The Expedition heads up the shallow Missouri River near present Mobridge, South Dakota. They camp near an active Arikara village where the interpreter Joseph Gravelines joins them. They find abundant Buffaloberries near the creeks.
The canoes safely pass several Clearwater River rapids. At the Potlatch River, a canoe hits a rock, turns sideways, and fills with water. With the help of the Nez Perce, the men are rescued and most of the cargo is recovered.