Robby that is nice. Is it on your own land? I would seriously consider having the landowner whomever it is, contact the nearest university or researcher of petroglyph's in the area and find out what it means. It would be very interesting in the least.
Wow that's really cool! My first thought was petroglyph as well, although all the petroglyphs I've seen have been quite abstract compared to yours. I don't think I've ever seen one with such a straightforward image. If I were you I'd get in contact with someone at the local university or historical society, I'm sure they'd be interested to know about it and could probably shed some light on its history. It certainly looks old, although I don't know if that means it's thousands of years old or just something that someone who was bored in the 19th century did.
Already on it but with this cor19 going on a reply might take some time. No rush. It has been there this long. Its not going anywhere. Not on my propery it is on public access land. Just no one in their right mind would go where i go in search of my next bottle discovery.
I went back with a decerning eye and a short sawsall blade and tested the hardness of the stone and it is not soft by any means. I could scratch the back side of the boulder barely and it made short work of the teeth. Must have taken then some time. Must have had a reason. Could have been real bored. I been doing tile work my own business for 35 years. They had to use a chisel or something. I dont see any scratches that even tell me what they used. I dont think i would even attempt to recreate it. Way to hard for me and i have more patience than anyone i know.