Where can you most easily cross the wide Missouri? In central Montana, three tributaries join to form the start of the United States’s longest river. The headwaters of the Missouri River are intimately connected with the Lewis and Clark expedition, and in particular, with the life of one of their members, the Lemhi Shoshone woman known to history as Sacagawea. It was here, as a young girl, that Sacagawea was taken captive by members of the Hidatsa tribe, and sold into forced marriage to Toussaint Charbonneau. In 1804, at Fort…