Nestled within the Glen Canyon National Recreation Area (GCNRA), Lake Powell is a testament to both human ingenuity and the enduring power of nature. The lake fills the entirety of the 170 mile length of Glen Canyon. Sometimes referred to as Utah’s “sixth national park,” this vast reservoir offers a unique blend of recreation and stunning geological beauty. Its sheer size and intricate shoreline distinguish it from any of Utah’s other lakes, while its geological story reveals a complex and fascinating past.

The first recorded European encounter with Glen Canyon comes from the Domínguez-Escalante Expedition of 1776. Just a few months after Thomas Jefferson signed the Declaration of Independence, the two Spanish explorers spent several weeks being led by Native American guides across a narrow passage through the canyon’s nearly impenetrable walls. Almost one hundred years later in 1869, John Wesley Powell, the lake’s namesake, explored the area by boating down the Colorado River and wrote the first known geologic investigation of the region.
Almost another century later, in 1956, construction began for Glen Canyon Dam near the Utah-Arizona border. Designed to regulate and store water from the Colorado River Basin for six states—Utah, Colorado, Arizona, New Mexico, Nevada, and California—the dam also became a vital source of hydroelectric power. Its construction followed years of debate among government agencies, conservationists, and water resource planners, underscoring its enduring role in regional water management and the ongoing discussions surrounding its impact. The completion of the dam led to the formation of Lake Powell, one of the largest reservoirs in the United States.

Perhaps Lake Powell’s most unique feature is its expansive cliff-lined shores. At full pool, its shoreline stretches greater than 1,900 miles, a figure that dwarfs the entire west coast of the continental United States. This remarkable length is a product of the flooding of Glen Canyon’s intricate network of slot canyons and translates to a myriad of opportunities for exploration in the 96 major canyons and countless smaller coves and inlets. Adding to its allure are the numerous natural features found within the recreation area, most notably iconic natural bridges and arches like Rainbow Bridge, Coyote Natural Bridge, Halls Creek Bridge, Broken Bow Arch, LaGorce Arch Dand many more in Glen Canyon’s Escalante arm. These natural wonders, sculpted by millennia of erosion, punctuate the landscape and provide a glimpse into the canyon’s ancient geological history.
The geology of Glen Canyon is a story spanning hundreds of millions of years. It represents a continuous sequence of rock layers, ranging from Early Permian (~295 million years old) to Late Cretaceous (~75 million years old). The oldest exposed rock layer, the Permian-age Cutler Group, lies at the base of this geological sequence and is exposed on the flanks of the Monument Upwarp on the northeast end of the lake. Above the Cutler lies the Late Permian-age (~270 million years old) Kaibab Formation and the Early Triassic-age (~250 million years old) Moenkopi Formation, which is visible on both the northernmost and southernmost areas of Glen Canyon National Recreation Area. Overlying the Moenkopi is the Middle to Late Triassic-age (~230 million years old) Chinle Formation, known for its vibrant colors and abundant petrified wood.

Perhaps the most impressive geologic unit in the region is the Early Jurassic-age (~200 to 190 million years old) Glen Canyon Group, a suite of sandstones that dominate the canyon’s landscape and borrows its name. This group consists of the Wingate Sandstone, known for its deep red sheer cliffs; the Kayenta Formation, characterized by its ledges and slopes of interbedded shale and sandstone; and the massive Navajo Sandstone, which forms large cliffs and slickrock canyons. This sequence of sandstones tells a story of ancient deserts with shifting sand dunes in a setting not unlike that of the modern Sahara Desert (see Survey Notes v. 44, no. 3). The entirety of the southern Utah Cretaceous sequence (~145 to 66 million years ago) is also visible from the southern and central parts of the lake, offering a complete picture of the region’s Mesozoic Era history.

The impressive collection of canyons that compose Glen Canyon National Recreation Area were carved by the Colorado River and its tributaries long after the deposition and lithification of rock layers on the Colorado Plateau. The age of uplift and erosion that created the canyons, as well as the Grand Canyon, is a subject of ongoing debate. While the prevailing view suggests that the majority of the modern Glen Canyon’s erosion occurred within the last five million years, evidence of earlier erosional activity exists. Small streams cutting through the tightly folded strata of the Waterpocket Fold and East Kaibab Monocline hint at river systems in the area dating back at least to the Laramide mountain-building event some 70 to 40 million years ago.

Part of what makes the geology of Lake Powell so unique is the juxtaposition of the lake’s completely level surface against the undulating regional geology. As one travels up lake from the dam, geologic rock formations separated by thousands of feet and millions of years take turns occupying the shorelines. This unique experience is caused by the regional folding of the Monument and Circle Cliffs Upwarps that have uplifted the lowest (oldest) layers to the surface in the northmost sections of the lake, exposing the Permian- and Triassic-age units. Conversely, downwarps like the Kaiparowits Basin, bring younger Cretaceous- and Late Jurassic-age layers to lake level. Adding to the geological intrigue are smaller geologic features visible from the lake, called laccoliths, caused by rising magma which bent the overlying rocks into unique dome-like structures seen at Navajo Mountain, Mount Ellsworth, and Mount Holmes.

Lake Powell stands as a significant testament to the interwoven forces of nature and human activity. It offers visitors a unique way to traverse Glen Canyon and explore its diverse topography and geology. The creation of this vast, and sometimes controversial, reservoir has transformed a once-wild, actively erosive landscape into a more tranquil blend of recreation and utility, offering visitors unparalleled access to breathtaking landscapes unique to those available up and downstream on the Colorado River.

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 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.

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.

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.

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.

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)

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)

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

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.