The Mexico–United States border (Spanish: frontera Estados Unidos–México) is an international border separating Mexico and the United States, extending from the Pacific Ocean in the west to the Gulf of Mexico in the east. The border traverses a variety of terrains, ranging from urban areas to deserts. The Mexico–United States border is the most frequently crossed border in the world, with approximately 350 million documented crossings annually. It is the tenth-longest border between two countries in the world. The total length of the continental border is 3,145 kilometers (1,954 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. Four American states border Mexico: California, Arizona, New Mexico, and Texas. One definition of Northern Mexico includes only the six Mexican states that border the United States: Baja California, Chihuahua, Coahuila, Nuevo León, Sonora and Tamaulipas.
