Arco caves got their name because there are some calcareous archs in the side where these caves get open. These archs, in very ancient times, could have been part of the same gallery joining these caves, which would have been part of the same karstic system. The disappearance of the primitive gallery could have been an effect of a strong erosive activity, leaving these archs as witnesses of this primitive gallery. The caves we are going to describe are Arco A and Arco B.

The cave of Arco A opens outside by an entrance five meters wide with a distance of 24 meters up to a big room.From here it forks in two directions. Towards the South, a small gallery gives access to a raised little room and to a very small catflap, both places where the representations are located. Half a dozen of animal figures have been counted in thE whole cave, these figures are limited to a few species, horse , goat , bison and aurochs situated in zones of difficult access in the cave. Besides the animals figures, there is one sign made by red dots, similar to the one in La Meaza cave. Most of the animal figures are painted in red, except a small figure of goat, made by the engraving technique. The images of the horse and the sign have been digitally treated in order to facilitate the vision of the pigments, because it is tremendously difficult to see them if it is badly preserved.

Arco B is a cave bigger than the previous one. The access is made through a mouth 8 meters wide and 4 meters high. At the end of the main gallery an engraved mammoth can be seen. This animal is scarcely portrayed in the Cantabrian caves. The rest of the figures are located in a room of tiny dimensions, located a few meters far from the entrance to the cave, where the height to the roof in the decorated area does not exceed 50 cm., difficulting the research works. In this catflap the representations were mostly hinds, caprids and other figures of difficult interpretation, as well as several squared signs of cantabrian type.