American–Mexican border

The Mexico–United States border is an international border separating Mexico and the United States, extending from the Pacific Ocean to the west and Gulf of Mexico to the east. The border traverses a variety of terrains, ranging from major urban areas to uninhabitable deserts. Approximately 350 million legal crossings occur annually, and is the most frequently crossed border in the world.

The total length of the continental border is 3,201 kilometers (1,989 mi). From the Gulf of Mexico, it follows the course of the Rio Grande (Río Bravo del Norte) to the border crossing at Ciudad Juárez, Chihuahua and El Paso, Texas. Westward from El Paso–Juárez, it crosses vast tracts of the Chihuahuan and Sonoran deserts to the Colorado River Delta and San Diego–Tijuana, before reaching the Pacific Ocean.

Following the Boundary Treaty of 1970 between Mexico and the United States that settled all the pending boundary disputes and uncertainties related to the Rio Grande (Río Bravo del Norte) border, the national continental border extends 3,145 kilometers (1,954 mi), excluding the maritime boundaries of 29 km (18 mi) in the Pacific Ocean and 19 km (12 mi) in the Gulf of Mexico.

According to the International Boundary and Water Commission, this continental border follows the middle of the Rio Grande—according to the 1848 Treaty of Guadalupe Hidalgo between the two nations, "along the deepest channel" (also known as the thalweg)—from its mouth on the Gulf of Mexico a distance of 2,019 km (1,255 mi) to a point just upstream of El Paso and Ciudad Juárez. It then follows an alignment westward overland and it is marked by monuments for a distance of 859 km (534 mi) to the Colorado River, when it reaches its highest elevation at the intersection with the Continental Divide. It then follows the middle of that river toward the north with a distance of 38 km (24 mi), and ultimately follows an alignment overland toward the west and marked by monuments with a distance of 227 km (141 mi) to the Pacific Ocean (excluding the maritime boundaries of 18 miles (29 km) in the Pacific Ocean and 12 miles (19 km) in the Gulf of Mexico).

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