Thuringia borders on the German states of Lower Saxony, Saxony-Anhalt, Saxony, Bavaria and Hesse. The ridges of the western Harz mountains divide the region from Lower Saxony on the north-west and eastern Harz similarly separates Thuringia from the state of Saxony-Anhalt to the north-east. To the south and southwest, the Thuringer Wald effectively separates the ancient region of Franconia, now the northern part of Bavaria from the rolling plains of most of Thuringia and the central Harz range extends southwards along the western side into northwest corner of the Thüringer Wald region making Thuringia a low land basin of rolling plains nearly surrounded by old somewhat-difficult mountains. The most conspicuous geographical feature of Thuringia is the Thuringian Forest, a mountain chain in the southwest. The Werra river, a tributary of the Weser River separates this mountain chain from the volcanic Rhön Mountains, which are partially in Thuringia, Bavaria and Hesse. In the northwest Thuringia includes a small part of the Harz mountains.