Geologic Triple Junction of Southern Utah

in the southwest corner of Utah next to the city of st. George is a unique triple junction of three great western physiographically jhin's here you'll find elements from all three areas that mix and overlap to create an unusual transition zone where you can see and experience those elements all in one place before I begin telling you about this distinctive area let me first say that the science of geology is a very broad and complex subject so for the purpose of this geological tour I'll be using the word province as a way to define an area that includes such things as its geology geography botany climate physiography and other factors these provinces are the Colorado Plateau the Mojave Desert and the Great Basin I'm going to show you some examples of all three of these provinces and how they look near this triple Junction you'll learn how to read the landscape and recognize what elements belong to what province as an example here's a Josh a tree of Mojave Desert Fame growing near some classic red Navajo Sandstone from the colorado plateau with sagebrush that is prominent in the Great Basin growing nearby I'll explain and explore some of the elements commonly found in each of the three provinces and where you can find them all coexisting in the triple Junction area I'll also talk about how elements of one province the Colorado Plateau has influenced this entire triple Junction area I believe that understanding the elements of all three provinces will help you to better understand what you see today in southwest Utah and I hope that it will increase your appreciation for all the forces that were once at work here so sit back and enjoy the scenery as we explore this fascinating area together in this video tour we'll start with this map that shows the states of the southwestern United States let me point out the approximate locations of those three provinces first there's the Colorado Plateau it is an area well known for unique and beautiful landscapes Colorado means colored red in Spanish which certainly describes the most common color found in much of the rock making up this provinces landscape second is the Mojave Desert it is best known for the area it covers in California but it also takes up small parts of Arizona Nevada and Utah it is commonly referred to as a high desert and is recognized as the home of the iconic Jascha tree and desert tortoise and third is the Great Basin this province is aptly named because rain that falls here stays in one of the many valleys or basins and never flows to an ocean it covers most of Nevada along with chunks of Oregon Idaho Utah and extreme eastern California one thing to notice on the map is this the location of the hurricane fault it is the very western boundary of the Colorado Plateau and the very eastern boundaries for both a great basin and the Mojave Desert the hurricane fault plays a vital role in the sites that you see in this triple Junction area incidentally in the st. George area the name hurricane is actually pronounced hurricane let me explain a little more about all three provinces starting with the star of the show that Colorado Plateau the geology of this province is quite complicated so I'll try to give you a condensed version the reason I call this the star of the show is because the layering of the Colorado Plateau is spread all over the triple Junction area what is now on the east side of the hurricane fault is also seen on the west side too but the seismic activity on the west side of the fault has twisted and contorted those same layers you'll see that the plateau is made up of very orderly layers but in the triple Junction areas of both the Mojave Desert and Great Basin mainly the hobby desert those layers have been chaotically jumbled up this in turn has created some very different scenery than what you see on the Colorado Plateau the Colorado Plateau wasn't always a plateau most geologists agree that it all started when sedimentary deposits were slowly laid down over hundreds of millions of years mainly in a wet environment during much of this time the Colorado Plateau was covered by a shallow sea then later vast sand dunes some of these deposits were laid down over extended periods of time creating thicker layers while other deposits were laid down in a shorter period making the thinner layers eventually these layers consisting mostly of sand and different muds solidified and created the sand stones we see today when you look at those layers around the triple Junction mainly on the Colorado Plateau side think of the layers you see when you slice open an onion each of those striped layers on the hillsides are a snapshot in time from Earth's geologic history although this process of horizontal layering is not unique it is unusual for the deposits to have stayed so intact a long period of time millions of years has gone by since these various layers were deposited and in most other places on earth they have since been twisted and deformed but not here on the Colorado Plateau starting around 70 million years ago portions of the Colorado Plateau began uplifting about 20 million years ago it truly began life as an actual plateau as the uplift accelerated forces from adjoining geological provinces pushed up the vast approximately 130,000 square mile large block which became the Colorado Plateau we know today amazingly the plateau was pushed up in a relatively short period of time geologically in some places it rose over a mile and a half during this time natural erosional forces mostly water were also at work they weathered away and cut deep into the horizontal layers of the plateau exposing them like a layer cake this erosion created places we now know as the Grand Canyon the Grand Staircase Zion Canyon and so many other canyons and ridges today we can go out and see the Grand Canyon where the Colorado River gouged a trench into the plateau a mile deep exposing those horizontal layers that were laid down so long ago in Zion Canyon the thickest layer in the Colorado Plateau is revealed this is the Navajo Sandstone formation and it's red and white vertical cliffs are found all over the plateau such as Capitol Reef and the Lake Powell area such as here at Rainbow Bridge later in this tour I'll explain how that