Introduction

      In the extreme eastern edge of the Cantabric Range, just in the limit with the Basque Mountains there is a set of valleys formed by the rivers: Asón, Gándara, Miera (Cantabria) y Trueba (Castilla y León) (Fig. 1). They are green and leafy valleys covered with beech trees in the upper parts of the valleys and ilex trees in the lower, and warmer, parts. The scenery is of great beauty. It’s a remote zone with little influence of man, whose way of life is typicaly rural, with a especial dedication on livestock farming.

Fig. 1		Figure 1: Location of High Valley of Asón and its environment. Caves: 1, Garma Ciega-Cellagua-Mortero; 2, Cueto-Coventosa; 3, Torca Tibia-Cueva Fresca; 4, Torca de la Canal-Cueva de los Moros; 5, Covalanas; 6, Cullalvera; 7, Salitre. Others places: A, Hoyo Masallo; B, Llana la Cueva; C, Mortero de Astrana; D, Canal del Haya; E, Hornijo karren.

In the area there are three distinct mountain ranges that exceed 1000 m in altitude, the Porracolina to the west, the San Vicente to the east and the Castro Valnera to the south. The  zone is fundamentaly composed of rocks of the urgonian complex, greatly afected by glacial and  karstic phenomenons, as a result there is a great geomorphology and landscape variety. Many of them suitable to be declared Geological Heritage: Convention for the Protection of the Natural and Cultural Heritage of the World. Paris, 23 November 1972. Which inclued natural monuments with geological and physiographical formations. Signed by de Spanish Goverment, Boletín Oficial del Estado  of  1 July 1982.

The Alto Asón is one of the most remakable places in Europe, and perhaps in the world, for the practice of caving. The number of cave visits, in the zone, is increasing day by day, producing accidents due to the lack of experience of some the visitors. This in becaming a problem for the local people and for the authorities incharge of the rescues.

In the present, the degree of conservation is acceptable, but the increasing preasure, which is the result proliferation of outdoor activities and rural turism, can put in danger for the future the geological heritage of the region. Therefore it is necessary a legal protection that can guarantee the preservation of the sites.

Sites of geological interes

In the region of the high valley of Asón there are many sites of geological interest, whose values are fundamentaly geological and geomorphological.

Stratigraphic

The most part of the region the rocks are of the urgonian complex, which is formed by the alternation of masive coral-reef limestone and limestone with detritic inserts (Aptense-Albense) whose potencial is near 800 m (García Mondejar y Pujalte, 1981). There is, near the town of Gándara, good examples of coral-reefs deposits of  very large dimensions. Also, it is remarcable the slump type of estructure in the talus of the coral-reefs. It can be also pointed out the sandstone of the Weald facies, in the headwaters of the Miera river with magnificent sedimentary structures.

Glacial  modelling

Glacial phenomena has been of great importance in the zone, as can be deduced from the existance of moraine deposits in an excelent degree of conservation. In the valley of Trueba river  there is glacial evidence at  800 m of altitude, in the valley of the Miera is at 620 m and in the valley of Asón is as low as 450 m, all atribuated to the Würm (Moñino et al., 1987). These are the some of the most lowest altitude sings of glacial evidence in Spain.

Karstic modelling

The karstic modeling is the most significant and spectacular feature of the Alto Asón. The first studies about the Asón karst and its morphological evolution was done by Mugnier (1969). The sistematic exploracions undertaken by caving groups in the decade of the 60 has exposed the cave richness of the region, where the discoveries increase the number and the length of the caves each year. Some of the caves a more than 45000 m en length and 800 in depth, with vertical pits of more than 300 m.

Concerning the exokarst, this is rich in diversity and forms, with great closed depresion with a glacial-karstic origen (Hoyo Masallo, Llana la Cueva), dolines, great shift wall  collapse dolines (the great chasm opening of Mortero de Astrana)  and a great variety of karrens of different tipologies (the karren of Canal del Haya, and the karren of Hornijo) (Fig. 1).

The zone has great underground cave systems which are the destination of many caving groups all the year round. In the present the total lenght of underground passages explored and surveyed  is more than 320 km, making the delights of national and foreign caving groups. We can point out some of the most remakable cave systems: Garma Ciega-Cellagua-Mortero, Cueto-Coventosa, Torca Tibia-Cueva Fresca, Sistema Torca de la Canal-Cueva de los Moros (Fig. 1). There are also important karstic springs, like the espectacular waterfall sources of the Asón river, o the sources of the Gándara river.

Other sites of interes

The numerous caves of the zone have permited human settlements as long ago as the Upper Paleolitic.  Fact that  has its proofs in the numerous cave wall painting that can be found in some of the caves. In the sorrunding of Ramales de la Vitoria there is an important grupo of  prehistoric caves: Covalanas1, Cullalvera2 y La Hada. Also in the valley of the Miera river the Salitre cave is a good example (Fernández Acebo, 1994) (Fig. 1).

Problems for conservation and conservation measures

At present, the problems for the conservation of the geological heritage of the region are moderate. They are principaly focused in the wound caused to the landscape, including: karrens, caves and moraine deposits, by the opening of new tracks that comunicate the upper parts of the highlands and the farming huts to the towns down valley. The moraine deposits are in especial danger, as they are used as constructing material for roads and tracks due to there granular nature.

The zone is one of the most remarkable sites for caving, fact that has produced important human problems. The local goverment through the couscils of: Culture, Education, Youth and Sports has issued a normative rule of 22 of febreary of 1991 that controls the access to natural caves in Cantabria, but it si not supported by any law in force. In the present the general failure to comply with the normative and the increasing volume of caving groups has lead to never ending list of accidents and  lost o trapped groups, that  make the situation alarming, from the human point of view, but also the posible damage on the environment.

The remoteness and the degree of consevation make the region a destination for tourist agencies  dedicated in rural tourism o adventure. Due to this, we must be able to make compatible the economic development of the region with the conservation of the natural valures, the only way to issue regulating laws that can preserve the natural valures of the Alto Asón and the biological and geological environment.

The actual normative in force which regulates the visits to natural caves in the Comunidad Cantrábrica has failed, from the begining, to control the visits. The ignorance in the formal steps to get the permits and burocratic slowness has driver to a situation where nobody uses the formal permission and goes on furtive. It is urgent to issued a new law3 and, at the same time,  set up a local office where, in a fast and agily maner, the permits can be giving in a number that the conservación of the karst can be garanted. This can avoid many accident by controlling and advising the caving groups not only of the hazards and state of a paticular cave to be visited, but also of recomendation to the visitors in order to minimize  the impact to the karst environment.

References

FERNÁNDEZ ACEBO, V. (1994): Estudios, patrimonio e inventario de las cavidades del municipio de Miera. Boletín Cántabro de Espeleología, 10, 144.

GARCÍA MONDEJAR, J. Y PUJALTE, V. (Dir.) (1981): El Jurásico superior y Cretácico inferior de la región vasco-cantábrica (Parte Occidental). Grupo español del Mesozoico. Reunión de campo. 133 p.

MUGNIER, C. (1969): El karst de la region de Asón y su evolución morfológica. Cuadernos de Espeleología, 4, 146 p. Santander.

MOÑINO, M; CENDRERO, A. y DÍAZ DE TERÁN, J.R. (1987): Glaciarismo en el alto Miera. Actas VII Reunión sobre el Cuaternario. Asociación Española para el Estudio del Cuaternario. 179-182. Santander.