How long is Idaho's western border?

Answer 1

The simple answer is 117° 15' W.

However, beginning in the southwestern corner of Idaho (latitude 42° N) and travelling north, Idaho's western border (alongside Oregon state) runs north along longitude 116.45°W until it intersects with the Snake River near the mouth of the Owyhee River.

The western border of Idaho then follows the path of the Snake River until it's confluence with the Columbia River at Lewiston, Idaho & Clarkston, Washington.

From that point Idaho's western border (slongside Washington state) runs north along longitude 116.57°W until it intersects with the Canadian border at a latitude of 49°N.

Answer 2

600 miles, give or take a few.