Chapter II: Front Matter (2)

David May, Assistant Chief of Interpretation and Resource Management, Moab office of National Park Service (oral commun., Oct. 1973), believes that if only those in the park having a minimum dimension of 10 feet in any one direction were considered to be arches, the number would boil down to about 56 or 57. The most complete count of arches and other openings in all of southeastern Utah was made by Dale J. Stevens, Professor of Geography at Brigham Young University, during the period February through April 1973. He considered those with openings of 3 feet or larger and found more than 300 in southeastern Utah, of which 124 are in Arches National Park, although he stated that several areas of the park were not intensively searched because of time limitations (written commun., July and Sept. 1973). The 124 arches and openings are distributed among the several named areas of the park, as follows: Courthouse Towers, 13; Herdina Park, 11; The Windows section, 25; Delicate Arch area, 3; Fiery Furnace, 19; Devils Garden, 25; upper Devils Garden (northwest of Devils Garden), 14; Eagle Park, 2; and Klondike Bluffs, 12.

Professor Stevens generally used a range finder or a steel tape to measure the width and height of the openings and the width and thickness of the spans, but estimated a few of the dimensions. In the text descriptions of arches or captions of figures that follow, I am including all or part of these measurements, without further acknowledgment.

All the arches in the park were formed in the Entrada Sandstone, mainly in the Slick Rock Member but partly in the Slick Rock and Dewey Bridge Members, and a few in the Slick Rock Member occur not far beneath the base of the overlying Moab Member. The sandstone of the three members is composed mainly of quartz sand cemented together by calcium carbonate (CaCO₃), which also forms the mineral calcite and the rock known as limestone, but the Dewey Bridge Member also contains beds of sandy mudstone. Limestone and calcite are soluble in acid, even in weak acid such as carbonic acid, HHCO₃, also written H₂CO₃, formed by the solution of carbon dioxide (CO₂) in water. Ground water, found everywhere in rock openings at different depths beneath the land surface, contains dissolved carbon dioxide derived from decaying organic matter in soil, from the atmosphere, and from other sources. Even rainwater and snow contain a little carbon dioxide absorbed from the atmosphere—enough to dissolve small amounts of limestone or of calcite cement from sandstone. The calcite cement in the Entrada and in many other sandstones is unevenly distributed, however, so that all the cement is removed first from places that contain the least amounts, and, once the cement is dissolved away, the loose sand is carried away by gravity, wind, or water.

Both nearly flat but slightly irregular beds of sandstone and relatively thin walls or fins of sandstone are prime targets for this differential erosion. Potholes, as shown in figure 18_A_, may be formed in relatively flat beds by the dissolving action of repeated accumulations of rainwater or snowmelt, even in arid regions like the Plateau.

Relatively thin walls, or fins as they are called in parts of the Plateau including Arches, are targets for the formation of alcoves and caves by solution of cement and removal of sand by gravity, wind, and water, aided by the prying action of frost in joints, bedding planes, or other openings. Once a breakthrough of a wall or fin occurs, weakened chunks from the ceiling tend to fall, and natural arches of various shapes and sizes are produced. Arches form the strongest shapes for supporting overlying rock loads, as the rock in the arch is compressed toward each abutment by the heavy loads. Blocks of compressed rock beneath a relatively flat ceiling tend to be dislodged also by expansion due to release of pent-up pressure, until a strong self-supporting arch is formed. Release of pent-up pressure in rock walls may help also in initiating the formation of alcoves or caves in cliff faces. Man, including the ancient Greeks, Romans, Egyptians, and others, has long made use of arches in building bridges, aqueducts, temples, cathedrals, and other enduring edifices.

As vividly shown in figure 12, the Entrada Sandstone on the northeast flank of the Salt Valley anticline has been broken by Earth forces into thin slabs mostly 10 to 20 feet thick between nearly parallel joints, but, as will be noted in the descriptions of individual arches, some rock walls are only 1 or 2 feet thick, whereas others are 50 feet thick or more. Some weak or thin slabs have weathered away, leaving the stronger or thicker ones as towering fins, particularly in the Fiery Furnace and Devils Garden areas. Jointing on a less spectacular scale also has broken the Entrada in areas south of Salt Valley, leaving walls or fins of rock.

Although all the arches in the park were carved from the Entrada Sandstone, slight differences in their mode of origin or placement within the Entrada allow them to be grouped into three classes: (1) vertical arches formed in the Slick Rock Member alone or in the Slick Rock and Moab Members, (2) vertical arches formed mainly in the Slick Rock Member but partly in, and with the aid of, the incompetent underlying Dewey Bridge Member, and (3) horizontal arches, or so-called pothole arches, formed from the union of a vertical pothole and a horizontal cave. Hereinafter, the three members will be referred to alone, without reference to the Entrada.

Before giving examples of arches in each of the three classes, it is appropriate to remark that the arches and other erosion forms in the park represent but a fleeting instant in geologic time. Many of the pinnacles or piles of rock may be the broken remains of former arches, and many of the arches we see may be gone tomorrow, next year, or a few hundreds of years and, certainly, before many thousands of years. On the other hand, many new arches will form by the processes described above as the geologic clock ticks on.

