Geological Destination - Four Corners Monument

Being located at the junction of four states, Four Corners Monument might just as well be considered a political park. However, geology is everywhere and therefore this is a perfect example of a geological park as well. The Four Corners Monument is a Navajo Tribal Park that designates the boundaries between the states of Utah, Arizona, Colorado, and New Mexico. It also designates the boundaries between the Navajo Nation and the Ute Mountain Ute Tribe Reservation. We visited the park on my birthday back in March of 2019. 

Me, laying across all four states at the monument. 

It has been said, by many people, that this point does not actually represent the point of intersection of the four states. These people are wrong. As noted by NOAA:

"... the Four Corners monument was established at the point he [surveyor Chandler Robbins] determined, to the very best of his ability and using the available technology, to be the prescribed location of 109 degrees 03 minutes West longitude and 37 degrees North latitude."

This precise location, however may be off by ~1,800 feet to the west of the monument. However, since this point was surveyed as the junction of the four states, and approved by the governments of the four states as well as the federal government, it IS the location of the junction, regardless of what the original intention of the surveyor may, or may not, have been.

It should also be noted that acclaimed geological landmark, nearby Ship Rock, was used as one of the marker locations for the designation of the Four Corners Monument. My next post will be on Ship Rock.

A closer look at the geodetic survey marker, designating the actual Four Corners point.

The Four Corners Monument sits within the Colorado Plateau. An area that is being forced upwards by the subducted Farallon Plate. 

Location of the Colorado Plateau. Image courtesy of Woodward, 1973.

Starting ~100 million years ago, along the west coast of North America was a subduction zone. This is where one plate goes beneath another plate. In this instance the Farallon Plate subducted, or went beneath, the North American Plate.

Graphic of the Farallon Subduction. Image courtesy of the NPS.

Over time the majority of the Farallon Plate was completely subducted, including the mid-ocean ridge (aka spreading center), leaving behind a new type of plate boundary along the coast of California. Instead of a subduction zone, there now was left a transform plate boundary, where one plate slides passed another one. This plate boundary is better known as the San Andreas Fault. Remnants of the Farallon Subduction Zone still exist along the coasts of northern California, Oregon, and Washington. 

Over the past ~10 million years, the subducted Farallon Plate was still a very hot plate, and therefore wanted to rise up underneath the North American Plate. Because of this, the Farallon Plate started to push upwards on North America, creating a region of the continent that is rising vertically upwards compared to the surrounding regions. This is the Colorado Plateau.

The geological features of the Colorado Plateau surrounding the Four Corners Monument. Image courtesy of Woodward, 1973.

The Colorado Plateau is made up of many of the world's most beautiful landscapes because of these geological forces playing around in the region. Looking specifically at the Four Corners region, anyone who has been to the Four Corners Monument will also notice that this area is a relatively flat, mountainless plain. This region is known as the Four Corners Platform. The platform is a relatively flat region that sits as an intermediary between adjacent basins and uplifts. In an area surrounded by mountains and canyons (and several anticlines (A-shaped bends in the rocks)) this region just happens to be in the middle of it all forming a flat surface. 

Geological Map of the Four Corners Monument. Image courtesy of NGMDB.

Looking at the rock units that cover the Four Corners Monument, they are represented on the map above by the symbols Jmw and Jmb, These are both members of the Upper Jurassic Age (~585 million years old) Morrison Formation. The Brushy Basin Member (Jmb), which covers the actual monument, is an interbedded green, purple, and grey mudstone and siltstone with grey and tan sandstone and conglomeratic sandstones. Known for its dinosaur fossils, the Brushy Basin Member was deposited from prehistoric rivers (fluvial) and lakes (lacustrine). The underlying Westwater Canyon Member (Jmw), is a yellowish-grey sandstone containing conglomeratic lenses and dark-reddish-brown siltstone. The Westwater Canyon Member is also a fluvial (river) deposited unit.

