The Lewis and Clark Expedition camped at the mouth of the river just east of here June 3, 1805. The Piegan people called it "The River that Scolds at all Others," but Lewis named it Maria's River in honor of his cousin, Miss Maria Wood (over time the apostrophe was dropped). Until exploration proved otherwise, most members of the party believed this river to be the main channel of the Missouri. On his return trip from the coast in 1806 Capt. Lewis explored the Marias almost to its source.
In the fall of 1831 James Kipp, of the American Fur Co. built Fort Piegan at the mouth of the river, as a trading post for the Blackfeet Indians, and acquired 2,400 beaver "plews" or skins by trade during the post's first 10 days. In 1832 the company abandoned the post and the Indians burned it to the ground. The company built Fort MacKenzie about six miles up the Missouri River in 1833. The fort closed in 1844 after post factors Francis Chardon and Alexander Harvey killed several Blackfeet and wounded many more who had come to the post to trade.