The Four Corners --- West --- Twentymile Creek

Location:   Twentymile Creek, New York
Year:   1785

Although most of the Commonwealth of Pennsylvania lies south of New York State, in 1785 New York ceded to Pennsylvania a small area of its extreme western frontier, giving the Quaker State access to Lake Erie. This created a longitudinal north-south border between New York and Pennsylvania at a right angle to their shared latitudinal east-west border. The borderline is mostly straight, a surveyor's plumb line on a map. 

The small tributary of Twentymile Creek, a popular bass fishing site, rises in western New York State, and meanders across the State line into Pennsylvania, tending northwestward to Lake Erie. 

At the point where Twentymile Creek crosses the State line, a slight curve in the river marks the extreme western border of New York State at 79.76 West. 

The spot is in the Township of Ripley, New York, modestly famous as the terminus of the New York State Thruway, and the onetime home of tire magnate B.F. Goodrich.