Lovely rocks around there…
But not granite! The Picos are the result of the uplift during the Variscan/Hercynian orogeny. The basin fill rocks were predominantly limestones and silty sediments, which have been uplifted and thrusted.
The principal rocks are:
- Carboniferous limestone — roughly 300–330 million years old
- Dolomitic limestone / dolomite, particularly in parts of the Picos de Europa Formation
- Locally shales, sandstones and conglomerates, particularly around the Liébana basin and its margins
- Quaternary glacial deposits and scree in the valleys and higher cirques.
The Spanish Geological Survey (IGME) describes the Picos as essentially a huge Carboniferous limestone massif, with the principal limestone formations repeated and stacked by numerous thrust faults.