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In the Pliocene period (5,2-1,8 millions years BC) very fluid basaltic lava erupted through the earth's crust in the area now called Marmilla.
The lava spread over the land which consisted mainly of marly rocks from the Miocene period (26-5,2 million years BC).
On cooling the basaltic lava flows turned into a dense blanket of hard rock which covered the soft marls.
Through the millennia water and wind eroded and carried away the marls around the area which was sheltered by the basaltic barrier. This is how the Giara was formed. It is a marly plateau, the summit of which is covered by a blanket of hard basalt.
The Giara of Gesturi has been inhabited since ancient times due to its position which overlooks the surrounding valleys. There are still the ruins of 23 nuraghi which are situated along the plateau perimeter. In the past they were used as observation posts.
?WHAT IS ...?
>Marl<: a type of rock formed by eroded debris transported by rivers, glaciers, wind, etc
>basalt<: effusive volcanic black rock, in other words resulting from the lava cooling off in the open air.