This area is called "Della Biscia" (of the Water Snake) because there are a lake an hill and a river all named the same "Della Biscia". It has all to do with the cult of the waters (very plentiful here as on the southern side of the mountain) and with the cult of the "fairy-eel". Water Snake and Eel are the same thing. But on the hill some engravings are showing also a fertility cult.
The area is not so far from Pietra Scritta, sited on the north-west of Monte Beigua. All around there are many engraved stones and a dolmen that has lost his roof-stone, which can be found next to it.
My big thanks again to Mr Italo Pucci and Mr Fenoglio. Their information has led me to the site.