Monterrey Amid Mountains

Mexico’s second-largest metropolitan area borders on folded rock layers of the Sierra Madre Oriental.

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Image of the Day for September 11, 2026

Mexico’s second-largest metropolitan area borders on folded rock layers of the Sierra Madre Oriental.

NASA Earth Observatory

Sep 11, 2026

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The curving, parallel mountain ridges of the Sierra Madre Oriental are an eye-catching feature of northeastern Mexico’s landscape. The spot where these folds nestle up against Mexico’s second-largest metropolitan area captured the attention of an astronaut aboard the International Space Station, who took this photo on August 26, 2026.

Monterrey, the capital of the state of Nuevo León, is an industrial hub supporting heavy industries such as ironworks and steelworks, as well as manufacturing facilities for goods ranging from textiles to processed foods to glass and plastics. The metropolitan area is home to 5.3 million people, according to the 2020 census. And while the city has seen overall population growth since 1990, the number of people living within 5 kilometers (3 miles) of the city center has declined, researchers have found—a trajectory shared with many of Mexico’s metropolitan areas.

In Monterrey’s case, urban expansion runs up against some unforgiving terrain. Along the city’s southern edge, layers of limestone, deposited in the late Mesozoic era and then folded between about 80 and 50 million years ago, form the Sierra Madre Oriental. Over millions of years, weaker rock layers have eroded away, leaving behind the distinct ridgelines that bound Monterrey today.

The Río Santa Catarina carves through the mountains and onto the semiarid floodplain where the city lies. Because of the dry environment, the river carries little to no water for much of the time. But its channel is crucial for collecting runoff from summer rains and serves as an important natural area for plant and animal life within the city.

The river runs through Monterrey’s urban core and between several island-like protrusions of folded rock. One of these is the Sierra Las Mitras, a state nature reserve established in 2000. The mountain ridge rises approximately 1,500 meters (4,900 feet) over the city and provides a haven for wildlife. As conditions become cooler and wetter with higher elevations, vegetation turns from cacti and thorny shrubs on lower rocky slopes to oak and pine forests higher on the ridge. Cerro de la Silla (Mount Silla or Saddle Hill) is another prominent feature of the landscape, contrasting with the built environment.

Near the city’s border with the Sierra Madre Oriental sits Universidad de Monterrey, a host venue for the NASA Space Apps Challenge. This annual hackathon will take place in November 2026 in person and virtually at sites around the world. Participating teams use NASA and partner agency data to tackle challenges in fields such as software development, astrophysics, space exploration, and agriculture.

Astronaut photograph ISS075-E-70481 was acquired on August 26, 2026, with a Nikon Z9 digital camera using a focal length of 400 millimeters. It is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit at NASA Johnson Space Center. The image was taken by a member of the Expedition 75 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. Story by Lindsey Doermann.

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August 26, 2026

International Parks, Sierra de las Mitras. Accessed September 10, 2026.

NASA Earth Observatory (2020, November 27) A Sliver of Mexico’s “Mother Mountain Range.” Accessed September 10, 2026.

NASA Earth Observatory (2017, May 10) Mount Silla and Monterrey. Accessed September 10, 2026.

NASA Space Apps Challenge (2026) Monterrey. Accessed September 10, 2026.

Universidad Autónoma de Nuevo León, La importancia ambiental del Río Santa Catarina. Accessed September 10, 2026.