Chapter I: Front Matter (1)

_The Geologic Story of_
Arches
NATIONAL PARK

By S. W. Lohman
Graphics by
John R. Stacy

GEOLOGICAL SURVEY BULLETIN 1393

UNITED STATES DEPARTMENT OF THE INTERIOR
ROGERS C. B. MORTON, _Secretary_

GEOLOGICAL SURVEY
V. E. McKelvey, _Director_

U.S. GOVERNMENT PRINTING OFFICE: 1975

Library of Congress Cataloging in Publication Data
Lohman, Stanley William, 1907-
The geologic story of Arches National Park.
(Geological Survey Bulletin 1393)
Bibliography: p.
Includes index.
Supt. of Docs. no.: I 19.3:1393
1. Geology—Utah—Arches National Park—Guide-books.
2. Arches National Park, Utah—Guide-books.
I. Title. II. Series: United States Geological Survey
Bulletin 1393.
QE75.B9 No. 1393 [QE170.A7] 557.3′08s [557.92′58]
74-23324

For sale by the Superintendent of Documents, U. S. Government Printing
Office
Washington, D. C. 20402
Stock Number 024-001-02598-1

Contents

Page
Beginning of a monument 1
Graduation to a park 5
Early history 9
Prehistoric people 9
Late arrivals 12
Geographic setting 18
Deposition of the rock materials 20
Bending and breaking of the rocks 24
Uplift and erosion of the Plateau 33
Origin and development of the arches 37
Examples of arches 46
How to see the park 50
A trip through the park 52
Colorado River canyon 52
Headquarters area 57
Courthouse Towers area 63
The Windows section 68
Delicate Arch area 74
Fiery Furnace 79
Salt Valley and Klondike Bluffs 82
Devils Garden 83
Summary of geologic history 98
Additional reading 104
Acknowledgments 105
Selected references 105
Index 109

Figures

Page
Frontispiece. Balanced Rock.
1. Arches National Park 6
2. Rock art in Arches National Park 11
3. Wolfe’s Bar-DX Ranch 14
4. Rock column of Arches National Park 21
5. Common types of rock folds 25
6. Common types of rock faults 26
7. Paradox basin 27
8. Geologic section across northwest end of Arches National Park 28
9. Index map of northwestern part of Arches National Park 28
10. Gravity anomalies over Salt Valley 31
11. Tilted block of rocks in Cache Valley graben 34
12. Jointed northeast flank of Salt Valley anticline 36
13. Index map 38
14. Tunnel Arch 43
15. “Baby Arch” 44
16. Broken Arch 45
17. Double Arch 47
18. Pothole Arch 48
19. Glen Canyon Group 53
20. Navajo Sandstone cliffs 54
21. Mouth of Salt Wash 55
22. Southeast end of faulted Cache Valley anticline 56
23. Faulted Seven Mile-Moab Valley anticline 58
24. Three Penguins 59
25. Moab Valley 60
26. Faulted wall of Entrada Sandstone 61
27. Park Avenue 62
28. Balanced rocks on south wall of Park Avenue 64
29. Courthouse Towers 65
30. The Three Gossips 66
31. Sheep Rock 66
32. Petrified sand dunes 67
33. “Hoodoos and goblins” 68
34. Eye of The Whale 69
35. Intricate crossbeds in Navajo Sandstone 70
36. Cove Arch and Cove of Caves 71
37. North Window 72
38. Looking southwestward through North Window 73
39. South Window 74
40. Turret Arch 75
41. Parade of Elephants 76
42. Suspension foot bridge across Salt Wash 78
43. Delicate Arch 78
44. Fiery Furnace 80
45. Trail to Sand Dune Arch 81
46. Sand Dune Arch 82
47. Tower Arch 84
48. Skyline Arch 85
49. Campground in Devils Garden 86
50. View north from campground 87
51. Southeastern part of Devils Garden trail 88
52. Pine Tree Arch 89
53. Landscape Arch 91
54. Navajo Arch 92
55. Partition Arch 93
56. Double O Arch 93
57. Dark Angel 94
58. “Indian-Head Arch” 95
59. Geologic time spiral 96

Beginning of a Monument

According to former Superintendent Bates Wilson (1956), Prof. Lawrence M. Gould, of the University of Michigan, was the first to recognize the geologic and scenic values of the Arches area in eastern Utah and to urge its creation as a national monument. Mrs. Faun McConkie Tanner[1] told me that Professor Gould, who had done a thesis problem in the nearby La Sal Mountains, was first taken through the area by Marv Turnbow, third owner of Wolfe cabin. (See p. 12.) When Professor Gould went into ecstasy over the beautiful scenery, Turnbow replied, “I didn’t know there was anything unusual about it.”

Dr. J. W. Williams, generally regarded as father of the monument, and L. L. (Bish) Taylor, of the Moab Times-Independent, were the local leaders in following up on Gould’s suggestion and, with the help of the Moab Lions Club, their efforts finally succeeded on April 12, 1929, when President Herbert Hoover proclaimed Arches National Monument, then comprising only 7 square miles.[2] It was enlarged to about 53 square miles by President Franklin D. Roosevelt’s Proclamation of November 25, 1938, and remained at nearly that size, with some boundary adjustments on July 22, 1960, until it was enlarged to about 130 square miles by President Lyndon B. Johnson’s Proclamation of January 20, 1969.

According to Breed (1947), Harry Goulding, of Monument Valley, in a specially equipped car, traversed the rugged sand and rocks of the Arches region in the fall of 1936 and, thus, became the first person to drive a car into The Windows section of Arches National Monument. Soon after, a bulldozer followed Harry’s tracks and made a passable trail.

