The orriginal UP Mainline is officially called the Los Angeles Subdivision. The former SP Mainline is indeed called the Alhambra Subdivision. With UP's practice of directional running, Eastward trains run on the Los Angeles Subdivision, Westward Trains run on the Alhambra Subdivision. There are many exceptions to this, depending on where the train is orriginating or terminating from. For example if an eastward train is headed to West Colton Yard, then it would usually take the Los Angeles Subdivision to Pomona, then the Alhambra Subdivision to West Colton. It is also up to the two dispatchers at West Colton to coordinate the moves on these lines. Normal practice also calls for Amtrak trains to operate on the Alhambra Subdivision and Metrolink trains opeate on the Los Angeles Subdivsion. Amtrak was supposed to do directional running on these lines a few years ago, UP and BNSF had approved it (Amtrak would have had to have used the BNSF San Bernardino Subdivision from West Riverside to the Town of Colton to make this work), but 1, Metrolink did not (as Train #2 would have used their River Subdivision, East Bank line from CP Pasadena Jct. to Soto St.) (where the Los Angeles Subdivision begins) and 2, the city of Ontario protested this, knowing they would loose Amtrak service with this practice. If Amtrak service becomes daily later this year, directional running may become a reality.
The Los Angeles Subdivision is on channel 27 (160.515 Mhz). The Alhambra Subdivision is on channel 42 (160.74 Mhz). There are several other channels in use as yard and terminal channels, but to numerous to mention here.
The old State Street Line is now the Metrolink San Gabriel Subdivision and is on channel 87 (160.415 Mhz). It was sold by SP to SCRRA, I think the year was 1991. Part of the deal was that SP could no longer use this line period, except to service local customers on the LA and El Monte end. I don't think there is any local freight business on the ends of this line segment anymore. The last Metrolink employee Timetable I ever saw, stated the freight trains were prohibited on the middle portion of this line.
Hope this is helpful and enjoy your visit!
THE END