Standing on the summit and overlook far away, the whole surface of this mountain looks like a plane. Geological study suggested that the surface formed at the end of Paleogene, 23 million year ago. At that time, ground surface had been weathered and denuded to a plane-to-be with no big difference in altitude. Today, the north China Plain is at the same level with Taihang Mountain, with the altitude difference just 70 to 100 m. Now this surface has been risen up with Tainhang Mountain to more than 1000m. Geologists call this surface Taihang Planation Surface.