High Quality Content by WIKIPEDIA articles! The Potlatch River is in the state of Idaho in the United States. About 56 miles (90 km) long, it is the lowermost major tributary to the Clearwater River, a tributary of the Snake River that is in turn a tributary of the Columbia River. Once surrounded by arid grasslands of the Columbia Plateau adjacent to the western foothills of the Rocky Mountains, the Potlatch today is used mainly for agriculture and irrigation purposes.