After decades of dispute over property boundaries, the proprietors of Maryland and Pennsylvania hired English astronomers and surveyors Charles Mason and Jeremiah Dixon to run out, settle, and define the boundaries between the provinces. In 1763, they were charged with running an east-west line 15 miles south of the southernmost part of Philadelphia. They surveyed from the Stargazers Stone in Embreeville, Pennsylvania, 15 miles south to latitude 39° 43' 18.2" in a field on the farm of Alexander Bryan. There, on June 12, 1764, they erected a 4" x 4" oak post with the word "West" on it, which Mason referred to in his journal as "the post mark'd west." The oak post lay on the latitude of the Maryland and Pennsylvania boundary, not on the east-west boundary. The post was eventually lost. In 1952, historian and Mason-Dixon hobbyist William T. Mahoney found the site on the property of Halleck DuPont and marked it with a small post. In 1953, DuPont put up a stone monument to mark the site.