Showing posts with label East Kaibab Monocline. Show all posts
Showing posts with label East Kaibab Monocline. Show all posts

Tuesday, June 24, 2014

A Land of Strange Standing Stones, and an Odd Connection to the Grand Canyon


There are a lot of strange landscapes on the Colorado Plateau and otherworldly scenes. Some are famous enough as to not surprise first time visitors, such as the spires and hoodoos at Bryce Canyon National Park. But others are hidden, strung along gravel roads far off the beaten track. Seeing them for the first time comes as a shock. These rocks just aren't "normal". 
The largest single park in the Colorado Plateau region is also one of the least familiar. Really, how many of you have heard of Grand Staircase-Escalante National Monument? It covers a huge swath of land north of Grand Canyon and Glen Canyon National Recreational Area, west of Capitol Reef National Park, and south of Bryce Canyon. It was controversial in its birth, as have been most of our National Monuments, but it is indeed worthy of protection. We are only just beginning to discover the treasures that lie within its borders.

Our journey on this day would take us from Glen Canyon Dam to Bryce Canyon National Park via Cottonwood Wash Road, a gravel track that runs for thirty miles along the East Kaibab Monocline, known here as the Cockscomb.
Part of the Cockscomb (East Kaibab Monocline) courtesy of Google Earth
A monocline is a step-like fold, flat on either side and flexing in the middle. Such folds often develop where fault moves beneath horizontal sedimentary layers. The Cockscomb is an extraordinary example of one of these features, with a vertical separation of nearly a mile (erosion has leveled off much of the uplifted rock, so the actual elevation change across the fold is much less). The fold is also very long. It extends for 150 miles and actually forms the eastern edge of the Kaibab Plateau where the Colorado River turns west to form the deepest part of the Grand Canyon. It formed during the Laramide Orogeny in Late Cretaceous-Early Paleogene time.
From Wikipedia
The rocks within the monocline have been twisted so much that the layers are vertical. They have also been attenuated (stretched) so that some of the layers are thinned out. The rocks have been brecciated (crushed) to some extent, which provides a probable explanation for the strange towers and pinnacles found here and there along Cottonwood Wash Road. Groundwater following the fractures would have left mineral deposits that had the effect of reinforcing and cementing some of the most deformed rocks. Erosion removed the surrounding softer rocks leaving behind the towers and spires.

Pareidolia is the tendency of humans to build patterns out of randomness, seeing things that aren't really there: faces in clouds, and human or animal figures in rocks. Who does the rock below bring to mind?

The final rock in our little mini-tour of the Grand Staircase is Grosvenor Arch, which is really two arches, and which once was called Butler Arch until people on an expedition with the National Geographical Society decided to name it after their boss. They apparently had more pull with the Board of Geographic Names. It's not part of the monocline, but is instead at the boundary between two layers of different erosional resistance. The upper rock is a conglomerate equivalent to the early Cretaceous Cedar Mountain Formation, while the lower layer is the Henrieville Sandstone of Jurassic age. The largest opening is 152 feet high and 100 feet wide.

Lastly I have pictures of flowers. Despite the ongoing drought, there were some beautiful wildflowers blooming in one of the side canyons we explored. There were Evening Primroses...

...and some beautiful Sego Lilies, the state flower of Utah.

Friday, July 19, 2013

Out in America's Never Never: Barriers and the Thin Line of Civilization

Photo by Mrs. Geotripper

In math, getting from Point A to Point B is hardly a problem. It's a straight line most of the time, or an arc, determined by some kind of equation. Getting from point A to point B can be a problem in a city, since buildings are often in the way, yet a good map or a vocal GPS unit gives you plenty of routes and choices to avoid traffic and delays.

Out in America's Never Never, the vast desert encompassing the Colorado Plateau and Basin and Range provinces, getting from Point A to Point B becomes a true challenge. Mountains may block the route, as the Forty-Niners found during the California Gold Rush (and earlier settlers like my ancestors, the Donners). There might be flat, open ground between one point and the other, but there might be no water. In a pre-automobile era, that was a serious problem. But out of all these examples the Colorado Plateau has one really impressive barrier: the Colorado River.
Photo by Mrs. Geotripper

