WHAT ARE MOQUI MARBLES? AND HOW DO THEY FORM?

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Many visitors to Utah’s Colorado Plateau run across the small marble like structures often eroding out of the the sandstone, and wonder what they are. They are colloquially known as Moqui marbles. Moqui marbles are small, brownish-black balls composed of iron oxide and sandstone that formed underground when iron minerals precipitated from flowing groundwater. They occur in many places in southern Utah either embedded in or gathered loosely into “puddles” on the ground near outcrops of Jurassic age Navajo Sandstone.

The word Moqui appears to have come from the Hopi Tribe. The Hopi were previously known as the Moqui Indians, named so by the early Spaniards, until their name was officially changed to Hopi in the early 1900s. According to some Internet sources, there is a Hopi legend that the Hopi ancestors’ spirits return to Earth in the evenings to play marble games with these iron balls, and that in the mornings the spirits leave the marbles behind to reassure their relatives that they are happy and content.

Moqui marbles (sometimes spelled Moki) are also known by collectors by many other names—Navajo cherries, Navajo berries, Kayenta berries, Entrada berries, Hopi marbles, Moqui balls, or Shaman stones. Geologists call them iron concretions.

These spherical iron concretions commonly range in size from a fraction of an inch (pea size) to several inches in diameter, although some can be as large as grapefruits. In addition to marbles or balls, iron concretions can be shaped like buttons, pipes, corrugated sheets, UFO “flying saucers,” plates, or doublets and triplets (two or three conjoined balls).

The host rock for the marbles, the Navajo Sandstone, was originally deposited around 180 to 190 million years ago as a huge sand dune field, similar to the modern Sahara, that covered parts of Utah, Arizona, Colorado, Wyoming, Idaho, Nevada, and New Mexico. A very thin, microscopic layer of hematite (an iron oxide mineral) coated the sand grains, giving the sand its red color. The sand was later buried by other sediments and eventually cemented into sandstone, during which time the hematite coatings continued to spread over the grains, ultimately giving us some of the most spectacular red sandstones visible in southern Utah.

But not all Navajo Sandstone is red; some Navajo Sandstone is white. While still buried, water containing reducing agents such as weak acids or possibly hydrocarbons (petroleum) traveled slowly through parts of the permeable sandstone, bleaching the red rock by dissolving the iron into the water. This iron-laden water eventually flowed to a place where the groundwater chemistry changed and caused the iron to precipitate. This precipitated iron surrounded and cemented the sand grains and in time formed iron concretions consisting of concentric layers of hard iron minerals enclosing loosely to well-cemented sand. Some recent studies have also proposed that microorganisms later helped convert the precipitated iron into iron oxide.

Once the overlying rock layers were eroded and the Navajo Sandstone revealed, weathering of the sandstone exposed the hard, weather-resistant iron concretions, many of which are amassed in large groups on the surface. Many concretions are located in State Parks, National Parks and Monuments, and Native American reservations where collecting is prohibited.

Martian Blueberries

Discovered on Mars by NASA’s Mars Exploration Rover Opportunity in 2004, the Martian blueberries are thought to have formed in a similar manner to the Moqui marbles on Earth, therefore providing some of the first evidence for water in Mars’ ancient past. And just like on Earth, these hematite concretions were found scattered on the ground and embedded in rock outcrops, “like blueberries in a muffin” according to one rover scientist.

Martian blueberries are gray not blue, and are much smaller than most marbles in Utah, usually about BB pellet-size. By continuing to study iron concretions in Utah, geologists can make analogies as to how these blueberries formed on Mars.

THE HENRY MOUNTAINS OF UTAH (Geology, Features & Attractions)

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Nestled in south-central Utah is a remote mountain range which epitomizes an entire era of unique volcanism in Utah and was one of the last mountain ranges in the United States to be fully explored and mapped. In fact, these intrusive volcanic mountains were the last mountain range in the United States to be named. It wasn’t until 1872 that the range was named and still three years later when the mountains were finally explored by the great American geologist G.K. Gilbert who first wrote about the incredibly unique geology of the Henry Mountains.

Utah’s Henry Mountains are in Garfield and Wayne Counties east of the Waterpocket Fold between Capitol Reef National Park and Glen Canyon National Recreation Area. They are composed of about a half dozen high peaks, three of which make the list of Utah’s top thirty highest. Mount Ellen at 11,522 feet above sea level is the 13th highest peak in the state. But what makes the Henry Mountains so interesting is not so much their height but their geology. Most of Utah’s mountain ranges were formed from large faulted or folded blocks of sedimentary rock. The Henry Mountains, however, are one of only a few volcanic mountains in Utah that were formed by large magma chambers injected between layers of sedimentary host rock. Geologists characterize these volcanic structures that make up the Henry Mountains as “laccoliths.”

Note: As a general rule, in contrast to the smoldering volcanic vent in the figure, these names refer to the fully cooled and usually millions-of-years-old rock formations, which are the result of the underground magmatic activity shown. (mediawiki, GNU Free Documentation License)

When a laccolith is pushed even closer to the surface by subsequent pressure after it cools, steep faults can form around its periphery. Geologists refer to the resulting feature with the even more specific term of “bysmalith.” Table Mountain on the northwest corner of the Henry Mountains is a great example of a bysmalith feature.

Unlike a typical volcano, which forcefully ejects the contents of a magma chamber onto the surface of the earth, or a batholith, which is a very large magma chamber that cools beneath the surface, a laccolith is a sizable magma body which attempts to come to the surface through a neck or conduit but spreads horizontally between sedimentary layers on its way up, pushing the host rock layers up into a dome shape before cooling beneath the surface. As a result, the “textbook” laccolith can look a little bit like an impact crater as the surrounding dome-shaped, upwarped eroding layers of sedimentary rock often form concentric circles around the underlying magma chamber in a way that resembles the central dome of a meteor impact.

