Historical clue formulations

• Missouri tributary — 2025-03-05
• Major tributary of the Missouri — 2024-08-15
• South ___, river through Denver — 2024-05-19
• Tributary of the Missouri — 2020-11-14
• Tributary of the Missouri — 2019-04-28
• River paralleled by I-80 through a long stretch of the Plains — 2017-08-17
• Missouri feeder — 2014-12-16
• River to the Missouri — 2014-01-16
• Nebraska river — 2011-08-31
• Gothenburg's river — 2011-01-22
• River facetiously described as "a mile wide at the mouth, but only six inches deep" — 2009-05-16
• Kearney's river — 2006-07-01
• Missouri feeder — 2006-01-22
• Nebraska river — 2005-11-08
• Divider of Nebraska — 2005-10-21
• River followed by the Oregon Trail — 2005-05-07
• Nebraska river — 2003-01-29
• River across Nebraska — 2002-08-08
• Missouri feeder — 2002-01-25
• River where the Oto once settled — 2001-11-24
• Nebraska river — 1999-08-31
• Missouri River tributary — 1999-07-06
• County in Missouri or Nebraska — 1998-04-10
• Oregon Trail river — 1998-01-10