When my family and I visited the monument in 1946, the entrance was about 12 miles northwest of Moab on U.S. Highway 163 (then U.S. 160), where Goulding’s old tire tracks led eastward past a small sign reading “Arches National Monument 8 miles.” This primitive road crossed the sandy, normally dry Courthouse Wash and ended in what is now called The Windows section. At that time there was no water or ranger station, nor were there any picnic tables or other improvements within the monument proper, and the custodian was housed in an old barracks of the Civilian Conservation Corps near what is now the entrance, 5 miles northwest of Moab.

Former Custodian Russell L. Mahan reported (oral commun., May 1973) that soon after our initial visit in 1946 a 500-gallon tank was installed near Double Arch in The Windows section and connected to a drinking fountain and that two picnic tables and a pit toilet were added. At that time the only access to Salt Valley and what is now called Devils Garden was a primitive dirt road which, according to Breed (1947, p. 175), left old U.S. Highway 160 (now U.S. 163) 24 miles northwest of Moab, went 22 miles east, then followed Salt Valley Wash down to Wolfe cabin (fig. 1).

According to Abbey (1971), who served as a seasonal ranger beginning about 1958, a sign had by then been erected at the crossing of Courthouse Wash which read:

WARNING: QUICKSAND
DO NOT CROSS WASH
WHEN WATER IS RUNNING

The ranger station, his home for 6 months of the year, was what Abbey described as “a little tin housetrailer.” Nearby was an information display under a “lean-to shelter.” He had propane fuel for heat, cooking, and refrigeration, and a small gasoline-engine-driven generator for lights at night. His water came from the 500-gallon tank, which was filled at intervals from a tank truck. At that time there were three small dry campgrounds, each with tables, fireplaces, garbage cans, and pit toilets. By that time an extension of the dirt road led northward to Devils Garden, and some trails had been built and marked.

Bates Wilson became Custodian of the monument in 1949 and later became Superintendent not only of Arches but also of the nearby new Canyonlands National Park (Lohman, 1974) and the more distant Natural Bridges National Monument. In the fall of 1969, Bates told me of some of his early experiences in the undeveloped monument, including the evening when 22 cars were marooned on the wrong (northeast) side of Courthouse Wash after a flash flood. Bates and his “lone” ranger brought ropes, coffee, and what food they could obtain in town after closing time, threw a line across the swollen stream, had a tourist pull a rope across, then took turns wading the stream with one hand on the rope and the other balancing supplies on his shoulder. After a fire had been built and hot coffee and food passed around, the spirits of the stranded group rose considerably, except for one irate woman from the East, who refused to budge from her car. Bates and his helper finally got the last car out about 1 a.m., after the flood had subsided, and Mrs. Wilson then supplied lodging and more food and coffee for those who needed it.

During and for sometime after World War II and the Korean War, lack of maintenance funds and personnel had prevented improvement of the facilities in many of our national parks and monuments, particularly in undeveloped ones like Arches. The day was saved through the wisdom and foresight of former Park Service Director Conrad L. Wirth, who saw the need and desirability of putting the whole “want” list into one attractive, marketable package. In the words of Everhart (1972, p. 36):

Selection of a name is of course recognized as the most important
decision in any large-scale enterprise, and here Wirth struck pure
gold. In 1966 the Park Service would be celebrating its fiftieth
anniversary. What a God-given target to shoot for! Why not produce a
ten-year program, which would begin in 1956, aimed to bring every park
up to standard by 1966—and call it Mission 66?

The ensuing well-documented and cost-estimated plan for Mission 66 was enthusiastically backed by President Dwight D. Eisenhower and approved and well supported by Congress to the tune of more than $1 billion during the 10-year period. For Arches, this included a new entrance, Park Headquarters, Visitor Center, a museum boasting a bust of founder Dr. Williams, and modern housing for park personnel, all 5 miles northwest of Moab. By 1958 (Pierson, 1960) a fine new paved road between Park Headquarters and Balanced Rock (frontispiece) was completed. These badly needed improvements were followed by the completion of the paved road all the way to Devils Garden, the building of the modern campground, picnic facilities, and amphitheater in the Devils Garden, and the construction of turnouts and marked trails.

Graduation to a Park

Arches graduated to a full-fledged national park when President Richard M. Nixon signed a Congressional Bill on November 16, 1971. The change in status was accompanied by boundary changes that reduced the area to about 114 square miles. The loss of most of Dry Mesa, just east of the present boundary (fig. 1), was offset in part by gains of new land northwest of Devils Garden. The present (1974) boundaries, roads, trails, and named features of the park are shown in figure 1.

The park was virtually completed at graduation time, and so far this change in status has shown up mainly in new entrance signs, a new 1972 brochure and map, and a very informative “Guide to an Auto Tour of Arches National Park,” keyed to numbered signs at parking spaces. About all that remain to be added are new wayside exhibits, some boundary fences, and spur roads and trails.

Although Arches had officially become a park in November 1971, it was not formally dedicated until May 15, 1972. The ceremony began by having the Federal, State, and local dignitaries and other guests totaling 140 persons board the _Canyon King_, a 93-foot replica of a Mississippi River sternwheeler (Lansford, 1972; Lohman, 1974, fig. 69), for its maiden voyage down the Colorado River. After about half an hour, the heavily laden boat became stuck on a sandbar, and after a 90-minute wait the passengers were rescued by jet boats. This delayed a luncheon at the Visitor Center put on by the Moab Lions Club. Following the luncheon, Park Superintendent Bates Wilson made a brief welcoming address, then introduced J. Leonard Volz, Director of the Midwest Region of the National Park Service, who served as master of ceremonies. Speakers included Utah Governor Calvin L. Rampton, Senator Frank E. Moss, a representative of Senator Wallace F. Bennett, Representatives Sherman P. Lloyd of Utah and Wayne Aspinall of Colorado, and Mitchell Melich, Solicitor General of the Department of Interior, representing Secretary Rogers C. B. Morton. After the speeches, a commemorative plaque, donated by the Canyonlands Natural History Association, was unveiled by Senator Moss and Mr. Melich.

