[2] According to the 1848 Treaty of Guadalupe Hidalgo, the initial border point is set as one marine league (three nautical miles) south of the southernmost point of San Diego Bay, and the border proceeds in a straight line towards the confluence of the Colorado River and the Gila River.

The significance of the monument is stated in the inscription on the west side of the original marble shaft:[2]"Initial point of Boundary between the United States and Mexico, established by the Joint Commission, 10 October, A.D. 1849, Agreeably to the Treaty dated at the City of Guadalupe, Hidalgo, February 2, A.D. 1848.

A white marble shaft was manufactured in New York, transported around Cape Horn on the USS Supply to San Diego, and erected and dedicated at the site in Imperial Beach in June, 1851.

Excepting for normal wear and tear and some slight vandalism, as of 1974 the marble monument as reconstructed in 1894 still stood at its original site.

[4] The current border fence passes several feet to the north of the marker, and it is possible to fully circumambulate the monument from Playas de Tijuana in Mexico, where it remains a popular attraction.