[2][3] The history of the formation of the Cascade Mountains dates back millions of years ago to the late Eocene Epoch.

[4] In addition, small fragments of the oceanic and continental lithosphere called terranes created the North Cascades about 50 million years ago.

[4] During the Pleistocene period dating back over two million years ago, glaciation advancing and retreating repeatedly scoured and shaped the landscape.

[2] 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.

As a result, the west side of the North Cascades experiences high precipitation, especially during the winter months in the form of snowfall.