About 150 metres from P.O. 11 the path curves 90° to the right; you need to leave the path and walk some metres to the left to reach P.O. 12. Here you can view the marvellous "Anfiteatro della Quacella". This is a concave slope, made up of the same dolomitic rocks seen at P.O. 7, affected by intensive weathering. You can see deep tracks, from where talus cone and debris flow start, isolated needle rocks, and nivation niches. A large scree slope partially covers the Numidian Flysch shales. The slope, slightly inclined, is characterised by several detachment niches, undulations, and back-tilting areas due to large landslide movements. The "Anfiteatro della Quacella" and the western slope of Monte Mufara represent the detachment area of the great Portella Colla landslide; this is one of the most extensive landslides in Sicily, about 6 km long and 2-3 km wide, of which the western end finishes at the Imera Settentrionale river bed.