But it wasn't quiet. There was this grinding, whining mechanical sound in the background all day, growing louder as we moved deeper into the woods. It turned out to be this conveyor belt, which carries gravel more than a mile from a pit on one side of the Interstate to a sorting and loading facility on the other.
I thought it had a real 19th-century feel, although it was actually built in 1967.
I especially like the way it turns corners; one belt just ends and dumps its stream of sand and gravel onto another. You can see the spout of orange-brown sand and gravel pouring from one belt onto another here.
Interesting, the things you stumble across sometimes.