Geologically speaking one can easily severn the left side and the right side of the Trebbia Valley in respect to its main watercourse.
To the left of the Trebbia River only one sedimentary rocky formation can be observed, called "the Mount Antola limestone ".
Such formation appears in a vast part of the middle oriental Liguria, from the Polcevera Valley to the provinces of Alexandria and Piacenza northwards, and eastwards to Chiavari.
The name "limestone" is given to rocks formed by  calcium carbonate (CaCO3) precipitations; nevertheless, the rock  also origins from the deposition of small fragments of preexisting rocks, such as sand and clay.
In such case speaking about marly limestone is more precise.
Millions of years ago, probably when Liguria started assuming its actual structure, such material, located on the edge of the continental slope, "slipped" into the oceanic bed, by a process known either as "pulp-ore current " or "flysch."
Overall this rocky formation is well stratified, where the calcareous, sandy or clayey component prevails depending on its layers.  The most calcareous layers show a clear grey colour; the ones more arenaceous, where the sand prevails, appear yellowish or clear brown, and they are rough to the touch; the clayey ones, which are the thinnest ones,  are dark grey or brown. Arenaceous and calcareous layers are more resistant to erosion, instead  clayey ones are very friable.
Between one layer and another enigmatic fossils called "elmintoid" can be found.
“Elmintoidi” originate from animals of which we know nothing about as these animals  did not possess any fossilized part, neither shell nor skeleton.
Even more interesting is the geologic situation of the slopes situated on the right side of the Trebbia River.
One should imagine an ocean bed, nowadays not existing anymore, situated between Africa and Europe, where a remarkable volcanic activity spread basaltic lava across the oceanic crust and mantle, formed by rocks called peridotites.
While subsequently the biggest part of the oceanic floor disappeared, swallowed by the two continents, some parts of the ancient ocean were pushed upwards, and eventually they emerged outcroping on the the Alpine and Appennine chains : the "ophiolites"  form this way , rocks so called because of their typical dark green colour.
Such magmatic rocks have changed and transformed later , giving birth to serpentinites, basalts not much metamorphic, ophiolitic breccias: one can observe them above all in Roccabruna’s area, Pietranera, Mount Castello del Fante  and Montarlone.
Nearby sedimentary rocks prevail, due to deposit of different materials: they could have sufferred transformation processes and metamorphism.
Also among sedimentary rocks there are the  sliceous ones (jaspers),  calcareous ones (“calpionelle” limestones), the ones due to ooze deposition (“arginiti”, “argilloscisti”) or sand (sandstones).
Jaspers, that outcrop on the surface along with ophiolites, are thin layers by reddish colour, sometimes grey or greenish .
 “Calpionelle” limestones which the name of the Pietre Bianche (White Stones) resort is related to, are typically clear.
“Arginiti” and “argilloscisti” often alternate with sandstones: while the first ones, by dark grey colour, are easy to wear away,  sandstones are clearer and more compact and resistant to the erosion. Important important sandstones are found in Casanova.

(Article based on the publication "Naturalistic Itineraries" by the Comunità Montana Alta Val Trebbia – High Trebbia Valley Mountainous Community).