In August 1805 Lewis and Clark were looking for the Shoshone Indians. The Corps (Lewis and Clark's expedition party) needed horses to cross the Rockies and the Shoshone had them. Sacagawea, a member of the Corps, was Shoshone, but she had been kidnapped by another tribe many years before.
The Corps were still recovering from their portage around the Great Falls of Missouri. Morale was low. Lewis and three men were scouting ahead when they finally met a band of Shoshone. They were the first white men the Shoshone had ever seen.