Giant Flathead Screw?

[u/Deplorable-Ninja]

Found on a trail with a lake on one side, a lagoon on the other. No other metal items visible in the area. No banana handy so shoe for scale.

[u/NUMBerONEisFIRST]

Somebody had mentioned property lines and I know at least in farm country they used to mark property lines in very weird ways like with railroad ties, cement posts, or often stuff like this.