References

https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.544.8012&rep=rep1&type=pdf

https://www.ngs.noaa.gov/INFO/fourcorners.shtml

https://bluffutah.org/four-corners-monument

https://ngmdb.usgs.gov/mapview/?center=-108.996,36.967&zoom=10

https://ngmdb.usgs.gov/Prodesc/proddesc_4550.htm

https://www.sciencedirect.com/science/article/abs/pii/0037073889900705

https://sed.utah.edu/Morrison.htm

Random Geology Pic - Grand Canyon National Park from the Air

Like the recent Dinosaur National Monument pic I posted earlier, I seem lucky enough to catch some of America's best National Parks while flying overhead. Here are a few of Grand Canyon National Park. The flight was from Salt Lake City to Phoenix back in October of 2016, which happened to perfectly line up with the Grand Canyon. I highlighted the Grand Canyon in my Geology of the National Parks Through Pictures a little while ago. 

Aerial view of the Grand Canyon.

The Grand Canyon is a massive erosional feature formed through the movement of the Earth's crust known as Plate Tectonics. Here, we are mainly focused on the interaction of the North American plate and the Farallon plate. 

Subduction of the Farallon Plate below North America. Image courtesy of the NPS.

Off the west coast of North America used to be a plate called the Farallon Plate. It was being subducted (going beneath) North America for several millions of years until the majority of the plate had been completely subducted. This recently subducted plate was rather hot and therefore pushed upwards on the overriding North American Plate. 

The Farallon Plate below North America. Image courtesy of Written in Stone. 

As the Farallon Plate traveled below North America, the upward force of the hot plate pushed up a section of North America known as the Colorado Plateau. Surface features, such as rivers, are then locked in place as the ground surface moves upwards, the rivers start to erode more and more downwards. This creates features such as the Grand Canyon and things called "entrenched meanders" where formerly meandering rivers are locked into place as they are now eroding downwards in that meander shape. 

An entrenched meander of the Colorado River

The Colorado Plateau has several entrenched meanders, besides just the one in the image above including at Natural Bridges National Monument, which I covered a little while ago.

View of the Grand Canyon.

As erosion within the canyon deepened, it also widened. This created one of the largest canyons on Earth seen here at the Grand Canyon. Although one of the largest canyons on Earth, the Grand Canyon is not THE largest. There are several larger canyons, specifically in areas where similar processes are occurring by the significant uplift of the ground surface, such as along the Himalayan Mountains. 

More far off view of the Grand Canyon.

Geology of the National Parks Through Pictures - Glen Canyon NRA

My next post about the Geology of the National Parks Through Pictures was another one long ago. The year is 2009 when the wife and I took our puppies down to go camping at Lake Powell, also known as the Glen Canyon NRA.  

You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

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Glen Canyon National Recreation Area
Glen Canyon National Recreation Area, also known more commonly as Lake Powell, is a rather large reservoir on the border of Utah and Arizona. It's a great place to go camping, but even a more fun place to take a boat and explore the canyon. Unfortunately this trip was long ago before I was collecting entrance signs, so no entrance sign shot for this one (yet).


Here is the view driving into the main canyon from the south. The geology within the Glen Canyon NRA is fantastic. There are rocks absolutely everywhere! The formation of the area occurred when the entire Colorado Plateau was forced vertically upwards. The reason for this is complicated and I won't go into it right here, but just know that this entire region is being pushed up vertically. Because the region is being pushed upwards, rivers in this region, specifically the Colorado River, are quickly eroding downwards into the ground, creating monumental canyons such as the Grand Canyon. Glen Canyon, upstream of the Grand Canyon, is also along the Colorado River. The Colorado River is dammed just across the Arizona border by the Glen Canyon Dam ,creating Lake Powell within Glen Canyon.

Glen Canyon NRA is so large that it covers a wide variety of rocks depending where within the canyon you are located. We camped near Bullfrog and stayed in this general vicinity for our entire trip so the rocks that we saw are all generally the same age and formation. Most of the rocks within the canyon are sandstones of various ages. The rocks above are rocks within the San Rafael Group, a late Jurassic (170 to 160 million year old) formation of rocks. 

 
The rocks within Lake Powell sometimes form nice little islands that is possible to walk around. Here is one such island. All of the sandstone pictured here are likely the Entrada Sandstone, a member of the San Rafael Group. Although many of the sandstone units have a tendency to look alike. The Entrada is an aeolian sandstone, meaning that it formed from prehistoric sand dunes. The bed lines seen in the foreground are what is known as cross bedding, formed from the stacking of sand over a sand dune, creating parallel lines that often form at an angle to the way the rock unit (bed) is laying.

 Within the Entrada sandstone I found these weird nodules as well. This is an iron oxide concretion within the sandstone. They likely contain goethite, as well as hematite where it is reddest according to sedimentologist Dr. Marjorie Chan of the University of Utah.

