When they arrived at the earthlodge villages, Lewis and Clark almost immediately (November 4, 1804) hired Charbonneau to serve as their interpreter among the Hidatsas. At some point during the winter it became clear that the expedition would need horses to cross from the Missouri to the Columbia watersheds by way of the Bitterroot Mountains, and that the Shoshone resided at or near the source of the Missouri. The journals of Lewis and Clark do not explain just how the captains decided to take Charbonneau and Sakakawea west along with the permanent party in April 1805, but it is certain that Sakakawea was brought along primarily to interpret among her natal people, the Shoshones. Her perceived value must have been considerable because the captains (especially Lewis) had already developed a relatively dim view of Charbonneau, and Sakakawea complicated the logistics of a military command by giving birth on February 11, 1805, to her first child, Jean Baptiste Charbonneau, who made the immense journey to the Pacific Coast and back again to the Hidatsa villages. The decision to take Charbonneau and one or both of his Shoshone wives on the 1805 journey seems to have been made on November 11, 1804. Clark still believed that both wives would be accompanying the expedition as late as April 1, 1805.

When the moment came, Sakakawea did in fact explain the expedition’s purposes, needs, and character to the Shoshones. One of the headmen of the tribe, whom Lewis and Clark called Cameahwait, proved to be Sakakawea’s brother. Although it is possible that “brother” carried a metaphoric rather than literal meaning for Sakakawea, Lewis and Clark were convinced that Cameahwait and Sakakawea were related by consanguinity rather than close cultural and family ties. Meriwether Lewis reported a tearful reunion in the beleaguered Shoshones’ one remaining lodge (August 17, 1805). In the Shoshone village near Lemhi Pass, Sakakawea was reacquainted with, and then formally released by, a Shoshone man to whom she had been betrothed as a girl. She also met a childhood playmate who had managed to escape from the Hidatsa raiders at the Three Forks. Undoubtedly Sakakawea hoped to establish a trust relationship between the Corps of Discovery and the Shoshones, but the journal keepers report that the Shoshones continued to be wary, even skittish in the presence of these exotic strangers. When the expedition said farewell to the Shoshones on August 30, 1805, the entire Charbonneau family continued with Lewis and Clark to the Pacific Ocean.