What's the problem? It's a fair sized river as such things go, the biggest of the American Southwest, but it is hardly a trickle compared to many rivers back east and in the Pacific Northwest. Those rivers were barriers to travel, but numerous ferries and bridges soon solved access problems a long time ago (and numerous boats used the rivers themselves as a highway). The Colorado, though, is a geologically young river. It is rapidly cutting downward through the sedimentary and metamorphic rocks of the recently uplifted continental crust, and the consequence of this is an unnavigable rapid-filled river ensconced in a deep vertical gorge along its entire pathway through the plateau country. Until the Navajo Bridge (above, left) was constructed in 1928 the only place to cross the river between Moab, Utah and Needles, CA, a river distance of 600 miles, was at Lee's Ferry, about five miles upstream of Navajo Bridge (the completion of which put Lee's Ferry out of business). The ferry was the only spot on the river whose approach was not overly complicated by vertical cliffs.

There are more bridges today, but there is still a 300-plus mile stretch between Navajo Bridge and Lake Mead at Hoover Dam where there are no crossings (except the footbridge in Grand Canyon near Phantom Ranch). Travel through the Colorado Plateau country is still complicated by this fact (and frankly, it should remain so).

The paved highways give us a somewhat false sense of easy access, as they must also surmount or circumvent barriers in the landscape formed by river canyons and vertical cliffs. As long as there is gas in the tank, a working air conditioner, and properly tuned engine, we give little thought to how tenuous our control is over our localized environment. A flat tire on a deserted road on a blazing hot day can be life-threatening. And small geological events can have far-ranging consequences.

The original plan for our trip (conceived a year earlier) was to leave the North Rim of Grand Canyon and scoot down the slopes of the East Kaibab Monocline into the Navajo Section of the plateau country. We would cross the Colorado River at Navajo Bridge, turn at Bitter Water onto Highway 89 to Page, Arizona, where we would have a slow-paced tour of Horseshoe Bend, Glen Canyon Dam, and the incredible Antelope Canyon. From there it would be a fairly quick drive to Navajo National Monument, where we would be camping for the night. It was meant to be the most leisurely day of the trip.

Oh well....

The picture above gives a hint about how geology made our day a constant exhausting race against time. The Vermilion Cliffs are a prominent part of the Grand Staircase, revealing early Mesozoic formations, including the Chinle, Wingate and Kayenta. The Chinle, at the base, is composed of easily eroded shale and siltstone, and is subject to slope failure. In the picture above, looking across House Rock Valley, the lower slopes look tilted because they are part of a huge rotational slide.
If you take a big group through this region, you will need to make the camping reservations five or six months in advance, and even at that I nearly missed getting reservations for Arches National Park and the North Rim of Grand Canyon. As such, once the schedule has been established, it can't be easily changed.

But geology can change. Highway 89 from Bitter Water to Page starts out in spectacular fashion, climbing a slope of Chinle to a big cut through the Echo Cliffs, composed of the Wingate, Kayenta and Navajo formations. The view from the upper highway is a stunning panorama of Marble Canyon, the Vermilion Cliffs, and the East Kaibab Monocline that forms the margin of the Kaibab Plateau and Grand Canyon.
Photo by Mrs. Geotripper
The problem for the road engineers was getting across the Chinle slopes. The Chinle doesn't like highways on the flatlands (swelling and settling of the clays turns the best planned highways into roller-coasters), but it especially doesn't like roads on slopes.

Ultimately they chose to put the road across an ancient landslide not unlike the one in the Vermilion Cliffs above. It is especially visible in Google earth images, where a white outcrop of Navajo Sandstone can be seen well out of place next to the highway (below).
Source: GoogleEarth

In February, a portion of the old slide gave way, destroying a significant stretch of the highway. This wasn't the kind of slide that could be fixed easily, and the road will be out of service for a long time. The Echo Cliffs constitute a significant barrier to east-west travel, and between Bitter Water and Tuba City, only one dirt road crosses it. The state is in the process of paving the track, but it was nowhere near done when we passed through.
Source: Lee Allison, at http://arizonageology.blogspot.com/2013/03/adot-estimates-35-million-to-repair.html

If we were going to see the Navajo Bridge and the Colorado River, we would need to make a 140 mile detour to get to Page and our other objectives. And then backtrack around 70 miles.We barely made it to our tour appointment at Antelope Canyon at 3 PM. We got to see Horseshoe Bend, but the visit to Glen Canyon was cut very very short, and we didn't reach camp until well after dark.
Source: Arizona Department of Transportation
It was a long day...but spectacular, just the same. More later!

For more information about progress with Highway 89, check out http://www.azdot.gov/us89/