The Picos de Europa mountains were originated by the sedimentation of submarine limestones 3,000 metres thick, during the Carboniferous Period of the Primary Era, comprising from 345 million years ago up to 280 million years ago. The slates, sandstones and conglomerates, all form the valley material surrounding them. 220 million years ago, in the Hercinian folding, the first mountainous relief arised, producing an elevated horst between the depressions of Liébana and Cares, to rise definitively in the alpine folding of the tertiary Era, 65 million years ago.