THE ROLE OF SALT IN THE

STRUCTURAL DEVELOPMENT OF

CENTRAL UTAH
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The Role of Salt in the Structural 

Development of Central Utah

By TRYING J. WITKIND

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 152

Multiple episodes of diapirism, probably salt-generated, have 

determined the structural pattern of central Utah. The 

causative salt and other evaporites are integral components 

of the Arapien Shale of Middle Jurassic age, one of the most 

unusual stratigraphic units in central Utah

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

Any use of trade, product, or firm names in this publication is

for descriptive purposes only and does not imply endorsement

by the U.S. Government.

Library of Congress Cataloging-in-Publication Data

Witkind, Irving Jerome, 1917-

The role of salt in the structural development of central Utah / by Irving J. Witkind. 

p. cm. (U.S. Geological Survey professional paper ; 1528)

Includes bibliographical references.

Supt. of Docs, no.: I 19.16: 1528

1. Diapirs Utah. 2. Salt domes Utah. 3. Geology, Structural Utah. 4. Geology, 

Stratigraphic Jurassic. 5. Arapien Shale (Utah). I. Title. II. Series. 

QE75.P9 no. 1528 

[QE606.5.U63

557.3 s dc20 92-15520 

[551.8'7] CIP

For sale by USGS Map Distribution

Box 25286, Building 810

Denver Federal Center

Denver, CO 80225
CONTENTS

Abstract........................................................................................

Introduction..................................................................................

Previous work.......................................................................

Current work........................................................................

Physiographic and geologic setting.....................................

Middle Rocky Mountains province ..............................

Southern Wasatch Range.......................................

Colorado Plateaus province..........................................

Wasatch Plateau.....................................................

Sanpete-Sevier Valley area...................................

Basin and Range province ...........................................

Great Basin section................................................

Disturbed zone..............................................................

Definitions.............................................................................

Stratigraphy.................................................................................

General stratigraphy............................................................

The Arapien Shale................................................................

Nomenclature................................................................

Twist Gulch Formation.................................................

Arapien Shale (geologic aspects).................................

Lithology.................................................................

Contact relations....................................................

Lower contact..................................................

Upper contact..................................................

Areal extent............................................................

Arapien embayment and the Arapien basin. 

Contained salt........................................................

Lithology..........................................................

Thickness of salt..............................................

Thickness of Arapien Shale...................................

Page

1

2

Diapiric structures.............................................

Intrusive aspects of the Arapien Shale ....

Minor structures.........................................

Thistle area.........................................

Dome near ancestral Willow Creek... 

Red Knolls area...................................

Cuesta north of Redmond ..................

Hogbacks in eastern Sevier Valley....

Small hill near Ninemile Reservoir... 

Major structures (diapiric folds)................

Sanpete-Sevier Valley diapiric fold...

Red Rocks-Sixmile Canyon area.

Red Rocks area......................

Sixmile Creek canyon area... 

Wales Gap.....................................

Ancestral Willow Creek area.......

Geologic setting.....................

Discussion..............................

Gunnison Reservoir area.............

Redmond diapiric fold.........................

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	Page

Diapiric structures Continued 

Major structures Continued

Sevier Bridge Reservoir diapiric fold .......................... 57

Geologic setting....................................................... 61

Complex structural relations.......................... 61

Anomalous depositional thinning................... 63

Red Canyon area (Valley Mountains)............ 63

Discussion............................................................... 66

First diapiric episode....................................... 66

Second diapiric episode................................... 67

Third diapiric episode ..................................... 67

Levan diapiric fold........................................................ 69

Pigeon Creek area .................................................. 69

Gardner Canyon-Red Canyon area ...................... 70

Gardner Canyon area...................................... 70

Red Canyon area (southern Wasatch Range) 75

Skinner Peaks area......................................... 75

Pole Creek diapiric fold................................................ 77

Geologic setting....................................................... 77

KOA Campground area................................... 77

Middle Fork Pole Creek.................................. 77

Discussion............................................................... 81

Footes Canyon diapiric(?) fold...................................... 81

Dry Hollow diapiric fold............................................... 83

Thistle Creek diapiric(?) fold........................................ 83

Geologic setting....................................................... 83

Charleston-Nebo thrust plate......................... 83

Sedimentary sequence of younger rocks........ 84

Strata north of Spanish Fork Canyon

("Billies Mountain" area)...................... 84

Strata south and west of Spanish Fork

Canyon................................................... 86

Discussion of alternative interpretations ...... 92

Faulted terrain......................................... 92

Diapiric deformation ................................ 92

Hjorth Canyon diapiric fold ......................................... 93

Geologic setting....................................................... 93

Discussion............................................................... 95

Little Clear Creek diapiric fold.................................... 96

Geologic setting....................................................... 96

Discussion............................................................... 96

Fairview diapiric(?) fold................................................ 98

Geologic setting....................................................... 98

Discussion............................................................... 98

West Hills diapiric(?) fold............................................. 100

Geologic setting....................................................... 100

Discussion............................................................... 101

Valley Mountains diapiric(?) fold................................. 101

Geologic setting....................................................... 101

Discussion............................................................... 102

Gravity data.......................................................................... 102

in
IV CONTENTS

Page

Diapiric deformation of the east flank of the Charleston-Nebo 

thrust plate .................................................................. 104

Implications of the tilted strata .................................... 104

Drag along normal fault or faults ......................... 105

Movement along the Wasatch fault zone.............. 105

Uneven compaction of unconsolidated North Horn 

Formation and younger sediments..................... 105

Uplift as a result of salt diapirism........................ 105

Discussion ....................................................................... 105

Depositional thinning............................................................ 107

Sanpete-Sevier Valley diapiric fold .............................. 109

Sevier Bridge Reservoir diapiric fold............................ 109

Pole Creek diapiric fold................................................... Ill

Thistle Creek diapiric fold.............................................. Ill

Discussion........................................................................ Ill

Diapiric processes ...................................................................117

Growth and collapse of diapiric folds.............................117

Growth of diapiric folds...........................................117

Slow upwelling................................................... 119

Rapid, upward, forceful surges.........................119

Diapiric processes Continued

Growth and collapse of diapiric folds Continued

Collapse of diapiric folds ........................................ 119

Paired, facing monoclines ................................ 121

Diapiric stages and episodes.......................................... 124

Geologic pattern.............................................................. 125

Cyclical aspects............................................................... 129

Localization and causative forces ......................................... 129

Economic implications ........................................................... 132

Oil and gas...................................................................... 132

Source beds.............................................................. 132

Mancos Shale.................................................... 132

Manning Canyon Shale.................................... 132

Arapien Shale................................................... 133

Reservoir beds......................................................... 133

Potential traps......................................................... 133

Salt-bearing and younger strata ..................... 133

Pre-salt strata................................................... 134

Overthrust belt and salt diapirs...................... 134

Mineral deposits ............................................................. 135

Summary................................................................................. 135

References cited...................................................................... 138

Index....................................................................................... 142

Page

ILLUSTRATIONS

Page

FIGURE 1. Map showing physiographic provinces in central Utah.............................................................................................................. 3

2. Index map of central Utah............................................................................................................................................................ 4

3. Index map showing sites of geologic maps................................................................................................................................... 7

4. Diagrammatic cross sections showing possible relations between thrust plate and Cretaceous and Tertiary cover............ 10

5. Cross section of diapiric fold ......................................................................................................................................................... 13

6. Photographs showing aspects of the Twist Gulch Formation and the Arapien Shale ............................................................. 17

7. Photograph of gypsum bed in the Arapien Shale, being mined near Nephi............................................................................. 19

8. Map showing distribution of Arapien Shale exposures .............................................................................................................. 22

9. Map showing location of major test wells in central Utah, and their spatial relation to recognized diapiric folds.............. 26

10. Photographs of deformed beds of the Arapien Shale.................................................................................................................. 28

11. Photographs showing intrusive aspects of the Arapien Shale in the Thistle area................................................................... 30

12. Geologic map and cross section of an intrusive mass of Arapien Shale in the ancestral Willow Creek area........................ 31

13. Geologic map of the Red Knolls area ........................................................................................................................................... 32

14. Photographs of features formed as a result of intrusion and uplift by the Arapien Shale ..................................................... 33

15. Geologic map and cross section of an isolated hill near Ninemile Reservoir ........................................................................... 34

16. Map showing distribution pattern of major diapiric folds.......................................................................................................... 36

17. Photographs showing deformation along east flank of Gunnison Plateau ............................................................................... 39

18. Photographs and annotated sketch of Red Rocks area............................................................................................................... 40

19. Geologic map and cross section of Red Rocks area..................................................................................................................... 42

20. Diagrammatic sketches illustrating how Red Rocks area may have evolved........................................................................... 44

21. Geologic map and cross section of Sixmile Creek canyon area, and annotated sketch of north valley wall,

	Sixmile Creek canyon ........................................................................................................................................................... 46

22. Diagrammatic sketches illustrating how Sixmile Creek canyon area may have evolved........................................................ 49

23. Photographs of overturned strata as exposed along east flank of Gunnison Plateau.............................................................. 50

24. Geologic map and cross section near Wales Gap......................................................................................................................... 52

25. Diagrammatic sketches illustrating how Wales Gap area may have evolved .......................................................................... 54

26. Photographs of cuestas in the ancestral Willow Creek area...................................................................................................... 56

27. Geologic map of ancestral Willow Creek area, and diagrammatic sketches illustrating how area may have evolved......... 58

28. Photograph of vertical, semiconsolidated gravels exposed near Gunnison Reservoir.............................................................. 61

29. Photographs of complex geologic relations along northeast flank of Valley Mountains, near Yuba Dam.............................. 62

30. Geologic map of northeast flank of Valley Mountains, and diagrammatic sketches illustrating how area may have

	evolved.................................................................................................................................................................................... 64
CONTENTS V

FIGURE 31. Photograph and annotated sketch of Red Canyon area. Valley Mountains ............................................................................

32. Diagrammatic sketches illustrating how Red Canyon area, Valley Mountains, may have evolved .....................................

33. Geologic map and cross section of Pigeon Creek area ..............................................................................................................

34. Photographs showing overturned fold as exposed in Pigeon Creek area................................................................................

35. Geologic map and cross section of Gardner Canyon-Red Canyon-Birch Creek area, Wasatch Range................................

36. Photograph of overturned fold as exposed in Gardner Canyon ...............................................................................................

37. Photograph of Twin Creek Limestone, Red Canyon, Wasatch Range .....................................................................................

38. Geologic map and cross section of Middle Fork Pole Creek (Pole Creek-Hop Creek area)...................................................

39. Photographs showing geologic relations in and near Middle Fork Pole Creek.......................................................................

40. Photographs of complex geologic relations along Hop Creek Ridge and in Hop Creek .........................................................

41. Geologic map and cross section of Dry Hollow area .................................................................................................................

42. Photograph showing angular unconformity between vertical Indianola beds and near-horizontal North Horn strata as 

	exposed near head of Dry Hollow........................................................................................................................................

43. Diagrammatic sketches illustrating development of Dry Hollow diapiric fold.......................................................................

44. Geologic map and cross sections of Thistle area .......................................................................................................................

45. Photographs of Thistle area showing relations between the Charleston-Nebo thrust plate and an overlying mantle of 

	Cretaceous and Tertiary rocks.............................................................................................................................................

46. Photographs showing Arapien sill intruded into the Twin Creek Limestone, "Billies Mountain"........................................

47. Sketches of two alternative interpretations of geologic relations in Thistle area ..................................................................

48. Geologic map and cross section, Hjorth Canyon area...............................................................................................................

49. Geologic map and cross sections, Little Clear Creek area .......................................................................................................

50. Photographs of landslide and earthflow phenomena along Wasatch front .............................................................................

51. Stereographic pair of vertical aerial photographs showing landslide block on which Mormon temple at Manti is built...

52. Bouguer gravity map of central Utah on which axes of major diapiric folds are superimposed...........................................

53. Photographic overviews of localities adjacent to Charleston-Nebo thrust plate.....................................................................

54. Geologic map of Salt Creek area.................................................................................................................................................

55. Geologic map of Black Canyon area...........................................................................................................................................

56. Geologic map and cross section of Taylor Fork area.................................................................................................................

57. Geologic map and cross section of Red Lake area.....................................................................................................................

58. Geologic map and cross section of Payson Canyon and Bennie Creek area ...........................................................................

59. Geologic map and cross section of Dry Mountain area.............................................................................................................

60. Diagrammatic cross sections illustrating two alternative interpretations of how diapiric folds may fail ...........................

61. Diagrammatic sketches of paired, facing monoclines in Sanpete-Sevier Valley area............................................................

62. Diagrammatic cross sections showing suggested geologic relations along both east and west flanks of Gunnison

	Plateau. ........................................................................................................................................................... ......................

63. Diagrammatic cross sections illustrating pattern of repeated growth and collapse of diapiric folds during three major 

	diapiric episodes ...................................................................................................................................................................

64. Diagrammatic cross section illustrating how extent of erosion can influence interpretation of a geologic pattern............

65. Sketch map of Utah showing alignment of several diapiric folds with major fault zones.....................................................

66. Geologic map and cross sections near "Redmond silver mine" ................................................................................................

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TABLES

Page

TABLE 1. Some stratigraphic units exposed in the Sanpete-Sevier Valley area, central Utah................................................................... 14

2. Some stratigraphic units exposed in the Charleston-Nebo thrust plate, Mount Nebo area, central Utah ................................ 15

3. Correlation chart for some Middle Jurassic formations in central Utah....................................................................................... 20
THE ROLE OF SALT IN THE STRUCTURAL DEVELOPMENT

OF CENTRAL UTAH

By TRYING J. WITKIND

ABSTRACT

Multiple episodes of salt diapirism can explain the complex 

structural history of central Utah. Previous workers in that area 

have ascribed the intense localized deformation between the Colorado Plateaus and the Basin and Range provinces either to multiple episodes of orogeny, or to repeated mobilization of plastic 

mudstones. An alternative interpretation, offered here, is that salt, 

contained within the Arapien Shale of Middle Jurassic age, has 

been moving continuously almost since it was deposited. Some of 

this movement has been a slow upwelling, but at times this slow 

upwelling appears to have been disrupted by sudden and sporadic 

upward surges of the salt during which the calcareous mudstones 

and gypsiferous shaly siltstones of the Arapien have been forced 

upward. They, in turn, have bowed up and folded back the overlying younger sedimentary strata to form elongate, narrow, saltcored anticlines (here termed diapiric folds). These upwarps are 

fan-shaped in cross section, and are as much as 100 kilometers 

(60 miles) long. I view the Arapien Shale, thus, as an intrusive 

sedimentary unit; and the contacts between it and the overlying 

consolidated sedimentary rocks, described by others in the past as 

strip-thrusts or unconformities, I consider as chiefly intrusive.

