Originally Posted by Laserschwert
I'm pretty sure I've found a plot-hole in part 3, but I can't quite remember exactly what it was... I think it had something to do with the Shonash Ravine being called Clayton Ravine back in 1955, although - with 1985-Doc already back in 1885 - Clara didn't fall into the Ravine, because Doc picked her up from the train station (so that the Ravine wasn't named after her), and 1955-Doc would've never known it as the Clayton Ravine (and still he calls it that).
Of course, we never know if Clara didn't fall into the Ravine AFTER Doc's death in 1885, so it might just as well not be a plot-hole at all.
Your 1955 Doc there is in a different timeline in which it is Clayton Ravine.
When Marty finally returns to 1985 from 1885, he is in a new timeline in which it is called Eastwood Ravine. And if he had decided to return to 1985 a day before the original time travel from the first movie, he would have encountered a 1985 Doc Brown who knew the ravine as Eastwood Ravine.
Though there are plotholes-- especially with the Biff returning to 2010 bit... a lot of the confusion about what to expect boils down to understanding the notion of each trip to the past creating a new divergent timeline.