The Line Becomes a River: Dispatches from the Border

by Francisco Cantú

The modern-day boundary between the United States and Mexico was defined largely by the Treaty of Guadalupe Hidalgo in 1848, signed after nearly two years of warfare between neighboring republics. The newly agreed-upon borderline was to begin “on the coast of the Pacific Ocean, distant one marine league due south of the southernmost point of the port of San Diego,” and run east “following the division line between Upper and Lower California” until it reached the Colorado River at the town of Yuma. The treaty dictated that the line would then follow the course of the Gila River from its intersection with the Colorado until it reached the border of New Mexico, at which point the boundary would leave the waters of the Gila in a straight line until it intersected the Rio Grande north of El Paso, where the line would again become fluid “following the deepest channel” of the river until it emptied into the Gulf of Mexico, to be forgotten in the waters of the ocean at a point “three leagues from land, opposite the mouth of the Rio Grande.” Article V of the treaty mandated that “in order to designate the boundary line with due precision, upon authoritative maps, and to establish upon the ground landmarks which shall show the limits of both Republics . . . the two Governments shall each appoint a commissioner and a surveyor, who . . . shall meet at the port of San Diego, and proceed to run and mark the said boundary in its whole course to the mouth of the Rio Bravo del Norte.” It a...