At the base and on the slopes of the Giara, you can see marine sedimentary rocks which date back to the Miocene epoch. They are mostly marl and clay sediments, sandstone banks, sandstones and limestones with intercalated limestone lenses, and corals.
Going up the slopes of the Giara, you can also see, within the forest of Su Padenti located on the northwest side of the plateau, the lithotypes of the marl, sandstone and conglomerate complex, due to the "Samassi rock formation”.
The volcanic rocks forming the top of the Giara are basaltic rocks with alkaline and sub-alkaline affinities. Along the slopes, it is possible to see numerous boulders that have been sliding down, due to the expansion of the basaltic material. These boulders of various sizes are mainly located near their point of detachment, but they can also be seen at a considerable distance from it, due to the rolling that leads them down to the base of the Giara.
In this area, the landscape is very irregular, due to the continuous alternation between rocky outcrops and shallow soils, which are rarely more than 50 cm deep. The soils have a substantial clay component, due to the alteration of the same basaltic lavas, which frequently cover the bottom of the Paulis. This mineral component has waterproofing characteristics, so it has favored the formation of these temporary reservoirs.
There are some alluvial deposits, which are mainly composed of large basalt blocks, pebbles, gravel and sand, along the beds of the main rivers that form the volcanic edges (Molinu, Paba, Franceschina and Setzu).