segment of the northern Rocky Mountains, paralleling the eastern bank of the Missouri River for about 80 miles (129 km) in west-central Montana, U.S. The range lies some 20 miles (30 km) east of the city of Helena and the Canyon Ferry Reservoir. The elevation of the Big Belts varies from about 3600 feet (1100 metres) near the Missouri River to 9,504 feet (2,897 metres) at Mount Edith, the highest point. Lying within a division of the Helena National Forest, the area was the scene of much gold prospecting in the late 1860s and was the site of renewed mineral exploration in the 1990s. The Big Belts were named for the prominent limestone belt that encircles the mountains.