There are specific sets of caves because of the geology of the area, each with their own characteristics. In the north east (from the up to the Sornin Plateaux) the caves are regarded as very deep and very demanding in the grading system, especially considering the variable weather in the area. In the north west of the system, the caves (including the Autrans and Meaudre systems) are of current interest, as many new caving discoveries are being made, particularly in the Meaudre area, on a regular basis. Further south the caves vary in their characteristics, with systems in the Herbouilly Plateau being of different gradings. The area surrounding the Vernaison and its associated river valley contains many caves and systems, with one of the most explored being the just south of Saint-Agnan-en-Vercors which is located at the Bournillon entrance, which is the largest cave entrance in Europe.