If this isn't the right place for thise please move it to where it is most appropriate. Several years back I was by a train track and saw several small vehicles traveling along the track. It appeared they were on a camping trip? This was an abandoned rail and I have always thought that was the neatest thing. I have no idea where any information could be found on this adventure or even if it is legit? Was wondering if maybe someone here had more info on this.
Welcome, simonsen!
It almost certainly was a legitimate expedition organized by an affiliate of http://www.narcoa.org/, the North American Railcar Operators Association. If you look under the "Excursions" tab on their site, they have a list of past trips - perhaps one went by the campground you stayed in? If it isn't on their site, try searching for "track speeder" and the location of the campground, as some other organizations have recurring (legitimate) trips along semi-abandoned railroads.
It's very rare in this era that private speeder operators risk their cars on track without permission, since the risk of arrest, destruction of (their) property, and injury or death is very real and very severe.