The National Trails System Act, Public Law 90-543, became law on October 2, 1968. The Act and its subsequent amendments authorized a national system of trails, and defined four categories of national trails:
National Scenic Trails (NST)
provide outdoor recreation and the conservation and enjoyment of significant scenic, historic, natural, or cultural qualities
National Historic Trails (NHT)
follow travel routes of national historic significance
National Recreational Trails (NRT)
are in, or reasonably accessible to, urban areas on federal, state, or private lands
Connecting or Side Trails
provide access to or among the other classes of trails
Since the designation of the Appalachian National Scenic Trail and the Pacific Crest National Scenic Trail in 1968, the system has grown to now include 22 National Scenic and Historic Trails as listed below. The Old Spanish National Historic Trail is of course the most recent addition to this very impressive group of trails representing the history of our country.