Capitol Reef's geology dominates the eye, wrapping the visitor in its multi-hued folds (Fig. 3). The enormous size, length, and variety of the cliff lines, canyons, and domes discourages the average visitor from probing deeper into the geologic answers so obvious before them. So awestruck by the world around them, few visitors note the subtle clues of Capitol Reef's geological blueprint.
Most of the rocks seen at Capitol Reef, as elsewhere on the Colorado Plateau, are sedimentary. This means the rock actually started out as ocean, river, or lake sediment that was brought here by water or wind. The slopes and cliffs directly across from the visitor center, for example, are composed of a series of colored, variably textured layers of sedimentary rock. Each layer is different because of climatic changes that took place over eons of time. Through the theory of tectonic plate action, one can better appreciate how all this rock came to form Capitol Reef.
The forces that shape the earth's crust are thought to be controlled by the movement of tectonic plates. These plates are like puzzle pieces that flow on top of the earth's molten interior. The continents and the ocean floors are made from these plates, and their very slow but constant movement away from and into each other causes most earthquakes, volcanic eruptions, or as in this case, warping of the rock layers.
The variety of rock layers at Capitol Reef is the result of the movement of the North American Continental plate northward from the equator over the last 250 million years. As the continent moved through northern latitudes, its climate changed accordingly. These climatic changes affected ocean depths, the extent of swamplands, and the abundance and energy of the water itself. Thus, it is the northward drift of North America through different latitudes that is ultimately responsible for producing the landscape that visitors now travel far to see.
There are thousands of feet of sedimentary rock below the surface (Fig. 4), but the oldest rock exposed at Capitol Reef is found in the bottom of the canyons west of the Scenic Drive. In the Fremont River gorge or in the canyons of Sulphur and Pleasant creeks are found the Coconino or White Rim sandstone that resulted from a coastal sand dune environment. At that time, this continent was along the equator, approximately where northern South America is today.
Then, either a general rising of the earth's oceans or a collapse of land to the west of Capitol Reef caused an ocean to cover most of western Utah. The ocean's weight depressed the older sedimentary layers below it, forming an enormous basin that would catch millions of years of sediment still to come. In this ocean were billions of tiny shell creatures that died and dropped to the bottom. The accretion of these calcium carbonate shells helped form the Kaibab limestone formation, which is exposed as small cliffs and shelves visible from the Sulphur Creek Goosenecks overlook and along the canyon walls west of the Fruita campground. The whitish-brown cliffs are formed of the limestone, whereas the shelves are limestone mixed with some sand and silt, probably due to years of ocean level fluctuations. This same Kaibab limestone also forms the top stratum of the Grand Canyon's North Rim.
As the ocean receded very slowly to the west, the top layer of Kaibab limestone eroded away, leaving a gap or unconformity between the strata. In this case, the unconformity is easily seen by the almost straight line and stark contrast between the white Kaibab limestone on the bottom and the deep, red Moenkopi mud and siltstones on top.
Since this area 230 million years ago was still near the equator, a hot, moist climate fed large rivers that flowed westward down from the ancestral Rocky Mountains. As those rivers poured into this large basin, the waters slowed and dumped their loads of fine silt and clay before merging with the ocean.
This delta and tidal basin environment of the early Triassic period is observable now at the base of cliffs along the Scenic Drive, as fine-grained, thin layers of red mud and siltstone that compose the Moenkopi Formation. These river, delta, and tidal basin systems must have persisted for eons, as the rock layer they produced is 1,000 feet thick in places. One of the best places in the park to see these alternating mud and silt layers is at Chimney Rock, which itself consists mostly of the Moenkopi Formation.
Also found in the Moenkopi is "ripple rock," delicately patterned slab-stone created by gentle currents moving over mud and silt; and, occasionally, the observant viewer will discern some unusual patterns of bumps in the otherwise gently undulating rock surface. The bumps are actually the trackways of early reptiles, ancestors to the dinosaurs, that would swim/wade across those streams, leaving their odd footprints impressed on the muddy bottom.
