 Running water has etched out the grain of the range, landslides have softened the abrupt edges, homegrown glaciers have scoured the peaks and high valleys and, during the Ice Age, the Cordilleran Ice Sheet overrode almost all the range and rearranged courses of streams.Erosion has written and still writes its own history in the mountains, but it has also revealed the complex mosaic of the bedrock.The Coast Mountains are the western range of the North American mainland cordillera, covering the Alaska Panhandle and most of coastal British Columbia.