Geoparque Mundial UNESCO

No. 25. ESPEJO DE FALLA – CANCHO DE LAS NARICES (Cancho de las Narices slickenside)

Geoparque Villuercas > No. 25. ESPEJO DE FALLA – CANCHO DE LAS NARICES (Cancho de las Narices slickenside)

LOCATION AND ACCESS

This geosite is located on the road between Castañar de Ibor and Robledollano, approximately halfway between the two localities. The slickenside (or fault mirror) is located in a trench created in the road under the “Cancho de las Narices”, in a bend with poor visibility, so you have to stop before entering the bend, coming from Robledollano, on a path on the right that goes down to the Viejas river. From here you can access the platform created behind the guard-rail, from which you can enjoy this place without danger.

To see the Cancho de las Narices, it is best to continue along the path, ford the Viejas river and climb right in front of it. This stretch of the Viejas river is a fantastic grove of gall oaks from where the best views of this ghostly site can be enjoyed.

ATTRACTIONS OF THE VISIT

In addition to the above, from this spot we can observe the Viejas river syncline, identifiable by the dip (inclination) of the materials of the slopes and ridges on both sides of the river (on the western slope of the Viejas mountain range and on the eastern slope of the Sierra Alta). In the vicinity we can also identify the rocks of the Navatrasierra Formation, black in colour and typical of the Middle Ordovician period (470-458 million years ago), with their characteristic fossils: trilobites, brachiopods, molluscs and graptolites.

On the slope of the Sierra Alta, facing west, there is a magnificent gall oak grove, and the riparian vegetation is dominated by ash trees and portugues laurel. It is also a good ornithological site, with the possibility of spotting black storks, Egyptian vultures, griffon vultures, booted eagles, eagle owls, etc.

GEOLOGICAL INTERPRETATION

Read Geological Interpretation

We are in the transition from the Ibor anticline to the Viejas syncline. At this point, the Viejas river flows towards the Ibor river, crossing the Viejas mountain range. Deeply embedded, the river changes its course in a perpendicular direction, taking advantage of some faults transverse to the mountain alignment. One of these faults can be identified at this point by the displacement it has produced in the quartzite formation of the Viejas mountain range, visible on both sides of the riverbed.

At the base of the Cancho de las Narices rock, the slickeside can be seen on the quartzite as a dark, polished and shiny surface, with directional striations, caused by the friction between two blocks of quartzite rocks that have been displaced. As a consequence of the tectonic stresses on these quartzites, minor folding and fracturing have also occurred, and a chevron fold can be observed to the right of the fault mirror, and the rocks of both blocks are partially crushed (mylonitised), which may facilitate small block detachments.

Exactly above it is the so-called Cancho de las Narices, a steep quartzite projection with a high concentration of iron oxides, to which erosion and former mining activity have given a singular cavernous shape whose entrance resembles a nasal septum.