Steep mountains coupled with an amazing variety of rock and water features contribute to the region's tremendous biodiversity. The mountains rise steeply to 9,206ft (2,806m) at Goode Mountain and fall to valley floors as low as 400ft (122m) along the Skagit River at the Complex's west boundary.
From the park's glaciers and over 300 lakes and ponds, flow thousands of miles of rivers and streams. Several major watersheds flow from the North Cascades including those of the Skagit, Stehekin and Nooksack rivers. The Skagit River and its tributary streams comprise the largest watershed draining into Puget Sound.
Variation in elevation, soil types, rainfall and exposure combine to form eight distinctive life zones from the lowland forests and wetlands to the alpine peaks and glaciers.