Part 1 shows the Colorado River and the arid deserts of the Southwest. Bulldozers build a road to the proposed dam site. A train brings in supplies and materials made throughout the U.S. The dam site is surveyed. Shows Boulder City, Nev., including workmen’s dormitories, kitchen, and mess hall. Workers ride to the dam site in trucks and drill and blast out diversion tunnels. Power shovels clear debris. In part 2, diversion tunnels are blasted open and coffer dams are constructed. Bulldozers and trucks clear excavated material. Sand and gravel is brought in by train and is screened, washed, and graded. Concrete is mixed and is carried by truck and locomotive to the dam site. In part 3, concrete is poured into forms. Shows the interior of a tunnel, the intake towers, spillways, and penstock valves. Tubing is made at the dam site and is assembled by workmen. In part 4, penstock pipe sections are trucked from factory to the dam site and lowered into position by cable. Concrete is poured into coffer dams. President Roosevelt speaks at the dedication ceremonies. Shows flashes of spillways, transmission towers, and power lines, and an aerial view of Boulder Dam and Lake Meade.