The first person killed during the course of building Hoover Dam was J.G. Tierney. Mr. Tierney drowned on December 20, 1922, while surveying in the waters of the Colorado River. Exactly 13 years later, on December 20, 1935, the last man who died was Patrick Tierney, his son. The younger Tierney fell off an intake tower shortly before construction of the dam was completed.