 Surrounding the base of the monument is a <unk> floor embedded with a " star map " . The map depicts the Northern Hemisphere sky at the moment of President Roosevelt 's dedication of the dam . This is intended to help future astronomers , if necessary , calculate the exact date of dedication . The 30 @-@ foot @-@ high ( 9 @.@ 1 m ) bronze figures , dubbed " <unk> Figures of the Republic " , were each formed in a continuous pour . To put such large bronzes into place without <unk> the highly polished bronze surface , they were placed on ice and guided into position as the ice melted . Hansen 's bas @-@ relief on the Nevada elevator tower depicts the benefits of the dam : flood control , navigation , irrigation , water storage , and power . The bas @-@ relief on the Arizona elevator depicts , in his words , " the <unk> of those Indian tribes who have inhabited mountains and plains from ages distant . " 