The salt has surged upward repeatedly, and time and again has 

been removed chiefly by extrusion or dissolution, causing the folds 

to fail. This cyclical growth and subsequent failure of the diapiric 

folds has occurred at least three times; each time the reactivated 

younger folds occupied the same sites and had the same trends as 

the previous older folds. This pattern, involving the growth and 

collapse of discrete diapiric folds, is here called a diapiric episode, 

and each episode is arbitrarily divided into three stages:

1. An intrusive stage during which the salt surges upward and 

forces the Arapien mudstones to deform the overlying sedimentary 

rocks into a diapiric fold.

2. An erosional stage during which the removal of the salt results 

in failure of the fold. Subsequent erosion removes the collapsed 

and brecciated remnants of the fold leaving a widespread surface 

of low relief.

3. A depositional stage during which younger sediments are 

deposited across this newly cut surface.

As the sedimentary units either wedge out or thin along the 

flanks of these folds, it is probable that the salt, during this stage, 

was slowly rising and gradually forcing up the overlying strata to

form a barrier in essence, a paleo-high. In those localities where 

the sedimentary units pass over the crests of the folds, the strata, 

invariably, are anomalously thin and represent the youngest parts 

of the formations. Seemingly, the slowly growing barrier was not 

high enough to block deposition completely, but was able to restrict 

it. The depositional stage ends with a renewed surge of salt, marking the intrusive stage of the next diapiric episode.

This repeated movement of the Arapien suggests that it has different "ages." Its depositional age is Middle Jurassic; it contains 

Middle Jurassic fossils. It has several emplacement ages different 

geologic ages of movement each reflecting an upward surge of 

salt.

Although tenuous evidence suggests that the first major diapiric 

episode occurred prior to Late Cretaceous time, possibly during the 

Late Jurassic, the earliest recognizable diapiric episode began in 

Late Cretaceous time and probably extended into the early Paleocene. A second episode began then and lasted into the late(?) Oligocene, or possibly the Miocene. The third major episode began in 

the late(?) Oligocene (or Miocene) and persisted into the Pliocene 

or Pleistocene. A minor diapiric episode may have occurred during 

the late Pliocene or Pleistocene; if so, this implies that the salt 

diapirs that underlie the area may still be active.

I recognize 13 major diapiric folds; of these, many of the smaller 

folds appear to branch off the larger ones much as distributary 

streams branch off a major stream. The longest fold appears to be 

the Sanpete-Sevier Valley diapiric fold, which extends northeastward at least 100 kilometers (60 miles) from near Richfield on the 

south to beyond Fountain Green on the north. Its core, exposed 

along the east side of Sevier Valley as a continuous belt of Arapien 

mudstones, is concealed northward beneath the alluvial fill of Sanpete Valley. The Redmond fold, which seems to branch off the 

south end of the Sanpete-Sevier Valley fold, extends northward 

about 50 kilometers (30 miles) from near Sigurd on the south to 

near Gunnison on the north. The Levan diapiric fold, possibly the 

northern extension of the Redmond fold, is about 40 kilometers (25 

miles) long, and extends northward along the west flank of the 

Gunnison Plateau. The Levan fold starts near Little Salt Creek; at 

Salt Creek, near Nephi, the fold appears to split into three 

branches. The western branch, for which I retain the name Levan 

fold, extends northward and passes beneath and deforms the
SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

Charleston-Nebo thrust plate. The eastern branch, known as the 

Pole Creek diapiric fold (probably about 25 kilometers (15 miles) 

long), extends northeastward and has determined the structural 

pattern of Cedar Hills; this branch is probably continuous with the 

Dry Hollow diapiric fold, of which only about 6 kilometers (4 

miles) is exposed near Thistle. The middle branch, which I call the 

Footes Canyon fold, is concealed for the most part but possibly is 

about 45 kilometers (27 miles) long. It may extend along and 

deform the east flank of the Charleston-Nebo thrust plate. The 

Sevier Bridge Reservoir fold extends northwestward about 24 kilometers (15 miles) from near Fayette to near Yuba Dam. Probably 

the Sevier Bridge Reservoir fold is an offshoot of the Redmond fold.

Other large diapiric folds are partly exposed in the IndianolaThistle area; Little Clear Creek follows the crest of a fold that I 

refer to as the Little Clear Creek fold, which is about 20 kilometers 

(12 miles) long. Another fold, the Hjorth Canyon fold, which I estimate to be about 10 kilometers (6 miles) long, crops out in Hjorth 

Canyon, and still a third fold, the Thistle Creek fold (about 20 kilometers (13 miles) long), is near the junction of Thistle and Soldier 

Creeks. The Thistle Creek fold may be the northern extension of 

the Footes Canyon fold. Tenuous evidence suggests that another 

diapiric fold (Fairview diapiric(?) fold) underlies the eastern fork 

of Sanpete Valley, extending northeastward from near Ephraim to 

near Indianola. This fold may be as long as 40 kilometers (25 

miles). Other diapiric folds may underlie the Valley Mountains 

(Valley Mountains diapiric(?) fold, about 30 kilometers (19 miles) 

long), and the West Hills, the southern extension of Long Ridge 

(the West Hills diapiric(?) fold; about 18 kilometers (11 miles) 

long).

Arapien mudstones have deformed the eroded upper plate of the 

Charleston-Nebo thrust fault, which forms the southern Wasatch 

Range. In places, they have intruded and broken the thrust plate; 

elsewhere they have bowed it up and arched it. This upper plate, 

known as the Charleston-Nebo thrust plate, is the lower limb of an 

overturned, almost recumbent anticline; most of the strata, thus, 

are overturned.

Collapsed diapiric structures, almost certainly salt-controlled, 

are along the southwest flank of the Gunnison Plateau between 

Mellor and Timber Canyons. A small salt plug probably underlies 

the westward-trending transverse graben that lies along the east 

margin of the Gunnison Plateau between Dry and Maple Canyons.

The trends of the diapiric folds appear to parallel the major tectonic lineaments, implying some form of structural control. Such 

control is emphasized by the striking linearity of the diapiric folds 

and their great lengths; two folds are collinear with major fault 

zones. Moreover, the cyclical nature of the diapirism also hints at 

some form of structural control the same sequence of diapiric episodes can be recognized in many widely separated exposed folds. 

This suggests that the diapirism is regional in extent, and that all 

diapirs in the area were reactivated, not only repeatedly, but more 

or less in unison.

I propose that the salt, under static load, was triggered into 

movement by reactivation of old well-established faults. The salt, 

presumably, was deposited in a Middle Jurassic saline Arapien 

basin that overlay preexisting, deep-seated, fundamental faults. As 

the salt was buried ever more deeply beneath younger sediments, 

it was placed under increasing static load. When these ancient 

faults reactivated, probably in response to regional compressive 

forces the Sevier orogeny in pre-Paleocene time and extensional 

forces from late(?) Oligocene time on, they broke through both the 

salt and the overlying beds. The salt and accompanying mudstones, under great confining load, sought relief by surging up the 

newly formed fault planes, using them as conduits. As a result, 

these parts of the fault planes were obliterated and in their place 

were formed a series of long, linear, fan-shaped diapiric folds, the

trends and extent of which reflect the trends and extent of the 

buried faults. Subsequent reactivation of these same ancient faults 

resulted in renewed movement of the salt and mudstones; predictably the younger diapiric folds followed the same trends and occupied the same sites as the older folds.

As a result of the repeated episodes of salt diapirism, there 

appears to be a contrast in structural style between an upper 

sequence of salt-bearing and younger rocks and a lower sequence 

of older pre-salt rocks. The upper sequence is intensely deformed 

by the repeated episodes of salt movement; the lower sequence, 

essentially uninfluenced by the salt, may not be as intensely 

deformed.

This division of the sedimentary stack into two structurally distinct sequences, as well as the type of structural deformation 

involved, implies that each sequence may contain specific types of 

potential oil and gas traps. Potential traps in the intensely 

deformed (salt-bearing and younger) beds would coincide closely 

with the salt walls and the upthrust masses of the Arapien. Potential traps in the pre-salt strata would include structures of various 

sizes and shapes that resulted from a variety of orogenic (compressive) forces; such structures may well be wholly unrelated to those 

formed in the salt-bearing and younger beds.

Possible source rocks for oil and gas include the Mancos Shale 

of Late Cretaceous age, the Manning Canyon Shale of Pennsylvanian and Mississippian age, and the Arapien Shale of Middle 

Jurassic age. Of these, however, the Mancos Shale probably 

extends no farther west than a north-trending line through Wales, 

the Manning Canyon Shale is probably supermature, and the 

Arapien Shale is submature.

Suitable reservoir rocks include the Ferron Sandstone Member 

of the Mancos Shale, and various sandstone beds in the Emery 

Sandstone Member of the Mancos Shale of Late Cretaceous age. 

Degree of fracturing may be more important than inherent primary porosity in determining which units are good reservoir rocks.

Mineral deposits, mainly zinc, were probably derived from 

saline solutions that appear to have been localized along the contacts between the intrusive Arapien Shale and the country rocks.

INTRODUCTION

A broad, ill-defined zone, commonly referred to as a 

transition zone, trends southward through central 

Utah, separating the Colorado Plateaus province from 

the Basin and Range province (fig. 1). Within this 

zone, the stratigraphic units, for the most part, are 

but gently to moderately folded; locally, however, they 

are tilted into vertical or overturned attitudes, and 

form belts of unusual structural complexity. Commonly these structurally complex belts are linear and 

narrow; some extend for many kilometers. Striking 

angular unconformities abound within these complex 

belts, and in places, several such unconformities are 

exposed in a single outcrop. Surprisingly, these unconformities do not persist for long distances perpendicular to the structurally complex belts. Strata that are 

separated by an angular unconformity, when traced 

away from these belts, rapidly approach parallelism 

and commonly become conformable in distances as 

short as three-fourths of a kilometer (V2 mi). These 

singularly complex areas tend to coincide with
INTRODUCTION

elongate, northward-trending upwarps that dominate 

the area. Where exposed within these structurally 

complex areas, an entire sequence of stratigraphic 

units thins anomalously toward the crest of one of 

these upwarps, and locally some units in the sequence 

pinch out against the flanks of the upwarp.

This unusual structural and stratigraphic complexity has attracted geologists since the days of Gilbert 

and Button, and its fascination stems in large part 

from the fact that the field evidence lends itself to 

conflicting interpretations. Many workers, both past 

and present, attribute this localized deformation 

either to multiple episodes of orogeny (Spieker, 1946, 

1949; Standlee, 1982; Lawton, 1985; Villien and Kligfield, 1986), or to mobilization of the plastic mudstone beds of the Middle Jurassic Arapien Shale 

(Gilliland, 1963). I believe, however, that much of the

complexity stems from multiple episodes of salt 

diapirism in essence, the repeated growth and collapse of salt-cored anticlines (here called diapiric 

folds). These folds, of prime importance, have determined both the local and regional structural framework of this sector of central Utah. Major geologic 

misconceptions are inevitable unless one grasps their 

significance. Nearly a half-century ago, Stokes (1952, 

p. 961), referring to salt-generated structures of the 

Sanpete-Sevier Valley area, wrote: "Caution is suggested in interpreting strong local structures of the 

sort found in these areas [central Utah] as evidence 

for orogenic activity." I concur in the strongest possible way.

