Rocks and Landforms

When viewed at a distance of 1 foot, the shaded relief map (fig. 1) shows the general shape of the land surface in and near Canyonlands National Park to the same horizontal scale as it would appear to a person in a spacecraft flying at a height of 250,000 feet, or about 48 miles. This map was prepared by artist John R. Stacy from parts of the reverse sides of four plastic relief maps[2]—Salina, Moab, Cortez, and Escalante quadrangles, at a scale of 1:250,000—using a simple time- and money-saving method he devised (Stacy, 1962).

An image of Canyonlands National Park and vicinity from a satellite at a height of about 570 miles is shown infigure 7. Note white clouds and black cloud shadows on right.

CANYONLANDS NATIONAL PARK AND VICINITY, from NASA’s unmanned Earth Resources Technology Satellite (ERTS-1), at height of about 570 miles. The space image map was prepared from simultaneous scanning in three color bands—blue green, red, and near infrared—that were combined to produce a false-color image in which vigorous green vegetation (forests and irrigated areas) appears bright red, water dark blue, and soils and bare rocks various shades of blue, blue green, or yellow green. Bright-blue area on west bank of Colorado River about 10 miles southwest of Moab is the group of large evaporation ponds of Texas Gulf, Inc., shown in figures31and71. Images were taken at 10:31:10 a.m., Aug. 23, 1972, during the 432d orbit, telemetered to Alaska, videotaped, then photographed. Sun elevation was 53 degrees above horizon from azimuth of 130 degrees. Image covers an area about 100 miles square. (See scale.) Location of Monticello is approximate; that of other towns is believed to be correct. Park boundaries are not shown because of difficulty in locating them accurately, but features such as Colorado and Green Rivers can easily be compared with those infigure 1. (Fig. 7).

The vivid and varied colors of the bare rocks and the fantastic canyons, buttes, spires, columns, alcoves, caves, arches, and other erosional forms of the canyon country result from a fortuitous combination of geologic and climatic circumstances and events unequaled in most other parts of the world.

First among these events was the piling up, layer upon layer, of thousands of feet of sedimentary rocks under a wide variety of environments. Sedimentary rocks of the region are composed of particles ranging in size from clay and silt through sand and gravel carried to their resting places by moving water, silt and sand particles transported by wind, and some materials precipitated from water solutions, such as limestone (calcium carbonate), dolomite (calcium and magnesium carbonate), gypsum (calcium sulfate with some water), anhydrite (calcium sulfate alone), common salt (sodium chloride), potash minerals such as potassium chloride, and a few other less common types. Some of the materials were laid down in shallow seas that once covered the area (fig. 8) or in lagoons and estuaries near the sea. Some beds were deposited by streams in inland basins or plains, a few were deposited in lakes, and some, like the Navajo Sandstone, were carried in by the wind. The character and thickness of the sedimentary rocks, and the names and ages assigned to them by geologists, are shown in the rock column infigure 9and in the cross sections in figures10and15, and the history of their deposition is discussed in the chapter “Summary of Geologic History.” The rock column was compiled mainly from generalized stratigraphic sections given by Baker (1933, 1946), McKnight (1940), Hinrichs and others (1967, 1971b), and F. A. McKeown and P. P. Orkild (U.S. Geol. Survey, unpub. data, Mar. 16, 1973).

Not exposed in the area but present far beneath the sedimentary cover, and exposed in a few surrounding places, are examples of the other two principal types of rocks: (1) igneous rocks, solidified from molten rock forced into or above younger rocks along cracks, joints, and faults and (2) much oldermetamorphic rocks, formed from other pre-existing rock types by great heat and pressure at extreme depths. The particles comprising the sedimentary rocks were derived by weathering and erosion of rocks of all three types in the headwater regions of the ancestral Colorado River basin. Igneous rocks of Tertiary Age (fig. 80) form the nearby La Sal, Abajo, and Henry Mountains (fig. 7).

