As the Corps of Discovery neared the headwaters of the Missouri River, the river grew increasingly less navigable. Meriwether Lewis's anxiety grew as the river shrank. In need of horses to continue the journey, Lewis wrote that "[i]f we do not find [the Shoshoni] or some other nation who have horses I fear the successfull issue of our voyage will be very doubtfull."
Sacagawea, a young woman who grew up among the Shoshone, had joined the Corps of Discovery along with her husband and baby. As a girl of 11 or 12, a Hidatsa raiding party took Sacagawea from her home and family. Traveling with the Corps of Discovery five years after her abduction, Sacagawea began to recognize features on the landscape as the group approached the land of the Shoshone.
In late July 1805, Meriwether Lewis recorded that “The Indian woman recognizes the country and assures us that this is the river on which her relations live … this peice of information has cheered the sperits of the party…” On August 8, Sacagawea saw Beaverhead Rock and at last knew she was home. According to Lewis, "this hill she says her nation calls the beaver's head from a conceived remblance of it's figure to the head of that animal. she assures us that we shall find her people on this river or on the river immediately west of it's source; which from it's present size cannot be very distant."
Indeed, a few days later the Corps found the Shoshone. By recognizing Beaverhead Rock and helping to direct the explorers to her people, Sacagawea proved herself critical to the success of the journey to the Pacific Ocean.
Beaverhead Rock is now part of the Montana State Parks system.
More information about Beaverhead Rock is available in the following books and web sites.
Way to the Western Sea, chapter 15 “The Great Divide."
Lewis and Clark Among the Indians, chapter 6 “Across the Divide."