Kangawa River

...The river originates from Mt. Danto (1,152m) in the north of the prefecture, flows south, joins its tributary, the Ure River (Miwa River), south of the ruins of Nagashino Castle, then changes course to the southwest and flows into Mikawa Bay north of Toyohashi City. The upper reaches are commonly known as the Kansa River. The upstream headwaters are the Mino-Mikawa Plateau, which continues south of the Kiso Mountains, and is made up of strata such as granite rock, Ryoke metamorphic rock, and Shitara volcanic rock, with flat areas in many places that retain the remnants of the uplifted peneplain. ...

*Some of the terminology explanations that mention "Samagawa" are listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…県北部の段戸山(1152m)に源を発して南下し，長篠城跡の南で支流の宇連（うれ）川(三輪川)を合わせ，そこから南西に流路を変えて豊橋市北方で三河湾に注ぐ。上流部は寒狭（かんさ）川と通称される。上流の水源地域は木曾山脈の南に続く美濃三河高原で，花コウ岩，領家変成岩，設楽火山岩などの地層によって構成され，随所に隆起準平原のなごりをとどめる平たん地が開けている。…

※「寒狭川」について言及している用語解説の一部を掲載しています。

出典｜株式会社平凡社世界大百科事典 第２版について | 情報