Lateral moraines, like terminal moraines, were formed as glaciers melted and deposited the rocks they were carrying along their margins.  These moraines show both the width and height of the glacier at its maximum extent in the past.  Visually comparing the height of lateral moraines to the valley floor shows how much thickness has been lost to melting.  Hiking into the now empty valleys once occupied by the glaciers shows the steep slopes of the lateral moraines towering above the valley floor, in some cases over 200 feet.

 

The gray ridge crossing the center of the photograph to the left is one of the lateral moraines of the Zmutt Glacier.