Examples of Arches

Tunnel Arch (fig. 14) is a good example of an arch eroded entirely within the massive Slick Rock Member. Just southwest of Sheep Rock (fig. 31) is an unnamed opening in the lower part of the Slick Rock Member which I call “Baby Arch,” because it is one of the newest ones visible from the park road (fig. 15). It is only 25½ feet wide and 14 feet high and penetrates a wall 14 feet thick. Note that the breakthrough probably began along the prominent recessed bedding plane at the base of the arch. Its youthfulness is also indicated by the sharp, angular breaks in the ceiling and by the pile of freshly fallen rocks. Some visitors have asked park personnel why they have not cleared away such debris! Despite its youthfulness, the ceiling has already taken on the shape of an arch.

Broken Arch (fig. 16) was formed near the top of the Slick Rock Member and is strengthened and protected by the more resistant overlying Moab Member, which forms the upper half of the span. The crest is only 6 feet thick at the thinnest point and is not broken as the name seems to imply.

Double Arch (fig. 17), “one” of the most beautiful in the park, is in The Windows section near the east end of the road. The southeast arch, which is 160 feet wide and 105 feet high, is the second largest in the park, but the west arch measures only 60 feet wide and 61 feet high. In common with most arches in The Windows section, these two arches of the Slick Rock Member rest upon bases of the weak, easily eroded Dewey Bridge Member. More rapid erosion of the Dewey Bridge undercut the arches and hastened their development.

The cause of the wavy bedding in the Dewey Bridge Member, as shown in figure 17 but as better shown in the frontispiece, is not known for sure but generally is regarded to be the result of irregular slumping during or just after deposition of the sediments in a body of water, caused by the weight of overlying sediments.

The last example I shall take up is Pothole Arch (fig. 18), which differs from all the other examples in that this arch is roughly horizontal rather than vertical. Most park visitors, including me, were not aware of this interesting feature until after publication of the pamphlet “The Guide to an Auto Tour of Arches National Park,” which, as previously noted, may be purchased at the Visitor Center. Pothole Arch caps a ridge high above the road half a mile northwest of Garden of Eden, so only those who happened to look up at the right place were aware of its existence.

A different mode of origin than that given in the caption for figure 18 is depicted on a poster in the Visitor Center, which shows the pothole being formed by a waterfall having an apparent flow rate of several cubic feet per second. Potholes can be formed in this manner in places where sufficient streamflow is available, either continuously or following rainstorms, but I believe the process depicted in figure 18 is a more likely mode of origin for Pothole Arch.

How to See the Park

As aptly stated on a poster in the Visitor Center, how to see the park depends in part upon the question “How long can you stay?” Inasmuch as the park entrance and Visitor Center are beside a through U.S. Highway (163), many motorists first become aware of the park’s existence from the entrance sign, and some take time for at least a quick visit, such as a round trip to The Windows section, which can be made in an hour or so.

For those who have or take more time and are able to walk at least short distances, a visit of 1 or 2 days is a very rewarding experience. Others, particularly avid shutterbugs and those with camping gear, profitably spend from several days to a week or more and hike all or most of the trails.

Regardless of how long you plan to spend, I urge at least a brief stop at the Visitor Center, where excellent displays and a narrated slide show help materially in conveying just what the park has to offer. At the counter you can purchase a copy of “The Guide to an Auto Tour of Arches National Park,” which explains the views from each of 25 numbered stops along the park road, as well as other reports describing arches or other parks and monuments.

The park is open the year round, but, like most high deserts, it gets rather hot in the summer and cold enough in the winter for occasional snows and is sometimes closed temporarily because of heavy snowfall. The weather generally is ideal during the spring and fall. Even though summer daytime temperatures may exceed 100°F (37.8°C) and slow down hikers, the nights are cool enough for comfortable sleeping beneath ample covers.

Before beginning our trip through the park proper, let us consider a beautiful part many people fail to realize actually belongs to the park—the Colorado River canyon forming the southeastern boundary.

A Trip Through The Park

Colorado River Canyon

The southeastern boundary of the park for about 11 miles is the Colorado River, from the bridge on which U.S. Highway 163 crosses the river to a point upstream about half a mile below the mouth of Salt Wash. Illuminated night float trips down part of this reach are run during the summer, as noted on p. 16. Partly paved State Highway 128 follows the southeast side of the river for about 30 miles to Dewey Bridge, then goes northward about 15 miles to Cisco, where it connects with Highway I-70.

The rocks of the Glen Canyon Group form the southernmost corner of the park, as shown in figure 19. About 2 miles northeast of the bridge, we cross the axis of the Courthouse syncline (fig. 9), which brings the Navajo Sandstone down nearly to river level, as shown in figure 20. The underlying Kayenta Formation is largely hidden by vegetation and alluvial deposits in this view.

About 11 miles above the Moab bridge is the mouth of Salt Wash (fig. 1), as viewed from State Highway 128. (See fig. 21.) Seventeen miles above the bridge (east of area shown in fig. 1), we get an excellent view of the southeast end of the highly faulted Cache Valley anticline, as shown in figure 22. The background shown in the photograph formerly was the easternmost part of the former monument, but when the monument graduated to a park on November 16, 1971, this part of Cache Valley along with most of Dry Mesa was withdrawn from the park and put under the supervision of the Bureau of Land Management, also a part of the Department of the Interior.

