As glaciers push through river valleys they erode the valley bottoms. When they retreat and melt away, a 'U' shape emerges. U-shaped valleys, which are found all over the Northwest United States, speak of an ice age in the recent past.
As glaciers push through river valleys they erode the valley bottoms. When they
retreat and melt away, a 'U' shape emerges. U-shaped valleys, which are found
all over the Northwest United States, speak of an ice age in the recent past.