As a glacier moves, it picks up loose boulders and carries them. These boulders scour the underlying rock, grinding it away much like sandpaper on wood. After thousands of years, large gorges are carved out as rock is removed by a glacier. The rocks and boulders a glacier carries is called till. Snow blown over the Continental Divide collected in east and north-facing valleys and formed glaciers.
Glacial valleys are distinctive for their U-shape.
Cirques lie high at the head of a glacial valley, and look as if someone removed the rock with an ice cream scoop. Meeker Cirque Mt. Fairchild Cirque Cirques may appear side by side, separated by thin ridges and a high point, called a horn. The Matterhorn in Europe is a classic example of a horn. As a glacier moves, some boulders are dropped along the sides of the glacier. These form lateral moraines.