The starting line was a line painted on a street that led up to Courthouse Square.
Emmett Brown positioned the line at a Blue Bird Motel billboard about a mile from the courthouse and instructed Marty McFly to drive to that point in the DeLorean time machine, push a hook and rod into the flux capacitor and wait for the brass alarm clock Doc had placed on the car's dashboard to go off.
When Marty suddenly remembered he was in a time machine, he reset the time circuits for ten minutes prior to Doc's death at the hands of the Libyans in 1985 so that he could warn Doc. The DeLorean's engine then died. Marty eventually started it up after the alarm went off, drove at speed from the starting line and made it to the cable just as lightning struck the clock tower and Doc was able to reconnect the cable.
Behind the scenes
- It is unclear on-screen as to whether the starting line was on Hill Street or Main Street.
- The real life filming location of the starting line was in Griffith Park.