The Black Forest stretches from the High Rhine in the south to the Kraichgau in the north. In the west it is bounded by the Upper Rhine Plain (which, from a natural region perspective, also includes the low chain of foothills); in the east it transitions to the Gäu, Baar and hill country west of the Klettgau. The Black Forest is the highest part of the South German Scarplands and much of it is densely wooded, a fragment of the Hercynian Forest of Antiquity. It lies upon rocks of the crystalline basement and Bunter Sandstone, and its natural boundary with the surrounding landscapes is formed by the emergence of muschelkalk, which is absent from the Black Forest bedrock.
Thanks to the fertility of the soil which is dependent on the underlying rock, this line is both a vegetation boundary as well as the border between the Altsiedelland (“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 160 km, attaining a width of up to 50 kilometres in the south, and up to 30 kilometres in the north. Tectonically the range forms a lifted fault block, which rises prominently in the west from the Upper Rhine Plain, whilst seen from the east it has the appearance of a heavily forested plateau.