Between 251 – 299 million years ago, during the Permian period of geologic time, all the continents on Earth were joined together to form the supercontinent of Pangea.

El Capitan, a part of the world's most well-exposed Permian fossil reefs, Guadalupe Mountains National Park / Rebecca Latson

Looking at this vast, barren, windswept and arid landscape, it might be difficult to imagine this area of West Texas was once covered by a shallow tropical sea known as the Delaware Sea, named for the Delaware Mountains that run south from Guadalupe Peak and El Capitan. The concept of geologic time might also be difficult to wrap our heads around. About 273 million years ago, forming along the edge of the Delaware Sea was a barrier reef known as the Capitan Reef. When we think of reefs, we think of the bright, colorful, myriad coral reefs of Florida or the Caribbean. But the Capitan Reef was different because it was not formed by corals, but rather by microbes and algae. Sponges helped form this reef, too, but they were not the framework of the reef. Fossilized brachiopods, crinoids, ammonites, fusilinids, and bryozoans are examples of the life thriving within and around Capitan Reef. 

Sea levels began dropping around 260 million years ago, cutting off the water supply the Delaware Sea had to the larger ocean existing at that time around the super continent of Pangea. Sediments ultimately buriedeverything there, including the Capitan Reef, which stayed buried for almost 250 million years. Dinosaurs walked the Earth then died out and heat waves baked the geography once buried beneath glaciers and ice sheets, all while continents shifted all around via tectonic plate movement. When the reef died, so did the life within the reef. Those skeletal remains became the sedimentary rock known as Capitan limestone.

Map of the Capitan Reef showing the exposed and buried sections as they are today, Guadalupe Mountains National Park / NPS file

According to park staff:

Around 14 million years ago, tectonic forces deep beneath the surface put tremendous amounts of pressure on the rock layers containing the Capitan Reef. Eventually, this pressure was released in the form of a massive fault that split the reef, uplifting the Western Escarpment of the Guadalupe Mountains to elevations up to 8,751 feet [2,667 meters] above sea level. The highest point sits more-or-less along this fault, and the reef slopes gradually downwards until it disappears below the surface again northeast of Carlsbad Caverns National Park.

Today, we know the Capitan Reef as the Guadalupe Mountains of Texas and New Mexico, with other fragments visible above the surface in the Glass and Apache Mountains of West Texas. These mountain ranges preserve an incredible window into what the world was like during the Permian Period and what types of organisms were present in the Delaware Sea.

You are likely to see evidence of creatures that lived on the reef during your visit. Fossils are common in the park, and they preserve organisms that lived on the reef, taking advantage of the very productive ecosystem that developed there, as well as the reef building organisms themselves.

To take a more in-depth look at the geologic history of Guadalupe Mountains National Park, click here.