SHALLOW INLAND SEA which covered Canyonlands and vicinity during Middle Pennsylvanian time. (Fig. 8)

Second among the main events leading to the formation of the canyon country was the raising and buckling of the Plateau by earth forces so that it could be vigorously attacked by various forces of erosion and so that the rock materials thus pried loose or dissolved could eventually be carted away to the Gulf of California by the ancestral Colorado River. Some idea of the enormous volume of rock thus removed is apparent when you look down some 2,000 feet to the river from any of the high overlooks, such as Dead Horse Point (fig. 15) or Green River Overlook (fig. 23), or when you lay a straightedge across the three high mesas infigure 10and note the large volume of missing rocks below. Not so apparent, however, is the fact that some 10,000 feet of younger Mesozoic and Tertiary rocks that once overlay this high plateau also has been swept away. In all, the river has carried thousands of cubic miles of sediment to the sea and is still actively at work on this gigantic earthmoving project. In an earlier report (Lohman, 1965, p. 42) I estimated that the rate of removal may have been as great as about 3 cubic miles each century. For a few years the bulk of it was dumped into Lake Mead, but now Lake Powell is getting much of it. When these and other reservoirs ultimately become filled with sediment, for reservoirs and lakes are but temporary things, the Gulf of California will again become the burial ground.

ROCK COLUMN OF CANYONLANDS NATIONAL PARK. One foot equals 0.305 meter. (Fig. 9)

AGE (millions of yrs ago)GEOLOGIC AGENAME OF ROCK FORMATIONKIND OF ROCK AND HOW IT IS SCULPTURED BY EROSIONTHICKNESS (feet)NAMED FOR OCCURRENCE AT OR NEAR150JurassicEntrada SandstoneCrossbedded white fine-grained sandstone at top (Moab Member); salmon colored to pink, fine-grained, generally crossbedded sandstone in middle (Slick Rock Member); red earthy sandstone and siltstone at base (Dewey Bridge Member, grades into Carmel Formation west of Green River). Forms steep-sided buttes north, east, and west of park.400-500Entrada Point, San Rafael Swell, Utah175Jurassic & Triassic(?)Glen Can GroupNavajo SandstoneCrossbedded buff to gray sandstone, some red sandstone, and thin beds of limestone. Residual rounded patches on highest mesas.325-550Navajo Country, Ariz., New Mexico, UtahLate Triassic(?)Kayenta FormationIrregularly bedded stream-laid gray, buff, lavender and red fine-to-coarse-grained sandstone and siltstone. Caps most high mesas and forms tops of highest cliffs. Contains fresh-water fossils.160-300Glen Canyon, S. Utah, Kayenta, Arizona200Late TriassicWingate SandstoneBuff and light red generally crossbedded medium-grained sandstone. Forms highest cliffs, many of which are coated with black desert varnish.210-340Ft. Wingate, New MexicoChinle Fm.Unnamed upper memberReddish siltstone, mudstone, and sandstone locally bleached to bluish or greenish gray, and few thin beds of limestone. Forms steep slopes at base of highest cliffs. Contains some fossil wood and reptile bones.205-740Chinle Valley, Ariz.Moss Back MbrGray, brown, and gray-green sandstone and conglomerate.0-80Moss Back Ridge, Utah215Middle(?) and Early TriassicMoenkopi Fm.Unnamed upper memberBrick red, reddish-brown, and brown mudstone and sandstone, and some conglomerate and gypsum. Forms slopes broken by thin ledges.250-940Moenkopi Wash, Ariz.Triassic(?)Hoskinnini TonguePale-brown fine-to-coarse-grained sandstone; forms ledges.0-120Hoskinnini Mesa, Ariz.250PermianCutler Fm.Undivided Cutler Formation in northeastern part of area is composed of buff, red, and purple arkosic sandstone and conglomerate. South of Indian Creek is the thick Cedar Mesa Sandstone Member, composed of massive mainly crossbedded white to pale red sandstone with thin beds of cherty limestone. Forms needles, arches and other erosional features. Thickening southwestward is the White Rim Sandstone Member of white crossbedded sandstone.800-1,000Cutler Creek, Colo.White Rim Sandstone MemberWhite Rim, Wayne Co., UtahOrgan Rock TongueOrgan Rock, UtahCedar Mesa Sandstone MemberCedar Mesa, S. E. UtahRico FormationBuff, red, and purple arkosic sandstone and conglomerate containing several thin beds of marine fossiliferous limestone. Forms moderately steep slopes.250-585Rico, Colo.300PennsylvanianHermosa FormationHermosa Creek, Animas River Valley, Colo.Unnamed upper memberBlue, greenish, and gray fossiliferous limestone interbedded with white, gray, and greenish sandstone and gray to green shale. Lower part known only from deep wells. Forms steep canyon walls.900-1,800Paradox MemberSalt, gypsum, and anhydrite with interbedded black and brown shale; some limestone.?Paradox Valley, Colo.

