This monument consists of the greatest source of karst origins in Sardinia, located at the foot of Supramonte of Oliena. It pours from a calcareous gorge more than 100 meters deep with a flow rate, in lean periods, about 60-70 liters per second, while the average rate is about 250 liters per second. Water temperature at the source is 11° C, stable throughout the year. During the rainy seasons, the river floods form an actual river that flows into Cedrino. The particular position of the source, not completely explored yet, compared to the karst areas, represents a kind of relief vale of the whole karst quarry complex on the territory and the only water supply in summer time.