Sardinia is the only region in Italy of Hercynian origin; actually, the Southwest is even older (Cambrian). The mineral riches of Sardinia are the consequence of heavy hydrothermalism during the Permo-Triassic. As in the rest of Hercynian Europe, erosion has taken its toll since the orogeny and has reduced elevations considerably. 30 million years ago, the Sardinia-Corsica block started to detach from mainland Spain and tilted toward its present position. The island is both aseismic and non volcanic.
Sardinia is the second largest island in the Mediterranean Sea (24090 sq. km [9300 sq. mi]); only Sicily is larger. The island is dominated by the Gennargentu Range (culminating at Punta La Marmora, 1834 m [6017 ft], highest elevation in Sardinia), along with the Monte Limbara, Monte di Ala', and Monte Rasu ranges (all below 1500 m [4900 ft]); isolated are the Sulcis-Iglesiente hills (1236 m [4055 ft]) of Southwestern Sardinia, once home to a large mining district. Plains are quite rare and reduced in extent, with the exception of the Campidano Plain from Oristano to Cagliari, which divides the main hill system from the Sulcis-Iglesiente, and the Nurra plain in the northwest (between Sassari, Alghero, and Porto Torres), which was once a mining district and quite forested, but is today mostly given to pasture. Sulcis proper (in the extreme Southwest) was a marshy area where malaria was still present in the 1940's (but eradicated since). Cagliari's neighbourhood is also flat and boggy; exploitation of salt is a major industry there.