The Surselva encompasses the valley of the Vorderrhein/Rein Anteriur (the Surselva) and all its side valleys, from the source near the Oberalp Pass all the way down towards Reichenau (where the Vorderrhein joins the Hinterrhein/Rein Posteriur to form the Alpine Rhine). The region ends before that confluence at the huge forest on the giant debris of Flims Rockslide that is responsible for the name of the region: The debris area lack of water and soil and were ever left as a big forest as it was useless for farming. This forest (romonsch: silva) is the border for Sur-silva (meaning above the forest).