The Cévennes are a partly mountainous hillcountry in south-central France, a part of the Massif Central. The mountain ridge runs southwest to northeast, and is bordered by the Grands Causses, the Montagne Noire, in the southwest, and by the Monts du Vivarais to the northeast. As it is a geographic region, its borders are different to the political borders. It covers parts of the départements of Gard, Lozère, Ardèche, and Haute-Loire. This means it belongs to three different régions: Languedoc-Roussillon, Rhône-Alpes, and Provence-Alpes-Côte d'Azur (PACA). Most of the Cévennes is protected by the Parc national des Cévennes (Cévennes National Park). The Cévennes are the watershed between the Atlantic and Mediterranean, also sometimes dubbed the European Watershed.
The Cévennes are the south eastern part of the Massif Central, separated from the Montagnes Noires by the limestone Causses. The basement rocks (granites and schistes) were uplifted by the Variscan orogeny forming a discontinuity. During the Permian and Triassic period (280–195 Ma) erosion of the mountains caused sedimentation in the surrounding lower parts. Downlift caused a transgession of the sea and only the tops of the Cévennes protruded as islands during the Jurassic. In this shallow and oxygen rich sea thick layers of limestone were formed. In the late Cretaceous and early Tertiary further mountain building occurred.
During the Alpine orogeny the Massif Central acted like a rigid block and was slowly uplifted while the layers remained mostly horizontal. At the same time the rivers of the region have cut deeply into the limestone forming deep gorges. The most important gorges are the Gorges du Tarn, Gorges de la Jonte, Lot, Gorges de l'Ardèche, and Cèze. With the formation of those valleys and gorges the drainage of the limestone went underground. The lower level of the drainage cause the formation of caves in this niveau, further lowering caused the formation of lower cave levels. Today the are is characterized by massive layers of limestone with intensive karstification and numerous huge multilevel cave systems.