sandstone formation plays a part in what you see in the triple Junction area by the way the word formation is what a geologist would call a lair capital reef national park has many of those layers exposed such as the chin Lai Wingate and Kayenta formations the waterpocket fold is a unique rupture in the Earth's surface where several of these layers are uplifted and can be viewed in a unique way such as here from strike Valley overlook along the burr trail there are exposures of these layers throughout the Colorado Plateau close to the triple Junction area and on the way to Zion is a familiar scene that displays many of the formations found throughout the Colorado Plateau this particular view is above Kolob Terrace Road and can be viewed from Smith Mesa Road here starting from the bottom and going up is the Moen kopi formation which was deposited starting around 250 million years ago Moe & Co P covers this area here with all of the striping here is another example of the Moe & Co P formation which can be found on Hurricane Mesa the Moen kopi is one of the most recognizable formations around the triple Junction area many people say it looks like bacon which I would agree with Moen kopi is found on the side of many mesas just east of the hurricane fault but is also found throughout the Colorado Plateau such as here near the town of its namesake Moen kopi Arizona in a place called coal mine Canyon next up is the chin lay formation that was deposited between about 220 and 200 million years ago chin lay is known for its colorful soils and outcroppings such as seen here at the pariah town site here is the MonaVie formation where a lot of fossils from animals that lived in the early Jurassic period can be found then there is the Kayenta formation deposited a hundred and ninety five million years ago in some places this formation is thinner than other formations simply because it was deposited over a shorter period of time Kayenta is easily spotted around zion as forming short cliffs that are reddish-brown as seen here along Zions Chinle hiking trail and above that is the most well-known of all the formations the Navajo Sandstone it was laid down between a hundred and ninety and a hundred and sixty million years ago a much longer period of time than the previous layers and the reason for its greater thickness as mentioned Navajo Sandstone can be found all over southern Utah as well as on the west side of the hurricane Fault such as near the town of leads in snow Canyon State Park and way into Nevada such as in valley of fire state park each layer above the previous one is a younger accumulation of rock and dirt so naturally the youngest formation is the one at the top and has the highest elevation in the plateau this is called the clairon formation it started depositing about 50 million years ago Bryce Canyon cuts into the clairon at about eight to ten thousand feet above sea level incidentally this is PowerPoint which is the highest point in the Colorado Plateau and is literally the highest point of all the formations PowerPoint named after the famous Explorer John Wesley Powell is a prominent landmark as seen from Bryce Canyon as well as most of southern Utah botanically the Colorado Plateau has a wide variety of plant communities because of all the different formations there is a wide variety of soils and with the elevations ranging from four thousand to over eleven thousand feet high there are opportunities for many different types of plants to grow everything from desert plants in the dry sandy washes to green pine trees growing at the higher elevations as we go along you'll see how understanding the Colorado Plateau and its formations is important and relative to understanding the rest of the triple Junction puzzle next there's the Mojave Desert the Mojave is probably best known for its iconic Jascha tree but it is also the smallest and driest desert in the United States the easiest way to identify this province is by finding a Jascha tree because typically they only grow in the Mojave Desert the four corners of this province are Josh a tree national park to the south Death Valley to the northwest our triple Junction area to the Northeast and into Arizona to the east there is currently some debate among geologists about whether or not the Mojave is its own province or just a southern extension of the Basin and Range province geologically however the Mojave is quite different from the repeating series of long ranges and valleys of the Basin and Range province one big difference is its relationship to the San Andreas Fault here on the map you can see the San Andreas which in fact is the Mojave deserts Southwest boundary further fracturing of the San Andreas starts roughly near present-day Joshua Tree National Park and leads Northwest across the Mojave Desert this created what geologists call the mojave rift zone on the map here are some of those fractures those fractures are nail faults that behave just like the San Andreas and are somewhat parallel to it this rift zone has given parts of the Mojave a unique structure geologically in fact over the past few hundred years more earthquakes have occurred here than on the San Andreas itself the mojave province has also experienced its fair share of volcanic activity recent activity is marked by numerous cinder cones such as these in the Mojave National Preserve there was older activity - such as the violent eruption at hole-in-the-wall also located in the preserve this shallow sea that covered most of the Colorado Plateau did not include the Mojave most of the plateaus formations fade out or were generally eroded away as they crossed into the mojave province traces of the vast Navajo Sandstone which is known in Nevada as the Aztecs sandstone formation can be found throughout the Mojave Desert in places like Valley of fire and Red Rock Canyon near Las Vegas and in locations around the triple Junction area such as snow Canyon and the Red Cliffs reserve near the ghost town of silver Reef as all this erosion took place broad alluvial slopes also known as bajas were created across the mojave these large slopes of well-drained soils would later become ideal ground for diverse plant populations to flourish which brings us to botany and the Mojave Desert many cactus and other