The NPS Organic Act (August 25, 1916),was a historic departure from prior unregulated
land development activities during the opening of the American West. This legislation established the National Park System, whose stewards were changed with the duty to conserve the scenery and the natural and historic objects and the wildlife therein and to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations.
www.csc.noaa.gov/opis/html/summary/npslink.htm

The Wilderness Act of 1964 was another watershed event in legislation affecting America's public lands. In this act, Congress recognized that the expansion of human activities posed a threat to the existence of natural lands.

Sec. 2. (a) 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.

The Wilderness Act mandated that public lands agencies identify public lands suitable for Wilderness designation and provided guidelines for their classification and management.
www.wilderness.net/nwps/legis/nwps_act.cfm#1
The Redwoods Act of 1978 provided further management guidance for public lands with the statement:
The authorization of activities shall be construed and the protection, management, and administration of these areas shall be conducted in light of the high public value and integrity of the National Park System and shall not be exercised in derogation of the values and purposes for which these various areas hae been established, except as may have been or shall be directly and specifically provided by Congress.
www.cr.nps.gov/history/online_books/anps/anps_7e.htm

ANILCA added 4 million acres to Denali, it provided the following purposes:
To protect and interpret the entire mountain massif, and additional scenic mountain peaks and formations; and to protect habitat for, and populations of fish and wildlife including, but not limited to, brown/grizzly bears, moose, caribou, Dall sheep, wolves, swans and other waterfowl; and to provide continued opportunities, including reasonable access, for mountain climbing, mountaineering and other wilderness recreational activities. Subsistence uses by local residents shall be permitted in the additions where such uses are traditional.

ANILCA reaffirmed the need for wilderness protection in Denali, by establishing the Denali Wilderness of about 1.9 million acres, comprising most of the original Mt. McKinley National Park. The Park road corridor and some already developed areas along the Park road were exempted from Wilderness designation (now known ad the "Front Country"). In addition, ANILCA mandated that NPS identify lands in the additions suitable for Wilderness designation. www.institutenorth.org/LegalProgram/anilca_index_page .htm

The National Environmental Policy Act (1969) provided a template for considering any material changes contemplated by NPS in the management of its lands. For any project involving significant change, an Environmental Impact Statement would be completed. In the EIS, the Park Service must perform research into the impacts of change and develop alternatives that are submitted to a public hearing process.
http://ceq.eh.doe.gov/nepa/regs/nepa/nepaeqia.htm

For further information on legislative and policy mandates covering National Parks, see the following link: www.redstonegroup.org/NPBPI/mandates.html