I'm not sure if this is what you are talking about, but I know here in Nebraska, there are "Auto-Tour" routes that kind of follow the Oregon Trail and the Morman Trail. Alot of it is on gravel roads, and follows along the approx. route, going by historical markers and the like. I used to have a map book of them as they crossed Nebraska that I picked up in Kearney at the Great Platte River Road Archway (also worth a stop, as it sits over I-80) but I seem to have misplaced the book. Hope that helps answer your question. Now, I have to find that book again...lol