The are a mountain range in the Tōhoku region of Honshū, Japan. The range is the longest range in Japan and stretches south from the Natsudomari Peninsula of Aomori Prefecture to the Nasu volcanoes at the northern boundary of the Kantō region. Though long, the range is only about wide. The highest point in the range is Mount Iwate, . The range includes several widely known mountains: Hakkōda Mountains, Mount Iwate, Mount Zaō, Mount Azuma, Mount Yakeishi, and Mount Adatara. Naming These mountains previously formed the boundary between historical provinces of Mutsu (陸奥国) and Dewa (出羽国). The kanji for the name of the mountain range was created from one kanji of the two provinces, 奥 and 羽, respectively. Geology The Ōu Mountains began to form in the Pliocene. They sit over the middle of the inner arc of the Northeastern Japan Arc. This is the result of the Pacific Plate subducting under the Okhotsk Plate. A chain of Quaternary volcanoes along the range forms the volcanic front. References Mountain ranges of Akita Prefecture Mountain ranges of Aomori Prefecture Mountain ranges of Iwate Prefecture Mountain ranges of Miyagi Prefecture Mountain ranges of Yamagata Prefecture Mountain ranges of Fukushima Prefecture