The highest peak in the Massif Central, the Puy de Sancy (1,886 metres) is a volcano that was born 1 million years ago. Today it forms a ridge between two very different slopes. Its western side, as well as the Chaudefour valley further south, is very steep with sharp peaks and deep valleys. The Aiguilles du Diable (Devil’s Needles), located below the summit of the Puy de Sancy on its south-western slope, are a group of dykes with a basaltic organ structure of irregular and twisted entablatures. These lava veins, pushed by the pressure of the magma chamber, have appeared over time under the effect of erosion.