Opposite the Grotta Giusti spa, on the left of the parking area, take the Monsummano Hill Geological Trail that leads to a fork at the edge of the forest, from where two geological walks start.
TRAIL No. 1
Following the fork towards the right, we reach the surface of the large fault that constitutes Monsummano Hill’s anticline. The trail is intersected diagonally by a large vein of calcite, while fragments of Selciferous limestone from the Grotta Giusti surface downhill. This stratified formation is typical of this area and includes microfossils from the sedimentation of lagoon waters during the Lower Jurassic.
On the uphill side, a limestone mass can be seen, which was formed by the sedimentation of marine waters during that same geological era. The trail leads to a disused quarry where a small fault marks the contact with the stratified red ammonite above. Extending for more than 20 meters, the quarry’s western face corresponds to a single surface-layer. Following along, we come upon the Limano flinty limestone and then descend towards the trail from where a third quarry wall is visible on the left. With a north-south orientation, it corresponds to the surface of a minor fault that can be seen on the right with Posidonia marl stratifications.
Back on the trail, Val di Lima flinty limestone surfaces for a short distance. After a dozen meters, a small outcropping of Tuscan red-violet jaspers appears. The trail leads to a small quarry of Sugame marls. Continuing along the mule track that rejoins the paved road that arrives at the castle in Monsummano Alto.
TRAIL No. 2
If we take the trail to the left of the junction at the forest’s edge, then turn right and pass through a sort of natural corridor to reach a circular quarry cut into the massive limestone. This is Cava Rossa, or the red quarry, whose name comes from the ferric-oxide incrustations covering the quarry walls. In the stretch approaching the quarry, a surface section of the Great Fault can be seen, represented by approximately 20 centimeters of thin layers of calcite alabaster. On the left wall of the quarry, a tunnel dug into the rock is still open.
The trail then descends towards the paved access road to the Cava Grande, or large quarry, on the western slope of the hill. An especially interesting trail in geological terms runs along the La Spezia (Rhaetian) Formation of the Great Western Fault, which surfaces for some meters in the large quarry area, from where the basal part of the massive limestone can be seen. The stratigraphic sections of the various formations are visible in detail for the almost entire vertical progression of the quarry cut. Continuing along the trail, we return to Lucchese State Road 435.