As noted on page 16, part of “Run, Cougar, Run” was filmed just upstream from the irrigated field in the foreground of figure 22, in a wide part of the valley called Professor Valley (fig. 7). This valley and the Richardson Amphitheater on the southeast side of the river were named after a Professor Richardson who settled in the area in the 1880’s. The long abandoned townsite of Richardson was 1¼ miles due east from the point from which figure 22 was taken.

Headquarters Area

The junction of the park road with U.S. Highway 163 is shown at the lower left of figure 23, and the entrance station, Visitor Center, parking lot, and several buildings are seen at the lower right. Several residences for park personnel and other buildings are shown in figure 25. As shown in the lower part of figure 23, the geology at the park entrance is rather complex, as the park boundary here is partly along the Moab fault and partly along a branch fault—both in the Seven Mile-Moab Valley anticline (fig. 7). The Moab fault extends northwestward from Moab for more than 30 miles (McKnight, 1940, p. 120, 121, pl. 1).

As shown in figure 23, soon after leaving the checking station the park road begins to ascend the first of several switchbacks, and cuts first into the Slick Rock Member, then the Dewey Bridge Member, and finally the Navajo Sandstone the rest of the way to and beyond the top of the hill.

From points a mile or so up the hill may be seen interesting features in several directions.[5] The view to the southwest is shown in figure 23, to the west are the Three Penguins (fig. 24). A good view of the Moab Valley is had by looking southeastward (fig. 25). A well in the Navajo Sandstone at the base of the hill supplies water to all the residences and to the Visitor Center, where a drinking fountain and modern restrooms are available to the public. Storage is provided by a steel tank hidden in a ravine above the buildings shown in figure 25.

To the north the wall of Entrada Sandstone is cut by a normal fault (fig. 6), as shown in figure 26.

Courthouse Towers Area

About 2.3 miles from the entrance station is a turnoff and parking area at the south end of the Park Avenue trail (stop 2), which is about 1 mile long and ends at another parking area 1.7 miles farther north. An interesting hike is best made from south to north in a downhill direction, and hikers generally meet the cars of relatives or friends awaiting them at the northern parking area. The trail begins in a canyon cut in the soft Dewey Bridge Member and walled by high fins of the Slick Rock Member (fig. 27), but farther north the canyon is floored by the bare Navajo Sandstone. The avenue was named from the resemblance of the east wall to a row of tall buildings. Atop the west wall, just to the left of the view in figure 27, are two balanced rocks (fig. 28). The one on the left, which resembles somewhat the head of an Egyptian queen, is offset to the right along a bedding plane, and this offset may have been caused by an earthquake.

As we progress toward Courthouse Towers proper, lofty fins and monoliths lie mostly on our left, and to the right are fine distant views of the La Sal Mountains (stop 4). A general view of the Courthouse Towers is shown in figure 29, and closeups of two of the named rock sculptures—the Three Gossips and Sheep Rock—are shown in figures 30 and 31. Just beyond Sheep Rock, which some think resembles the Sphinx, we see “Baby Arch,” shown in figure 15.

Five miles from the entrance station, the road crosses Courthouse Wash on a modern bridge (stop 6)—a distinct improvement over the two tracks in the sand we used in 1946. The Courthouse syncline, named after the wash, extends northwestward through here. (See figs. 8, 9, 20.) About a mile west of the bridge, Professor Stevens found another pothole arch. A mile and a half north of the bridge is stop 7, where attention is called in the booklet to the vast area of “petrified dunes” east of the road, which are simply dunelike exposures of the crossbedded Navajo Sandstone formed originally by the cementation of a vast area of sand dunes. My view of these was taken about 1 mile beyond the stop (fig. 32).

West of the road between the petrified dunes and The Windows section, the Entrada Sandstone, particularly the Dewey Bridge Member, has been weathered into grotesque spires and pinnacles resembling the so-called “hoodoos and goblins” in Goblin Valley State Park, just north of Hanksville, Utah. Typical examples of “hoodoos and goblins” are shown in figure 33 (near stop 8). It seems reasonable to assume that some of these spires are the skeletal remains of former arch abutments. From here may be seen North and South Windows and Turret Arch on the skyline to the northeast (figs. 37-40).

The Windows Section

The Windows section, one of the most beautiful parts of the park, once was the only readily accessible part of the former monument and is still the only collection of arches seen by many visitors who either do not have or do not take time to travel farther north. All the arches and erosion forms are on or near a high crest called Elephant Butte (Dane, 1935, p. 126, 127), which separates Salt Valley from the Courthouse syncline. The ridge also marks the south edge of several minor anticlines and synclines termed by Dane the “Elephant Butte folds.”

Guarding the approach to The Windows section is Balanced Rock (stop 9). As shown in the frontispiece, it is accompanied on the right by another balanced rock and a third one may be seen in the distance. The original route to The Windows section, pioneered by Goulding, passed just north of Balanced Rock. Traces of the old road between here and the Garden of Eden parking area are still visible but no longer used. To the west, however, a part of the old road is the starting point of a jeep trail leading northwestward through Herdina Park to a point near Klondike Bluffs, where it joins the dirt road in Salt Valley (fig. 1). Visitors having four-wheel-drive vehicles may wish to drive at least as far as Eye of The Whale (fig. 34), which is about 2 miles northwest of Balanced Rock. There are several picnic tables at the beginning of this jeep trail, but no water.

