Nothing in this chapter shall be construed to limit the authority of the Secretary to acquire lands and interests in lands within the boundaries of any unit of the National Park System. The Secretary is to give prompt and careful consideration to any offer made by the owner of any valid right or other property within the areas named in section
1905 of this title to sell such right or other property, if such owner notifies the Secretary that the continued ownership of such right or property is causing, or would result in, undue hardship.