Cinder Cone, a volcanic cone composed of ash, lapilli and scattered ropy and breadcrusted bomb fragments, was constructed during two periods of eruptive activity. The first eruptive period produced a tuff ring and a long basaltic andesite lava flow about 100,000 years ago following a period of glacial retreat. Strombolian eruptions during the second and final eruptive period about 10,000 years ago constructed a small pyroclastic cone on the eastern rim of the older basaltic andesite tuff ring. A long lava flow, ranging from basalt to mugearite, issued from the base of the cone and travelled in a north-trending U-shaped valley on the eastern flank of The Black Tusk.