Moondance Jam

Yeah, I've never heard of this either. I'm surprised a fest like this slipped by me for the past couple of years.
 
I've had a few friends that have gone to past Moondance Jam shows. They have enjoyed it. It is a good 4 hour drive from the Minneapolis/St Paul area.

There is also Rock Fest (http://rock-fest.com/index.cfm) that is very similar. This one is closer to the Minneapolis/St Paul (2 hours +). I have gone for a single day there a few times. If you go to the FAQ, the past lineups are listed.

They are usually one to two weeks apart in July also.