Definitely death traps. But, I don't think it's the mine opening kind. I'm not sure there's anything of value. I think it was a somewhat-fortified camp. There's a matching area, nearly symmetical 20 feet away, and it's just flat land with no rocks and a tree. At this site, there are at least 100 monuments, probably more then 30 turtles.
I've seen several deathtraps within a 10-mile radius of the site, and they can't all be hiding silver and gold. Actually, this was a coal mining town, so if there was precious metal, someone would have probably found it. My wife, who has no interest, spotted one off the side of the road (with a horsehead, no less). We're talking 10'-20' high boulders or even rock walls. They are solid enough for me to sit on/climb up and down, but many are notched at the bottom.
Gorgias
PS Oroblanco, I think it looks like a ship, too. . . Especially after watching The Holy Grain in America.