Friday, March 20, 2026

Dinos in Pop Culture - The Wall Drug, SD

Continuing my travels across country, moving from Utah to New York, we have stopped at our next non-National Park geological stop. Well ... maybe not "geological" per say, but it does have a dinosaur!

Wall Drug, SD


The Wall Drug is in my opinion THE road side attraction. Located just off Interstate 90, the Wall Drug is a massive Drug Store (?) located in the town of Wall, SD. But it is so much more than that. The reason many people visit the Wall Drug is their constant barrage of billboards as you drive down the highway for hundreds of miles in all directions. Per their website they also have signs globally: 
Over the years, Hustead’s Wall Drug signs could be seen in sites as distant as Morocco, Amsterdam, and London, and during World War II, American G.I.s carried the Wall Drug message across the globe, proclaiming how many miles it was back to Wall Drug.
And what started out as a drug store where you could get "free Ice Water", has turned into an ever expanding cavalcade of displays, stores, food, and attractions. But, the one attraction that got my attention was the animatronic Tyrannosaurus rex (AKA a T. rex), located towards the back of the store. 


And like a good animatronic, just taking a picture isn't enough, so here is a video of it in action.


Obviously this display is reminiscent of Jurassic Park, which also included a T. rex under lockdown. To give a general background on the T. rex, the first Tyrannosaurus rex skeleton was discovered in 1902 by Barnum Brown, the then assistant curator for the Department of Vertebrate Paleontology at the American Museum of Natural History (AMNH) in New York. The bones, discovered in the Hell Creek Formation near Hell Creek, Montana, were identified by a local land owner who then told Brown. The skeleton, only 10% complete, took 3 years to excavate and was then transported to the AMNH where the paleontology curator of the museum, Henry Fairfield Osborn, named the fossil in 1905 Tyrannosaurus rex, meaning "Tyrant Lizard King". 

Original mount of the T. rex. Image courtesy of the AMNH

All fossils of the T. rex have since been found in western North America, ranging from southern Canada down into southern New Mexico and Texas. The T. rex was also one of the last living non-avian dinosaurs, having lived during the late Cretaceous period from about 68 to 66 million years ago, which is when the meteorite struck the Earth, wiping out those non-avian dinosaurs. Although the skeleton discovered initially by Brown was only a partial skeleton, an even more complete skeleton was discovered by Brown 6 years later that became the basis for the skeleton seen above, mounted at the AMNH. It is this mount that went on to influence pop-culture for most of the next hundred years, where the T. rex was almost always portrayed in a vertical pose. Unfortunately this pose was set up mostly because of the steel armature could not do a more dynamic pose. Many of the tail vertebrae even needed to be broken in order to get the T. rex to be standing like this. 

And of course, me with the T. rex during the times of Covid.

It wasn't until 1993's Jurassic Park, that movie and tv makers really started to take a look at the advancing science behind the dinosaurs and adjusted their models accordingly. For the movie, the T. rex is presented in a much more accurate model, where the body of the beast is balanced over the legs, with the tail acting as a counterweight, forming a giant see-saw. This remodeled T. rex also gives us a much more accurate depiction of its size, where an adult can grow up to ~12 feet tall at the hip and ~40 feet long from tip of the tail to snout. But one of the most notable features of a T. rex were its teeth, that ranged in size up to 12 inches long, which included the root, still leaving approximately a 6 inch tooth exposed. And despite this animatronic being installed in the Wall Drug around 2006, it still does seem to maintain that more upright, incorrect, pose, than the one more closely associated with the Jurassic Park franchise, where the T. rex is balanced horizontally across its legs. The teeth however in this model do appear to be appropriately sized, although they be a little small in comparison to the smaller size of this T. rex compared to a full grown one. 
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Friday, March 13, 2026

Geology of the National Parks in Pictures - Wind Cave National Park

My next post about the Geology of the National Parks Through Pictures is from our move across the country from Utah to New York. Along the way we visited 13 National Parks as well as some other sites. This was the 8th National Park along the way.


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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Obligatory entrance sign

Geological map of the Black Hills, including Wind Cave National Park (noted just below the southernmost point of the purple rocks). Image courtesy of the NPS.

