16 U.S.C. § 228f
Where any Federal lands within the Grand Canyon National Park, as enlarged by sections 228a to 228j of this title, are legally occupied or utilized on January 3, 1975, for grazing purposes, pursuant to a Federal lease, permit, or license, the Secretary shall permit the persons holding such grazing privileges to continue in the exercise thereof during the term of the lease, permit, or license, and periods of renewal thereafter: Provided, That no such renewals shall be extended beyond the period ending ten years from January 3, 1975, except that any present lease, permit, or license within the boundaries of the Grand Canyon National Monument as abolished by section 228b(b) of this title may be renewed during the life of the present holder which renewals shall terminate upon the death of the present holder.
16 U.S.C. § 228f