The Valsassina is divided in two river basins from the spur of Baiedo; that one of Pasturo - Barzio, the largest, and that one of Introbio - Taceno, lengthened for one ten of kilometers. Is in this river basin that finds the country of Primaluna, moreover rather extended, covering it a territory of kmq. 22,82. To south is delimited from the Grigne, to north from the Argella Mount, to est from Troggia torrent that divides it from Introbio and to the west from the fraction of Cortenova, Saint Prato Peter. In the middle of its territory, ther's a zone much extending of fertil fields, crosses by the Pioverna torrent.
