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

Geology of the National Parks Through Pictures - Colorado National Monument

My next post about the Geology of the National Parks Through Pictures is a park we decided to go to during the quarantine when we wanted to get out but were limited on our social distancing options for Father's Day weekend. Turns out Colorado National Monument was the perfect location.

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.

Colorado State Geological symbols can also be found HERE.

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Colorado National Monument

Colorado National Monument is a park we had driven near a few times but never actually gone to before now, not realizing how truly beautiful it was. The overlooks are simply astounding and everything about the park screams geology. It is directly outside Grand Junction and Fruita, Colorado and is a quick jump from either of those cities in SW Colorado.

The western entrance to Colorado National Monument. 

Colorado National Monument is an interesting park. Most of the park is located on top of a high cliff that looks out over the Grand Valley where Fruita and Grand Junction are located. The reason for the high cliff is that the park resides on the upturned side of a giant fold. Within geology as a whole, there are several different types of folds within rock units. The most common folds are the syncline, when the rocks are bent like a "U", and the anticline, where the rocks are bent the other way like an "A". The Colorado National Monument fold is a different type of fold though, known as a monocline, where only one edge of the fold is bent. It's like an anticline with only half of the "A" is bent. You can see the cross section of rocks within the fold and the park. The oldest rocks of the fold are those located near the valley floors, which are the Upper Triassic age Chinle Formation (~200 million years old). The rock units progressively get younger until you get to the top layer of the fold, represented by the Cretaceous age Dakota Sandstone (~100 million years old). You can see the rocks in this park cover a large span of time. Image from the Rock Layers of the Monument brochure from the NPS.

View of Independence Rock from Otto's Trail. Within these large formations here we have a series of rocks. The base of the valleys are the really old rocks. Below the Chinle Formation described above is some Precambrian metamorphic rocks called the Black Canyon Group. These include gneiss, dark schists, and light pegmatites, which are all extremely hard, erosion resistant rocks. The Black Canyon Group is estimated to be 1.7 billion years old. The erosion resistance of these rocks are what caused the erosion of the valleys to essentially stall once it reached this level, unable to erode very quickly through the metamorphic layer.

Here is a view at the end of Otto's trail looking north towards Fruita in the distance. Immediately on top of the Black Canyon Group is the Chinle Formation. Between them is a gap in time equal to 1.5 billion years. This gap in time is known as an unconformity, specifically a nonconformity, where the rocks that used to be here were eroded away before the newer rocks were deposited later. These newer rocks are the 200 million year old Chinle Formation. The Chinle Formation is comprised of red mudstones, shales, conglomerates, and thin limestones. Shales and mudstones are all extremely easy to erode, so they typically form smooth slopes when eroded. That is what you see at the base of the cliffs, where the tree line starts. The Chinle Formation extends from the tree line down to about where the underlying red soil stops. The Chinle Formation was deposited in a stream and floodplain environment.

Here is a view from a little further down the main road at Grand View. I love these types of stops because they provide a display with the geology overlaid on the rocks as you see them. A picture of the geology sign is directly below to compare. Directly above the Chinle Formation is where the cliffs start. This is the Wingate Sandstone. The Wingate is a very thick bed of dune sandstone from a prehistoric desert deposited during the Lower Jurassic. Most of the geologic formations within this park are located within the Wingate.

The Wingate continues up until a slight color change in the rocks can be seen near the top of the cliff. The rocks on the very top here are more grey in color than the yellow of the Wingate. This is the Kayenta Formation, another sandstone but with more shale and conglomerate mixed in. The Kayenta Formation represents a period of time when the environment started to bounce back from the Wingate desert and rains started to fall a bit more. 

Here is a view from the Grand View looking back towards the cliff edge. You can see here the next series of rock units above the Kayenta Formation. This is the Entrada Sandstone, seen here most clearly on the right hand portion of the photograph as the smooth yellow sandstone cliff face just below a thin strip of green plants at the top of the rock series. The Entrada Sandstone is a Middle Jurassic aged sandstone (~150 million years old) that was deposited from the dunes of a nearby sea. This is the same rock formation that the arches are from at Arches National Park. 

View from the Grand View looking towards the north at Fruita.

Here is a closer look at the Entrada Sandstone where we can just barely make out the next series of rocks. Immediately on top of the Entrada Sandstone is the Wanakah Formation, a thin Middle Jurassic series of mudstones, shales, and sandstones from the lake and stream environments.

View of the canyon from Artist's Point looking down on the Wingate erosional features. 

