The largest source of obsidian in Sardinia, hidden in the bowels of a volcanic mountain. The green cloak of the Monte Arci massif rears out of the Uras plains, to the far north-east of Campidano, covered by basaltic lava flows that reveal its origins and history over the millennia. The volcanic chimneys culminate in its peaks: the 812 metre high Trebina Longa, 795 metre Trebina Lada and 463 metre Corongiu de Sizoa. Three peaks that bring to mind a tripod.

The area of the Acri regional park (270 squarekilometres) includesland from elevenmunicipalities in the Oristano area - Ales, Marrubiu, Masullas, Morgongiori, Palmas Arborea, Pau, Santa Giusta, Siris, Usellus, Villaurbana and Villaverde.