I have been working the last week or so on a Third Division D&RGW video, and it covers Gunnison(Marshall Pass), and Monarch. Both are really nice places. I remember years ago we stopped at Sargent which is right off the main highway east of Gunnison. There used to be a lot of remnants of buildings and things there, at this former helper spot.
US 50 crosses the Monarch line several times. Going north about the 2nd crossing of the old roadbed would have the Garfield Switchback with the tail of the lower end to the west, and the middle part of the switchback to your right. Standing at the crossing you should be able to see the approach to the crossing and the section they had to back through going upgrade. It was a really neat piece of railroad from seeing the films and books, etc. Not much to see in Salida as I recall, although you can see where the NG left town and the old bridge.
Was out that way in 97 and we shot the SG before it was mothballed over Tennesses Pass. I remember you could see the old NG roadbed west of Salida a ways, probably to Poncha Springs(Jct).
I always felt there was so much good steam to see with the D&S and C&TS that in recent times I never did much looking at former lines,except Chama-Durango once or twice.
Sounds like your inital plans were pretty solid though.Have fun and be safe.
Greg