Aerial view of massive Hoover Dam —which straddles the border between Arizona and Nevada in the Black Canyon of the Colorado River — as well as a portion of the dammed river that became Lake Mead, the locus of a widespread national recreation area. Called Boulder Dam from the date of its dedication in 1935, the concrete-arch dam was renamed after former U.S. president Herbert Hoover in 1947. Now a popular tourist attraction, the dam’s generators provide power for electric utilities as far away as California. Photo by Carol Highsmith, 2018.