Due to the synclinal-anticlinal structure of the hills on the left bank of the Rhine which runs from southwest to northeast, these bulges in the northern and central parts of the Wasgau, i.e. in the region of the South Palatine Saddle (Südpfälzer Sattel) are particularly prominent, with the result that their surface layers were more heavily eroded. Because the formations of the Zechstein, for example, the Annweiler and Speyerbach beds, consist more of fine-grained sandstones with clayey binding and shales and therefore have a softer consistency, this material could be more easily carried awayl leaving the older rocks of the Zechstein and Rotliegendes exposed. This resulted in erosion surfaces and broad valleys, as are particularly characteristic of the northeastern Wasgau, for example, in Gossersweiler and Völkersweiler, also in Hauenstein, Busenberg or Fischbach bei Dahn. At the same time, parts of the Lower Bunter Sandstone, the so-called Trifels and Rehberg beds remained, because they mostly consist of harder quartz sandstone and are therefore particularly resistant to weathering and erosion. The micro-relief of the Wasgau was developed during the Neogene period (23.8 to 2.8 million years ago), and especially the Quaternary period (2.8 to 0.01 million years ago), as a result of erosion, that is characterized by diversely-shaped, often conical and isolated hills with bizarre rock formations (the Wasgau Rock Country or Wasgau Felsenland). This rock country extends from Annweiler in the northeast roughly to the stream of the Falkensteiner Bach at Phillipsburg in the southwest and forms the actual core area of the Wasgau.