Junction of Highway # 12 (The Northwest Passage Scenic Byway ) City of Lewiston, Idaho. West to Idaho / Washington State Line. Lewiston, Idaho is located at the confluence of the Snake and Clearwater Rivers at an elevation of 738 feet above sea level. The valley is rather narrow with a range of hills to the North sloping abruptly to about 2,000 feet above the valley floor. The celebrated Lewis and Clark Expedition brought Captains Meriwether Lewis and William Clark to the Clearwater Valley in 1805. Lewis and Clark embarked on a search for a trade route through the Northwest. They followed the Clearwater River from the Bitterroot Mountains to its merger with the Snake River, the site of the present day twin cities of Lewiston, Idaho and Clarkston, Washington.