Mission Range, segment of the northern Rocky Mountains, in northwestern Montana, U.S. The range trends northwest to southeast and extends some 45 miles (72 km) from Flathead Lake in the north along the Swan River toward the city of Missoula. McDonald Peak (9,868 feet [3,008 metres]) is the highest point in the range. Embracing parts of the Flathead National Forest and the Flathead Indian Reservation, the range was named for the nearby St. Ignatius Mission, established in 1854 by Jesuits.