 Both peaks are sometimes included in the geographic perimeter of the Hachimantai plateau, although they form distinct volcanic groups.In a general sense, the Hachimantai plateau is an ancient volcanic shield, levelled by erosion or deformed by landslides or lateral overlaps, or covered by products of more recent volcanic activity.The deepest layer is composed of Tertiary bedrock resting on a layer of Paleozoic sedimentary rocks containing Cretaceous granite blocks.