Saturday, November 19, 2011

A Geology Field Trip to Grand Canyon - Toroweap Overlook and Vulcan's Throne

Over Halloween this year, I embarked on a five-day field trip with many of my former geology students from Yavapai College in Prescott. I've been semi-retired from formal teaching for a few years now but the magic of geology just doesn't seem to wane for these die-hards. I love it! They choose a location and off we go. This posting is written by me but with illustrations from Bruce, Carol, and Mary Lea. I asked the class for photo's to show off what we saw and learned here. You can also view some of my photo's and narrative here from a trip I took in April.

The trip began with an overnight stop at Lees Ferry on the Colorado River. We meant to hike down Cathedral Wash but a recent storm had filled mudholes along that creek making it impassible. So, off to the hoodoos and here I am pointing out the amount of "deflation" on the landscape since this Shinarump boulder rolled down from the cliff above. The boulder is a conglomerate rock from this member of the Chinle Formation. The pedestal below is carved into the underlying Moenkopi Fm. This deflation is probably on the order of a few tens of thousands of years in length (just an educated guess). These features are found everywhere along the base of the Vermilion Cliffs and you can see two other large boulders in the background awaiting more defaltion so that they can have their pictures taken.

We finally arrived at the edge of the canyon and this is one of the viewpoints looking east. Many images from this place have been featured in mainstream advertising in recent years.

Contemplating the Grand Canyon. What a marvelous place.

At the main overlook we got a great view across the Colorado River into Prospect Valley. The lighting here does not easily show it, but this was once a deep side canyon that became filled with lava. The shadowed, inverted V canyon is what has been re-excavated since the lava filled the old canyon. On the left side of the photo but not as obvious is the Toroweap fault. It lies at the base of the scarp across the river to the left hand side of the photo. The vast majority of the Esplanade surface in the center of the photo is down dropped about 500 feet here.

Students on the edge of Grand Canyon looking into Lava Falls. Note the cross-bedding in the Esplanade Sandstone here.

One of the days, we hiked from camp over the sandstone ridge to Vulcan's Throne. There are few things as wonderful as walking on slickrock in the southwest.

Ken is checking to see if we have arrived at the top of this 500-foot tall cinder cone and his calculations verified that we ran out of volcano and were at the end of the hike. Actually, he is looking in the trail register located in a cairn on top of the feature.

What are the chances that a cinder cone would have erupted at the edge of the Esplanade over the Colorado River? This has got to be one of the most spectacular settings for a volcano - on the lip of a 3,000 foot gorge.

Pointing out the trace of the Toroweap fault across the Colorado River.

A group shot from the top of Vulcan's Throne. Note the wide, Toroweap Valley in the left background. This was also once the site of a big side canyon in Grand Canyon but was filled with numerous lava flows from the Uinkaret Volcanic Field. Recent offset on the Toroweap fault interrupted a small drainage on the north side of Vulcan's Throne and caused a playa lake to form just beyond and below the group. There is so much to see and learn here.
Back at camp, it was time for the Halloween celebration and here you see my very first pumpkin carved.

A basalt boulder with many native petroglyphs etched into it.

One last shot before leaving the Toroweap area. From left to right - Sharon, Clint, Ken, Louise, Mary Lea, Brenda, Carol, Bruce, Chris, Wayne, Barbara, Russ, Alice, George, and Dennis. Great folks - one and all.

Sunset from Toroweap Overlook.

Brenda wrote poem about our trip here:

Toroweap Time Shared by Brenda

"River's high,"
Sinyala sighs,
while Lava Falls'
 sirens call
"Come close."
From his cinder throne
Vulcan moans
"Where's the fire?"
Two-toothed Jack with Buddha smile
knows where embers glow and
shine magic 

on this hallowed night
Chris too:

Although too old to do some treks,
You are never too ancient to attempt
that first Pumpkin.  With skill, you
carved out eyebrows that resembled the
narrow curves of the Colorado.  Again
with competence, you lead our group of
aging Geonuts on another journey.
Adroitly you presented information for all to
digest, no matter how clogged are our skulls.
We observed hot air rising out of the canyon,
with birds capturing the drafts, and occasional
explosions of campfire discussion addressing
inflamed bodily emissions.
A new volcanic hill was scaled and all
groupies are content with another rewarding outing.
Thanks for being there,

and Dennis:

The Professor and the Pumpkin    
 by Dennis Peterson

Our leader, professor Wayne Ranney
can rhapsodize for days on carving
the Grand Canyon,
from Apatites to Xenoliths
but has never carved into a pumpkin.
How can that be?

Well, last Halloween history was made.
George and Carol, the pumpkin providers
for our Toroweap geology trip
during the Halloween celebration
presented the spheroidal object
to Professor Ranney.
Even though it wasn't stratified
or volcanic in origin, he went
at it like the mighty Colorado.

With pen first drawing the face
giving place for the knife to follow
not unlike those early miners
who dug out the Grand Canyon
those many many years ago;

a place to insert their shovels.  The orb now looking like a topo map  and with directions coming from all sides  the first slice was made, erosion by knife.  The face began to take shape, first the eyes, then nose  and lastly the mouth.   Oh schist! a slip of the knife,  a tooth has been mass wasted.  Emergency call to Dr Weld  our groups' staff Dentist.  But how to reattach it?  Forward comes Ken, Dr Welds  able assistant with a toothpick  for the attachment;  now the Grand Toroweap Pumpkin  has its smile restored.  With candle inserted and lit  casting an eerie smile over us  not unlike professor Ranney's  when he stumps the class  with questions like  "who here has ever seen or lit a fart?"  Questions like that, deep thinking  and reflective cause his students  into long and meaningful discussions.  Meanwhile the Grand Toroweap Pumpkin  all lit up and smiling, wondering  what all this talk is about  and what it has to do with geology.  Even though the Grand Toroweap Pumpkin  has an internal flame glowing  and could work very nicely  as a flame thrower,  it's of no use for the topic now discussed  for no thought was given  to hollowing out a fumarole.   With only a carved head and nothing below  the Grand Toroweap Pumpkin can only laugh with us.

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