The ofiolites are volcanic rocks which erupted in an underwater environment about 150 million years ago and are present in the flaky clay. Particularly evident are those of Rossena, which represent the most important ones in the Reggiano Apennines. Here Four main volcanic masses are visible, one of which surmounted by the same rock. In this location you can observe the typical structure of the "cushion lava": you notice on the rocky walls a number of convex and lengthened shapes, for this reason called "cushion", which range in size from a few decimeters and a meter, which are typical of underwater lavic effusions. A little south of Rossena, in th location called Campotrera, the volcanic walls rise up vertically for tens of meters dominating for a large stretch the valley of the Cerezzola torrent;
following the path which goes up the torrent you will take in its entire power the gigantic volcanic "ruin", with its unmistakable brownish-reddish hue. The shape of these rock spurs, so selective compared to the clay, derives from the remarkable resistance that these basalt lavas have towards erosion. During the course of their long geological history the lava flows have been fractured. The mineralized water was thus able to deposit calcium, silicon boron, aluminum salts: and therefore various minerals were able to form.
(Town hall of Reggio Emilia, Civic Museum, Geology of the Reggiano apennines and "the Reggiano hills", 1992).