Last but far from least among the factors responsible for the grandeur of the canyon country is the desert climate, which allows us to see virtually every foot of the vividly colored naked rocks and has made possible the creation and preservation of such a wide variety of fantastic sculptures. A wetter climate would have produced a far different and smoother landscape in which most of the rocks and land forms would have been hidden by vegetation. In the canyon lands the vegetation is mainly on the high mesas and on the narrow flood plains bordering the rivers, but scanty vegetation does grow on the gentle slopes or flats.

The desert climate has combined with the nearly flat lying layers of sediments of different character, hardness, and thickness to produce steep slopes having many cliffs and ledges and generally sharp to angular edges rather than the subdued rounded forms of more humid regions. This has led geologists to refer to such terrain as having “layer-cake geology,” and this is brought out by the profile in the rock column (fig. 9), by the cross section (fig. 10), byfigure 15, and by many of the other photographs. But the baker of this cake was rather careless—not only do the layers range widely in thickness and character, but some are wedge shaped, thick on one side of the cake but thin or absent on the other. Then too, when he ran out of icing in the midst of a layer, he was apt to finish with a different kind or color, for no inspector was on the job to insure orderly construction.

If all the rock strata in the park were present at one locality, their sequence and thickness would be those shown on the right-hand side of the graphic section infigure 9. However, because of the lateral changes in thickness and character and the wedging out of certain beds, such as the White Rim Sandstone Member of the Cutler Formation, no two sections of the strata are exactly alike. This will be brought out in photographs of different exposures of rocks in various parts of the park.

An often-asked question is, why are most of the rocks so red? This can be answered by one word—iron, the same pigment used in rouge and in paint for barns and boxcars. Various oxides of iron, some including water, produce not only brick red but also pink, salmon, brown, buff, yellow, and even green or bluish green. This does not imply that the rocks could be considered assources of iron ore, for the merest trace of iron, generally only 1 to 3 percent, is enough to produce even the darkest shades of red. The only rocks in the park that contain virtually no iron are white sandstones of the White Rim Sandstone Member of the Cutler Formation (figs.21-24) and the Navajo Sandstone.

Fig. 10, first section

SECTION ACROSS CANYONLANDS NATIONAL PARK from North Point at west (left), via Grand View Point in middle, to Needles Overlook at east (right), showing the three principal topographic levels and character of the rock strata. Line of section bends at Grand View Point, which is northernmost part. (Fig. 10)

As pointed out by Stokes (1970, p. 3), microscopic examination of the colored grains of quartz or other minerals shows the pigment to be merely a thin coating on and between white or colorless particles. Sand or silt weathered from such rocks soon loses its color by the scouring action of wind or water, so most of the sand dunes and sand bars are white or nearly so.