Some more iron oxide concretions within the sandstone. These are more common in the Navajo Formation, known colloquially as "Navajo berries". It is uncertain exactly how they form though.

 Walking with the puppies along the slickrock surfaces of the Entrada Sandstone.

 View into the distance of what is likely the Romana Sandstone, another Late Jurassic sandstone, which lies on top of the Entrada Sandstone.

Nice, puppy free, view of the Entrada Sandstone.

 View across the water from the Entrada Sandstone island.

 View of the lake from our campsite near Bullfrog.

References

http://www.npshistory.com/publications/glca/nrr-2016-1264.pdf

Geology of the National Parks Through Pictures - Canyon de Chelly NM

My next post about the Geology of the National Parks Through Pictures was from a rather snowy trip to Arizona where my wife ran an Ironman and then we did a tour of some of Arizona's National Parks, that unfortunately got snowed out towards the end of the trip.

You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

Arizona State Geological symbols can also be found HERE.

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Canyon de Chelly National Monument
Our final park this trip, after a shortened visit to Petrified Forest and needing to skip another park entirely was Canyon de Chelly, which we ended up staying the night at the park hotel. Because of the snowstorm, the roads ended up being a bit hit or miss, with the lower elevation roads practically snowless and the higher elevation roads nearly impassable.

The entrance sign. The name of the canyon is a Spanish corruption of the Navajo word "Tsegi" meaning rock canyon. The pronunciation of "de Chelly" has slowly morphed over time from the Spanish "day shay-yee" to the modern day pronunciation of "d'SHAY". 

Canyon de Chelly is a unique park, since it is an actively lived in park. The park is run in conjunction with the Navajo Nation, where members of the Navajo Nation also live in the park and actively help preserve the ancient cliff dwellings within the walls of the canyon. The park is composed of several canyons, the primary two being Canyon de Chelly (the southern canyon with views from the road facing north) and the northern canyon, Canyon del Muerto, with views towards the south. The two canyons split off from each other towards the visitor's center.

When we arrived in the evening, we were advised to do the southern rim drive, along Canyon de Chelly, first. Then hold off and do the northern rim drive, along Canyon del Muerto, in the morning to get the best light in both. This is a view from Tunnel Overlook up the end of the Canyon de Chelly before the Canyon del Muerto splits off.

 A little bit further along the canyon, this is a view across the Canyon de Chelly from the Tsegi Overlook.

 View from the next stop at Junction Overlook. The canyon is made up almost entirely of one rock unit, the De Chelly Sandstone, which is a Permian age (~200 million years old) aeolian sandstone. Aeolian means that it is formed by blowing wind, in particular sand dunes, or a desert environment. When sand dunes are frozen in time, such as when they become rocks, and eroded you can see features termed cross-bedding. These rock preserve an ancient desert that used to be located here. We will look a little bit more into cross-bedding in a later photograph below.


A cross section of the Canyon de Chelly National Monument geology from the USGS. Although most of the canyon walls are composed of sandstone, there is a bit of the Triassic age Shinarump Conglomerate along the tops of the cliffs and the older Permian Organ Rock Formation along the base of the canyon.

View from the White House Overlook, looking down on the White House cliff dwelling. Many of the cliff dwellings on the southern side are not as easily seen from the road, however we can get a closer look at some of the later houses.

Here is the Face Rock overlook with the cliff dwellings located within the center of the cliff face in the center of the photograph.

A zoomed in view of the Face Rock cliff dwellings. These, and most of the cliff dwellings in the park, were built between 1100 and 1300 CE by the ancestral Puebloan people before the arrival of the modern day Navajo. This time period corresponds with other cliff dwellings in the region such as Mesa Verda and Tonto National Monument.

Along the Canyon del Muerto on the northern part of the park there are not as many overlooks but the views of the cliff dwellings are far better. This is the first stop along the northern rim at Antelope House Overlook with Antelope House below the cliff on the right part of the image.


Here is a closer up view of Antelope house. The buildings were constructed using a combination of the De Chelly Sandstone as building blocks and adobe bricks that were created from the mud and baked.

View from the Mummy Cave overlook. The cliff dwellings are located along the left side of the photo.


Close up view of the Mummy Cave cliff dwelling.

