Geoparque Unesco

12 The end of a geological Age (Bestué)

Geology and landscape (Bestué)

Localización: Plaza de Bestué

Coordenadas. 262821 4716384 31 N

Textos Esperanza Fernández (Geopage)

Panorámica del paisaje que se observa desde el mirador situado en la plaza de Bestué. La forma del terreno, la presencia de vegetación diversa, los usos del suelo… todo ello está relacionado con el tipo de sustrato geológico que sustenta dicho paisaje. Fotografía: Ander Gómez.

From this viewpoint we can see how geology determines the landscape which lies before us.

  • Before us stands the ridge of Los Sestrales
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  • Its base is formed from Marboré sandstone. Sandstone is formed from compacted sand and is very resistant to erosion. When it does erode, it creates a substrate suitable for colonisation by plants. This fact, together with the low altitude (below 1800m), explains why the mountainsides in this area are wooded.
  • The crest of the ridge forms a wall of exposed rock, composed of what are known as the Salarons dolomites and the Gallinera limestones. Both of these rocks are formed of calcium carbonate and magnesium, which dissolve when exposed to slightly acidic rainwater. When this happens, the dissolved rocks generate thin but rich soils which favour the development of pastureland.

Detalle de Os Puyos y Los Sestrales. La parte más alta de esta estructura está formada por rocas resistentes a la erosión de ahí que destaquen en el relieve frente a otras zonas más deprimidas, como las colinas próximas. Fotografía: Ander Gómez.

To our right is the striking outline of Castillo Mayor, a remnant of the rocky materials that were transported during the formation of the Pyrenees and which remains standing because of the hardness of the limestones and dolomites from which it is formed.

El reconocible relieve de Castillo Mayor está originado por la presencia de un conjunto de rocas antiguas, situadas en esta zona mediante un cabalgamiento posteriormente erosionado y del que permanecen los restos de esta pequeña mole. Fotografía: Esperanza Fernández.

Between the ridges ofSestrales and Bestué extends a series of rolling hills, where streams have carved out small gullies that converge in a central valley.

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Unlike the ridge, these hills are formed of very soft rocks, marls, which are easily eroded by torrential rain and ice. They originated from marine deposits in the Eocene, and have traditionally been used as agricultural soils, facilitated through the creation of terraces along the side of the slope, sometimes reinforced by stone walls or vegetation.

Estas colinas son el resultado del modelado geológico de un sustrato de rocas endebles (margas y margocalizas). Precisamente este rasgo es el que ha posibilitado el cultivo tradicional de los suelos que se desarrollan sobre ellas. Fotografía: Esperanza Fernández.

Bestué itself is built of geological materials formed by thick layers of very soft rock (marl) alternating with thinner layers of more resistant rock (sandstone). These Eocene materials are often called "flysch" and play an important role in our understanding of the geography of Sobrarbe.

The presence of sandstones is important because they provide construction materials, both for masonry walls and roofing slabs.

Tejado de losas de arenisca en los alrededores de Bestué. Casi todas las construcciones de esta localidad están realizadas con areniscas procedentes de las rocas denominadas turbiditas que forman el sustrato de Bestué. En las utilizadas para el enlosado de la plaza pueden observarse diversas estructuras sedimentarias que informan sobre el origen, en un fondo marino profundo y con corrientes de turbidez, de estas rocas. Fotografía: Esperanza Fernández.

Did you know that…?

This landscape is the result of a long history: the deposition of sediments on the seafloor, their transformation into rocks, their elevation during the formation of the Pyrenees and their gradual destruction. The valleys we now travel through were formed when erosive agents (water, ice, gravity, living beings) destroyed the less resistant rocks. What we see today as towering cliffs are the remains of this destruction, formed by rocks which nature has not yet destroyed.

Recomentations in your visit to Sobrarbe-Pirineos Geopark

  • Safe visits, unforgettable experiences. There are companies who collaborate with the Geopark where you can hire specialized guides to make your tour a unique and safe experience.
  • Respect the geological outcrops. Do not break off samples of rock, mineral or fossils.

Avda. Ordesa 79. 22340 Boltaña. Huesca. 974 518 025.