Do you mean private, non-tourist carriers (and not the former Rio Grande lines in Colorado)?In 1976 we got a cab ride on the US Gypsum line out by Plaster City, Ca., but that was in the "good old days" and not likely to happen today.
There are a few other small industrial carriers here and there but they generally don't accept visitors.
The Carson & Colorado (Independence, CA) is working at restoring an engine back to operation and getting some track built, but it will take a while...
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