In most of the Yukon, u-shaped valleys and rounded hills mark where glaciers scoured the earth. In Beringia, however, the valleys are V-shaped. Other clues to the Beringian landscape are the rocky outcrops called tors. From a distance, these craggy outcrops on the tops of hills can look like castles. Tors are formed of a hard granite core. Frost and water action break of the outer rock but leaves the dense granite core. This action takes hundreds of thousands of years and only happens in unglaciated terrain.