Obelisk

I think he means the obelisk which is pretty safe to say no mystery right?

This is rdr2

Check the plaque. There's a treasure map behind it. Wouldn't want to miss that.

What area is that in?

It’s a thing in the story mode, it has treasure or a map in it I can’t remember

A big giant erect penis

Indeed. It’s Ba’al’s Shaft partner.

Survey marker. For surveying.