Okay I have had a chance now to look over these documents. Just because something is an historic site does not make it public land. Those are great links for the history of the site, but do you have any evidence about this being public land?
This does look like SFPRP - single family private residential property - from the property outline on Google Maps in layers, to the street view of the mailbox and driveway to the property. Just being adjacent to a public trail is not enough, as clarified here: Private Residences, Farmland & K-12
A search on the address in your screenshot brings up listings for a single family home that last sold in 1996, but nothing about this becoming public land. Or do you have a resource that shows this is a business where riding lessons are taught? I couldn’t find anything that would show that this property could be eligible.