Monday, April 22, 2013

Grand Staircase-Escalante National Monument and Capitol Reef - In Snow!

During the week of April 15 to 19, I led a group of seven explorers to southeast Utah and the stunning landscapes of Grand Staircase-Escalante National Monument. The first half of the week saw the arrival of winter storm Yogi. We were "encamped" in Boulder Utah at the southern edge of this large storm. And we were treated to a rare sight of the red rocks in snow. It was a fantastic experience.

On the way up to Utah, the wind was howling which explains the bad hair day. But we stopped at Grosvenor Arch and took a re-photograph of a picture published in the September, 1949 issue of National Geographic. Even the trees were still there 64 years later (although the pinyon pine had died at the height of the last drought).

Morning, April 17. Here is Long Canyon in Grand Staircase-Escalante. There aren't many days in the spring when you can see it this way.

This is Steep Creek mantled in snow. The cliffs inside the canyon are composed of Wingate Sandstone with caps of the Kayenta Formation on top.

Wingate cliff and pinyon pine in the snow on the floor of Long Canyon

This cottonwood tree was beginning to leaf out when it was caught in the storm

The round balls on the cottonwood will eventually open and disperse the "cotton", more correctly called seeds.

Ron H. looking up into a narrow slot canyon

Box elder trees in the slot canyon. The  box elder is a member of the maple family and is the state tree of Utah.

The end of the slot canyon - a magical place


Frosty branches

Snow covered trees. The snow was completely melted by the time we returned in the mid-afternoon.

Farther down the Burr Trail, we caught a glimpse of the Waterpocket Fold (middle distance) and the snow covered Henry Mountains in the far distance. The snow was at a relatively low elevation.

A wider view

A closer view

A western view

An enticing view

A happy crew. John G., Ron H., Ed H., John K., Catherine E., Stan B., Kate K., Wayne R., and Gail M.

We soon got a view over the top of the Fold, down to the Strike Valley

We walked the Burr Trail Switchbacks!

The road is visible at the bottom of the canyon

Look at the angle of folding on these once flat-lying strata. Fine-grained river deposits of the Kayenta Formation (left) with the light-colored Navajo Sandstone on top to the right.

A pull-away view of the same contact and angle of folding

On the floor of the canyon

Heading home! This trip was conducted as part of the Museum of Northern Arizona Ventures Program. These are fantastic trips!

Friday, April 12, 2013

The Highway 89 Slump Near Page - A Re-Evaluation

A colleague in Page, AZ walked up the lower slope of the Chinle Formation beneath the base of the slump along Highway 89. He did this only three days after it happened and got some really good shots, which he shared with me. It is clear from his pictures that the slump is truly a geologic event as ore than just road metal is involved. See my previous posting here where I postulated that maybe just the backfill in road construction was what failed. However, you will clearly see here that Chinle Formation bedrock also broke away from beneath the road.

This is a sequence of four pictures that progressively approach the lower scar of the break. You can see it here beginning in the upper right and traversing across the center towards the large white boulder in the lower left.

It is more clearly visible here. It looks like the material has collapsed vertically downward.

The break is likely about four to five feet in height. This is located well beneath the roadbed.

This material may have risen upwards as the mass of the slide exerted pressure from above

Another view from above of other parts of the failure. Now we'll look at the road damage itself.

The small crack running from the bottom center of the photograph up towards the top shows that a long stretch of highway was affected by movement

It was this unusual (?) straight break in the roadbed that initially caused me to think that perhaps only road metal hade been involved in the movement. A purely geologic event didn't seem to make sense with such an ordered break.

Note the oil streak likely caused when a very surprised driver "discovered" that something was horribly wrong with Highway 89 below the Big Cut at approximately 5 AM on February 20, 2013. As this person was driving north (uphill) in the slow lane (and this is purely a guess), their left wheels must have dropped into the slumped portion of the highway, causing the entire vehicle to lurch to the left. It looks like their oil pan or some other vehicle reservoir ruptured, leaving the oil streak. Looks like they gained control (?) and steered back to the right as shown by the streak going toward the upper right.

Close-up of the oil streak

Look at these tension cracks beneath the break. They look cavernous in this close-up view and they likely go down into bedrock on the slope of the Echo Cliffs. Remember that larger, older slumps are located on this slope.

Damaged road

It's hard for me to tell if this oil streak is part of the previous one shown or if it is another one that pre-dates the slump. But it shows a few inches of offset here and on the white line.

Yikes! That's a pretty good gape.

It looks like some surface rocks were also involved in the gravity affair

Note how the tension ripped apart the metal guardrail

View in the downhill direction (south) showing the extent of the damage in a telephoto shot. The prominent oil streak shown earlier is barely visible in the center of the photograph crossing the double yellow line back to the left. It looks like someone was clearly surprised by this early morning collapse. It is fortunate that no one was seriously hurt and that the geologic event was rather small.

An earlier human mishap on the slope below - the car obviously is well rusted

Monday, April 08, 2013

Nevada's Valley of Fire - A Tortured and Magnificent Desert Landscape

I just finished a fantastic four-day exploration of Nevada's Valley of Fire State Park. The trip was a reunion of sorts with past students and friends from my teaching days at Yavapai College in Prescott and Sedona. They scouted the trip, planned the itinerary, and executed a fine geology program. I am so lucky to have such wonderful alumni and friends! They are awesome.