The Henry Mountains formed between 23 and 29 million years ago during the Oligocene epoch when portions of subducted oceanic crust melted beneath Utah to form huge viscous masses of rising magma. During the period of about 20 to 30 million years ago, many large igneous bodies were emplaced in Utah and the surrounding region. These include the nearby laccoliths and stocks (similar to batholiths but smaller) of the Abajo and La Sal Mountains, as well as Navajo Mountain and the Pine Valley Mountains in Utah, and the La Plata Mountains in Colorado.  Other large igneous intrusions were also emplaced during this time in the Wasatch Range, Oquirrh Mountains, and Pilot Range.

Most of these enormous magma bodies made their way to, or near the surface within about a 10-million-year window of time during the Oligocene and Miocene epochs.

Geologists come from all over the world to study the unique properties of Utah’s laccoliths. For instance, the Pine Valley Mountains laccolith in southwestern Utah is thought to be one of the largest in the world (see Survey Notes, v. 34 no. 3). Its northern flanks are bordered by massive landslides which occurred when the laccolithic magma was rapidly injected into the subsurface, sufficiently steepening the ground surface and causing the overlying layers to slide off in a rapid mass-wasting event. The speed of emplacement of laccoliths like the Henry and Pine Valley Mountains is unknown, but features such as the North Pine Valley landslides suggest that laccoliths can form quite rapidly.

The Henry Mountains are also notable for the free-roaming herd of bison that live there, one of only three such herds in the country. The population was established in 1941 after relocation of 18 individuals from Yellowstone National Park. The herd is often grazing in the saddles between the central peaks of the range. The mountains are also home to antelope, mule deer, bighorn sheep, wild burros, and mountain lions. As one of the most isolated high mountain ranges in the United States, the unique geology of the Henry Mountains makes them worth the effort to explore and enjoy.

Table Mountain on the northwestern edge of the Henry Mountain Range is a textbook example of a laccolithic bysmalith. (Image credit. Google Earth)
View from the southeast of Mount Hillers in the central Henry Mountains. Colored bands around the periphery are Mesozoic sedimentary layers folded into a near-vertical attitude from the rising magma of the main igneous stock. (Image credit. Google Earth)
How to Get to the Henry Mountains:
The Henry Mountains are best accessed from the east by paved Utah State Routes 95 and 276 or from the north by Utah State Route 24. One of the best dirt access roads is accessed by traveling south on 100 East Street in Hanksville. This street becomes Sawmill Road and winds south for approximately 23 miles before reaching the Lonesome Beaver Campground. The road then gets considerably steeper and rougher as it climbs south and then west to the McMillan Springs Campground on the west slopes of Mount Ellen. 

THE FACINATING GEOLOGY OF THE WASATCH PLATEAU

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The Wasatch Plateau is located south and east of the southernmost part of the Wasatch Range in central Utah and is in the transition zone between the Colorado Plateau and the Basin and Range physiographic provinces. The plateau is a table-like mountain range with an abundance of lakes and reservoirs along its axis. These many lakes and reservoirs are the result of three very different geological processes that continue to shape the area. These include landslides, which are responsible for most of the plateau’s smaller lakes; extensional faulting, which created valleys (or grabens) that accommodate the plateau’s largest modern reservoirs as well as a few mid-size lakes; and Pleistocene-age (about 2.6 million to 12,000 years ago) glaciation, which created many of the plateau’s smaller high-elevation lakes. 

The Wasatch Plateau is home to many mid- to high-elevation wooded shallow ponds and lakes that create amazing opportunities for camping, fishing, and recreating. However, most do not realize that the small, relatively flat basins that house many of these lakes are actually closed depressions that form near the uppermost part, or head of large ancient landslides. Although the bottom, or toe, of landslides can often form lakes as they dam stream drainages, few of these types of lakes last because they are prone to overtopping and erosion. However, the top part of landslides commonly form what is known as a sag pond or closed depression just below the head. The Wasatch Plateau contains many of these with classic examples existing in areas such as Mayfield Canyon’s Twin Lake or the many ponds in the Spring Hill area and other headwaters of Twelvemile Creek. Ponds can also form between the toe and head of the landslide due to the uneven, jumbled, or hummocky topography, such as Slide Lake west of Joes Valley Reservoir.

Landslide morphology showing the pond-forming, closed depressions that develop below the head of a landslide.

The abundance of ancient landslides that created these lakes and ponds is largely the result of the composition of the North Horn Formation. This formation formed during the Late Cretaceous Period and Early Paleocene Epoch, approximately 75 to 60 million years ago, and consists of a series of alternating layers of sandstone and clay-rich siltstone and mudstone. These clay-rich layers make the formation particularly susceptible to landslides. When wetted, the clay layers become weak surfaces that allow the rock layers on top to move down slope.

Occasionally, the instability of the North Horn and a few other similar geologic units has led to massive modern landslides and debris flows that have caused significant damage to infrastructure on the plateau. 

One such example occurred in Twelvemile Canyon, which has a long history of damaging landslides. In the spring of 1983, a massive landslide in the canyon temporarily blocked the creek, which soon overtopped the natural dam and created a debris flow. The debris flow traveled 2.4 miles down the South Fork of Twelvemile Creek before burying part of Pinchot Campground. Another 1983 landslide, below nearby Twin Lake, closed the road and threatened to block Twelvemile Creek entirely. Less than two decades later, in 1998, another large landslide from the North Fork of Cooley Creek traveled 1.8 miles down the South Fork of Twelvemile Creek, depositing large amounts of landslide material in the creek. In addition to these historical landslides, prehistoric landslides are common in the canyon, and evidence shows that some have blocked and deflected creeks.

