The landscapes of this defile offer a wonderful insight into the effects of erosion. Following the course of the Segre, you will see that it seems to finish in a small cultivated basin. But to get there, it crosses a gorge between the limestone rocks of Ares and Montsec de Tost. Before that it winds its way through dark-coloured rocks (puzolana) and green pastures. In fact, following its course is almost like a treasure hunt!