"Pipes running throughout a wooded area. Spotted near a quarry in PA. What are they for?"
A: "They are for tapping syrup sap to make syrup. They no longer use taps and buckets (for large scale production), they string it back with pipes to a central large collector like this."
Thanks Internet.
"... and the liquid will drop through the slit in the middle."
Let's keep it clean; this is not an AO site.