Completed in 1945, this massive concrete barrier is the keystone structure of the Central Valley Project, a vast network of dams, canals and pumping stations designed to control flooding and supply irrigation water to the farmlands of the Sacramento and San Joaquin Valleys. Measuring 602ft high and 3,460ft long, the dam is taller than the Washington Monument in the nation's capital, and its central spillway is three times as high as Niagara Falls. The Sacramento, McCloud and Pit rivers and Squaw Creek are impounded behind the dam to create beautiful Shasta Lake, the state's largest reservoir and one of the area's most popular recreation sites. When full, the lake boasts 365mi of shoreline and 29,500 acres of water surface. Houseboating is popular here, with the state's largest fleet of houseboats for rent.An overlook on the road approaching the dam allows a stunning view of the dam and lake; Mt. Shasta looms in the background. Historical displays in the visitor center recount the fascinating story of the dam's construction and of the Central Valley Project.