The map (fig. 1) and cross section (fig. 10) of the park show that in general the major features of the landscape lie at three different and distinctive levels. A recently erected plaque on Grand View Point appropriately refers to these levels as the “Three Worlds.” The high plateaus, or mesas, in and adjoining the park dominate the skyline—in fact, the central one, between the Green and Colorado Rivers, is appropriately named Island in the Sky. If you stand on either the east or the west shore of this towering cliff-bordered island, you can look across a sea of fantastic erosional forms to a similar cliff-bordered shore at about the same level. Closer inspection of the sea of rocks on either side shows relatively flat benches or platforms about halfway to the bottom; below these are the generally steep sided or cliff-bordered canyons of the two rivers and their larger tributaries. From some vantage points along the shore, such as Dead Horse Point (fig. 15) or Green River Overlook (fig. 23), you can see the deepest level of all—the channels and flood plains of the Green and Colorado Rivers.

What caused the “Three Worlds” and the formidable cliffs supporting the high mesas or forming towering monoliths like Angel Arch or Druid Arch (figs.43,54)? Differences in the composition, hardness, arrangement, and thickness of the rock layers determine their ability to withstand the forces of fracturing anderosion and hence their tendency to form cliffs, ledges, or slopes. Most of the cliff- or ledge-forming rocks are sandstones consisting of sand grains deposited by wind or water and later cemented together by silica (SiO₂), calcium carbonate (CaCO₃), or one of the iron oxides (such as Fe₂O₃), but some hard, resistant ledges are made of limestone (calcium carbonate). The rock column (fig. 9) shows in general how these rock formations are sculptured by erosion and how they protect underlying layers from more rapid erosion. The nearly vertical cliffs supporting the highest mesas consist of the well-cemented Wingate Sandstone protected above by the even harder sandstone of the Kayenta Formation. To borrow from an earlier report of mine (Lohman, 1965, p. 17),

Vertical cliffs and shafts of the Wingate Sandstone endure only where the top of the formation is capped by beds of the next younger rock unit—the Kayenta Formation. The Kayenta is much more resistant than the Wingate, so even a few feet of the Kayenta * * * protect the rock beneath.

In some places remnants of the overlying Navajo Sandstone make up the topmost unit of the cliff.

Petroglyph

The question of how to see the park has no simple answer, for the park is too vast and complex to comprehend by a quick visit to any one of its many and varied parts or by any one means of transportation. Some, as did Major Powell, view it only from the rivers—by boat plus a few back-breaking climbs up the bordering canyon walls. Others see only the small parts reachable by passenger cars. The more venturesome see vastly more by jeep, foot, or horseback. And a few prefer to view it as the birds do—from the air. Many, those who put aside their magazines long enough, get bird’s-eye views without half trying, for Canyonlands is beneath the principal air routes connecting Los Angeles with Grand Junction and Denver. Actually, a full appreciation of all the wonders and beauties of the park is possible only by combining all these approaches and methods of locomotion, but only a few fortunate souls such as Bates Wilson have thus been able to inspect virtually every square foot of it.

The task clearly before me, then, is how best to present such a complex wonderland to you, the reader. The method I selected, after considerable thought and a few false starts, is to begin at the top—the high mesas—and work my way downward much as the rivers have done in carving out this fantastic area, to some of the broad benchlands beneath the mesas and eventually to the river channels and deep canyons. Although the approach I selected may not be the best, and admittedly is but one of several that comes to mind, I hope it gets the job done.

Even though the “peninsular” mesas east and west of Island in the Sky, known respectively as Hatch Point and the Orange Cliffs, lie outside the present boundaries, they provide breathtaking views of important features within the park, so brief descriptions of them are included below. But first, let us take a closer look at Island in the Sky.

