Historical clue formulations

• Plains tribe — 2016-07-28
• Great Plains tribe — 2015-08-04
• Midwest tribe — 2010-07-12
• Plains Indian — 2005-09-21
• Great Plains tribe — 2002-02-25
• Plains Indian — 2001-03-28
• Plains tribe — 1999-01-29
• Plains Indians — 1995-07-09