Brisighella.org

The low hilly terrain of western Romagna, set in a continuous strip from the Sillaro valley to the Ronco valley, is marked by a peculiar barren landscape, streaked with narrow valleys and sharp rocky ridges. These are the "calanchi", a geological phenomenon due to the clayey terrain and to the atmosferic agents, most of all the washing action of the water

These rocks belong to the the Blue Clays period that can be dated between the Pliocene era and the Pleistocene era (5.3 to 1 millions years old), with a tickness of 1-2 km, amd it's a very remarkable feature in the Brisighella landscape.

From a scientific perspective these terrains are mostly made up of sedimentary impermeable soils formed with microscopic particles, like dust, caused by the erosion of the rocks.

Due to their peculiar structure, these particles slowly soak up a large amount of water and change their phisical status, forming a mass of mud and the typical mussy outflows. On the contrary in the summertime water evaporates and the muddy clay shrinks creating deep cracks on the ground.

How did it form?

After the closure of the Strait of Gibraltar and the creation of a great salted sea, at the beginning of the Pliocene era the Strait opened up again and the Atlantic salty water filled up again the Mediterranean basin; the Padana plain, now covered by the sea, became a large gulf bounded to the north by the Alps and to the West by the Apennines. The Blue Clay Ravines are the remains of the old muddy seabed that till one million of years ago covered the Padan Gulf: these are sedimentary rocks formed by blue-gray clays in medium deep sea.

The existence of an old sea is proved by many fossil remains, and part of them (shellfishes) can be seen with a naked eye.