The origin of the Giara’s’ tabular morphology has been described by several authors. According to Castiglioni (1979), the lava flows, especially those in fluid form, poured into the depressions in the valleys formed by sedimentary lithologies that tend to fossilize, exerting a protective and conservative action. This action significantly reduces the effects of sub-aerial erosion. However, the sides of the valley remain uncovered, which makes them more vulnerable to degradation. As a result, an inversion of the relief occurs: the lava emerges, in the form of a plateau, compared to the surrounding area.
The current morphology of the plateau is due to intense differential erosion created by the contact between the upper basaltic lavas and the underlying marl and sandstone sediments, which were carved by waterways and date back to the Miocene epoch. The collapse phenomena that ensue lead to a progressive reduction in the extent of the plateau.
Furthermore, the engravings of the waterways have gradually affected the margin of the plateau, creating the sweet morphologies called scale (stairs), which enable access to the top of the Giara (Scala s’Olioni, Scala Ecca, Scala S’Eremida, Scala Murta, Scala Pomposa, Scala Cabirada, Scala Margiani,…).
Giuerru and Giuerreddu, isolated reliefs located in the northwest of the Giara, as well as the isolated peaks of Santu Antine and Cuccuru Corongiu, which are part of the Zepparedda volcanic complex, provide evidenceof the intense erosion caused by the flows of basaltic lava from the Zeppara Manna crater.