For Back to the Future Part III , Hill Valley 1885 was filmed in Sonora, California . The producers were able to use the land rent free as long as they left the buildings there. They agreed to leave everything except the Clock Tower. Interestingly, on August 10 , 1996 , a lightning bolt struck the town and it burned down. An arson fire on the Universal Studios Hollywood backlot on November 6 , 1990 had previously destroyed much of Courthouse Square, the setting in which all the other time periods were filmed. However, the Courthouse itself survived the devastation.  Another backlot fire on September 6 , 1997 again damaged Courthouse Square. In both cases, the backlot facades were then rebuilt. The Sonora location was not rebuilt. In addition, a February 14 , 1999 fire at Whittier High School , where some (mostly exterior) scenes were filmed  , destroyed the old men's gym there.