 [ARPA – Carta Geologica d’Italia-foglio 155 Torino Ovest, 2009]

The ridges are cut by perpendicular overflow channels which drain the spill-way valleys and form little alluvial fans (both Villarbasse and Corbiglia are built upon these deposits).The Prato Perosino (Basse) spill-way is a well preserved fluvioglacial form [I Geositi nel paesaggio alpino della Provincia di Torino, Provincia di Torino, 2004]

During every glacial pulsation, the material carried down by the Glacier is deposited at the end of the valley.Later on, erosion agents will remove part of the material and only the biggest blocks of rocks will be left behind