The causative rock salt (halite) is contained within 

the Arapien Shale of Middle Jurassic depositional 

age, and I propose that upward, near-vertical, local

Approximate west 

margin of transition 

zone

Approximate east 

margin of transition 

zone

110°DO'

100 KILOMETERS 

I

50 MILES

FIGURE 1. Physiographic provinces in central Utah. Parts of three major physiographic provinces 

meet in central Utah the Colorado Plateaus on the east, the Basin and Range on the west, and 

the Middle Rocky Mountains, represented by the southward-pointing wedge of the southern 

Wasatch Range, on the north.
SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH
INTRODUCTION

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SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

FIGURE 2 Continued. Locality file for index map of central Utah

Name

Ancestral Willow Creek 

Arapien Valley 

Aurora 

Axhandle Canyon

Birdseye 

Burrville

Canyon Mountains

Castle Dale

Castle Gate

Castle Valley

Cedar Hills

Centerfield

Chicken Creek Reservoir

Clawson

Cleveland

Colton

Deep Creek 

Dividend 

Dry Canyon 

Dry Hollow

East Tintic Mountains

Elsinore

Ephraim

Eureka

Fairview 

Fayette 

Ferron

Footes Canyon 

Fountain Green 

Freedom

Gardner Canyon

Gilson Mountains

Glenwood

Goshen

Gunnison

Gunnison Plateau (San Pitch Mountains)

Gunnison Reservoir

Helper 

Hiawatha 

Hjorth Canyon 

Huntington

Indianola

Joes Valley

Joes Valley Reservoir

Joseph

Juab Valley

Kenilworth

KOA Campground

Koosharem

Lake Fork

Levan

Little Clear Creek

ral Utah.

ocation

G-3

G-3

H-2

D-3

A-4

J-3

E-l

F-7

B-8

E-7

B-4

F-3

D-2

F-7

E-8

B-7

D-3

A-2

E-3

A-5

B-l

1-1

E-4

A-l

C-5

F-3

G-6

B-3

C-4

D-4

B-3

C-l

T-9 L £4

A-2

F-3

D-3

F-3

C-8

D-7

A-5

E-7

B-5

E-6

E-6

J-l

C-2

C-8

B-3

T 9 t) &

A-5

C-3

B-5

FIGURE 2 Continued. Locality file for index map of ce

Name

Little Salt Creek

Loafer Mountain

Long Ridge

Manti

Maple Canyon (Northeast flank-Gunnison Plateau)

Maple Canyon (Southeast flank-Gunnison Plateau)

Mayfield

Mellor Canyon

Middle Fork Pole Creek

Milburn

Mona

Monroe

Moroni

Mount Nebo

Mount Pleasant

Musinia Peak

National

Nebo Creek

Nephi

Oak Creek

Orangeville

Painted Rock Canyon

Pavant Range

Pigeon Creek

Pole Creek

Price

Price River

Red Canyon (Valley Mountains)

Red Canyon (Wasatch Range)

Red Rocks

Redmond

Richfield

Rock Canyon

Round Valley

Salina

Salina Canyon (Salina Creek Canyon)

Salt Creek

Sanpete Valley

San Pitch Mountains (Gunnison Plateau)

San Pitch River

Santaquin

Scipio

Scipio Lake

Scipio Valley

Scofield

Scofield Reservoir

Sevier Bridge Reservoir (Yuba Lake)

Sevier Plateau

Sevier River

Sevier Valley

Sigurd

Silver City

Sixmile Canyon (Sixmile Creek canyon)

Soldier Creek

ntral U

Locatioi

D-3

A-4

B-2

E-4

C-4

E-3

F-3

E-3

B-4

B-5

B-3

J-l

D-4

B-3

D-5

G-4

C-7

B-4

B-3

C-5

F-7

E-2

H-l

C-3

B-4

C-8

B-8

E-2

B-3

F-3

G-3

1-1

E-3

F-2

G-3

H-3

B-3

E-4

D-3

E-4

A-3

F-l

F-2

E-l

B-6

B-6

E-2

J-2

1-2

G-2

H-2

A-l

F-4

A-5
INTRODUCTION

FIGURE 2 Continued. Locality file for index map of central Utah

Name

South Valley (Valley Mountains)

Southern Wasatch Mountains (Wasatch Range)

Spring City

Spring Glen

Sterling

The Washboard 

Thistle 

Thistle Creek 

Timber Canyon 

Twelvemile Creek

Valley Mountains

Valley Mountains monocline

Wales

Wales Gap

Wasatch monocline

Wasatch Plateau

Wasatch Range (Southern Wasatch Mountains)

Washboard, The

Wattis

West Hills

White Hills

Willow Creek

Yuba Dam

Yuba Lake (Sevier Bridge Reservoir)

Location

G-2 

A-3 

D-5

C-8 

F-4

D-2 

A-5 

A-4 

E-3 

F-3

G-2 

G-2

D-4 

D-4 

E-5 

F-5 

A-3 

D-2 

D-7 

D-2 

G-3 

G-3

E-2 

E-2

movements of the buried salt are ultimately responsible for the intense deformation. I am much 

impressed by the striking similarities between the 

salt-generated features exposed in the Paradox Basin 

of southwestern Colorado and southeastern Utah and 

almost identical features exposed in this sector of 

central Utah (fig. 2). Stokes (1982), similarly 

impressed, has proposed the name "Arapien basin" 

for this salt-rich sector of central Utah.

In this Professional Paper, I bring together many 

of the data and views that I have published elsewhere, either as articles in scientific journals or as 

descriptive textual material accompanying geologic 

maps. This report is thus a synthesis in essence, a 

comprehensive discussion in one publication of my 

views on the role of salt in the structural evolution of 

central Utah. It might ease the burden of searching 

for and digging out the pertinent literature even for 

those who have ready access to modern, well-stocked 

geologic libraries.

Locations mentioned in the text are keyed to 

figure 2, the index map of central Utah, by an 

arbitrary grid placed on the map. Figure 3 

shows those areas for which geologic maps have been 

prepared.

20 3D KILOMETERS

20 MILES

FIGURE 3. Index map of central Utah showing locations of all 

geologic maps discussed in this report, listed by illustration 

number. Figure 12, Intrusive mass of Arapien Shale; 13, Red 

Knolls area; 15, Hill near Ninemile Reservoir; 19, Red Rocks 

area; 21, Sixmile Creek canyon area; 27, Ancestral Willow 

Creek area; 30, Northeast flank of Valley Mountains; 33, 

Pigeon Creek area; 35, Gardner Canyon-Red Canyon area, 

Wasatch Range; 38, Middle Fork Pole Creek; 41, Dry Hollow 

area; 44, Thistle area; 48, Hjorth Canyon area; 49, Little 

Clear Creek area; 54, Salt Creek area; 55, Black Canyon area; 56, Taylor Fork area; 57, Red Lake area; 58, Payson Canyon and Bennie Creek area; 59, Dry Mountain area. Base 

from Grand Junction (T-3) Sectional Aeronautical Chart, 

U.S. Coast and Geodetic Survey (1954, rev.).
SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

PREVIOUS WORK

Stokes, in two perceptive abstracts (1952, 1956), 

first advanced the possibility that the growth and 

collapse of salt structures might be significant in the 

structural development of central Utah. Regrettably, 

he never fully developed his views in the published 

literature. Because the evidence, on the whole, is 

inconclusive, Stokes' views initially failed to gain 

much acceptance. As the search for oil in central 

Utah led to more and more exploratory drilling, the 

extent of the Arapien salt became evident, and the 

importance of salt diapirism in the structural development of central Utah was again emphasized by 

Christiansen (1963), Eardley (1969), Moulton (1975), 

and Baer (1976). Baer, in particular, stressed the 

importance of periodic diapirism in the area, noting 

that diapirism seemingly had persisted from the Cretaceous through the Pleistocene, and he attributed 

much of the structural deformation in central Utah 

to this diapirism. The diapiric concept has gradually 

gained adherents, and additional papers by workers 

in central Utah have added to our knowledge. Runyon (1977a; 1977b) described collapsed diapirs near 

Indianola. Hawks (1980) described several diapiric 

localities in the Cedar Hills, and Taylor (1980) has 

attributed the deformation in the Sterling area to 

diapirism. Recently Picard (1980) discussed the 

stratigraphy and petrography of the Arapien Shale, 

and speculated about the origin of this salt- and 

evaporite-rich unit. Hansen (1976) suggested that the 

beds of salt in central Utah are but part of a much 

larger Jurassic evaporite belt that extends from 

southeast Arizona to southeast Idaho.

CURRENT WORK

I began work in central Utah in 1977 as part of the 

U.S. Geological Survey's Coal Exploratory Program. 

By 1979 I had become convinced that salt had 

played, and continues to play, a dominant role in the 

structural evolution of central Utah. My views have 

been offered in a series of maps and papers published 

in various guidebooks and journals (Witkind, 1981, 

1982, 1983, 1986, 1987, 1988, 1992; Sprinkel, Witkind, and Baer, 1982; Witkind and Page, 1984; Witkind, Weiss, and Brown, 1987, and Witkind and 

Marvin, 1989). Those who oppose the salt-diapiric 

concept question whether the vast amounts of salt 

called for by that concept ever did underlie central 

Utah (Standlee, 1982, p. 376-377).

The existence of concealed salt diapirs in central 

Utah is inferred to some extent from test-well data, 

but chiefly from the shapes of the minor and major

landforms that extend across this sector of Utah. 

Although the area has been crisscrossed repeatedly 

by seismic surveys, all the resultant reflection profiles are proprietary. Chevron USA, Inc., has been 

kind enough to permit me to examine some of their 

seismic profiles that cross the Wasatch Plateau and 

the Sanpete Valley area. The general structural pattern reflected by various of the reflection profiles is 

perhaps best described as upturned Cretaceous beds 

overlain by downturned Tertiary strata a pattern 

displayed in many surface exposures (p. 121).

PHYSIOGRAPHIC AND GEOLOGIC SETTING

This sector of central Utah includes parts of three 

major physiographic provinces: the Middle Rocky 

Mountains, the Colorado Plateaus, and the Basin and 

Range (fig. 1). A broad north-trending lowland formed 

by the collinear alignment of three major valleys 

Utah, Juab, and Sevier Valleys effectively divides 

the area into two unequal sectors. Parts of both the 

Middle Rocky Mountains and Colorado Plateaus provinces are east of the lowland; the Basin and Range 

province is wholly west of the lowland.

MIDDLE ROCKY MOUNTAINS PROVINCE

SOUTHERN WASATCH RANGE

The north-trending Wasatch Range, one of the 

great mountain masses of Utah, extends for about 

240 km (150 mi) from near the Idaho border into central Utah. The south half of the range is formed by 

the upper plate of a thrust fault that I refer to as the 

Charleston-Nebo thrust fault. Other geologists, notably Bruce Bryant (U.S. Geological Survey, written 

commun., 1989), have objected to this coupling of 

what they perceive to be two separate thrust faultsthe Charleston and the Nebo thrust faults. Bryant 

believes that my Charleston-Nebo upper plate is 

divisible into two parts a lower segment that is the 

upper plate of the Charleston thrust fault, and an 

upper segment that is the upper plate of the Nebo 

thrust fault. In Bryant's view, then, the Nebo thrust 

fault is an upper split off the Charleston thrust fault, 

and the Nebo fault dies out in the area northeast of 

Nephi (fig. 2, B-3) and southwest of Thistle (A-5).

I disagree with Bryant's interpretation. The stratigraphic units that I have mapped as part of the 

upper plate of the Charleston-Nebo thrust fault can 

be traced northeastward to Thistle where they join 

similar units that are part of the upper plate of the 

Charleston thrust fault. Neither the Nebo nor the
INTRODUCTION

Charleston thrust fault is exposed in the sector 

between Nephi and Thistle. Consequently, I am 

uncertain not only as to how many thrust faults 

underlie the area, but also as to where the fault(s) 

end (fig. 4). I believe that the Nebo thrust fault 

trends northeastward and eventually merges with 

the Charleston thrust fault; hence my use of the 

terms "Charleston-Nebo thrust fault" and "upper 

plate of the Charleston-Nebo thrust fault."

This upper plate of the Charleston-Nebo thrust 

fault, which reaches from near Salt Lake City southward to Nephi (B-3) (fig. 2, inset map), consists of a 

mass of basin-type rocks, at least 9,150 m (30,000 ft) 

thick (Crittenden, 1961) that was transported southeastward and eastward along the Charleston-Nebo 

thrust fault. How far the plate moved is unknown; 

various lines of evidence suggest a displacement of 

about 65 km (40 mi) (Crittenden, 1961, p. D-129).

Very generally, this upper plate can be divided into 

two segments: A northern part, east of Provo, that 

extends as far south as Spanish Fork Canyon; and a 

southern part, a wedge-shaped, imposing mountain 

range known locally as the southern Wasatch Mountains (or the southern Wasatch Range), that extends 

southward from Spanish Fork Canyon to Nephi (B-3). 

The extent of the plate south and west of Nephi is less 

certain, owing to basin and range structures. Part of 

the plate may be preserved west of Juab Valley (C-2), 

near the south end of Dog Valley (C-2), along the 

northwest flank of the West Hills (C-2). An erosional 

outlier near Levan (C-3) may be still another part of 

the plate (Witkind, 1983, p. 49). Morris (1983, p. 77) 

has suggested, however, that near Nephi the causative, underlying Charleston-Nebo thrust fault may 

merge with the Leamington transcurrent fault.

The southern Wasatch Mountains now appear as 

the huge, intensely dissected east limb of an overturned, almost recumbent anticline. At the north end 

of the mountains, near Santaquin (A-3), the beds are 

right side up and dip moderately southeastward. Farther south the beds steepen, and near Mona (B-3), 

they are vertical. Still farther south, at the south end 

of the mountains, near Nephi, the beds are overturned and dip moderately to the northwest. The 

Wasatch fault zone truncates the west edge of the 

mountains, which thus appears as a straight, commanding escarpment overlooking Juab Valley. The 

east margin of the mountains which I view as an 

erosional escarpment cut across the Charleston-Nebo 

thrust plate is much less imposing, chiefly because 

it has been extensively eroded and then partly buried 

beneath younger Mesozoic and Tertiary rocks (Witkind, 1987). This erosional escarpment, which 

extends northeastward from Nephi toward Thistle

(A-5), may be the distal margin of the thrust plate 

(fig. 4B), or the distal margin may be concealed 

somewhere to the east beneath younger Mesozoic and 

Tertiary strata (fig. 4C). Near Thistle, the attitude of 

the beds that form the thrust plate in the subsurface 

is conjectural; they may be overturned.

COLORADO PLATEAUS PROVINCE

The terrain south and east of the southern 

Wasatch Mountains, and east of the lowland formed 

by the collinear alignment of Utah, Juab, and Sevier 

Valleys, is within the Colorado Plateaus province. I 

arbitrarily divide the area into two parts: the huge 

mass of the Wasatch Plateau, and the remainder to 

which I apply the well-established name SanpeteSevier Valley area.

WASATCH PLATEAU

The Wasatch Plateau, the northernmost of the 

High Plateaus of Utah, is a flat-topped mass about 

130 km (80 mi) long that extends from Salina Creek 

Canyon (fig. 2, H-3) on the south to the valleys of 

Soldier Creek (A-6) and Price River (B-8) on the 

north. The plateau trends about N. 20° E., maintaining a nearly constant width of about 40 km (25 mi), 

and an altitude of about 3,050 m (10,000 ft). It separates Sanpete Valley (E-4) on the west from Castle 

Valley (E-7) on the east.

The plateau is underlain by flat-lying Cretaceous 

and Tertiary beds, most of which are well exposed in 

the dissected cliffs that delineate its eastern flank. 

These strata flex down sharply along much of the 

western flank of the plateau to form the Wasatch 

monocline (E-5). The monocline, about 100 km (62 mi) 

long, extends northward from Salina Creek Canyon 

(H-3) to its end, north of Milburn (B-5) and east of 

Indianola (B-5), near the north end of the east fork of 

Sanpete Valley. Westward-flowing consequent streams 

on the monocline have locally cut through the tilted 

beds, exposing them along the walls of deep, serpentine canyons that extend far back toward the crest of 

the plateau. Much of the plateau and the monocline 

are broken by high-angle normal faults that trend 

between due north and about N. 20° E. and that 

locally are paired to form grabens.

