The snow-covered buttes of the Sweet Grass Hills, near the border of Montana and Alberta, Canada, are visible in this southeast-looking, low-oblique photograph. Each of the hills, formed approximately 50 million years ago, is a miniature mountain range composed of igneous intrusions and older sediment rocks. During the Bull Lake Ice Age, the great glacier flowed around the three big buttes of the Sweet Grass Hills, leaving them to stand as islands above a sea of ice. Visible is the narrow valley of the Milk River in southern Alberta, Canada (lower left).