desert dwelling plants including the distinctive Jascha tree live in well-drained soils so expect to see them growing in these vast alluvial plains because of all the erosion that takes place in this province a lot of drainages washes or dry riverbeds are created these features are relatively sandy with a wide variety of soil types desert plants indigenous to the Mojave thrive in these washes the Mojave is considered a high desert with elevations ranging from two to eight thousand feet and above there are plants that live in the alkaline rich soils of the lowest spots and pinyon Pines and juniper trees that live at the highest elevations now there is a reason why I'm telling you about this just wait for it because now you need to know a little about the Great Basin before we can get to our triple Junction area of southwest Utah bear with me alright so here's some specifics about the Great Basin this province stretches out west and north of the triple Junction area it covers western Utah most of Nevada and small portions of California Idaho and Oregon there's also the much larger Basin and Range province the Great Basin and the Mojave Desert are part of the basin and range along with encompassing these two sub provinces it also covers other desert regions south and east into Arizona and Mexico as you can see on this map the Basin and Range province is an area where mountains and valleys were typically formed and became what is known geologically as horst's and grabens these formations were created by a geologic process where the Earth's crust was stretched through plate tectonics which I'm not going to cover since it's a big subject however just know that typically a mountain or a range is a horst and a valley or basin is a graven the Great Basin province on the other hand is a large region where water typically does not drain to the ocean instead water drains to large inland lakes also known as playas or dry lakes or basins examples of such large inland lakes that do not drain to the sea are the Great Salt Lake or severe Lake in Utah and Walker Lake in western Nevada the basin and range literally consists of long basins or valleys and ranges as in mountain ranges in the Great Basin all of these Basin and ranges run parallel to each other and trend almost north-south as you can see in this topographic relief map of Nevada rainwater falls in the ranges and flows to the basins often the water just collects in basins and goes no further in other areas the water flows into rivers is carried to a larger basin and flows into a large lake then goes no further in the triple Junction area however most runoff flows into the Virgin River and will eventually get to the ocean one of the most iconic basins in the basin and range is Death Valley Badwater Basin is the lowest elevation in the Western Hemisphere at 282 feet below sea level in dramatic contrast less than 15 miles to the west telescope peak rises high in the Panamint mountain range to 11,000 feet creating one of the greatest topological offsets in North America botanically one of the most common plants found in the Great Basin is the sagebrush so naturally sagebrush is common in the triple Junction area all right so we've talked a little bit or maybe too much about all three provinces now imagine taking the characteristics from all of them putting them into a blender and then turning it on for about 30 seconds the result would be the landscape you see in the triple Junction area [Music] remember the hurricane fault well it actually saved the Colorado Plateau from being in that blender by separating it cutting it off from the geologic activity that was happening on the west side of the fault that's why the layering is so obvious when you look into the distance anywhere from the triple Junction area so everything on the west side of the fault went into the blender and the result is the chaotic landscapes you see today along Interstate 15 this landscape was originally layered long ago just like the Colorado Plateau but then the younger hurricane fault sliced it clean off and the compression and the geologic forces from the Mojave and Great Basin provinces warped twisted and jumbled it all up here's a closer map of the triple Junction area of st. George I'm going to point out where you can find some of the jumbled up areas of the Mojave Desert and Great Basin as well as where you can compare it to the finally organized layers of the Colorado Plateau just beyond the hurricane fault our first look will be this familiar scene along i-15 of a sharp outcropping known as Black Ridge also known as hurricane cliffs which is an extremely uplifted portion of the hurricane fault standing on top of black Ridge which is high above the little town of Tocqueville one gets a good view of the triple Junction area to the south it was near here that one of the first European pioneers set eyes on this area for the first time his name was parley P Pratt in 1850 Pratt reported that the country southward opening to the view as it were a wide expanse of chaotic matter huge Hills sandy desert cheerless grassless waterless planes perpendicular rocks loose barren clay dissolving beds of sandstone various other elements lying in inconceivable confusion in short a country in ruins dissolved by the pelting of the storm of Ages or turned inside out upside down by terrible convulsions in some former age blender certainly didn't exist during Pratt's time but if they did he may have used the same analogy I used earlier to describe how the triple Junction became the mixed-up geological puzzle we see today one great place to view the triple Junction region is from the historic mining town of silver reef the view you are seeing is from the town's Museum just to the west of silver reef is this big block of Navajo Sandstone this is where miners in the 1870s discovered silver deposits in a very improbable place within the sandstone itself it is extremely rare to find precious metals like silver in sandstone there are only one or two other places known on earth where this has occurred looking north then east you can see the sharp Ridge of the Huracan fault beyond it is the Colorado Plateau in the distance you can see various mesas most of which are made up of the Moen kopi formation much of the ground between