In the upper Triassic period, about 210 million years ago, the Kössen strata were formed from sediments in a shallow sea that was hardly deeper than 50 meters. The conditions were partly rather hostile to life, so that no large coral reefs could form. Only partly smaller coral reefs developed. As white regular structures fossilized corals can be found in the Koessen layers.
The rocks of the Kössen strata are very diverse. The dark marls are good source rocks for soil formation. Due to the high clay content these rocks are easily weathered, they do not form peaks but flowery alpine meadows. On the other hand, dark or light colored limestones may be intercalated, forming steep steps or rock faces.