Pre-Amtrak, I thought most NYC-California pas train traffic was routed through Chicago and not the Southern route.
Pre Amtrak there were a handful of gateways to the west. Chicago being the main one between the eastern trunk roads and the grangers. It should be noted only two of the Chicago roads actually reached the pacific namely the Santa Fe and Milwaukee Road.
The secondary gateway was St. Louis which used to service the New York Central, Pennsylvania Railroad, Baltimore&Ohio, Southern Railway, Wabash, Nickel Plate Road, Illinois Central, Louisville&Nashville, Gulf Mobile & Ohio, Rock Island, Missouri Pacific, Frisco, Saint Louis and San Francisco (cotton belt), Chicago and Eastern Illinois, Missouri Kansas Texas, and probably some I've forgotten. At its peak St Louis Union Station was over forty tracks and the busiest train station in the world.
Then you have New Orleans as a gateway back then which had the Louisville and Nashville, Kansas City Southern, Southern Railway, Southern Pacific, Gulf Mobile and Ohio, Illinois Central, and a few others.
The other western gateway was Minneapolis Saint Paul between the western roads and the grangers. At one time services by the Milwaukee Road, Chicago and Northwestern, Chicago and Great Western, Soo Line, Rock Island, Burlington, Great Northern, Northern Pacific, and I think that's it.
And the smallest of the gateways was Memphis of whom I forget every railroad that served it. But I know Southern Railway, Rock Island, Illinois Central, Gulf Mobile and Ohio, Louisville and Nashville, and maybe a handful of others. But like I said a very small hub.
A more eastern Midwest gateway was Cincinnati.
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Amtrak Routes I've riden: Silver Star(NYP-ORL), Silver Meteor(KIS-NYP),Carolinian(CLT-NWK), Palmetto (FLO-NYP), Acela(WAS-NYP), NE Regional(WBG-RVR), Pacific Surfliner(SAN-OSD), Piedmont(CLT-SAL), Crescent(NYP-CLT), Cardinal (WAS-CHI), Capitol Limited (CHI-WAS), Cascade (PDX-SEA)
Steam Engines I've worked behind: Norfolk & Western No. 611; Nickel Plate Road No. 765; Southern Pacific No. 4449