Big Sioux (sōō), river, 420 mi (676 km) long, rising in NE S.Dak. and flowing S into the Missouri River. It passes through an agricultural region that produces corn, oats, hogs, and beef cattle. The river's meandering course drops 20 ft (6 m) and services a hydroelectric station there. The Big Sioux forms part of the border between Iowa and South Dakota.
"Big Sioux." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (April 20, 2018). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/big-sioux
"Big Sioux." The Columbia Encyclopedia, 6th ed.. . Retrieved April 20, 2018 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/big-sioux