The famous Halloween 1967 San Francisco psychedelic concert poster designed by Alton Kelley, Stanley Mouse and Rick Griffin. “Trip or Freak” — a take-off on “trick or treat,” of course — was a Halloween Ball featuring the Grateful Dead, Big Brother & The Holding Company (featuring Janis Joplin) and the Quicksilver Messenger Service. This poster is rich in hidden, magical detail, and is enthusiastically discussed by collector Pete Howard of PosterCentral.com (phone 805-540-0020, email pete@postercentral.com). If you like posters like this, be sure to check out more vintage psychedelic concert posters shown on this page right here on my web site: http://www.postercentral.com/psychedelic.htm