Legislative History

In 1968, the National Trail System Act was passed into law paving the way for the National Trail System as we know it today. Even though only the Appalachian Trail and Pacific Crest Trail were the first trails designated when the Act was codified into law, there were numerous other trails proposed. One of those trails was the Potomac Heritage National Scenic Trail, which was designated in an amendment to the 1968 Act in 1983.
The trail has had numerous plans and studies conducted prior to the designation.

Trails for America: Report on the Nationwide Trails Study (1966)

This document introduced the potential trails that could be added to what would become the National Trail System Act of 1968. Released by the Secretary of the Interior and the Secretary of Agriculture in 1966, the document examines the feasibility of a national trail system. The Potomac Heritage Trail was one of three additional proposed trails to follow in the footsteps of the Appalachian Trail.

“Trails normally are associated with a single type of landscape- mountain, lake shore, or river course. Few traverse more than a single physiographic region. Practically, all are connected with a single strong landscape feature such as a mountain range, river valley, or historical pathway. Thus, few trails offer diverse recreation, scenic, and cultural opportunity. Yet such an opportunity exists with the Potomac River as its backbone.
…
The Potomac Heritage Trail would follow the course of the Potomac River from source to mouth, linking an astounding array of superlative historic, scenic, natural, and cultural features, and offering an outstanding recreation opportunity for the residents of the Potomac Valley and its annual millions of visitors.”

The Potomac Heritage Trail: A Proposed National Scenic Trail (1974)

In 1974, a feasibility study was conducted and created the basis for authorizing the Potomac Heritage Trail into legislation in 1983. Completed by what was formerly known as the Bureau of Outdoor Recreation, the study elaborated on the Trails for America: Report on the Nationwide Trails Study (1966) and the unpublished A proposal, Potomac Heritage
Trail: A Trunk Trail in The Nationwide System of Trails (1965) providing in depth propositions for the trail alignment. The trail, at the time of the proposal, was divided into 8 segments, going from the headwaters of the Potomac in West Virginia and Pennsylvania down to the mouth of the river into the Chesapeake Bay in both Maryland and Virginia.

“Those characteristics which make the trail worthy of national scenic designation are both individually impressive and collectively significant. The variety is truly remarkable, ranging from historic battlefields and fortifications--Fort Necessity, Fort Washington, Antietam, and Balls Bluff, to historic homes-- Stratford Hall, Mount Vernon, Gunston Hall, and the White House, from the urban complex of metropolitan Washington with all of its government functions and its central place in the development of American life to the remoteness of the Dolly Sods in Monongahela National Forest, from the strenuous hiking in the Savage River country of western Maryland to the leisurely stroll through historic Alexandria, and from the tranquility and isolation of Zekiah Swamp to the somber melancholy of Antietam Battlefield. And above all, there is the River itself.”

National Trails System Act - Amendment of 1983

In 1983, an amendment to the 1968 National Trails System Act designating the Potomac Heritage National Scenic Trail, as well as other well-known trails like the Natchez Trace National Scenic Trail and the Florida National Scenic Trail.

“The Potomac Heritage National Scenic Trail, a corridor of approximately seven hundred and four miles following the route as generally depicted on the map identified as 'National Trails System, Proposed Potomac Heritage Trail' in 'The Potomac Heritage Trail', a report prepared by the Department of the Interior and dated December 1974, except that no designation of the trail shall be made in the State of West Virginia.”

You can find the rest of the amendment on congress.gov