The rock mass is made up of marl, limestone, dolomite rock and siltstone with veins of fibrous gypsum. The different types of rock alternate greatly in places, but they do occur in regular layers.
Over a length of around 450 metres in the western part of the tunnel there are formations of the Upper Buntsandstein (red sandstone) typical for the area. The section between 480 and 530 metres starting from the east end of the tunnel is primarily clay. The mountain groundwater level is well below the floor of the tunnel. Water may flow in between the Wellenkalk and Buntsandstein layers or in the clay section after rainy periods.