You had me until I saw that PRR baggage car go by. 
I like the high-low layout, feels like moving through the SOCAL Passes. Looking forward to seeing more progress.
Joe
MTL
Thanks for the comments!
I run all the trians on the current setup to, both, test the cars as built/bashed, and to prove the layout in it's current trackplan form...the below-the-track landforms are pretty much 'set'...(I'll 'dig' a shallow wash where the upper track 'girder bridge' is...the lower track will cross it on a ballasted deck timber trestle)
The area in the center of the layout will be filled with the the eroded rock hills that form this part of Kingman Canyon...the foam is simply painted with a latex Earth paint to hide the blue and pink foam temporarily...it's will be exposed again as I permanently shape the landforms and add celluclay and sculptamold...
As I started, in earnest, to model Santa Fe's # 7 and 8, the Fast Mail...I received an amazing amount of help with info about this train...and specifically learned that interchanged cars were a very common sight in the consists...specifically cars from NYC, Erie, New Haven (added @Chicago...bound for LA) and cars from PRR, B&O, ACL, MP, MKT (added @Kansas City...bound for Texas and LA and points in between)
I was fortunate to be able to acquire the various components of a Hell Gate Models PRR B60b kit... a frequent sight on the Fast Mail, as is the X-29 Express Box...I'm in the process of adding a couple of NYC converted troop sleepers, and doing my best to acquire an Erie baggage...trying to have a representative consist from 1957...up to 19-20 cars...in various forms, sometimes with an appearance of express reefer blocks for Eastbound markets...others with sealed baggage-express with Holiday periodical and mail bound for the west Coast...extra cars will find their way onto the Grand Canyon!
Thanks again,
Bruce
