The border city of Laredo is visible on the east side of the Rio Grande, with Nuevo Laredo, its Mexican counterpart, on the west. Lake Casa Blanca lies northeast of Laredo. The color infrared film does not produce a meaningful rendering of the sandstone and claystone beds that underlie this region of south Texas. White dots (bottom third) show the distribution and density of gas and oil fields. The semiarid climate, receiving less than 20 inches (50 centimeters) of precipitation per year, combined with a very high rate of evaporation promotes the growth of cactus and thornbrush.