Most of the color photographs were taken by me on 4- × 5-inch film in a tripod-mounted press camera, using lenses of several focal lengths, but a few were taken on 35-mm film, using lenses of various focal lengths. I am grateful to several friends for the color photographs credited to them in the figure captions. The black and white photographs were kindly loaned from the Moab and Arches files of the National Park Service. The points from which most of the photographs were taken are shown in figure 13.

Early History

Prehistoric People

The Canyon lands in and south of Arches were inhabited by cliff dwellers centuries before the first visits of the Spaniards and fur trappers. Projectile points and other artifacts found in the nearby La Sal and Abajo Mountains indicate occupation by aborigines during the period from about 3000-2000 B.C. to about A.D. 1 (Hunt, Alice, 1956). The Fremont people occupied the area around A.D. 850 or 900, and the Pueblo or Anasazi people from about A.D. 1075 to their departure in the late 12th century (Jennings, 1970). Most of the evidence for these early occupations has been found in and south of Canyonlands National Park (Lohman, 1974), but some traces of these and possibly earlier cultures have been found also within Arches National Park.

Ross A. Maxwell (National Park Service, written commun., 1941) investigated two caves in the Entrada Sandstone in the upper reaches of Salt Wash that contain Anasazi ruins. He mentioned that perhaps a dozen or more other caves should be checked for evidence of former occupation and, also, that he found several ancient campsites littered with flint chips and broken tools.

One cave Maxwell explored some 5 miles north of Wolfe Ranch and north of the park is about 300 feet long and 100 to 150 feet deep. It contains the remains of one or more ruins of a structure he thought may have covered much of the floor. The remaining parts of walls now are only two to four tiers of stones in height, although originally they may have been more than one story high. Maxwell explored a second cave on the east side of Salt Wash, about 2 miles north of Wolfe Ranch, which contains 16 storage cists of adobe.

The faces of many older sandstone cliffs or ledges are darkened by desert varnish—a natural pigment of iron and manganese oxides. The prehistoric inhabitants of the Plateau learned that effective and enduring designs, called petroglyphs, could be created simply by chiseling or pecking through the thin dark layer to reveal the buff or tan sandstone beneath. Most petroglyphs were created by the Anasazi, but those showing men mounted on horses were done by Ute tribesmen after the Spaniards brought in horses in the 1500’s. The Fremont people and some earlier people painted figures on rock faces, called pictographs, and some of these had pecked outlines.

The so-called “Moab panel” was described by Beckwith (1934, p. 177) as a petroglyph, but, as pointed out by Schaafsma (1971, p. 72, 73), it comprises figures having pecked outlines and painted bodies, which actually are combinations of petroglyphs and pictographs. This beautifully preserved group of paintings is shown in the upper photograph of figure 2. Mrs. Schaafsma goes on to say, concerning the “Moab panel”:

The long tapered body, the antenna like headdresses, and the staring
eyes are characteristic features of Barrier Canyon style figures
elsewhere * * *. Of special interest here are the large shields held
by certain figures. A visit to this site indicated that the shields,
although apparently of some antiquity, have been superimposed over
some of the Barrier Canyon figures. Whether or not this was done by
the Barrier Canyon style artists themselves or later comers to the
site is impossible to tell.

Although definite proof seems lacking, she suggested (written commun., Nov. 3, 1973) that the “‘Barrier Canyon style’[3] * * * is earlier than the work in the same region clearly attributable to the Fremont.” Note the three bullet holes in and near the right-hand shield. A ledge above the panel that contained petroglyphs during her earlier visit had fallen to the base of the cliff by the time my wife and I inspected the panel in September 1973.

Mrs. Schaafsma believes the petroglyphs in the lower photograph of figure 2 to be the work of Ute tribesmen, not only because of the horses, but also because of the stiff-legged appearance of the mountain sheep. Note the bullet hole above the panel.

Late Arrivals

Later arrivals in and near Arches National Park included first Spanish explorers, then trappers, cattlemen, cattle rustlers and horse thieves, followed in the present century by oil drillers, uranium hunters, jeepsters, and tourists. Butch Cassidy, the Sundance Kid, and other members of The Wild Bunch are known to have frequented parts of what is now Canyonlands National Park (Baker, Pearl, 1971), but it is not certain whether or not any of them traversed what is now Arches National Park.

The first settler in what is now Arches National Park was a Civil War veteran named John Wesley Wolfe, who was discharged from the Union Army about 3 weeks before the Battle of Bull Run because he suffered from varicose veins. In 1888 his doctor told him he had to leave Ohio for a dryer climate or he would not live 6 months, so he took his son Fred west and settled on a tract of 150 acres along the west bank of Salt Wash, where his “Wolfe cabin” still stands (figs. 1, 3). From family letters and newspaper clippings compiled by Mrs. Maxine Newell and other members of the National Park Service (Maxine Newell, written commun., 1971), we learn what life in the area was like:

We have started a cattle spread on a desert homestead. We call it the
Bar-DX Ranch. Fred and I live in a little log house on the bank of a
creek that is sometimes dry, sometimes flooded from bank to bank with
roaring muddy water. We are surrounded with rocks—gigantic red rock
formations, massive arches and weird figures, the like of which youve
[sic] never seen. The desert is a hostile, demanding country, hot in
summer, cold in winter. The Bar-DX Ranch is a day’s ride from the
nearest store, out of the range of schools.

