Glacial Lobe Dam at Green Monarch Ridge View Point

As the Purcell Trench ice lobe of the Cordilleran Ice Sheet advanced south from Canada, it was stopped by the Green Monarch Ridge, building an ice dam 4,000 feet (1219 m) tall and nearly 40 miles (64 km) wide that blocked the Clark Fork river, thus filling glacial Lake Missoula. View the Green Monarch Ridge and the Purcell Trench from a large pullout on Idaho State Route 200, about one mile (1.6 km) west of Hope, Idaho and 15 miles (24 km) east of Sandpoint, Idaho.