It runs from San Diego, California, and Tijuana, Baja California, in the west to Matamoros, Tamaulipas, and Brownsville, Texas, in the east, and traverses a variety of terrains, ranging from major urban areas to inhospitable deserts. From the Gulf of Mexico it follows the course of the Rio Grande (Río Bravo del Norte) to the border crossing at El Paso, Texas, and Ciudad Juárez, Chihuahua; westward from that binational conurbation it crosses vast tracts of the Sonoran and Chihuahuan Desert, the Colorado River Delta, westward to the binational conurbation of San Diego and Tijuana before reaching the Pacific Ocean. (wikipedia)
