Chiricahua National Monument was formed 20 million years ago when a fierce volcanic eruption shook the land. This eruption was one thousand times greater than the 1980 eruption of Mount St Helens and spit out two thousand feet of highly silicious ash and pumice. This ashy mixture formed a rock called rhyolitic tuff and eventually eroded into the spires and unusual rock formations of today.
Interesting information from a postcard.
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