Surrounding the base of the monument is a terrazzo floor embedded with a " star map " . The map depict 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 " Winged Figures of the Republic " , was each formed in a continuous pour . To put such large bronzes into place without marring the highly polished bronze surface , they was placed on ice and guided into position as the ice melted . Hansen 's bas @-@ relief on the Nevada elevator tower depict 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 visages of those Indian tribes who have inhabited mountains and plains from ages distant . "