In May of 1967, The Dead, largely holidaying and rehearsing at the Russian River, had a regular Monday night gig at The Rendezvous Inn. The Rendezvous was a gay bar on Sutter Street, just above Powell, near Union Square. I don't know for certain the exact days, but McNally says they began "a brief series of Monday nights" (p.193) and the dates listed here are the first four Mondays in May. The band had a gig on May 29 in Napa, so I have assumed they played the first four Mondays in May.
There had been gay bars in San Francisco since at least the 1950s, though they kept a much lower profile than they did subsequently. The Wildflower, an Oakland group, played at least some of the gigs, and their manager was Bill Belmont (McNally, p. 288). Belmont worked for the Dead in late 1969.