An island built by the federal government on land deeded to it free and clear by act of the South Carolina legislature. It belonged to the federal government. Only Congress could dispose of it.
Recently, Fort Monroe in Hampton Rhoads, Virginia was returned to the State of Virginia. I take it that you consider that a gift from the feds?
Yes, unless Virginia bought it.
Virginia owned it before there was a federal government!
Who would they have bought it from, King Charles prior to the revolution?
The Declaration of Independence disposed of it. Same way it disposed of all the states from the United Kingdom.