Puy Ferrand – in the background to the left in this photo – is the highest point of the Chaudefour valley, one of the three glacial valleys of the Massif du Sancy. The altitude of the valley’s slopes, formed by the glaciers that used to cover the whole massif, varies between 3,723 feet (1,135 metres) – at the House of the Nature Reserve – and 6,082 feet (1,854 metres) at Puy Ferrand. They are the remains of two craters which collapsed 2.5 million years ago.