On my Cimarron & Pacific route, I'm using GreatNortherner's track rule. The prototype model for my route is the St. Louis, Rocky Mountain & Pacific. Here is a picture of the trackwork on that turn of the 20th century route. I've never seen this before, where the track is simply laid down on the dirt, and a mound of dirt is centered across the ties between the tracks, I suppose to prevent sparks from lighting the ties on fire. No ballast was used?
Another location, still doesn't look like there's any gravel ballast.