As the map (fig. 1) shows, Island in the Sky is really a fork of a wedge-shaped peninsula extending southward between the two rivers. An outlier to the south named Junction Butte has already been severed from the main peninsula by erosion and now is a true island. (Seefrontispieceandfig. 22.) A large chunk of Island in the Sky south of The Neck was about to be severed by erosion from the main peninsula to become a true island, when recent widening and grading of the road gave it a temporary reprieve. When my family and I first squeaked over this narrow neck in 1960 by jeep, furtive glances to right or left showed the two canyons perilously close, and complete severance seemed imminent. The road builders have staved off disaster for a few thousand years, but ultimately the large section to the south will become another island, and a bridge will be required to connect it to the mainland. Its appearance from the air before the road widening is shown infigure 11.

AERIAL VIEW OF THE NECK AND SHAFER TRAIL, looking southwest, taken before rebuilding of park road on mesa top. Cliff-walled canyon to right of The Neck, in middle, drains westward to the Green River; south fork of Shafer Canyon to left drains eastward to Colorado River. This is the narrowest part of Island in the Sky. Photograph by National Park Service. (Fig. 11)

The entrance road to Island in the Sky intersects U.S. Highway 163 at a point 10 miles northwest of Moab, or 21 miles southeast of Crescent Junction on Interstate Highway 70. From U.S. 163 a paved road climbs colorful Sevenmile Canyon past sandstone cliffs of the Wingate, Kayenta, and Navajo Formations to reach the high mesa. There, just “offshore” to the north, are anchored the “battleships” that guard the island—Merrimac and Monitor Buttes (fig. 12). These landmarks are composed of the Entrada Sandstone—the same rock that forms Church Rock at the entrance to the Needles district (fig. 37) and that shapes the spectacular arches in ArchesNational Park. All three members of the Entrada (Wright and others, 1962), as noted in thefigure 12caption, are present here as well as at Church Rock. Eleven miles from the junction with U.S. Highway 163 a graded road to the right, called Horsethief Trail, goes 16 miles down to the Green River, where it connects with roads following the river both upstream and downstream. The road upstream leads to two uranium mines in the lower part of Mineral Canyon which were reactivated in 1972 and 1973. The switchbacks are quite spectacular and are reminiscent of the Shafer Trail. Three miles south of the Horsethief Trail turnoff is a fork in the road—to the left the pavement continues to Dead Horse Point, and straight ahead a graded road leads southward to the Island in the Sky district of Canyonlands National Park.

MERRIMAC (LEFT) AND MONITOR BUTTES guard north entrance to Island in the Sky. White rock near middle is Navajo Sandstone. Buttes comprise all three members of Entrada Sandstone: remnant white top of Moab Member, vertical cliffs of Slick Rock Member, and sloping base of Dewey Bridge Member. (Fig. 12)

Most of Island in the Sky has a scattered growth of piñon and juniper trees, but several large flat areas, such as Grays Pasture, contain sufficient sandy soil to support a mantle of grass and weeds, which is used for grazing; however, grazing in this part of the park will be discontinued in 1975.

Let us follow the paved road from U.S. Highway 163 all the way to Dead Horse Point, which was set aside as a state park in 1957. The park has a visitor center, museum, modern campgrounds and picnic facilities, and piped water, which is hauled all the way from Moab. An entrance fee of $1 permits us to drive across the narrow neck to a parking area near the point proper, which is protected by stone walls and is provided with a ramada, benches, paths, and sanitary facilities. From Dead Horse Point we get breathtaking views in several directions, including a loop of the Colorado River called the Goose Neck, 2,000 feet nearly straight down.