Just beyond Balanced Rock, a branch paved road turns eastward 2½ miles to the main parking lots in The Windows section. Between the Garden of Eden (stop 13) and Cove of Caves are spectacular exposures of the Navajo Sandstone showing the crossbedding typical of the original dunes (fig. 35). Just east of the crossbedded Navajo Sandstone, shown in figure 35, we pass Cove Arch and Cove of Caves (stop 10) on the north side of the road (fig. 36).

Just around the curve east of Cove of Caves is the first of two parking lots (stop 11) forming a one-way loop at the end of this branch of the road. From the loop may be seen the greatest concentration of readily accessible arches in the park, all of which are roofed by the Slick Rock Member and floored by the Dewey Bridge Member. Let us take the short paved trail from the upper lot to the southeast, where we come first to North Window (fig. 37). If we walk through this arch and climb the rock beyond (fig. 37 caption), we see one of the best views in the park (fig. 38). A short walk south of North Window brings us to South Window (fig. 39). The other side of this arch may be reached either by walking around the nearby southeast end of the fin or by walking through North Window. A short walk to the southwest brings us to Turret Arch—the one seen through North Window in figure 38. Figure 40 was taken from the southwest side of Turret Arch, viewed northeastward toward South Window, one corner of which appears at the left. Both North and South Windows may be seen in one photograph taken from points near Turret Arch.

From the lower parking lot (stop 12), a short walk by paved trail takes us to spectacular Double Arch, shown in figure 17. This arch is visible from the parking lot but is best seen and photographed from at or near the end of the trail. Looking westward from near the trail’s end, we see the Parade of Elephants, shown in figure 41. This feature is described on pages 16 and 17 of “The Guide to an Auto Tour of Arches National Park” as “whimsical stone statuary resembling a circus pachyderm parade. With tail in trunk, the elephants rumble toward you along a sandstone roadway.”

Ribbon Arch, on the north side of Elephant Butte, is one of the most delicate ones in the park (fig. 1). Although it is 50 feet wide and 55 feet high, the rock span is only 1½ feet wide and 1 foot thick.

On the way back to the intersection with the main park road, we pass stop 14, from which may be seen Pothole Arch (fig. 18). One and one-half miles north of the intersection with the main road is the Panorama Point parking area (stop 15), which affords fine distant views of Salt and Cache Valleys and points beyond. A roadside exhibit portrays the gradual development of the Salt Valley anticline, which supplements my description on pages 27-32. A parking space a short distance farther down the hill (stop 16) provides good distant views of the Fiery Furnace. I tried several telephoto shots from this viewpoint, but preferred my closeup views, such as the one shown in figure 44.

Delicate Arch Area

Two and a half miles northeast of the road intersection near Balanced Rock, a gravelled side road leads northeastward to several points of considerable interest. The photograph in figure 11 was taken from this side road about half a mile northeast of the intersection. About 2 miles to the northeast, just beyond Salt Valley Wash, is a parking area (stop 17) at the beginning of the trail past Wolfe’s Bar-DX Ranch (fig. 3) to famed Delicate Arch, which is featured on the front cover. Although the trail to the arch is only 1½ miles long, it crosses several hills at the outset, then climbs 500 feet, mostly on bare Entrada Sandstone, so is considered quite strenuous, particularly in hot weather. The Park Service advises hikers to carry water. The Walt Disney crew, cameras, gear, cougars, and all climbed this trail in the hottest part of the summer of 1971 (see p. 16), while my wife and I were working in the vicinity. Visitors who do not wish to make the hike may get a distant view of Delicate Arch by driving to a parking area (stop 18) 1.3 miles farther east.

After leaving Wolfe’s Ranch, the trail to Delicate Arch crosses Salt Wash on a suspension foot bridge (fig. 42). Just beyond the bridge, a short walk to the left (north) leads to the Ute petroglyphs shown in the lower photograph of figure 2. The most difficult part of the trail, on bare sandstone, is marked by cairns of stones placed at sufficient intervals to keep hikers from losing the barely visible trail. When the summit finally is reached and the last corner rounded, one suddenly sees perhaps the most sublime view in the park—famed Delicate Arch, framing part of the La Sal Mountains beyond (fig. 43). This graceful arch and mighty Landscape Arch (fig. 53) were considered to be in serious jeopardy during the era of sonic booms, but hopefully this danger now is past. (See p. 16-17.)

It may be of interest to shutterbugs that professional photographer Hal Rumel lugged an 8- × 10-inch camera plus a heavy tripod and accessories up the steep trail to get the excellent photograph of Delicate Arch shown in figure 43. The late afternoon sun intensified the red somewhat, but my shots made earlier in the day using both 4- × 5-inch and 35-mm equipment resulted in unwanted shadows, even though the salmon color of the Slick Rock Member was more nearly normal.

After leaving the junction with the side road, the main park road traverses slices of vertical strata squeezed between faults along the north side of Salt Valley, then gradually climbs out of the valley for about 2 miles to a parking area (stop 19), from which good views are had of the southeast end of Salt Valley and of the grabens in the west end of Cache Valley. (See fig. 11.)

