The San Francisco section of the "From the Music Capitals of the World" Feature in the November 21, 1970 issue of Billboard (p. 25, available via Google Books), written by Mary Turner, indicates that the New Riders of the Purple Sage performed at an event called "Marathon 70," put on by Both/And Productions, over the Halloween Weekend of 1970. The image is below.
We know that GD and NRPS were at SUNY Stony Brook on Halloween night (Saturday). We also know that the GD were in Port Chester from Thursday, November 5th.
Did the NRPS (and Jerry) come back to the Bay Area rather than just hanging around the east coast? Hard to say for sure, but there seems to be enough evidence (fragmentary, but independent) suggesting that they did, and thus that this gig might well have happened.
First, the Jerry Site lists a Monday, November 2nd "Jerry Garcia and Friends" show at the Harding Theater, SF, based on information contributed by Joey Newlander from a listing in the Berkeley Barb. TJS further speculates that the gig did not happen, what with the GD out east. OK.
Second, the PERRO tapes (in this case, sessions for David Crosby's If I Could Only Remember My Name) include at least one cut ("Cowboy Movie") said to have been laid down at Heider's in SF on Tuesday, November 3rd. (This has always been important to me, since that was the date of my birth and I *love* the idea that that's what Jerry was doing on that day!)
Third, Good Times (v.3 n.43, 10/30/70, p. 16) ran a listing for a Garcia/Saunders show at the Matrix on this same night, Tuesday, November 3rd.
Fourth, though not independent of #2, I also have a PERRO session listed for Wednesday, November 4th, though I have no notes on where that information might have come from.
Now we have a fifth piece of evidence in the indication that NRPS might have been back in the Bay Area in between Stony Brook and Port Chester.
I am going to go ahead and speculate that the "Halloween Weekend" notion plus the gigs seemingly booked for every other night during this short window, both militate in favor of a Sunday, November 1, 1970 listing.
I'd like to hear from anyone who knows more about this event ("Marathon 70") and/or the Both/And. Thoughts?