 Even before Congress approved the Boulder Canyon Project , the Bureau of Reclamation was considering what kind of dam should be used . Officials eventually decided on a massive concrete arch @-@ gravity dam , the design of which was overseen by the Bureau 's chief design engineer John L. Savage . The <unk> dam would be thick at the bottom and thin near the top , and would present a convex face towards the water above the dam . The curving arch of the dam would transmit the water 's force into the abutments , in this case the rock walls of the canyon . The wedge @-@ shaped dam would be 660 ft ( 200 m ) thick at the bottom , narrowing to 45 ft ( 14 m ) at the top , leaving room for a highway connecting Nevada and Arizona . 
