The range has much seismic activity, with the Pacific Plate being subducted into the earth's mantle. Large earth quakes have led to crumbling mountains, land slides, and the formation of fissures. For example about one quarter of the Mount Colonel Foster massif was turned into rubble by an earthquake in 1946.
During the last ice age 18000 years ago, ice covered most of the mountains. Glaciers that flowed down toward the ocean steepened the valley sides and eroded their floors. These valleys became fjords after ice melted and the sea level rose. Remnants of ice, such as the Comox Glacier still remain today. The erosion created the steep faces of Mount Elkhorn.
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