Beaverhead Rock State Monument - MT. After seeing "The Beaver's Head" on August 8, 1805, Sacagawea was positive that they were in Shoshone country. She told the captains that it was near "the summer retreat of her nation, who lived on a river beyond the mountains which run to the west." The captains were almost certain that this river was the Columbia, or at least a major tributary leading to it.
