Interesting. But I think you're confusing the famous Sutro Baths at Lands End with the gay bathhouse "The Sutro Baths" that operated sporadically in 1970s in the SOMA-Castro area.
There were several exposes written about the latter establishment, and people frequently confused the gay goings on South-of-the-Slot with the much more sedate activities at the historic Sutros.
BTW, the historic Sutro Baths closed down in 1952. Well, the pools did at any rate. And since those pools were open air affairs surrounded by bleachers for thousands of spectators, any sex (gay or straight) would have been difficult to perform.