The fertility of the soil is dependent on the underlying rock; this line is a vegetation boundary as well as the border between the (old settlement land) and the Black Forest, which was not permanently settled until the High Middle Ages. From north to south, the Black Forest extends for over , attaining a width of up to in the south and in the north. Tectonically, the range forms a lifted fault block, which rises prominently in the west from the Upper Rhine Plain; from the east, it has the appearance of a heavily forested plateau.