East Portal

After more than 50 years of dreaming and 14 years of planning and building, the first water from the Colorado River flowed east June 23, 1947 through the Alva B. Adams Tunnel under the Continental Divide. 

Today, the U.S. Bureau of Reclamation maintains the 13.1 mile tunnel. Once a year it is shut down and Reclamation engineers drive a specially-designed Jeep through to inspect the tunnel.

The tunnel is named for a U.S. senator from Colorado who played a key role in convincing Congress to fund and construct the Colorado-Big Thompson Project. The Adams Tunnel is the longest in the United States to provide water for irrigation. 

The inaugural water coursed through the tunnel seven years to the day after construction began. During that time, the nation entered World War II, endured war-time labor and resource shortages, then began building and rebuilding at home and abroad. 

The idea of boring a tunnel through the divide was considered as early as the 1890s, but nearly four decades passed before the technology and impetus - water shortages - converged during the 1930s.

After years of planning, excavation from the East Portal began June 23, 1940, just southwest of Estes Park. Work went on simultaneously from each portal. 

Excavation crews spent four years, from 1940-1944, drilling the tunnel. Work stopped twice because of wartime demands on labor and materials. When the two crews met June 10, 1944, they were off by less than the width of a penny. During the next three years, the tunnel was lined with concrete and readied for water deliveries. 

East Portal by the Numbers