The geological formation of the Dentelles de Montmirail massif dates back to the Secondary era, between 200 and 60 million years ago. Tectonic movements have straightened rock bars of Jurassic origin which have eroded and split over time. The different rocks that make up the massif are representative of the various periods of its formation. It comprises red dolomitic clays and gypsum marls from the Triassic, limestones from the Jurassic, and sandy arenas from the Cretaceous.