Looking directly below the International Space Station, an astronaut took this photograph of Saltillo and its gray cityscape. The urban region, with 823,000 inhabitants, is the capital and largest city in the state of Coahuila. Saltillo is sometimes called the “Athens of Mexico” for its classical architecture. Founded in 1577, it is also one of the oldest post-European conquest cities in Mexico.

Saltillo lies on the doorstep of the Chihuahuan Desert, which is west of the city. The city obtains its water from the high, well-watered mountains to the east that reach altitudes of more than 3,700 meters (12,000 feet). These curling and straight green ridges are the oak-covered slopes of the Sierra Madre Oriental. These distinctive ridges immediately indicate to astronauts that they are flying over northern Mexico.

The topography is the result of a mountain-building event about 60 million years ago that folded and faulted thick layers of rocks, which were later modified by erosion. Saltillo is located on a fault zone, visible as an approximately straight line across the center of the photo. The fault separates the Sierra from the meandering shapes of low desert hills.

Astronaut photograph ISS041-E-102204 was acquired on October 26, 2014, with a Nikon D4 digital camera using a 210 millimeter lens, and is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by a member of the Expedition 41 crew. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Caption by M. Justin Wilkinson, Texas State University, Jacobs Contract at NASA-JSC.