Like the Mount Rushmore National Memorial and the Crazy Horse Memorial, Wind Cave National Park is located within the Black Hills dome. But unlike those parks, Wind Cave National Park is not located within the Harney Peak Granite. The rocks in this region started forming about 1.6 billion years ago, during the Proterozoic. This is when magma began to work its way up through the surrounding rocks in this area at the time. While still well below the surface of the earth, that magma cooled slowly to form the Harney Peak Granite. Due to the hardness of the granite, from its formation at 1.6 billion years to about 500 million years ago, several rocks formations were likely deposited on top of it and then eroded away leaving no trace.  However, starting around 500 million years ago, new rocks that were deposited on the Harney Peak Granite have been preserved. These rocks include the green "Limestone Plateau" rocks as pictured in the map above. 

Geological map of Wind Cave National Park. Map courtesy of the NPS. 

Legend for the Wind Cave NP Geological Map. Image courtesy of the NPS. 

The "Limestone Plateau" can be subdivided into numerous different rock formations, once we zoom in on the part of the dome within Wind Cave National Park. Deposited directly on top of the Harney Peak Granite is the Ordovician Age Deadwood Formation (~480 million years old). This is a mixture of sandstones and limestones, as well as some other rocks, that represent a transgression, where the sea level started to rise and the oceans started to cover this region. On top of that is the Mississippian Age Englewood Limestone (~ 363 –358 million years old). The Englewood represents a shallow marine environment. 


And on top of the Englewood Formation is the primary rock of interest for Wind Cave National Park, the Pahasapa Limestone (AKA Madison Limestone). This is a Mississippian Age limestone that dates to about 358 to 341 million years old. This is the limestone from which Wind Cave is formed within. The Pahasapa Limestone is up to 420 feet thick and formed from the deposition of seashell fragments within a warm shallow sea across the region. Following deposition of the Pahasapa Limestone, the seas started to recede away ~320 million years ago. This is when the first parts of Wind Cave started to form. 

When the seas started to come back, (~300 million years ago) rocks were deposited on top of the Pahasapa Limestone. This time they were made up of limestones, sandstones, and red clay shales. This formation, called the Minnelusa Formation, created a semi-permeable barrier on top of the Pahasapa, limiting water flow down through the rock from the surface. An interesting thing to note is that the Minnelusa Formation can actually also be seen within Wind Cave as well, with some of the red clay visible in higher parts of the cave near the Garden of Eden and Fairgrounds rooms. The inclusion of the Minnelusa Formation within Wind Cave is how scientists know that the cave started forming over 300 million years ago, making it one of the oldest known cave systems in the world. Following deposition of the Minnelusa Formation, sea levels continued to rise and fall, slowing dissolving out the cavern system. This transgression-regression cycle of the seas continued until around 70 million years ago when the entire area started to be uplifted into the Black Hills dome. As the dome was being uplifted, fracturing of the rocks allowing more water to flow through the rocks, quickening the pace of cave formation.

Cross section of the Black Hills. Image courtesy of A Textbook of Geology.

In geological terms, a dome is an anticlinal structure where the rocks dip gently away from the center in all directions. After folding, fracturing, and faulting, this causes the overlying rocks to break apart in the middle, allowing for easier erosion of the them. Once these younger rocks have eroded away, the older rocks are exposed with the oldest rocks exposed in the center. As before, due to the extreme hardness of the Harney Peak Granite, they withstood erosion and remained around much longer. Their hardness is also why the Black Hills have these granitic mountain peaks that have not eroded away. 


Most limestones are comprised primarily of the mineral calcite, which is a variety of calcium carbonate (CaCO3). Calcite is the mineral that most sea shells are made out of. Calcite has a physical property that it will dissolve in slightly acid waters, which is where you get the formations of caves. One of the unique properties of the Pahasapa Limestone though, is that when it formed, it had significant quantities of gypsum, another type of mineral, within the rock. Gypsum (CaSO4) has the ability to absorb large quantities of water, and when it does so it, expands and then contracts when that water is expelled. Over time, as water entered and left the limestone, the gypsum expanded and contracted, fracturing the surrounding rocks. As time progressed, the water that flowed through these fractures within the limestone slowly started to replace the gypsum with calcite. 

