The Treaty of Guadalupe Hidalgo established an International Boundary Commission. The commission resurveyed the boundary in the 1890’s and rebuilt many of the boundary monuments that were first built in the 1850’s. Most of the monuments still exist but many are difficult to approach from the US side because of the increased militarization of the border.

The International Boundary Commission continues to resolve issues regarding the shifting course of the Rio Grande River and the exact placement of border crossings.

Until the 1930’s, crossing the US-Mexican border was informal and unregulated. Since then crossing restrictions have steadily increased and the once unfenced border has turned into an armed barricade.
This 1867 map of Mexico shows El Paso (the red dot) on the Mexican side of the Rio Grande. Before the US-Mexican
war began in 1846 El Paso was the name used for the area on both sides of the river. The El Paso on the Mexican side was the larger of the two settlements. In the 1860’s the US side of the border grew faster than the Mexican side and took the name El Paso. In 1888 Mexico’s El Paso changed its name to Cuidad Juarez in honor of Benito Juarez who fought the French intervention. Juarez had his government in exile in the area in 1862. Farther west is the area (blue dot) which today is the site of the border cities Nogales, Sonora and Nogales, Arizona. Neither city existed until the 1880’s. Today the twin cities have a combined population of over 350,000 and the border crossing handles more than 1500 trucks per day.