The northwest-to-southeast-flowing Rio Grande, which forms the border between the United States and Mexico, is easily traced across the arid landscape by the cultivated fields on its broad floodplain. Apparent are the north-south-oriented Franklin Mountains, a tilted faulted block mountain range north of El Paso; the Hueco Mountains, less than 20 miles (32 kilometers) east of El Paso; and Cuidad Juarez (center of photograph), El Paso’s neighbor across the Rio Grande. South of the Rio Grande the desert environment is broken only by smaller mountains. An extensive area of sand dunes is visible near the upper left corner.