Historical clue formulations

• Home of Mount Rushmore: Abbr. — 2020-02-23
• Badlands locale: Abbr. — 2018-04-10
• Mt. Rushmore's state: Abbr. — 2016-08-16
• Neb. neighbor — 2015-04-29
• Where I-90 and I-29 cross: Abbr. — 2014-11-13
• Mt. Rushmore's home: Abbr. — 2013-10-20
• Home of Wind Cave Natl. Park — 2013-09-08
• Home to Ellsworth A.F.B. — 2012-07-07
• Its state sport is rodeo: Abbr. — 2012-05-03
• Only U.S. state in which the name of the state and its capital share no letters: Abbr. — 2011-05-20
• It's bisected by the Missouri R. — 2011-05-05
• Pierre is there: Abbr. — 2011-04-17
• Pierre's state: Abbr. — 2011-01-10
• Badlands locale: Abbr. — 2010-10-13
• Wounded Knee's locale: Abbr. — 2010-09-09
• Neb. neighbor — 2010-02-28
• Its motto is "Under God, the people rule": Abbr. — 2009-10-25
• Neb. neighbor — 2009-08-23
• Mt. Rushmore's locale: Abbr. — 2008-06-17
• Where Wounded Knee is: Abbr. — 2008-01-24
• Mount Rushmore's state: Abbr. — 2007-01-10
• Neb. neighbor — 2005-12-18
• Mt. Rushmore's place: Abbr. — 2005-02-03
• Badlands Natl. Park's state — 2004-11-10
• Mount Rushmore locale: Abbr. — 2003-07-22
• Badlands state: Abbr. — 2003-06-11
• Wind Cave Natl. Park locale — 2002-09-06
• Neb. neighbor — 2002-05-19
• Nebr. neighbor — 2001-01-24
• Badlands Natl. Park locale — 2000-12-20
• Minn. neighbor — 2000-11-09
• Mont. neighbor — 2000-03-09
• Minn. neighbor — 2000-03-01
• Pierre's state: Abbr. — 1999-05-10
• Badlands Natl. Park locale — 1999-03-12
• Wounded Knee locale: Abbr. — 1998-07-30
• Mt. Rushmore's state: Abbr. — 1997-06-04
• Neighbor of Minn. — 1997-04-09
• Mount Rushmore's site: Abbr. — 1997-04-08
• Mt. Rushmore site — 1996-10-26
• Neb. neighbor — 1996-10-17
• Neb. neighbor — 1996-08-10
• Neighbor of 16-Down: Abbr. — 1995-06-25
• It's north of Neb. — 1993-12-28