On June 2, 1805, the expedition came to a fork its Hidatsa informants had not prepared it for: two large rivers, one from the north, muddy like the Missouri they had been climbing for a year, and one from the southwest, clear and swift. Nearly every man in the party, the boatman Pierre Cruzatte foremost, was sure the muddy north fork was the Missouri. The captains thought otherwise. The Hidatsa had told them the Missouri ran clear at its great falls, and the south fork looked like a mountain river.
They camped on the point between the rivers and spent days finding out, climbing this rise for the view and sending parties up both forks. On June 8 Lewis named the north fork Maria's River for his cousin Maria Wood; the apostrophe has since worn off. The captains held to the south fork, the men followed though few were persuaded, and within days Lewis heard the falls. On the way home, in July 1806, he came back to explore the Marias.
The captains thought the point a fine site for a trading post, and in 1831 James Kipp of the American Fur Company built Fort Piegan near the confluence for the Blackfeet trade, a post that lasted only a season. The rivers have shifted since, so the 1805 junction cannot be placed exactly. A quarter-mile trail climbs from a parking area off Loma Ferry Road, just south of US-87 at Loma, to the overlook and its interpretive signs.
The closest stops worth working into your route