Fiery Furnace

About half a mile farther uphill is a parking area for viewing the southeastern part of the Fiery Furnace (stop 20), a vast array of towering fins and pinnacles of the reddish Slick Rock Member separated by narrow slots, vaguely resembling flames shooting skyward. The view of the Fiery Furnace in figure 44 was taken about 1 mile farther up the hill. It is not difficult to get lost among this myriad of fins and narrow slots, so ranger-guided tours are conducted during the summer.

About 1 mile farther northwest is a parking area (stop 23) from which a short walk to the north end of Fiery Furnace leads to a narrow slot between high fins (fig. 45), along which a short sandy trail leads to a recess along the southwest wall containing Sand Dune Arch (fig. 46). This hidden arch receives sunshine only near the middle of the day and is a delightful, shady place to rest.

From the entrance to the slot leading to Sand Dune Arch, a trail goes half a mile north across an open field to Broken Arch, shown in figure 16. This field, which separates the Fiery Furnace and Devils Garden areas, is seen from the air in figure 12.

Salt Valley and Klondike Bluffs

Before proceeding to the end of the paved road, let us take an unimproved side road, which turns south about a third of a mile beyond the last stop, in order to see more of Salt Valley and to visit Klondike Bluffs in the northwestern part of the park. After descending 2.3 miles of winding road we reach the normally dry bed of Salt Valley Wash, and turn abruptly to the northwest. For the next three-fourths of a mile the “road” is simply two tracks in the loose, sandy bed of the wash, which obviously should not be travelled when flooded or when there is even a hint of rain. In dry weather, however, this road may be travelled by ordinary passenger car. This stretch of the wash cuts through an intruded block of the Paradox Member of the Hermosa Formation consisting mainly of gray and brown gypsum, the common salt having been dissolved out by ground water. Such an intrusive block of salt-bearing rock is known to geologists as a diapir—not to be confused with the garment (diaper) worn by infants.

From here on the road traverses a rather uninteresting stretch of valley north of Salt Valley Wash. Eleven miles from the starting point, the road reaches an intersection from which a side road leads southwestward three-fourths of a mile to a parking area at the foot of Klondike Bluffs, which form the south side of Salt Valley. From here, one may make a strenuous hike over a primitive trail about 1½ miles long to beautiful Tower Arch (fig. 47).

The valley road continues northwestward from the intersection to and beyond the northwest end of the park and connects with roads to Crescent Junction, Thompson, and the Yellow Cat mining district, north of the park (p. 14).

Let us return to the paved road and continue our tour of the park.

Devils Garden

Turning left (northwest) at the intersection with the paved park road, we enter Devils Garden—another large maze of towering red fins separated by narrow slots, which resembles the Fiery Furnace. After a third of a mile, we reach stop 24 and walk 100 feet or more to the north for a good view of Skyline Arch (fig. 48). This arch is very appropriately named, as it forms the skyline viewed either from the road on the south or from the campground on the north, from points south of the amphitheater. Less well known is the fact that Skyline Arch is clearly visible to the naked eye or through binoculars from stretches of Highway I-70 (or old U.S. Highways 6 and 50) about 11 miles to the north. Most arches and other erosion forms do not change appearance much from day to day or year to year, but some, like “Baby Arch” (fig. 15), show evidence of relatively recent origin. In November 1940 (Abbey, 1971, p. 42) Skyline Arch suddenly doubled in size by the fall of a large rock that occupied what is now the northwest half of the arch. Photographs taken before and after this event appear on pages 24 and 25 of the road guide and also in the museum at the Visitor Center.

Another half mile brings us to a one-way (to right) loop at the end of the park road. Just beyond the beginning of the loop is a parking lot and very attractive picnic area containing several picnic tables shaded by piñon pines at the foot of a towering red fin of the Slick Rock Member. Just north of this picnic ground, a paved side road leads eastward into a truly beautiful, well-equipped campground comprising both back-in and drive-through campsites for trailers, campers, or tents; three pairs of modern restrooms, hydrants, and drinking fountains; and an amphitheater, where illustrated campfire talks are given nightly during the summer. The east end of the campground is shown in figure 49.

Devils Garden in general and the campground in particular are on the crest of a ridge separating Salt Valley to the southwest from the Sagers Wash syncline to the northeast, which lies north of Yellow Cat Flat and north of the area shown in figure 1. From the higher parts of the campground striking views are to be had toward the north and northeast, particularly late in the afternoon, as shown in figure 50.

In about the middle of the one-way loop at the end of the park road is a well that supplies water to the campground from early in the spring until the return of freezing weather late in the fall. The well, which was drilled in 1962 to a depth of 900 feet, obtains a small amount of water from the Wingate Sandstone. No water was found in the overlying Navajo and Entrada Sandstones because of the pronounced dip of the rocks toward the northeast, which allows any water in these rocks to drain northeastward (Ted Arnow, written commun., 1963). Water from this well is pumped to a steel tank in a high part of the campground, whence it flows by gravity to the three sets of restrooms.

At the northwest end of the one-way loop is a large parking area for use by people hiking the Devils Garden trail. This trail leads to seven of the most interesting arches in the park, all of which are in the Slick Rock Member, and there are many more farther to the northwest. The approximate distances to the seven arches are given in the paragraphs that follow. The trail is paved for about 1 mile as far as Landscape Arch (fig. 53), but from there to Double O Arch (fig. 56) the trail is primitive, and the Park Service recommends rubber soles as part of the trail is on bare sandstone. For these reasons, many visitors hike only as far as Landscape Arch.

