segment of the Northern Rocky Mountains, northern Idaho, U.S. The mountains extend in roughly triangular form south for about 60 miles (100 km) along the Montana border from Pend Oreille Lake (Pend Oreille, Lake) to St. Joe River. The highest peaks (6,000–7,000 feet 【1,800–2,100 metres】) are in the east; most of the western range is a high plateau cut by narrow canyons and river valleys. Mines in this region produce most of Idaho's silver, lead, and zinc. Coeur d'Alene National Forest spreads across most of the range.