Boxwork Formations

Geologically speaking, Wind Cave is most well known for its boxwork speleothems (cave formations) (as seen in the image above). The boxwork is a result of these gypsum fractures that were refilled with calcite. The calcite crystals that filled in the fractures were more resistant to dissolution than the surrounding limestone was, so as the limestone rock dissolved away, revealing the cave, the calcite crystals that filled the gypsum fractures remained behind. These calcite crystals are what primarily form the boxwork speleothems. The fracture pattern, and therefore the speleothem pattern, forms a very angular, boxy configuration, giving the speleothems the term boxwork. 

Map of Wind Cave

Even looking at a map of the cave itself, it also forms an angular and boxy configuration, producing a fractal pattern (where a pattern is repeated over different scales). Overall, the cave descends 643 feet and extends over 167 miles (as of 2024). As the dome was uplifted, the water started to drain out of the cave about 40 to 50 million years ago. The current day water levels are located about 500 feet below the surface in an area of the cave known as "the Lakes". 


Although the most well know, boxwork isn't the only cave formation within Wind Cave. There are other formations such as popcorn ceiling and frostwork. However, formations such as flowstones and dripstones, like stalactites and stalagmites, are more rare here due to the drier climate and the semi-permeable Minnelusa Formation overlying the cave that limits the amount of water flowing through.  

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Thursday, February 26, 2026

Geology in the Wild - Crazy Horse Memorial

During our travels from Utah to New York, we had been visiting numerous National Parks along the way. (You can read more about those in my Geology of the National Parks Through Pictures series.) We had also hit up some other sites. The first non-National Park geological site that we visited was the Crazy Horse Memorial in Crazy Horse, South Dakota. 

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View of the Crazy Horse Memorial on May 30th, 2021

The Crazy Horse Memorial is currently the largest mountain carving project in progress in the world. The work honors not only the Lakota leader Crazy Horse, but all of Native American culture. The planning for the Crazy Horse Memorial started in earnest in 1939 "when Lakota Chief Henry Standing Bear asked sculptor Korczak Ziolkowski to carve a memorial to the spirit of Lakota leader Chief Crazy Horse and his culture. 'The red man has great heroes, also,' Chief Standing Bear said." Deadwood.com. This is two years before the completion of nearby Mount Rushmore. The actual blasting and carving started on June 3rd, 1948, and continues to this day. 

Geological map of the Black Hills region with the Crazy Horse Memorial highlighted. Image courtesy of the NPS.

The geology of the Crazy Horse Memorial is nearly identical to Mount Rushmore, with both monuments being carved out of the Harney Peak Granite (so I apologize if some of the geological text is repeated here). The Harney Peak Granite is the central rock unit of the Black Hill Dome. The large geologic dome is a region where all of the land is bowed upwards, like an overturned bowl. After erosion, the result is a bullseye pattern of rocks, where the oldest rocks are in the center of the bullseye and progressively get younger towards the outside. 


The Harney Peak Granite started to form about 1.6 billion years ago, when, during the Proterozoic, magma began to work its way up through the rocks in this area. While still well below the surface of the earth, that magma cooled slowly to form the granite that makes up the carving stone for the Crazy Horse Memorial. The great thing about the Crazy Horse Memorial, from a geologists perspective, is that you get to take a piece of the mountain home. While the Harney Peak Granite magma was cooling, it cooled unevenly. This caused some portions of the rock to cool quickly, producing smaller, fine-grained, crystals, while other parts of the granite cooled more slowly with very large grained crystals. These large grained crystal granites are known as pegmatites. The granite with the finer grained crystals are easier to carve and are what comprises most of the Crazy Horse Memorial mountain. 

Cross section of the Black Hills. Image courtesy of A Textbook of Geology.

