Ah, what the heck.
@slip, everyone needs to know about this:
If you make the hike from the parking area out to the Pu'uloa Petroglyphs inside Volcano National Park, you'll end up on a wooden loop walkway. As you look around, there are any number of petroglyphs in the lava rock surrounding this walkway. It looks like this:
But check this picture:
Go to the far end of the loop walkway, then step down off of it. Walk straight ahead, and around the back of the hillside to the right of it, as indicated by the arrow I've put on the picture above. Don't walk on the plants - stay on the dirt. There is no trail at this point, so pay attention to where you are, and how to get back to the wooden walkway.
Here's the secret: There are THOUSANDS of petroglyphs on the backside of that hill. I was told about this by a Ranger more than 20 years ago, and she was right. They're everywhere back there. It's worth the extra effort to find them.
Ssshh! Don't tell anyone!
Dave