Between Regensburg and Passau, there is a marked difference in height between the forested mountains to the northeast and the Danube plain (Gäuboden) to the southwest. This dividing line between the Tertiary Hill Country and the Bavarian Forest is marked by the Danube Edge Fault (Donaurandbruch), a geological disruption between the sunken crystalline basement, lying beneath the Tertiary and Quaternary deposits of the molasse basin, and the still visible part northwest of this line, which belongs to the Bavarian Forest.