High Quality Content by WIKIPEDIA articles! Gibson Dam is a concrete arch dam on the Sun River, a tributary of the Missouri River, about 60 miles (97 km) west of Great Falls, Montana in the United States. Located on the eastern edge of the Rocky Mountains, the dam was built by the U.S. Bureau of Reclamation (USBR) between 1926 and 1929 as part of the Sun River Project to develop about 93,000 acres (38,000 ha) of irrigated land in the Sun River Valley.