Interesting. So are ALL abandoned tracks technically still owned by various railroads? I know nothing about this stuff.
Well... kinda, but no. Don't quote me on this, but as I understand it...
Tracks have to be maintained up to a certain standard before they meet official abandoned criteria. If a track is officially abandoned, any railroad can move in and claim it, if they get it back up to running shape. Obviously there is a lot of value in railroad lines, so if a company isn't using a line, they'll put it on the back-burner and do the bare minimum to keep it up to FRA standards. Bare minimum is limited to 10 MPH, by freight traffic only. Many industrial tracks are maintained to that standard.
We have a track that we care for that doesn't get used, but we maintain it. The Tennessee Pass is crazy, it's steep and climbs to over 10,000 feet elevation at Leadville, CO. Winters are BRUTAL up there, I hear stories about it all the time. We were actually up there this Summer repairing a crossing.