The San Francisco Peaks existed as a geologic mystery to modern science until 1980. Geologists simply could not understand how an odd-shaped mass of peaks could form in total isolation from plate tectonics. Volcanic activity was a theory, but no existing models could prove how a volcano could erode in such an unexplicable way. Mount St. Helen's eruption in 1980 changed all of that. Scientists were able to understand that a volcano could erupt causing an entire face of the mountain to disappear. Aerial photos and geologic testing helped to conclude that such was the San Francisco Peaks' fate long ago. Geologists believe that the original peak was over 16,000 feet high.

Driving on I-17 through Arizona, you have to blink when you see the mountain range. It's huge, isolated, and totally unexpected. The San Francisco Peaks contain one ski resort (Arizona Snowbowl), a protected alpine environment (Inner Basin), and the highest point in Arizona (Humphreys Peak).