Friday, July 31, 2020

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

Colorado State Geological symbols can also be found HERE.

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.


Wednesday, July 29, 2020

Geology of the National Parks Through Pictures - Yucca House National Monument

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

Colorado State Geological symbols can also be found HERE.

Yucca House National Monument
After Hovenweep we traveled to what may be the least visited National Park in the whole system. I had read reports that this park only gets about 1,000 visitors in a year and I can understand why. Even though it is fairly close to a very popular park, Mesa Verde, this park has no facilities whatsoever, and you even end up parking in someone's front yard in order to access the grounds. It's a weird park to visit for sure.
 Yucca House National Monument's rather unique entrance sign.

 Yucca House NM preserves several ancestral Puebloan structures that generally haven't been excavated. This means that most of the structures remain hidden from view under mounds of dirt. In a geological sense, Yucca House NM resides within the Colorado Plateau in the high desert. Making water an extremely scarce commodity, as it was for several other ancestral Puebloan communities,  like the nearby Hovenweep NM.

The preserved pueblos are mostly identified as mounds within the park. Here here is a look at the much larger building towards the western part of the park.

The name "Yucca House" is an updated name of the monument. It was initially known as "Aztec Spring", however since the Aztec people of Mexico were known to have not built this site, it was decided to change the name. The name was changed in reference to Sleeping Ute Mountain, which you can see in the distance shot above to the east of the park. The Utes refer to the mountain as the "mountain with lots of yucca growing on it", hence the park's name being changed to "Yucca House", despite not having any yucca within the park grounds.

The most obvious geological feature within the park are the building stones. These rocks can be found throughout the grounds of the park and were the source of the pueblo building structures. Likely many of the rocks in the park currently were previous building blocks that had since been scattered by erosion, building degradation, and possible human activity. The only bedrock that is present within Yucca House is the Juana Lopez Member of the Mancos Shale. These were deposited during the Late Cretaceous (~90 million years ago) within the Western Interior Seaway. The Western Interior Seaway was a major body of water that essentially broke North America into two parts, the western and eastern sections with a Mediterranean type body of water splitting them.

 The rocks of the Juana Lopez Member are generally calcareous shales with some hard calcarenite layers. The harder calcarenite, a type of limestone, beds preserve a rich assemblage of fossils as well, including bivalves and ammonites. Within the rocks here are several bivalves (such as clams and gastropods).

And here you can see the edge of an ammonite (the ribbed feature in the center of the picture), which is a relative to modern day squids that had a spiraled shell.


Tuesday, July 28, 2020

Geology of the National Parks Through Pictures - Hovenweep National Monument

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

Hovenweep National Monument
After leaving Arches NP, we hit up a small park on the border of Utah and Colorado, Hovenweep, which preserves several ancestral Puebloan buildings within a local canyon. The park has a nice short trail that leads around the canyon allowing you to get a 360 degree view of the canyon and all of the buildings located within it.

 Entrance sign highlighting the high desert of the Colorado Plateau.

Hovenweep is represented by several buildings within this area that are estimated to have been built between 1230 and 1275 CE by the ancestral Puebloans. The name "Hovenweep" means "deserted valley" in the Ute/Paiute language and was given that by William Henry Jackson, a pioneer photographer who was here in 1874. Hovenweep itself is located on top of the Cajon Mesa, which is tilted towards the southwest. There are other districts and buildings of the Hovenweep National Monument across the border in Colorado, however they were not accessible at the time we were down there.

 There are two rock units within the park. The primary rock unit is the Dakota Sandstone. This is the rock that forms the rim of canyon. The Dakota Sandstone is Early Cretaceous in age, ~100 million years old, and represents the western shore of the very large Cretaceous Interior Seaway. The Dakota is made up of yellow to grey sandstones, mudstones, and a few thin beds of coal. These were deposited within a wide range of coastal environments including deltas, alluvial fans, and coastal deposits.

Cross bedding is definitely visible within the Dakota Sandstone, indicating prehistoric sand dunes.

The Dakota Sandstone was so sturdy, that the ancestral Puebloans used it as the building stone for all of their buildings in Hovenweep. Below the Dakota Sandstone is the other rock unit within the park, the Burro Canyon Formation. The Burro Canyon is also early Cretaceous in age and is made up of conglomerates, shale, mudstones, and sandstones, all deposited within river and floodplain environments. 

 Here is part of the Hovenweep Castle, showing of the Dakota Sandstone building blocks.

 Another part of the Hovenweep Castle from a different angle.