Between the formation of the granite 1.6 billion years ago and 500 million years ago, new rocks were deposited and eroded on top of the Harney Peak Granite batholith. However, due to the extreme hardness of the granite, the Harney Peak Granite remained behind while these other rocks had been lost to erosion and time. After this period of time, between 500 and 100 million years ago, there were some rocks deposited from which we do have remains of. Immediately on top of the granite is the green rock seen in the geological map above. This green rock, titled the "limestone plateau" on the map, can be seen surrounding the central granite bullseye. The "limestone plateau" is made up of several different rock layers and will be discussed in more detail in the Wind Cave National Park post (since that is where Wind Cave is located). After deposition of these rocks, the whole region started to be uplifted around 70 million years ago. This uplift is related to the uplifts seen across the Rocky Mountains at the same time. 

View of the Crazy Horse Memorial with the model for the final carving. Picture taken May 30th, 2021.

In geological terms, a dome is an anticlinal structure where the rocks dip gently away from the center in all directions. After folding, fracturing, and faulting, this causes the overlying rocks to break apart in the middle, allowing for easier erosion of the them. Once these younger rocks have eroded away, the older rocks are exposed with the oldest rocks exposed in the center. As before, due to the extreme hardness of the Harney Peak Granite, it withstood erosion and remained around much longer. The hardness of the Harney Peak Granite is also why the Black Hills have this large core of granitic mountain peaks that have not eroded away.

For comparison, here is my photo of the carving from when I visited the Memorial back in 1996. 

Although it is a bit fuzzy, I had visited the Crazy Horse Memorial back in 1996 during a cross country trip with my father. You can kind of see the differences between the two carvings, separated by 25 years. Progress is coming along slowly. Mostly it appears that in this time the finer details of the upper portions of the Memorial have been carved. 

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Monday, February 09, 2026

Geology of the National Parks in Pictures - Mount Rushmore National Memorial

My next post about the Geology of the National Parks Through Pictures is from our move across the country from Utah to New York. Along the way we visited 13 National Parks as well as some other sites. This was the 7th National Park along the way.


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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Obligatory entrance sign photo.

Geological map of the Black Hills, including Mount Rushmore (noted just below the slice through the map). Image courtesy of the NPS. 

Mount Rushmore is set within a large geologic dome. This is a region where all of the land is bowed upwards, like an overturned bowl. After erosion, the result is a bullseye pattern of rocks, where the oldest rocks are in the center of the bullseye and progressively get younger towards the outside. 

Tȟuŋkášila Šákpe, AKA Mount Rushmore, before being carved. Image courtesy of nativehope.org.

Although this could be considered outside the normal realm of geology, I do want to note that before being known as Mount Rushmore, the Lakota referred to the mountain as Tȟuŋkášila Šákpe, Lakota for The Six Grandfathers. The mountain named by Lakota medicine man Nicolas Black Elk after seeing a vision “... of the six sacred directions: west, east, north, south, above, and below. The directions were said to represent kindness and love, full of years and wisdom, like human grandfathers.”


As you drive up to the main entrance looking northeast, you first pass the profile view of Washington. From this direction you get a good view of the mountain sans most of the demolition work that was done with the carvings. You can see what would be the normally weathered surface of the granite before the carving brings out the fresh surface. This surface is also more reminiscent of the uncarved mountain seen in the image above. About 1.6 billion years ago, during the Proterozoic, magma began to work its way up through the rocks in this area. While still well below the surface of the earth, that magma cooled slowly to form the granite that makes up the carving stone for Mount Rushmore. This rock unit is known as the Harney Peak Granite. 


While the magma was cooling, it cooled unevenly. This caused some portions of the rock to cool quickly, producing smaller, fine-grained, crystals, while other parts of the granite cooled more slowly with very large grained crystals. These large grained crystal granites are known as pegmatites. The upper portion of Mount Rushmore is comprised mostly of the fine grained crystal variety, which is an easier rock to carve from. This large body of magma is known as a batholith. 


