Corrected entry: The outdoor night scenes are illuminated by high-pressure sodium vapor streetlights, which did not come into use until the mid-1980s. Streetlights of the 1970s used mercury vapor lamps, which give a quite different bluish-white light.
Corrected entry: When Darlene is parking her car in a "more quiet place", you can see the tire marks of where she is going to park, from previous takes.
Corrected entry: Some of the computers shown in the scenes at the newspaper, set in the 1970's, are a newer style than what was available at the time. They look like they are from the 1980's.
Corrected entry: In the scene the morning after the taxi driver murder, the detectives were driving on a San Francisco street where a 'bus lane only' diamond was visible/painted on the street. These did not exist then.
Corrected entry: Toward the end of the movie there is the scene where Robert Graysmith goes to Arthur Leigh Allen's work place and stares at him for a long time. In this scene you can see Leigh's name tag, but his name is spelled "Lee" not "Leigh". This could be considered not a mistake, however in an earlier scene we see case files with his name specifically spelled "Leigh".