Dillon Reservoir and Roberts Tunnel West Portal Access, Colorado

The ten-foot diameter Roberts Tunnel begins at its west portal, underwater in the reservoir, controlled and accessed by a valve facility on a peninsula. It then runs for 23.3 miles in a nearly straight line, passing 4,000 feet below the Continental Divide, to its east portal, near the town of Grant. In the 1950s, Denver Water captured the Blue River watershed, which flows out of the former mining town of Breckenridge, and built the Dillon Reservoir and Roberts Tunnel to deliver it to Denver. The Dillon Reservoir is the largest reservoir for the City of Denver. Construction started in the 1950s, before agreements were even reached. The reservoir began filling in 1963, after the town of Dillon was moved.