The Datong-Fengzhen volcano group, also known as Ta-T'ung or Fanjiatun, is located at the intersection of two regional fault zones. The volcanic field contains about 80 volcanic vents, including cinder cones and small lava domes. The central Datong group contains 12 cones. An historical eruption reported during the 5th century (Chen 1986) has been shown to have originated from spontaneous combustion of a Jurassic coal seam (Zhang 1989, pers. comm.). The 13 youngest cones of the volcanic field have been Potassium-Argon dated at 0.34-0.37 million years.