Block diagram showing the formation of a graben between normal faults as Earth’s crust extends and pulls apart.

The second process responsible for the location of the largest lakes on the Wasatch Plateau is extensional faulting. The Wasatch Plateau has many north-to-south-oriented normal faults that are created by the incredibly slow westward extension or pulling apart of the plateau. The rocks on either side of a normal fault move up or down relative to each other and the down-dropped side creates a depression or valley called a graben. Several major Wasatch Plateau lakes, such as Scofield Reservoir and Joes Valley Reservoir, are located in such fault-bounded valleys. A string of smaller graben lakes also exists along the upper axis of the Wasatch Plateau in the Island Lake and Three Lakes area of White Mountain.

The third factor responsible for the many lakes on the Wasatch Plateau is glaciation. During the Pleistocene the upper elevations of the plateau accumulated several sprawling glaciers. Existing mostly above an elevation of 9,500 feet, these glaciers carved out many notable steep-sided, bowl-shaped depressions called cirques, leaving behind several small lakes and ponds called tarns. Some examples of lake basins formed by glaciation are Ferron Reservoir, Blue Lake, and Emerald Lake, which are located in the high southeast section of the Wasatch Plateau. 

The lakes, ponds, and reservoirs of Utah’s Wasatch Plateau are hidden gems for recreation. A trio of geological processes contributed to the formation of its many small and large water bodies, which include a unique combination of ponds from landslides, reservoirs in extensional faulted valleys, and lakes in ancient glacial cirques.

Many of the Wasatch Plateau’s lakes are visible in this aerial image looking southward along the axis of Skyline Drive east of Gunnison, Utah. Deep Lake, the WPA ponds, and many of the other unnamed lakes and ponds of the Step Flats area are sag ponds created at the head of landslides within the Twelvemile Creek drainage. Island Lake and several other small lakes along the axis of the Plateau are graben lakes bounded by normal faults. Solid and dashed orange lines are normal faults, the bar and ball symbol indicates the down-dropped side of the fault. Emerald Lake is in a Pleistocene-age glacial cirque. Aerial imagery courtesy of ESRI, Earthstar Geographics.

What Makes the Rock Red (in Utah/Arches & Zion National Park)

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Utah’s Colorado Plateau is famous for its striking vistas and dazzling colors. Hues of red, pink, maroon, yellow, brown, and white create an array of stunning rock colors that attract visitors from all over the globe. From the red rocks of the Navajo Sandstone to the Vermilion Cliffs of the Moenave and Kayenta Formations to the pink, crimson, and chocolate cliffs of the upper Grand Staircase, many who visit the Colorado Plateau wonder what gives the rocks their brilliant colors. This question has spurred much research by geologists, involving chemical and physical analysis. The answers can be complicated, as many different minerals can cause coloration in rocks; however, for the most part, the red, pink, yellow, and brown colors of Utah’s “Red Rock Country” simply comes down to one element—iron.

Coloration of the Navajo Sandstone caused by post-depositional movement of the iron mineral hematite. (Photo credit Peter Fitzgerald, GNU Free Documentation License)

Since minerals form the basis for many pigments and dyes, it should be no surprise that they are also responsible for the coloration of rocks. Of all the common colorful minerals found in Earth’s crust, few are as abundant, dynamic, and multi-colored as iron. Depending on how it combines with other elements, iron can form a veritable rainbow of colors. When iron combines with oxygen it becomes iron oxide, and its degree of oxidation largely determines its color. Ochre, a mixture of clay, sand, and iron oxide, has been one of the most commonly mined mineral pigments for tens of thousands of years and is composed of the same minerals that often color rocks. Obtained from iron-bearing clays, ochre can produce several colors and hues that are used as natural coloring agents. Red ochre comes from hematite (Fe2O3), a mineral named for the same Greek root word for blood, and has long been used as a red pigment. Some iron oxides, when hydrated (combined with hydrogen and oxygen), can form bright yellows such as yellow ochre which comes from the mineral limonite (FeO(OH)+H2O). Brown ochre comes from the mineral goethite (FeO(OH)) and is a partially hydrated iron oxide. Iron can also form black pigments from minerals such as magnetite (Fe3O4), or even blue and green hues from minerals such as glauconite and illite. For the most part, these iron minerals, and particularly hematite, are responsible for coloring the Colorado Plateau’s sedimentary rock layers.

The Amazon River’s “meeting of waters” is a fantastic example of the different water chemistries likely responsible for the coloration of ancient sediments. The Rio Negro, a tributary of the Amazon, is a “blackwater” river which is clear, slightly acidic, and contains high concentrations of reduced iron. The Amazon, however, has lower concentrations of iron and dissolved solids, but a higher sediment load and oxidized iron giving it its reddish-brown color. (Photo credit Gabriel Heusi, Wikimedia, Creative Commons license.)

Researchers have questioned how the pigment-bearing iron minerals get into rocks like sandstone and shale as well as how the minerals are dispersed within the rock. One might suspect that the brightly colored minerals might be sprinkled throughout the sand and clays or cements that composed the sandstone and shale units—something like chili powder, evenly mixed within the salt. However, by looking at thinly cut sections of rock under a microscope, it becomes clear that this is typically not the case in Utah’s Color Country rock. Instead, the very sand grains that form the matrix of the rock units are actually “frosted” or coated with a layer of iron-rich mineralization. These grains are then cemented together with a pale to white calcite or silicate glue. In the case of sandstone units like the prominent Navajo or Wingate Sandstone, the sand is composed almost entirely of translucent or white quartz grains that are coated with a thin veneer of red hematite mineralization. Although the exact timing is debated among geologists, this “coating” of iron-bearing minerals likely began forming as the grains were transported from their place of erosion to their respective areas of deposition. The same process can be seen today as mineral-rich waters of semi-arid to tropical rivers mineralize large amounts of sediment as it is transported and deposited into adjoining basins.

