The "Stein" is a 547 meter high molasse mountain southeast of the town of Weiach. On top of the sandstones and marls of the molasse lies a layer of so-called "middle cover gravel". The former river gravel is partially cemented together. This means it resists erosion better than the deeper molasse layers and therefore forms striking rock faces on the north side facing the Rhine and on the southwest side. These contrast with the plateau-like plateau at the top of the "Stein".
Rock face formed by middle cover gravel on the southwest edge of the "Stein"; in the background, steam rises from the cooling tower of the Leibstadt nuclear power plant.
On the plateau-like plateau at the top of the "Stein".
The best view from the edge of the plateau of the "Stein" is in winter, when the deciduous trees are bare. In places, the view then extends as far as the Alps.
At the foot of the rock face formed by the middle cover gravels, a small cave has been formed by weathering.
The middle cover gravels were deposited in an earlier ice age, not the last one, and are therefore at least 200,000 years old. If the molasse beneath them is removed by erosion, the cover gravels can temporarily form unstable overhangs. Eventually, rock masses break off and fall as small rockfalls over the mountain flanks. The fallen cover gravel blocks now form magical miniature landscapes in some places on the wooded slopes.