Although John Wolfe had promised his wife and his other children that he would return home the first fall that his cattle sales netted enough money, he and Fred stayed on and on, and his wife refused to go west and join her husband and son. Eighteen years later he sent money from his pension check to his daughter, Mrs. Flora Stanley, his son-in-law, Ed Stanley, and his two grandchildren, Esther and Ferol, to join him and Fred at the ranch. Their train was met at Thompson Springs (now Thompson), Utah (fig. 7), by John Wolfe for the 30-mile ride to the ranch by horse and wagon. Sight of the tiny log cabin with only a dirt floor brought tears to his daughter’s eyes, but her spirits rose considerably after John Wolfe promised to build a new log cabin with a wooden floor. But the children were enchanted with this strange country, with the building of the new cabin, and, especially, with getting to go rabbit hunting with Grandpa Wolfe. The Stanleys stayed at the ranch until Esther was 10, then moved to Moab to await the arrival of their third child, Volna.

In 1910 John Wolfe sold the Bar-DX Ranch, and the entire family moved to Kansas. John Wolfe later moved back to Ohio, and died at Etna, Licking County, on October 22, 1913, at the age of 84, 25 years after his doctor had warned him to move to a dryer climate or face an early death.

Wolfe had sold his spread to Tommy Larson, who later sold it to J. Marv Turnbow and his partners, Lester Walker and Stib Beeson. The old log cabin gradually came to be known as the “Turnbow cabin,” and this name appeared on early maps of the area by the U.S. Geological Survey and on early pamphlets by the National Park Service, partly because Marv Turnbow served as a camphand in 1927 assisting in the first detailed geologic mapping of the area (Dane, 1935, p. 4). In 1947 the ranch was sold to Emmett Elizondo, who later sold it to the Government for inclusion in what was then the monument.

From information supplied by Wolfe’s granddaughter, Mrs. Esther Stanley Rison, and his great-granddaughter, Mrs. Hazel Wolfe Hastler, who visited the cabin in July 1970, the original name Wolfe cabin, or Wolfe Ranch, has been restored, and appears on the newer maps and pamphlets. (See fig. 1.) What remains of Wolfe’s Bar-DX Ranch is shown in figure 3.

Arches National Park is surrounded by active uranium and vanadium mines and by many test wells for oil, gas, and potash; it is underlain by extensive salt and potash deposits. Oil and gas are produced a few miles to the north and east, and potash is being produced about 12 miles to the south (Lohman, 1974).

Uranium and vanadium have been mined on the Colorado Plateau since 1898 (Dane, 1935, p. 176) and in the Yellow Cat area (also called Thompson’s area), just north of the park (fig. 1), since about 1911 (Stokes, 1952, p. 7). The deposits in the Yellow Cat area occur in the Salt Wash Sandstone Member of the Morrison Formation (fig. 4). According to Pete Beroni (U.S. Atomic Energy Commission, oral commun., August 6, 1973), some ore is still being produced in the Yellow Cat area, and the production of vanadium ore will increase as soon as the uranium mill at Moab is converted to also handle vanadium ore. The Corral and so-called Shinarump mines along the southwest side of Moab Canyon just north of Sevenmile Canyon (fig. 1) are still actively producing uranium ore from the Moss Back Member of the Chinle Formation, according to Mr. Beroni.

The occurrences of salt and potash in and near the park and the attempts to find oil and gas nearby are discussed in a recent report (Hite and Lohman, 1973), and the deposits beneath Moab, Salt, and Cache Valleys are discussed in later chapters.

In 1955 and 1956 the Pacific Northwest Pipeline, known also as the “Scenic Inch,” was constructed by the Pacific Northwest Pipeline Corp. to transmit natural gas from wells in the San Juan Basin of northwestern New Mexico for a total of 1,487 miles to the Pacific Northwest, with additional pickups from gas fields in northeastern Utah, northwestern Colorado, and southwestern Wyoming (Walters, 1956). This 26-inch pipeline follows the general route of U.S. Highway 163 from Cortez, Colo., past Moab to Sevenmile Canyon 10 miles northwest of Moab, where it turns abruptly to the northeast and crosses about the middle of Arches National Park. It crosses the park road and the flat area between the Fiery Furnace and the southeast end of Devils Garden, but the scars are so well healed that most visitors are unaware of its existence unless they happen to look southwestward across Salt Valley, where the filled excavation is still visible. The filled trench also appears in the lower middle of figure 23.

Unlike Canyonlands National Park a few miles to the south, Arches was not on the route of the famous early-day river expeditions of John Wesley Powell or of most of those that followed; however, the southeastern boundary of the park is the Colorado River, formerly the Grand, which was traversed by the first leg of the ill-fated Brown-Stanton expedition (Dellenbaugh, 1902, p. 343-369; Lohman, 1974).

The canyon of the Colorado River along the southeastern park boundary is deep and beautiful and is a favorite stretch of quiet water for boaters and floaters. Partly paved State Highway 128 on the east bank is a part of a most scenic drive from Moab to Cisco—a small railroad town about 32 miles northeast of the eastern border of figure 1 (fig. 7). This road has been variously called the “Moab Mail Road,” the “Cisco Cutoff,” the “Dewey Road,” or the “Dewey Bridge Road” after an old suspension bridge (fig. 7) across the Colorado River at the old townsite of Dewey about 12 miles south of Cisco. During the summer this deep colorful canyon may be viewed at night by artificial illumination. Each evening one-half hour after sundown, an 80-passenger jet boat leaves a dock north of the highway bridge, carries passengers several miles upstream, then floats slowly downstream followed by a truck on the highway carrying 40,000 watts of searchlights which play back and forth on the colorful red canyon walls, while the passengers listen to a taped discourse. The entire trip requires about 2 hours.

The spectacular arches and red rocks of Arches and vicinity have been used to advantage in making color movies and color TV shows. Parts of the recent Walt Disney film “Run, Cougar, Run” were filmed beneath Delicate Arch (fig. 43), in Professor Valley of the Colorado River just east of the park (fig. 7), and in other sections of the canyon country.

