The mountain massif close to the lagoon is the most eastern outcrops of Sulcis. From north to south, we observe the Monte Arcosu (SCI ITB041105 and WWF sanctuary), the wild valley of the Rio Mannu Gutturu (and Guttureddu), the mountain area of Cirifoddi (with the nineteenth-century Mine of San Leone), Poggio dei Pini (with Rio San Girolamo and Punta Pauliara where they are other itineraries of the Park “Gilia for All”), Is Cannoneris (famous for the wild beauty of its forest). A mountain range whose core is predominantly of Paleozoic Era (the oldest), bounded by faults and tectonic subsidence ditches which originated in the Tertiary and resumed during the neo-tectonic movements of the Quaternary.