It calls for a very large quantity of masonry ; in fact , there will be no less than 800,000 cubic yards . In this connection it may be of interest to note that it will be the largest block of masonry in the world , excepting the Egyptian pyramids . There are three distinct features of the dam , the spillway at the north end ; the main stone dam crossing the valley and the embankment at the south end .

The spillway wall is built on the side of the valley , curving up stream from the stone dam ; it is 1,000 feet long , to feet ; high at the end and 150 feet high at its junction with the dam . It is rubble masonry , faced on the water side with cut stone in regular courses and the lower side is in steps of large blocks of stone . A channel for the overflow is excavated in the rock back of the wall leading down to the river below the dam .

The main stone dam , according to the original plan , was to be 600 feet long , extending from the spillway to the foot of the slope at the south side of the valley , thence an embankment and core wall 568 feet long was to continue to the end , making a structure 2,168 feet long . The main stone dam is rubble masonry , faced on both sides , above the surface of the ground , with cut stone in regular courses .

It is 297 feet high from the deepest point of the foundation , which is 131 feet below the bed of the river . Its greatest width at the base is 206 feet and the width at the top is 20 feet .