Yucca Cave cliff dwellings.

View up Canyon del Muerto at Massacre Cave Overlook.

View at the Massacre Cave Overlook with the cross-bedding in the De Chelly Sandstone highlighted by the snow. The cross-bedding is the angular lines through the sandstone layers. While here the layers of sandstone are generally horizontal, the cross-bedding is at an angle. The way cross bedding forms within a dune is illustrated below:


As sand is pushes up over a dune by the wind, the sand grains form parallel lines on the slipface of the dune. These parallel lines of the grains are what we see preserved within the rock. Image from Carleton.edu.

References

http://web.archive.org/web/20181001030919/https://3dparks.wr.usgs.gov/coloradoplateau/canyondechelly_strat.htm

http://web.archive.org/web/20170220180015/https://www.nature.nps.gov/Geology/parks/cach/index.cfm

http://npshistory.com/newsletters/sw_mon_rpt/special-report_no_20.pdf

https://serc.carleton.edu/NAGTWorkshops/sedimentary/images/cross_bedding.html

Geology of the National Parks Through Pictures - Petrified Forest NP

My next post about the Geology of the National Parks Through Pictures was from a rather snowy trip to Arizona where my wife ran an Ironman and then we did a tour of some of Arizona's National Parks, that unfortunately got snowed out towards the end of the trip.

You can find more Geology of the National Parks Through Pictures as well as my Geological State Symbols Across America series at my website Dinojim.com.

Arizona State Geological symbols can also be found HERE.

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Petrified Forest National Park
Following our visit to Tonto National Monument, we stayed the night in Winslow, AZ just as a massive snow storm struck the region. This forced us to change our plans a bit. The snow storm ended up closing most of Petrified Forest National Park, however we were able to at least hike along the Giant Logs Trail at the southern entrance while we waited for the gates to the rest of the park to be opened. They ended up never opening after several hours of waiting so we had to take the long way around the park without ever actually traveling through the park as planned.


The entrance sign during the blizzard.

A view up the Giant Logs Trail, showing how many of the logs there really are. Each of those boulders is a part of a petrified tree. This area really is littered with the remains of the enormous petrified trees. The logs here are preserved within a rock unit called the Sonsela Member of the Chinle Formation, a rock unit that spreads throughout much of the Southwestern United States.

Here is a view from up on top of one of the hills, looking down towards the visitor's center. A petrified log, is really just a fossilized tree. These particular logs lived ~216 million years ago, during the Late Triassic Period. When they died, they fell into a river, becoming buried under sand, silt, mud, and volcanic ash. After they were buried the cells of the tree were eventually replaced with silica (quartz) that was within the groundwater. Over time all of the original organic material was replaced with the silica, leaving behind the fossils.

 After fossilization, the petrified trees are no longer organic, they are essentially rocks completely composed of silica. Normal, organic trees, when broken will break into long splinters. However, these trees are broken as if someone came through with a chainsaw and neatly chopped up the trunks of the trees. This happens because when silica breaks, it will often break along these smooth surfaces, especially when it is in the elongated form that is in here. These trees are harder than the surrounding landscape so they resist weathering creating these mounds which the trees sit upon. But over time, the ground surfaces are eroded beneath the trees and as the trees start to feel the pressure of gravity they are pulled down, eventually breaking under the pressure.


The colors within the petrified wood are created from the mixture of minor amounts of contaminants within the silica body. The contaminants are mostly comprised of iron and manganese. The iron produces the yellow, orange, reds, ochres, and black colors while the manganese produces the blue, purple, brown, and black colors.

Some of these trees are truly massive in scale. The base of this tree, named Old Faithful, which still preserves some of the roots is around 5 feet across. Although, in today's park, the park would let these fossil succumb to the natural elements, back in the day that wasn't always the case. You can see here a concrete pad was placed under the tree to help prevent future collapsing of the base. 


The amount of detail preserved in the trees in truly astounding as well. Here you can see several of the knots within the trunk still preserved.

And here we have the traces of insect burrows through the wood preserved (the vertical lines here through the horizontal wood grains).

 A gorgeous petrified log.

 View down a slope with several of the petrified logs in view.

Cross section of one of the logs, highlighting the colors within the rock. The detail preserved within the petrified logs is so fine that often scientists can still count the tree rings from the original trees to determine the ages and environmental conditions within which these trees initially lived.