The Amazon River’s “meeting of waters” is a fantastic example of the different water chemistries likely responsible for the coloration of ancient sediments. The Rio Negro, a tributary of the Amazon, is a “blackwater” river which is clear, slightly acidic, and contains high concentrations of reduced iron. The Amazon, however, has lower concentrations of iron and dissolved solids, but a higher sediment load and oxidized iron giving it its reddish-brown color. (Photo credit Gabriel Heusi, Wikimedia, Creative Commons license.)

Multicolored sections of the Navajo Sandstone in the Zion National Park area.

After the sediment is buried, moving groundwater can further mineralize and alter the red rock to change it to varying shades of pink, vermilion, maroon, or even white. In southern Utah, the upper parts of the Navajo and Entrada Sandstones often exhibit areas referred to as “bleached zones.” This term refers to areas where reducing groundwaters have partially removed the iron oxide coating from the sand grains. A reducing agent is a solvent that can remove oxygen from a compound. So in the case of the iron pigments that colored the Navajo Sandstone, groundwater that was slightly acidic or contained other reducing agents seems to have dissolved large amounts of iron mineralization from the upper sections, often redepositing the iron in cracks, joints, or different sections of the sandstone that possess irregularities in grain size. Areas that have lost iron oxide become lighter shades of pink and white, whereas areas that gained additional iron oxide from the groundwater movement become darker shades of maroon and even black. In most cases, these color alterations likely happened while the units were deeply buried beneath the surface. However, because these units are so permeable, allowing water to flow easily through them, water has continued migrating, dissolving bits of iron and other minerals even after they have been exposed by erosion. The dissolved minerals often get left behind on canyon walls and surfaces as the water evaporates, contributing to the creation of the well-known “desert varnish” on the rock face.

Iron nodules, often called “Moqui marbles,” weathering out of the Navajo Sandstone. The nodules here range from about 1 to 4 inches in diameter.

Iron nodules, often called “Moqui marbles,” weathering out of the Navajo Sandstone. The nodules here range from about 1 to 4 inches in diameter.

Another interesting feature of post-depositional iron-oxide movement within southern Utah’s sandstones are Moqui marbles (see “Glad You Asked” article in the September 2017 issue of Survey Notes). Moqui marbles are spherical concretions or nodules of hematite and sandstone that are formed as large amounts of reducing water dissolve hematite and illite minerals from one part of the sandstone and redeposit them around a point of nucleation. It is unclear what creates the nucleation spot for these iron concretions, but once the hematite begins to bind to some type of ionized nucleus, a chemical reaction begins causing more dissolved hematite to precipitate out of solution around existing nodules.

The amount of iron-oxide mineralization that gives Utah’s sandstones their color is typically very small. One in-depth analysis of rock coloration in the Navajo Sandstone found that minuscule differences in iron-oxide mineralization can mean the difference between red, pink, and white sandstone. For instance, red sandstone contained an average of 0.7 percent of iron oxide within the samples, whereas a sample of “bleached” white sandstone contained 0.2 percent. Pink samples seem to have nearly the same amount of iron minerals as the deep red samples; however, the iron in the pink sections of rock is largely stripped from the original grain coatings and redeposited in voids between the sand grains.

Although geologists are confident about the minerals involved in coloring Utah’s red rocks, many questions remain. Some of these involve the extent to which ancient folding, petroleum migration, or even deep geothermal waters might have played a role in the mineralization and coloring of the rocks. Regardless of the answers, all can agree that the colors of the rocks in Utah’s Colorado Plateau region make for some of the most spectacular scenery on Earth.

FOR MORE INFORMATION SEE:

Nielson, G. B., Chan, M. A., and Petersen, E.U., 2009, Diagenetic coloration facies and alteration history of the Jurassic Navajo Sandstone, Zion National Park and vicinity, southwestern Utah, in Tripp, B.T., Krahulec, K., and Jordan, J.L., editors, Geology and geologic resources and issues of western Utah: Utah Geological Association Publication 38, p. 67–96.

Cottonwood Wash of Grand Staircase Escalante National Monument (aka The Cockscomb Monocline)

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Tourists and geologists alike come from all over the world to see and study the magnificent exposures of geologic units displayed in Utah’s Colorado Plateau region. Of particular interest is the Grand Staircase, which is an immense sequence of sedimentary rock layers that stretches south from Bryce Canyon National Park and Grand Staircase–Escalante National Monument (GSENM) into Grand Canyon National Park.

Some have compared these exposed rock layers to the pages of an open book which invite visitors to look back in time at the geologic history of the area. This is especially true on the edges of massive geologic folds such as the Kaibab uplift, which extends across much of the Grand Staircase area. Where the eastern edge of the Kaibab uplift crosses GSENM, normally flat-lying rock strata tilt abruptly to the east as part of a sharp fold known as the East Kaibab monocline. Erosion of the steeply tilted strata has formed a long, imposing ridge called The Cockscomb—named after the ridge’s resemblance to the colorful “comb” on a rooster’s head.

