Portneuf River (Idaho)

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The Portneuf River is a tributary of the Snake River, approximately 96 mi (156 km) long, in southeastern Idaho in the United States. It drains a ranching and farmer valley in the mountains southwest of the Snake River Plain near the Utah border. The city of Pocatello sits along the river near its emergence from the mountains onto the Snake River Plain.

It rises in western Caribou County, approximately 25 mi (40 km) east of Pocatello, along the eastern side of the Portneuf Range. It flows initially south, passing westward around the southern end of the range, and then turning north to flow between the Portneuf Range to the east and the Bannock Range. It flows northwest through downtown Pocatello and enters the Snake at the northeast corner of American Falls Reservoir, approximately 10 mi (16 km) northwest of Pocatello.

The valley of the Portneuf provided the route of the Oregon Trail and California Trail in the middle 19th century. After the discovery of gold in Idaho, it became a significant stage route for the transportation of people and goods. In 1877 the valley was used as the route of the Utah and Northern Railway, the first railroad in Idaho.