SANPETE-SEVIER VALLEY AREA

The term "Sanpete-Sevier Valley area" refers to 

an ill-defined area drained by both the southflowing San Pitch River and the lower reaches of 

the north-flowing Sevier River. Over the years the
10 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

WEST EAST

Erosional 

escarpment

Tertiary and

Cretaceous

sedimentary and

volcanic rocks

CHARLESTON-NEBO 

ALLOCHTHON

(chiefly Paleozoic 

strata)

Autochthon

WEST

Erosional 

escarpment

EAST

Tertiary and

Cretaceous

sedimentary and

volcanic rocks

CHARLESTON-NEBO 

ALLOCHTHON

HARLESTON-NEBO 

THRUST FAULT

B

Autochthon

WEST EAST

Tertiary and

Cretaceous

sedimentary and

volcanic rocks

CHARLESTON-NEBO 

ALLOCHTHON

(chiefly Paleozoic 

strata)

Distal margin of allochthon concealed 

beneath sedimentary and volcanic 

cover (beyond illustration)

Autochthon

"CHARLESTON-NEBO 

THRUST FAULT

FIGURE 4. Diagrammatic cross sections illustrating possible relations between an eastward-facing erosional escarpment formed 

on the Charleston-Nebo thrust plate and a partial cover of Cretaceous and Tertiary rocks. Escarpment was formed as the plate 

was thrust eastward. A, After eroded plate ground to a halt, 

sedimentary units of Cretaceous and Tertiary age, as well as 

some Tertiary volcanic units, were deposited against it, and in 

time may even have buried the entire plate. B, Erosional escarpment is at the distal margin of eroded thrust plate. C, Erosional 

escarpment is along east flank of eroded thrust plate but not at 

distal margin, which is farther to the east concealed beneath the 

Cretaceous and Tertiary cover. B and C represent two possible 

alternatives to explain present geologic relations. Both alternatives are viable; lack of data precludes a definitive statement as 

to position of the thrust plate's distal margin.

name San Pitch derived from the name Sam Pete, 

a local Indian has been garbled to Sanpete (M.P. 

Weiss, Northern Illinois University, oral commun., 

1989), and this latter name is applied to the valley 

occupied by the San Pitch River. The SanpeteSevier Valley area has figured prominently in the 

geologic literature describing central Utah, and 

although certain localities in central Utah discussed 

in this report extend beyond the generally accepted 

limits of the Sanpete-Sevier Valley area, the name 

is so well known that I have used the name for the 

larger area.

In general, the Sanpete-Sevier Valley area appears 

as a series of north-trending plateaus and low hills, 

considerably lower than the adjacent Wasatch Range. 

Among the major landmasses in the Sanpete-Sevier 

Valley area are the Gunnison Plateau (D-3) (also 

known as the San Pitch Mountains), 1 the Cedar Hills 

(B-4), and the Valley Mountains (G-2).

Jurassic, Cretaceous, and Tertiary sedimentary 

strata underlie the Sanpete-Sevier Valley area. 

Locally, these units are overlain by layered volcanic 

rocks and volcaniclastic detritus of Tertiary age. 

Commonly, both the sedimentary strata and the volcanic units are gently warped, to form broad folds 

that are broken, in places, by small high-angle normal faults. Here and there, however, these strata are 

complexly deformed into narrow elongate belts that 

trend northward.

lrThe range of hills known to geologists as the "Gunnison Plateau" is known 

to governmental agencies as the "San Pitch Mountains." Indeed, the latter 

name is used on published topographic maps of the U.S. Geological Survey. 

Nevertheless, the name Gunnison Plateau is so deeply entrenched in the geologic literature, chiefly as a result of the reports of the late Prof. E.M. Spieker 

and his many Ohio State University graduate students, that the name is 

retained and used throughout this report to avoid confusion.
INTRODUCTION 11

BASIN AND RANGE PROVINCE

GREAT BASIN SECTION

The Great Basin section is an arid lowland that 

ends abruptly eastward against the north-trending 

lowland formed by the collinear alignment of Utah, 

Juab, and Sevier Valleys. The abrupt change is 

emphasized by the impressive topographic high 

formed by the combined masses of the southern 

Wasatch Range (A-3) and the Gunnison Plateau (D-3) 

along the east side of the lowland. This abrupt topographic change is directly attributable to movement 

along the Wasatch fault zone, a major high-angle normal fault zone that trends northward across this part 

of central Utah, and along which the crustal block 

west of the fault zone has been downthrown relative 

to the block east of the fault zone.

The Great Basin sector consists of a series of 

thrust slices, composed chiefly of Precambrian and 

Paleozoic rocks. These thrust slices were deeply 

eroded during transport and after being emplaced, 

then buried beneath younger rocks, and broken by 

block faulting. Much of our knowledge of the Great 

Basin sector within this part of central Utah comes 

from two major mountain ranges that dominate the 

area: the Canyon Mountains (E-l), on the north, 

which have been described by Campbell (1979), 

Christiansen (1952), and Stolle (1978); and the 

Pavant Range (H-l) on the south, which has been 

described in part by Crosby (1959), and Lautenschlager (1952). As this discussion of diapirism in 

central Utah is confined chiefly to areas east of these 

ranges, no summary description is given here of the 

units that form them.

DISTURBED ZONE

Previous workers have suggested that the SanpeteSevier Valley area is best visualized as a transition 

zone between the Basin and Range province on the 

west and the Colorado Plateaus province on the east 

(Spieker, 1949). I suggest instead that although a 

zone does separate the two provinces, that zone is not 

a true transition zone in which features of one province gradually give way laterally to features of the 

adjacent province. Rather, I see the area between the 

two provinces as a disturbed zone marked by 

unusual, almost unique structural features that, for 

the most part, are foreign to both provinces. So, for 

example, the zone is unusual in that, in places, it is 

marked by both localized depositional thinning and

complex structural deformation. Elongate, northwardtrending upwarps huge upthrown masses of sedimentary rock dominate the zone, yet comparable 

downwarps of the sedimentary units are nowhere to 

be found. In places, the beds are overturned, stand on 

end, or are downdropped to form long, linear grabens. 

Angular unconformities, otherwise sparse throughout 

this part of central Utah, are common and widespread. Locally, single outcrops contain several angular unconformities (figs. 19 and 32). The sedimentary 

beds thin drastically and anomalously, and locally 

pinch out near the crestal parts of these upwarps, but 

assume their regional thicknesses just short distances 

away. Those sedimentary units that do extend across 

the crestal parts of the upwarps are the uppermost, 

youngest parts of the formations. The contrast 

between the attitudes of the beds exposed in this zone 

and those flanking it is striking, and made even more 

so by the fact that this intense structural complexity 

is localized. In places, the overturned beds, traced laterally, resume their near-horizontal attitudes in distances as short as a kilometer (half a mile). Units 

that are in angular discordance can be traced laterally and within several kilometers become conformable. The rocks in the zone have been much 

disturbed, hence my preference for the term Disturbed Zone, rather than the more commonly 

accepted Transition Zone.

In my opinion, the trend and position of this disturbed zone reflect a fundamental flaw in the underlying basement rocks. This view is supported by the 

fact that three major structural elements have influenced this part of central Utah during time periods 

that span most of geologic time:

1. During the Paleozoic, the hingeline between 

the Cordilleran geosyncline on the west and the eraton on the east trended northward through this area.

2. During the Jurassic, essentially the same geographic area was occupied by a major, structurally 

determined saline basin, termed the Arapien basin 

by Stokes (1982).

3. During the Tertiary and Quaternary, the structural seam between the Basin and Range and the 

Colorado Plateaus provinces extended northward 

through the area.

The disturbed zone overlies much of Stokes' 

Arapien basin. The greatest thickness of salt appears 

to have been deposited in this saline basin (D.A. 

Sprinkel, Placid Oil Co., oral commun., 1983), implying strongly that the anomalous sedimentary thinning 

and the complex structures so characteristic of the 

disturbed zone stem, in one way or another, from
12 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

movement of these thick salt deposits. As Halbouty 

noted (1967, p. 5): "The major salt basins of the world 

* * *are not simple, arbitrarily positioned evaporite 

pans* * *but rather* * *reflect major negative 

elements which are probably related to re-activation 

of basement structures."

DEFINITIONS

I use four terms throughout this Professional 

Paper, and it seems wise to explain my usage of them 

and how they differ from similar or comparable 

terms used in and near the Gulf Coast.

Salt diapir. As used along the Gulf Coast, "salt 

diapir" commonly refers to a body of almost pure 

rock salt, generally round or crudely elliptical and 

with nearly vertical sides, whose shape has determined the configuration of a salt-cored dome. By contrast, in this part of central Utah, I believe that the 

salt diapirs are elongate, narrow, somewhat sinuous 

bodies of salt and intercalated mudstone that extend 

for tens of kilometers. They appear to be comparable 

to the linear "salt cores" of the Paradox Basin, Colorado and Utah (Shoemaker and others, 1958, p. 39), 

or the "salt walls," described by Trusheim (1960, 

fig. 4), that formed in the Zechstein salt of northern 

Germany. Rather than almost pure rock salt, the salt 

diapirs in central Utah consist of thick beds and 

stringers of salt and anhydrite interlayered with calcareous mudstone and shaly siltstone. I visualize 

these salt diapirs, like those along the Gulf Coast, as 

piercement structures which, in their upward rise, 

intruded, arched, and deformed the overlying sedimentary rocks (fig. 5). The salt diapirs in central 

Utah probably stem from one or more source beds of 

salt.

Diapiric sheath. I believe that each salt diapir in 

central Utah is sheathed by calcareous mudstone and 

shaly siltstone beds that deformed plastically with 

the rising salt. These rocks are part of the Arapien 

Shale; pushed up by the driving salt they have 

intruded and deformed the overlying sedimentary 

rocks. I interpret them as intrusive sedimentary 

beds. In most places, I suspect that these calcareous 

mudstone beds are in intrusive contact with those 

consolidated and semiconsolidated rocks that overlie 

them. Although a similar sheath, but of shale, was 

called a "diapiric shale" by Atwater and Forman 

(1959), I believe the term "sheath" better describes 

the relations between the enveloping mudstone beds 

and the salt diapir.

Diapiric fold. The younger sedimentary rocks 

deformed by the diapiric sheaths are generally flexed 

up to form elongate, faintly sinuous, narrow

upwarps, whose trend and extent reflect the underlying causative salt diapir. These upwarps, most of 

which probably were originally fan-shaped in cross 

section, can be traced for long distances through central Utah. Other workers (Spieker, 1949; Gilliland, 

1963; Willis, 1986) have referred to these linear 

upwarps as "anticlines," but I prefer the term "diapiric folds," to emphasize the critical concept that 

only the salt-bearing and younger beds have been 

intensely deformed by the rising salt. The pre-salt 

units may be greatly deformed, but that deformation 

probably stems from erogenic forces, and not from 

the rising salt (p. 16). In this sense, then, I view the 

stack of sedimentary units in central Utah as consisting of two parts: the salt-bearing and overlying 

younger rocks, and an older pre-salt sequence. The 

complex structures I describe stem from repeated 

movement of the salt-bearing and younger rocks. 

Another acceptable term to describe these .upwarps is 

"salt-cored anticline"; I arbitrarily chose "diapiric 

fold" because it clearly conveys the diapiric concept 

and also contains fewer letters.

Salt is the motive force ultimately responsible for 

development of the diapiric folds. Subsequent withdrawal of the salt, by dissolution or extrusion, 

resulted in failure of the folds. Prior to erosion, 

these diapiric folds must have resembled the "salt 

anticlines" (salt-cored anticlines) of the Paradox 

Basin.

Diapiric core. The core of a diapiric fold consists 

of both the innermost salt diapir and its surrounding 

diapiric sheath. In most localities in central Utah, it 

is mainly the diapiric sheath of Arapien Shale mudstone beds that is exposed.

STRATIGRAPHY 

GENERAL STRATIGRAPHY

The sedimentary rocks that crop out in this part of 

central Utah consist of two sequences: one sequence 

comprises the autochthonous plate that underlies 

much of the Sanpete-Sevier Valley area (table 1); the 

second forms much of the Charleston-Nebo thrust 

plate, which extends northeastward from the Mount 

Nebo area to Thistle and beyond (table 2). No attempt 

is made to describe either of these sequences in detail. 

The rocks of the Sanpete-Sevier Valley area have 

been described repeatedly and thoroughly by Spieker 

and his many graduate students (Spieker, 1946, 1949; 

Gilliland, 1948, 1951; Hardy, 1952; Schoff, 1951; 

Hardy and Zeller, 1953; and McGookey, 1960, among 

others). Those underlying the area are from Cambrian 

to Holocene in age; most of the indurated units that
STRATIGRAPHY 13

Diapiric sheath

of crumpled

mudstone

Diapiric sheath

of crumpled

mudstone

1 MILE

FIGURE 5. Possible geologic relations between a salt diapir, the diapiric sheath of mudstones of the Arapien Shale, and the upturned 

country rock that together form the diapiric fold. The salt diapir and its diapiric sheath compose the diapiric core of the fold. 

Arrows denote general direction of movement of plastic and mobile salt and mudstone. In places, vertical forces, stemming from the 

intrusive salt diapir, are translated laterally into horizontal compressive forces. Scale is approximate.

figure prominently in my report are of Mesozoic and 

Cenozoic age. The rocks of the thrust plate have been 

described by Eardley (1933a, 1933b), Muessig (1951), 

Johnson (1959), Hintze (1962), Bissell (1962), Rigby 

and Clark (1962), Black (1965), and most recently by 

LeVot (1984), Banks (1986, 1988), and Biek (1988a, b). 

Exposed units range in age from Pennsylvanian to 

Jurassic. Tables 1 and 2 summarize the salient details 

of the stratigraphic section.