The Cockscomb has a long geologic history that can be simplified into three phases. The oldest layers exposed at the base of this unique geologic feature were deposited between about 270 and 185 million years ago in the Permian to Early Jurassic periods. During this time, Utah was situated on the west coast of North America with much of present-day California and Nevada existing as offshore islands. Warm, shallow seas accumulated thick layers of siltstone and limestone which form the cap rock for much of the Kaibab uplift, but represent the lowest exposed layers of The Cockscomb. As North America drifted westward, Utah was uplifted above sea level, transitioning into a terrestrial environment of west-flowing rivers and streams that deposited thick layers of colorful sediments now exposed in the Vermilion and Chocolate Cliffs of The Cockscomb and Grand Staircase (seen best from Stop #1 on the map).

Beginning sometime after 200 million years ago, the rivers, lakes, and streams of the previous phase began to dry out as the climate in Utah transitioned to that of a desert. In this second phase of the region’s evolution, sediments deposited by the older river systems were blown into sweeping dune fields up to thousands of feet thick. These dune fields were inundated by a shallow, narrow seaway that provided minerals to cement the sand deposits now known as the Navajo and Sandstones, which form the impressive White Cliffs of the Grand Staircase and The Cockscomb (best seen from Stop #2 on the map). Other deposits associated with these shallow seas include interbedded limestone, siltstone, and mudstone of the late Jurassic period.

By the beginning of the third phase, in Early Cretaceous time about 145 to 79 million years ago, regional drainage became completely reversed from that of the first phase. Instead of rivers draining westward into the Pacific Ocean, they now drained eastward into a large sea that covered most of eastern Utah and Colorado. Sea level fluctuations in this Cretaceous seaway left thick, alternating layers of sand, mud, and silt. These more dull-colored deposits make up The Cockscomb’s iconic layers such as the Dakota Sandstone, Tropic Shale, and Straight Cliffs Formation. These units form the Gray Cliffs and Straight Cliffs of the Grand Staircase and can be seen from Stop #3 on the map or along the east side of the Cottonwood Canyon Road. During the end of the Cretaceous period, the Kaibab uplift and East Kaibab monocline began to take shape due to compressive forces affecting western North America. As this massive fold rose and was eroded by tributaries of the Colorado River, the scenic features of the Grand Staircase such as The Cockscomb and Bryce Canyon and the Grand Canyon began to form along its tilting periphery.

Geologists are not completely sure when the Colorado River drainage took its present shape, but most agree that sometime in the past 65 million years (and possibly as recently as 6 million years ago) rivers started to cut their way across the Kaibab uplift, eventually finding their current outlet into the Gulf of California. Small Colorado River tributaries which slice their way across the seemingly impenetrable cliffs of The Cockscomb include Cottonwood Wash, Hackberry Canyon, Paria Canyon, Catstair Canyon, and Buckskin Gulch. These drainages originate near Bryce Canyon National Park and flow southeast across the northern reaches of the Kaibab uplift, only to join the Colorado River and then turn and recross the southern part of the Kaibab uplift in the Grand Canyon!

How these rivers were able to cut their way through the uplift is a subject geologists have been debating for many years. Do the rivers predate the East Kaibab monocline? Did the rivers erode through the uplift after it was fully formed? Either way, these drainages provide important clues to geologists as they attempt to reconstruct the sequence of events that formed the present topography. And The Cockscomb, as an eastern expression of the Kaibab uplift, will continue to attract visitors and geologists from around the world as they not only enjoy its beauty, but use the feature to study the geologic processes that shaped the Grand Staircase.

Utah’s ‘Old Faithful’, Crystal Geyser

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When most people think about geysers, they picture a Yellowstone- like hot spring where pressure from steam sends a tall column of water into the air. In Utah, however, several “geysers” erupt due to the same process that causes soda pop to shoot out of the can when you hold your finger over t

he lid and shake it. Although technically not true geysers, these cold-water eruptions look so much like hot-water geysers that they are referred to as “soda pop geysers.” In Utah, the largest of these is Crystal Geyser.

Crystal Geyser is a partially human-made geyser located on the shore of the Green River, approximately 10 miles south of the town of Green River, Utah. The geyser originated in 1936 when an oil exploration well tapped into a groundwater system under immense pressure caused by a reservoir of trapped carbon dioxide (CO2) gas. However, the high-pressure system that the well penetrated had previously created a series of ancient natural springs and tufa deposits which were first referenced by John Wesley Powell in 1869. On his way down from the present town site of Green River and the state park museum which now bears his name, he wrote, “an hour later, we run a long rapid, and stop at its foot to examine some curious rocks, deposited by mineral springs that at one time must have existed here, but are no longer flowing” (Powell, 1875, Report on the Exploration of the Colorado River of the West and Its Tributaries, p. 51–52).

Perhaps because of a geologic investigation published in 1914 that reported a series of oil seeps in the area, an exploratory oil well, the Ruby No. 1, was drilled in 1935 on the margin of the ancient spring deposits. In November of that year, a Moab newspaper reported on the progress of the well stating that a significant flow of water had been encountered at a depth of 44 feet. By January 1936, the newspaper reported that drillers had encountered CO2 gas at a depth of 360 feet at high enough pressures to shoot 105 pounds of drilling mud 60 feet into the air.

The well was abandoned after drilling to a total depth of 2627 feet, but in its aftermath, a geyser was created that quickly became a regional attraction. The November 1936 front page of Moab’s Times-Independent boasted of a new geyser that spouted an 80-foot column of water at regular intervals of about 15 minutes and a 150-foot column at intervals of about 9 hours.

The pressurized CO2 gas that drives Crystal Geyser is likely derived from rocks close in age to those that have produced much of the oil and natural gas in the adjoining Paradox Basin of southeastern Utah—an ancient sedimentary basin containing oil-producing shale and evaporite rocks deposited more than 250 million years ago. The gas migrated upward into the Jurassic-age Navajo and Entrada Sandstones, where it became trapped and pressurized.

