The Chaudefour valley is six hundred thousand years old and the result of the lateral collapse of the Sancy volcanic massif following a violent eruption. The explosion opened an amphitheatre in which a lake settled, and thirty volcanic formations emerged, forming the backbone of the current ridges. The trough-like landscape was shaped by glacial and fluvio-torrential erosions, which released lava needles and dykes. The bottom of the valley is occupied by grazed and hay meadows, covered in snow in this photo.