Yes, this is the old GM&O Alton Route.
Currently under Union Pacific ownership, but it has relatively light freight traffic, as UP has two other Chicago to St. Louis routes, the ex C&EI and the ex C&NW. The map in July Trains shows 8 trains per day north of Ridgely Yard (Springfield) and 10 south thereof on the old GM&O. These must be UP trains only.
(I say this because looking over the trains map shows 4 trains Hiles Jct. to San Jose, which is less than the Amtrak number of trains. Also, Santa Barbara to Los Anbgeles shows 16 trains, with an average tons per train of 5,000 to 6,999. If this included Amtrak, no way the average train weight could be that high.)
There is something wrong with the map, however, as it indicates one line from Ridgely to St. Louis, and there should be two, as the ex C&NW line out of Nelson IL goes all the way into St. Louis, and actually passes west of Springield not touching Ridgely Yard at all.
One main problem is the attempt to do the upgrade on the cheap. A full rail relay and good T&S (tie and surfacing) are a crying need, but only the curves are getting new rail. My understanding is that the majority of the line will be left with the 50 plus year old 115 and 112 pound rail.