View of the canyon wall from Upper Ute Canyon overlook. Here we get a great shot of the Wingate Sandstone (large orangy yellow sandstone on the bottom) with the Entrada Sandstone (thinner orangy yellow sandstone on top (after a break of green plants and grey rocks, which are the Kayenta Formation). On top of the Entrada is the Wanakah, and on top of the Wanakah is the highest rock formation we can see within this portion of the park, the Morrison Formation. The Morrison Formation is an Upper Jurassic age (~155 million year old) series of mudstones and occasional sandstone lenses that is world famous for its dinosaur fossils. The Morrison Formation  ranged through several terrestrial environments including lake, river, and floodplain deposits. 

Here is another geological overlay view with the geology sign below. This area shows the Black Canyon Group, small bits of the Chinle Formation, the thick Wingate Sandstone, and topped with the Kayenta Formation. We have moved far enough to the southeast of the monument now that we are looking out onto Grand Junction instead of Fruita. 

Geological overlay of the above image.

Here we get a closer look at some of the cross bedding within the Wingate Sandstone, the curved lines going through the rock unit. Cross-beds indicate that these rocks formed from sand that were once sand dunes that were eventually cemented together. 

Below we will look at some of  the several fantastic erosional features throughout the park.

View of the Coke Ovens, which are geological erosional features that are reminiscent of the old coke ovens. Coke ovens are often beehive shaped structures that process coal by burning the impurities out of coal producing a product known as "coking coal" or just "coke". These features are within the Wingate Sandstone. 

View of the Coke Ovens from the top, at the end of the Coke Ovens Trail.

Within the rock units, the faulting and joints that formed as a result of the folding create areas where erosion is able to get a foothold. Once water then starts to consolidate within those cracks, valleys begin to form, further enhancing the cracks that were there. Sandstones, and other very hard rocks, have a tendency to fracture in a grid formation. This grid formation leads to erosion that follows that pattern, as seen here with river valleys forming a right angle to one another. 

A physical view of the valleys seen in the image above. Once erosion proceeded vertically low enough, it hit the resistant Precambrian Black Canyon Group, and the erosion slowed drastically. Afterwards, erosion proceeded in a more horizontal direction, widening and lengthening the already existing valleys and canyons.

Natural joints and fractures within the rock allow erosion to slowly create spectacular features such as Balance Rock, located within the Wingate Sandstone. Water and wind erosion slowly expanded a fracture that was located between the rock and the main cliff face, leaving behind this precariously balance protrusion. 

And the last of the erosional features that I'll highlight is Window Rock, an arch within the Wingate Sandstone, seen here on the left side of the photo. The trail to Window Rock leads you right up to the top of it, however since you are basically on top of the arch (the actual arch is off limits by a fence), it is difficult to get a nice photo of it. This is another instance of erosion removing material along a preexisting crack in the rock, widening it until an arch was formed.

References

https://www.nps.gov/colm/learn/nature/precambrian-black-canyon-group.htm

https://www.outtherecolorado.com/adventures/the-coke-ovens-of-redstone/article_53cc5185-a447-556e-af48-06ddcb02ebc7.html

https://irma.nps.gov/DataStore/Reference/Profile/2259850

Geology of the National Parks Through Pictures - Rocky Mountain National Park

My next post about the Geology of the National Parks Through Pictures is a park we hit up after the wife did a race outside of Denver.

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.

Colorado State Geological symbols can also be found HERE.

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Rocky Mountain National Park

Even though there are a lot of scenic views within Rocky Mountain National Park, the basis for Rocky Mountain National Park is geology. The reason the mountains are here is geology and the features seen on the mountains are geological. So even though this isn't a strictly geological park, geology in imbibed everywhere. 

The obligatory entrance sign

The mountains within Rocky Mount National Park are a result of orogenic events (mountain building) that took place over three periods within the planets history. The first orogeny (mountain building event) took place 1.7 billion years ago during the Precambrian. This event laid down the foundation of faults that will later be activated during the most recent mountain building. The next orogeny, known as the Ancestral Rockies Orogeny, was 285 million years ago during the Pennsylvanian. Afterwards, the Ancestral Rockies were entirely eroded away, but again the faults were left behind. The final mountain building event was the one which produced the mountains we see today. This occurred 70 to 40 million years ago and is known as the Laramide Orogeny.

The Earth is made up of giant plates which are all moving around. When two plates are moving towards each other they push each other up, forming mountains. This is what is currently happening in the Himalayas where the Indian Plate is moving northward into the Eurasian Plate. As the two plates collide, the edges get "wrinkled". It is this wrinkle that are the mountains.  Here is a view of the Rocky Mountains from the visitors center. 

 The Laramide Orogeny occurred due to the presence of a plate off the western coast of the United States known as the Farallon Plate. The Farallon Plate was an oceanic plate that was pushing up against the west coast of the United States and Mexico. Since the plate was made up of oceanic crust, it was denser than the North American continental crust and therefore ended up going beneath the North American Plate in a process known as subduction. As the plate went under North America, it still ended up compressing North America, forming those mountain wrinkles. The mountain building occurred along those long ago created faults that were reactivated during this renewed time of mountain building. Eventually, most of the Farallon Plate was completely subducted, leaving behind only a small piece known as the Juan de Fuca plate off the coast of Washington and Oregon.

