Learning While Hiking

December 16, 2022

By Ernie Pratt

West of Flagstaff is the seldom visited Red Mountain area. These features seen in the amphitheater are called Les Demoiselles, which are softer rocks capped by more resistive volcanic bombs.

One of the good things I have noticed about being a Sedona Westerner is that we are always willing to learn, this day we went down a different trail that had a heavy component of learning along with the hiking.  A number of Westerners and other OLLI students attended an OLLI Sedona, Yavapai College class, “A Geological Field Trip to Red Mountain”. 

The day started chilly in the parking lot as we were adjusting our packs and poles. There was a chance to handle a collection of unusual rocks that had been found along local trails by our facilitator.   He also showed us on poster boards the different kinds of volcanos that make up the San Francisco volcanic field and discussed how they relate to the zones of weakness in Northern Arizona.

A little further up the trail we were accorded great views of three such volcanos. They were a Stratovolcano, Mount Humphries, the Slate Mountain dome and the Red Mountain cinder cone.  The trail is wide with only gently climbs, and is an easy, relaxing hike.   

Red Mountain, according to NAU geologists N.R. Riggs and W.A. Duffield, is a 740,000-year-old volcano that “represents the formation of a Strombolitic scoria cone along a Proterozoic steeply dipping normal fault with sector collapse and rafting resulting in a final stage of low fountaining and clastogenic lava flows along with a phreatic blowout and it is currently subject to water and wind erosion”.  Translation:  It ticks all the boxes for a volcano that blew out.

Reaching the main streambed that comes out of the volcano, we immediately noticed the first of a number of unique features that typifies this volcano.  On this bright, sunny day the sand in the wash fairly sparkled with what turned out to be dark crystals of resorbed amphibole and pyroxene.  There were also some less common xenocrysts of feldspar and clear quartz.  From that point onward, hiker focus greatly suffered as we continued up the trail, some bent over or on hands and knees, always trying to find that better and bigger and shinier crystal.

The various geographic features were brought into play; the high cliff far above us was actually the rim of the caldera facing away from us in a horseshoe pattern to the west.  It turns out we were actually entering the side of the volcano into what is locally known as the amphitheater, which was a result of an ancient steam blowout.

Part of our group experimented with walking up a nearby lapilli (cinder) covered trail, which turned out to be a very taxing and memorable experience for them.  The old adage two steps forward, one step back came to mind.  The rest of us climbed a short ladder and entered into a tuff-based wonderland.

After considerable jaw dropping observations, and some tense discussion, we agreed with the NAU authors: it sure looked like a phreatic blowout to us.

Changing topics, we briefly paused our geological endeavors as we learned how a number of peregrine falcons nest in these high cliffs, breeding late March through May.  Arizona is fortunate to have this naturally developed area, ideal for peregrines to breed and hunt.  Their nests were easy to spot little caves that had a multiple white streaks below them.

Nearby we climbed to a slight viewpoint in order to get a good look at a number of hoodoos (demoiselles).  More resistant blocks (volcanic bombs), of varying size, cap and protect the underlying, softer rock from erosion forming the pinnacle shaped towers.  It is a bit of a fairyland. 

Further into the amphitheater, this natural sculpting surrounded us and fueled our imagination at every turn.  We wandered a bit aimlessly up deeply incised slot canyons noting weathering, large dense volcanic blocks still caught up in the multi colored scoria beds.  These features signaled more hoodoos just beginning to form.  

After lunch we reluctantly but happily left this geological wonderland and returned to the trailhead.  We are now a bit more educated thanks to this OLLI class and hike.

The Sedona Westerners always welcome new members, and we have hikes multiple days of the week for all abilities. If you are interested in joining the club, please visit our website at sedonawesterners.org.  You will find an interesting history, the whole season’s list of planned hikes, and a handy membership link. It only takes five minutes to sign and start your new adventures here in the Red Rocks.

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