Doc: Marty. You're not thinking 4th dimensionally! You'll instantly be transported to 1885, and those Indians won't even be there.
Marty: Right.
Doc: Well, good luck, for both of our sakes. See you in the future.
Doc pats Marty on his shoulder.
Marty: You mean the past.
Doc: Exactly!
Doc runs to the building with a pistol. It's the same pistol he used in 1985 to try and shoot the Libyans in Part 1.
Doc: Happy trails Marty! Ready Marty?
Marty: Ready!
Doc: Set!
Marty: Hi ho silver.
Doc pulls the trigger and Marty sets off.
Doc: Viya con dios!
Just before he hits the screen and the mural of Indians, he travels through time.
SEPTEMBER 2, 1885
Marty arrives in 1885, only to see a tribe of real Indians heading towards him.
Marty: Indians! Argh!
Marty turns around and heads away from them, but they are chasing him. Marty spots the cave Doc mentioned in 1955.
Marty: The cave!
Marty drives the DeLorean into the cave as the Indians leap over it. They seem to be riding away from something. Marty gets out and discovers what they were riding away from...
Marty: Shit, the cavalry!
Marty runs back into the cave as the Cavalry ride past. They don't see him. Once it is safe, Marty checks the DeLorean. There is an arrow in the side of the car.
Marty: Damn, I ripped the fuel line.
Marty pulls the arrow out and some of the gas starts dripping out. Marty's reckless driving over rocks has damaged the fuel line. He goes back into the car and pulls out the photo of the tombstone, the boots Doc gave him and the letter. We cut to behind Marty, as we hear a growl. Marty turns around to see a big bear heading for him.