The Snake River is the defining geographical feature of Idaho.

Rising in the Rocky Mountains, it flows into Idaho from Wyoming in a northwest direction, turning sharply south at a point some 20 miles north of Idaho Falls.

It then makes follows an arc across the entire state, meeting the state of Oregon and forming a joint border with it through Hells Canyon. After Oregon, it forms Idaho's border with Washington for a few more miles before turning west at Lewiston, eventually to join the Columbia River on its course to the Pacific.