A major part of the mountains around Kandersteg consists of sedimentary rock from the primordial ocean Tethys. Thanks to the fossils occurring therein, geologists are enabled to determine the various layers according time and location. In this way geologists found evidence that the area at the Lake Oeschinen is essentially formed by three so-called nappes, the Wildhorn, Gellihorn and Doldenhorn nappes. These belong to the so-called Helvetic nappes and consist mainly of limestone and sand stone. Particularly well visible are the typical folds and fractures at the Bire, the Fisistöck and the Jegertosse in the Gastern valley, which reveals to the observer the elemental force of the Alpine folding.