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The Bismantova Formation

The majestic masses of Mounts Baco, Sole and Salvaro, and the ridges that branch off from these mountains, consist of light hazelnut brown sandstone, ivory white when freshly fractured, comprising mainly limestone grains. These are rocks that underwent sedimentation during the Lower Middle Miocene (about 15 million years ago) on sea beds that were a few dozen meters deep, after a major orogenic phase had caused the basins to rise once again, bringing about a radical change to the type of sedimentation.

These rocks belong to the Bismantova Formation (named after the homonymous spur in the Reggiano Apennines mentioned by Dante in the Divine Comedy), as do the younger gray marls (13-10 million years ago), that are exposed in the badlands at Marzabotto and at the Burrone Gorgone Brook.

These marls, intercalated with thin-bedded turbidite sandstones, indicate, instead, a subsequent lowering of the ocean floors.