Geoparque Mundial UNESCO
Geoparque Villuercas > Nº07 – Estrecho de la Peña Amarilla
The Estrecho de la Peña Amarilla (Strait of the yellow crag) is located to the east of the town of Alía and can be reached via the EX-102 road, at kilometre 92.5, where there is a viewpoint and car park on the north side of the road.
From a geological point of view, it is located on the natural boundary between Sierra Palomera, on the western flank of the Guadarranque syncline, and the gentler reliefs of the Ibor anticline.
During the visit, in addition to the impressive geology of the outcrops of the Armorican Quartzite offered from the viewpoint of the Estrecho de la Peña Amarilla, you can observe good examples of trilobite trace fossils (Cruziana) in the road cuts, as well as some cross-sections of these trace fossils, making this geosite a unique palaeontological site.
Pay attention also to the biological rock communities. Among these, perhaps the most remarkable are the characteristic encrusting lichens of a striking yellow colour (Acarospora oxytona) that cover the rocky walls and give the strait its name. There are also examples of protected, threatened or relict vegetation (Portuguese laurel, junipers, etc.), as well as the contrast between the exuberant vegetation present on the shady slopes and the more exposed vegetation that survives on the sunny slopes.
From this viewpoint we will have the opportunity to observe the breeding colonies of griffon vultures and also some isolated nests of Egyptian vultures and black storks, which take advantage of the vertical cliffs to build their nests.
It is also interesting to know a historical reference to this site:
In the year 1133 King Alfonso VII of Castile passed through the Roman road that crosses Estrecho de la Peña Amarilla towards Talavera, coming with his army from Al-Andalus. The army returned from Seville at the end of the campaign against the Arabs: “Deinde rex movit castra et transivit illum Portum de Amarela et exivit in civitatem suam, quae dicitur Talavera” (Then the king moved his camp and crossed Portum deAmarela and went out to his city, which is called Talavera) (Luis Sánchez Belda, Paragraph 42). This old path has since been called “Camino Sevillano de Talavera”, through which the first Christian settlers entered our region during the Reconquest.
Estrecho de la Peña Amarilla is a fluvial gorge produced by the Jarigüela stream as it flows through the strata of the Armorican Quartzite that make up this spectacular landscape.
These quartzite walls have their origin in the Lower-Middle Ordovician rocks (more than 470 million years ago), having undergone important tectonic movements, so that, despite being very compact and hard rocks, they are also very fragile and are highly broken up, with numerous rracturures. These fractures, unlike faults, have no displacement of the resulting blocks.
Ruptures along the stratification planes are the cause of numerous rock slides that have given rise to the striking caves and steep cliffs on the slopes of this gorge.
The Estrecho de la Peña is “a window between two worlds”: the Ediacaran-Lower Cambrian and the Ordovician, both separated by a prolonged period of emersion with continental deposits, followed in the Ordovician by a marine transgression. That is to say, the progressive advance of the seas over the land that emerged during the Cadomian orogeny (Ediacaran-Cambrian) making possible the new deposit of materials during the following periods, which, in turn, will later emerge when they are folded during the Variscan orogeny.
We can observe at the base of the gorge the shaly Ediacaran rocks, folded by the Cadomian orogeny, and above them conglomerates and quartzite rocks of the Ordovician, folded during the Variscan orogeny. In geological terms, this separation between strata of different nature and folded by different orogenies is called an angular and erosional unconformity.
In this geosite you can observe some of the most characteristic trace fossils (burrows, galleries, etc. left by ancient organisms that have not fossilised) of the Armorican Quartzite, especially Cruziana. They are attributed to traces of displacement – and probably feeding – of arthropods with appendages (legs) such as trilobites. These traces appear not only when the animal moved on the original surface, but also when it moved within the sediments. You can also see these interesting fossils at various places in the Geopark, but here they can be seen in cross-section (view), which is very rare.
The animal was burrowing into a layer with nutrients (mud in this case) and the upper layers (sand) were falling behind it, filling in and casting the excavation.
