The river originates in Todd County in south central South Dakota, at the confluence of Antelope Creek and Rock Creek near the town of Hidden Timber.[9] It flows in a generally southeasterly direction through Todd and Tripp counties in South Dakota and then through Keya Paha and Boyd counties in Nebraska.[1] It ends at its confluence with the Niobrara River about 7 miles (11 km) west of Butte, Nebraska.[10] The river has a year-round flow, except for winter ice, and has a quality of water better than all other South Dakota rivers.[11]
In 1861, the border between the Nebraska and Dakota territories followed the Keya Paha River from the 43rd parallel to the river's confluence with the Niobrara; it then followed the Niobrara to Missouri. This situation lasted until 1882 when the boundary was changed to follow the 43rd parallel all the way to Missouri;[12] the change added portions of Keya Paha and Boyd counties to Nebraska.[13]
Discharge
At a gaging station south of Naper in Boyd County, the river's mean discharge was 138.6 cubic feet per second (3.92 m3/s). The maximum mean annual discharge was 389.4 cubic feet per second (11.03 m3/s), recorded in 1962; the minimum mean annual discharge was 44.5 cubic feet per second (1.26 m3/s), recorded in 1976.[14] The peak flow recorded at that point was 9,280 cubic feet per second (263 m3/s), registered on July 1, 1962.[15] From July 22 to July 30, 1976, the discharge was recorded as zero.[16]
^Seaber, Paul R., F. Paul Kapinos, and George L. Knapp (1987). USGS Hydrologic Unit Maps. U.S. Geological Survey Water-Supply Paper 2294. Cataloging unit 10150006, on p. 39. Retrieved 2011-02-26.
^McNally, Hannah, and Diana Lambdin Meyer (1997). Nebraska: Off the Beaten Path. Morris Book Publishing LLC. p. 81.
^U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National MapArchived 2012-03-29 at the Wayback Machine, accessed March 30, 2011
^Nebraska Atlas and Gazetteer. Freeport, Maine: Delorme. 3rd edition, 2005. p. 23.
^Hogan, Edward Patrick; Fouberg, Erin Hogan (2001). The Geography of South Dakota (Third ed.). Sioux Falls, SD: The Center for Western Studies – Augustana College. ISBN0-931170-79-6.