Ever since military jet aircraft broke the sound barrier, there has been a growing number of protests from concerned citizens, organizations, and National Park Service officials concerning the dangers sonic booms have posed to Indian ruins and delicate erosional forms in our national parks and monuments, such as natural bridges, arches and windows, balanced rocks, and natural spires or towers. Many instances of damaged ruins, roads, erosional forms, and broken windows were reported. My wife and I can vouch for the destructive power of such booms, for in October 1969, while we were having breakfast at Squaw Flat Campground in The Needles section of Canyonlands National Park, a particularly severe blast from a low-flying jet not only violently rocked our jack-supported trailer but broke the windshield of our car.

At Arches National Park, particular fear was felt for Landscape Arch (fig. 53), thought to be the longest natural stone arch in the world, and many a special round trip from headquarters involving 47 road miles and 2 trail miles was made to check on the condition of this arch after especially loud sonic booms were heard. Finally, in April 1972, following a rash of newspaper and magazine articles that spread across the nation, the Secretary of the Air Force put a virtual stop to this danger by ruling that, except in an emergency (Moab Times-Independent, April 12, 1972):

Supersonic flights must not only avoid passing over national parks,
they also may not fly near them, according to the new regulation. For
each 1,000 feet of altitude, the pilot must allow one-half mile
between the flight path and the park boundary. The regulation also
prohibits supersonic flights below 30,000 feet (over land) so the high
speed planes must allow 15 miles between the nearest park boundary and
the flight path.

Let us hope that with the aid of this long-needed regulation and cooperation from visitors, the arches will remain intact for many more generations to see.

Geographic Setting

Geologists have divided the United States into many provinces, each of which has distinctive geologic and topographic characteristics that set it apart from the others. One of the most intriguing and scenic of these is the Colorado Plateaus province, referred to in this report simply as the Colorado Plateau, or the Plateau (Hunt, C. B., 1956, fig. 1). This province, which covers some 150,000 square miles and is not all plateaus, as we shall see, extends from Rifle, Colo., at the northeast to a little beyond Flagstaff, Ariz., at the southwest, and from Cedar City, Utah, at the west nearly to Albuquerque, N. Mex., at the southeast. Arches National Park occupies part of the Canyon Lands Section, one of the six subdivisions of the Plateau. As the names imply, the Canyon Lands Section of the Plateau comprises a high plateau generally ranging in altitude from 5,000 to 7,000 feet, which has been intricately dissected by literally thousands of canyons.

Arches National Park is drained entirely by the Colorado River, whose deep canyon borders the park on the southeast (fig. 1). Most of the park is drained by Salt Wash, which enters the Colorado River just southeast of The Windows section, but the southwestern part is drained by Courthouse Wash and Moab Canyon, whose flows join the Colorado just west of the bridge on which U.S. Highway 163 crosses the river.

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 Arches 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 47.5 miles. This map was prepared from part of the reverse side of a plastic-relief map[4] at a scale of 1:250,000 by the U.S. Army Map Service of the Moab quadrangle, using a simple time- and money-saving method (Stacy, 1962).

Deposition of The Rock Materials

The vivid and varied colors of the bare rocks and the fantastic buttes, spires, columns, alcoves, caves, arches, and other erosional forms of Arches National Park result from a fortuitous combination of geologic and climatic circumstances and events unequalled 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 clay, silt, sand, and gravel carried and deposited by moving water; silt and sand 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 beds were laid down in shallow seas that once covered the area or in lagoons and estuaries near the sea. Other beds were deposited by streams in inland basins or plains, a few were deposited in lakes, and the constituents of deposits like the Navajo Sandstone, were carried in by the wind. The character and thickness of the exposed sedimentary rocks and the names and ages assigned to them by geologists are shown in the rock column (fig. 4) and in the cross section (fig. 8). The history of their deposition is summarized on pages 98-102. Figure 4 was compiled mainly from generalized sections given by A. A. Baker (1933), Dane (1935), McKnight (1940), and Wright, Shawe, and Lohman (1962), and, in part, from Hite and Lohman (1973).

AGE (millions of yrs ago)
GEOLOGIC AGE
NAME OF ROCK UNIT
KIND OF ROCK AND HOW IT IS SCULPTURED BY EROSION
THICKNESS (feet)
NAMED FOR OCCURRENCE AT OR NEAR

