Two that seem likely to have happened, but which have yielded zero expost trace took place on June 2, 1973 at the Marin Civic and on June 15, 1975 at the SF Civic. The first, especially, has always drawn me, because JGMS shared the bill with the brand-new Pointer Sisters and a Herbie Hancock aggregation transitioning from its Mwandishi to its Headhunter periods. Given the chance, I'd be awfully tempted to set my time machine back to this night to check out the action.
Let me just briefly drop some breadcrumbs on each.
June 2, 1973: Marin Civic Auditorium
An organization called Sausalito Is Spring organized three shows June 1-3, landing some major talent. The Saturday, June 2 gig was a benefit for the autistic classroom of the Henry C. Hall Elementary School in Larkspur, with the killer bill identified above. I have gathered up the following ex ante materials:
! preview: "Concerts Will Aid Autistic Children Class," Independent-Journal [San Rafael, CA], May 29, 1973, p. 11;
! ad: San Francisco Examiner, May 31, 1973, p. 25;
! listing: "Scenedrome," Berkeley Barb, June 1-7, 1973, p. 22;
! listing: San Francisco Chronicle, June 1, 1973, p. 48;
! listing: San Francisco Examiner, June 2, 1973, p. 10;
! ref: handbill.
The 5/31 ad in the Examiners bills "Jerry Garcia & Merle [sic] Saunders," with Pamela Polland following in the same font, and then the Pointers and Herbie Hancock in smaller print.
Did this gig happen? Was anybody there? Was Gaylord Birch drumming for the Pointer Sisters? Did the Headhunters do what I imagine they must have, which would be drop down some deep, thick, funky fusion?
June 15, 1975: SF Civic Auditorium
This was a marathon, all-day boogie billing the following: JGMS / Country Joe McDonald and The Energy Crisis / Van Morrison / Dr. Hook and the Medicine Show / Larry Coryell / Chi Coltrane / Barefoot Jerry / Brother Mouse Band / Hoodoo Rhythm Devils / Soundhole / Brotherly Love / Pegasus / Caesar's Band / Lyons & Clark.
! ad: SFSECDB19750525p11;
! preview: "Marathon of Boogie," San Francisco Examiner, May 27, 1975, p. 30;
! preview: "The All-Day Boogie," San Francisco Examiner, June 13, 1975, p. 25;
! listing: SFSECDB19750615p07;
! ref: Wasserman 19750817.
It was a benefit for the Community Fairs Broadcast Foundation. Wasserman 19750817 doesn't mention JGMS, leading with CJ, and says the whole event was put on by amateurs and was an unmitigated disaster - BASS sold only 227 tickets.
I reproduce my extremely low-res scan of a flier below.