On 4/29/90, Garcia sat in with "Nick Gravenites and Animal Mind" for a Brian Wilson Defense Fund Benefit at the South of Market Cultural Center in San Francisco. If you haven't heard it, the circulating fileset is well worth seeking out. The whole thing is great, but "Small Walk-In Box" will leave you marveling at Jerry's ability to pick up a tune (presumably with little preparation) and nail it. I tend to conceive of Jerry's various one-off guest shots from the 1986-1990 period as of a piece with each other, with a relatively healthy/happy Jerry really on his game, but that's a matter for another post or several.
What I want to mention here is an otherwise unknown-to-me gig that Garcia seems to have played around 1973 at San Quentin. Lost Live Dead did a post on Grateful Dead performances at San Quentin, to which this might need to be added.
In Jimbo Juanis's regular Relix column that discusses the 4/29/90 thing (seemingly mis-dated 4/30, but anyway), he reports a bit of chatter with Nick Gravenites. Nick the Greek says that he had played with Garcia once before:
About 17 years ago, Garcia and I and Jules Broussard (a local sax player) played for the inmates at San Quentin Prison. All the inmates at the gig were musicians and they all brought their horns and we all played together. We did the gig in the room that used to house the gallows.
I don't have a lot to add, except that I sure would like to learn more! I wonder if records of this sort of thing might be requestable under some kind of state of California open records provision?
(1) Jimbo Juanis, "Bay Area Bits," Relix 17, 4 (August 1990): p. 25.