By 13,000 years ago, retreating ice revealed a scoured landscape of rounded hills and deep, U-shaped valleys and fjords. The precipitous peaks in this landscape were taller than the glacier was deep and so the glacial ice flowed around them. Unlike the lower peaks rounded and eroded by the glacier's force, these taller peaks remained jagged in appearance. The land was swept clean of valley sediments.
During the Wisconsin Ice Age, the weight of the ice on the earth’s crust was so great it pushed the crust down several hundred feet into the semi-liquid mantle. As the ice melted and the weight relieved, the earth’s crust began to spring back in a phenomenon known as “isostatic rebound.”