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The Black River is a river in west-central Wisconsin and tributary of the Mississippi River. The river is approximately long.〔U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. (The National Map ), accessed October 5, 2012〕 During the 19th century, pine logs were rafted down the Black, heading for sawmills at La Crosse and points beyond. ==Geography== The river begins in central Wisconsin, rising in Taylor County at approximately west of the village of Rib Lake. It flows south-southwest through Medford, Greenwood, Neillsville and Black River Falls. The Black River first mingles with the Mississippi River in Lake Onalaska in the Upper Mississippi River National Wildlife and Fish Refuge. The lower of the river channel have been absorbed by Lake Onalaska, an impoundment of the Mississippi River formed by Lock and Dam No. 7 at Onalaska. The river exits Lake Onalaska through a channel between French Island and the city of Onalaska and rejoins the Mississippi River at ,〔 northwest of La Crosse. The Black River can be divided into two sections by the dam at Black River Falls. The upstream section averages 6.6 feet/mile gradient, while the lower section through the Driftless Area only averages 1.7 feet/mile gradient.〔(Black River - WDNR )〕 An additional distinction is that the upper section has a substrate predominantly rocky and soil that contributes tannin, while the lower section has a predominantly sandy substrate. The tannin content of the water is the source of the river's name. The East Fork Black River rises in Wood County at , southwest of Marshfield and flows 〔 south and west into Lake Arbutus on the Black River at . The Little Black River is formed by the confluence of the East and West Branches at and flows into the Black River at south of Medford. The West Branch Little Black River rises at , south of Rib Lake and less than from the source of the main branch of the Black River. The East Branch Little Black River rises at south of Rib Lake. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Black River (Mississippi River)」の詳細全文を読む スポンサード リンク
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