1929-June: Herbert Hoover takes charge of negotiations as six of seven basin states approve the Colorado River Compact. The basin states include Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming. Arizona, unhappy with the proposed plan for water distribution, is the one state that held out against the Compact. The resulting agreement leads to passage of the Boulder Canyon Project Act.
1931-March: The Bureau of Reclamation opens bids for the construction of Boulder (Hoover) Dam and Power Plant. The contract is awarded to Six Companies, a construction and engineering firm made up of some of the West's most successful builders and designers of dams, bridges, roads, and tunnels, on March 11. The winning bid was $48,890,995.
1932-November: The Colorado River is diverted around the dam site.
1933-June: First concrete is poured at Hoover Dam site.
1935-February: The Hoover Dam starts impounding water in Lake Mead.
1935-May: The last concrete is poured at the dam site.
1935-September: President Franklin D. Roosevelt attends and speaks at the dedication of Boulder (Hoover) Dam.
1947-March: House Resolution 140, officially declaring that the dam at Boulder Canyon be named Hoover Dam, for former President Herbert Hoover, is introduced to Congress. It is passed two days later, moves on to be approved in the Senate.
1947-April: President Harry S. Truman signs resolution officially declaring that the dam at Boulder Canyon be named Hoover Dam.
These facts copied from http://www.pbs.org/wgbh/amex/hoover/timeline/index.html , a PBS page about Hoover Dam.