The Mason-Dixon Line, surveyed by Charles Mason and Jeremiah Dixon from 1763-1767, effectively is the southern border of Pennsylvania (though Mason and Dixon also surveyed the western border of Delaware).

I call The Line between West Virginia and Pennsylvania "the forgotten frontier." While a great deal of information is available about the segment of The Line between Pennsylvania and Maryland, little is written about the "forgotten frontier," the Mason-Dixon Line between the Keystone State and West Virginia, which was born in 1863.

Did you know that travelers on Interstate 79 crossing the state line between Monongalia County, W.Va., and Greene County, Pa., see no indication they've crossed the Mason-Dixon Line? And in other locations, such as U.S. 19 north of Morgantown, there are few historic markers heralding what might be the most-famous border in the U.S. So how was this 18th-century work done? Mason and Dixon surveyed the line using ASTRONOMY!!

The western end of the Mason-Dixon Line was resurveyed by Cephas Sinclair from 1883 to 1885. The markers you may find on The Line were placed during this resurvey.

Why do I call Pennsylvania's southwest corner "the end" of the Mason-Dixon Line even though Mason and Dixon never got here?

It's because it's HERE they were headed.

While Indians stopped Mason and Dixon's survey in October, 1767, a team headed by David Rittenhouse and Andrew Ellicott completed The Line to the southwest corner of Pa. The Cornerstone (placed in the Cephas Sinclair Resurvey of 1883) is 5 degrees in longitude from the Delaware River -- which is the distance that was awarded William Penn in his charter of 1681. No Mason and Dixon-related surveying was done westward beyond this point even though an "extension" serves as the border between Wetzel and Marshall counties in West Virginia. The Missouri Compromise of 1820 led to the general perception that the Mason-Dixon Line runs through far-off states such as Illinois. It does not! The actual surveying of The Line ended at the southwest corner of Pennsylvania. From there the Rittenhouse-Ellicott team began the survey of Pennsylvania's western border -- the Ellicott Line.