 Here is a view down into the canyon, looking at the Square Tower. The Dakota Sandstone is a rather porous sandstone and therefore rain water has a tendency to soak up into it. The underlying Burro Canyon Formation, however, is impermeable and therefore the water will not go through the Burro Canyon and flows off the top of it. The result is a series of springs and seeps along the canyon walls next to the buildings, which is likely the reason that the ancestral Puebloans settled here in the first place.

 View up the canyon from the far end of the trail loop.

 View across the canyon of the Castle.

 One of the other structures, Tower Point I believe.

Another view of the canyon from the end.


Monday, July 27, 2020

Geology of the National Parks Through Pictures - Arches 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

Arches National Park
Following our visit to Canyonlands we hit up Arches National Park for a quick visit. We had done most of Arches already back in 2011 but we figured it would be a fun place to get a quick hike in. Out of the five National Parks in Utah, Arches may be the most popular because of the fantastic geological structures and the extremely close distance to Moab, a popular tourist town in the area. The pictures below are a combination of both previous trips.

 The entrance sign shot.

In order to get into Arches, you must switchback up this rather steep road initially from the main entrance. Here is a shot from the top of the entrance road looking down on the main entrance/visitor's center.

Arches National Park is another park within the Colorado Plateau region of North America, where the ground has been forced upwards. Because of this the upper layer of rocks have a tendency to have a lot of erosion and cracking within the rock layers. Within Arches, the dominant rock formation is known as the Entrada Sandstone, a Jurassic age (~150 million years old) sandstone, formed from a coastal dune environment. There are a ton of geological erosional features throughout the park and I will highlight  few of them. Here is an area shortly upon entering the park known as Park Avenue.

Here is a precariously balanced rock within the Park Avenue area.
 Within the central part of the park is a fantastic congregation of arches, all within a very short hike. Here are two arches attached to each other with the larger arch known as Turret Arch. The structures in Arches National Park formed from the process of erosion. Over time, erosion widened the cracks that had formed during the uplift of the region. These cracks, or joints, created long, parallel breaks in the rocks called fins.

 Turning around from Turret Arch are two very large arches, known as the Window Arches. This is the South Window, with the North Window to the right out of frame. Not only does water erode the outside of the rock but water soaks into the rock itself. The Entrada Sandstone is very porous, allowing for the rain water to easily soak into the rock. As the water filters its way down into the sandstone it eventually reaches the base of the sandstone at the contact with the lower rock unit, the Carmel Formation. The Carmel Formation is a slightly older, Jurassic age, series of mudstones, siltstones, and sandstones, formed in a tidal flat environment. The much higher percentage of mud prevents water from flowing through it, so as the water flows through the Entrada, it eventually pools at the base of the sandstone on top of the Carmel Formation.

The cement in the Entrada Sandstone is one of the key ingredients. Many sandstones are cemented by silica, which is basically a dissolved type of quartz, a very hard mineral. Those types of sandstones are incredibly difficult to erode. The Entrada Sandstone, however, is cemented with calcite, a mineral that easily dissolves in slightly acidic water, such as the calcite in caves. As the water sits at the base of the Entrada, it slowly dissolves away the calcite cement. Then as the water freezes and thaws over the winter months, the expansion and contraction of the water breaks apart the rocks and carries away the sand. Leaving an ever widening hole at the base of the rock formation.

Within the same area we have my favorite set of arches in the whole park, Double Arch. Here is a view across the parking lot. Eventually, as more material erodes away, these holes are widened over time, creating thinner and thinner pieces of overarching rocks, that will eventually erode away all together.

Here is a view of the Double Arch from underneath. The formation of these arches is a precarious balance between too much and not enough water though. Even though you want water to dissolve the cement and carry away the sand, too much rain would erode these formations way too quickly. This region only gets 8-10 inches of rain a year, making this a desert, and also providing just enough water to slowly break down the rocks. The erosion of the arches is so fantastic that it can leave behind these thin bands of stone, until eventually erosion will make the stone too thin to support itself and eventually will collapse.

  Perhaps the most famous arch in the park is Delicate Arch. There are two ways to see Delicate Arch. Either you can do the harder, and longer, hike to the arch itself. Unfortunately, we were unable to do that, so we opted for the shorter and easier hike to the overlook.

Here is one of the more famous formations, Balanced Rock. Besides just the arches there are other geological erosional features such as this. Here more resistant rocks overly softer rocks. The Entrada Sandstone is the large bolder sitting upon a pedestal of the softer Carmel Formation, described above. Since the Carmel Formation is a softer rock, it erodes away easier than the Entrada Sandstone, creating features like this.

 Distant view of some more geological formations.

 View of the Courthouse Towers.