The history of the formation of the Cascade Mountains dates back millions of years ago to the late Eocene Epoch. With the North American Plate overriding the Pacific Plate, episodes of volcanic igneous activity persisted. Glacier Peak, a stratovolcano that is north of Indian Head Peak, began forming in the mid-Pleistocene. Due to Glacier Peak's proximity to Indian Head Peak, volcanic ash is common in the area. In addition, small fragments of the oceanic and continental lithosphere called terranes created the North Cascades about 50 million years ago.