Geoparque Unesco

A look at the geology in the Geopark

At the heart of the Pyrenees, Sobrarbe-Pirineos Geopark enjoys a privileged location where one can discover the secrets of the formation of the Alpide belt..

The most important aspect of the collision giving rise to the Pyrenees is the disposition of rocks as layers:

General geological scheme of the south-central Pyrenees.

From north to south, we can distinguish the classic geomorphological units of the southern Pyrenees:

The Axial zone where we find summits higher than 3000m above sea level, on the axis of the Pyrenean mountain range, and the most ancient rocks in the area (older than 500 million years)..

Attached to the axial zone, we find the Inner mountain ranges, whose Cretaceous and Paleocenous rocks shape, among others, the Monte Perdido Massif, the highest limestone massif in Europe, and the Cotiella Massif. Three aspects are especially remarkable in both units: the ancient mine workings (coal, iron, cobalt, etc.), currently abandoned, the signs of the ice activity along the last Quaternary glaciations and the karstic systems with worldwide known caves, such as the "Gruta de Casteret"..

The most ancient rocks and the highest mountains in Sobrarbe are found in the Axial Zone and in the Inner Mountain Ranges, respectively. .

The Middle Depression stretches over the central area of the County; on the softest Tertiary materials (marlstones and sandstones), we find the bright Cinca and Ara Valleys, where the majority of the 7000 inhabitants in Sobrarbe dwell (600m above sea level). This is the area where geologists have carried out the largest number of studies, since it allows the reconstruction, step by step, of the formation of the Pyrenees, from the relationship between the tectonic impulses, that gave rise to the Pyrenees and marine sedimentation in the Eocene Basin. In this area, we can find a wide variety of fossils, from tiny coastal Nummulites to the huge ancestors of the hippopotamus, as well as tortoises and both salt and fresh water alligators.

On the soft rocks in the Middle Depression, the Ara River drains a wide valley.

Not reaching 1500m above sea level, the Olsón, Sevil and Balcés mountain ranges belong to the Outer Mountain Ranges bordering Sobrarbe County. Along this relief, we find sea rocks and other rocks of continental origin shaped after the Tertiary sea withdrawal, at the end of the Eocene and during the Oligocene, while the Pyrenees formation was in its last stage.

At the south-west of this area, the Guara mountain range, with its limestone rocks, offers a peerless karstic landscape, with gorges where you can combine extreme sports and environmental education activities. Southwards, the Pyrenean domain meets the rocks in the Ebro Basin which were not deformed by the Alpine orogeny,.

The majority of the Olsón mountain range is shaped by sedimentary rocks of continental origin..

Sedimentary carbonatic rocks and detritic rocks prevail in Sobrarbe, although metamorphic rocks are also represented in the Paleozoic (slate, schist, marble,…) and igneous rocks (granites, granodiorites,…).:

Geological map of Sobrarbe

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