; (2) the designation of a new unit of special airspace over a wilderness area or addition; or (3) the use or establishment of a military flight training route over a wilderness area or addition. (g) Horses Nothing in this Act precludes horseback riding in, or the entry of recreational or commercial saddle or pack stock into, a wilderness area or addition— (1) in accordance with section 4(d)(5) of the Wilderness Act ( 16 U.S.C. 1133(d)(5) ); and (2) subject to such terms and conditions as the Secretary determines to be necessary. (h) Law enforcement Nothing in this Act precludes any law enforcement or drug interdiction effort within a wilderness area or addition, in accordance with the Wilderness Act ( 16 U.S.C. 1131 et seq. ). (i) Withdrawal Subject to valid existing rights, the wilderness areas and additions are withdrawn from— (1) all forms of entry, appropriation, and disposal under the public land laws; (2) location, entry, and patent under the mining laws; and (3) operation of the mineral materials and geothermal leasing laws. (j) Incorporation of acquired land and interests Any land within the boundary of a wilderness area or addition that is acquired by the United States shall— (1) become part of the wilderness area or addition in which the land is located