As noted previously, I attribute much of the structural deformation in central Utah to multiple episodes 

of salt diapirism. The rock salt (halite) and other 

evaporites that I believe are ultimately responsible for 

this structural complexity in central Utah are contained within the Arapien Shale one of the most 

unusual stratigraphic units in central Utah. Consequently, in the following pages, I discuss that unit in 

considerable detail.
14 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH 

TABLE 1. Some stratigraphic units exposed in the Sanpete-Sevier Valley area, central Utah

[Query, age, boundary, or thickness uncertain!

SYSTEM

Quaternary

-»

Tertiary

Cretaceous

SERIES

Pleistocene!?

Pliocene!?)

Miocene

Oligocene 

 ? 

Eocene

Paleocene

Upper 

Cretaceous

UNIT

Axtell Formation 

of Spieker (1949)

Osiris Tuff

Gray Gulch Formation 

of Spieker (1949)

Bald Knoll Formation 

of Gilliland (1951)1

Crazy Hollow Formation 

of Spieker (1949)

Green River Formation

Colton Formation

Flagstaff Limestone

North Horn Formation

Price River Formation

West of East of 

Sanpete Valley: Sanpete Valley:

. ,. _ Sixmile Canyon 

Indianola Group, un- P . 

_r _! _i mtr- i TAr, Formation

(3,000-7,000 ft)): Conglomerate, red to Funk Valley 

reddish brown, thick- Formation 

bedded to massive.

well-cemented; consists of well-rounded A||en Vg||ey 

pebbles, cobbles, and ,,, . 

boulders of quartizite.

limestone; few interleaved reddish-brown Sanpete 

sandstone beds. Formation

APPROXIMATE 

THICKNESS

METERS

15-23

152

0- 

213

305?

0- 

305

365

137- 

487

16

548

45

915

6- 

609

830

685

182- 

245

410

FEET

50-75

500

0- 

700

1,000?

0- 

1,000

1,200

450- 

1,600

50

1,800

150- 

3,000

20- 

2,000

2,725

2,250

600- 

800

1,350

LITHOLOGY

Conglomeratic sandstone and sandstone, locally conglomeratic; 

light gray to gray; thin bedded to massive; semiconsolidated; 

forms broad gravel-capped benches that flank modern major 

stream valleys.

Tuff, light-gray to dark-gray to black, thick- bedded to massive, 

fine-grained, porphyritic; disintegrates into angular blocks and 

fragments that form extensive debris fields.

Volcanic ash beds, with interbedded sandstone, shale, and 

limestone; mostly light gray, thin bedded to massive; friable; 

weathers to moderate slopes.

Mudstone, siltstone, and sandstone, light-gray to tan, 

thin-bedded; few thin intercalated light-gray, aphanic limestone 

beds.

Sandstone, shaly siltstone, and some conglomerate; light gray 

to reddish brown; thin to medium bedded, locally crossbedded. 

Light-gray salt-and-pepper sandstone containing distinctive 

black, well-rounded chert pebbles at base.

Consists of a limestone unit underlain by a shale unit. Limestone 

unit. Yellowish gray to yellow brown to light brown; thin to thick 

bedded; even bedded. Contains thin sandstone and tuff beds. 

Limestone beds are dense and commonly oolitic. Forms resistant 

ledges and low cliffs. Shale unit. Light green to grayish green; 

fissile; thin bedded; a few interleaved limestone beds. Forms 

gentle slopes.

Claystone and mudstone, variegated in shades of red and gray; 

few thin interbeds of light-brown to reddish-brown siltstone, 

fine-grained sandstone, and conglomerate; sparse thin beds of 

light-gray aphanic limestone; irregularly bedded. Locally, basal 

units are coarsely conglomeratic.

Limestone and dolomitic limestone, light-gray to yellowish-gray 

to light-brown; locally pale red; thin to thick bedded, locally

massive; even bedded, aphanic. Contains subordinate interbedded dark-gray, gray, and greenish-gray shale.

Mudstone, sandstone, conglomeratic sandstone, and sparse 

limestone; units alternate irregularly. Light yellow, buff, and light 

brown, locally reddish brown; thin to thick bedded. Unstable, 

marked by many mass-wasting deposits.

Conglomerate, conglomeratic sandstone, sandstone, and sparse 

shaly siltstone; light gray to gray; thin to thick bedded, locally 

crossbedded. Forms steep slopes and low cliffs.

Sandstone, conglomeratic sandstone, carbonaceous shale, and 

some coal; brown to brownish gray, locally light tan to light gray; 

thin to medium bedded; conglomeratic in basal part.

Sandstone and interbedded shale; sandstone is light brown to 

yellow brown, thin to medium bedded, fine to medium grained; 

shale is gray, even bedded, and fissile.

Shale, dark-gray to black, thin- and even bedded; contains thin 

beds of "siltstone, of very fine-grained sandstone, and gray 

limestone" (Spieker, 1946, p. 128).

Sandstone and conglomeratic sandstone, brown to 

brownish-gray; thin- to medium bedded: sandstones are fine to 

medium grained; basal part of formation is conglomeratic.
STRATIGRAPHY

TABLE 1. Some stratigraphic units exposed in the Sanpete-Sevier Valley area, central Utah Continued

15

SYSTEM

Cretaceous

Jurassic

SERIES

Lower 

Cretaceous

Middle 

Jurassic

Lower 

Jurassic

UNIT

Cedar Mountain Formation

Twist Gulch Formation

Arapien Shale

Members of the 

Twin Creek Limestone

Navajo Sandstone 

(Nugget Sandstone)

APPROXIMATE 

THICKNESS

METERS

90- 

610

915

1,220- 

3,960

100- 

137

ISO305

FEET

300- 

2,000

3,000

4,000- 

13,000

320- 

450

500- 

1,000

LITHOLOGY

Shaly siltstone and mudstone; reddish brown to light gray, but 

locally variegated in shades of pink and violet; contains white 

limestone bed. Contains abundant light-gray, small, rounded 

limestone nodules. Unstable, marked by many earthflows and 

landslides.

Shaly siltstone and sandstone, reddish-brown, thin- and even 

bedded; contains many very thin interbeds of light-gray, 

fine-grained sandstone and siltstone.

Calcareous mudstone, shaly siltstone, shale, sparse limestone, 

with much salt and other evaporites. Variegated; commonly 

mottled red and gray.

Dominantly limestone, light- to dark-gray, thin to massive, 

even-bedded, dense, argillaceous. In places, intensely folded and 

fractured. Includes the following seven members in descending 

order: Giraffe Creek, Leeds Creek, Watton Canyon, Boundary 

Ridge, Rich, Sliderock, and Gypsum Spring. All members except 

the Giraffe Creek are exposed in central Utah.

Sandstone, light-brown to buff, locally reddish orange, mediumto thick-bedded, massive, fine- to medium-grained, quartzose.

1 Recent work by Willis (1986) has suggested that the Bald Knoll strata exposed in the type section are not correlative with other rocks mapped as Bald Knoll 

elsewhere in central Sevier Valley. Pending resolution of this problem, Willis (1986, p. 6) used the term "The formation of Aurora" for the units here designated 

as the Bald Knoll Formation of Gilliland (1951).

TABLE 2. Some stratigraphic units exposed in the Charleston-Nebo thrust plate, Mount Nebo area, central Utah

[Query, boundary or thickness uncertain]

SYSTEM

Jurassic

Triassic

Permian

Pennsylvanian

SERIES

Middle 

Jurassic

Lower 

Jurassic

Upper to 

Lower 

Triassic

Lower 

Triassic

Lower 

Permian

Upper to 

Lower 

Pennsylvanian

UNIT

Twin Creek Limestone

Navajo Sandstone

Ankareh Formation

Thaynes Limestone

Woodside Sandstone

Park City Formation

Diamond Creek Sandstone

Kirkman Limestone

Oquirrh Group

APPROXIMATE 

THICKNESS1

METERS

?

180

122

90- 

305

120

200

120

113

3,505

FEET

?

600?

400

300- 

1,000

400

650

400

320

11,500

LITHOLOGY

Chiefly light gray, thin-bedded limestone; includes interbedded 

reddish-brown shaly siltstone members.

Orange-brown to reddish-brown to light-brown, thick-bedded, fine- to 

medium-grained quartzose sandstone.

Reddish-brown shaly siltstone and crossbedded sandstone with some 

intercalated thin conglomerate beds.

Chiefly light gray limestone with some reddish-brown to light-gray shaly 

siltstone and sandstone beds.

Reddish-brown shaly siltstone and crossbedded, fine- to medium-grained 

sandstone.

Chiefly light gray to pale-red, thin- to thick-bedded limestone; includes beds 

of brownish-black cherty limestone.

Reddish-brown to light-brown crossbedded sandstone; some intercalated 

limestone.

Light- to medium-gray, thin- to thick-bedded limestone; contains chert.

Gray to brownish-gray, thin- to thick-bedded limestone and interbedded 

light-brown, fine- to medium-grained sandstone.

1 Thicknesses from Eardley, 1933a; Johnson, 1959; and Black, 1965.
16 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

The stratigraphic units that form the autochthonous plate are divisible into two parts the saltbearing (Arapien Shale) and younger strata, which 

locally are intensely deformed, and the pre-salt 

units, which, although deformed, owe their deformation to orogenic forces and not to the repeated movement of the salt. This division of the sedimentary 

stack is important, not only in visualizing more 

clearly the structural relations, but also for economic 

reasons: suitable traps for the accumulation of oil 

and gas may be formed either along the flanks of the 

salt diapirs, or in those folded, older rocks that 

underlie the masking blanket of diapirically folded 

rocks. Unless one recognizes this structural discontinuity, one might never realize that two different 

types of structural traps are in the area.

THE ARAPIEN SHALE

NOMENCLATURE

The Arapien was originally defined by Spieker 

(1946, p. 123-125) who recognized five lithologic rock 

types. He described them as follows (1946, p. 124):

* * *there are five different types of lithologic assemblage, in 

which the order of succession, beginning with the lowermost, is 

commonly but by no means regularly as follows: (1) Gray limestone, generally thin-bedded; (2) light-gray siltstone and shale, 

very thin-bedded, with occasional thin beds of finely rippled sandstone; (3) gray shale, argillaceous and gypsiferous, with irregular 

red blotches, which locally become dominant; (4) compact red saltbearing shale; (5) thin-bedded red siltstone and shale with many 

thin layers of greenish white siltstone and occasional zones of gray 

sandstone, some of which is fairly coarse grained.

Of the five units recognized, Spieker believed that 

the first four could not be traced over long distances. 

Type 5, by contrast, appeared to Spieker to be sufficiently consistent in lithology and appearance to warrant its being a named member. Spieker, therefore, 

divided the five types into two members; he named 

type 5 the "Twist Gulch member," and grouped and 

named the underlying four units the "Twelvemile 

Canyon member."

In the late 1940's, Clyde T Hardy, then one of 

Spieker's graduate students, began a study of the 

Twelvemile Canyon Member. Hardy soon became 

convinced that the Twist Gulch and Twelvemile Canyon Members were sufficiently distinct and widespread to warrant separate formational status. 

Spieker agreed, and consequently Hardy (1952, p. 

14) noted: "The Arapien shale was defined by E.M. 

Spieker in 1946, as a formation with two distinct 

members (Spieker, 1946, pp. 123-125). The term is 

now restricted to the strata formerly included in the 

Twelvemile Canyon member, and the Twist Gulch 

member is redesignated as a formation because of its

great areal extent in central Utah (Hardy and 

Spieker, in preparation)."

The Hardy-Spieker paper was never published, but 

most subsequent authors seemingly assumed that the 

paper was in print, or simply accepted the reasonableness of Hardy's proposal, and used the term 

"Arapien shale" in a formational sense much as proposed by Hardy, and as an exact replacement for the 

name "Twelvemile Canyon Member." Regrettably, 

Hardy's proposal infringed on the existing code of 

stratigraphic nomenclature, which forbade using the 

original name of a unit ("Arapien shale") for one of its 

divisions ("Twelvemile Canyon Member"). The result 

was dual usage of the name "Arapien shale." U.S. 

Geological Survey geologists used the name in its 

original sense, as a formation with an upper Twist 

Gulch Member and a lower Twelvemile Canyon Member. Industry and academic geologists used the name 

in its formational sense and as a direct replacement 

for the term "Twelvemile Canyon member." This dual 

usage caused much confusion. To resolve the problem, 

Hardy and I proposed (Witkind and Hardy, 1984) that 

the Twist Gulch Member be raised to formational 

rank, that the units now grouped as the Twelvemile 

Canyon Member be known as the Arapien Shale, and 

that the name Twelvemile Canyon Member be abandoned. Although this action also violates Article 19g 

of the North American Stratigraphic Code (North 

American Commission on Stratigraphic Nomenclature, 1983), we believed that widespread and common 

usage argued persuasively for such a change. In this 

Professional Paper I follow this terminology and treat 

the Twist Gulch and the Arapien Shale as separate 

formations.

FIGURE 6 (facing page). Aspects of the Twist Gulch Formation, 

and the Arapien Shale. A, Exposure of the Twist Gulch Formation at north end of a low hogback near an ancestral 

course of Willow Creek. Twist Gulch strata, downthrown 

along a near-vertical, normal fault, dip westward and abut 

vertical beds of the Flagstaff Limestone. Structural relations 

in this locality are discussed in the section, "Ancestral Willow 

Creek area." B, Arapien Shale exposure in the White Hills, 

Willow Creek area. Masses of pale-red mudstone scattered 

irregularly through light-gray mudstone give unit a distinctive mottled appearance. As mudstone beds are readily dissected, badland topography commonly characterizes Arapien 

exposures. C, View looking eastward across Sanpete Valley at 

a low, gray, unnamed, north-trending ridge (west of Ninemile 

Reservoir), composed of Arapien strata, chiefly overturned 

beds of limy mudstone, siltstone, and sandstone. Overturned 

beds of the Indianola Group (foreground) are part of the exposure that makes up the Red Rocks area. D, Exposure about 5 

km (3 mi) east of Nephi, along north valley wall of Salt 

Creek, of light-gray, thin, vertical platy beds characteristic of 

some facies of the Arapien Shale.
NORTH

Sixmile Creek Canyon

SOUTH
18 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

TWIST GULCH FORMATION

The Twist Gulch Formation consists of a series of 

reddish-brown to brown, thin- to medium-bedded 

shaly siltstone and fine- to medium-grained sandstone beds. Light-gray to gray, thin, fine- to mediumgrained sandstone beds and laminae are interleaved 

in the sequence. The unit weathers to moderate 

slopes broken by small steplike ridges formed by the 

more resistant sandstone beds (fig. 6A). The unit is 

distinctive and differs strikingly in details of weathering and lithology from the underlying Arapien 

Shale (fig. 65). The thickness of the Twist Gulch 

Formation ranges from about 60 m (200 ft) to about 

915 m (3,000 ft) (Spieker, 1946, p. 125).

