Gallatin River
The Jefferson River flows north through the Jefferson Valley towards Whitehall and then east, where it is joined by the Boulder River before passing through the narrow Jefferson River canyon near Lewis and Clark Caverns State Park. After the canyon, the river passes into a broad valley again near Willow Creek. The Jefferson converges with the Madison River at Missouri Headwaters State Park near Three Forks to form the Missouri River, joined a short distance downstream by the Gallatin River.