In July of 1805, Lewis, Clark and the Corps of Discovery sailed west toward the mountains until they came to the three forks of the Missouri River. Lewis and Clark named them the Gallatin, the Madison, and the Jefferson. The Corps decided that taking the Jefferson fork was the best course of action, although it was shallow and proved difficult to navigate. Before long, Sacagawea began to recognize landmarks that she associated with her old village before she was sold to Charbonneau as a prisoner of war. On August 8, 1805, Sacagawea spotted Beaverhead Rock and informed Lewis and Clark that they were near the headwaters of the Missouri River and the location of Shoshone tribe. Lewis wrote in this journal:
| The Indian woman recognized the point of a high plain to our right which she informed us was not very distant from the summer retreat of her nation on a river beyond the mountains which runs to the west. this hill she says her nation calls the beaver’s head from a conceived re[se]mblance of it’s figure to the head of that animal. she assures us that we shall either find her people on this river or on the river immediately west of it’s source; which from it’s present size cannot be distant. as it is now all important with us to meet with those people as soon as possible I determined to proceed tomorrow with a small party to the source of the principal stream of this river and pass the mountains to the Columbia;
Lewis decided to scout ahead on land with three men in the hopes of finding the tribe and their horses. Upon crossing Lemhi Pass (on the present-day border between Montana and Idaho), Lewis expected to see the passage that had tantalized explorers since the 1500’s – The Northwest Passage. Instead, all he saw were more mountains. Nevertheless, the Corps discovered the Shoshone village. Lewis and Clark were hopeful they could negotiate the acquisition of horses so the quest through the mountains could continue. When negotiations began, the Shoshone chief, Cameahwait recognized Sacagawea as his sister! The negotiations turned out to be successful.