The summit of Tres Creus o La Pola (930 m), in the range of L’Obac, is the perfect example of the round summits that result from the erosion of the polymictic conglomerate rock, like the neighbouring summits of Montcau and Cortins. On the opposite, south in the same range, the summit of Castellsapera displays the edged shape from the oligomictic, limestone conglomerates. One layer of paler though stronger limestone conglomerates with lineal breaks outstands on the basement of the summit of Tres Creus.
[photo Jordi Badia]
See the article Conglomerat (= Conglomerate), in Catalan, by Jordi Badia.