Since the downfaulting of the Upper Rhine Graben during the Eocene epoch, the two shoulders on either side have been uplifted: the Black Forest to the east and the Vosges to the west. In the centre lies the Kaiserstuhl volcano, which dates to the Miocene. In the times that followed, the Mesozoic platform on the uplands was largely eroded, apart from remains of Bunter Sandstone and Rotliegend Group, but it has survived within the graben itself. During the Pliocene a pronounced, but uneven bulge especially affected the southern Black Forest, including the Feldberg. As a result, the upper surface of the basement in the northern part of the forest around the Hornisgrinde is considerably lower. In the central Black Forest, the tectonic syncline of the Kinzig and Murg emerged.