Plenty of folks insist that yes, it happened; a few photographs suggest as much ... but the person in question cannot positively be identified as Guaraldi. It's known that Guaraldi occasionally played with Jerry Garcia at the Matrix's Monday night jam sessions during the late 1960s; Guaraldi and Garcia also fronted a quartet -- with bassist Seward McCain and drummer Mike Clark -- during the summer of 1972 (venue unknown, alas!). But those were gigs with Garcia, not the Dead ... and despite all the tapes available, and all the archive material carefully saved by Deadheads, smoking-gun proof of Guaraldi's participation with the Dead has yet to be found.
All of which makes the ongoing debate even more enticing. I'll turn the rest of this post over to my colleage and Dead historian Corey, who runs his own blog, which you'll want to investigate.
Any idea what Vince Guaraldi was doing on New Year's Eve 1968-69? Because jamming with the Grateful Dead fits a number of timelines. Various parties--Jerry Garcia, Dead road manager Bill Belmont and Dead keyboardist Tom Constanten, among others--all agree that Vince sat in on stage with the Dead, but no one can recall exactly when. So let me take a stab at proposing that at least one of those times was New Year's Eve 68'/69 at Winterland.
1) During this period, the Dead were booked by Bill Graham's Millard Agency. The band had borrowed $12000 from Graham, and they paid it back by making Graham (Millard) their booking agent. Bill Belmont went on tour with them to collect Graham's money (to be fair, he was a friend and ally, but he was on tour at Graham's behest). The Millard period for the Dead was roughly Fall '68 to Summer '69, so that brackets Belmont's time as an eyewitness to a Guaraldi/Dead jam.
2) NYE '68 at Winterland featured 3 Millard bands (GD, Santana, Its A Beautiful Day, along with Quicksilver), and it must have been a staff party as well as an event. Gretchen (Vince's girlfriend, and BGP employee) would have been there, right, regardless of which Graham entity she worked for at the time? So that makes Vince's presence plausible. Also, the show went on until dawn, so Vince could have done something with his family, put them to bed, drove over to Winterland and still had 5 hours left to hang out.
3) No one remembers a thing about this show except that it was "legendary." I have a blog post about this subject:
Interestingly, a few commenters dredge up a flashback or two--Quicksilver seems to have played at midnight, not the Dead, for example. So the Dead's second set would have been at 3 am or something. If Vince played with the Dead on their second set on New Year's Eve, sometime between 3 and 6am, this would explain a few things. Jerry Garcia, Tom Constanten and Bill Belmont are sure that Vince played with the Dead, but can't remember when, there were no eyewitness accounts because all witnesses auto-deleted (the person who comments on my blog concedes that he remembers nothing after midnight).
Belmont is confident that Vince jammed, but can't remember when. Since Belmon't job was to collect money for Graham, he wasn't going to get wrecked in Chicago or Texas, but at what was in effect a BGP house party in San Francisco? Batter up.
If Constanten suffered "electrical damage" in the wee hours, whose to say that Vince didn't sit down and let it fly? As I said, I had been under the impression that Vince would have played melodic jazz on a Fender Rhodes. Now I realize he wanted to hammer down the organ stops so he could hear it through a Leslie magnified by a dozen souped up MacIntosh amps. New Year's Eve as dawn approached would be a fine opportunity for Vince to have some fun with the Dead, apparently fondly but fuzzily remembered by anyone there. Much of the audience would have had no idea who Vince was--for that matter, they wouldnt have known who Constanten was either.
Just a thought. Don't know who's around who would still know, and of course if they were there they forgot. Still, maybe someone remembers something, and it would be nice to nail down the mysterious Dead/Guaraldi jams for certain.