To find the slip up, you must watch the movie to the point where the main character is in an accident when riding with the "Weekend Hippie". Pay close attention here. The time line of the movie is set sometime in the sixties, but in a moment you'll see something that's out of place.

Namely, the exact next shot has the main character standing beside train tracks with a train passing. Note the type of train. That's something called a "Double Stack". It's something you see really often these days, with containers stacked atop each other to make transportation easier. There's just one problem.

Double-stacks didn't come into use until the late Mid 1990's. Which, is about the time this movie was made. It's funny in a way, the director wanted a train in the shot, but couldn't pay to have a special "period" one set up just for the shot. So, they supposedly went to a nearby main line and just used whatever was available.