Continuity mistake: When Jack's trying to outrun the guys shooting at him, they shoot his tire, sending the trim ring flying. However, when the car nails the tree, the tire looks completely undamaged and the trim ring is back on.
Continuity mistake: There's a very cool shot of Katherine Cross and Hollis Mulwray's reflection in the camera lens as Jake takes their picture from a roof top while they're having lunch. The problem is as the cameraman zooms in, Jake's hands are shaking but the reflection in the lens doesn't. (00:16:05)
Continuity mistake: In the very first scene of the movie Curly looks at the pictures of his wife that Jake took. He gets to the fourth picture and rotates it 45 degrees to get a better look. As he goes on to the next picture he lifts the fourth one up, and in the next shot he's holding a different picture. (00:02:00)
Continuity mistake: Gittes finds Mrs. Mulray's big house being shut down, finds the eyeglasses in the saltwater pond and races to the small house where Mrs. Mulray's daughter had been staying. All their luggage was there at the small house because they were leaving there to go directly to the train station to make their escape to mexico. The Mulray entourage (daughter and servant) hurriedly leaves the smaller house without their luggage since Gittes had called the detectives. After Gittes takes the detectives on a deceptive trip to Curly's and eludes the detectives by Curly driving away with him, the next scene has Curly and Jake putting the last of Mrs. Mulray's entourage's luggage into Curly's truck in front of the Mrs. Mulray's large home, not the smaller house where the daughter had been staying and where they had all their luggage together to go straight to the train to escape to Mexico. The sequence should have had Gittes retrieving luggage from the smaller house.
Other mistake: While reading a book in the Hall of Records, Jake notices some names are pasted in. One of the pasted in names is spelled "Clarence Speer." The name comes up again as Jake Gittes and Evelyn Mulwray are driving away from the orchards. The name is spelled in the subtitles "Clarence Speer" and Jake pronounces it "Clarence Speer." Later Jake and Evelyn are reviewing the Mar Vista Rest Home Activities Board. Here the name is spelled "Clarence Speers." (01:07:35 - 01:17:25)