The NNE–SSW trending Upper Rhine Graben is a segment of the European Cenozoic Rift System located north of Basel, filled with Paleogene–Neogene sediments of 2–3 km thickness. It is up to 40 km wide and separates the Haute-Saône Platform to the west from the South German Platform to the east. The graben shoulders are bounded by steep normal faults and include isolated, lowered blocks of Mesozoic platform sediments along the rift-internal sides (the so-called Vorberg Zone, e.g., Isteiner Klotz north of Basel). The Schwarzwald Fault forms the eastern border of the graben. The southwestern border of the graben with the Haute-Saône Platform forms a flexure. In the southeast, the graben borders the External Folded Jura; the corresponding flexure is accentuated and overprinted by Alpine deformation.