a road to the site, and tours Boulder City's new dormitories, kitchens, and mess halls built to house the workforce. Part two shows crews blasting diversion tunnels and raising coffer dams while trains haul in screened and graded sand and gravel for the concrete mix. Part three moves inside the tunnels to the intake towers, spillways, and penstock valves, with workmen assembling tubing on site. Part four brings in the penstock pipe sections, trucked from factory to canyon and lowered into place by cable, before President Franklin Roosevelt speaks at the dedication ceremony. The film closes on finished spillways, transmission towers and power lines, and an aerial view of the completed dam holding back Lake Mead. The camera treats the project as an industrial process, tracking materials from truck to form to finished structure.