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Roger Weller, geology instructor

Tonto Natural Bridge
Noel Adams

Historical Geology
Spring 2005


                                           A GEOLOGICAL WONDER


Tonto Bridge is a magnificent place. Considered to be the largest travertine bridge in the world, its geological history is as fascinating to read about as the bridge is to explore. 






The Cave’s First Visitors…

As far back as four-hundred years, the Apaches used the area of Tonto Natural Bridge for seasonal hunting and farming.  However, it was not until 1877 that a Scottish Gold prospector, David Gowan, would document the site for the first time.  Running from the Apaches, Gowan found himself hiding on a shelf high up in the cave for three days awaiting a safe exit.  Gowan left the area at the time but was so impressed by the beauty of the little valley and its rainforest-like grottos that he later, in 1882,  took advantage of the Homestead Act  and laid his own claim to this tiny one-hundred and sixty acre piece of paradise.

            By 1908, word of the bridge spread like wildfire.  Gowan persuaded family members from Scotland to join him on his land to help him take care of it.  Gowan’s nephew, David Gowan Goodfellow, was among those who traveled from Scotland.  Working together, they carved out the harrowing entrance road to the canyon that still exists today.  To accommodate the flood of visitors, they also built a small guest lodge, which, after being updated in 1927, landed itself on the National Register of Historic Places.


The Bridge’s Dimensions…      

In 1990, Arizona declared the area a state park.  Since then, visitors have been able to hike down its steep trails into the cave and witness the marvel of its enormity first hand.  The bridge itself is over 183 feet high, 400 feet long, 150 feet wide, and about 100 feet thick at the top.  That is huge!  Pictures really do not do it any justice.  You have to see the bridge and stand in the cave first hand. If that isn’t enough, wait until you hear how it was formed.

Rocks, Water, and Lava, Constantly At Odds…


Tonto Natural Bridge went through many stages of complex development to arrive at it’s present state of being.  The water source that runs through the valley and under the bridge, known as Pine Creek, plays a significant role in the formation of the travertine wonder.




According to the description on the Arizona state parks web site (, this is how it was formed.  “The west side of Pine Creek was formed by a flow of rhyolitic lava.  The rock eroded then leaving in its path purple quartz sandstone.  The rock layers were then lithified, tilted and faulted.  The area was then covered by sea water, (1.7 million years ago), leaving behind sand and mud sediments.”  The very active volcanics of the area must have then covered the area and its rock layers with Lava, forming a cap of basalt.  Through tectonic shifting and years of erosion, it is thought that Pine Creek Canyon was formed.

            The web site further explains “Precipitation began seeping underground through fractures and weak points

in the rock, resulting in limestone aquifers.  As a result, springs emerged, carrying and depositing the calcium carbonate required to form a travertine dam. Over time, Pine Creek, with the awesome power of water behind it, eroded through the travertine and formed the Natural bridge we see today.”








Tonto Natural Bridge is something of a must see for those who haven’t.  At its 4500 foot elevation, there are several beautiful trails leading all around the bridge with wonderfully fascinating geological formations to explore.  Pine Creek shows itself not only in the bottom of the enormous cave but seeping out of fissures all over the place as well.  Bright green moss grows abundantly near these fissures making them an obvious stopping point on the trails.



So if you love Geology like I do, spend the day exploring this travertine wonder of Northern Arizona.        








Sources, 5/01/05, 5/02/05, 5/02/05, by Jill Florio,  4/28/05