Active logging operations: The Old Railroad Grade is subject to active logging operations, which means you could encounter log trucks. Such activity typically occurs during the work week, and less so on weekends, particularly on Sundays. If you hear a log truck approaching, get off the road and wait for it to pass. This is for your own safety and in recognition that you are a guest on private property.
Log truck gravel: Most of these roads have reasonable sized gravel much of the time. For that, I recommend a minimum recommended tire width of 40mm. However, these roads are subject to being freshly graveled with big and loose gravel from time to time. For this kind of gravel, you likely will be happier on tires that are at least 2" (~50mm) wide.