The lower slopes of Cima di Gratera expose rocks from the lithospheric mantle that contain pseudotachylites, which are the relics of former earthquakes.
1 km north of Patrimonio, a bit uphill from the main road, the mountain slope above the Fium Albino river offers outcrops of variably serpentinized peridotites. These medium-grained ultramafic rocks mainly consist of olivine, clino- and orthopyroxene and represent rocks from the lithospheric mantle. In some places, these rocks are cut by mm- to cm-wide dykes that are often weathered out relative to the host rock. These dykes have irregular orientations and contain an extremely fine-grained or even glassy black rock. Since they look similar to (sub-)volcanic melt injections, these were termed pseudotachyllites. However, the melt in these dykes does not have a volcanic origin, but was formed by frictional heating during earthquakes in the Alpine subduction zone.