CANE CREEK ANTICLINE, looking northeast toward the La Sal Mountains from Dead Horse Point. Colorado River cuts across crest at middle right, above which is Anticline Overlook. (Seefig. 31.) Jeep trail and part of Shafer dome lie below. (Fig. 13)

How did such a magnificent viewpoint get such a macabre name? Dead Horse Point was named for a sad but colorful legend concerning a band of wild horses that once roamed the high mesas. The point is really an embryo island separated from the mainland by a narrow neck barely wide enough for the present road. In the early cowboy days the island was used as a natural corral in which wild mustangs were penned up behind a short fence across the neck so that the better ones could besorted out and driven to mines in the San Juan Mountains of Colorado. A band of horses corralled too long without water allegedly died of thirst within sight of the river 2,000 feet below, hence the name of the point, or at least so one version of the story goes. Some versions allude to the wranglers as cowboys; others, as horsethieves.

To the northeast we can see the Cane Creek anticline—an upward fold of the rocks—behind which loom the La Sal Mountains (fig. 13). A cutaway view of a typical anticline is shown infigure 14. A better view of the Cane Creek anticline can be seen from Anticline Overlook, as shown infigure 31. From our vantage point at Dead Horse Point, we can see much of Hatch Point, including Anticline Overlook, by looking east and southeast. Spectacular views of the northern part of Canyonlands National Park lie to the south, southwest, and east. Looking southwest (fig. 15), we see most of the rock formations exposed in Canyonlands—more than can be seen from any other vantage point in or near the park. The names of the visible rock units shown infigure 15can be compared with the complete list in the rock column (fig. 9). Parts of Shafer dome, a “closed” rounded anticline, are visible in the lower left offigure 15and in the lower right offigure 13. Its general domelike shape is outlined by the bluish-white Shafer limestone, a marker bed which also caps the bench on the peninsula within the Goose Neck of the river. This limestone, which here forms the top of the Rico Formation, is not shown in the rock column (fig. 9) because its exposure is limited to the Shafer dome and the Cane Creek anticline and its name is used only locally by prospectors for oil and gas.

CUTAWAY VIEW OF ANTICLINE, or upfold of the rocks. From Hansen (1969, p. 31). (Fig. 14)

LOOKING SOUTHWEST FROM DEAD HORSE POINT toward Island in the Sky on right skyline, Orange Cliffs on left skyline, Colorado River and White Rim Trail below, and Shafer dome at lower left. Sketch from photograph shows names of rocks. (Compare withfig. 9.) (Fig. 15)

Fig. 15, cont.

Note that the White Rim Sandstone Member of the Cutler Formation, referred to hereinafter simply as the White Rim Sandstone, becomes thinner toward the right (northeast) infigure 15but is absent entirely infigure 13, just a short distance to the northeast. The gradual disappearance of recognizable beds of this type toward the northeast, including the disappearance of some limestone beds containing marine fossils, are examples of what geologists call facies changes. Here the changes result from the fact that while strata were being deposited in or near ancient seas that lay to the southwest, beds of different character were being laid down on land by streams emanating from the northeast. This will be gone into in more detail in discussions that accompany illustrations to follow, particularlyfigure 27,fig. 31, andfig. 35.

The north entrance to the Island in the Sky district of Canyonlands National Park used to be 6 miles south of the junction with the paved road to Dead Horse Point, but since the land additions of November 1971, it is only 4½ miles south of this junction. A temporary trailer-housed entrance station marks the old boundary.

During the early 1950’s a remarkable but hair-raising road known as Shafer Trail was cut down the face of the cliffs below The Neck to reach the C Group of uranium claims near the head of Lathrop Canyon. It branches southward from the park road a mile south of the new entrance, then descends in a series of switchbacks. The aerial view (fig. 11) shows the upper trail and The Neck before the park road was graded and widened, and a view from near The Neck (fig. 16) shows the precipitous cliffs the trail descends. It follows the general route of an old foot trail.

