Trebbia basin covers a territory of about 1.070 Sq. m., of which 86% is made of hills and mountains. It is located on the right of Po river, between the basins of Tidone and Staffora rivers to the east, Nure river to the west, Scrivia river to the south-east, Taro river to the south-west and Sturla river to the south. Trebbia river flows from Mount S. Lazzaro in the Liguria Apennine and dives into Po river slightly to the west of Piacenza, after a path 116 km long. Along the watershed to the south there are mounts Penna (1.735 m above sea level), Maggiorasca (1.799 m above sea level), to the east Mount Cavalmurone (1.670 m above sea level) and to the west Mount Crociglia (1.578 m above sea level). It receives numerous tributaries, among which the most important is the Aveto stream, about 30 km long. Other tributaries are Bobbio, Perino and Dorba streams.
On the morphological side, the area belongs to Piacenza Apennine and is characterized by a valley floor formed by hard limestone rocks, in which the river digged a tortuous and suggestive track that by cutting through the sedimentary layers brought to light interesting fossils. The high Trebbia valley, with large woods, is characterized by resurfacing ophiolites (Pietra Parcellara, Pietra Marcia, Pietra Perduca). The tectonic window of Bobbio is unique for the presence of Neolithic sediments called “Arenarie di Bobbio” and “Arenarie dell’Aveto”, which are the most recent aggregations of Piacenza Apennine area now visible thanks to the erosion of Trebbia and Aveto rivers. The high Trebbia and Boreca valleys are characterized – the second above all – by a profile in the shape of a V with close axes represented by mounts Cavalmurone, Chiappo, Alfeo and Lesina.
From the point of view of settlements, Bobbio dominates the valley. In the Middle Ages it played a crucial role and Bobbio developed around the original monastery founded by St. Columba, but then the village passed on to the Visconti family, then the Savoia and finally was taken over by Pavia. Recently, the area saw the birth of Trebbia Regional River Park, a protected area that spans from Po confluence up to the foot of the mountains in Rivergaro, partially including the plain.
The flora is diversified according to the large areas of consolidated gravel occupied by steppe-like lands with low bushes, home to numerous Apennine species and some orchids. In the low Trebbia there are poplars and willows. In Croara woods there is the oak, turkey oak, chestnut tree, whereas in the underwoods there is also the butcher’s broom. Trebbia river geographical position is perfect as stop-over and transit stage for migrant birds such as the great white heron, the night heron, the snowy egret, shorebird birds and birds of prey, moving from winter settlements to those dedicated to nesting. The cone-shaped Trebbia valley also plays a key role in the preservation of the Stone-Curlew, a protected species at European and national level. There are also reptiles and various species of fish such as the common cobitis, the barbus caninus and common barbus and the South European nase.
At Passo Penice, on the sloping sides of the mountain bearing the same name, from December to March the ski facilities are open. In the Ceci village there is also a 10 km cross-country trail distributed on rings of different lenght.