 Within the park there are also significant amount of glacial features, this divot out of the side of the mountain being one of them. When a glacier is forming on the side of a mountain, the snow continually accumulates near the peak. Eventually the snow builds up enough that it compresses down into ice, and then eventually the entire ice block starts to flow downhill. As the ice flows downhill it picks up rocks and starts to erode into the mountain that it is sitting on, creating a bowl shaped depression. That bowl shaped depression is what eventually becomes known as a cirque, once the glacier melts entirely away. 

 Here's the view of another cirque from a distance.

 Here are a whole bunch of glacier features, as well as some glaciers still present (where some of the snow and ice doesn't melt completely in the summer time). Within this photo we also have some more cirques. Since cirques erode down into the mountains, creating a bowl shaped depression, these often eroded down into bedrock. The bedrock creates a nice seal against water escaping and eventually can create a lake. This specific type of lake is known as a "tarn". When two cirques are on the the same mountain but going in different directions (i.e. back to back), they can form a ridge between themselves. This steep, knife-like ridge of rock is a glacial feature known as an "arête", which you can also see within the central portion of the photo.

 Here is a view looking down into a cirque. Although there is snow here, it is not a glacier until the snow starts to build up over time and compact into ice. Right now these are just seasonal snow fields.

After the glaciers move downward from the mountains, they start to fill up the valleys between the mountains. This ends up eroding the valleys in a specific pattern. When rivers erode out valleys, the valley cross section forms a "V" shape, where the stream erodes straight downward at the bottom of the V. However, when a glacier enters a valley, it is much larger and erodes over a much larger area. The result is a valley with more of a "U" shape, created as the glacier erodes on all of the edges of the valley. Here is a look towards the mountains centered on a glacial U-shaped valley.   

Another erosional glacial feature is when the glaciers make it further down slope and erode out and widen existing valleys. The valleys were initially eroded by streams and rivers, but glacial erosion widened and flattened these stream valleys far beyond what was initially dug out. After these valleys are eroded out by glaciers, eventually the glacier melts and water returns to the former streams. The large flat areas are then filled in as a series of interconnected lakes called paternoster lakes.

One of my favorite features of western National Parks is the Continental Divide. This is essentially a high point of the country where water at the divide goes one of two ways. Within this picture (which I am facing south when I took), water on the left, or eastern side all flows to the Atlantic Ocean, while all of the water on the right, or western side, all flow to the Pacific Ocean. The signs are not often perfect, but they are pretty close. The Continental Divide is actually a line of mountain ridge tops that runs up the entire length of the continent, dividing the drainage between the two oceans. There are other divides within the country as well, such as the one that divides water going north into Canada's Hudson Bay, or water going into the Great Salt Lake, which is an end-basin where water goes to die.

References

https://www.sciencedirect.com/topics/earth-and-planetary-sciences/laramide-orogeny

https://www.nps.gov/romo/learn/education/upload/Teacher_Guide_to_RMNP_Geology.pdf

Geology of the National Parks Through Pictures - Mesa Verde National Park

My next series of posts about the Geology of the National Parks Through Pictures will follow along on a birthday trip that we took back in March of 2019 hitting up some of the parks in southeastern Utah and southwestern Colorado.

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.

Colorado State Geological symbols can also be found HERE.

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Mesa Verde National Park
The last park from out 2019 Spring Break trip was Mesa Verde. Typically you can take tours of some of the different buildings, however apparently mid-March is too soon to do that due to snow cover still prevalent in the area. But we were able to tour the overlooks and some of the ruins preserved within buildings.

 Mesa Verde National Park entrance sign within the glory of winter snow. In the background on the left you can see Point Lookout mesa. There are four main rock units within the park. The oldest rock unit is the Mancos Shale, located at the base of the mesa. The Mancos Shale is Cretaceous in age (~86 million years old) and was deposited within the deep waters of the Cretaceous Western Interior Seaway that covered a large portion of North America across the middle of the continent. Because of the deep waters, the Mancos is mostly gray shale. On top of the Mancos, and capping the mesa, is the very hard Point Lookout Sandstone. The Point Lookout Sandstone is a Cretaceous age (~81 million year old) rock unit composed mostly of sandstone but it does have some layers of shale, that was deposited along the shore of the Cretaceous Western Interior Seaway as the seaway was retreating.


