In the scholarly article "The Pantoja Map of 1782 and the Port of San Diego..." 46 Journal of San Diego History 119 (2000), USD School of Law Professor Jorge Vargas explored the historic and legal beginnings of the U.S.-Mexico border.

Using historical research, various articles, as well as the actual treaties and conventions that govern the creation of the U.S.-Mexico border, Professor Vargas provides a background for the interesting proposition that the border is incorrectly located miles within what should be Mexico. As Vargas states: 

The determination of the Californias’ boundary was a particularly   crucial issue for the United States. Upon this decision depended whether the port and the bay of San Diego would be included as part of the territories to be "ceded" by Mexico to the United States, pursuant to the Guadalupe Hidalgo Treaty.

Vargas, 46 J. of S.D. History at 120-121.

The Treaty of Guadalupe Hidalgo is the bilateral instrument first establishing the international boundaries between Mexico and the United States. Since 1848, when this treaty was signed, some have claimed that the treaty gave the United States more territory than was intended. The language of the treaty states:

...it is agreed that the said limit shall consist of a straight line, drawn from the middle of the Rio Gila, where it united from the Colorado, to a point of the Pacific Ocean distant one marine league due south of the southernmost point of the Port of San Diego, according to the plan of said port, made in the year 1782 by Don Juan Pantoja.

Vargas, 46 J. of S.D. History at 121.

This language is critical to the determination of where the boundary should be located. The Treaty reads that the Initial Point should be placed "one marine league due south of the southernmost point of the Port of San Diego." [Treaty, Article V] But the official reports of the commission overseeing the border clearly indicate that the marine league was measured not from the port of San Diego "which was at that time located some 9.5 miles north" but from the lowest coastline of the Bay of San Diego." Vargas, 46 J. of S.D. History at 122.

Thus there appears to be a giant discrepancy between the intent of the Treaty and the actual commission’s work. However, Vargas argues that the commission was empowered to reach an agreement on this issue and that it seems well settled by the documentary evidence. The official minutes of the Joint Commission of October 10, 1849, states that Mexican and U.S. members "agreed" on the location of the Initial Point of the boundary on the Pacific Ocean. See, Report of the Secretary of the Interior, Senate Executive Document No. 119, 32^nd Congress, 1^st Session (Serial 626).

The Treaty itself is specific in stating that "the two Governments shall each appoint a Commissioner and a Surveyor" to mark the boundary, and "the result, agreed upon by them, shall be deemed part of this Treaty, and shall have the same force as if it were inserted therein." Treaty of Guadalupe Hidalgo, Treaty Series No. 207, Treaties and Other International Acts of the United States, vol. 5, doc. 129; 9 Stat. 922-43 (1848). Another, stronger argument is that the precise location of the international boundary was marked in red ink on the map used and added to the Treaty. Vargas, 46 J. of S.D. History at 124. The map was then signed by each of the three Mexican officials and the U.S. commissioner sealing the agreement. Id.

Article V of the Treaty concludes by stating that "[t]he boundary line established by this article shall be religiously respected by each of the two republics, and no change shall ever be made therein, except by the express and free consent of both nations..." That statement punctuates the finality of the product created by the commission – leaving us with the international boundary we use to this day. Vargas thus concludes that the commission was within its powers to set the boundary where they did, despite the Treaty language, and that border was indeed set where it is today.