The history of the formation of the Cascade Mountains dates back millions of years ago to the late Eocene Epoch.
During the Pleistocene period dating back over two million years ago, glaciation advancing and retreating repeatedly scoured the landscape leaving  deposits of rock debris.
The last glacial retreat in the area began about 14,000 years ago and was north of the Canada–US border by 10,000 years ago.
The U-shaped cross section of the river valleys are a result of that recent glaciation.
Uplift and faulting in combination with glaciation have been the dominant processes which have created the tall peaks and deep valleys of the Cascade Range.
The history of the formation of the Cascade Mountains dates back millions of years ago to the late Eocene Epoch. During the Pleistocene period dating back over two million years ago, glaciation advancing and retreating repeatedly scoured the landscape leaving  deposits of rock debris. The last glacial retreat in the area began about 14,000 years ago and was north of the Canada–US border by 10,000 years ago. The U-shaped cross section of the river valleys are a result of that recent glaciation. Uplift and faulting in combination with glaciation have been the dominant processes which have created the tall peaks and deep valleys of the Cascade Range.
Little Comrade (Washington)