The Portneuf River is a 124mi tributary of the Snake River in southeastern Idaho in the United States. It drains a ranching and farming valley in the mountains southeast of the Snake River Plain. The city of Pocatello sits along the river near its emergence from the mountains onto the Snake River Plain.The river is part of the Columbia River Basin.CourseThe Portneuf River rises in western Caribou County, approximately 25mi east of Pocatello, along the eastern side of the Portneuf Range. It flows initially south, passing westward around the southern end of the 60-mile range, and then turning north to flow between the Portneuf Range to the east and the Bannock Range to the west. It flows northwest through downtown Pocatello and enters the Snake at the southeast corner of American Falls Reservoir, approximately 10mi northwest of Pocatello.Watershed and dischargeThe Portneuf watershed drains 850290acre in southeastern Idaho and is bounded by Malad Summit to the south, the Bannock Range to the west, the Portneuf Range to the southeast, and the Chesterfield Range to the northeast. Marsh Creek is the only major tributary to the Portneuf River. Other creeks in this watershed include Mink, Rapid, Garden,Hawkins, Birch, Dempsey, Pebble, Twentyfourmile, and Toponce creeks. The total area of the Chesterfield Reservoir is estimated at.