SHAFER TRAIL, from just south of The Neck (fig. 1,fig. 11). Navajo Sandstone is above road at left, Kayenta Formation forms upper half of cliff below road, and Wingate Sandstone forms lower, vertical half of cliff; lower part of road is in Chinle Formation. (Fig. 16)

Shafer Trail connects with the White Rim Trail, which, as the name suggests, is built mainly on the White Rim, after which the White Rim Sandstone was named. The White Rim Trail can be followed northeastward to join the pavement at Potash, or it can be followed southward along the Colorado River canyons to Junction Butte, thence northward along Stillwater and Labyrinth Canyons of the Green River to and beyond the northern boundary of the park. At Horsethief Bottom, you can leave the canyon by Horsethief Trail and rejoin the paved road leading northward to U.S. 163. At Lathrop Canyon, 8 or 10 miles south of where Shafer Trail meets the White Rim Trail, a branch of the White Rim Trail leads downward to the Colorado River, where picnic tables and sanitary facilities are provided. This is used as a lunch stop by some boating groups.

Although some two-wheel-drive cars or trucks have traversed the White Rim and Shafer Trails, they may encounter trouble with deep sand, washouts, or fallen rocks, so four-wheel-drive vehicles are recommended. In the summer these trails should not be attempted without plenty of water, and two vehicles traveling together provide an added margin of safety. All vehicles should carry emergency equipment including a shovel, tow chain or rope, jack, tire tools, and other necessary items. Geologists and uranium prospectors working along the White Rim Trail have obtained good drinking water from small springs that flow from the base of the White Rim Sandstone in many places (Neal Hinrichs, U.S. Geol. Survey, oral commun., Feb. 1973). After rains, runoff gathers in large potholes in the White Rim Sandstone in some places and affords emergency drinking water. Several such potholes filled with water are shown infigure 17. Some potholes occur also in the Cedar Mesa Sandstone in the Needles district.

About a mile southwest of The Neck, the road crosses Grays Pasture—the widest and flattest part of Island in the Sky. The drive over this flat grassland yields not the slightest hint of the awesome cliff-walled chasms on either side of the island. Some 5 miles southwest of The Neck, both the island and the road branch like a Y. At a point 0.4 mile north of the Y, Mesa Trail leads one-quarter mile east to Canyon Viewpoint Arch, which frames the Colorado River canyon and the La Sal Mountains (fig. 18). This arch, at the very top edge of the cliff, is composed of the lower part of the Navajo Sandstone. The only other arch of Navajo Sandstone in or near the park that I know of is the small one shown infigure 33, but of course there may be others.

NATURAL TANKS, filled with runoff from rain, serve as emergency sources of drinking water. Largest tank in foreground contains 4 feet of water and small fresh-water shrimp. So-called tanks, or potholes, are formed partly by water dissolving the calcium carbonate cement and partly by wind or water removing the resulting loose sand grains. View is north toward Junction Butte from point about a mile south of the White Rim Trail. Red rocks in hill on right are in lower part of Moenkopi Formation. Photograph by E. N. Hinrichs. (Fig. 17)

CANYON VIEWPOINT ARCH, framing Colorado River canyon at east end of Mesa Trail 0.4 mile north of Y in Island in the Sky road. Arch is in lower part of Navajo Sandstone. (Fig. 18)

INDEX MAP showing localities where most of the photographs were taken. Arrows point to distant views. Numbers refer to figure numbers. (Fig. 19)High-resolution Map

THE WHITE RIM, looking northeast toward La Sal Mountains from overlook 3 miles north of Grand View Point. White Rim Sandstone here is thicker than near Dead Horse Point (fig. 15) but thinner than in Monument Basin and Stillwater Canyon (fig. 21,fig. 23). (Fig. 20)

Let us now take the branch south of the Y and follow the narrow crest of Grand View Point for about 6 miles to the main overlook. About 0.9 mile south of the Y, a short walk to the west over the lower part of the Navajo Sandstone affords a magnificent view of Stillwater Canyon of the Green River, including Turks Head (fig. 23,fig. 24). Half way to the point is a parking area and overlook, from which we get a spectacular view of canyons cutting the White Rim and of the La Sal Mountains beyond (fig. 20). Note that the White Rim Sandstone, which forms the broad bench appropriately named the White Rim, is here much thicker than where seen near Dead Horse Point (fig. 15).