100
Late Cretaceous
Mancos Shale
Lead-gray fossiliferous marine shale. Forms slopes.
?
Mancos, Colo.
Dakota Sandstone
Conglomeratic sandstone, gray shale, carbonaceous shale, and
coal. Forms ledge.
100
Dakota, Nebr.
Unconformity
Late Jurassic
Morrison Fm.
700
Morrison, Colo.
Brushy Basin Member
Variegated shale, some sandstone and conglomerate, petrified
wood, chert, and dinosaur bones. May contain some beds
of Burro Canyon (Early Cretaceous) age.
Salt Wash Member
Crossbedded white and gray conglomeratic sandstone beds and
lenses, locally carnotite bearing, and red and gray
sandy mudstone. Forms slopes.
Unconformity
160
San Rafael Group
(San Rafael Swell, Utah)
Summerville Fm.
Thin bedded red sandstone and shale. Some cherty limestone
concretions. Forms slopes.
0-40
Summerville Point, Utah
Entrada Ss.
(Entrada Point, Utah)
Moab Member
White, crossbedded fine-grained sandstone. Caps Slick Rock
Member north of Devils Garden and Fiery Furnace and on
Klondike Bluffs.
0-100
Moab, Utah
Slick Rock Member
Salmon-colored to pink and white fine-grained generally
crossbedded sandstone, containing some medium- to
coarse-grained sand. Generally forms cliffs or narrow
fins many of which contain arches or windows.
0-240
Slick Rock, Colo.
Dewey Bridge Member
Red muddy sandstone and sandy mudstone, with contorted
bedding. Forms easily eroded bases to arches in
Windows Section, hence aided in their development.
0-175
Dewey Bridge, Utah
Unconformity
190
Jurassic and Triassic(?);
Glen Canyon Group
Navajo Sandstone
Massive crossbedded buff, gray, and white fine-grained
sandstone, and local beds of gray limestone. Forms
cliffs along Colorado River, floors Windows Section.
0-350
Navajo Country, Four Corners (Glen Canyon, U.)
Late Triassic(?)
Kayenta Formation
Lavender, gray, and white lenses of sandstone, red sandy
shale, and conglomerate. Contains some freshwater
shells. Caps and protects cliffs of Wingate Sandstone.
0-250
Kayenta, Ariz.
Late Triassic
Wingate Sandstone
Massive, horizontally bedded and crossbedded reddish buff
fine-grained sandstone. Forms vertical cliffs along
Colorado River, Cache Valley, Salt Wash, and
Courthouse Wash.
0-350
Fort Wingate, N. Mex.
200
Chinle Formation
Irregularly bedded buff to red sandstone, red mudstone,
limestone, and conglomerate. Lenticular sandstone and
conglomerate (Moss Back Member) locally at base.
Freshwater shells, petrified wood, reptile bones.
Forms slopes.
0-700
Chinle Valley, Ariz.
Moss Back Ridge, Utah Unconformity
Middle(?) and Early Triassic
Moenkopi Formation
Thin-bedded brown shale, gray and brown sandstone, arkosic
grit, and conglomerate. Crops out on southwest side of
Moab Valley and in several places in Salt and Cache
Valleys. Forms slopes.
0-1,300
Moenkopi Wash, Ariz.
Unconformity
250
Permian
Cutler Formation
Chocolate brown and red sandy shale, maroon and pinkish-gray
arkose and conglomerate. Lower part probably
equivalent in age to Rico Formation in areas to south
and east. Crops out in Moab Canyon west of Moab fault.
Forms slopes.
0-2,500
Cutler Creek, Colo.
Pennsylvanian
Hermosa Formation
Unnamed upper member
Gray marine fossiliferous sandy limestone, gray and
greenish-gray sandstone and sandy shale, and red sandy
shale. Exposed in ledges southwest of Moab fault in
highway cut west of park entrance.
0-1,500
Hermosa Creek, Animas River Valley, Colo.
300
Paradox Member
Salt, gypsum, and anhydrite, with black and gray shale and
limestone. Few exposures in Salt and Cache Valleys.
Forms slopes.
0-11,000
Paradox Valley, Colo.
Unconformity
Pennsylvanian(?)
Unnamed conglomerate
Yellow sandstone with boulders of limestone and chert
containing Mississippian fossils. Exposed at two
places in Salt Valley.
?

Not exposed in the area but present far beneath the sedimentary cover and exposed in several places a few miles to the northeast are examples of the other two principal types of rocks—(1) igneous rocks, solidified from molten rock forced into or above preexisting rocks along cracks, joints, and faults, and (2) much older metamorphic rocks, formed from other preexisting rock types by great heat and pressure at extreme depths. Igneous rocks of Tertiary age (fig. 59) form the nearby La Sal Mountains. The particles comprising the sedimentary rocks in the area were derived by weathering and erosion of all three types of rocks in various source areas.

Arches National Park and nearby Canyonlands National Park are both in the heart of the Canyon Lands Section of the Plateau; therefore, it is only reasonable to wonder why the differences in their general character seemingly outweigh their similarities. First, let us consider the similarities. Both parks are underlain by dominantly red sedimentary rocks, both parks feature unusual erosional forms of sandstone, and both contain beautiful natural arches, although the arches in Canyonlands are restricted almost entirely to the southeastern part of The Needles section and are in much older rocks than those in Arches.

To be sure, differences in the rocks themselves play a part in the dissimilarity of the two parks, and these differences are of two types. First, there are lateral changes in the character of the strata, known to geologists as facies changes, brought about by differences in the environment, in the type of materials, and in the mode of deposition even within relatively short distances. Thus, during parts of the Permian Period while sand, later to be known as the Cedar Mesa and White Rim Sandstone Members of the Cutler Formation, was being deposited in the southern part of Canyonlands, red mud, silt, and sand of the Cutler were laid down farther north in Canyonlands (Lohman, 1974, fig. 9), and similar, though somewhat coarser, beds of the Cutler were laid down at Arches (fig. 4). Further comparisons of the rock columns in the two parks show that while limestones of the Rico Formation were being deposited in a shallow sea in the southern part of Canyonlands, additional red mud, silt, and sand of the Cutler were being laid down above sea level in areas to the northeast. The source of the coarser materials was the ancient Uncompahgre Highland, which stood above sea level from Late Pennsylvanian time to Late Triassic time (figs. 7, 59). Although wider and longer, it occupied about the same position as the present Uncompahgre Plateau between Grand Junction and Gateway, Colo. Streams eroded the hard igneous and metamorphic rocks from this ancient landmass and dumped the material into basins to the northeast and southwest. The basin to the southwest, now called the Paradox basin (after Paradox Valley, Colo.), at intervals contained shallow seas and lagoons, which I will discuss later.

Comparison of the rock columns for the two parks also reveals other differences. Both parks contain exposures of rocks as old as the Pennsylvanian Paradox Member of the Hermosa Formation. However, only in the Horseshoe Canyon Detached Unit of Canyonlands are rocks as young as the Jurassic Entrada Sandstone, whereas all the spectacular natural arches that make Arches famous were formed in the Entrada Sandstone, and Arches also contains several younger formations of Jurassic and Cretaceous age (fig. 4).

