Flash Flood Man

 Last week I had the great fortune to spend time wandering around the Cedar Mesa sandstone (one of my favorite Permian deposits) Usually I am content to examine the red and white layering. The white a nice beach sand and the red debris from the Ancestral Uncompahgre Mountains.  But this time we happened to spy some rock art high on the Cedar Mesa cliffs.

This was one of my favorite panels. The cliff face is directly above the confluence of three nice sized drainages.

Below is a close up showing the image of arms help out to the side and wavy lines extending across the picture. It doesn't take much imagination to see that the arms were once connected to a body that has ironically been dissolved by water running down the cliff face. Often times these wavy lines indicate water and so this image looks like a figure standing in belly button deep water. 

Given the location of this image at the confluence of three drainages it is not a big stretch to suggest that this figure was made to warn people of high water.  Below is a flash flood sign taken from a National Park web site. There are just a few similarities between the ancient rock art and the modern traffic sign.

homogeneity of rock units

Over the years I have noticed that students have a tendency to assume that rock units are very homogeneous in both shape and texture. They expect the Navajo sandstone to be made of white sand grains in distinctive sand dune cross bedding everywhere they look. When you point out "different" structures in the middle of a rock unit they get confused ( just for a short time). Most of my students also seem to expect sedimentary rock units to be of equal thickness throughout their extent. I guess I can't blame them since I am just as guilty of using these stratigraphic columns that show nice rectangles for rock units.   The White Rim sandstone is a great example of a rock unit that noticeably gets thinner as you ride east. 

A few weeks ago I had the awesome pleasure of riding the White Rim Trail in Canyonlands National Park, an 80 mile jeep track created by the atomic energy commission in the 1950's which has made more money as a tourist destination than all the uranium ore pulled out.

   The White Rim is a resistant rim of Permian aeolian beach sand that delineates the inner canyons of the Green and Colorado Rivers.

 Early in the trip you can see the thickness of the White Rim sandstone.  There is a bicycle on top of the cliff in the distance for scale...It is a big cliff.

 Again, there are dots across the gorge showing the scale of the White Rim cliff.

 Halfway through the trip you can see that the formation thickness is much less than in the first two images.

Here, near the end of the trip we can see the thin white line, all that is left of the White Rim just pinches out in the Cutler formation. The beach sand ends and the debris running off the Ancestral Rockies takes over.

arborglyphs

While hiking around the San Juan Mountains we sometimes see some ornate tree carvings usually from sheep herders from the last century. These carvings tell us about the lonely life in the mountains these men lived.  Today I was riding down an old road when I saw what looked like a rock hammer carved into an aspen tree. I can't help but wonder what the story is behind this particular arborglyph.

The half moon moraine

While climbing to the top of Colorado I turned around and saw this great example of the moraine we had climbed earlier in the morning. 

The cirque above is now empty of any snow. 

There was once ice here

I had the good fortune of changing venue last week and do some hiking in my old graduate research area in Rocky Mountain National Park. Most of my work was done in the library but here on the eastern side of the Colorado Rockies we had the chance to look at some of the evidence left by glaciers. 

In this image you can easily see  the snow field up high, the remnants of the glacier that once filled this valley. I never made it up to the snow in this valley. In other nearby places we were able to see what little blue ice that was left. 

Below the snow lies the terminal moraine of the most recent advance, a small push that we dated about 1850 ish. That date always amazed me because of the advance of white guys and their families across the North American continent while the climate could support a glacial advance albeit a small one.   

Below the highest moraine is a solid rock outcrop that has been shaped by the passage of ice. This roche moutonnee shows ice movement from above downward. The upstream side is smoothed by the ice while the down stream side shows evidence of ice plucking. The ice partially melts by pressure, fills in the cracks and then refreezes with rock chunks stuck to the ice. The rocks move down stream leaving this choppy steep hillside behind.  

Below the image although unseen here is a great U-shaped valley. It doesn't get any more classical-glacial-terrain than here.

To study for my comps, I climbed into a number of these high valleys and physically touched all that the ice had left behind. Not only was it a fun way to study but it must have worked!

rock unit behavior

A few weeks ago I spent some quality time "under the Wingate" my all time favorite Canyonlands rock unit. In fact, the Wingate sandstone has its own facebook page. The Wingate sandstone was formed in the early Jurassic as a large sand sea or erg in the western US. It is quite easy to find cross bedding indicative of sand dunes. The sand grains are all very uniform in size and shape which creates some great erosional formations. In these images you can see how the Wingate has eroded to make some impressive towers. This is a classic formation found once the over-laying Kayenta formation erodes away. The Kayenta formation, is a combination of siltstone, sandstones and even some conglomerates and it acts as a cap rock for the easier-to-erode Wingate sandstone. 

With the protective layers above gone, the uniformed grained Wingate starts to fall apart with equally spaced cracks running vertically down the cliff face. As time proceeds and geology happens the crack widen until there are separate Wingate towers and eventually even they will erode down to nothing. 

This area along the Green River in Labyrinth Canyon shows the whole sequence of events from a large cliff face to totally missing.

The Wingate Towers

 The Wingate Towers head on

 The whole sequence: The left side shows an intact cliff face with an intact cap rock. The towers are found in the center while the right side shows the Wingate missing from the stratigraphic sequence. 

Class time in the back of beyond

Ah field work! well, less field work and more field sharing. This is the time of year where I head into the middle of the Colorado Plateau and share basic geology ideas with K12 teachers. We spend a day on campus at the Colorado School of Mines before we head to Moab UT to spend the next 5 days paddling down the Green River through Labyrinth Canyon. Our classroom is both the modern day transport of material down the river and the mid-Mesozoic climate of the dry arid sand dunes of the Entrada, Wingate and Navajo formations. But, it is not a one direction sharing, sure I do most of the talking but all of the teachers get together and share struggles, concerns, methods and triumphs of getting their students to understand the basic tenets of science. After a winter's worth of reading some newspaper's ideas of how our public schools are doing it is always refreshing to hear from the teachers themselves. It gives me hope about the next crop of scientists who are currently residing in Middle School.

It is truly a week of learning for all participants!

Sunrise on the river!

 Class time on the river.  We barge up and discuss the formations and their forming environments as we float past. 

 Hiking up a side canyon looking for petrified wood and dinosaur tracks. Did I mention that it was 113 degrees F that day? 

 The Wingate above the Chinle

 Moving between classrooms.