Andy Capp Cartoon On Rocks

Hi, I hope somebody can help me with this cos its been driving me mad! I'm from the South Wales valleys originally and remember seeing in my childhood a cartoon of Andy Capp which someone had drawn onto a rock. I think it was in the Llangynidr or possibly Rhigos area but just can't remember! Does anyone else remember seeing this in the 60's or early 70's - I have no idea if the drawing is still there...