The ridges in the Salmon-Huckleberry Wilderness belong to the Western Cascades (Old Cascades), a broad volcanic mountain range that erupted 10 million years before the High Cascades. Devils Peak and Salmon Butte are likely remnants of once-tall volcanoes, but have been reduced to ridges by the millennia of ice and water erosion. The wilderness contains several U-shaped valleys formed by glacial activity.