Caves and potholes in the Serra de l'Obac geological unit

The Serra de l'Obac, a unit of the Serralada Prelitoral, contains 141 cavities: 81 caves and 60 pits. The whole sums 4515 m of passage and reaches a maximum depth of 123 m. It is a conglomerate sector near Sant Llorenç del Munt, between Bages and the Vallès, rich in cavities of the same formation.

Among the longest cavities are the Cova-avenc del Picarol, with 340 m of passage, an entrance shaft of 7.5 m and a system of galleries on three levels; the Avenc de l'Espluga, with 320 m of passage and 123 m of depth, with a history of explorations since 1953; the Avenc del Llest, with 265 m of passage and 56 m of depth, with a large chamber and the Galeria Sardi; the Avenc de la Pinassa, with 190 m of passage and 58 m of depth, with a funnel-shaped entrance, shafts of 6, 36 and 27 m, a flowstone deposit and a final crawl; and the Coves de Mura, with 184 m of passage, with a single N-S gallery, aragonite formations and a history that begins in the 19th century.

The deepest pits are the Avenc de l'Espluga, at 123 m; the Avenc de Castellsapera, at 84 m, with an entrance 7 by 2 metres, an entrance shaft of 45 metres and a large final chamber; the Avenc de la Pinassa, at 58 m; the Avenc del Llest, at 56 m; and the Avenc de la Brega, at 52 m, with a circular entrance just over one metre in diameter and a single shaft.