First Lady Ladybird Johnson officially dedicated Glen Canyon Dam on Sept. 22, 1966, more than 10 years after work was started on the diversion tunnels to reroute the mighty Colorado River during construction. The dam is 710-feet high and holds back Lake Powell, one of the largest man-made reservoirs in the U.S. The dam topped out in 1963 and the first hydro-power from its massive turbines was transmitted to hungry customers in Phoenix in 1964.