This route proposed goes along mid Pas riverside, from where we can see the beech forest of Bercedo and Zurriaga and the oak grove of Dehesa and Tromeda.

Starting from Vejorís and going southeast, to the pastures of Calamuco, we can appreciate the effect of human intervention on the regulation of river flows and how this changed its natural dynamics. This heavily disturbed the habitats surrounding this river, which are still clear to the eye.

Still, the river is considered as a LIC and included in the European Ecological Network NATURA 2000 and the network of Natural Protected Spaces of Cantabria.

We soon access Calamuco, a farming area with pastures and cottages that then dissolves into La Dehesa, a forest of beech and oak trees. We must take the trail going to Cotero Lobos.

We cross Bala La Lastra and Regato Barrueda, while slowly seeing more oak trees.

Slightly lower than the line between Cocina Caliente and Cotero Lobos, the path continues with barely any changes between the oak grove and some re-population areas of birch and pine trees.

We have the option to lengthen our walk close to Hayal de Aloños, leaving left the rocky trail of La Peña, with jurassic materials.

Once in San Martín, we cross the oak grove of El Carmen towards the river. Here there have more than 260 specimens of Quercus robur.

We return to Vejorís following a nice walk along the river next to the old railway of Ontaneda.