The Beaverhead Boundary run is a popular whitewater river run in Montana, starting at Sec. 22, T4S, R4W and ending at Upper Branham Lake, Sec. 5, T4S, R3W. This segment of the river covers a distance of approximately 20 miles and is rated as Class III to IV, making it suitable for experienced kayakers and rafters. The ideal streamflow range for this run is between 800 and 1,500 cfs, which typically occurs during the spring and early summer months.

The river is known for its challenging rapids and obstacles, such as the "Big Timber Rapid" and "The Notch." These obstacles require skilled navigation and careful consideration to avoid accidents. It is also important to note that this river run is subject to regulations, including the use of personal flotation devices and adherence to Leave No Trace principles. Additionally, motorized vehicles are not allowed in the area, and camping is only allowed in designated areas.