Historical clue formulations

• Boulder locale — 2019-08-17
• Home of the Canyon of the Ancients — 2015-03-28
• Dinosaur National Monument site — 2007-07-22
• Avalanche setting — 2007-07-06
• Black Canyon carver, with "the" — 2002-12-19
• Middle of the Rockies — 1998-01-21