The Little Grand Wash fault, which runs in an east-west direction adjacent to Crystal Geyser, served as a barrier to the upward migration of gas in these geologic units, trapping it in an underground reservoir of permeable rock. Weakness in the fault also served as a conduit for fluids in this pressurized system to leak upward, creating carbonate-rich springs and oil seeps which early geologists reported in the immediate vicinity.

When the 1935 oil exploration company penetrated the cap on this gas reservoir, water from higher geologic units flowed down the hole to meet gas escaping from lower geologic units. The mixture of the gas and water continues between eruptions until a CO2 saturation point is reached. As soon as the water becomes oversaturated, the CO2 violently bursts out of solution and forcefully ejects the water from the borehole. Holes in the casing of the well allow much of the ejected water to flow back down the well and the whole process begins again.

Crystal Geyser is not the only CO2-driven geyser in this region of Utah. The same type of gas deposits in the northern Paradox Basin are responsible for several nearby springs and smaller but similar geysers around the town of Green River and Woodside. Other cold-water CO2 geysers are known in California, Germany, France, Serbia, Slovakia, and New Zealand. At its highest historically documented eruption of around 200 feet, Crystal Geyser is certainly one of the largest in the world.

In recent years, Crystal Geyser appears to be decreasing in both its height and reliable frequency of eruptions. Much of this was likely caused by visitors dropping rocks down the borehole, creating a significant plug less than 50 feet down. Plans to clear the major obstructions have never materialized. Plans have also been made, but never carried out, to pressure cap the geyser in a way that might increase the frequency or reliability of the eruptions.

Because major eruptions can often be more than 24 hours apart, and can often occur in the middle of the night, seeing them can be a difficult task and major time commitment. Studies carried out over the past two decades have used sensors to map the exact frequency and height of eruptions. These studies found that minor eruptions were somewhat unpredictable and ranged in height from 2 to 10 feet. Major eruptions attained heights of 40 to 80 feet and occurred on a schedule ranging from 17 to 27 hours apart. Eruption durations ranged from 3 to 49 minutes.

Crystal Geyser is a unique geologic feature that has fascinated tourists for decades. For those willing to wait around for its eruptions, Crystal Geyser can provide the unique experience of watching or even playing in one of the world’s few large cold-water geysers.

map to crystal geyser, utah

Access Crystal Geyser from I-70 exit 164, at the east end of the town of Green River, Utah. From there, head east for 2.4 miles on the frontage “New Area 51 Road” to the junction with “Crystal Geyser Safari Route.” Follow this well-graded dirt road south then west for 4 miles until arriving at a parking lot adjacent to both Crystal Geyser and the Green River boat access. Warning: Roads may be impassable in wet weather or winter conditions.

The Geology of Zion National Park

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view from Observation Point Trail of Zion National Park

View from Observation Point Trail of Zion National Park, Utah

Although the geology of the Zion National Park includes nine known exposed formations, Zion is predominately the result of one spectacular unit, the Navajo Sandstone. Zion’s formations represent about 150 million years of mostly Mesozoic-aged sedimentation in a large ancient Jurassic basin. The Navajo is part of a super-sequence of rock units called the Grand Staircase, the time exposed in the Zion and Kolob area were deposited in several different environments that range from the warm shallow seas of the Kaibab and Moenkopi formations, streams and lakes of the Chinle, Moenave, and Kayenta formations to the large deserts of the Navajo and Temple Cap formations and dry near shore environments of the Carmel Formation.

Subsequent uplift of the Colorado Plateau slowly raised these formations much higher than where they were deposited (near & at sea-level). This steepened the stream gradient of the ancestral rivers and other streams on the plateau. The faster-moving streams took advantage of uplift-created joints in the rocks to cut gorges into the plateau. Zion Canyon was cut predominately by the North Fork of the Virgin River and its tributaries. Lava flows and cinder cones covered parts of the area during the later part of this process.

Zion National Park includes an elevated plateau that consists of sedimentary formations that dip very gently to the east. This means that the oldest strata are exposed along the Virgin River in the Zion Canyon part of the park, and the youngest are exposed in the Kolob Canyons section and moreso on the Makagunt Plateau to the north (Cedar Mountain). The plateau is bounded on the east by the Sevier Fault Zone, and on the west by the Hurricane Fault Zone. Weathering and erosion along north-trending faults and fractures influence the formation of landscape features, such as canyons, in this region.

Navajo Sandstone (Lower to Mid Jurassic)

Cream colored on top of reddish colored rock

Approximately 190 to 136 million years ago in the Jurassic the Colorado Plateau area’s climate increasingly became arid until 150,000 square miles (388,000 km²) of western North America became a huge desert, not unlike the modern Sahara. For perhaps 10 million years sometime around 175 million years ago sand dunes  accumulated, reaching their greatest thickness in the Zion Canyon area; about 2,200 feet (670 m) at the Temple of Sinawava in Zion Canyon.

Most of the sand, made of 98% translucent, rounded-grain quartz, was transported from coastal sand dunes to the west, in what is now central Nevada. Today the Navajo Sandstone is a geographically widespread, pale tan to red cliff and monolith former with very obvious sand dune cross-bedding patterns . Typically the lower part of this remarkably homogeneous formation is reddish from iron oxide that percolated from the overlaying iron-rich Temple Cap formation while the upper part of the formation is a pale tan to nearly white color. The other component of the Navajo’s weak cement matrix is calcium carbonate, but the resulting sandstone is friable (crumbles easily) and very porous. Cross-bedding is especially evident in the eastern part of the park where Jurassic wind directions changed often. The crosshatched appearance of Checkerboard Mesa is a good example .

