The village of Calders is placed onto a thick stratum of limestone sourced from a reef coral barrier in Low Priabonian period (Eocene, 35 million year). The whole pack relates to the member Tossa of limestones, the highest one in geological formation Santa Maria of marine, sedimentary rocks, beneath the formations Cardona of evaporites or Artes of sandstones, mudstones and other sedimentary, reddish rocks from continental origin.
The biggest pack of reef limestones from La Tossa is precisely in the area of Calders. The valley of river Calders cuts out this so resistant stratum that outstands in the landscape. The stratum combines layers of lumpy and fine limestones. It contains many fossils, obviously most of them from corals.