The National Geopark GrenzWelten lies in the border region between North Hesse and North Rhine-Westphalia. At the transition from the Rhenish Slate Mountains in the west and the Hessian Depression in the east, the Geopark has 400 million years of Earth history. The rocks of the Sauerland were deposited in the Devonian Sea 400 Ma ago. 300 Ma ago, the Sauerland was formed by folding during the Variscan orogeny. 250 Ma ago, the Zechstein Sea surged onto the eastern edge of the Sauerland. The red sandstones of North Waldeck and Burgwald were formed in extensive desert plains. 100 million years ago, dinosaurs roamed the Cretaceous karst landscape near Brilon. And finally, in the Eocene, the lignite deposits were deposited in the West Hessian depression.