Black and white image of the construction phase of the Boulder Canyon Project, also known as Hoover Dam. This image features the first round of drilling to enlarge the upper portal of diversion tunnel No. 2. The welded steel "Jumbo Rig" mounted on the truck has 25 air drills on it. The swing shift crew standing next to the rig prepare for work. Note: Boulder Dam was officially renamed Hoover Dam in 1947.

Black and white image of the Bureau of Reclamation Commissioner, Ellis L. Armstrong (right), greeting Art Linkletter (left) upon arrival to a party held by the Young Presidents' Organization. The party for nearly 1,000 people was held on the roof of the powerhouse at Hoover Dam. The visitors, all wearing hard hats, were the first to use this setting.

Black and white image of an abandoned steam tractor. Description from Special Collections accompanying image: "According to the story told, this was one of the first three tractors ever built. One was shipped here to Eldorado Canyon to move ore and one was shipped to Death Valley for the Borax works (it is still in Death Valley). The other one was sent to South America to a mine. The one in Death Valley supposedly worked out fairly well being used mostly in sand. This one, it is told, was not too successful. The drive mechanism was by way of teeth on the inside of the big black wheels, driven by a pinion gear at the top. Small stones fell into the wheel and stuck in the grease necessitating frequent stops to remove the stones. The driver stood on a platform at the rear. May 1947."