By the mid-Triassic period, about 200 million years ago, North America had drifted northward from the equator and entered monsoon latitudes. This was a climate like that of Malaysia or India, where the rain pours down for six to nine months and bakes under a hot sun the rest of the year. But geologists are unable to trace the transition from the low-energy deltas of the Moenkopi to the fast-moving flood waters and large lakes that produced the overlying Chinle Formation: another unconformity here shows that transitional sedimentary record to be lost. The difference between the two formations is easily seen in the white and black Shinarump Member of the Chinle. It is composed of coarse-grained sand and silt swept down into this basin by a new, very large, fast-flowing river system that resulted from those monsoonal rains.
This river-deposited sandstone is much harder than the underlying Moenkopi mudstones. Because it is harder to erode, it caps and protects the tops of cliffs, preserving the underlying, soft muds and silts. An example of this condition is the Egyptian Temple, visible from the Scenic Drive. This contrast between hard and soft rock can also create isolated, balanced cap-rocks such as the Twin Rocks just off Utah Highway 24 west of the visitor center.
This river channel contact between the Moenkopi and Shinarump was the focus of many 1950s prospectors who scoured the Waterpocket Fold for uranium, as evidenced by the Oyler mine tunnels in Grand Wash.
The Chinle Formation is composed of the colorful, banded slopes reposing at the foot of the red cliffs on the west side of the Waterpocket Fold and within its deeper canyons. The distinctive gray, blue, green, yellow, purple, and ubiquitous red bands were produced largely by the varying amounts of water that once covered the sediments. For instance, iron-rich sediment deposited by wind and water at the earth's surface, where it is exposed to abundant oxygen, becomes oxidized and turns rust-red. Conversely, volcanic ash, mud, and silt that becomes deeply buried or submerged is subjected to an oxygen-poor, reducing environment, in which ferrous minerals cannot oxidize or "rust." The reducing environment then produces sedimentary rock of white, gray, green, blue, or yellow.
The absence of red coloring in the rock serves as a clue to rock hounds and fossil collectors. Submerged, dead plants and animals are more protected from scavengers and the decaying effects of sun, wind, and microscopic organisms. The trees washed down by monsoonal rains and floods sank deep into lakes and were buried under tons of volcanic ash, mud, and silt, preserving them intact. Slowly, over millions of years, the wood cells were replaced by the silicates from overlying volcanic ash, thereby petrifying entire trees. Petrified wood is found throughout the Chinle Formation, both at Capitol Reef National Park, and further south at Petrified Forest National Park.
The next layer in Capitol Reef's geologic column is probably the most dominant cliff- forming rock found throughout southern Utah. The deep red-to-purple Wingate sandstone forms the imposing, sheer cliff face that looms over visitor center and fronts the Scenic Drive. The formation continues southward for another 60 miles to meet the Colorado River.
Wingate sandstone is made up of windblown sand that apparently began accumulating in an enormous field of dunes around 190 million years ago. The continent's northward drift had carried the region into a desert climatic regime that may not have seen rain for centuries, drying the rivers and lakes of the Chinle Formation and killing its rich vegetation. Unanchored, the sand was swept into a massive field of dunes.
In a windstorm, sand grains are whipped in all directions. At ground level, the quartzite grains begin to accumulate, eventually forming dunes. Thereafter, the sand dune itself is pushed before the wind. Looking closely at the Wingate sandstone, one can still see angled and flowing lines in the rock, evidence of those sand grains and entire dunes that were continually reshaped. These lines, called crossbedding, tell geologists that wind (as opposed to water or other depositional agents) helped to form the rock.
This arid climate and resulting sea of sand dominated the landscape throughout southern Utah and northern Arizona from the late Triassic through the middle Jurassic period--about 50 million years. Sometimes, rivers would flow into oasis-like pools over the sand, carrying down sediment down from nearby mountains and plateaus. The best evidence of these rivers is seen in the Kayenta Formation, between the red Wingate cliffs and the white Navajo sandstone domes. The benches that make up the Kayenta were produced by softer river sediments mixing with the coarser, more resistant sand particles. Erosional agents, mostly water, attack these softer layers in the Kayenta until a hole is sometimes punched through beneath the harder layer, forming natural bridges and arches.
The Navajo sandstone, also composed of windblown sand, looms high above the cliffs of the Waterpocket Fold. Interestingly, the Navajo has been eroded into domes, such as the Capitol Dome visible from Utah Highway 24, resembling the sand dunes that originally produced the formation. More fantastic shapes and colors in the formation can be seen best by climbing out among the Navajo tops or into its narrow-walled canyons.
