This Geopark is a true natural laboratory for understanding the geological processes that have shaped our planet over the last 120 million years. The interaction between rock layers and marine action has created a spectacular set of coastal forms: cliffs, arches, islets, coves, beaches, tombolos, dunes, and estuaries. These outcrops reveal fossils of ancient tropical reefs, prehistoric beaches, and petrified ecosystems, bearing witness to events such as continental collisions, climate changes, and biological extinctions.
The stretch between San Juan de la Canal and the Miengo Marsh is included in the Global Geosites catalog as one of the most significant geological sites in the world, under the designation “Liencres Dunes and Costa Quebrada Coastline.”
Discover the Global Geosite
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Costa Quebrada not only displays, in a short stretch, an extraordinarily rich and attractive array of coastal landforms but also clearly demonstrates the processes shaping the coastline, allowing us to reconstruct its evolution over time.
This Global Geosite has a primary geomorphological interest and is included in the Inventory published by IGME under code Geosite CB010, and forms part of the International Relevance Geological Context (Law 42/2007): Coasts of the Iberian Peninsula. Its inclusion is due to its importance in illustrating the evolution of a retreating cliffed coast.
Socavón de Pedrondo
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Immediately west of the La Arnía platform lies the Pedrondo Sinkhole, a relatively large collapse depression formed by undercutting, covering 985 m², with a depth of 42 m and an excavated volume of approximately 18,000 m³. Its origin is due to the opening of a passage through the Altamira Formation calcarenites at the base of the cliff by wave action. This opening was created by the fall of a series of blocks defined by the orthogonal network of joints, characteristic of these Cenomanian materials. Wave action penetrates and effectively erodes the Turonian marly materials previously protected by the resistant limestone. About 50 meters west of the sinkhole lies the La Baselga formation, which follows the same erosive pattern as the La Arnía platform.
Covachos
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From east to west, the Covachos formation is dominated by the El Castro Islet, resulting from the wave-driven dismantling of the surrounding area. In addition to the characteristic leafy appearance of the cliffs, composed of marl-limestone rhythmites with subvertical dips, featuring large slabs formed from the strata’s tops in the southern cliffs, one can observe the effects of coastal cliff retreat in lithologies with dips favorable for sliding of large slabs along the bedding planes. The summit of the islet is formed by residual relief, a remnant of the pre-existing landscape of gentle hills before marine action, where soils and vegetation are preserved. However, the most remarkable features of this formation are the depositional forms on the platform, particularly the tombolo linked to the islet.
La Arnía
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Next is the geomorphological complex of La Arnía, a particularly rich assemblage of geomorphological features, along with additional stratigraphic and paleontological elements. Broadly, it consists of a cove with a small beach at its base, and an elliptical intertidal abrasion platform, separated by a residual relief of the former fluvial valley that ran parallel to the coast before coastal retreat. The resistant lithologies, formed by Cenomanian limestones, close the complex to the north, forming a row of needles and rock outcrops of varying sizes. The base of the beach is occupied by the El Castruco promontory, a residual feature protected from erosion by the Cenomanian cliffs, which preserves the characteristic profile of the fluvial valley that once developed in this sector. In addition, the cliffs display excellent examples of differential erosion on marl-limestone sequences.
Portío
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The El Portío cove lies immediately to the west. It is a broad, elliptical cove of about 40,000 m², formed by the advance of marine erosion through an extensive breach, about 250 m long, in the Cenomanian limestone ridge. Here, the dismantling of the pre-existing relief is more advanced than in the rest of the coastal stretch. Sandy beaches form on the eastern and western margins, resting on the abrasion platform. Behind the eastern El Portío beach lies one of the most visually striking outcrops in the area, due to the subvertical dip of the Turonian marly series, combined with differential erosion controlled by the alternation of layers of varying wave resistance and the presence of joint networks with different patterns and dimensions for each layer.
Somocuevas
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Immediately following the cove is the Somocuevas Peninsula, composed of Aptian limestones, the oldest rocks of the Geosite, forming a set with the line of islets of the same nature called the Urros de Liencres, which extends eastward. The western end is occupied by the depositional complex of the Liencres dunes, formed by the Pas River’s entry into the Cantabrian Sea. The extensive beach (excluding its extension at Canallave) measures a total length of 1,500 m, half of which consists of a NE-SW oriented coastal spit. The beach front slope varies longitudinally: the northeastern end has low slopes and is clearly dissipative, while the spit end presents a markedly reflective character. From the beach, in the direction of prevailing NW winds, a large, powerful climbing dune forms, ascending the slopes of the nearby Monte Tolío. The system includes a primary dune of variable height between 10 and 15 m, with secondary and tertiary dunes progressively increasing in height towards the SE, alternating with interdunal depressions that, in some areas, form wetlands due to the proximity of the water table.
Access to the Global Geosite
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The main access points to the Geosite are: on the western edge, via the A67 motorway heading towards Santander, taking the Boo de Piélagos exit, then following the CC231 towards Liencres, entering through the Las Dunas de Liencres Natural Park and Costa Quebrada.
On the other hand, from the eastern end, follow the S20 from Santander towards Torrelavega, exiting at Corbán and continuing along the CC231 towards Soto de La Marina, where signs guide you to the Covachos and La Arnía beaches.
Internal accessibility within the proposed Geosite is good, with most points of interest reachable via paths and roads, and some sections of the coastline walkable on foot. In these areas, it is important to respect private estates and properties and to avoid crossing privately owned meadows. When undertaking routes, it is crucial not to remove plants or disturb the local wildlife or livestock; therefore, dogs must be kept under control in accordance with the regulations of each area.
