The highest point of the Monts Dore, the Puy de Sancy, was born from an intense volcanic activity which stopped 250,000 years ago. This volcanic activity is also at the origin of many cold or hot water sources, rich in iron and other minerals, which rise to the surface laden with gas, such as the Sainte-Anne source in the Chaudefour valley or the thermal springs of Le Mont-Dore and La Bourboule, two towns located at the foot of the Sancy.