The Alva B. Adams Tunnel is the principal component of the largest transmountain water project in Colorado, the Colorado-Big Thompson Project (C-BT). The tunnel transfers water from the western slope of the Colorado River drainage to the eastern Front Range of Colorado. It is 13.1 miles (21.1 km) long, with a concrete lined diameter of 9.75 feet (2.97 m). The tunnel drops 109 feet (33 m) in elevation along its length and runs in a straight line under the Continental Divide from west to east, passing under Rocky Mountain National Park. At its deepest point, the tunnel is about 3,800 feet (1,200 m) below the surface of the mountain peaks. Construction began on 15 June 1940, but was suspended as a result of World War II priorities, from the end of 1942 to August 1943. The tunnel was holed thr