The main visual difference between the Wingate and Navajo sandstones is color. The Navajo is almost pure quartzite sand, with very little of the iron-rich clays that color the Wingate. Another difference is the general manner in which the two layers have eroded. Unprotected by a hard, Kayenta cap, the Navajo has been eroded by water from its top down. Thus, the crowns as well as the exposed sides of the Navajo are being slowly eaten away, sculpting the softly rounded domes that give Capitol Reef its name.
The focus of this discussion so far has been on sedimentary layers exposed on the western face of the Waterpocket Fold. The other layers, found along the eastern and northern boundaries of the park, make up an additional 100 million years of sea level and climatic changes.
Another significant period of erosional processes resulted in another unconformity between the Navajo sandstone and the next visible layer, the Carmel Formation. Made up of different layers of limestone, mudstone, sandstone, and gypsum salts, the Carmel caps and colors the very highest Navajo domes, such as the Golden Throne near Capitol Gorge. All this material was carried in by a shallow sea that continuously advanced and receded. Each time the sea flooded the region, it brought a different kind of sediment; and each time the waters receded, they left behind tidal mud flats. These layers built up over time, resulting in contrasting bands of red, orange, yellow and green. More recent erosion of the Carmel Formation has exposed lovely, banded chevrons that can be seen along the Notom-Bullfrog Road south of Utah Highway 24.
As the shallow Carmel sea receded, oceans of sand invaded once again, this time mixing with the sea's abandoned silts and clays and producing the Entrada sandstone formation. This mixture has made Capitol Reef's Entrada much softer than the block-like Entrada sandstone near Hanksville and Goblin Valley, or the beautiful sculpted Entrada that predominates in Arches National Park. The formation is best seen in the park's North District, particularly in Cathedral Valley where the escarpments almost seem to be melting in the hot summer sun. Here, large mesas of Entrada have been slowly eaten away to form sculpted escarpments and towering monoliths that give Cathedral Valley its name.
The stark, white Curtis Formation that caps the Cathedral Valley buttes and cliffs is evidence of another shallow sea that once inundated the basin (now the Colorado Plateau). This sea advanced only a short distance into what is now Capitol Reef. As the water slowly retreated, the resulting tidal and mud flats accumulated into the thin, even layers of the Summerville Formation. The Summerville is easily seen just west of Hanksville and north of the Cedar Mesa campground along the Notom-Bullfrog Road. Because the Summerville was created by the same processes that formed the familiar, deep red Moenkopi, it looks like that formation.
The next stratum, the Morrison Formation, is common and well-known throughout the Intermountain West: its lush riverine and lacustrine habitat was ideal for supporting (and preserving) dinosaurs. The remains of these Jurassic creatures have been found in the Morrison from eastern Colorado to northern Utah, although only a few bones and trackways have been identified in the vicinity of Capitol Reef. The Morrison also provides more colorful, banded hills of bentonite clay. The clay formed from weathered volcanic ash, first noted in the Chinle, only here there is no hard sandstone cap to protect it from erosion. Thus, the bentonite hills are fully exposed to the sculpting powers of water and wind, creating a badlands landscape in the eastern, northern, and southern portions of Capitol Reef.
During the Cretaceous Period, 65 to 135 million years ago, another invading sea covered most of interior North America and left behind enormous sedimentary deposits. As this sea encroached and subsided, sand bars formed and provided habitat for millions of sea creatures. At Capitol Reef, some of those sand bars now make up the Dakota sandstone exposed in the park's South District, where which fossil crustaceans can be found in the Oyster Shell Reef.
That Cretaceous sea caused all kinds of loose sediment to be deposited throughout the Four Corners basin. Most abundant are the Mancos shales, stretching from the Book Cliffs near Grand Junction and Green River, and from the barren slopes below Mesa Verde, to the badlands near Capitol Reef's eastern boundary. The dull, gray color of the Mancos, again, is attributable to the deep submergence of its sediments underwater. This underwater environment also preserved gryphaea, shark's teeth and other marine fossils within the shales. The various sandstone members that cap the Mancos shale are due to later fluctuations in that inland, Cretaceous sea.
The sedimentary rock layers exposed at Capitol Reef National Park are literally the building blocks of the area's natural bridges, arches, walls, cathedrals and spires. The primary "builder," as it turns out, was the powerful geological force of uplift.
Capitol Reef's sedimentary rocks were deposited in horizontal layers and then subjected to eons of erosional forces. The scenic result should therefore be something akin to the Grand Canyon: layer-cake stratification exposed by cuts, canyons and gorges. Yet, the park's scenery is quite different, because the geologic story hasn't ended there. Thrusting forces from deep within the earth have uplifted, broken, and tilted the strata, producing a unique and gigantic tear in the earth's fabric: the Waterpocket Fold.
The Waterpocket Fold, enclosed and protected by the boundaries of Capitol Reef National Park, stretches over 75 miles between Thousand Lake Mountain and Lake Powell. In geological parlance, a fold is any kind of warping of the earth's surface; but the Waterpocket Fold warps in only one direction, making it a monocline. Thus, its layers tilt dramatically on the east side of the fold and, where not eroded away, gradually slope to horizontal on the west side.
Just what event produced this monocline about 65 to 80 million years ago is still debated. One explanation is that two tectonic plates compressed somewhere west of this area. The resulting pressure buildup then caused the sedimentary rock here to bend like plastic over many millions of years, creating a monocline fold. We do know that the same forces that produced the Waterpocket Fold also buckled earth's crust in the Four Corners region and thrust the Rocky Mountain range upward.
Then, the argument goes, between 2 and 10 million years ago, the entire huge basin that cradled all the sedimentary formations described earlier was uplifted (perhaps by tectonic plate action), forming the mile-high Colorado Plateau.
The stunning result was a high-elevation plateau with mountain ranges and a huge fold in its crust. The finishing touches were added by two other geological processes, erosion and volcanism.
The newly exposed, tilted rock layers were now subject to the forces of erosion, with water playing a particularly active role. Exposed soft layers, such as the Mancos shales and other marine deposits, were relatively quickly scoured away by a young Colorado River drainage system (including the Fremont River and its tributaries), which developed as a result of the uplifted plateau and mountains. All that remains today is the more resistant sandstone "backbone" of the Waterpocket Fold, which protects those Chinle and Moenkopi deposits that underlie it. Yet, even the harder sandstone is constantly under attack by agents of erosion, particularly water. In a moister climate, all the sedimentary layers might be now be gone, leaving little reason for a national park. Capitol Reef's colorful "sleeping rainbow" of stacked sedimentary strata owes its preservation largely to the fact that the park receives only six to seven inches of rain each year.
But even under desert conditions, hungry water and wind continue to nibble at the rock, grain by grain, year by year. Few visitors to Capitol Reef realize that the still pool, crystalline snow, and sheet of ice can wear away at rock, changing its shape over eons. These forms of water carry small amounts of natural organic acids, which dissolve the calcite mineral gluing individual sand grains together into stone. With the calcite dissolved, the particles are susceptible to movement by rain and wind. Thus, tiny, water-retaining cracks, dimples, and pockets grow slowly into large water holes, grain by grain.
Besides using chemical agents to alter rock, water also works mechanically through freeze and thaw cycles. Even a tiny amount of water deep in a crack can freeze and expand, exerting a surprising amount of force against the rock. During warmer daytime temperatures, the ice melts a little and settles deeper into the crack, where the next night's freezing wedges it once more against its natural container. Slowly, over many winters, large fissures grow and eventually cause collapse. Rockfalls typically occur in late winter and early spring, when day and night temperature variations are greatest.
The large red and white sandstone blocks littering the slopes beneath the Wingate cliffs bear mute testimony to the cumulative effectiveness of these tiny actions over thousands of years. Sometimes, all these erosional processes interact to create impressive rock sculptures, such as Cassidy Arch above Grand Wash, nibble by nibble. And other times, they manage to take a quick, large bite.
A ravenous flash flood can consume everything in its path: earth, vegetation, even vehicles and people, as many visitors to Grand Wash and Capitol Gorge during the thunderstorm season could testify. During a summer cloudburst, the rain pounds hard and fast against expanses of slickrock and loose desert soils. Channeled into joints and cracks in the rock and into normally dry canyons and washes, the resulting torrents snap and chew, hurling boulders and vegetation, scouring with sand. The water typically cuts new channels, washes out loose or soft deposits, undercuts mighty sandstone cliffs, deepens fissures in the stone, and leaves debris and scars in its wake. Even the toughest rock--including volcanic rock--succumbs to this kind of destructive energy.
Some 20 million years ago, molten lava oozed from a vent in the earth's crust and flowed over the high plateaus to the west, creating a tough, andecite cap rock. Later, during the Pleistocene era that ushered in the world's most recent ice age, glaciers formed on those high plateaus, including what are now Boulder and Thousand Lake mountains. The tremendous force of glacial ice began breaking up the cap rock, and when the ice began to recede, rushing torrents of meltwater rolled chunks of andecite down into the lowlands. The scenario played out perhaps three or four times over the past two million years.
The intriguing black boulders, strewn about the benches and canyons of the park like abandoned bowling balls, are the products of those events. Their round shapes resulted from being rolled miles down the mountainsides, and their large size tells geologists that the currents that moved them were powerful. Many geologists believe that most of the canyon cutting in this area resulted from these same glacial outwashes.
At the same time that the lava flows were capping the western plateaus, magma also seeped into cracks in the buried sedimentary layers. There, it cooled and hardened, molded by the surrounding rock. When the area was uplifted, the softer, sedimentary material eroded away and exposed the hard, volcanic casts. Where the cracks were vertical, the standing walls of volcanic rock are called dikes. Where the lava flowed horizontally, parallel to the surface, the formations are called sills. Dikes and sills can easily be seen in Cathedral Valley, in the park's North District. Resistant to erosion and protected by the dry environment, these formations will persist for a long, long time.
Today, erosional processes continue their relentless work of leveling the scenery at Capitol Reef National Park. The broken-down rocks return to sediment, easily seen and felt during wind storms. Because of the lack of vegetation, the wind lifts the sediment and generates sand dunes, much as it did millions of years ago. Today, the new layers of sediment can be seen covering the older layers, all evidence of the constant geological processes at work here at Capitol Reef and throughout the Colorado Plateau.
Collier, Michael. The Geology of Capitol Reef National Park. Torrey, Utah: Capitol Reef Natural History Association, 1987.
Davidson, E. S. Geology of the Circle Cliffs Area. U.S. Geological Survey Bulletin 1229. Washington, D.C.: U.S. Geological Survey, 1967.
Dubiel, Russell F. "Capitol Reef National Park Geology Class." MS 919, Box 25046, U.S. Geological Survey, National Archives - Rocky Mountain Region, Denver, 1992.
Dutton, Clarence E. Geology of the High Plateaus of Utah. U.S. Geographical and Geological Survey of the Rocky Mountain Region. Washington, D.C.: U.S. Geographical and Geological Survey, 1880.
Gilbert, Grove K. Report on the Geology of the Henry Mountains. U.S. Geographical and Geological Survey of the Rocky Mountain Region. Washington, D.C.: U.S. Geographical and Geological Survey, 1877.
Gregory, H. C., and J. C. Anderson. Geographic and Geologic Sketch of the Capitol Reef Region. Geological Survey Association Bulletin 50. Washington, D.C.: Geological Survey Association, 1939.
Hunt, C. B. Geology and Geography of the Henry Mountains Region. U.S. Geological Survey Professional Paper 228. Washington, D.C.: U.S. Geological Survey, 1953.
Smith, J., L. C. Huff, N. E. Hinrichs, and R. G. Luedke. Geology of the Capitol Reef Area, Wayne and Garfield Counties, Utah. U.S. Geological Survey Professional Paper 363. Washington, D.C.: U.S. Geological Survey, 1963.
1 The first two chapters of this section are introductory essays on the geology and archeology of Capitol Reef National Park. While these are by no means the only resources within the park, they are the primary reasons why Capitol Reef National Monument was established in 1937.
Because of the general overview nature of these two chapters, they do not provide the detail common elsewhere in this administrative history. Chapter 1 provides only a basic review of the area's fascinating geological history. The references at the end of the chapter should be consulted for more in-depth information. Chapter 2 broadly examines the American Indian presence within the park and mentions some of the early, significant archeological survey work and current management concerns. Since this chapter is sparsely footnoted and contains little specific information on protohistoric and historic American Indian occupation, the reader is referred to the references at the end of the chapter, provided by Rosemary Sucec of the Intermountain Regional Office's Applied Anthropology Program and Capitol Reef National Park Archeologist Lee Kreutzer.
Last Updated: 10-Dec-2002