Between 250 and 300 million years ago, the Permian Sea covered a vast area, including much of what is now Texas and New Mexico. This warm, shallow, equatorial sea teemed with life and was home to organisms that built massive carbonate deposits.These deposits would eventually reshape the landscape and give rise to the fascinating geological formations we see today. Many of the stops highlighted in this blog lie within the Permian Basin, which spans roughly 100,000 square miles, including the Delaware and Midland sub-basins. However, deposits from the Permian Sea also influenced landscapes farther west, such as the Tularosa Basin. These ancient deposits left behind the cliffs, caves, and springs that we will explore along the Permian Highway, forming the geological backbone of the region. In this blog, "Permian Highway" references the route my class traveled as we explored these geological formations in September 2025.
Map of the regional extent of the Permian Basin. Basemap sources: National Geographic Society and i-cubed (2013); Esri, TomTom, Garmin, FAO, NOAA, USGS, OpenStreetMap contributors, and the GIS User Community. Additional data: PermianBasin_Boundary_Structural_Tectonic. Map created by Brittney A. Hawley in ArcGIS Pro
At the heart of this ancient seascape was the Capitan Reef, a massive barrier reef that stretched for hundreds of miles along the edge of the Delaware Basin. Built primarily by sponges, algae, and other reef-forming organisms, the Capitan Reef was the backbone of the Permian marine ecosystem. Over millions of years, these organisms deposited thick layers of limestone and other carbonates, which eventually lithified into the towering cliffs and ridges we see today in the Guadalupe Mountains. As the Permian Sea retreated and tectonic forces uplifted the region, the reef transformed from a thriving underwater structure into exposed rock formations, eventually creating caves and springs. It was truly a journey from ocean to outcrop. Exploring the Capitan Reef allows us to read the ancient story of the Permian Sea written in stone, from fossilized reefs to modern landforms.
View of El Capitan Peak viewed from the Salt flats viewing point.
The influence of the Capitan Reef and the Permian Sea extends far beyond the cliffs of the Guadalupe Mountains. As you travel along the Permian Highway, you can see this legacy in a variety of landscapes and geological features. At Carlsbad Caverns, the limestone deposited by the ancient reef was sculpted over millions of years into vast underground chambers and stalactite formations. Rattlesnake Springs and Bull Springs owe their waters to aquifers flowing through these same carbonate rocks. Further west, White Sands National Park tells a slightly different story, where gypsum left behind by evaporating Permian seas creates a striking, otherworldly landscape. Even along the Permian Trail, the ancient reef’s fossilized remnants allow visitors to walk through the very structures built by marine organisms hundreds of millions of years ago. Together, these sites form a continuous geological story: a journey that begins beneath the waves of the Permian Sea and unfolds across modern deserts, mountains, and caves.
By tracing the remnants of the Permian Sea and the Capitan Reef, we begin to understand how ancient oceans shaped the landscapes we explore today. In the posts that follow, The Permian Highway describes our geological field trip across these remarkable formations, revealing the geological processes and ancient life that created them. The adventure I'll unfold before you takes a slightly different route than than the one we traveled, as our plans changed according to the weather. This is something you'll want to keep in mind if you travel to the same locations. Rainy days make for muddy paths... and rental vehicles you might have to pay a cleaning fee for.
All photographs are original and taken by Brittney Hawley unless otherwise noted
Map of the stops taken along the journey. Basemap sources: National Geographic Society and i-cubed (2013); Esri, TomTom, Garmin, FAO, NOAA, USGS, OpenStreetMap contributors, and the GIS User Community. Additional data: PermianBasin_Boundary_Structural_Tectonic. Map created by Brittney A. Hawley in ArcGIS Pro
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