The cache is coming from inside the guardrail!
I was thinking to myself, "Why isn't there a geocache here already?" as I was approaching GZ, and as it turns out, there IS a geocache here already! It's just not on the map for some reason.
Well, that container was pretty old and grody anyway, so I replaced it with a new bigger container (and a new listing) with some trade items inside. No pen; please bring your own.
Unfortunately, if you logged the cache that was here before, you will have to come back and do so again with this one.
Congratulations to 2bJPN for the FTF!