An interesting thread, thanks.
Here in SW Ohio, there's essentially zero gravel roads. Even the lane-and-a-half farm roads are paved.
New York State
I rode part of this route in New York State last summer, found on a "riding the Catskills" blog. The route was tagged "Worth the Trip". Yes, it was.
The gravel roads were all nicely maintained and graded. A nice mix of woods and farmland. Some steep hills along the way.
Here's the blog post with a map and photos:
Meridale 43
A couple of snapshots from my ride:
Old rock fences in the woods.