ROOSEVELT DAM, the greatest engi neering work in connection with the Salt River irrigation project in Arizona, which ranks first among the works of the United States reclama tion service, was completed in 1910. This won derful structure of sandstone and cement, cost ing nearly $9,000,000, rises 284 feet above Salt River, about 75 miles northeast of Phoenix. It is 1,080 feet long on top and 170 feet thick at the base. Placed by the side of a 20-story building, it would rise 10 feet above it, while its length on top would be equal to four blocks on Broadway, New York City. Across its top is a roadway 20 feet wide. The structure is set in a mountain gorge, being in the form of a huge W, closed at the top and bottom, and curved with a bulge up-stream so as to present an arched resistance to the great body of water it has to withhold. Very large stone is used in the dam wall, technically °cyclopean," and this is securely bonded together and filled in with Portland. cement, thus solidifying it into
a great monolith. The discharge is through a 500-foot tunnel to six great service gates, each of which will discharge 1,670 cubic feet of water per second. Spillways carry the surplus water around the dam, and serve to relieve it in time of flood. The reservoir created by the Roosevelt dam is the largest artificial body of water in the world. Its capacity is 61,000,000,000 cubic feet, and if its water were spread over the State of Delaware it would cover the en tire surface of the State a foot in depth. The lake formed by the dam is 25 miles long, and at its greatest two miles wide. It was formally opened by Theodore Roosevelt 18 March 1911.