Boso Hills

The hills occupy the southern part of the Boso Peninsula in Chiba Prefecture. They extend from the area south of a line that connects Cape Isonezaki, south of Cape Futtsu, to the area around Oami Shirasato City in the Kujukuri Plain. The altitude is about 300 to 400 meters, with the highest peak being Atagoyama at 408 meters. The geology is mainly composed of the Miura Group from the Tertiary Period and the Kazusa Group from the Quaternary Period, but it has become complicated due to crustal movements. The line that runs from Nokogiriyama through the Kamo River rift valley to the sea cliffs of Osenkorogashi in Kamogawa City divides the area into the Kazusa Hills in the north and the Awa Hills in the south. The Yoro River, Obitsu River, and Koito River meander in a north-south parallel direction through the Kazusa Hills, forming a valley bottom plain. There is a series of steep mountains from childhood to early adulthood, such as Nokogiriyama, Kanozan, Takagoyama, and Kiyosumiyama, and the scenic spots of Tsukumo Valley and Yoro Valley are prefectural natural parks. From Kiyosumiyama to Yoro Valley, mixed oak forests prevail, while other areas are widely covered with oak, chestnut, evergreen broadleaf forests, and artificial forests of Sanbu cedar. In recent years, the prefectural Boso Skyline and Kamogawa Toll Road have passed through the former firewood and charcoal production areas, and Kanozan Mother Farm, Seiwa Prefectural Forest, Lake Mishima, and Takagoyama Natural Park have been opened, and many golf courses have been developed in the Yoro River basin, transforming it into a recreational area. In the Mineoka Mountains to the north of the Awa Hills, there are landslide areas where serpentine has weathered, and the surrounding area is the center of Awa dairy farming and is a major producer of raw milk. The hills in the southern part of the Tateyama Plain are covered with tropical forests of castanopsis and thrush, and the Tateyama Wild Bird Forest is located there.

[Yamamura Junji]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

千葉県、房総半島の南部を占める丘陵。富津岬(ふっつみさき)南部の磯根岬(いそねざき)付近から九十九里平野の大網白里(おおあみしらさと)市付近を結ぶ線以南の地域に展開する。標高は約300～400メートルで、最高峰は愛宕山(あたごやま)の408メートル。地質はおもに第三紀の三浦層群、第四紀の上総(かずさ)層群からなるが、地殻変動を受けて複雑に入り組んでいる。鋸山(のこぎりやま)から加茂(かも)川の地溝帯を通り鴨川(かもがわ)市のおせんころがしの海食崖(がい)に至る線によって、北部の上総丘陵と南部の安房丘陵(あわきゅうりょう)に二分される。上総丘陵を南北方向に並行して養老川、小櫃(おびつ)川、小糸川が蛇行して流れ、谷底平野を形成する。鋸山、鹿野山(かのうざん)、高宕(たかご)山、清澄(きよすみ)山など幼年期から早・壮年期の険しい山々が連なり、九十九谷や養老渓谷の景勝地が県立自然公園になっている。清澄山から養老渓谷にかけてはカシ類混交林が優先し、そのほかの地域は広くコナラ、クリ、常緑広葉樹林と山武(さんぶ)スギの人工林が展開する。かつての薪炭生産地は近年県営房総スカイライン、鴨川有料道路が通じ、鹿野山マザー牧場、清和県民の森、三島湖や高宕山自然公園などが開かれ、また養老川流域では多くのゴルフ場が開発され、レクリエーション地へと変貌(へんぼう)しつつある。安房丘陵北の嶺岡(みねおか)山地では蛇紋岩が風化した地すべり地帯がみられ、付近一帯は安房酪農の中心地をなし生乳生産が盛んである。館山(たてやま)平野南部の丘陵はシイ、タブの暖帯林が茂り、県営館山野鳥の森がある。

［山村順次］

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