Grotte e abissi nell'unità geologica Muntanyes de l'Ordal

The mountains of l'Ordal, straddling Baix Llobregat and Alt Penedès, extend inland the limestone karst of Garraf. The group contains 290 cavities: 202 pits and 88 caves, with a total length of 9,574 metres and a maximum depth of 184 metres. The dominant lithology is limestone (173), followed by dolomite (102), conglomerate (8), travertine (3), sandstone (2), marl (1) and gypsum (1).

Among the most notable cavities are the Avenc dels Esquirols, 184 metres deep in Vallirana, with two entrances and shafts of 23, 8, 42, 9, 21, 16, 36, 18, 22, 13, 30 and 25 metres, and the directa, Montesinos and Esquirols routes. Other notable pits are the Avenc Pompeu Fabra, with a drop of 104 metres in Vallirana; the Avenc de Sant Marçal, 121 metres deep in Olesa de Bonesvalls, located by the E.I.E.-PCB in 1970 and explored in 1971; the Avenc de les Alzines, 34 metres deep in Begues, with three access entrances, the Sala Fantasma and the Sala dels Templers; and the Esquerda Nº3 del Mas de les Fonts, 53 metres deep in Vallirana.