Much of the trail, particularly the first part, lies in a narrow slot between fins of the Slick Rock Member, as shown in figure 51. After about half a mile, a side trail to the north leads to a Y, the right-hand fork of which goes to Tunnel Arch (fig. 14). The left-hand fork leads to Pine Tree Arch, obviously named for the piñon pine framed by this arch (fig. 52).

At the end of the improved part of the trail, we reach Landscape Arch (fig. 53), claimed by the Park Service to be the longest known natural arch in the world. According to Ouellette (1958) it is 291 feet long and 118 feet high, but Professor Stevens’ measurements indicate it to be 287 feet long and 106 feet high. At its thinnest point on the right, the span is only 11 feet wide and 11 feet thick. In 1958 three young men made what was claimed to be the second known ascent of Landscape Arch, using ropes and other climbing gear, after which they walked across (Ouellette, 1958). This crossing was made with the permission of a park ranger, but such permission is no longer given, for the safety of both the arch and of would-be climbers.

Wall Arch is about a quarter of a mile beyond the end of the improved part of the trail, and another three-fourths mile brings us to Navajo Arch (fig. 54) and Partition Arch (fig. 55). A distant view of Partition Arch may be had just before reaching Landscape Arch. Part of the remaining trail to Double O Arch (fig. 56) is on the top of a low sandstone fin, in part between somewhat higher fins and in part above lower slots.

Beautiful Double O Arch (fig. 56) is at the end of the Devils Garden trail about 2½ miles northwest of the trailhead. About half a mile northwest of the trail’s end is a prominent landmark called Dark Angel (fig. 57), which is visible in figure 12 and from the unimproved road in Salt Valley.

GEOLOGIC TIME
The Age of the Earth

The Earth is very old—4.5 billion years or more according to recent
estimates. Most of the evidence for an ancient Earth is contained in
the rocks that form the Earth’s crust. The rock layers
themselves—like pages in a long and complicated history—record the
surface-shaping events of the past, and buried within them are
traces of life—the plants and animals that evolved from organic
structures that existed perhaps 3 billion years ago.

Also contained in rocks once molten are radioactive elements whose
isotopes provide Earth scientists with an atomic clock. Within these
rocks, “parent” isotopes decay at a predictable rate to form
“daughter” isotopes. By determining the relative amounts of parent
and daughter isotopes, the age of these rocks can be calculated.

Thus, the results of studies of rock layers (stratigraphy), and of
fossils (paleontology), coupled with the ages of certain rocks as
measured by atomic clocks (geochronology), attest to a very old
Earth!

Professor Stevens found 14 arches in what he called upper Devils Garden, northwest of Double O Arch, and two arches in the northwesternmost extension of the park known as Eagle Park (fig. 1). One of the unnamed arches in upper Devils Garden is shown in figure 58. I am tentatively calling it “Indian-Head Arch,” because of the rather obvious resemblance.

This ends our journey through Arches National Park, but there remains for consideration a summary of the principal geologic events leading to the formation of this beautiful part of the Colorado Plateau and a brief comparison with the geology of other national parks and monuments on the Plateau.

Summary of Geologic History

Having finished our geologic trip through Arches National Park, let us see how the arches and other features fit into the bigger scheme of things—the geologic age and events of the Earth as a whole, as depicted in figure 59. As shown in figure 4, the rock strata still preserved in the park range in age from Pennsylvanian to Cretaceous, or from about 300 million to 100 million years old—a span of about 200 million years. This seems an incredibly long time, until one notes that the earth is some 4.5 billion years old, and that our rock pile is but 1/23 or 4½ percent of the age of the Earth as a whole. Thus, in figure 59, the rocks exposed in the park occupy only about the left half of the top whorl of the spiral.

But this is not the whole story. As indicated earlier, younger Mesozoic and Tertiary rocks more than 1 mile thick that once covered the area have been carried away by erosion, and if we include these the span is increased to about 250 million years, or nearly a full whorl of the spiral.

Deep tests for oil and gas tell us that much older rocks underlie the area, and we have seen that some of these played a part in shaping the park we see today. In addition to the Precambrian igneous and metamorphic rocks, there is about 2,000 feet of Paleozoic sedimentary rocks older than the Pennsylvanian Paradox Member of the Hermosa Formation, most of which was laid down in ancient seas. This includes strata of Cambrian, Ordovician, Devonian, Mississippian, and Pennsylvanian ages (fig. 59). There are some gaps in the rock record caused by temporary emergence of the land above sea level and erosion of the land surface before the land again subsided below sea level so that deposition could resume. Silurian rocks are absent, presumably because, here, the Silurian Period was dominated by erosion rather than deposition.