MONUMENT BASIN FROM GRAND VIEW POINT, Needles Overlook on left skyline, Abajo Mountains on right skyline. Red spires and cliffs in basin are Organ Rock Tongue of Cutler Formation. (Fig. 21)

Three more miles southward takes us to Grand View Point and its nearby picnic area. Though named after the former Grand River some 2,000 feet below, Grand View Point has a double meaning, for we see from here a truly grand view (fig. 21)! At our feet is spectacular Monument Basin, cut below the White Rim into the brick-red Organ Rock Tongue of the Cutler Formation. The White Rim Sandstone here is slightly thicker than to the northeast (fig. 20) but thinner than to the west (fig. 23), because it forms a wedge-shaped body that thickens westward. In the distance southeastward are the Abajo Mountains, just west of Monticello, Utah. The prominent projection on Hatch Point on the left skyline is Needles Overlook, from which the photograph infigure 27was taken. A closeup view of Monument Basin, showing Junction Butte and Grand View Point in the background, is shown infigure 22. The slender spire in the foreground has a measured height of 305 feet (Findley, 1971, p. 78).

MONUMENT BASIN FROM THE AIR, looking north to Junction Butte and Grand View Point. Spire of Organ Rock Tongue in foreground is 305 feet high. White top of Cedar Mesa Sandstone is at bottom of photograph. Photograph by National Park Service (Fig. 22)

About a quarter mile west of the Y, a left fork of the road goes about a mile and a half to Green River Overlook, which provides a superb view of Stillwater Canyon of the Green River, the Orange Cliffs beyond, and the Henry Mountains in the extreme distance (fig. 23). Note that here the White Rim Sandstone is much thicker than in preceding views. The prominent butte enclosed by the loop of the river is known as Turks Head and is better seen from the air (fig. 24). The light-colored band near the base of the cliffs in the background offigure 24is characteristic of the bleached upper part of the Moenkopi Formation in this part of the park. According to F. A. McKeown and P. P. Orkild (U.S. Geol. Survey, unpub. data, Feb. 16, 1973), petroliferous material or odor generally occurs in this bleached zone and in the basal beds of the Moenkopi.

The campground just north of Green River Overlook has no water at this writing (1973), but water from wells in Taylor Canyon will eventually be piped to nearby parts of Island in the Sky.

Five miles northwest of the Y we come to Upheaval Dome, one of the most unusual geographic and geologic features of the park. Viewed from the air (fig. 25), it resembles somewhat a volcanic or meteor crater and has been called such by some. Because beds of salt are known to underlie the park, some have suggested that the salt may have thickened and welled upward to form a salt dome, similar to domes along the Gulf Coast (Mattox, 1968). However, only 1,470 feet of salt was encountered in an oil test just east of Upheaval Dome (Robert J. Hite, U.S. Geol. Survey, oral commun., Feb. 13, 1973); so although salt may have played a role, Upheaval Dome clearly is not a salt dome with dimensions similar to the Gulf Coast types. It may be related to a mound on the deep-seated Precambrian rocks (Joesting and Plouff, 1958, fig. 3; Joesting and others, 1966, p. 13, 14, 17), but the exact origin of the dome is not clear.

The central part has the structure of a dome, in that the strata dip downward away from the middle. A ringlike syncline, or downward fold in the rock layers (fig. 26), surrounds the dome, beyond which the strata resume their nearly flat position. The white rock in the bottom of the craterlike depression is not salt, but jumbled large fragments of the White Rim Sandstone. Surrounding that are slopes of the Moenkopi and Chinle Formations, cliffs of the Wingate Sandstone, a circular bench of the Kayenta Formation, and outer ramparts of the Navajo Sandstone. Upheaval Canyon leads to Stillwater Canyon of the Green River at the upper left.

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