The river Ardèche has its source in the Massif Central. In its lower course it crosses a limestone plateau. Then the Ardèche falls into the river Rhone.
The Ardeche once run on top of the plateau, but the erosion cut an impressive gorge. All the time, the river was the drainage of this area, and as soon as it ran deeper than the plateau, the subterranean drainage of the plateau started. The development of caves is always connected with the level of the drainage. Along the ground water surface a cave storey was formed. Later, when the river cut its bed deeper into the plateau, the cave level became dry and the next level was formed some meters below.
Many caves are accessible along the valley, through the former water exits of the cave systems. Some more can be found on top of the plateau. They are accessible through roof collapses or shafts.