While Pennsylvanian and Permian rocks were being laid down in and southwest of the park, a large area to the northeast, called by geologists the Uncompahgre Highland (because it occupied the same general area as part of the present Uncompahgre Plateau), rose slowly above sea level. Whatever Paleozoic rocks were on this rising land plus part of the underlying Precambrian rocks were eroded and carried by streams into deep basins to the northeast and southwest. Thus, while some marine or near-shore deposits were being laid down in and south of the park, thousands of feet of red beds were being laid down by streams between the park and what is now the Uncompahgre Plateau. During part of Middle Pennsylvanian time, a large area, including the park, known as the Paradox basin, was alternately connected to or cut off from the sea, so that the water was evaporated during cutoff periods and replenished during periods when connection with the sea resumed. In these huge evaporation basins were deposited the salt and gypsum plus some potash salts and shale that now make up the Paradox Member of the Hermosa Formation.

Arches National Park contains four northwesterly trending major folds—the Salt Valley and Cache Valley salt anticlines, the Courthouse syncline, and the faulted Moab-Seven Mile anticline, which forms the southwestern border. How these folds were formed was explained on pages 27-32. The history of their growth, however, was a long one that began about 300 million years ago in the Pennsylvanian and ended about 50 million years ago in the early Tertiary. The growth of these folds occurred in two stages. The first stage, which involved the development of the salt cores of the anticlines, ended in the Jurassic with the beginning of Morrison time; the second stage, which involved additional folding that intensified the magnitude and shape of existing folds, occurred in the early Tertiary and was followed later by collapse of the salt anticlines. The formation and collapse of the Salt Valley and Cache Valley anticlines was accompanied by pronounced jointing (fig. 12), which allowed differential erosion to produce the tall fins in which the arches were formed.

The old Uncompahgre Highland continued to shed debris into the bordering basins until Triassic time, when it began to be covered by a veneer of red sandstone and siltstone of the Chinle Formation (Lohman, 1965). The area remained above sea level during the Triassic Period and most, if not all, of the Jurassic Period, although the Jurassic Carmel Formation was laid down in a sea that lay just to the west.

Late in the Cretaceous Period a large part of Central and Southeastern United States, including the eastern half of Utah, sank beneath the sea and received thousands of feet of mud, silt, and some sand that later compacted into the Mancos Shale. This formation, as well as all younger and some older strata, has long since been eroded from most of the park area, but a little of the Mancos is preserved in the Cache Valley graben (fig. 11), and the entire Mancos Shale and younger rocks are present in adjacent areas, such as the Book Cliffs north of Green River, Crescent Junction, and Cisco (figs. 7, 50, 56).

The land rose above the sea at about the close of the Cretaceous and has remained above ever since, although inland basins and lakes received sediment during parts of the Tertiary Period. Compressive forces in the Earth’s crust produced some gentle folding of the strata at the close of the Cretaceous, but more pronounced folding and some faulting occurred during the Eocene Epoch, when most of the Rocky Mountains took form. During the Miocene Epoch igneous rock welled up into older rocks to form the cores of the nearby La Sal, Abajo, and Henry Mountains. Additional uplift and some folding occurred in the Pliocene and Pleistocene Epochs.

Much of the course of the Colorado River was established during the Miocene Epoch, with some additional adjustments in the late Pliocene and early Pleistocene Epochs (Hunt, C. B., 1969, p. 67). Erosion during much of the Tertiary Period and all of the Quaternary Period plus some sagging and breaking of the crest of the anticlines, brought on by solution and lateral squeezing of salt beds beneath the Moab-Seven Mile, Salt Valley, and Cache Valley anticlines, combined to produce the landscape as we now see it.

The Precambrian rocks beneath the area are about 1.5 billion years old; so an enormous span of time is represented by the rocks and events in and beneath Canyonlands National Park.

If we consider the geologic formations that make up the national parks (N.P.), national monuments (N.M.) (excluding small historical or archaeological ones), Monument Valley, San Rafael Swell, and Glen Canyon National Recreation Area, all in the Colorado Plateau, it becomes apparent that certain formations or groups of formations play starring roles in some parks or monuments, some play supporting roles, and in a few places the entire cast of rocks gets about equal billing. Let us compare them and see how and where they fit into the “Geologic Time Spiral” (fig. 59).

Dinosaur N.M., with exposed rocks ranging in age from Precambrian to Cretaceous, covers the greatest time span (nearly 2 billion years), but has one unit—the Jurassic Morrison Formation—in the starring role, for this unit contains the many dinosaur fossils that give the monument its name and fame, although there are several older units in supporting roles. Grand Canyon N.P. and N.M. are next, with rocks ranging in age from Precambrian through Permian (excluding the Quaternary lava flows in the N.M.), but here there is truly a team effort, for the entire cast gets about equal billing. Canyonlands N.P. stands third in this category, with rocks ranging from Pennsylvanian to Jurassic, but we would have to give top billing to the Permian Cedar Mesa Sandstone Member of the Cutler Formation, from which The Needles, The Grabens, and most of the arches were sculptured; the Triassic Wingate Sandstone and the Triassic(?) Kayenta Formation get second billing for their roles in forming and preserving Island in the Sky and other high mesas.

Now let us consider other areas with only one or few players in the cast, beginning at the bottom of the time spiral. Black Canyon of the Gunnison N.M., cut entirely in rocks of early Precambrian age with only a veneer of much younger rocks, obviously has but one star in its cast. Colorado N.M. contains rocks ranging from Precambrian to Cretaceous—equal to Dinosaur in this respect, but Colorado is unique in that all the rocks of the long Paleozoic Era and some others are missing from the cast; of those that remain, the Triassic Wingate and the Triassic(?) Kayenta are the stars, with strong support from the Jurassic Entrada Sandstone.

