16 U.S.C. § 1131 : US Code - Section 1131: National Wilderness Preservation System

    (a) Establishment; Congressional declaration of policy; wilderness
      areas; administration for public use and enjoyment, protection,
      preservation, and gathering and dissemination of information;
      provisions for designation as wilderness areas
      In order to assure that an increasing population, accompanied by
    expanding settlement and growing mechanization, does not occupy and
    modify all areas within the United States and its possessions,
    leaving no lands designated for preservation and protection in
    their natural condition, it is hereby declared to be the policy of
    the Congress to secure for the American people of present and
    future generations the benefits of an enduring resource of
    wilderness. For this purpose there is hereby established a National
    Wilderness Preservation System to be composed of federally owned
    areas designated by Congress as "wilderness areas", and these shall
    be administered for the use and enjoyment of the American people in
    such manner as will leave them unimpaired for future use and
    enjoyment as wilderness, and so as to provide for the protection of
    these areas, the preservation of their wilderness character, and
    for the gathering and dissemination of information regarding their
    use and enjoyment as wilderness; and no Federal lands shall be
    designated as "wilderness areas" except as provided for in this
    chapter or by a subsequent Act.
    (b) Management of area included in System; appropriations
      The inclusion of an area in the National Wilderness Preservation
    System notwithstanding, the area shall continue to be managed by
    the Department and agency having jurisdiction thereover immediately
    before its inclusion in the National Wilderness Preservation System
    unless otherwise provided by Act of Congress. No appropriation
    shall be available for the payment of expenses or salaries for the
    administration of the National Wilderness Preservation System as a
    separate unit nor shall any appropriations be available for
    additional personnel stated as being required solely for the
    purpose of managing or administering areas solely because they are
    included within the National Wilderness Preservation System.
    (c) "Wilderness" defined
      A wilderness, in contrast with those areas where man and his own
    works dominate the landscape, is hereby recognized as an area where
    the earth and its community of life are untrammeled by man, where
    man himself is a visitor who does not remain. An area of wilderness
    is further defined to mean in this chapter an area of undeveloped
    Federal land retaining its primeval character and influence,
    without permanent improvements or human habitation, which is
    protected and managed so as to preserve its natural conditions and
    which (1) generally appears to have been affected primarily by the
    forces of nature, with the imprint of man's work substantially
    unnoticeable; (2) has outstanding opportunities for solitude or a
    primitive and unconfined type of recreation; (3) has at least five
    thousand acres of land or is of sufficient size as to make
    practicable its preservation and use in an unimpaired condition;
    and (4) may also contain ecological, geological, or other features
    of scientific, educational, scenic, or historical value.