Conventional geographic understanding holds that the Missouri River begins near Three Forks, Montana, where the Jefferson, Madison and Gallatin Rivers meet. This confluence, and the names of the rivers, provide a useful reminder of just how arbitrary the beginning points of rivers can be. Lewis and Clark, in their journals, made an argument for declaring this point the beginning of the Missouri, but they could, with equal justification, have named any of the three rivers — the Madison, Jefferson or Gallatin — as the upstream extension of the Missouri.

While all four of the rivers found here were significant routes for Native American commerce and for the fur trade, none made the transition to industrial river commerce. The Great Falls of the Missouri, over a hundred miles downstream, blocked navigation for boats that could not be portaged and thus became the head of steamboat navigation in the 19th century.