Well, well, well ... just found a review of a Maria Muldaur show at BCT on Saturday, October 12, 1974 in the Berkeley Barb (Wikarska 1974). Maria worked with three bands this night.
1) David Nichtern (I presume "and the Nocturnes"): Nichtern, Hank DeVito on steel, Larry Jones on bass, and Claude Pepper on drums. Nicolette Larson sang some.
2) Great American Music Band: Maria sang and played violin with the main band of Richard Greene (fiddle), David Grisman (mandolin), Ellen Kearney (rhythm guitar, vocals), John Carlini (guitar) and Joe Carroll.
3) Maria's band: Merle [sic] Saunders, Paul Humphrey, John Kahn, Jerry Garcia, Martin Fierro.
Beyond being new to The List, this is the earliest confirmed Garcia-Humphrey shared stage event, supplanting the next night at the Santa Barbara County Bowl. No mention of what this act played (some songs are given for the other acts), but either way, JGMS serving as Maria's backing band certainly tickles the imagination.
! ref: Wikarska, Carol. 1974. Maria Muldaur's Body Song. Berkeley Barb, October 18-24, 14.