In Idaho, the river begins in the Palisades Reservoir in the south on the eastern border of the state. As it heads west it parallels U.S. 26 to the American Falls Reservoir. From there it follows Hwy. 78 to the Oregon border near Caldwell. Then it continues north along the border to Lewiston, where it exits into Washington.
Numerous tributaries feed into the Snake River.
The national forest covers more than a million acres in the southeastern corner of Idaho. The area contains many streams and several north-south mountain ranges with elevations ranging from 5,000 feet to 9,953 feet at Meade Peak, just north of Montpelier. There are 1,200 miles of hiking trails, many of which are well-maintained and marked. Trail, the Lander Cutoff Trail, Wrights Creek Nat'l. Trail and the Boundary Trail.