Deadlists states, "On page 162 of the Art Of Rock the poster for this show is reproduced. This does not, however, prove that the show actually took place, and in fact it seems a little unlikely."
Ryan Shriver's Jerry Site has a setlist for this show (which was billed as NRPS with Jerry Garcia, Marmaduke, and Mickey Hart) at http://www.thejerrysite.com/Search.do?action=date&date=7-7-1970 Of course the setlist could be from an incorrectly dated show but you'll have to ask Ryan about that. Iver
