I suspect that this isn't the answer Vance is looking for but here goes anyhow.

The Columbia river flows through the Cascade mountain range between The Dalles OR and Cascade Locks OR. Both the UP on the south bank and BNSF on the north bank follow the Columbia all the way from the east side of the Cascades to the west side.

The Missouri in Montana is another possibility. It starts at Three Forks and flows north and northeast beyond Ft Benton before turning east. Along the way it skirts the Big Belt mountains which are to the east, and goes around them to the north. The BNSF line from Helena to Great Falls follows the Missouri all the way. This line is intact but out of service and is used for car storage.

How about another hint, Vance? Maybe like North east, South east, Rocky mountain states, or far west.