The Marias River starts in Glacier County at the confluence of the Two Medicine River and Cut Bank Creek. It flows generally southeastward from this point and is impounded by the Tiber Dam to form Lake Elwell. About 50 miles downstream of the dam, it receives its principal tributary, the Teton River, shortly before entering the Missouri River at Loma. T he Marias River was named in 1804 by Meriwether Lewis for his cousin, Maria Wood. There are three BLM river access sites: Sullivan Bridge launch site, Pugsley Bridge Recreation Area, and Moffat Bridge Recreation Area. Located at the headwaters of the Marias River, the confluence of Two Medicine River and Cut Bank Creek, this scenic launch point has a gravel road access and beautiful riparian vegetation adjacent to sheer cliffs.