Between the formation of the granite 1.6 billion years ago and 500 million years ago, new rocks were deposited and eroded on top of the Harney Peak Granite batholith. However, due to the extreme hardness of the granite, the Harney Peak Granite remained behind while these other rocks had been lost to erosion and time. After this period of time, between 500 and 100 million years ago, there were some rocks deposited from which we do have remains of. Immediately on top of the granite is the green rock seen in the geological map above. This green rock, titled the "limestone plateau" on the map, can be seen surrounding the central granite bullseye. The "limestone plateau" is made up of several different rock layers and will be discussed in more detail in the Wind Cave National Park post (since that is where Wind Cave is located). After deposition of these rocks, the whole region started to be uplifted around 70 million years ago. This uplift is related to the uplifts seen across the Rocky Mountains at the same time. 

Google Earth image of the Black Hill dome. 

The uplift formed the dome that we had discussed above. This dome is easily noticeable in the aerial image of the region as well, as seen in the Google Earth Image above. This dome structure stretches across South Dakota and Wyoming, even up to the area in which Devils Tower is located. 


Cross section of the Black Hills. Image courtesy of A Textbook of Geology.

In geological terms, a dome is an anticlinal structure where the rocks dip gently away from the center in all directions. After folding, fracturing, and faulting, this causes the overlying rocks to break apart in the middle, allowing for easier erosion of the them. Once these younger rocks have eroded away, the older rocks are exposed with the oldest rocks exposed in the center. As before, due to the extreme hardness of the Harney Peak Granite, they withstood erosion and remained around much longer. Their hardness is also why the Black Hills have these granitic mountain peaks that have not eroded away. 


As you walk up to the main entrance to the main viewing platform, you come across a rather more grand entrance sign than the wooden one at the park entrance. Another interesting decision that was made for the refurbishment of the memorial in the 1980's and 1990's was the inclusion of several areas encased with granitic blocks. These granitic blocks are found within the Visitor’s & Interpretive Center, the Avenue of Flags, and Grand View Terrace, which, while they are granite, are not the Harney Peak Granite of the mountain. These granitic blocks were trucked in from elsewhere.


Here you can see the granitic blocks in the framing of the memorial at the distal end of the Avenue of Flags. In construction terms, these granitic rocks are known as "Rockville Beige granite" and are from the quarry company Coldspring. Quarried from Rockville, MN, this granite is more commonly known in geology as the Rockville Granite. 

Closeup of the Rockville Granite at Mount Rushmore

Known for its very large mineral crystals and minimal amount of metamorphism, the Rockville Granite presents as a very nice, consistent granite comprised mainly of quartz, feldspar, biotite, and hornblende with other accessory and background minerals. Minnesota has several granitic bodies that all date to around the same age. The Rockville Granite in particular is dated to being 1.812 billion years old (Ga), which is considered the Late Penokean of the Paleoproterozoic Era. When compared to the varying cooling rates of the Harney Peak Granite producing varying textures with metamorphic inclusions throughout, it is no wonder whey they decided to use a more picturesque granitic rock for the entrance and viewing terrace.

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Thursday, January 22, 2026

Geology of the National Parks in Pictures - Devils Tower National Monument

My next post about the Geology of the National Parks Through Pictures is from our move across the country from Utah to New York. Along the way we visited 13 National Parks as well as some other sites. This was the 6th National Park along the way.


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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Obligatory entrance sign shot, however this is probably one of my favorite alignments of the sign to the feature of the park. 

While describing the geology of Devils Tower you would probably want to start with the tower first (duh). However, in order to understand how the tower formed, you need to understand the rocks that were here before the tower, or what would become the tower, some of which still remain. 

While many of the rocks that Devils Tower formed within have long since eroded away, there are still significant amounts of older rocks that the tower currently resides on. You can see some of these rocks as you drive up to the tower from the main entrance (photo with the entrance sign and directly above). 

Geology of the Devils Tower sedimentary rocks. Image courtesy of NPS. 

The bright red rocks at the base of the hillside are the Spearfish Formation, which can be seen most easily in the photo above without the entrance sign. These rocks, dark red sandstones and maroon siltstones, formed during the Permian and Triassic Periods (~ 225 to 195 million years ago) when this area was covered by a shallow inland sea. The deep red color is from the oxidation (rusting) of iron within the deposits. After the Triassic Period, during the Middle Jurassic (~170 million years ago), the inland seas periodically withdrew producing periods of evaporation. This evaporation lefts gypsum rich deposits in the form of the Gypsum Springs Formation. 

