What is this Structure?

Gate. no motor vehicles.

#OsmAnd

campsite. backcountry

Gate. no access to private property.

#OsmAnd

Gate here is general access yes

#OsmAnd

there is no track connecting to main road

#OsmAnd

I don't think there's a monument here. On older topo maps the word "monument" is there, but its along a line that later says "border" so it's just saying a line along there is a "Monument Border".

From Bing Satellite imagery, this looks like either a mine shaft or just some excavations done for mining exploration.

this is a path here.

grade 5 or worse... very over grown track