Historical clue formulations

• Port at the west end of Lake Superior — 2018-05-16
• Minnesota city that shares a harbor with Superior, Wis. — 2012-12-24
• Lake Superior port — 2010-08-10
• Minnesota port — 2005-03-28
• University of Minnesota campus site — 2004-06-21
• St. Lawrence Seaway terminus — 1997-11-09