The rocks of the Mourres in Forcalquier are made up of massive, slightly chalky limestone that was originally embedded in beige marls before being exposed by erosion in the Miocene (23 to 5 million years ago). The ruiniform and sub-desert landscape of the site alternates friable zones and compact benches sculpted in the shape of heads, mushrooms, arches, or bridges. It dominates the Forcalquier basin, the Durance and the Valensole plateau.