Another pic from this mystery show. I do believe the 6/22/68 date from the site; the estimable Dead Essays says this:
A newspaper review: “”Last weekend’s Grateful Dead concert was a smash. Too bad not everyone knew it. The further the Dead got into their music the quicker some people got out to their cars.” [deadlists]
I believe this photo bears out the review: our heroes have assumed, in Mr. Completely’s wonderful phrasing, Jamming Formation with Lonely Keyboardist (Pigpen is off to the left somewhere), and the crowd is sitting down and bored-seeming. Phoenix, Arizona, not getting the Dead in 1968 sounds right as hell.