A commonly asked question is “Why are most of the rocks so red, particularly those in which the arches were formed?” This can be answered with 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 as sources of iron ore, for the merest trace, generally only 1 to 3 percent, is enough to produce even the darkest shades of red. The white or nearly white Navajo Sandstone and the Moab Member of the Entrada Sandstone contain little or no iron.

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 that most of the sand dunes and sand bars are white or nearly so.

Bending And Breaking of The Rocks

Perhaps the greatest geologic contrast between these two closely adjacent parks lies in their different geologic structure—the kind and amount of bending and breaking of the once nearly flat lying strata. Consolidated rocks, particularly brittle types, are subject to two types of fracturing by Earth forces. Joints are fractures along which no movement has taken place. Faults are fractures along which there has been displacement of the two sides relative to one another (fig. 6). As noted in the report on Canyonlands National Park (Lohman, 1974), the strata there, particularly along the valley of the Green River, are virtually flat lying or have only very gentle dips. Along the Colorado River above the confluence with the Green, however, the slightly dipping strata are interrupted by several gentle anticlinal and synclinal folds (fig. 5) and by at least one fault (fig. 6). The largest of these folds—the Cane Creek anticline, which crosses the Colorado River north of Canyonlands—has yielded oil in the past and is now yielding potash by solution mining of salt beds in the Paradox Member of the Hermosa Formation.

In strong contrast to Canyonlands, Arches National Park contains three northwesterly trending major folds and is bordered on the southwest by a fourth. The largest and most important are the collapsed Salt Valley and Cache Valley anticlines, which separate the two most scenic groups of arches and other erosional forms—Eagle Park, Devils Garden, Fiery Furnace, and Delicate Arch on the northeast, and Klondike Bluffs, Herdina Park, and The Windows section on the southwest. Farther southwest is the Courthouse syncline, containing the attractive group of erosional forms called Courthouse Towers (fig. 1). Finally, near the southwest edge of the park, is the Seven Mile-Moab Valley anticline (also known as the Moab-Spanish Valley anticline), whose southwest limb is cut off by the Moab fault (figs. 7, 23). The folds just named and the sharply contrasting geologic structures of the two parks are well shown on sheet 2 of the geologic map of the Moab quadrangle (Williams, 1964), and the geologic formations are shown in color on sheet 1.

Arches National Park and most of nearby Canyonlands National Park lie within what geologists have termed the “Paradox basin,” which contains a remarkable assemblage of sediments called the Paradox Member of the Hermosa Formation. These deposits were laid down in shallow seas and lagoons during Middle Pennsylvanian time, roughly 300 million years ago (fig. 59). As indicated in figure 4, the Paradox Member contains, in addition to shale and limestone, minerals deposited by the evaporation and concentration of sea water—common salt, gypsum, anhydrite, and potash salts. For this reason such deposits are collectively called evaporites. Figure 7 also shows that the northeastern part of the Paradox basin, which is the deepest part, contains a series of partly alined anticlines which have cores of salt and, hence, are called salt anticlines. As might be expected, roughly alined synclines intervene between the anticlines, but are not shown because of space limitations. According to Cater (1970, p. 50): “The salt anticlines of Utah and Colorado are unique in North America both in structure and in mode of development.” To this may be added that they also are relatively rare in the world.

A section across the Salt Valley anticline and the Courthouse syncline in the northwestern part of the park is shown in figure 8, and the axes of these structures are shown in figure 9.

Normally, a series of roughly parallel northwestward-trending folds would result from shortening of a segment of the Earth’s crust by compressive forces from the northeast and the southwest, but such does not seem to be the origin of these folds. The folds occur in a relatively narrow belt along the northeastern part of the Paradox basin, the deepest part, which was broken by a series of northwesterly trending normal faults (fig. 6) that cut the deep-lying Precambrian and older Paleozoic rocks (fig. 8) prior to the deposition of the salt-bearing Paradox Member of the Hermosa Formation. Movement along these faults continued intermittently during and after deposition of the Paradox, however, and resulted in the formation of a series of northwesterly trending ridges and troughs. Following Paradox time, normal sediments derived from a rising landmass to the northeast began to fill the basin. These sediments accumulated most rapidly and to greater thicknesses in the fault-derived troughs. Salt differs from normal sediments in two properties critical to the development of salt anticlines: first, salt is considerably lighter (fig. 10), and, second, salt under pressure will flow slowly by plastic deformation, much like ice in a glacier flows slowly downstream. Thus, salt in the troughs underlying the thicker and heavier masses of sediments was squeezed into the adjoining ridges, causing them to rise. Once started, this process tended to be self-perpetuating, as the flow of salt from beneath the thick masses of sediments in the troughs made room for the accumulation of still greater thicknesses of normal sediments. Consequently, the troughs receiving most of the sediments began to form downfolds, or synclines, and the ridges receiving little or no normal sediments began to form huge salt rolls that later were to become the cores of the salt anticlines when finally the ridges too were buried by sediments. Thus, the cross section (fig. 8) shows about 12,000 feet of the Paradox Member beneath the crest of the Salt Valley anticline and only about 2,000 feet beneath the Courthouse syncline. Near the middle of these structures farther to the southeast, all the Paradox Member has been squeezed out from beneath the bordering synclines.

The general shape of the Salt Valley anticline is shown also by cross-section _B-B′_ (fig. 10), taken along the northeast-southwest line _B-B′_ in figure 9, which is based upon so-called gravity anomalies over Salt Valley. The lighter Paradox Member, having an average density of 2.20, has a lower gravitational attraction than the heavier rocks on each side, which have an average density of 2.55.

