Grotte di Os de Balaguer

Os de Balaguer, a municipality in the comarca of the Noguera, has 11 inventoried cavities: 8 caves and 3 pits. The group totals 1,931 metres of passage and reaches a maximum depth of 78 metres. All the cavities develop in limestone.

The longest cavity is the Cova Negra de Tragó, with 1,032 metres of passage, two entrances at different levels and a vertical extent of 78 metres (+52/-26). It is followed by the Cova Fonda de Tragó, at 277 metres, explored on 2 November 1910 by Jeannel; Lo Foric, at 115 metres, with a main gallery of 40 metres and side chambers; the Forat d'Os, at 110 metres, with three levels formed by collapses and movements of strata, and the Avenc de la Plana, at 102 metres.

Among the deepest cavities are the Forat la Neu, 57 metres deep, on the N slope of the serra de Blancafort, with an entrance of 14x2 metres and a SE-NW joint; the Avenc de la Plana, at 27 metres, on the right bank of the barranc del Molí de Boix; the Avenc de la Penya dels Ulls, at 24 metres, a tectonic fissure of some twenty metres, and Lo Foric, at 21 metres.