Uonuma Hills

A mountain range that runs in a staggering pattern through the center of Niigata Prefecture. It is a Tertiary hilly mountain range that forms the border between the Tokamachi Basin and the Muikamachi Basin, with the highest peak being Atemayama (1,017 meters) in the southern part of Tokamachi City. The average elevation is 600 to 700 meters. The mountain body is made up of alternating layers of shale and sandstone from the Tertiary Uonuma Group, with thick agglomerates called Shibakura conglomerate intruding in places. The mountain ridge runs parallel to the Tokamachi Basin and the Muikamachi Basin, stretching from northeast to southwest, and is a tilted massif with a steep slope to the east and a gentle slope to the west. The Shinano Riverbank is formed by a group of high-level river terraces caused by Quaternary ground movement. At the northern end, a typical cuesta topography caused by differential erosion of hard and soft alternating layers can be seen, and the fault scarps on the eastern foot of the mountain have many steep slopes, making them a mecca for ski resorts along the JR Joetsu Line. Tochikubo Pass and Hakka Pass, which connect the two basins, are long-standing crossing roads. The Uonuma Skyline, which runs along the ridgeline, was recently completed, and the entire area has been designated as part of the Uonuma Mountain Range Prefectural Natural Park.

[Hisao Yamazaki]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

新潟県の中央部を雁行(がんこう)する山地。十日町盆地と六日町盆地の境をなす第三紀の丘陵山地で、最高峰は十日町市の南部にある当間山(あてまやま)（1017メートル）。平均標高は600～700メートル。山体は第三紀魚沼層群の頁岩(けつがん)と砂岩の互層からなり、所々に柴倉礫岩(しばくられきがん)とよばれる厚い集塊岩が貫入している。山稜(さんりょう)は十日町盆地、六日町盆地に並走して北東から南西方向に延び、東側に急斜面を向け、西側に緩斜面をなす傾動地塊で、信濃(しなの)川べりは第四紀の地盤運動による高位河岸段丘群から形成されている。北端には硬軟互層の差別侵食による模式的ケスタ地形もみられ、東麓(とうろく)の断層崖(がい)は急斜面が多くJR上越沿線のスキー場のメッカになっている。両盆地をつなぐ栃窪峠(とちくぼとうげ)、八箇峠(はっかとうげ)は古くからの横断道。最近は稜線を縦走する魚沼スカイラインも完成して、全域が魚沼連峰県立自然公園地区に指定されている。

［山崎久雄］

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