The boundaries drawn were, however, quite varied. In 1931, Robert Gradmann called the Central Black Forest the catchment area of the Kinzig and in the west the section up to the lower Elz and Kinzig tributary of the Gutach. A pragmatic division, which is oriented not just on natural and cultural regions, uses the most important transverse valleys. Based on that, the Central Black Forest is bounded by the Kinzig in the north and the line from Dreisam to Gutach in the south, corresponding to the Bonndorf Graben zone and the course of the present day B 31.