- "There were new explosions — this time from that strange silver railroad car in front of the locomotive — three explosions and three flashes of light. And then, that strange car vanished from the tracks — just completely disappeared except for two trails of flame! But the locomotive, still beside them [Doc and Clara, floating on the hoverboard] roared onward, through a barrier erected across the half-built bridge, over the end of the tracks and down into the ravine. There was an explosion greater than any Clara had heard before as the locomotive hit the rocks below."
- —From Back to the Future Part III by Craig Shaw Gardner (quote, page 199)
Locomotive 131 was a Central Pacific Railroad steam locomotive that hauled passenger and freight trains ton a one-way circuit on a single track, stopping along its westbound route at the Hill Valley Railroad Station, with San Francisco, California at the end of the line. It was able to complete the circuit in three days, and normally cruised at 25 miles per hour with a top speed of 55, although "fearless" Frank Fargo allegedly pushed the speed to nearly 70 past Verde Junction. The engine was a wood-fired 4-6-0 (two axle leading truck followed by three driving axles) Ten-Wheeler type steam locomotive.
The chalkboard next to the ticket window at the station displayed the train schedule as of Thursday, September 3: Sacramento on Monday at 8:00, Haysville on Tuesday, San Francisco on Wednesday, and Carson City on Thursday at 3:30. 
Penultimate visit to Hill Valley Station
On Friday, September 4, 1885, the train brought the town's new school teacher Clara Clayton among its passengers, and delivered the clock for the new courthouse. "Doc" Emmett Brown and Marty McFly took the opportunity to ask the engineer whether a steam locomotive could go as fast as ninety miles per hour (which theoretically could be done if the train wasn't hauling any cars behind it and if the boiler was heated to dangerous levels), and the day and time the train would return, in order to devise a way to push the DeLorean that fast.
Last visit to Hill Valley Station
The train returned to Hill Valley with several passenger cars three days later with a different engineer. It departed from the Hill Valley Railroad Station at 8:00 AM on Monday, September 7, 1885, during the duel between Marty McFly and Buford Tannen.
Clara Clayton, the barbwire salesman and another man were among the passengers leaving town on the train. After Clara overheard from the two men how much Emmett Brown loved her, she intervened and stopped the train to go back to him.
The train restarted, and before reaching Carson Spur, it was hijacked by Doc and Marty as part of a "science experiment". Under the guise of handkerchiefs, they ordered the engineer and his fireman to uncouple the cars from the tender just before the junction. Doc and Marty took the locomotive to the DeLorean time machine, which they had unloaded onto the tracks in front of the silver mine.
The "science experiment" and its destruction
Doc and Marty pulled up to the DeLorean and begin to push it. Doc also showed Marty his presto logs that he would throw into the fire. As the train left the mine, Clara came over the hill on horseback. Clara caught up to the train just as the green presto log ignited. While Doc walked along the edge of the locomotive's boiler towards the DeLorean, Clara neared the cab and the second yellow log exploded, throwing her backward on the wood pile. When she reached the cab, Doc was already up to the front of the locomotive and she blew the train's whistle, getting his attention. As they passed the Point of No Return, they attempted to reach each other, and soon thereafter, the red log exploded, and the train began to fall apart. Clara lost her balance and dangled from the locomotive by her dress.
At about ¼ mile, Marty placed his hoverboard out the door of the DeLorean and released it, and Doc caught it with his foot. Doc grabbed Clara as her dress tore and they escaped from the locomotive. Marty closed the hatch on the DeLorean as it reached 88 mph, and entered temporal displacement at the last second before crashing into a wooden "End of Track" barrier. The locomotive crashed through the barrier, continued off the incomplete bridge, plunged into Shonash Ravine and was destroyed in an explosion. Marty soon arrived back in the present where his DeLorean was destroyed by an oncoming freight train.
In the years that followed Marty's trip back to 1985, Doc constructed a new time machine made from the same train that got destroyed.
Behind the scenes
- The locomotive that portrayed No. 131 was "Sierra Railway No. 3", built in 1891 by Rogers Locomotive Works of Paterson N.J., and brought to California in 1897 — one of several historic trains at Railtown 1897 State Historic Park in Jamestown, Calif. It is also known as the "movie star" steam locomotive because of its appearance in over 100 films and television shows. Sierra No. 3 underwent restoration in 1998, and was returned to service on July 3, 2010  at Railtown 1897 State Historic Park in Jamestown, California. Unlike the Central Pacific No. 131, Sierra Railway No. 3 is an oil burning steam locomotive.
- By 1885, the Central Pacific Railroad was bought out by the Southern Pacific Railroad, but the Central Pacific name wasn't dropped until 1891.
- Filming the train scene in Back to the Future Part III took around seven weeks.
- The footage of the train moving forward is reversed. To prevent the DeLorean from rolling off the tracks on the curves, Sierra No. 3 was pulling the car backwards to minimize chances of injury to the cast. However, tender engines such as Sierra No.3 can only reverse at around 40 m.p.h. or the tender will derail. Hence, on-screen the Locomotive No.131 appears to only be traveling at around 40 m.p.h.
- Railtown 1897 State Historic Park in Jamestown, was used constantly throughout the 20th century for Hollywood Western Films, most of which featured Sierra No. 3. Films and TV series such as Bonanza, Petticoat Junction, Back to the Future Part III and The Kansas Pacific all filmed their train scenes with Sierra No. 3 on the tracks of Railtown 1897 State Historic Park in Jamestown.
- The real Central Pacific #131 was a 4-4-0 American (4 pilot wheels in the front and 4 driving wheels in the back) built by the Rhode Island Locomotive Works in November 1868 and it carried the name Greyhound. It was sold to an unknown buyer in January 1872.
- The whistle was later reused for the Polar Express in the 2004 movie The Polar Express.
- Back to the Future Part III
- Back to the Future Part II & III
- Back to the Future Part III (video game)
- Back to the Future: The Animated Series
- Back to the Future: The Card Game
- Back to the Future: The Game
- Back to the Future: The Game - Episode 1: It's About Time (One of Edna's newspapers describes Clint Eastwood plunging to death on a runaway locomotive.)
- Back to the Future: The Game - Episode 4: Double Visions (Mentioned only)
- "4-6-0 locomotive" on Wikipedia
- "Clint Eastwood? Hill Valley Online. Accessed 12 February 2008.
- Steam locomotive profile: 4-6-0 Ten-Wheeler Classic Trains Magazine, June 24, 2006.
- "Fundraising Campaign Goes Full Steam Ahead to Restore Sierra “Movie Star” Steam Locomotive No. 3" Railtown 1897 State Historic Park.
- Hill, Kevin, "Return of the Movie Star Sierra #3 is Back", YouTube.com, posted July 6, 2010.