Advancing the national park idea :
National Parks Second Century Commission report.

APA Citation

National Parks Second Century Commission., National Parks Conservation Association. (2009). Advancing the national park idea: National Parks Second Century Commission report. [Washington, D.C.]: National Parks Conservation Association.

MLA Citation

National Parks Second Century Commission, and National Parks Conservation Association. Advancing the National Park Idea: National Parks Second Century Commission Report. [Washington, D.C.]: National Parks Conservation Association, 2009.