This stretch of track was originally part of the Franklin & Clearfield Railroad. The F&C was a temporary subsidiary of the Lake Shore & Michigan Southern Railway, which was in turn controlled by the New York Central. The F&C was part of a larger plan by the NYC to establish an east-west trunk line through Pennsylvania.
The Lake Shore directed construction of the F&C with initial groundbreaking getting underway in late 1905 or early 1906. The new line branched from the Lake Shore's subsidiary, Jamestown & Franklin Railroad on the south side of Franklin. Shortly after laying track south towards Belmar the F&C started work on an alternate route that ultimately extended from Polk Junction, through the valley of Sandy Creek and on to Belmar. At Belmar the two alignments merged at a wye before crossing the Allegheny River en route through the rugged hills of Venango and Clarion counties.
The NYC's master plan to establish a through route through Pennsylvania was predicated on the NYC acquiring a controlling interest in the Philadelphia & Reading Railroad, which would provide the NYC the required access to Philadelphia. When this failed to materialize the NYC curtailed its plans for the F&C and, rather than lay track to Clearfield, terminated construction at Brookville in Jefferson County. The NYC negotiated track sharing agreements over the Pennsylvania Railroad and the Buffalo, Rochester & Pittsburgh Railroad, which provided the NYC access to Clearfield and the NYC's own, Beech Creek Railroad.
Construction on the F&C was largely complete by 1909. In that year, the Lake Shore merged the F&C with the Jamestown & Franklin to create the Jamestown, Franklin & Clearfield Railroad. Via a string of mergers and track sharing agreements the NYC established something of a through route between Philadelphia, Cleveland, and Chicago, but it was far from ideal. Not surprisingly, the numerous interchange points made for poor operating efficiency. Nevertheless, the NYC operated a couple of scheduled through freights over the line into the early 1950s. The NYC terminated any and all through service over the route by 1958.
This segment of F&C alignment was rendered redundant by the Polk Junction-to-Belmar route. At the time of abandonment in 1933, the NYC had been using the Franklin-to-Belmar segment for car storage. The remainder of the old F&C route, between Polk and Brookville, continued in use into the mid-1980s, primarily as an outlet for Clarion County coal. The line had gone from NYC control to Penn Central and, finally, Conrail, who operated the route as the Clarion Secondary.
Because the NYC had anticipated a through route, it built a robust, low-grade line with a couple of heavy bridges over the Allegheny and Clarion rivers and three tunnels. The Sandy Creek Trail occupies the western leg of the F&C and a bike ride over the line reveals the extent of the NYC's optimism. The roadbed and bridge abutments and piers were built to accommodate a double-track route. When it became apparent that a trunk line was likely not in the cards, the NYC settled on a single track route. The heavy grading and excavating for a major thoroughfare, however, remains evident.