The NYC law allows "significance" evaluations and designations for
buildings older than thirty (30) years. There are also other
landmarking organizations that nominate and designate based on their
own criteria. As far as I know the problem is still in archaeology
sites though. A lime kiln site in a NYC park (in Hudson River's
Riverdale Park) may not be able to be nominated to a NYC Landmark, as
it covers "standing" structures, and NY State will not, though I think
it can be on the State list of sites, because it is part of the City's
jurisdiction. I am not sure what that actually means when it comes to
the NYC Parks Dept. design for flora restoration plans, recreating
gardens for example at, "the last Federalist, signer, first US
Ambassador to England" Rufus King Manor Park in Jamaica, NY but in
general the archaeology has been done where necessary, using others
administrative guidelines, though not necessarily legally defensible,
perhaps.