Clark was ahead of Lewis, looking for traces of Sacagawea's tribe, when on July 25, 1805, he reached the headwaters of the Missouri. Lewis' contingent, following written instructions Clark left on the river bank, arrived two days later.
For Sacagawea, the place may have been a difficult reminder. It was there, five years earlier, that she was kidnapped and taken from her people by the Hidatsa. Lewis remarked that if the memory was upsetting to her, he could see no sign of it:
"I cannot discover that she shows any emotion of sorrow in recollecting this event, or of joy in being restored to her native country."
Her recognition of the area was, at any rate, comforting to the captains. She identified the place as an important hunting ground that had been in use by the tribes for centuries.
Lewis and Clark were at first unsure if they had actually reached the headwaters. When they decided that they had, they then had to determine which fork would take them to the mountains. The rivers were roughly the same width and appearance, so they picked the most westward-moving, naming it the Jefferson River for "the author of our enterprise."
Albert Gallatin, Jefferson's Treasury secretary, had been instrumental in gaining support for, and negotiating, the Louisiana Purchase. The eastern river was named for him. The middle river became the Madison for the Secretary of State, James Madison.