The cache is not located at the posted coordinates, but there is a sign with clues.
The final is at :: N39 14.671 W84 45.6X0
There's a little graphic titled "cut-away view of sinkholes" in the corner of the sign. X is the number of whole blocks (rocks) on the bottom row (below the sink hole) of the graphic (don't count the half blocks on the left and right ends.)
The cache is a preform tube.