Tucson, near the center of the photograph, is an excellent example of topography helping shape the development of a city. The city’s westward expansion has been affected by the Santa Cruz River, which flows northward toward Phoenix, and, more significantly, by the Tucson Mountains. South of Tucson, numerous drainage channels fan out in an alluvial arrangement that is not conducive to urban development. To the northeast and east, the Mount Lemmon Mountains provide a formidable barrier to development—Mount Lemmon, northeast of the city, rises 9157 feet (2791 meters) above sea level, and Mount Mica, east of the city, climbs 8666 feet (2641 meters) above sea level. The Tanque Verde Wash is the highly reflective drainage channel near the northern edge of the city. Large open-pit copper mines and their spoil banks are clearly visible south of the city and west of the Santa Cruz River. The northwest-southeast-oriented runways of Davis-Monthan Air Force Base and Tucson International Airport are barely visible in southern Tucson.