Twist Gulch strata, in central Utah, seemingly 

grade into the overlying mudstones of the Cedar 

Mountain Formation of Early Cretaceous age. Much 

uncertainty surrounds both the age of the Twist 

Gulch and the units with which it is correlative. 

Imlay (1980, p. 74) assigned the Twist Gulch to the 

Middle Jurassic (Callovian). Its upper age limit is 

uncertain. It may extend into the Late Jurassic 

(Witkind, Standlee, and Maley, 1986), or Early Cretaceous (Villien, 1984, p. 40). Although Imlay (1980, 

p. 74) suggested that the Twist Gulch is essentially 

equivalent to the Entrada, I follow Hardy (1949, 

p. 36), and believe the Twist Gulch is probably correlative with the Middle Jurassic (Callovian) Entrada, 

Curtis, and Summerville Formations of the San 

Rafael Group.

ARAPIEN SHALE (GEOLOGIC ASPECTS)

LITHOLOGY

Hardy's (1949, 1952) exhaustive study of the 

Arapien Shale (then known as the Twelvemile Canyon 

Member) was an attempt to understand better the 

bewildering lateral and vertical changes in that unit. 

As a result of his work, he divided Spieker's original 

four rock types into five lithologic units. Hardy's 

description of these units (which exclude the Twist 

Gulch Formation) is listed, in ascending order, herein 

(Hardy, 1949, p. 15-16):

Unit E:

Brick-red silty shale locally salt-bearing. The salt appears to be 

stratified and commonly contains a considerable amount of red 

clay. At least 200 feet 160 ml of salt is exposed east of Redmond, 

and north of Redmond in the Sevier Valley.

Unit D:

Alternate layers of bluish-gray and red gypsiferous shale. 

Blotched appearance of the outcrop due to lenticular nature of the 

beds, facies changes, and complex structures.

Unit C:

Bluish-gray calcareous shale with gray thin-bedded calcareous 

sandstone. Several prominent layers of arenaceous limestone with 

fossils. Massive lenticular beds of gypsum.

Unit B:

Bluish-gray and red gypsiferous shale. Blotched appearance as 

Unit D. Red gypsiferous shale in upper part locally salt-bearing.

Unit A:

Gray shale, gray thin-bedded limestone weathers brown, red 

shale, gypsum in thin lenticular beds; or gray thin-bedded argillaceous limestone with massive lenticular beds of gypsum.

Although these units appear as sequential stratigraphic units in the Salina area (Willis, 1986), in 

most places where I have examined the Arapien, the 

units appear to intermingle, and are perhaps best 

described as distinctive lithologic rock types. Seemingly, these units occur irregularly at various stratigraphic intervals, and, as a result, rapid lateral 

changes in lithology and color are characteristic.

In some localities, as in Salt Creek Canyon east of 

Nephi (B-3), the Arapien Shale changes radically in 

appearance from place to place. Commonly, the 

Arapien is a light-gray calcareous mudstone mottled 

here and there with pale-red blotches. This is its 

appearance in the White Hills (G-3) near Mayfield 

(F-3) (fig. 6B). In other places, it is uniformly drab 

gray, as in the Pigeon Creek-Chicken Creek (C-3) 

area along the west flank of the Gunnison Plateau 

(D-3); still elsewhere, it is uniformly reddish brown, 

as in the North Fork of Salt Creek (east of Nephi), or 

near Redmond (G-3).

[n general, the Arapien consists of an alternating 

sequence of beds of calcareous mudstone (the 

"micrite" of Picard, 1980, p. 137), gypsiferous shale, 

siltstone, fine-grained sandstone, and sparse limestone. Most of these units are so soft that the formation tends to form badland topography marked by 

intricately dissected low hills and ridges separated by 

narrow, sinuous valleys. Thin to thick beds of evaporite, chiefly rock salt (halite), gypsum, anhydrite, and 

calcite are integral parts of the formation (fig. 7). 

Selenite crystals litter many outcrops. At one time 

salt was mined in Salt Creek, north of the KOA 

Campground (B-3), and near Sterling (F-4). Currently, it is being mined near Redmond; large 

amounts of it underlie central Utah (Moulton, 1975), 

and large amounts have been dissolved and removed. 

Virtually all the diapiric features discussed in this 

report formed in response to movement of salt 

masses many of which have since been dissolved. The 

critical factor is not how much salt underlies central 

Utah at the present time, but rather how much salt 

underlay the area in the past when most of the diapiric structures were formed.
STRATIGRAPHY 19

EAST WEST

- Gunnison Plateau

FIGURE 7. Gypsum mass within the Arapien Shale. Mine is about 

1.5 km (1 mi) east of Nephi.

In places, the Arapien Shale appears as an uninterrupted sequence, traceable for thousands of 

meters, of alternating thin sandstone and mudstone 

beds (fig. 6C), but elsewhere it crops out as an amorphous mass totally devoid of bedding.

Although other workers (Hardy, 1949; Hunt, 1950; 

Spieker, 1949, p. 17; Standlee, 1982, p. 363) have 

suggested that considerable limestone (Hardy's unit 

A) is in the Arapien Shale, I suggest that the formation, in fact, contains little actual limestone. The 

Arapien is certainly calcareous; the mudstone beds 

that compose the bulk of the formation contain much 

carbonate, but these mudstone beds are wholly different from the limestone beds other workers have 

included in the Arapien Shale.

The assumption that the Arapien Shale contains 

much limestone probably stems from geologic 

mapping at the north end of the Gunnison Plateau 

(Hunt, 1950). A major north-trending anticline is well 

exposed in Chicken and Pigeon Creeks along the 

northwest flank of the Gunnison Plateau, east of 

Levan (C-3). Exposed units consist of light-gray to 

gray, thin to massive, dense beds of fine-grained limestone. East of and abutting these limestone beds are 

drab-gray calcareous mudstone beds of the Arapien 

Shale. The limestone beds, much crumpled, were considered to be the lower part of the Arapien (Spieker, 

1949, p. 48), and the mudstone beds the upper part 

(Hardy, 1949, p. 16). Consequently, these limestone 

beds were grouped with the contiguous well-exposed 

mudstone beds of the Arapien Shale, and both units 

were mapped as the undivided Arapien Shale (Hunt, 

1950).

I believe, however, that the limestone beds are 

correctly assigned to the Twin Creek Limestone of 

Middle Jurassic age (Bajocian to Callovian). Seemingly, long after these Twin Creek strata were thrust 

into position, probably as part of the Charleston-Nebo 

thrust plate, the Arapien Shale intruded, crumpled, 

and deformed them. Regrettably, the presence of 

Jurassic fossils in both units led to the two lithologies 

being assigned to one formation.

This infelicitous grouping led to a major misconception: that attitudes measured on Arapien Shale 

beds would give some indication of the configuration 

of the underlying, concealed Navajo Sandstone (also 

known as the Nugget Sandstone north of Thistle, 

Utah (A-5)), one of the major reservoir rocks in central Utah. In my opinion, however, contorted Arapien 

strata exposed in central Utah have been deformed 

too intensively too many times to indicate the configuration of the underlying strata. By contrast, where 

the limestone beds of the Twin Creek are exposed in 

the Chicken and Pigeon Creek area, attitudes measured on them do indeed indicate the configuration of 

the fold, and also reflect the attitude of the underlying Navajo Sandstone; they have no bearing on the 

attitude of the Arapien Shale which intrudes that 

fold, deforms it, and probably underlies it.

CONTACT RELATIONS 

LOWER CONTACT

Although other workers (Spieker, 1949, p. 17; 

Moulton, 1975, p. 9; Picard, 1980, p. 131; Standlee, 

1982, p. 363) have stated that the Arapien Shale 

rests on the Navajo Sandstone, I believe that the 

Arapien rests on the Twin Creek Limestone. Seemingly, our different interpretations stem from the fact 

that these other workers have included the limestone 

beds, here considered to be the lower and medial 

parts of the Twin Creek Limestone, in the lower part 

of the Arapien Shale.

In Wyoming and northern Utah, the Twin Creek 

Limestone consists of seven members, which are, in 

ascending order: the Gypsum Spring, Sliderock, Rich, 

Boundary Ridge, Watton Canyon, Leeds Creek, and 

Giraffe Creek (Imlay, 1967). In central Utah, the 

series of sandstone and limestone beds intercalated 

between the Arapien and the Navajo Sandstone consist of the lower five members of the Twin Creek, in 

essence, from the Gypsum Spring up to and including 

the Watton Canyon. This Gypsum Spring to Watton 

Canyon sequence has been repeatedly cut by exploratory wells drilled by Placid Oil Company in the 

Juab and Sevier Valleys (Sprinkel, 1982). The 

sequence thins eastward. Although Arapien
20 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

TABLE 3. Correlation chart for some Middle Jurassic formations in central Utah

IModified slightly from correlation charts prepared by Imlay (1980, p. 74), and D.A. Sprinkel (Placid Oil Company, written commun., 1981). Query, relationship uncertain]

SERIES

Middle 

Jurassic

Lower 

Jurassic

STAGE

Callovian

Bathonian

Bajocian

Toarcian and 

older

Charleston-Nebo thrust plate

7

Creek Twin Limestone

Not exposed

Leeds Creek Member

Watton Canyon Member

Boundary Ridge Member

Rich Member

Sliderock Member

Gypsum Spring Member

Sanpete-Sevier Valley area

Twist Gulch Formation

Arapien Shale

Carbonate beds of the 

Twin Creek Limestone

Wasatch Plateau, 

San Rafael Swell

Summerville and Curtis 

Formations and 

Entrada Sandstone

Formation

V

CD 

O

Upper part

Lower part

Navajo Sandstone (Nugget Sandstone)

mudstone may locally rest on the Navajo Sandstone, 

in most localities throughout the Sanpete-Sevier 

Valley area, the mudstone probably rests on one or 

another of the members (Gypsum Spring to Watton 

Canyon) of the Twin Creek Limestone.

I suspect that this intercalated sequence of Twin 

Creek beds is correlative with the lower part of the 

Carmel Formation of the San Rafael Group. If so, the 

Arapien is probably correlative with the Leeds Creek 

Member of the Twin Creek Limestone the member 

that commonly overlies the Watton Canyon. Table 3, 

modified from correlation charts prepared by Imlay 

(1980, p. 74), and by D.A. Sprinkel (1982), summarizes the stratigraphic relations between the Twin 

Creek Limestone and the Arapien Shale.

In Red Canyon (B-3) near Nephi (B-3), in the 

Thistle (A-5) area, and in the Pigeon Creek-Chicken 

Creek (C-3) area, the Arapien is underlain by beds of 

the Gypsum Spring to Watton Canyon sequence. I 

believe that in all three localities these Twin Creek 

units are part of the Charleston-Nebo thrust plate, 

and that they have been intruded and deformed by 

the adjacent Arapien Shale (Witkind, 1983, p. 51-54, 

55; Witkind, 1987). Exposures in the three areas suggest that the Arapien, originally in its normal stratigraphic position, was mobilized, and, as a result, 

intruded and deformed the adjacent rocks.

UPPER CONTACT

Where exposed in central Utah a bewildering 

variety of units, ranging in age from Jurassic to

Holocene, overlies the Arapien Shale. This variety 

probably reflects the intrusive nature of the Arapien. 

The Twist Gulch Formation probably overlies the 

Arapien conformably; seemingly the two formations 

do not intertongue. In most localities where I have 

seen the contact, the Twist Gulch strata that overlie 

the Arapien have been turned on end or tilted 

upward moderately to steeply. Thus, in the Middle 

Fork Pole Creek (B-4) (east of Nephi), the Twist 

Gulch beds are vertical where they abut the Arapien 

(fig. 39). In the ancestral Willow Creek area (G-3) 

(northeast of Salina (G-3)), Twist Gulch beds that 

overlie the Arapien are inclined westward at dips 

that range from 35° to 85°, and they abut vertical 

beds of the Flagstaff Limestone (fig. 6A). Although 

the contact between the Twist Gulch and the underlying Arapien, in both localities, appears conformable, I believe the beds of the Twist Gulch have been 

tilted upward by the upthrust mudstone beds, which 

have been forced upward by the driving salt.

In various localities throughout the Sanpete-Sevier 

Valley area, the Arapien is unconformably overlain 

by tilted oolitic limestone beds of the Green River 

Formation. These beds, integral parts of the flanks of 

salt-cored anticlines, dip away from the crests of 

these folds.

AREAL EXTENT

The Arapien Shale is exposed here and there 

throughout central Utah (fig. 8). The most extensive 

exposures are in the southern sector of the Sanpete-
STRATIGRAPHY 21

Sevier Valley area, chiefly in Sanpete, Sevier, and 

Juab Counties. There the Arapien is concentrated in 

three belts reflecting, in my opinion, the exposed 

cores of five major salt-cored anticlines, here called 

diapiric folds (fig. 8).

1. A northeast-trending broad belt of Arapien 

Shale, along the east side of the Sevier Valley, that 

extends into Sanpete Valley and reaches from near 

Richfield (1-1) on the south to near Manti (E-4) on 

the north. This is the exposed core of the Sanpete 

Sevier Valley diapiric fold.

2. A much smaller and narrower belt of Arapien 

Shale, trending north, that crops out along the west 

side of the Sevier Valley. This belt, which extends 

from near Redmond (G-3) on the south to near Gunnison (F-3) on the north, is part of the exposed core 

of the Redmond diapiric fold.