Here's a good breakdown of the rock units from Mesa Verde's Archaeological Museum. You can see here that Mesa Verde is tilted towards the south, with all of the rock units similarly tilted, at a 7 degree angle. This actually makes Mesa Verde not a mesa, but a cuesta instead, which by definition is a tilted mesa. The very high Point Lookout Sandstone in the previous picture ends up being below ground by the time we get to the cliff houses further into the park, and below the other two rock units in the park, the Menefee Formation and the Cliff House Sandstone.


Here is a view towards the north from the Visitor's Center. Even though we are fairly high up here, we are still at a fairly low spot compared to Point Lookout because of the tilt of the "mesa" (cuesta).

Before the fantastic cliff houses were built, there are several pit houses excavated and preserved within buildings across the "mesa".  The pit houses were constructed of mud plaster and adobe on top of a wooden frame between 550 to 750 CE. It is because of that wooden frame that scientists were able to accurately date the houses through a process known as dendrochronology. I'll go more into dendrochronology below.

 Eventually, as we travel far enough to the south, we are able to travel up onto the Mesa and look down onto the cliff dwellings. From the overlooks you can get a great view of the Cliff House Sandstone, as well as the underlying and slightly older, Menefee Formation. The Menefee Formation is series of thin sandstone beds, shales, and coal that were laid down 78 million years ago and is what separates the Point Lookout Sandstone below from the Cliff House Sandstone above. During the deposition of the Menefee Formation, the Western Interior Seaway was completely gone and a coastal plain was here with swamps scattered about. Within this view, if you zoom in, you can see Cliff Top Palace on the left and Sunset House on the right.

 The cliff dwellings were built between the 1190s to late 1270s CE. The cliff houses are both built within and built from the Cliff House Sandstone. This is a Cretaceous age (~75 million year old) sandstone that was deposited when the Cretaceous Western Interior Seaway again advanced across North America. With the advance of the sea, large amounts of sand were deposited, much of it with ripple marks indicating a shoreline. Here we are looking at the Square Tower House.


Although fossils are far from common within the Cliff House Sandstone, there are some examples of something that may be confused for a fossil, however these are what are known as concretions. As harder, iron-rich minerals, flow through the sandstone, the minerals will often consolidate around objects within the sandstone such as shells and other fossils, forming these erosion resistant tubes or balls.

 Here is a view of the Oak Tree House cliff dwellings. You can see here the alcove that had naturally been created within the rock, as erosion breaks off the outer rocks into the valley below due to the softer Menefee Formation not supporting the upper Cliff House Sandstone. You can also see quite a bit of desert varnish, AKA manganese staining, located above the cliff house. The desert varnish is created when manganese and iron particles are brought to the rocks by the wind and cemented in place by bacteria and water on the rocks.

 Here are some more cliff dwelling further down from the Oak Tree House (located to the right in this picture). These are known as Fire Temple and New Fire House.

 One of the most remarkable overlooks in the entire park is from the Sun Temple overlook, looking down on the Cliff Palace. An absolutely gorgeous construction feat.


A zoomed out view from the Spruce Tree House overlook showing the weathering along horizontal cracks within the rock, which end up creating ledges along the edge of the canyon by water erosion over time.


Here is the Spruce Tree House, the best preserved cliff dwelling according to the park brochure. From this overlook you can a truly spectacular view of the cliff house itself without even going on the trail to the house (which was closed at the time we visited).


On the top of the surface of the "mesa" are several buildings as well, including the massive Sun Temple, the remains of which only show partially how big it really was with estimated 11 to 14 foot high walls. The entire building was built from the readily available Cliff House Sandstone, on which the building sits.


Due to the snow some of the surface buildings were a little more difficult to get to, but that didn't stop me. Here are two of the buildings from the Far View sites, also using the Cliff House Sandstone.


Here is another of the Far View Sites building. This building was interesting because of the carved spiral within the central block on the building.

 As discussed above, dendrochronology was used to date many of the buildings within the park. Dendrochronology is the process of counting tree rings and using the various thicknesses to match them up to known tree ring thickness. Every year a tree, when alive, creates a ring, so it is possible to date how old a tree is by counting the rings. But it doesn't stop there, trees also create rings of various thicknesses depending on wet vs dry years, so they are able to provide a local climate report for each year it was alive. You can use the different thicknesses to then compare modern trees to older cut down logs and slowly piece together a timeline for a specific region. Using this technique, scientists were then able to date the buildings based on when the tree was chopped down.

Within the archaeology museum there is a nice display of the various fossils found throughout the park within each rock unit. Here are the Mancos Shale and Point Lookout Sandstone fossils.

And here are the fossils from the Menefee Formation and the Cliff House Sandstone.

References

https://www.nps.gov/meve/planyourvisit/upload/geology_web.pdf

https://www.nps.gov/meve/learn/nature/geology.htm

https://www.gutenberg.org/files/45535/45535-h/45535-h.htm