16 U.S.C. § 459i-3
With the exception of any property deemed necessary by the Secretary for visitor facilities or administration of the seashore, any owner or owners of improved property on the date of its acquisition by the Secretary may, as a condition of such acquisition, retain for themselves and their successors or assigns a right of use and occupancy of the property for noncommercial residential purposes, for twenty-five years, or, in lieu thereof, for a term ending at the death of the owner or his spouse, whichever is later. The owner shall elect the term to be reserved. The Secretary shall pay to the owner the fair market value of the property on the date of such acquisition less the fair market value on such date of the right retained by the owner: Provided, however, That, in addition, for so long as a right of use and occupancy remains in effect by the donors of land of one hundred acres or more, the Secretary shall not, with respect to such lands, develop any public use facilities except for trails, road access, and utilities: Provided further, That when acquiring lands, waters, and interests therein from the National Park Foundation, its successors and assigns, the Secretary shall acquire such lands, waters, and interests subject to the written terms and conditions contained in those transactions, including but not limited to options, entered into by the National Park Foundation prior to January 1, 1973, and that such previous written rights and interests shall prevail over provisions of this subsection.
A right of use and occupancy retained or enjoyed pursuant to this section may be terminated with respect to the entire property by the Secretary upon his determination that the property or any portion thereof has ceased to be used for noncommercial residential purposes and upon tender to the holder of a right an amount equal to the fair market value, as of the date of tender, of that portion of the right which remains unexpired on the date of termination.
The term "improved property", as used in this section shall mean a detached, noncommercial residential dwelling, the construction of which was begun before February 1, 1970 (hereinafter referred to as "dwelling"), together with so much of the land on which the dwelling is situated, the said land being in the same ownership as the dwelling, as the Secretary shall designate to be reasonably necessary for the enjoyment of the dwelling for the sole purpose of noncommercial residential use, together with any structures accessory to the dwelling which are situated on the land so designated.
16 U.S.C. § 459i-3