5Trails for America[R/OL]. [1968]. http://www.nps.gov/nts/publications. html.
6Bridget Helwig, Eric Otto, Patrick Nelson. The National Trails System Issue Briel[EB/OL]. [2009-03-12]. http://www.forestry. umn.edu/courses/ RRM4232/National_Trails _System.pdf.
7National Trails System - General lnformation[EB/OL]. [2008-07-28]. http://www.nps.gov/nts/info.html.
8Johnson, Sandra L. An overview of the NATIONAL TRAILS SYSTEM ACT[EB/OL]. [2008]. http://www.americantrails.org/resources/feds/ NatTrSysOverview.html.
9History and facts about the National Trails System[EB/OL]. [2008]. http:// www.americantrails.org/resources/feds/40yearfact.html.
10Thomas L. Gilbert. The National Trails System: What It Is And How It Came To Be [EB/OL]. [2008]. http://www.americantrails.org/resources/ feds/FEDNatTrSysOverview.html.