Bitterroot Range, part of the Rocky Mts., on the Idaho-Mont. line. The main range, running northwest-southeast, includes Trapper Peak (10,175 ft/3,101 m high); Mt. Garfield (10,961 ft/3,341 m), in an east-running spur to the south, is the highest peak. Discovered in the 1804–5 expedition of Lewis and Clark, the rugged mountain range has long been one of the most impenetrable in the United States; except for its foothills, it remains almost completely unexploited.