These three volcanic craters were formed by a series of small but violent steam-blast eruptions on the summit and south flank of Deer Mountain about 600 years ago, blanketing the region with several inches of ash and adding to the inventory of obsidian used by native peoples. The two southernmost craters contain small lakes. Two short trails that loop together lead up from the parking area and restrooms to the summit of the first crater. Access in winter is by snowshoes, skis or snowmobile.