Limestones and dolomites
A wide band of sedimentary rocks spreads around the crystaline massif of Argentera, right on the boundary of the Park. Sedimentary rocks form the ridges between the lower Valle Gesso and the Stura and Vermenagna valleys, with vast outcrops of limestones and dolomites. These are much lighter in colour than the gneiss and often with evident stratification. The solubility of calcareous rocks is one of the main causes in the formation of deep, narrow gorges, like the well known Gorge della Reina near Entracque. In the Park the most evident karst features are the Grotte del Bandito caves in Valle Gesso, now a Nature Reserve, and the bare, deeply scarred rocks eroded by run-off water in Val Grande above Palanfré.