 On December 21 , 1928 President <unk> signed the bill authorizing the dam . The Boulder Canyon Project Act appropriated $ 165 million for the Hoover Dam along with the downstream Imperial Dam and All @-@ American Canal , a replacement for Beatty 's canal entirely on the U.S. side of the border . It also permitted the compact to go into effect when at least six of the seven states approved it . This occurred on March 6 , 1929 with Utah 's ratification ; Arizona did not approve it until 1944 . 