I had driven through the area briefly in the 1970's and knew the area would be a good one to visit. But I had no idea that it would be OUTSTANDING!! The geology is "off the charts" fantastic and we visited during the spring wildflower season.

East entrance to the park

The main story here is that during the Early Cretaceous (145 to 100 million years ago), western North America was subjected to compression from the west and gray Paleozoic limestones were shoved horizontally to the east over Jurassic sandstones. In this overview shot, you can see the result. In the foreground is the Jurassic Aztec Sandstone, while in the background are the Paleozoic limestones. The thrust fault that created this inverted relationship is known as the Muddy Mountains thrust fault.

First, let's describe the Aztec Sandstone, the rock unit that gives the park its name. It is time equivalent to a common Colorado Plateau unit known as the Navajo Sandstone. They are one in the same but when they were named no one knew that. Geologists could attempt to remedy the discrepancy but they are not generally "lumpers". The Aztec and the Navajo are one in the same.

The Aztec has beautiful eolian textures like these wind ripple marks

Another set of ripple marks located on the lee side of an ancient dune. Note how the ripples appear to climb up the lee face of the dune. I have seen this occurrance on modern dunes in India and the Middle East.

Close-up of the ripple marks

Balanced Rock shows that the Aztec Sandstone has experienced many episodes of deformation. Here the beds dip steeply to the left (north) recording an anticline that overprinted the thrust.

Balanced Rock framed by a Beavertail cactus in bloom. The flowers on the trip were spectacular.

Petroglyphs on the Aztec near Mouse's Tank

Although the plane of the Muddy Mountains thrust fault is not directly visible here, the result definitely can be seen. The limestones are 500 to 300 million years old and the red sandstone beneath is only 180 million. Imagine the first geologist to ponder this odd relationship and the wonder they must have felt when they realized what this represented. If that is not enough, later studies showed that the limestone here traveled more than 50 miles along the thrust!

From our camp we could look to the Virgin River Valley to the east, known locally as the Overton Arm of Lake Mead (the reservoir has backed up into the valley of the Virgin about 35 miles). The rocks in the distance contain an almost complete section as seen in the walls of the Grand Canyon. The cliff-top unit is the Kaibab Limestone and the prominent cliff in the middle is the Redwall Limestone. I always love seeing the Grand Canyon section of rocks outside of its "normal" home.

A camp scene in Group Site #3

On the second day we explored the northern part of the park to Rainbow Vista. It is aptly named.

Desert marigolds in bloom

The colors in the Aztec Sandstone are a big part of the geologic story here but involve groundwater fluids that remobilized certain iron oxides within it. First the sandstone was colored red by the dissolution of iron rich minerals within it such as mica or hornblende. The iron coated each grain of sand. Then fluids traveled along faults and fractures and removed some of the iron oxide to make the rocks white. Then a third period of groundwater movement brought in purple and yellow staining (limonite and goethite). Thus was formed the rainbow colors of the park.

In some areas the colors blend wildly

Groundwater fluids also hardened the cement within fractures and joints in the rocks

A geology talk in the field is worth five talks in the classroom. I did  not have to lead this trip - some of the students did the research and presented to the group

We next took a hike into a fantastic area that is reminiscent of Coyote Buttes in the Vermilion Cliffs

Along the way, the Chinle Formation made an appearance. It is seen as the drab gray claystone in the foreground at the base of the red sandstone.

Fantastic colors

Eroded into wonderful shapes

Valley of Fire reflection time

At the end of the hike we could see the Cretaceous Willow Tank Formation, an assemblage of coarse rocks that unconformably overlie the Aztec

The deposit contains some well rounded quartzite clasts as well as clasts of the Aztec. Hmm?

The lower part is colored red with an upper part that is more gray. This color difference likely reflects what kind of rocks were eroding with the lower, redder beds derived from areas of Aztec Sandstone and the upper grayer lenses from Paleozoic limestone terrain. The interpretation is that this unit is the debris being shed off of the thrust front a few miles west of here. Imagine a highland to the west that originated when limestone deposits were being thrust up to the east over the Aztec Sandstone. As erosion attacked the thrust front, gravel was washed to the east over the Aztec. That is what is exposed here.

Brittlebush in bloom on the conglomerate

We next hiked to the White Domes. Primroses were in bloom along the way.

View into the slot canyon area at the White Domes. Note the dark wall of adobe near the sandy patch on the floor of the canyon?

It is the remnants of a Hollywood set for the 1966 movie, "The Professionals". The movie starred Lee Marvin, Burt Lancaster, and Jack Palance and many scenes were filmed here and in Death Valley. Ironically, Helen and I watched the movie last night, just days after returning home! I can highly recommend the movie for southwestern scenery.

Many scenes in the movie were filmed in this slot canyon, carved in the Aztec Sandstone

Sandstone, fractures, and light

On the third day, we drove to the Lake Mead National Recreation Area and hiked to the Bowl of FIre. Here Dennis gives the group a short lecture. But this blog is long enough and its time to end.

Sunset on the Muddy Mountains from camp

The group photo at Frenchman's Mountain. Thank you everyone for this wonderful trip!