The relief of the Giara of Gesturi consists of a base of Miocene sedimentary rocks of marine origin surmounted by a deposit of basaltic lavas from the Pliocene epoch.
The strong sequence of marl and sandstone that forms its base represents the typical sedimentation correlated with tectonic movements. The tectonic movements, in this case, led to the detachment and migration of the Sardinian-Corsican block from the Pyrenean-Provencal continental margin (Miocene epoch) to the center of the Mediterranean Sea. The series of outcrops dating back to the Miocene epoch, located at the base and on the slopes of the Giara, has an output of about 450 meters and are characterized by their highly fossiliferous layers.
The emplacement of the basalt was preceded, during the Pliocene epoch, by a phase of continentality and by the emplacement of the “Samassi rock formation", which is a complex consisting of a marl-sandstone-conglomerate, caused by the rearrangement of Miocene sediments.
The basaltic hedges are related to volcanic events with alkaline and sub-alkaline affinities, which date back to the late Pliocene epoch. The morphology of the area suggests the presence of two emission centers: Zeppara Manna (580 meters), located in the northwest of the plateau, where the basalts reach a maximum thickness of approximately 48 meters and Zepparedda (607 meters), located in the southeast sector, where the basalts have a maximum thickness of 8.7 meters. Moreover, in Zepparedda, basalts are presented in a scoriaceous form and with a marked fracturing, albeit without a clear preferred direction.
In the quaternary cover, there are numerous basalt blocks that, following the phenomena of the undermining baseline (which have affected the Miocene marl-sandstone substrate), have collapsed and slid quickly.