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NATURALIST ITINERARIES OF TUSCANY The Balze del Valdarno, also known as Smotte, stand as a distinctive geotope characterized by stratified sands, clays, and gravels, rising to a height of up to a hundred meters, exhibiting diverse forms interspersed with deep gorges. These formations are the result of the erosion of Pliocene lacustrine sediments in the Upper Valdarno by atmospheric agents and watercourses.

The present-day valley floor of the Valdarno is a consequence of geological phenomena occurring after the extinction of the Pliocene Lake in the Upper Valdarno. From this point onward, an erosive phase commenced, still ongoing: the hydrographic network, comprising a larger river in the valley floor, the Arno, and several smaller transverse tributaries, began dismantling the lacustrine sediments accumulated in various stages, transporting them downstream. The course of the Arno gradually lowered from the old infill surface to its current elevation, approximately 150 meters lower. The sediments are relatively young and offer minimal resistance to erosion, resulting in the formation of valleys with steep slopes. The lacustrine sediments consistently follow a stratigraphic sequence: finer sediments (clays) are found lower, deposited when the lake was deeper, while coarser sediments (pebbles) transported by inflows during shallower periods are higher up. This stratigraphic alternation of soft, clayey soils overlaid by more resistant materials (pebble conglomerates) allows for the formation of vertical walls. The transition between these geological formations is distinct and readily visible even to the less experienced eye:

- The lower part consists of yellow and grayish clayey and sandy silts, lacking in cohesion.
- The upper part comprises rounded, cemented, and resilient arenaceous pebbles in a brown hue, featuring horizons with a more rust-colored appearance (paleosols) when the old sediments remained dry.

Leonardo da Vinci, upon observing the Balze del Valdarno, comprehended these processes centuries ahead of modern theories on erosion and sedimentation:

"… this valley (Upper Valdarno) received on its bottom all the soil carried by the water, which is still seen at the foot of Pratomagno, where the rivers have worn it away. In the midst of this soil, one can observe the deep grooves made by the rivers that have passed through, descending from the great mountain of Pratomagno. In these grooves, there is no trace of marine deposits."

The Arno flows more toward the Chianti Mountains than the center of the valley, owing to the greater force of right-bank tributaries descending from Pratomagno. Consequently, sediments on the left side are dismantled more rapidly. For the same reason, the Balze exhibit their most prominent and spectacular forms near the slopes of Pratomagno, in the municipalities of Terranuova Bracciolini, Castelfranco di Sopra, Loro Ciuffenna, Pian di Scò, and Reggello. To admire more distinctive formations, one can traverse the SP1 Setteponti provincial road along the ancient Cassia Vetus route.

The plateau lands above the Balze and those resulting from disintegration below are heavily anthropized: towns, hamlets, farmsteads, vineyards, olive groves, and cultivated fields. The landscape, with names of estates hinting at enchanted scenarios and magical presences like Inferno, Purgatorio, and Case Fate, is remarkably evocative. Along watercourses, small ponds or lakes have formed, serving as crucial breeding grounds for amphibians, insects, crustaceans, mollusks, and aquatic plants. Discussions on projects for the protection and tourist enhancement of the Balze have been ongoing, but initiatives remain limited, and this miniature "Monumental Valley" in the heart of Tuscany remains unknown to many. Numerous CAI trails, suitable for cycling or walking, provide opportunities to behold the awe-inspiring beauty of the Balze.