Geologic Formations

Rock formations in sunset light
Rhyolite formations at Chiricahua National Monument

NPS Photo

By far the most noticeable natural features in the park are the rhyolite rock pinnacles for which the monument was created to protect. Rising sometimes hundreds of feet into the air, many of these pinnacles are balancing on a small base, seemingly ready to topple over at any time. The Civilian Conservation Corps (CCC), during their occupation here in the 1930s, named many of the rock formations that can be seen today.

Other geologic features of the park include shallow caves, faults, mountain formations, ancient lava flows, and a giant volcanic caldera. The Turkey Creek Caldera is located just to the south of the park. A cataclysmic volcanic eruption, roughly 27 million years ago, spewed ash and molten debris at super-sonic speeds and formed the approximately 12 mile wide caldera.* Ash and debris settled and compacted, forming a thick layer of rock called rhyolite tuff. This rock layer has fissured and eroded over time, forming the spectacular rock pillars of Chiricahua National Monument. The Chiricahua Mountains are one of many sky islands in southern Arizona, and are part of the larger Basin and Range Province.

An important natural feature found in the park, and integral to the presence of flora and fauna, is water. Although water flows only intermittently on the surface, the park contains all or parts of five major watersheds in the the northern Chiricahua Mountains. Seeps and springs are vital to the survival of most faunal species, and the one wetland marsh in the monument is host to two sensitive plant species. Groundwater supplies 100% of that needed by both the visitors to the monument and the monument staff. The combination of these natural features as related to geology and water, along with other resource necessities, have helped to determine the floral communities of the monument. Rich in diversity, the monument boasts many plant communities, including grasslands, deciduous and evergreen forests, scrublands, and deserts. These plant communities intermix throughout the monument, creating a truly diverse mosaic of species associations.

* Arizona Geology Magazine,, accessed April 6, 2017.

Want to learn more about the geologic features of Chiricahua National Monument? This 2009 NPS Geologic Resources Inventory Report provides detailed information, as well as maps and photographs. Also check out the Geodiversity Atlas for the monument (and many other parks).

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    Last updated: December 13, 2018

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