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 , California and Tijuana before reaching the Pacific Ocean .
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 .