A rock slide that was described as "very minor" hit one vehicle in the old Sepulveda Boulevard tunnel in Sepulveda Pass Sunday.
City firefighters said a 40-year-old woman was taken to a hospital with minor injuries.
Traffic in the tunnel was stopped while the city Bureau of Street Services workers inspect it.
The three-lane wide tunnel was opened in 1930, and is used today as an alternative to the parallel San Diego (405) Freeway, now under reconstruction.
Sepulveda Boulevard is also being used as an overflow route for traffic displaced by the Coldwater Canyon Avenue closure on Mondays-through-Saturdays.