View facing away from the tower. You can see the Spearfish Formation in the distance towards the let half of the photo.

Afterwards, the Middle Jurassic (~165 million years old) Stockade Beaver Shale then represents the deepening of the inland seas, with the shales deposited in deeper waters than the previous Spearfish Formation. The final sedimentary deposits that remain within the park are the Late Jurassic (~155 million years old) coastal dunes and beach deposits of the Hulett Sandstone. Within these rocks that form the cliff edge surrounding the tower, ripples from the former beaches can still be seen. 


The formation of the tower itself is uncertain though. There are several theories that have been proposed with none, to date, taking precedence. It is without a doubt that the tower formed from some variety of magmatic intrusion within the surrounding sedimentary rocks one to two miles below the (former) surface that began about 50 million years ago. This magma then cooled and solidified, forming the basis of the tower itself. Then, around 5 to 10 million years ago, the overriding sedimentary rocks started to erode away and expose the tower, leaving behind the much more resistant rocks. 


The prevailing theories are that Devils Tower formed as a:
  1. Igneous stock. The magma intruded into the sedimentary rock layers forming a body roughly the shape of the modern day tower. The magma then cooled, and eventually the overriding sedimentary rocks eroded away, along the outer edges of the igneous body for the last several million years. 
  2. Laccolith. This is a larger igneous intrusion with a more mushroom shape to it. Again, the magma solidified and then eroded away once the overlying sediment was removed and eventually eroded down to the tower shape as we know it today.
  3. Volcanic plug. Essentially this was the root of a volcano, where magma was rising up through the volcano and eventually as the volcano went extinct, the magma within the volcano solidified. This is deeper within the earth than what is known as a "volcanic neck". The volcanic neck theory is discussed below. 
  4. Maar-diatreme volcano. This is the most recent suggestion where the magma caused the groundwater to become superheated and eventually explode, creating a crater. The crater was then filled with magma and solidified. Eventually the surrounding rocks eroded away, again, leaving the tower as we see it today.


The rock itself is what is known as a phonolite porphyry. Phonolite is a type of igneous rock that is rich in alkali feldspar and moderate amounts of silica (quartz). As you can see in the diagram below, phonolite has one of the highest percentages of alkali feldspar. The alkali feldspar in this instance is orthoclase, which makes up the second part of the rock name - porphyry. Porphyry, AKA porphyritic rocks, are rocks composed of two principle grain sizes, a background, where the mineral crystals are usually indistinguishable, and the much larger crystals, known as phenocrysts. In the photo above, orthoclase is the mineral that makes up the phenocrysts, the large white crystals on a background that is more grey in color.  
Igneous rock diagram. Image courtesy of Moayyed et al., 2008.

But one of the most distinguishable factors of the tower, besides its size amongst a fairly featureless plain, is the columnar jointing. Columnar jointing is what produces those vertical lines seen at a distance of the tower. These columns are roughly hexagonal in shape, however they are not consistent and Devils Tower has many that are pentagonal columns as well, as well as ranging in diameter from 10 feet across to 4 feet across. These columns are formed when the igneous body (magma) is cooling and the magma starts to shrink (contract). This contracting produces stress lines which radiate out through the resulting rock, forming this columnar jointing pattern. These joint lines align perpendicularly to the direction of the cooling front. Since the jointing lines are running vertical, it can be assumed that the cooling front was essentially horizontal above the tower. With the fractures running vertically through the height of the tower, boulders breaking off and forming a pile of boulders, the scree, are fairly common, especially through geological history.


One other theory of the tower's formation is that of a volcanic neck. A volcanic neck is related to the volcanic plug, however a neck would be seen as the central portion of a volcano, as opposed to deep within the earth. In this instance, if this were a volcanic neck, what we would see is that Devils Tower is the core of the volcano, with the sloped sides having been eroded away. However, the jointing pattern, which runs vertically and curves towards the bottom of the tower, indicates that this theory of a volcanic neck is incorrect. If this were a former volcanic neck, the jointing pattern would run towards the center of the tower, as opposed to running nearly vertical.  

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