US and Mexico border map

Main border crossings, west to east

There are 48 official crossings in total, with 330 ports of entry counting rail and pedestrian gates. Several carry railway track as well as road, among them Piedras Negras, Nuevo Laredo and Matamoros.

Border states

How the line was drawn

The boundary is a treaty line, fixed in two stages. The Treaty of Guadalupe Hidalgo of 2 February 1848 ended the Mexican–American War, transferred about 1,370,000 km² to the United States and ran the line up the middle of the Rio Grande to the southern edge of New Mexico and on to the Pacific below San Diego. Where New Mexico ended had to be read off J. Disturnell's map of 1847, bound into the treaty: it put El Paso del Norte roughly 50 km too far north and 100 km too far east, so the line could not be drawn on the ground and the surveyors argued for five years over the Mesilla valley. The Gadsden Purchase of 30 December 1853, the Tratado de La Mesilla, settled it — about 76,800 km² south of the Gila for ten million dollars, bought to give a southern railway a level route. Nothing has moved since. See old maps of Mexico.

A boundary that moves: the Chamizal and the 1970 treaty

A river frontier does not stay put. The convention of 1889 created the International Boundary Commission — the IBWC in the United States, CILA in Mexico — with the rule still applied: where the Rio Grande shifts slowly by erosion the boundary follows it; where a flood cuts a new channel it stays in the old bed. The 1944 treaty made it the International Boundary and Water Commission, its two sections facing each other in El Paso and Ciudad Juárez.

That rule produced the Chamizal dispute. Between 1852 and 1868 the river worked south, leaving about 240 hectares of former Mexican ground on the El Paso bank; Mexico called the change sudden, the United States gradual; an arbitration award of 1911 was rejected in Washington. The convention of 29 August 1963 settled it: 437 acres of the Chamizal passed to Mexico, the river went into a concrete channel and about 5,000 El Paso residents were moved, the transfer completed in 1967. The Bridge of the Americas crosses the new cut, and the Chamizal parks and the colonias behind them are a piece of Ciudad Juárez that a treaty made. The boundary treaty of 1970 disposed of the tracts still in dispute and fixed the middle of the channel as the line.

Geography of the line

From the Pacific at Playas de Tijuana the border climbs the coastal hills, crosses the Sierra de Juárez and drops to the Colorado delta. East of it the line runs straight across the Sonoran Desert, past the Altar dunes and the Pinacate lava field; at Sásabe the Altar valley opens north into Arizona, and by Nogales the desert has become oak grassland at about 1,200 m. Past Agua Prieta the line steps north from 31°20′ to 31°47′, the jog that gives New Mexico its bootheel, and meets the Rio Grande above El Paso, where the river cuts the gap between the Franklin Mountains and the Sierra de Juárez that gave El Paso del Norte its name. West of El Paso the ground is desert basin and range. The bed below the city is often dry until the Río Conchos comes in at Ojinaga; the river then cuts the Big Bend canyons and spreads into the lower valley at Reynosa and Matamoros, farmed on both banks, before the delta at Playa Bagdad. The rivers map traces the course.

Note that New Mexico is a US state, not part of Mexico — it has its own New Mexico map.

Twin cities and trade

Almost the whole border population lives in paired towns, the largest being Tijuana–San Diego at about 5 million and Juárez–El Paso at about 2.5 million.

Laredo, Texas is the highest-value port of entry in the United States, land, sea or air, and its World Trade Bridge takes more trucks than any other crossing; almost everything exported from north-east Mexico leaves through Nuevo Laredo on Highway 85D from Monterrey. The plants behind the fence date from the Border Industrialization Programme of 1965, which let components be imported duty-free for assembly and re-export; the maquiladora belt now runs the whole length of the line, with the largest workforces in Ciudad Juárez, Tijuana, Reynosa and Mexicali. See the road map and Northern Mexico.

Water and the 1944 treaty

The 1944 treaty on the Colorado, the Tijuana and the Rio Grande gives Mexico 1,850 million m³ of Colorado water a year, taken at Morelos Dam for the Mexicali valley, and obliges Mexico to send an average of 432 million m³ a year north from named Rio Grande tributaries, chiefly the Conchos, counted over five-year cycles. It also authorised the joint dams, Falcon (1953) and Amistad (1969). Deliveries are contested in dry years.

Crossing the border

Northbound queues are the constraint: SENTRI lanes carry pre-vetted travellers and Global Entry members may use them, but without one San Ysidro can take well over an hour at peak. Southbound, the border strip — about 25 km deep, and all of Baja California — is treated differently from the interior: beyond it a visitor needs an FMM form and a car a temporary import permit, issued at a checkpoint inland. Tijuana airport can be reached without a road queue at all, by the Cross Border Xpress footbridge from Otay Mesa, open since December 2015.

Questions about the US–Mexico border

How long is the US–Mexico border?

3,145 km (1,954 miles) from the Pacific at Tijuana–San Diego to the Gulf at Matamoros–Brownsville. The Rio Grande (Río Bravo) forms 2,018 km of it; the rest is a surveyed land line across the deserts of Arizona, New Mexico and Chihuahua.

How many states are on the US–Mexico border?

Four US states (California, Arizona, New Mexico, Texas) and six Mexican states (Baja California, Sonora, Chihuahua, Coahuila, Nuevo León, Tamaulipas). Texas has the longest share, 2,018 km; Nuevo León the shortest, 15 km.

What is the busiest US–Mexico border crossing?

San Ysidro (San Diego–Tijuana), the busiest land crossing in the Western Hemisphere with roughly 70,000 vehicles and 20,000 pedestrians a day. Laredo–Nuevo Laredo is the busiest for trucks and trade.

Where does the border line come from?

The 1848 Treaty of Guadalupe Hidalgo set the Rio Grande and a line to the Pacific; the 1853 Gadsden Purchase added southern Arizona and New Mexico and fixed the current line. See old maps of Mexico.

What was the Chamizal dispute?

An argument over about 240 hectares at El Paso that changed banks when the Rio Grande shifted south between 1852 and 1868. A 1911 arbitration was rejected by the United States; the convention of 1963 transferred the land to Mexico, moved the river into a concrete channel and rebuilt the strip of Ciudad Juárez behind it.