In a “Girls of the Golden West” pre-premiere conversation onstage at the San Francisco Opera House on Tuesday, Nov. 21, director/librettist Peter Sellars, along with longtime opera collaborator and composer John Adams, told dramaturg Kip Cranna they’ve been working on the project for years because “everyone’s always talking about California.” Sellars seemed turned on, animated, eager to share ideas — perfect qualities for a collaborator.