The Site of Community Importance "Giara di Gesturi" is located in the region of Marmilla, a wide area, which is mostly flat and is characterized by its particular mix of gentle hills and volcanic plateaus called "Giare". This territory is marked by the course of the Flumini Mannu River, which comes from the Sarcidano and receives waters from the Murera River and the many streams that come from the Giara.
It is customary to distinguish the Lower Marmilla from the Upper Marmilla. The lower area, mainly characterized by its hills and plains, starts from the Giara and reaches the plains of Medio Campidano in the west and the Medio Flumendosa and Mulargia reservoirs in the east. The upper area features a larger geomorphological variability, which includes the northwestern part of the Giara, reaching the relief of Monte Arci that separates it from the Campidano of Oristano.
The Giare of Gesturi, Serri and Siddi constitute the dominant element of the landscape in the region. The Giara of Gesturi is within the territories of Tuili, Gesturi, Genoni and Setzu, and it covers an area of 42 square kilometers. Its creation was due to the expansion of ancient lava flows that had cooled down, forming its current shape, with an altitude of about 500-600 meters above sea level. On the top of this plateau, two small volcanic cones Zepparedda (609 meters) and Zeppara Manna (580 meters) are still recognizable. The land surrounding the Giara, not protected by the coverage of effusive rocks, so its level decreased and it was slowly eroded by water and wind. Because of its unusual shape, the Giara is naturally isolated, a feature that is responsible for the development of an extraordinarily rich heritage of floral and fauna. This, along with the presence of rare natural habitats, is why this area is considered a Site of Community Importance (SCI).
Among the most interesting elements of the plateau are the paùlis, natural depressions in the ground in which rainwater accumulates during the winter. These are mainly near the small volcanic cones that interrupt the flat nature of the Giara. Generally, the paulis are temporary small ponds, however, some of them reach great extensions, retaining their waters throughout the year. The paùlis spread on the top of the Giara are essential for the survival of many plants and animals, and, therefore, they are considered "habitats of community interest" by the European Union.
The presence of water is linked to the existence of important water sources, which are scattered throughout the territory of the SCI. Besides the paùlis, there are numerous underground springs, flowing under the rocky edge of the Giara. Only in the territory of Assolo, the springs of Funtana Carusa; Mitza Cabirada; Mitza Masoni; Sinnigas; Mitza en Truncu; Mitza Crabaxius Masoni; and Sa Stiddiosa are worth mentioning. The last one is well-known for the quality of its water. Moreover, the territory features numerous geo-paleontological sites of great interest, e.g. Duidduru in the territory of Genoni and Muru 'e Cubeddu in Nureci. In particular, the last one has one of the most remarkable concentrations of fossils in the Mediterranean and documents the geological events that have affected this part of the island.