Rocks that formed beneath the waves of an ancient sea now make up some of the loftiest peaks in Texas. Rising above the Chihuahuan Desert in West Texas and southern New Mexico, the Guadalupe Mountains are part of one of the best-preserved fossil reefs from the Permian Period. The cemented accumulation of plant and animal material constitutes a revealing record of aquatic life before a mass extinction event at the end of the Permian.
The Texas portion of this range is part of Guadalupe Mountains National Park, established in 1972. The park is outlined in the image above, acquired with the OLI-2 (Operational Land Imager-2) on Landsat 9 on July 7, 2024. To the northeast, where the exposed fossil reef stretches into New Mexico, sulfuric acid has eaten away at the rock to form the massive caves within Carlsbad Caverns National Park.
In the Permian Period, which lasted from about 300 to 250 million years ago, this area was situated on the edge of a shallow inland sea on the supercontinent Pangea. The Capitan Reef formed in this coastal environment and was composed mostly of sponges and algae. Other fossilized marine life found here includes ammonites, bivalves, brachiopods, crinoids, snails, and trilobites.
Global sea levels fell toward the end of the Permian, and Capitan Reef became buried under thousands of feet of newer sediments. It remained preserved this way for more than 200 million years. Within the past 20 million years, tectonic forces moved the rocks skyward. Softer rock layers then eroded away and left the more resistant reef exposed. Along with the Guadalupe Mountains, uplifted portions of Capitan Reef also comprise the Apache and Glass Mountains in Texas.
El Capitan (above) is a striking display of the fossilized reef and one of the more iconic vistas in Guadalupe Mountains National Park. Its sheer, 1,000-foot-high limestone cliff tops out at 8,085 feet (2,464 meters), making it one of the 10 highest peaks in the state. Most of Texas’s highest mountains—including the very tallest, Guadalupe Peak at 8,751 feet (2,667 meters) above sea level—are also in the park.
People seeking a more immersive encounter with the deep past may find it in the park’s northeast corner. The Permian Reef Trail brings hikers close to fossil beds and serves as a tour through the former marine environment, from seafloor to reef, as it ascends the north side of McKittrick Canyon. The canyon itself is sometimes referred to as the “most beautiful spot in Texas,” and a trail winding through it (below) is popular for viewing autumn colors.
The western side of the park offers an entirely different sort of landscape. There, piles of bright-white gypsum grains form dunes up to 60 feet (18 meters) tall. The dunes are located in a low-lying basin with no outlet; water that intermittently flows there evaporates to leave behind these mineral deposits. Today, with significant rain, an inches-deep lake may form temporarily in the basin. Otherwise, the deposits are left to be shifted about by prevailing westerly winds.
Editor’s Note: Explore satellite imagery of other national parks for National Park Week.
NASA Earth Observatory image by Wanmei Liang, using Landsat data from the U.S. Geological Survey. Photo of El Capitan courtesy of NPS. Photo of McKittrick Canyon courtesy of Matthew Lee High. Story by Lindsey Doermann.