3. Other extensive exposures of the Arapien 

Shale, along the west flank of the Gunnison Plateau, 

that extend around the north end of the plateau and 

into the north-trending sector of Salt Creek canyon 

(B-3). These outcrops form parts of the cores of the 

Levan, Footes, and Pole Creek diapiric folds. As 

these Arapien exposures along the west flank of the 

Gunnison Plateau appear to align with similar outcrops farther south that form the core of the Redmond diapiric fold, it may be that the Levan and 

Redmond folds are joined in the subsurface.

In the northern sector of the area, a few small, isolated Arapien exposures are between Indianola (B-5) 

and Thistle (A-5). Most of these exposures are part 

of the Thistle Creek diapiric fold.

Although the three belts represent the major outcrops of the Arapien Shale, the Arapien probably 

underlies a large area. Just how large, however, is 

difficult to determine. Test wells indicate that the 

Arapien underlies much of Sanpete Valley; apparently the core of the Sanpete-Sevier Valley diapiric 

fold continues northward beyond Manti (E-4) but is 

concealed beneath the surficial deposits that floor the 

valley.

The Arapien Shale may also underlie all of central 

Sevier Valley (that sector between the Valley Mountains (G-2) on the west and the Wasatch Plateau (F5) on the east) possibly at shallow depth. At least 

one water well in the valley, near Centerfield (F-3), 

penetrated red shale and found saline water at a 

depth of about 165 m (550 ft) (Gilliland, 1948, 

p. 109).

The exposures of the Arapien Shale in Salt Creek 

(B-3) seemingly are concealed beneath the CharlestonNebo thrust plate (Witkind, 1983, p. 51-54; this report, 

fig. 35). How far to the north the Arapien extends 

beneath the thrust plate is unknown. Deformation

along an erosional escarpment along the east flank of 

the thrust plate has led me to suggest that the Arapien 

extends at least as far north as Payson Canyon (A-4) 

(Witkind, 1987). Northeast of Salt Creek, the Arapien 

crops out near Thistle (A-5), and there too, the field 

relations imply that the unit is concealed beneath the 

Charleston-Nebo thrust plate (Witkind, 1983, p. 55; 

Witkind, 1988; this report, fig. 44). I am uncertain how 

far the Arapien extends to the north beyond Thistle. 

Possibly the salt in the lower part of the Preuss Sandstone, of southwestern Wyoming and northern Utah, 

may be correlative with the uppermost units of the 

Arapien Shale. Probably, the bulk of the Preuss correlates with the Twist Gulch Formation of central Utah.

I am also uncertain how far the Arapien extends to 

the east. If the many north- and northeast-trending 

grabens that mark the crest of the Wasatch Plateau 

do stem from dissolution of salt beds, as proposed by 

Stokes and Holmes (1954, p. 40), and implied by Walton (1955, p. 409-410), the Arapien may once have 

reached at least as far east as a north-trending line 

through Scofield Reservoir (B-6). I, too, favor the 

concept that the many grabens and high-angle faults 

that break the crest of the Wasatch Plateau are the 

result of dissolution of salt beds once contained 

within the Arapien Shale. Several proprietary seismic reflection profiles that I have examined through 

the courtesy of Chevron Oil Company convince me 

that the faults do not extend below the Arapien and 

Carmel Formations. Walton (1955), discussing the 

gas fields of the Wasatch Plateau, cited a thickness of 

375 m (1,230 ft) of highly contorted Arapien (1955, 

p. 398) cut by the Gordon Creek well (fig. 9). This 

well, in the SEV4 NEV4 sec. 24, T. 14 S., R. 7 E., was 

drilled about 19 km (12 mi) southeast of the Scofield 

Reservoir (B-6). Both Moulton (1975, fig. 13), and 

Stokes (1982, fig. 1) have drawn the zero isopach of 

the salt near the east edge of the Wasatch Plateau.

To the south the Arapien Shale disappears beneath 

volcanic flows east of Richfield (1-1). Little evidence 

indicates how far south the Arapien persists beneath 

this volcanic mantle. The Paxton No. 1 test well 

(SWV4 NWV4 sec. 28, T. 23 S., R. 3 W) (fig. 9), drilled 

by Placid Oil Company near Elsinore (a small community about 16 km (10 mi) south of Richfield), penetrated both mudstone beds and salt of the Arapien 

Shale.

The western extent of the Arapien, too, is uncertain. 

Recent drilling in the Valley Mountains (G-2), in 

Round Valley (F-2), and in the West Hills (D-2) indicates that the Arapien extends at least as far west as 

the east flanks of the Pavant Range (H-l) and Canyon Mountains (E-l). Brown and Cook (1982, p. 123) 

proposed, on the basis of gravity data, that the
22

112°00'

SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

30' 11H5'

EXPLANATION 

Arapien Shale exposures

A Part of exposed core of Footes Canyon

diapiric(?) fold

B Exposures of Thistle Creek diapiric fold 

C Part of exposed core of Hjorth Canyon

diapiric fold 

D Parts of exposed core of Pole Creek diapiric

fold

E Parts of exposed core of Levan diapiric fold 

F Part of exposed core of Redmond diapiric

fold 

G Part of exposed core of Sanpete-Sevier

Valley diapiric fold

 Diapiric fold Dashed where inferred

1 Sanpete-Sevier Valley

2 Redmond

3 Levan

4 Sevier Bridge Reservoir

5 West Hills

6 Valley Mountains

7 Fairview

8 Little Clear Creek

9 Hjorth Canyon

10 Dry Hollow

11 Thistle Creek

12 Pole Creek

13 Footes Canyon

15 MILES

FIGURE 8. Distribution of Arapien Shale exposures throughout the Sanpete-Sevier Valley area. These exposures represent parts of 7 of 

the 13 major diapiric folds (salt-cored anticlines) recognized. Base from Grand Junction (T-3) Sectional Aeronautical Chart, U.S. 

Coast and Geodetic Survey (1954, rev.).
STRATIGRAPHY 23

Arapien lenses out under the Pavant Range. Eardley 

(1969, p. 58, fig. 2), however, seemingly considered the 

Arapien to underlie the Pavant Range; and if this is 

correct, the Arapien may extend still farther west, at 

least to the east edge of the Sevier Desert. Deformation along the northeast flank of the Valley Mountains 

suggests that a major diapiric fold reaches as far west 

as Yuba Dam (E-2) and probably extends much farther to the west (Witkind and Page, 1984).

In summary, then, it would appear that in central 

Utah the Arapien Shale underlies an area of at least 

11,700 km2 (4,500 mi2 ). On the basis of exposures or 

test-well data, the Arapien extends westward some 80 

km (50 mi) from the Wasatch Plateau to the Canyon 

Mountains and the Pavant Range. It extends southward some 150 km (90 mi) from Thistle (A-5) on the 

north to near Elsinore on the south. I suspect that the 

Arapien underlies a vastly larger area.

ARAPIEN EMBAYMENT AND THE ARAPIEN BASIN

Sprinkel and Waanders (1984) have suggested that 

most of Utah, during Middle Jurassic time (Bajocian, 

Bathonian, and Callovian), was the site of a large 

marine embayment, which they named the "Arapien 

embayment." As visualized by them, the embayment 

probably extended westward into what is now eastern Nevada, northward into southern Idaho, southward at least as far as northern Arizona, and 

eastward to the Utah State line. Highlands on the 

west, south, and east flanked the embayment during 

its early stages. Subsequently, as an uplift, now 

known as the Uinta Mountains, rose above sea level, 

the embayment also became confined on the north.

During the early stages of the embayment, carbonates were deposited that now form the lower and 

medial parts of the Twin Creek Limestone interval. 

Most likely, the lower five members the Gypsum 

Spring, Sliderock, Rich, Boundary Ridge, and Watton 

Canyon Members of the seven members of the Twin 

Creek Limestone were formed during that time. Subsequently, the embayment shrank to form a smaller 

basin the Arapien basin of Stokes (1982) and 

shallow-water and saline deposits, the bulk of the 

Arapien Shale, formed in that basin under hypersaline conditions. Apparently, Arapien mudstones and 

evaporites were being deposited even as units of the 

Leeds Creek Member of the Twin Creek, above the 

Watton Canyon, were forming in deeper waters marginal to the basin.

The extent of the Arapien basin is problematical. 

Stokes (1982, fig. 1) suggested that it occupied most 

of Sevier and Sanpete Counties. Sprinkel and 

Waanders, on the basis of isopach maps, chiefly of

Arapien strata, proposed that the basin was considerably larger. In their view, the basin occupied most of 

central Utah, reaching as far north as Provo, as far 

east as Green River, as far south as St. George, and 

as far west as Delta. The deepest part of the basin 

underlay Sanpete and Sevier Counties; presumably 

most of the evaporites accumulated there.

Much salt must have been deposited in the 

Arapien basin, and large volumes of that salt must 

have been dissolved and moved elsewhere. Indeed, 

that an Oligocene salt diapir was penetrated by the 

Argonaut-Federal well near Delta, far to the west of 

the Sanpete-Sevier Valley area (p. 24), implies such 

dissolution and mobilization of the Jurassic salt. 

Although Standlee (1982) has argued that the well 

data for central Utah indicate only relatively minor 

to moderate amounts of salt in essence, insufficient 

salt to support the salt diapiric concept the critical 

factor is not the amount of salt currently available, 

but rather the amount of salt that was available in 

the geologic past.

Moulton (1975, p. 90, and fig. 13), prior to the work 

of Sprinkel and Waanders, and of Stokes, had speculated that the depocenter for much of the Arapien 

Shale must have been a northeastward trending rift 

valley, which Moulton named the "Sanpete-Sevier 

rift." In his view, the rift, bounded by growth faults, 

contained the thickest accumulations of salt and was 

filled with about 3,350 m (11,000 ft) of evaporites and 

shales. Moulton believed that the east edge of the rift 

was delineated by an "ancient Ephraim fault," and, 

thus, he saw the saline basin as being essentially 

asymmetric deepest along its east edge as a result 

of repeated movement along this ancient fault. In 

Moulton's view (1975, p. 91), the ancient Ephraim 

fault has been inactive since Middle Jurassic time. 

Picard (1980, p. 133) objected to the concept of a rift 

valley and proposed that the basin be termed instead 

a "Jurassic marginal basin." He believed that the 

position of the basin and its general shape were 

determined by the regional uplift of a western Mesocordilleran anticline.

CONTAINED SALT

LlTHOLOGY

Salt is mined from the Arapien Shale near Redmond (G-3), and is exposed in the mines there; salt 

also crops out in several small salt mines in Salina 

Canyon (H-3) east of Salina (G-3). As far as known, 

salt is not exposed elsewhere in this part of central 

Utah, although it was mined by the Great Western 

Salt Company from pits some 8 km (5 mi) northeast
24 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

of Salina. Salt was also mined near Sterling (F-4), 

and from two rock-salt pits in the Arapien Shale 

along the north bank of Salt Spring Creek (a tributary to the North Fork of Salt Creek), some 11 km 

(7 mi) east of Nephi (B-3). In all localities, the salt is 

intercalated with mudstone beds of the Arapien 

Shale, chiefly red shaly siltstone and earthy material, probably correlative with Hardy's unit E. Its 

great extent, however, is evident in the names the 

early settlers gave to the creeks and communities in 

central Utah Salt Creek, Little Salt Creek, Salina.

Picard (1980, p. 145), has described the salt in the 

Redmond area: "In general appearance, the salt is 

massive and coarse-grained. * * *because of the 

intense deformation and flowage much of the salt is 

oriented and drawn out into acicular crystals* * *."

The salt is ordinary halite, but tinted a pale to 

deep reddish brown by disseminated clay particles.

Although the salt exposed in the Redmond mines is 

highly deformed, at least one small salt mine east of 

Salina exposes bedded salt somewhat of a surprise, 

for one might not expect bedded salt in an area 

marked by intense and repeated diapiric activity 

Jackson (1985, p. 4), however, discussing Iranian 

diapirs, noted that although most of the Iranian salt 

is intensely deformed, some "* * *rock salt is horizontally stratified in some diapirs* * *suggesting 

emplacement in a pistonlike manner with little internal deformation* * *."

THICKNESS OF SALT

Where exposed in most places the salt is much 

crumpled and contorted; near Redmond (G-3), for 

example, the salt beds are vertical, and may range in 

thickness from 180 to 300 m (600 to 1,000 ft) (Pratt 

and others, 1966, p. 54). One bed being mined in the 

Redmond area in 1980 was about 60 m (200 ft) thick 

(Picard, 1980, p. 145).

Although the drilling that has been done in central 

Utah demonstrates that salt is widespread in the 

subsurface (Moulton, 1975; Standlee, 1982, fig. 5), 

little salt is exposed at the surface. Probably this 

lack of surface exposures is due to the extreme solubility of the salt; no sooner is it exposed than it is 

dissolved and removed. Pratt and his co-workers 

(1966, p. 55) have suggested that the salinity of 

Great Salt Lake may stem in some measure from the 

solution of exposed Arapien salt by the ancestral 

Sevier River, which flowed north and discharged into 

Lake Bonneville during Pleistocene time.

The salt diapir cut by the Argonaut-Federal well 

(C, NW, sec. 23, T. 15 S., R. 7 W., Millard County),

near Delta (some 70 km (45 mi) northwest of the 

Sanpete-Sevier Valley area), also suggests dissolution and transport of Arapien salt. This well passed 

through some 1,570 m (5,152 ft) of salt (Mitchell, 

1979, p. 505). On the basis of palynological studies 

and fission-track dating of intercalated volcanics, the 

basin sediments penetrated by the well have been 

tentatively dated as late Oligocene (Lindsey and 

others, 1981). The salt, part of these basin sediments, 

has been interpreted as former Mesozoic salt deposited during Oligocene-Miocene time in the large 

ancestral Sevier Lake into which the ancestral Sevier 

River emptied (Mitchell, 1979, p. 505-508). Presumably when the salt-rich units of the Arapien Shale in 

this part of central Utah broke through to the surface during the late Oligocene or Miocene, the 

exposed salt was dissolved by the ancestral San Pitch 

and Sevier Rivers and their tributaries, carried north 

and west around the north ends of both the Valley 

(G-2) and Canyon (E-l) Mountains, and discharged 

into ancestral Sevier Lake. Subsequent evaporation 

resulted in the deposition of the salt, which eventually migrated laterally to form the discrete diapir 

drilled by the Argonaut-Federal well. I believe that 

many other salt diapirs, comparable to the one penetrated by the Argonaut-Federal well, are in the general area near Sevier Lake.

