Two unidentified men operating heavy equipment on the Hoover Dam construction site near Boulder City, Nevada, 1931.

A colored postcard showing an artist's representation of The Babcock and Wilcox Pipe Plant next the construction site of Boulder Dam, a title that would later be changed to Hoover Dam. Because the penstock pipes at Hoover Dam were too large to be carried over railroads, this plant was built to fabricate the largest penstock pipes in the world. Transcribed onto the top border of the image: "The Babcock & Wilcox Pipe Plant, Boulder Dam."

A colored postcard showing an artist's representation of the downstream face of Hoover Dam and the Lake Mead Recreational Area in Black Canyon. Constructed in the 1930s, Hoover Dam crosses the Colorado River on the state line between Arizona and Nevada. Also considered to be an engineering wonder and the world's largest dam during its time of construction, Hoover Dam provides much-needed irrigation and hydroelectric power to the Southwest region of the United States. From this angle, intake towers can be seen sticking out of Lake Mead, along with the U-shaped power house at the base of the dam. Transcribed onto the bottom of the image: "Lake Mead Recreational Area."