I found this information at http://www.wildleaves.com/austin.htm. There's a small graphic after the text which may or may not be the poster for this show.
****************** 1972 Thanksgiving Doug Sahm plays the Armadillo World Headquarters with suprise guests Jerry Garcia and Leon Russell. It is a free show, attended by many who just walked in off the street. ************* > > Was the 11-23-72 with Jerry, Phil, Bill the Drummer, Doug Sahm, Leon > Russell et al. from the Armadillo open to the public, or was this a > private jam? I am wondering how the show was billed if it was open to > the public. My ultimate motive for asking this question is to > determine > how to list the show.