Surveyed in 1799 to mark the 31° North Latitude, this line formed the first southern boundary of the United States, separating the U.S. from Spanish Florida. It was marked at one-mile intervals by earthen mounds approximately fifteen feet square and three feet high with a charred lighter-pine post at the center, giving rise to the name Mound Line. Major Andrew Ellicott, U.S. Commissioner, and Esteban Minor, Spanish Commissioner, jointly surveyed it to determine boundaries as agreed in the Treaty of San Lorenzo in 1795. Beginning at the Mississippi River, it ran east along 31° North Latitude to the Chattahoochie River and eventually to the Atlantic Ocean. Stockton was divided by this boundary, with some residents living in the United States and some in Spanish Florida, though U.S. law generally prevailed in the area.