Tony Saunders is the bassist on these two tapes.
The Jerry Site has listings for Jerry Garcia and Merl Saunders at Keystone, Berkeley, on July 21 and July 22, 1974. I doubt both date/venue combinations, for reasons I'll lay out below.
A) "JGMS 7/21/74, Keystone, Berkeley"
This first date is so obviously spurious that it barely bears laying out, but in the interests of completeness I'll do it anyway.
1) The GD played the Hollywood Bowl this date. Depending on show times both would be possible, but this seems extremely unlikely on its face.
2) Keystone billed Moby Grape and Earthquake on Sunday, 7/21, as evidenced by a Scenedrome listing in the Berkeley Barb:
Regarding "7/21/74", I therefore conclude that this date was attached to some Betty Board snippets merely as an anchor (i.e., for ease of identification). When/where the material is actually from is anybody's guess (and I'll take a flyer below).
B) "JGMS 7/22/74, Keystone, Berkeley"
This may be the tougher case, since there is a quite delicious Betty Board (e.g., shnid 86198) in long circulation. (If you don't have it, get thee to the to your favorite Bit Torrent site forthwith!) The tape is notable for an as-yet untitled standard that starts things off, as well as the only-known (to me) JGMS version of Cucumber Slumber.
However, there is some reason to doubt this date/venue combination.
1) Saunders and Fierro appear to have been billed at the Sand Dunes bar on this Monday night:
posted about the Sand Dunes and the fact that Merl and Martin were playing there on Monday nights, with Jerry's at-least occasional participation. It seems likely that all three of them were at the edge of the Western World (i.e., the far western Sunset District of SF) on 7/22.
2) The bassist on these tapes is confirmed to be Tony Saunders. Tony Saunders played in his father Merl's bands at the Sand Dunes and The Generosity.
3) Keystone Berkeley's listing in the Hayward Daily Review, July 19, 1974, p. 36, bills Nite Shift and audition bands. Now, this could easily be moved for a Garcia appearance, I am sure, but it's just another strike against a JGMS show at Keystone Berkeley on this night.
4) As the Jerry Site notes, in remarks added by slip and seemingly attributed to 'strumminsix,' the recording features "Boogie On Reggae Woman" from Stevie Wonder's Fullfillingness' First Finale, which was apparently released on July 22, 1974. Now, it wouldn't shock me that Merl and/or John might run down to the record store first thing and get the new Stevie Wonder album. But I'd be slightly more surprised if the band could have absorbed it enough to play it that night. This leads me to question whether the circulating material dated as 7/22 is actually from that date.
5) Finally, reinforcing these doubts just expressed, the newest iteration of this "7/22/74" material (again, shnid 86198), may not be all from one performance. This would have to be checked more carefully than I am able to do, i.e., in listening for source changes in the recording, but it's a possibility that joins with all the others to raise some doubts.
Based on all of this, I conclude that Garcia and Saunders were not at the Keystone, Berkeley on July 22, 1974. The material circulating as "JGMS 7/22/74, Keystone, Berkeley" is either from another date, or from another venue, or is a hodge podge of material from other dates/venues.
C) A Final Thought
Putting things together this way reveals a tantalizing possibility: maybe all of this material is actually from the Sand Dunes from around this time (e.g., 7/21/74)? Everything we have, including a tape label the dating of which coincides with a brief flurry of Martin-related items in the Oakland Tribune, and includes Tony Saunders, who played in the band at the Sand Dunes.
Alternatively, maybe it's from The Generosity. The newly polished/circulated Castelli tapes from 2/14/75 (shnid 108896) and 5/9/75 (May 9th) (shnid 107829) reveal some things in common with these "1974" tapes, the appearances of "When I Die" and other seemingly-very-rare instrumentals (Cucumber Slumber, What's Going On, and the unidentified tunes) being most prominent. [Note added 20111216: These song selections are only unusual if this is actually JGMS, which it almost certainly isn't. This may have been the standard Monday night set for the Merl Saunders/Martin Fierro outfit at the Sand Dunes, or Aunt Monk at The Generosity! Tony Saunders played bass in both outfits, and he is present here.] The possibility identified in point B4 above, that BORW might need to be from later than 7/22/74, could be seen as reinforcing this possibility.
If forced to bet I'd say that both of these tapes are approximately-correctly-dated performances of the Merl Saunders-Martin Fierro group --Saunders, Fierro, Garcia, Tony Saunders, and an undetermined drummer-- at the Sand Dunes, 3599 Taraval Street in the Sunset District of San Francisco, CA, 94116.
And, regardless of all of this, I highly recommend all of these recordings to you. They're awesome and show Jerry playing amazing, unfamiliar material when he is truly at the top of his game. Two snaps up.