The pass is an ideal location to witness the tremendous power that glaciers have had on the landscape. On the west side of the road at the pullout, travelers can see evidence of the millennial processes of past ice ages. Low, near-horizontal ridges mark the locations of glacial moraines near the tops of the mountains. These ridges, like bathtub rings, indicate changing ice depths as the former valley glacier thinned, retreated and then re-advanced short distances in response to short-term climatic changes. The ice was, at the time, over 2,000 feet thick. The youngest major glaciation ended about 10,000 years ago.