Original 1st printing 8&1/2 x 11" hand-addressed mailed concert flyer 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 on 11/25-26/1966.
Art by Victor Moscoso, image is # 36 in the Family Dog/Avalon series (OHB-D in the Eric King guide, this one has a hand-written (in blue pen) address, canceled 5 cent stamp and 11/23/1966 stamped postmark on the reverse).
Thin flat stock flyer is in decent/used (B/B- to B-) condition; there are a pair of horizontal folds (as issued, item was folded into 1/3rd for mailing purposes), tack holes in all corners, a set of staple holes in the top/bottom center margins, a few tiny edge/corner dings, a fair amount of toning and a few stray light surface scuffs hiding within the image area, otherwise fine.
While the condition on this example may not be perfect, it is still a hard-to-find early Family Dog mailer. 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