By this time you are doubtless wondering why prominent upfolds of the rocks, such as the Salt Valley anticline and associated Cache Valley anticline and the Seven Mile-Moab Valley anticline, now underlie relatively deep valleys bordered by prominent ridges. The formation of these valleys was not simple and involved many steps extending over a considerable amount of geologic time, as portrayed by Cater (1970, fig. 13; 1972, fig. 4). For a part of the story, let us reexamine the cross section (fig. 8); the rest of the story will be told in the section on “Uplift and Erosion.”

Figure 8 shows that the unnamed upper member of the Hermosa Formation and the overlying Cutler and Moenkopi Formations are thickest beneath the Courthouse syncline but wedge out against the flanks of the anticline. Although the Chinle Formation and younger rocks appear to extend across the fold, and may have extended across this part of the fold, in Colorado all rocks older than the Jurassic Morrison wedge out against the flanks of the salt anticlines (Cater, 1970, p. 35) and also in the widest part of the Salt Valley anticline southwest of the section in figure 8. The salt anticlines were uplifted in a series of pulses so that some formations either were not deposited over the rising structures or were removed by erosion before deposition of the next younger unit. By Morrison time the supply of salt beneath the synclines seems to have become used up; hence, the anticline stopped rising, and the Morrison and younger formations were deposited across the structures. Thus, in figure 4, the minimum thickness of all units older than the Morrison is given as zero. Figure 4 shows the marine Mancos Shale to be the youngest rock unit exposed in the park, but the Mesaverde Group of Late Cretaceous age and possibly the early Tertiary (fig. 59) Wasatch Formation may have been deposited and later removed by erosion.

Uplift And Erosion of The Plateau

Next among the main events leading to the formation of landforms in the park was the raising and additional buckling and breaking of the Plateau by Earth forces partly during the Late Cretaceous but mainly during the early Tertiary. After uplift and deformation, the Plateau was vigorously attacked by various forces of erosion, and the rock materials pried loose or dissolved were eventually 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 one looks down some 2,000 feet to the river from any of the high overlooks farther south, such as Dead Horse Point (Lohman, 1974, fig. 15). Not so apparent, however, is the fact that younger Mesozoic and Tertiary rocks more than 1 mile thick once overlaid this high plateau but have been swept away by erosion. In all, the river has carried thousands of cubic miles of sediment to the sea and is still actively at work on this gigantic earth-moving 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 the sediment 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.

According to Cater (1970, p. 65-67), who made an intensive study of the salt anticlines, collapse of their crests seemingly occurred in two stages—the first stage following Late Cretaceous folding; the second following uplift of the Plateau later in the Tertiary. Solution and removal of salt by ground water played the leading role in the ultimate collapse.

As shown by Dane (1935, pl. 1, p. 121-126), collapse of the Salt Valley and Cache Valley anticlines was accompanied by considerable faulting and jointing, particularly along their northeast sides; by the upward intrusion of two large areas of the Paradox Member of the Hermosa Formation, one just northwest of the park and one in the middle of Salt Valley south of the campground; and by two downdropped masses of rock known to geologists as grabens (pronounced gräbǝns)—one just northwest of the park and one called the Cache Valley graben, which extends both east and west from Salt Wash. The Cache Valley graben has preserved from erosion the youngest rock formations in the park, as shown in figure 11.

The remarkable jointing of the rocks on the northeast limb of the Salt Valley anticline is shown in figure 12. All the arches in this section of the park were eroded through thin fins of the Slick Rock Member of the Entrada Sandstone, and some, like Broken Arch, figure 16, are capped by the Moab Member.

Differences in the composition, hardness, arrangement, and thickness of the rock layers determine their ability to withstand the forces of fracturing and erosion and, hence, whether they tend to form cliffs, ledges, fins, or slopes. Most of the cliff- or ledge-forming rocks are sandstones consisting of sand 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. 4) 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 along the lower reaches of Salt and Courthouse Washes and the Colorado River canyon upstream from Moab consist of the well-cemented Wingate Sandstone protected above by the even harder sandstones of the Kayenta Formation. (See figs. 21, 22.) 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, as shown in figures 19 and 20, the overlying Navajo Sandstone makes up the topmost unit of the cliff.

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

The combination of layers of sediments of different composition, hardness and thickness, the bending and breaking of the rocks, and the desert climate, has produced steep slopes having many cliffs, ledges, and fins with generally sharp to angular edges, rather than the subdued rounded forms of more humid regions.

Origin And Development of The Arches

Among the questions commonly asked by visitors are, “How do arches form?”, “Why are some openings called windows, others arches?”, “What is the difference, if any, between arches or windows and natural bridges, such as those at Natural Bridges National Monument?”, and “How many arches are there in Arches National Park?” Before taking up the origin and development of arches, I shall attempt to explain the differences between the three types of natural rock openings named above and comment upon the number of arches.

I believe most geologists and geographers are in general agreement with Cleland (1910, p. 314) that “a ‘natural bridge’ is a natural stone arch that spans a valley of erosion. A ‘natural arch’ is a similar structure which, however, does not span an erosion valley.” According to this definition, Natural Bridges National Monument includes three true bridges, whereas all the larger rock openings in Arches National Park with which I am familiar are properly termed “arches,” but some are called windows. If we were to distinguish between arches and windows, we might say that arches occur at or near the base of a rock wall, as do the doors of a house or building, whereas windows are found well above ground level. This distinction was not followed in naming the rock openings in the park, however; for example, Tunnel Arch (fig. 14) is considerably higher above the ground than North Window (figs. 37, 38) or South Window (fig. 39).

As to the number of arches in the park, I might begin by saying that there is no universal agreement as to how large a rock opening must be to qualify as an arch. The pamphlet formerly handed to visitors entering the park proclaimed that “Nearly 90 arches have been discovered, and others are probably hidden away in remote and rugged parts of the area,” but the average visitor probably sees less than a third of this number.