The Guadalupe Mountains are stunning to view, which begs the question: How were they formed? At more than a mile and a half above sea level, El Capitan (8,085 feet) and adjacent Guadalupe Peak (8,749 feet) are the two tallest mountains in Texas. The peaks are the most obvious sections of the Capitan Reef, most of which still lies buried thousands of feet below the desert's surface.
More than 250 million years ago, the immense reef enclosed about 10,000 square miles of a shallow inland sea. The reef was formed as the remains of lime-secreting algae and other primitive creatures that lived in the sea washed ashore. Gradually the climate of the region changed, and the sea dried up, leaving much of the reef exposed.
More millennia passed, and the seabed and the reef were buried beneath a vast plain, where they remained for millions of years. Then, about 12 million years ago, geologic processes deep beneath the earth raised and tilted the ancient seabed and reef, leaving the 40-mile section now known as the Guadalupe Mountains high and dry. In the process, the reef was fractured in several places.
Over more millions of years, wind and water worked to turn these deep cracks into lovely canyons that slice into the mountains we see today. These chasms, including McKittrick Canyon, Dog Canyon, and many others, are the heart of Guadalupe Mountains National Park.