Ten Years After appeared at the St. Paul Civic Center on April 9, 1971, opened by Humble Pie.  Some source I can’t find now said that King Crimson and Black Sabbath were also there, but after Alessandro from Italy wrote to question this, even a thorough search by a heroic librarian named Carol at the St. Paul Public Library could not find confirmation:

I was able to confirm that Humble Pie and Ten Years After did play at the Civic Center on April 9, 1971, but I was not able to confirm if Black Sabbath or King Crimson were there.  Black Sabbath supposedly played at the St. Paul Civic Center on July 2, 1971, but there were no reviews or advertisements for that concert either in the St. Paul newspapers or the Minneapolis newspapers.  The published itinerary of Black Sabbath does make it possible that they could have played in St. Paul on either April 9 or July 1.  It seems less likely that King Crimson was here since they were in Europe shortly before and shortly after those dates and airfare was considered extremely expensive at that time.

Wow!  Wish I could hire Carol as a research assistant!