The authority is not limited to the erection of forts ... etc.
As for state laws, reread the first clause of that paragrah and tell me who has EXCLUSIVE legislative rights over that parcel of land.
Keep trying to allow people to assert squaters rights and you are going to end up in a socialist country at the least and a communist country at the worst.
and to exercise like authority over all places purchased by the consent of the legislature of the state in which the same shall be , for the erection of forts, magazines, arsenals, dockyards, and other needful buildings.
No where are they building anything on this land. They are setting it aside for a turtle. Setting land aside for a turtle is NOT listed in Art 1 Sec 8.
Period.