The oldest rocks in the region can be observed: red sandstones from the Lower Triassic (“Buntsandstein”). The red colour is due to oxidyzed iron concentrations in the rock. These older sandstones are outcropping at the surface in this area because the geological strata buckles here upwards and forms an arch-like structure, the “Born saddle”. The river Sauer has exposed the red sandstones by incising and eroding deeply into the landscape. While doing so, it has dug its way through the more recent rock strata from the Middle Triassic (“Muschelkalk”), which lie on top of the sandstone strata: yellowish-green sandstones, marl with gypsum layers and dolomite.
Red sandstone (“Born sandstone”) was mined in the mid-20th century in a small disused quarry above the bicycle lane. The uppermost red sandstone areas are very suitable as building stone and ashlar.
The Girsterbaach valley is a tributary to the Sauer. Several quarries from which various materials were extracted marked this valley. These products were in addition to red sandstone, the yellow-greenish shell sandstone and gypsum from the Middle Triassic (“Muschelkalk”). Most of these quarries are presently no longer accessible.