Niobrara (nīəbrâr´ə), river, c.430 mi (690 km) long, rising in the High Plains, E Wyo., and flowing E across N Nebraska to the Missouri River on Nebraska's northeast border. The Mirage Flats irrigation project uses water impounded by Box Butte Dam (completed 1946). A scenic 76-mi (122-km) portion of the river comprises Niobrara National Scenic River (see National Parks and Monuments, table).
"Niobrara." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (September 20, 2018). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/niobrara
"Niobrara." The Columbia Encyclopedia, 6th ed.. . Retrieved September 20, 2018 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/niobrara