This was the former Dunkirk, Allegheny Valley and Pittsburgh Railroad line between Dunkirk, NY and Titusville, PA. It extended 90 miles from the NYC mainline at Dunkirk, NY south-southwest to Titusville, PA. It served small farm towns in upstate New York and reached into the oil field region of northwestern Pennsylvania. An extensive history of this line is available at the link below.
A portion of the right-of-way can still be easily seen where it parallels US Route 62 between Akeley and Warren in northern Pennsylvania.
Thanks to Mike Palmer for contributing information about this route.