MARIAS RIVER

river, formed by the confluence of Cut Bank Creek and Two Medicine River, in Glacier county, northwestern Montana, U.S. It flows generally southeast and is joined by several creeks. The river is impounded by the Tiber Dam to form Lake Elwell, an irrigation and recreation reservoir. Beyond the dam it flows for 50 miles (80 km) to enter the Missouri River at Loma. The Marias, used by pioneer and trading expeditions, was named in 1804 by the explorer Meriwether Lewis for his cousin Maria Wood. In 1806 Lewis proceeded up the river to a point near the site of Cut Bank, where Fort Piegan, an American Fur Company trading post, was later established (1831). The Marias receives its principal tributary, the Teton River, near its junction with the Missouri.