silver reef and the hurricane fault is part of the Great Basin but as we pan more to the south you can start seeing a land that belongs to the Mojave Desert for instance downtown st. George is roughly located in the Mojave Desert whereas silver Reef is more inside of the Great Basin let's look at another panoramic view this one can be seen at the confluence park trailhead at the north end of Main Street in the town of hurricane at the trailhead there is this great sign that explains and points out the area's geology from the trailhead looking east to north you can easily see this steep cliff known as a scarp which is the hurricane fault just above it is hurricane Mesa where again you can easily make out the narrow layers that make up the mo and copii formation these thin stripes are very obvious in most of the mesas around here they are especially visible when driving from hurricane to Zion National Park panning to the north you see a massive bulge in the fault this is where the hurricane fault was dramatically pushed up for some reason possibly by what's called the Virgin anticline this is black Ridge the place that mr. Pratt stood on and made his observation on maps this portion of the fault is known as the hurricane cliffs or black Ridge incidentally you can follow the hurricane cliffs on a map northward along Interstate 15 all the way to the town of Beaver just behind the hurricane cliffs is a prominent outcrop of Zions famous Navajo Sandstone this is a side view of the Kolob canyons section of Zion National Park that is just inside the Colorado Plateau panning now to the north we cross into the Great Basin here you begin to see the jumbled up landscape caused by the blender notice the striping on some of the hills see how they are not level unlike what you see on Hurricane Mesa in the distance you see the Pine Valley mountains they roughly make up the first range in the Great Basin these mountains however are quite different than any of the others in this province the Pine Valley mountains were formed from the Pine Valley laccolith which is an intrusion of magma that's been injected between the layers of sedimentary rock the pressure from this magma was so strong that it pushed the layers above it up forming a dome shape think of it as a volcano that never got the chance to erupt and even more special is that this laccolith is the largest in the United States and possibly the largest in the world it's just one more exciting piece of the geologic puzzle that is the triple Junction to the far left is an area known as Babylon below notice how this Canyon carved out by the virgin river cuts through volcanic basalts which are ancient lava flows this basalt has come from volcanic eruptions all along the Huracan fault for the past 1 to 2 million years lava oozed up to the surface through the fractures in the fault and erupted as small volcanoes called cinder cones these cinder cones can be seen along the fault all the way south into the Grand Canyon Babylon is a ghost town just south of the towns of silver reef and leads this area has excellent examples of jumbled up sandstone from various formations that are otherwise found neatly layered in the Colorado Plateau since much of the colorful sandstone found here is from the blender it is difficult to identify which formations they came from some of it looks like Navajo Sandstone but undoubtedly material from other formations has been mixed in to one of the main contributors to our blender action is what's known as the Virgin anticline that thing I mentioned earlier an anticline is an upward curved fold in the layers of rock in the Earth's surface and this one is a classic example the Virgin anticline was caused by geologic forces from the larger Basin and Range province as it crumbled up the Earth's crust when it pushed up against the hurricane fault in the large block of the Colorado Plateau behind it using Google Earth we're looking down at the st. George area see this area here this is the landscape the anticline left in the area let's now zoom in and look up the anticline towards the north this force literally created a large bulge in the Earth's surface that pushed up formations deep within such as the Moen kopi in the Navajo Sandstone an excellent way to see the anticline in its topsy-turvy geology of the triple Junction is along highway 9 about a mile and a half east of the i-15 freeway here's an aerial view of the same area notice the pushed up or angled Ridge here and the other one over here the tops of these two ridges used to be connected like this all of the rock and material from the center of the anticline has since eroded away leaving these exposed layers for us to enjoy and to notice how this hillside along highway 9 looks very similar to the side of hurricane mesas MO and copii formation that's because it is the same formation the only difference is that here it's at a much lower elevation than in hurricane Mesa that's because hurricane Mesa was lifted up along with the rest of the Colorado Plateau in this area wasn't driving along highway 9 or taking the turnoff to Quail Creek State Park is a great way to view the Virgin anticline and the unique landscapes it created you just saw a few of the areas where you can go to see and experience where all three provinces converge in other videos we'll cover more places to visit including how to get there where you can see other features of this geologically amazing region okay have you seen enough hopefully after watching this video you'll feel compelled to visit the triple Junction area of southwest Utah when you arrive and are looking to learn more a few places to visit include the BLM office in st. George the silver reef museum near Leeds and or the dinosaur Discovery Center also in st. George and stay tuned to our blog or YouTube channel to watch for more video tours showcasing the remarkable landscapes and places to see where these three physiographic provinces join together thanks a lot for watching you

Channel: BackRoadsWest1

Views: 82,968

Rating: 4.8930602 out of 5

Keywords: Utah, Southwest Utah, St. George, Colorado Plateau, Mojave Desert, Great Basin, Triple Junction, Hurricane fault, Silver Reef, Virgin Anticline

Id: 9Tfrpo94vKY

Length: 38min 57sec (2337 seconds)

Published: Mon Mar 23 2020