The villages at the far northern end were isolated by a landslide near the Mortier tunnel. Another example is the Peuil plateau in the east. During the Ice Age, the Grésivaudan glacier reached the Peuil plateau leaving a marsh. Sub-divisions The central part of the Vercors Massif is divided into several regions. The Coulmes, in the north-west, are heavily covered in forest. Folds of Urgonian limestone are rounded, making the area appear mountainous. The four mountains area has been developed for tourism and skiing but is also known for its traditional activities such as the breeding of dairy cows and cheese making. The main villages, Autrans, Méaudre, Lans-en-Vercors, and Villard-de-Lans, are spread over two plateaus covered by wooded hills. The Drômois Vercors is an area made up of a number of smaller plateaus. In the north of the Drômois Vercors there are several gorges which are traversed by roads cut into the cliffs. Grassy areas are used as pastures in the summer months, and the biannual migration (transhumance) of animals is a period of celebration for the people of Die. The Haut-Plateaux (high plateaus) are the highest wilderness areas of the massif. The area is managed and the pastures are used for grazing in the summer. At the fringes of the massif, the Vercors regional park has four geographical areas. The Royans, the north-west foothills are the location of walnuts growing. Three valleys descend to the edge of the Royans: the Gorges de la Bourne, the cirque of the Combe Laval, and the Échevis valley, including the Grands and the Petits Goulets. The Gervanne, in the south-west, is a rugged area of hills at the foot of the plateau, with picturesque villages. It looks towards Crest. The Diois is a part of the Drôme valley around Die. This region has a Mediterranean character, with vineyards and fields of lavender. It acts as a buffer between Gervanne and the interior of the massif. The Trièves, in the east, is a low hilly plateau, which lies between the highest summits of the Vercors and the gorge carved out by the Drac. Principal summits From north to south: Le Moucherotte, m, the summit which dominates Grenoble, most northerly of the massif Le Pic Saint-Michel, m Roc Cornafion, m Les Arêtes du Gerbier, m La Grande Moucherolle, m La Petite Moucherolle, m La Tête des Chaudières, m Les Rochers de la Balme, m Le