The rocks crossed by this route were formed in deep marine environments during the Middle Eocene epoch. Most of them are sandstone and marlstone..
At the first point of interest, we can observe the typical braided course of a Pyrenean river. It is characterized by the presence of braided channels divided by rocky islets, some of them even with vegetation..
From the next point, we can observe the Boltaña Anticline, one of the most important tectonic structures in the geological history of the Eocene Basin in Aínsa..
From Guaso, heading towards Santa María de Buil, we can observe the transition from rocks formed in deep marine environments (blue-greyish colour) to those formed by rivers and torrents (reddish colour).At the final point, we can observe some vertical cylindrical pipes running inside the sandstone layers. They are examples of the activity of organisms fleeing towards the surface of the layer.
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