Springs, such as Weeping Rock, form in canyon walls made of the porous Navajo Sandstone when water hits and is channeled by the underlying non-porous Kayenta Formation. The principal aquifer in the region is contained in Navajo Sandstone. Navajo is the most prominent formation exposed in Zion Canyon with the highest exposures being West Temple and Checkerboard Mesa. The monoliths in the sides of Zion Canyon are among the tallest sandstone cliffs in the world.

Temple Cap formations (Middle Jurassic)

Large dome of rock

The Temple cap formation is the thin redish sandstone unit which caps many of the major spires in Zion National Park. Utah and western Colorado were deformed as the rate of subduction off the west coast increased in the Middle Jurassic Sevier Orogeny. At the same time, an inland sea began to encroach on the continent from the north. Broad tidal flats and streams carrying iron oxide-rich mud formed on the margins of the shallow sea to the west, creating the Sinawava member of the Temple Cap Formation. Flat-bedded sandstones, siltstones, and limestones filled depressions left in the underlying eroded strata. Streams eroded the poorly cemented Navajo Sandstone, and water caused the sand to slump.

Desert conditions returned briefly, creating the White Throne member, but encroaching seas again beveled the coastline, forming a regional unconformity. Thin beds of clay and silt mark the end of this formation. The most prominent outcrops of this formation make up the capstone of West Temple in Zion Canyon. Rain dissolves some of the iron oxide and thus streaks Zion’s cliffs red (the red streak seen on the Altar of Sacrifice is a famous example). Temple Cap iron oxide is also the source of the red-orange color of much the lower half of the Navajo Formation

Erosion and Canyon Formation

Red rocks

Although the units that form Zion are ancient in geologic terms. It’s erosion and canyon formation is fairly recent. Stream downcutting continued along with canyon-forming processes such as mass wasting; sediment-rich and abrasive flood stage waters would undermine cliffs until vertical slabs of rock sheared away. This process continues to be especially efficient with the vertically jointed Navajo Sandstone.

All erosion types took advantage of preexisting weaknesses in the rock such as rock type, amount of lithification, and the presence of cracks or joints in the rock. Basalt flows concentrated in valleys but subsequent erosion removed sedimentary rock that once stood at higher elevations. The resulting inverted relief consists of ridges capped by basalt which are separated by adjacent drainages.

In all about 6,000 feet (1,800 m) of sediment were removed from atop the youngest exposed formation in the park (the Late Cretaceous-aged Dakota Sandstone). The Virgin River carved out 1,300 feet (400 m) of sediment in about 1 million years. This is a very high rate of downcutting, about the same rate as occurred in Grand Canyon during its most rapid period of erosion. About 1 million years ago, Zion Canyon was only about half as deep as it is today in the vicinity of Zion Lodge.Assuming that erosion was fairly constant over the past 2 million years, then the upper half of Zion Canyon was carved between about 1 and 2 million years ago and only the upper half of the Great White Throne was exposed 1 million years ago and The Narrows were yet to form.

Downcutting and canyon widening continue today as the process of erosion continues to try to reduce the topography to sea level. In 1998 a flash flood temporarily increased the Virgin River’s flow rate from 200 to 4,500 ft³/s (6 to 125 m³/s). Geologists estimate that the Virgin River can cut another thousand feet (300 m) before it loses the ability to transport sediment to the Colorado River to the south. However, additional uplift will probably increase this figure.

The Virgin River Narrows (how far is it? geology of?)

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What is the Zion Virgin River Narrows? (Zion National Park)

The Narrows is the narrowest section of Zion Canyon. It is an 18 mile gorge or canyon filled by the Virgin River just upstream from the part of Zion where the roads and trails end. This gorge, with walls a thousand feet tall and the river sometimes just twenty to thirty feet wide, is one of the most popular areas in Zion National Park. You can see the bottom section of the Narrows by hiking along the paved, wheelchair accessible Riverside Walk for one mile from the Temple of Sinawava. If you wish to see more, you will be walking in the Virgin River. Travel upstream in the Virgin River Narrows is allowed for the first 5 miles (until Big Spring) at which point travel is restricted to down canyon, permitted travelers only.

Wall-Street section of the Virgin River Narrows.

 

How far is the Virgin River Narrows Hike top to bottom?

Most resources out there (including the Park Service brochure) like to say the Virgin River Narrows is a 16 mile hike from top to bottom. It is not!  This number is based on old information, back when hikers used to be able to start at the end of the dirt road at Chamberlain Ranch.  This is now against the rules, and hikers must start two miles sooner at the toilet facilities and parking lot above Chamberlain Ranch. A sign is posted saying “authorized vehicles only”, which forces hikers to hike the two mile dirt road making the entire hike from parking lot to parking lot 18 miles.

Distances Map of the Virgin River Narrows

download a pdf printable version of the map here.

Interesting Geology Sites in the Virgin River Narrows

coming soon.   Why Big Springs exists.  What makes all the springs in the wallstreet section.  Kolob Creek.  Joint Systems.

How can I hike The Narrows?
A hike through The Narrows requires hiking in the Virgin River. You must get your feet wet since there is no trail. Most people choose to start their hike from the Temple of Sinawava via the Riverside Walk and then walk upstream before turning around and hiking back down to the Temple of Sinawava.

Bottom Up Hike From the Temple of Sinawava (no permit required)
Hiking in The Narrows upstream as far as Big Spring does not require a permit. Doing the hike this way allows you to see some of the most spectacular and narrowest parts of the canyon. You can hike in the river for an hour and have a great experience, or you can hike as far as Big Spring, a strenuous, ten-mile round trip, all-day adventure.