All the bridges in Natural Bridges N.M. were carved from the Permian Cedar Mesa Sandstone Member of the Cutler Formation, also one of the stars in Canyonlands N.P. In Canyon de Chelly (pronounced dee shay) N.M. and Monument Valley (neither a national park nor a national monument, as it is owned and administered by the Navajo Tribe), the De Chelly Sandstone Member of the Cutler Formation—a Permian member younger than the Cedar Mesa—plays the starring role.

Wupatki N.M. near Flagstaff, Ariz., stars the Triassic Moenkopi Formation. Petrified Forest N.P. (which now includes part of the Painted Desert) has but one star—the Triassic Chinle Formation, in which are found many petrified logs and stumps of ancient trees. The Triassic-Jurassic Glen Canyon Group (fig. 19), which includes the Triassic Wingate Sandstone, the Triassic(?) Kayenta Formation, and the Triassic(?)-Jurassic Navajo Sandstone, receives top billing in recently enlarged Capitol Reef N.P., but the Triassic Moenkopi and Chinle Formations enjoy supporting roles.

The Triassic(?)-Jurassic Navajo Sandstone, which has a supporting role in Arches N.P., is the undisputed star of Zion N.P., Rainbow Bridge N.M., and Glen Canyon National Recreation Area, despite the fact that the latter is the type locality of the entire Glen Canyon Group. The Navajo also forms the impressive reef at the east edge of the beautiful San Rafael Swell, a dome, or closed anticline, now crossed by Highway I-70 between Green River and Fremont Junction, Utah.

As we journey upward in the time spiral (fig. 59), we come to the Jurassic Entrada Sandstone, which stars in Arches N.P., with help from the underlying Navajo Sandstone, and a supporting cast of both older and younger rocks. The Entrada also forms the grotesque erosion forms called “hoodoos and goblins” in Goblin Valley State Park, north of Hanksville, Utah.

Moving ever upward in the spiral, we come to the Cretaceous—the age of the starring Mesaverde Group, in which the caves of Mesaverde N.P. were formed, and which now house beautifully preserved ruins once occupied by the Anasazi, the same ancient people who once dwelt in Arches N.P. and nearby areas.

This brings us up to the Tertiary Period, during the early part of which the pink limestones and shales of the Paleocene and Eocene Wasatch Formation were laid down in inland basins. Beautifully sculptured cliffs, pinnacles, and caves of the Wasatch star in Bryce Canyon N.P. and in nearby Cedar Breaks N.M. This concludes our climb up the time spiral, except for Quaternary volcanoes and some older volcanic features at Sunset Crater N.M., near Flagstaff, Ariz.

Thus, one way or another, many rock units formed during the last couple of billion years have performed on the stage of the Colorado Plateau and, hamlike, still lurk in the wings eagerly awaiting your applause to recall them to the footlights. Don’t let them down—visit and enjoy the national parks and monuments of the Plateau, for they probably are the greatest collection of scenic wonderlands in the world.

Additional Reading

Many reports covering various aspects of the area have been cited in the text by author and year, and these plus a few additional ones are listed in “Selected References.” A few works of general or special interest should be mentioned, however.

Between 1926 and 1929 the entire area now included in the park was mapped geologically in classic reports by Dane (1935) and by McKnight (1940). These men and their field assistants mapped the area by use of the plane-table and telescopic alidade without benefit of modern topographic maps or aerial photographs, except for topographic maps of the narrow stretch along the Colorado River mapped under the direction of Herron (1917). Only small sections could be reached by automobile, so nearly all the area was traversed using horses and mules or by hiking. This work plus mapping done in nearby areas to the south and to the north (Stokes, 1952) during the uranium boom of the mid-fifties was used by Williams (1964) in compiling a geologic map of the Moab quadrangle at a scale of 1:250,000.

Several early reports on the Colorado River and its potential utilization contain a wealth of information and many fine photographs, including two by La Rue (1916, 1925) and one by Follansbee (1929).

You may be interested in brief accounts of the geology of other national parks and monuments, or other areas of special interest, such as the reports on the Uinta Mountains by Hansen (1969), Mount Rainier by Crandell (1969), Yellowstone National Park by Keefer (1971), and ones by me on Colorado National Monument (Lohman, 1965) and Canyonlands National Park (1974).

For those who wish to learn more about the science of geology, I suggest the textbook by Gilluly, Waters, and Woodford (1968).

Acknowledgments

I am greatly indebted to Bates Wilson, former Superintendent, and to former Assistant Superintendent Joe Carithers, for their splendid cooperation in supplying data and information; to Chuck Budge, former Chief Ranger; Dave May, Assistant Chief of Interpretation and Resource Management; Joe Miller, former Maintenance Engineer; Bob Kerr, new Superintendent; Maxine Newell, Park Historian and member of the staff at Arches National Park; Jerry Banta, former Park Ranger at Arches; and Carl Mikesell, Park Ranger at Arches, for their many favors.

I am grateful to several colleagues and friends for the loan of photographs, for geologic help and data, and for reviewing this report. I am also deeply grateful to my wife, Ruth, for accompanying me on all the fieldwork and for her help and encouragement.

Selected References