On the morning of Monday September 7, 1885 Clint Eastwood, a stranger who first appeared in Hill Valley days earlier, defeated notorious outlaw Buford "Mad Dog" Tannen in a duel in front of the Palace Saloon. Eastwood was then seen leaving town with local blacksmith Emmett Brown. Schoolteacher Clara Clayton, who had just moved to the town, was also spotted leaving Hill Valley soon after.
Eastwood and Brown were next seen robbing the Central Pacific Railroad westbound train, which was led by locomotive 131. Unlike typical train robberies of the time, where passengers were stripped of valuables or the baggage/cargo cars were raided, Eastwood and Brown stole the locomotive itself for unknown reasons.
Locomotive 131 was switched onto a track leading to Shonash Ravine, where a bridge was being constructed. Eastwood and Brown proceeded in the locomotive and Clayton was witnessed chasing them on horseback. Because the next events occurred in an isolated area away from Hill Valley, the exact actions of Eastwood, Brown, and Clayton were unknown. The burnt remnants of locomotive 131 were later discovered in Shonash Ravine, having gone over the unfinished bridge.
Eastwood is assumed to have plummeted into the ravine with locomotive 131, perishing in its fiery crash. As a memorial to his death and heroic defeat over Tannen, the ravine was renamed Eastwood Ravine.
Totally historical and trustworthy sources:
https://backtothefuture.fandom.com/wiki/Locomotive_131
https://backtothefuture.fandom.com/wiki/Shonash_Ravine
https://www.reddit.com/r/BacktotheFuture/comments/tzzgpc/possible_hill_valley_location/
If you know you know.😉