Mills Glacier is an alpine glacier in Rocky Mountain National Park at the base of the east face of Longs Peak in Colorado. It is one of the park’s high-mountain ice features and occupies a cold, sheltered basin beneath the mountain’s steep eastern wall, where snow and ice endure at high elevation. Its significance lies in this dramatic setting within a larger alpine landscape shaped by harsh mountain weather, cirques, and the long geologic history of glaciation in the Colorado Rockies.