The Corps left the Mandan village and soon found themselves in the Rockies

They couldn't use boats during the crossing, and had to trade for horses. Fortunately their interpreter, Sacagawea, was related to the chief of the people who could sell them the horses they needed.

All the same, they could not find an easy pass over the mountains, and there was no game to catch for food. They nearly starved before being helped by the Nez Perse.