For now, the basic question: when did they first play together?
In a ca. 1995-6 interview included on the DVD release of The End of the Road: The Final Tour '95 (Monterey Video DVD 313302), Merl indicates that he went down to Golden Gate Park and played with the Grateful Dead sometime in the late 1960s. I can't offer any precision or evaluation - it's certainly possible, but is presumably utterly unknowable from this vantage point unless someone's diary or some old photographs or some other account turns up.
The Jerry Site's first listing for "Jerry Garcia and Merl Saunders" is for October 12, 1970, though if you go to the band summary for that "artist" entry it lists the first show as 12/1/70. slip_not added some Merl content (a quote about he and Jerry came to play together) on the 9/7/70 Jerry Garcia & Friends entry, but there's no obvious ex ante reason for that information to be attached to that date.
So we are in a bit of a quandary, but I have a few data points to offer.
My MO here is to examine gigs and studio sessions that might have been relevant to understanding when Jerry and Merl started together. For gigs, I am especially interested in looking at the evolution of the Monday Night Jam sessions at the Matrix, since the standard story is that Howard Wales dropped out at some point and Merl joined in. It may not have been a clean/linear break, but the data might help. For sessions, I am interested because of the Merl quote listed under 9/7/70 TJS listing linked above. There seems to have been a Heider's connection where the GD, the whole PERRO crowd (Crosby and the Jeffersons), Brewer & Shipley, and Danny Cox (the latter two of whom were under the same management) were jumping into each others' sessions to an astonishing degree.
Anyway, here are what I consider some relevant data.
- 4/20/70: Jerry Garcia and Howard Wales [double-check]; Matrix; "Scenedrome" (calendar listing), Berkeley Barb, April 17-23, 1970, p.6.
- 4/27/70: Jerry Garcia, Howard Wales, & Friends; Matrix; display ad; listed as jam session in Scenedrome; Berkeley Barb, April 24-May 1, 1970, p. 8.
- 5/18/70: Jerry Garcia and Howard Wales [double-check]; Matrix; calendar listing, Good Times v.3 n.20, 5/15/70, p. 24. I believe this is the show that was released as Side Trips, vol 1. (Aside: "Thank you, sir. May I have another?")
- 5/25/70: Howard Wales, Jerry Garcia & Friends; Matrix; Scenedrome listing in Berkeley Barb, May 22-28, 1970, p. 18. Doubtful JG was there, given GD show in the UK the night before.
- 6/1/70: Jerry Garcia and Howard Wales [double-check]; Matrix; calendar item in Good Times v.3 n.22 (5/29/70), p. 24.
- 6/7/70: this appears not to have happened.
- 6/8/70: Jerry Garcia and Howard Wales; Matrix; [source suppressed]
- 6/15/70: Jerry Garcia and Howard Wales [double-check]; Matrix; calendar item in Good Times v.3 n.24 (6/12/70), p. 24.
- 6/22/70: Jerry Garcia and Howard Wales [double-check]; Matrix; calendar item in Good Times v.3 n.25 (6/19/70), p. 23.
- 7/6/70: Jerry Garcia and Howard Wales [double-check]; Matrix; calendar item in Good Times v.3 n.27 (7/3/70), p. 17.
- 7/15/70: the first "PERRO" session at Heider's that I can document; Kantner session working on "Starship" and "Old Man" for what would become Blows Against The Empire; this and all related listings provided below show Jerry present [source suppressed]
- 7/17/70: as above, but working on "Mau Mau";
- 7/20/70: Howard Wales and Friends listed at Matrix for this Monday and the next night (Tues., 7/21/70); calendar item in Good Times v.3 n.28 (7/17/70), p. 18; no mention of Garcia.
- 7/21/70: as above.
- 7/22/70: Kantner session at Heider's ("Mau Mau"; "Together"); see 7/15/70.
- 8/6/70-9/16/70: I have the GD's American Beauty sessions at Heider's from these dates; source: McNally, LST, p. 378.
- 8/10/70: Kantner session at Heider's ("Starship"; "Old Man"); see 7/15/70.
