On December 2021 we made a geological itinerary from Santa Comba to Razo.
Something of geological history: the oldest rocks are found in Canada. Geological changes are so slow that they are not noticeable. Galicia originated in arched volcanic islands located between two major continents: Gondwana and Laurusia. The collision of the two about 300 Ma ago, resulted in a very long and very high mountain range, more than the current one of the Himalayas (Varisca Orogeny). This mountain range eroded in the Mesozoic Era and gave rise to a relief in the form of piano keys. The mountains that are observed have rounded peaks but they are not so as the orogeny mentioned, since then there would be only flat lands, without relief, in about 18 Ma later (average wear: 1 mm / year).
You can find out the full project at this link.