The Hoge Kempen, or the Kempens Plateau, is actually a large rubble cone formed by boulders and stones from the Ardennes, deposited by the Meuse during the Ice Age in the southeast of the Limburg Kempen, later covered with sand by sea winds. Subsequently, a new, relatively deeply worn valley was created where the Grensmaas found its way through its own rubble. The transition to the Kempens Plateau, west of the Meuse valley, is very steep and forms a staircase of 45 meters on average. This steep edge runs from Opoeteren near Maaseik in the north to Gellik near Lanaken in the south. It forms an unbroken line more than 20 kilometers long, one of the most spectacular geological phenomena in the rather flat Flanders. About half of this escarpment is located in the National Park. The height of the park varies between 45 and 155 m above sea level, with the northern slag heap of Waterschei, built up with waste from coal production, as the highest point.