Located south of Twin Bridges along Hwy 41, Beaverhead Rock is a large rock formation that has a notable place in history. It was here in early August 1805 that the sole female member and only Native American of the Lewis and Clark Expedition, Sacajawea, recognized the rock as being near her tribe. The expedition needed horses in order to cross the looming Rocky Mountains to reach the Pacific. Without the horses it would have been impossible. Sacajawea's role was therefore essential to the expedition's success.