Official promoter-issued 1967 3rd printing 14 x 20" concert poster for the Grateful Dead appearing with Oxford Circle at the Avalon Ballroom in San Francisco, CA on 9/16-17/1966.
Art by Stanley Mouse and Alton Kelley (central image borrowed from Edmund Sullivan), image is # 26 in the Family Dog/Avalon series.
Medium flat index stock poster is in near mint/excellent (A- to A-/B+) condition; there's a couple of subtle handling dings, a corner bump or two and a soft 2" vertical bend in the right margin, but other than that, it's just about as/crisp and bright as you can ask for.
An overall GORGEOUS example of the classic "Skeleton and Roses" image. Have a listen to the show (PRIMAL '66 Dead) HERE: