forms the monoliths of Land of Standing Rocks in the Maze District and the pillars of Monument Basin in the Island District.
Overlying the Organ Rock Shale is another rock formation that is widespread in Canyonlands but crops out only in the deepest canyons in Capitol Reef, the White Rim Sandstone. Despite the thinness of the White Rim, it is a distinct scenery producer in Canyonlands. These rocks form a prominent bench above the inner gorges of the Green and Colorado rivers beneath the Island in the Sky mesa. This sandstone also forms the western rim of The Maze, and resistant caprocks of the White Rim protect the softer beds of the Organ Rock Shale in places, such as on the Chocolate Drops and Nuts and Bolts in the Maze District and the spires of Monument Basin in the Island District.
Following deposition of the White Rim, a dolomitic stratum of marine origin was deposited in south-central Utah and northern Arizona, the Kaibab Limestone. This mostly white rock forms the broken cliffs in the Goosenecks of Sulphur Creek and in the Fremont River canyon in Capitol Reef National Park.
Deposition of the red Moenkopi Formation beds occurred about 225 million years ago. These rocks are exposed in all Utah national parks except Bryce Canyon. The Moenkopi is composed of deep red, thinly layered sandy shale and silty sandstone, forming slopes, low cliffs, fluted columns, and ledges. Tracks of small reptiles and amphibians are found in the Moenkopi, but most abundant are ripple marks, formed after shallow, wind-rippled water created a corrugated surface on the sediments just below the water surface.
Around 200 million years ago the wide variety of sediments that compose the Chinle Formation were deposited. Dinosaur tracks, fossil freshwater fish, fossil plants and leaves, and petrified wood from a coniferous genus found in the Chinle show the evolution of life on the planet.
Like the Moenkopi, Chinle rocks are found in all Utah national parks except Bryce Canyon, where younger rocks predominate. The Chinle consists of sandstones, conglomerates, bentonitic mudstones, limestones, and siltstones. It is a varicolored unit, ranging from red and purple to yellow, green and gray. The gray layer is composed primarily of volcanic ash.
The Shinarump Conglomerate, the lowermost layer of the Chinle, forms a prominent white or tan cliff band that discontinuously caps the Moenkopi in Zion and Capitol Reef. This rock consists of lithified coarse sand and stream-polished pebbles. In Canyonlands, however, the Shinarump is absent. Instead, its place in the stratigraphic sequence is taken by the Mossback member of the Chinle. The Mossback is similar in composition to the Shinarump, but its dark gray-green color sets it apart.
Around 200 million years ago, vast deserts of drifting sand dominated the Colorado Plateau landscape. One of these windblown sand deposits is the Wingate Sandstone, and whenever it is exposed in Capitol Reef, Arches, or Canyonlands, it forms cliffs that have been major barriers to travel. The Wingate most often forms sheer, but sometimes broken and fluted, cliffs as high as 400 feet. These rocks are typically orange-red in color, but are often stained with patches and streaks of desert varnish—a dark brown, black, or bluish coating of iron and manganese oxides formed as mineral-laden water evaporates on the rock’s surface.
The vast Wingate desert did not extend as far southwest as Zion National Park. Instead, its corollary in Zion is the thin but prominent Moenave Formation, composed of red siltstones and yellow sandstones of floodplain origin.
The thin beds of the Kayenta Formation that overlie the Wingate and Moenave range in color from nearly white to reddish-brown, and usually form ledges, low cliffs, and slopes. In Zion, the Kayenta is soft, and consequently it erodes into slopes rather than the ledgy cliffs it forms in Arches, Capitol Reef, and Canyonlands.
The resistant Navajo Sandstone was also deposited around 200 million years ago, when once again the region was buried under drifting sands. Perhaps no other rock formation on the Colorado Plateau is as famous as the Navajo. These rocks erode into gigantic cliffs both sheer and rounded, and great domes, for which Capitol Reef was named. The Navajo also composes the great cliffs of Zion Canyon, the Petrified Dunes of Arches, and the domes that cap the Island in the Sky mesa in Canyonlands. The Navajo achieves its greatest thickness, approximately 2200 feet, in Zion.
Cross-bedding, the sweeping diagonal lines most obvious in the hummocky structures of the Navajo, reflects the advance of the ancient dunes across the landscape as northerly winds swept the region.
Overlying the Navajo in Zion is a thin, discontinuous layer of shale and sandstone, the Temple Cap Formation. Most of this reddish-brown layer has been removed from the Markagunt Plateau by erosion.
Bulging Navajo Sandstone walls embrace the narrow wash of lower Courthouse Wash
Less than 200 million years ago, the limestones, shales, sandstones, and gypsum of the Carmel Formation were deposited. The soft rocks of the Carmel cap much of the Markagunt Plateau in Zion, and outcrop on the eastern flanks of the Waterpocket Fold in Capitol Reef.
The Entrada Sandstone is the most widespread rock unit in Arches, and its rocks form most of the scenic highlights of the Park. This formation has been divided into three subunits, each with its own special characteristics. The Dewey Bridge member is the lowermost and softest layer of the Entrada, and erosion attacks it vigorously. Dark red in color, the beds of this silty sandstone are often contorted and irregular. Its relatively soft nature allows it to erode more readily than the overlying Slick Rock member. The result has been the formation of many fascinating hoodoos, such as those found along The Great Wall, and these rocks form the pedestals for many balanced rocks in Arches.
The Slick Rock member of the Entrada Sandstone is the dominant rock in Arches, and its presence is responsible for the unusual scenic beauty of the Park. This rock is orange- or salmon-hued, occasionally nearly white. The Slick Rock member forms rounded-to-vertical cliffs, domes, and fins—the narrow sandstone walls that dominate the scene in Devils Garden and Fiery Furnace in Arches. This is the rock that Arches visitors encounter more than any other, for the arches they have come to see are formed almost exclusively in it.
The uppermost member of the Entrada, the Moab Tongue, could easily be mistaken for the Navajo Sandstone, since it has many of the same characteristics and is similar in color. The Moab Tongue is a white, fairly thin bed of wind-deposited dune sand, and this rock displays the cross-bedding common in wind-blown sand deposits.
Anyone familiar with the Entrada in Arches will hardly recognize that formation in Capitol Reef. Here much of the soft red beds of the Entrada has been eroded away, and only a few low domes crop out in and near the valleys east of the Waterpocket Fold. In Capitol Reef, the Entrada is a soft, thinly bedded formation composed of sandstones and siltstones.
Tower Arch is formed entirely within the Entrada’s Slick Rock Member
The Curtis Formation lies above the Entrada only in Capitol Reef’s Cathedral District. This gray, limey marine sandstone is prominent on the rim of The Hartnet, and it forms a protective caprock on the monoliths of Cathedral Valley and South Desert.
Another formation unique to Capitol Reef is the Summerville, composed of thinly bedded red mudstones and siltstones. Three members of the Morrison Formation are found in Arches, and two of these also occur in Capitol Reef. Sand, mud, silt, and volcanic ash make up the various layers of the Morrison.
The red silty shales of the Tidwell member of the Morrison outcrop in a few locations only in Arches National Park. This is a relatively thin layer, and it is most easily identified where the abundant white concretions, composed of silica, have weathered from the formation and now litter surrounding slopes.
The
