Historical clue formulations

• It reaches Washington heights — 2021-07-17
• Only so-called "Decade Volcano" in the continental U.S. — 2013-11-22
• *Like Seattle vis-à-vis Phoenix — 2011-03-10
• Volcano in a national park — 2010-09-03
• European head of state for nearly 56 years — 2005-06-25
• Prince of Monaco — 2001-05-29
• Washington height — 1998-08-12
• Washington summit — 1998-02-27