Yeah, that's the one. Most of the tracks have now been removed, but they still exist through that canyon. They probably still exist on the Lawyer Canyon trestle shown in the picture.
Back when I first walked up that route, it was still active. In fact, as I was about to start out, I saw a train on it. I had driven to the top of the grade, where it emerges onto the prairie, left my car there, then biked back down to the bottom to start up. I had seen the train at the top, about to head down the grade, so by the time I got down to the bottom by bike, which was mostly downhill and fast, I wasn't sure whether the train had passed or not.
The first thing I did was go through a curved tunnel where you couldn't see either end from a point in the middle. That was a bit interesting, with the possibility that a train might be coming. From there, it was just a matter of crossing trestle after trestle. The rest of the tunnels were short, and I could see all the way through them. Most of the trestles weren't bad, either, but there is one that featured prominently in Breakheart Pass (it's the trestle where the fireman falls to his death) because it is so VERY high and fairly long. The area between the rails had been covered in sheet metal, so walking was really easy, as you couldn't fall between the ties, but on a warm summer day, the sheet metal was pinging steadily as it heated in the sun. I couldn't tell whether there was a train coming or not, and on the other side of the trestle, the tracks went through a bit of a curved cut, so I couldn't see far ahead, either.
I watched and listened, sometimes convinced the train was coming, other times thinking it was just pinging metal. Eventually, I sprinted up to the first fire platform and stood there listening for a time, before sprinting to the next platform, and so on across the trestle. As it turned out, the train had passed long before I even reached the bottom of the hill by bike, and I never saw it. Sure made for an engaging hike, though.

