 It was formed 15,000 to 20,000 years ago from pyroxene andesite flows and has since been intruded by a hornblende dacite dome.There are many buried glacial scars on the mountain which were created in recent glacial periods ("ice ages") of the present Wisconsinian glaciation.Most have since been filled in with andesite lava, pyroclastic flows, and talus from lava domes.