Original 1st printing 15 x 19&7/8" concert poster for Quicksilver Messenger Service appearing with Big Brother & the Holding Company (featuring Janis Joplin) and Country Joe & the Fish at the Avalon Ballroom in San Francisco, CA from 11/25-26/1966.
Art by Victor Moscoso, image is # 36 in the Family Dog/Avalon series (this is the type "B" version with the dark red ticket outlet strip).
Medium-thick flat vellum stock poster is in very good to excellent (B/B+ to B+) condition; there are a series of thin vertical creases/bends and edge nips (tiny tears) running along left/right margins and a stray pinch ding or two hiding within the image area, otherwise fine.
Aside from the relatively minor degree of wear along the margins, this is a REALLY nice-looking example. Check out the original radio spot for the show!
https://ia802304.us.archive.org/34/items/PsychedelicPromosRadioSpotsVol.1/49.%20Family%20Dog%20-%20Concert%20Promo%20Spot.mp3