are you inferring that the rise in case counts in September is somehow correlated to the summer tourism season, which is pretty well over by September? I see no evidence that points to this. surely if the summer tourism season caused a spike in cases(!), you would see it during the summer tourism season, and not afterward?
You keep talking about Sturgis, which ended on Aug 16. There is known incubation time between contact and testing positive, and even by 10 days later (Aug 26) the rate was at ~1200. Also July -> Aug was a 55% increase in cases as well, even before that, which coincides more with summer.
I'm not going to say definitively what caused what here, but your anecdotal recollection of what happened in SD is not really supported by the numbers.