Glacial Geology

The map below shows the extent of Colorado glaciers in blue during the last ice age (about 26,000 years ago). The brown areas are sand dunes and the arrows show the direction the dominant winds blew during formation of the dunes.
Pleistocene glaciers shown in blue, sand dunes shown in brown. Arrows show wind direction. Glacial outlines prepared by Jack Reed (USGS) and sand distribution prepared by Rich Madole (USGS).

A crevasse in Andrews Glacier in Rocky Mountain National Park.

Colorado has about a dozen glaciers in Colorado today. These are not remnants of the Pleistocene glaciers, but were formed about 500 years ago during the Little Ice Age. During the Little Ice Age cooling, thick snow accumulated in protected areas where winds could blow extra snow into high-altitude cirques. The snow gradually changed into ice which eventually began moving down the valleys. The maximum extent of the glaciers occurred about 1850. As the climate began warming again, the ice began to melt and the glaciers began retreating back into the cirques.

Pictured to right: A crevasse in Andrews Glacier in Rocky Mountain National Park.