Grotte di Alt Urgell

The Alt Urgell brings together 177 inventoried cavities: 106 caves and 71 pits. The group totals 8,697 metres of passage and reaches a maximum depth of 137 metres. Limestone is the dominant lithology (156 cavities), accompanied by conglomerates (13), sandstones (5), gypsum (2) and marls (1).

Among the cavities most notable for passage length are the Font Bordonera, with 955 metres and a drop of -80 m at Coll de Nargó, and the Font d'Andana, with 679 metres and 137 metres of drop at La Vansa i Fórnols. Other notable cavities are the Avenc de la Cabana d'en Garraba, 425 metres long and 62 metres deep at Pont de Bar, known since ancient times, explored in 1910 and surveyed in 1973; the Forat de les Encantades del Pont d'espia, 312 metres long, temporarily swallowed by the Oliana reservoir; and the Cova de Montaner, 232 metres long with two entrances at Fígols i Alinyà, explored by the GE Lleidatà in 1995.

As for depth, after the Font d'Andana (137 m) come the Grallera Gran del Boixeder, 81 metres, in the Serra del Cadí, with access from Josa del Cadí via the coll de Jovell and the GR 150.1; the Font Bordonera, with -80 m; the Avenc del Cataplanell, 63 metres at Coll de Nargó (Boumort), explored for the first time by the SAS del CGB on 16 January 1966; and the Avenc de la Cabana d'en Garraba, 62 metres.