New Melones Dam is an earth and rock filled embankment dam on the Stanislaus River, about 5 miles west of Jamestown, California, United States, on the border of Calaveras County and Tuolumne County. The water impounded by the 625-foot-tall dam forms New Melones Lake, California's fourth-largest reservoir, in the foothills of the Sierra Neva…New Melones Dam is an earth and rock filled embankment dam on the Stanislaus River, about 5 miles west of Jamestown, California, United States, on the border of Calaveras County and Tuolumne County. The water impounded by the 625-foot-tall dam forms New Melones Lake, California's fourth-largest reservoir, in the foothills of the Sierra Nevada east of the San Joaquin Valley. The dam serves mainly for irrigation water supply, and also provides hydropower generation, flood control, and recreation benefits.