El Capitan

About 100 miles east of El Paso, just south of the New Mexican border looms one of the most iconic mountain peaks in Texas, El Capitan. A part of the Guadalupe Mountains National Park, this ancient limestone reef was lifted up over 8,000 ft by geologic activity between 66 and 100 million years ago, in the late Cretaceous period.

(1899)

The reef itself was even older, a relic of the Permian era almost 300 million years ago, when an inland ocean called the Delaware Sea covered much of New Mexico and the Trans-Pecos region of Texas (the little nub of western Texas that lies west of the Pecos River). El Capitan is only the southern terminus of the reef, which is 350 miles long.

Eventually, the sea was cut off from the oceans and its mineral- rich waters evaporated over the millennia, leaving behind massive deposits of gypsum, calcite, and other minerals, that were buried by sand as new rivers began to flow across the land. There the reef lay buried for 150 million years until tectonic upheaval thrust the Guadalupe Escarpment upwards, where the sediment layers were stripped away by weather, leaving the reef exposed.

NPS Photo.

Unlike a coral reef, which is a mound or ridge of corals, a limestone reef is an accumulation of animal skeletons and plant material. E Capitan was formed by the accumulation of algae, sponges, bryozoan skeletons, which are tiny animals that live in colonies. These skeletons are eventually stabilized and fused together by successive layers of organisms that grow over the pile, cementing it together into the towering limestone structure we see today.

Sea Urchin Fossil from El Capitan, NPS photo.