Top Down Hike from Chamberlain’s Ranch (permit required)
You can also hike sixteen miles downstream over one or two days, entering the park soon after starting the hike and then exiting at the Temple of Sinawava. Those who choose this option must get a permit and arrange transportation for the one and a half hour ride to start the hike outside the park at Chamberlain’s Ranch.

What about flash floods?
The Narrows are susceptible to flash flooding because much of the surrounding area is bare rock that does not absorb water. During storms, runoff is funneled rapidly into the Narrows. During a flash flood the water level rises almost instantly–within seconds or minutes. Flash floods are common in Zion and hikers have been stranded, injured, and even killed by venturing into narrow, flood prone canyons.

Always check the weather forecast and the flash flood potential before you start your trip. Despite the forecast, flooding is possible at any time, and floods have occurred on days they were not expected. Your safety is your responsibility.
 
Hiking in the river is strenuous. The water is often murky and the bottom of the river is covered with rocks about the size of bowling balls. This makes proper footwear and bringing in trekking poles or a walking stick essential. The Narrows may be closed in the spring due to flooding while the snow melts off the upland areas to the north if the flow rate is higher than 120 cubic feet per second (3.4 m3/s). Thunderstorms can cause The Narrows to flash flood during the summer. Rain showers upriver can cause flash floods in the canyon without it raining over the canyon itself. Thus, hikers should exercise caution when hiking The Narrows during rainy periods as the winding canyon and sheer walls make approaching flash floods all the more sudden and difficult to evade.
 
Geology of the Narrows
The Virgin River narrows is a deep narrow canyon traversing one geologic unit, the Navajo Sandstone.  Much of the canyon fallows joint systems which the river has exploited and deepened.  For details on the geologic nature of the Navajo Sandstone, see my educational article on that unit here…

Utah’s Three Types of Volcanoes

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Perhaps because it is covered in detail in Grade School and Middle School curriculum, one of the most asked geologic questions I hear from youth has to do with differentiating between the three types of volcanoes.

Three Main Types of Volcanoes*
The three main types of volcanoes differ in shape, size, and make-up; the differences partly result from the different types of eruptions.
Volcano Type Volcano Shape Volcano Size Volcano Materials Eruption Type Utah Example
Cinder Cone

Steep conical hill with straight sides
Small
less than 300m high
cinders
Explosive
Diamond Cinder Cone,
Washington County
Shield Volcano

Very gentle slopes; convex upward (shaped like a warrior’s shield)
Large
over 10s of kms across
fluid lava flows (basalt)
Quiet
Cedar Hill,
Box Elder County
Stratovolcano

Gentle lower slopes, but steep upper slopes; concave upward
Large
1-10 km in diameter
numerous layers of lava and pyroclastics
Explosive
Mount Belknap,
Tushar Mountains, Paiute County

In the State of Utah there are many examples of the three main types of volcanoes. The following is a brief introduction to Utah’s volcanoes; only several of numerous volcanoes are mentioned.

Stratovolcanoes

Stratovolcanoes erupted in western Utah between about 40 to 25 million years ago. At this time, Utah was closer to a continental-oceanic plate boundary where an oceanic plate (Farallon) was subducting underneath the North American continental plate. Stratovolcanoes are found at these types of plate boundaries.

Today’s active stratovolcanoes include those in the Cascade Range in Washington, Oregon, and California where an oceanic plate (Juan de Fuca) is subducting underneath the North American continental plate.

Two examples of Utah’s most recent stratovolcanoes are Mount Belknap in the Tushar Mountains and Monroe Peak on the Sevier Plateau. These stratovolcanoes exists on the tail end of a line of explosive volcanism that extended from near Richfield, southwestward to the Nevada border. Like ancient Yellowstone National Park, many of these volcanoes were among the largest volcanoes to ever erupt in North America.

Because these volcanoes are old and have been extensively eroded, it is difficult to distinguish the original volcano shapes.

Shield Volcanoes and Cinder Cones

Shield volcanoes and cinder cones started to erupt about 12 million years ago after plate motions and resulting crustal forces changed.

Compressional forces had eased, and the crust started to stretch between the Wasatch Range in Utah and the Sierra Nevada Range in California. This extension created splintered zones in the Earth’s crust where magma rose to the surface creating shield volcanoes and cinder cones. These types of volcanoes are far less explosive than stratovolcanoes and tend to create smaller deposits.  Because the lava from shield volcanoes comes from a deeper source and contains more iron and less silica than stratovolcanoes, they tend to leave darker and thinner magma deposits.

The most recent volcanic activity in Utah occurred about 600 years ago in the Black Rock Desert (Millard County). The only place in the United States were these types of volcanoes are currently active is Hawaii.

Iceland and Hawaii are great modern examples of the shield volcanoes which have periodically erupted in Utah over the last 15 million years.

Iceland and Hawaii are great modern examples of the shield volcanoes which have periodically erupted in Utah over the last 15 million years.

Science Language

Volcano – a vent (opening) at the Earth’s crust through which magma (molten rock) and associated gases erupt.
Magma – molten rock beneath the surface of the Earth.
Lava – magma that has reached the surface.
Cinders – lava fragments about 1 centimeter in diameter.
Pyroclastics (“fire fragments”) – ash, cinders, angular blocks, and rounded bombs (block and bomb fragments can be over 1 meter in diameter).
Explosive eruptions – eject lava and pyroclastics.
Quiet eruptions – fluid lava flows out of a volcano’s vent.

Utah Volcano Map

Use this map to zoom in and explore Utah’s various volcanic deposits. Each element can be clicked for more details.  The top arrow opens a Legend which explains the meaning of the maps various features.