Grotte e abissi nell'unità geologica Serres marginals - Oest

The Serres marginals - Oest are a unit of the Prepirineu, formed by limestone ranges on the western margin of the Lleida Prepirineu, above the Noguera, with scattered cavities. It brings together 59 cavities: 43 caves and 16 pits, with a total passage of 5,037 m and a maximum depth of 161 m.

Among the most notable cavities are the Cova Negra de Tragó, with 1,032 m of passage, with two entrances at different levels and a vertical extent of 78 m (+52/-26); the Forat del Balconet, 161 m deep, discovered by the GELL in January 2007 and in the exploration phase; the Cova Fonda de Tragó, 277 m, explored on 2 November 1910 by Jeannel; the Cova de l'Escaleta, 265 m, long known to the inhabitants of the area; and the Cova de les Caixes, with 239 m of passage and 49 m of vertical extent, with a surveyed passage of 238.9 m and a vertical extent of 48.5 m (-45.1/+3.40).

Other relevant cavities are the Avenc de Sant Urbà, 57 m deep, with an entrance shaft of 17 m, and the Forat la Neu, also 57 m deep, in Os de Balaguer. The lithologies present are Limestone (57), Dolomite (1) and Gypsum (1).