The Universal Studios backlot was used for Courthouse Square in 1985A.
This is the transcript of Commentary with Bob Gale and Neil Canton during the scene where 1985 Doc meets 1955 Doc who is setting up the "weather experiment":
Bob Gale: "And this scene was shot the Friday night of the first week of shooting. We had to get all this 1955 stuff finished so that the art department could tear down the '50s and turn the back lot into Biff’s hellacious 1985 -- 1985A, as it’s referred to in the movie."
Using special effects, only an image of the Plaza Hotel in Las Vegas was inserted above the courthouse, plus a neon sign reading "Biff's" at the top. Western Union 06:48, 8 March 2008 (UTC)