The story
The Hoh Valley's broad, flat-bottomed, U-shaped profile was carved by glaciers during the last ice age, when ice thousands of feet thick filled the valley. The river later occupied the trench left behind, giving the valley its characteristic form.
Notice the shape of this valley, the way it opens up wide and flat-bottomed with steep walls. A river didn't carve that. A glacier did. During the last ice age, a tongue of ice thousands of feet thick filled this whole valley and ground its way down toward the coast, bulldozing out the broad U-shape you're driving through right now. The river came later. It just moved into the trench the ice left behind.
Photo: Dirtsc · CC BY-SA 3.0
