I have seen rotting tree stumps and debris create something similar to this. Especially from oily trees such as cedar and pine. Oil or gas would seem to be a more probable cause however.
Captain your the man!! I bet that's what it is. I have cut down about 17 trees in this area just above this and still have about 5 stumps I have not ground out yet. They were cedar trees and Hickory trees. I wonder if its coming from them rotting in the ground? A couple of these trees were a good 25 inch in diameter.
