76 Marin Headlands Line on Golden Gate Bridge, June 13, 1976. SFMTA Photo | SFMTA.com/Photo
Photo by Bill Owyang, Public Utilities Commission Photographer.
Sadly, the 76X, the successor line, has not been reinstated after it suspension in early 2020, so it's not currently possible to take a weekend visit to the Marin headlands by public transport alone. It might well be the last route brought back, but I really hope it makes it at some point.