One of the most iconic views in Central Arizona is the Bulldog Cliffs as they tower over the calm waters of the Lower Salt River.
Formed 18 to 25 million years ago during a period of violent volcanic activity, these cliffs are made of rhyodacite — a tan-pink fine-grained igneous rock.
Now extinct, the volcanos here produced thick, silica-rich lava flows. Too viscous to run horizontally across the landscape, these volcanos built upward as bulbous domes.
And with gases unable to escape, eventually a lava dome would blow its top, sending thick layers of hot volcanic ash into the atmosphere and showering down on the region.
After each explosion, a large crater would remain atop the volcano’s high ridges — known as a caldera. And if you could watch the volcano over millions of years, you would see a cycle of lava flows building domes, an eventual explosion leaving behind a caldera, and then a restart of the cycle.
Geologists call this type of volcano a “resurgent caldera”, and the most famous of which we see today is the Yellowstone Caldera. The media likes to ominously call it a “supervolcano” and create alarm over its destructive potential every time an earthquake is detected nearby.
Fortunately for us in the southwest, the resurgent calderas of central Arizona have been extinct for over 15 millions years. So we need not worry — they’ve left only these ruggedly beautiful cliffs for us to fawn over.
The Bulldog Cliffs are part of the Goldfield Mountains, which along with the Superstition Mountains, are the most prominent remnants of the deceased resurgent calderas.
That’s it for today’s Daily Dose! Let me know if you enjoyed it.
-Jake
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