The line in front of Cabela's is currently out of service. It is the former UP line. UP stashed some empty flat cars on it a couple of years ago, but it hasn't seen real traffic in years - maybe since about the mid to late 80s. At that point, the rising Great Salt Lake threatened the Rio Grande line between Salt Lake and Ogden, so the Rio Grande and the UP worked out a deal: The Rio Grande ran on the UP from North Salt Lake to Ogden, and the UP ran on the Rio Grande from Salt Lake to Provo (a much flatter line - it goes through the Jordan Narrows rather than over Point Of The Mountain).

I'm not sure who owns the line right now. It could be the UP, or it could be UTA. My guess would be UTA.

Yes, the D&RGW went over Soldier Summit. It deviated from the current line, though, by not making the big loop at Guilluly. There is a location named Detour a bit further down the hill (about at the highway overpass - not the one at Guilluly, the overpass below that). I presume that this Detour is where the new, lower-grade line departed from the previous, steeper line.