Santerno valley is formed by the hill country of the Imola area.
The lower zone is characterised by the gullies, massive eroded rock formations that break the clayey land of the hills. These are the main features of the hill country between Emilia and Romagna. The vegetation on the gullies blooms mainly in Spring when there is plenty of brooms and other herbaceous plants. Sharp clayey slopes hardly covered by a scars vegetation cut surrounding hills soft grass lawns, therefore, in spite of their dry and deserted look, gullies create an enchanting effect of harsh cliffs among mild hills. The higher zone is dominated by the Vena del Gesso, a gypseous formation that crosses the valleys between Brisighella and Mount Sillaro. It is a quite thin line of selenite two kilometres high and twenty-five kilometres long; it is parallel to the plain and perpendicular to the course of the rivers. This famous and anomalous formation is an important boundary line between gullies and sandstone.
      The higher course of river Saterno flows among sandstone rocks, and a wild and flourishing vegetation.
This valley includes the villages of Castel del Rio, Fontanelice, Tossignano, Borgo Tossignano and Castelfiumanese, whose past is rich of historical events and sieges and battles.
Two of them earned fame as important tourist resorts: Tossignano and Borgo Tossignano. The former rises on a gypseous hill 300 metres high, while the latter, situated downhill, is nowadays the seat of a town hall.
Nearby, Fontanelice is noteworthy for its Villanovan finds that witness the antique origins of this village and its intense handicraft and farming activity.
      Castelfiumanese, a XI century commune, is worth a visit for its beautiful town hall. Castel del Rio is famous for a bridge, called Ponte d'Osta, for the local excellent chestnuts, and it is also a well-renowned tourist resort.