- 8/11/70: as above ("Starship"); see 7/15/70.
- 8/21/70: Brewer & Shipley session at Heider's, for what would become Tarkio; Garcia listed ("50 States of Freedom"; "Oh Mommy"); [source suppressed]
- 8/24/70: Garcia & Wales [double-check] Monday night Matrix session; calendar item in Good Times v.3 n.33 (8/21/70), p. 21.
- 9/7/70: Jerry Garcia & Friends; Matrix; calendar item in Good Times v.3 n.35 (9/4/70), p. 16.
- 9/8/70: PERRO jams at Heider's: JG, Jorma, Jack, Kreutzmann ("Jam"); source: PERRO tapes.
- 9/14/70: Jerry Garcia & Friends; Matrix; calendar item in Good Times v.3 n.36 (9/11/70), p. 16.
- 10/12/70: "Jerry Garcia, Merl Saunders and Friends"; Matrix; based on newspaper advertisement as listed at TJS; first TJS listing for Garcia & Saunders; spurious JG listing since GD were playing in Paterson, NJ.
- 10/13/70: as above, though GD had no gig until 10/16 in Philly, and JG could well have flown home.
- 10/14/70: as above.
- 10/19/70: Jerry Garcia and Merl Saunders; Matrix; calendar item in Good Times v.3 n.41 (10/16/70), p. 20; in the past we would have discounted this, since GD was in Minneapolis on 10/18 and Washington, DC, on 10/23, but I have increasingly come around to the view that he flew home more often than I might have thought, and likely as not played a gig whenever a night was open around this time. So I buy that this could have happened.
- 10/26/70: Jerry Garcia and Merl Saunders; Matrix; calendar item in Good Times, v.3 n. 42 (10/23/70), p. 14. GD were between St. Louis (10/24) and Stony Brook (10/30), but on the logic just above I believe this could have happened.
- 11/1/70 or 11/2/70: Janis's wake. Not relevant, just wanted to keep the record straight.
- 11/2/70: I have a Jerry Garcia & Friends listing for the Harding Theater, but no source info. We have discussed this a little bit, but I am not sure where things stand.
- 11/3/70: PERRO/If I Could Only Remember My Name (IICORMN) session at Heider's ("Cowboy Movie"); based on Steve Silberman "Crosby Connection" show played on KPFA, ca. 2001.
- 11/3/70: Jerry Garcia and Merl Saunders; Matrix; note that this is a Tuesday; calendar item in Good Times v.3 n.43 (10/30/70), p. 16.
- 11/4//70: PERRO session at Heider's; no source information listed.
- 12/1/70: Jerry Garcia and Merl Saunders; Matrix; note: Tuesday; calendar item in Good Times v.3 n.47 (11/26/70), p. 20).
- 12/2/70: Jerry Garcia and Merl Saunders; Matrix; listed at TJS based on Joey Newlander newspaper research (Berkeley Barb).
Thatsalotta data, I know, but I wanted to put it out there for you all to see.
What do I infer from all of this about the titular question? The pivot looks to be right around the time of the 8/21/70 Brewer & Shipley session. (Full disclosure: in personal email, Corry played up the Brewer & Shipley connection to Danny Cox, and thence to Merl; so credit should go to Corry for helping me see the break in the series.) There's only one Wales listing a few days later, and then come the "Jerry Garcia & Friends" listings. I would guess that Merl became a "Friend" at the 9/7/70 Matrix show (otherwise why not list Wales, as they had all year?), but there is no smoking gun in these data. Merl's name doesn't appear in listings until 10/12/70, which has the drawback of being a listing known to conflict with GD performance 3000 miles away. But it certainly suggests that Merl was definitely around by this time.
I believe I spoke with Danny Cox, and he doesn't have any old paperwork regarding his sessions at Heider's. I have not tried to contact the Brewer & Shipley people, but that might be a better lead.
In sum, in answer to the question of when Jerry and Merl first played together (qua Jerry & Merl), I'll say September 7, 1970. And maybe walk back and say that slip_not may know a thing or two. ;-)