period dating back over two million years ago, glaciation advancing and retreating repeatedly scoured the landscape leaving deposits of rock debris. The U-shaped cross section of the river valleys are a result of 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 North Cascades area. Gallery See also Geography of the North Cascades List of mountain peaks of Washington (state) References External links Mountains of Washington (state) Mountains of Snohomish County, Washington