A colored postcard showing an artist's representation of the construction site of Hoover Dam, previously known as Boulder Dam, 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. Transcribed onto the top border of the image: "Black Canyon, Boulder Dam Site."