Other workers have assumed that although salt is 

in the area, there just was not enough for it to have 

played any significant role in the structural development of central Utah (Gilliland, 1963, p. 123; 

Standlee, 1982; Lawton, 1985). I suggest instead that 

large amounts of salt have been removed from the 

area in the past and that large amounts still underlie 

the area. The Phillips Price "N" well, in Sanpete 

Valley near Moroni (D-4) (fig. 9) (SEV4SEV4 sec. 29, 

T 15 S., R. 3 E.), penetrated salt and interbedded 

subordinate calcareous mudstone some 621 m (2,038 

ft) thick. Near Salina (G-3), the Chevron U.S.A. 

Salina Unit No. 1 well (sec. 33, T. 22 S., R. 1 W.) cut 

more than 300 m (1,000 ft) of salt and interbedded 

mudstone (Standlee, 1982, p. 366). In the West Hills 

(D-2), west of Juab Valley, Placid Oil Company's 

Howard 1-A WXC well (NEV4 NWV4 sec. 5, T. 14 S., 

R. 1 W.) cut about 170 m (550 ft) of salt. And Chevron's Chriss Canyon No. 1 well (NEV4 SWV4 sec. 33, 

T. 16 N., R. 1 E.), near the center of the Gunnison 

Plateau (D-3), cut through about 245 m (800 ft) of 

salt (Standlee, 1982, p. 362).

Moulton's (1975, fig. 13) isopach map shows the distribution and thickness of the salt. His sparse data 

show a remarkable lack of uniformity, suggesting that 

the salt varies greatly in thickness. Data from test 

wells indicate that great thicknesses of salt give way
STRATIGRAPHY 25

laterally to zones that either contain no salt or contain but thin salt stringers. So, although the Price 

"N" well penetrated a great thickness of salt, the 

Moroni wells (sec. 14, T. 15 S., R. 3 E.), only 5 km 

(3 mi) to the east, found none, even though they cut 

great thicknesses of Arapien mudstone. In like fashion, the State No. I well (sec. 36, T. 15 S., R. 1.5 W.) 

cut through 1,050 m (3,450 ft) of salt. The Monroe 

13-7 well (sec. 13, T. 16 S., R. 2 W.), about 5 km 

(3 mi) to the southeast, cut only about 210 m (688 ft) 

of salt, and the Barton No. 1 (sec. 32, T. 16 S., R. 1 

W.) well, about 8 km (5 mi) southeast of the Monroe 

well, found none, even though it drilled great thicknesses of Arapien mudstone.

It seems to me that the absence of salt from some 

wells does not necessarily mean nondeposition, or 

areally erratic dissolution, but rather lateral migration of salt toward the diapirs. Much of the salt, thus, 

may now be in the diapirs. Those wells that cut great 

thicknesses of salt, such as the Phillips Price "N" 

well, or Chevron's U.S.A. Salina Unit No. I (sec. 33, 

T. 22 S., R. 1 W.), probably are near the axial part of a 

diapiric fold (fig. 5). Those wells that found no salt 

but did drill through much mudstone (such as the 

Hanson wells) either are along the flanks of the diapiric core, or have drilled into localities where the 

source ("mother") bed of salt has been depleted. As 

Sannemann (1968) noted, once salt diapirs begin to 

form, the bedded salt migrates laterally toward the 

rising salt stocks (diapirs). It seems unreasonable to 

assume that salt was deposited only in restricted 

areas of the large Arapien basin.

Furthermore, the amount of salt found throughout 

the area now may have little or no bearing on the 

purported thickness of the salt. The critical factor is 

the amount of salt that was available during the 

times the diapiric folds were formed. Much of the 

salt that was present then may have been removed 

as a result of either dissolution or extrusion.

This migration of the salt may be the result of 

autonomous, isostatic movement (halo-kinesis), or the 

result of tectonic impulses (halo-tectonism) (Trusheim, 

1957; see also pages 129 and 131).

THICKNESS OF ARAPIEN SHALE

In most exposures the Arapien Shale is greatly 

deformed; crumpled and contorted beds are widespread, small folds accompany larger ones, and overturned folds are common (fig. 10). Deformation is 

intense, and so many beds are repeated that the original thickness of the Arapien is uncertain; estimates 

range from 1,200 to 4,000 m (4,000 to 13,000 ft) 

(Spieker, 1949, p. 17; Gilliland, 1948, p. 30; 1951,

p. 11; Hardy, 1949, p. 16, 17; Eardley 1933a, p. 331; 

Standlee, 1982, p. 363). Standlee (1982, p. 363), in 

particular, suggested that a thickness of about 

1,675 m (5,500 ft) "* * *closely approximate(s) the 

original stratigraphic thickness of the Arapien * * * 

in the Gunnison Plateau region." Standlee's thicknesses, based on the Dixel Resources and the Chevron U.S.A. Chriss Canyon wells (fig. 9), include 

oolitic limestone beds that I assign instead to the 

Twin Creek Limestone. Thus, his Arapien includes 

not only Arapien mudstones but also Twin Creek 

limestones.

I doubt whether any of the thicknesses cited above 

is a reliable indicator of the original thickness of the 

Arapien. The Arapien is probably thickest near the 

axes of the diapiric folds, thinnest between them.

AGE

The .Arapien Shale is of Middle Jurassic (Callovian) depositional age. Formerly the Arapien was 

assigned to the Bathonian (Witkind and Hardy, 1984). 

Sprinkel and Waanders (1984, p. 950), through study 

of the Twin Creek and Arapien relations, identified 

three distinct dinoflagellate assemblages which they 

assigned to the Bajocian(?), Bathonian, and Callovian 

Stages of the Middle Jurassic. The Bajocian(?) assemblage characterizes the lower part of the Twin Creek 

sequence, essentially the Sliderock and Rich Members. The Bathonian assemblage marks the medial 

part of the Twin Creek, chiefly the Boundary Ridge 

and Watton Canyon Members. And the Callovian 

assemblage is found in the Arapien Shale (Waanders 

and Sprinkel, 1984) additional support for the contention that the Arapien is essentially equivalent to 

the Leeds Creek Member.

Although the Arapien Shale was deposited during 

the Middle Jurassic, its age seemingly has changed 

throughout geologic time. In places, it deforms Cretaceous beds, elsewhere Eocene or Oligocene strata, and 

in several places it probably has deformed Pliocene or 

Quaternary units. Thus, although its depositional age 

is Middle Jurassic; its emplacement ages have 

changed repeatedly. To indicate the several emplacement ages, I have, on a published map (Witkind, 

1981), and on figures in other published articles (Witkind, 1982; 1983), used such symbols as "Q(Jat)," 

"K(Jat)," and 'T(Jat)" to indicate the major times 

(Q=Quaternary, K=Cretaceous, and T=Tertiary) during 

which the country rocks were deformed by the upward 

movement of the Arapien Shale (formerly known as 

the Twelvemile Canyon Member of the Arapien Shale; 

J=Jurassic, a=Arapien Shale, t=Twelvemile Canyon 

Member). In this paper I have omitted the "t" from the
26 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

112°30'

40°00

15' 112°00' 111°OQ'

45'H

38°30'

39°00'h40 KILOMETERS 

J

FIGURE 9 (above and facing page). Major test wells in central Utah, and their spatial relation to recognized diapiric folds. All wells 

are approximately located. Index A, location of figure 9; index B, general structural setting.
DIAPIRIC STRUCTURES 27

EXPLANATION

 Diapiric fold Dashed where inferred

1 Sanpctc-Scvicr Valley

2 Redmond

3 Levan

4 Sevier Bridge Reservoir

5 West Hills

6 Valley Mountains

7 Fairview

8 Little Clear Creek

9 Hjorth Canyon

1C Dry Hollow

1 Thistle Creek

1- Pole Creek

13 Footes Canyon

Well names and locations (Listed alphabetically)

A American Quasar-Chicken Creek Fed. No. 16-34, sec.

16, T. 15 S., R. 1 E.

B Amoco-Sevier Bridge No. 1, sec. 11. T. 16 S., R. 1 W. 

C Anderson No. 13-14, sec. 14, T. 18 S., R. 2 E. 

D Anschutz Corp., Williams Energy Monroe Fee No. 1,

sec. 14, T. 20 S., R. 2 W. 

E Chandler and Assoc.-Barton No. 4-2, sec. 2, T. 18 S.,

R. 2E. 

F Chevron U.S.A.-Chriss Canyon No. 1, sec. 33, T. 16

S., R. 1 E. 

G Chevron U.S.A.-Salina Unit No. 1, sec. 33, T. 22 S.,

R. 1 W. 

H Dixel Resources-Gunnison State No. 1, sec. 15, T. 16

S., R. 1 E.

I Exxon-Mt. Baldy, sec. 24, T. 12 S., R. 3 E. 

J Forest-Sigurd No. 1, sec. 14, T. 22 S., R. 1 W. 

K Hanson-Moroni No. 1, sec. 14, T. 15 S., R. 3 E. 

L Mobil-Larson No. 1, sec. 1, T. 17 S., R. 2 E. 

M Pacific Western-Gordon Creek No. 1. sec. 24, T. 14

S., R. 7 E.

N Phillips Petroleum-Nielson, sec. 1, T. 13 S., R. 2 E. 

O Phillips Petroleum-Price "N", sec. 29, T. 15 S., R. 3 E. 

P Phillips Petroleum-USA "D", sec. 20, T. 22 S., R. 3 E. 

Q Phillips Petroleum-USA "E", sec. 27, T. 19 S., R. 3 E. 

R Placid-Barton No. 1, sec. 32, T. 16 S., R. 1 W. 

S Placid-Howard 1-A WXC, sec. 5, T. 14 S., R. 1 W. 

T Placid-Howard 2 WXC, sec. 5, T. 14 S., R. 1 W. 

U Placid-Monroe No. 13-7, sec. 13, T. 16 S., R. 2 W. 

V Placid-Paxton No. 1, sec. 28, T. 23 S., R. 3 W. 

W Placid-State No. 1 WXC, sec. 36, T. 15 S., R. 1.5 W. 

X Placid-State No. 2 WXC, sec. 1, T. 15 S., R. 2 W. 

Y Placid-USA-1-2 WXC, sec. 24, T. 19 S., R. 2 W. 

Z Standard Oil of California-Levan Unit No. 1, sec. 17,

T. 15 S., R. 1 E. 

AA Standard Oil of California-Sigurd No. 1, sec. 32, T.

22 S., R. 1 W. 

BB Tennessee Gas Transmission-J.W. Irons No. 1, sec. 16,

T. 15 S., R. 3 E.

CC Union Oil-G-24, sec. 24, T. 11 S., R. 4 E 

DD Union Oil-J-9, sec. 9, T. 11 S., R- 4 E.

-Wasatch fault zone

I Great 

Salt 

Lake

41-K-rvoM L_ 11 °

"0\SALT LAKE CITY 

I Provo 1- « . -- ' 

| Utah Lafce 

Spanish Fork

' Cany Nephif 'Sbuthern

Charleston-Nebo 

thrust plate

39 L

-^ai ivui i i^ Nt'(

Wasatch 

Range

Wasatch 

fault zone

B

symbol to conform with the recent Witkind-Hardy 

(1984) proposal that the name "Twelvemile Canyon 

Member" be abandoned and its units be known simply 

as the "Arapien Shale" (p. 16).

DIAPIRIC STRUCTURES

INTRUSIVE ASPECTS OF THE ARAPIEN SHALE

The evidence I have seen in central Utah suggests 

that the salt in the Arapien Shale has been moving 

since shortly after it was deposited, and may well be 

moving today. Some of this movement has been a 

slow, continuous, persistent up welling, best demonstrated by the anomalous thinning of sequences of 

sedimentary units near the crests of major upwarps, 

but at times the salt seemingly has moved upward 

rapidly. 2 During these rapid upward movements the 

salt has acted much like a viscous fluid and has 

repeatedly pushed the enveloping Arapien mudstones 

both vertically and laterally, forcing them to intrude 

and deform, and locally to bow up and break the 

overlying sedimentary beds. Although I describe the 

Arapien Shale as an intrusive sedimentary unit, it is 

mainly the salt that is intrusive; the mudstones, 

shales, and other lithologic units of the Arapien, 

essentially passive, have been forced upward and laterally by the dynamic salt. Salt is the driving force, 

driven to some extent by buoyancy, and to some 

extent by static load stemming from the gradual 

accumulation of sediments in nearby areas. An analogy that comes readily to mind is that of a hydraulic 

car jack. The salt represents the hydraulic fluid, the 

Arapien mudstones and shales, the bearing platform 

of the jack, and the uplifted younger strata, the car. 

The buoyancy and static load, in this analogy, represent the mechanism that pumps the fluid in 

essence, the person laboriously raising and lowering 

the handle of the car jack.

Locally, where the beds have been bowed up, folded 

back, and overturned, the uppermost (older) beds 

have been shoved along bedding planes and across 

the underlying (younger) beds to create a series of 

both low- and high-angle reverse faults of minor displacement. Seemingly, the upward movements of the 

Arapien mudstone beds have been translated laterally into localized horizontal compressional forces. 

This has resulted in the many features along the east 

flank of the Gunnison Plateau (Weiss, 1982), or along 

the northeast flank of the Valley Mountains, that

2I use the term "rapid" in the context of geologic time. The upward movements I visualize are not sudden, cataclysmic events. The salt-generated folds 

described in this report probably developed quickly when contrasted with the 

time needed to form most other geologic features.
28 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

."iff"> -- f 'f.'-~' _ ' -&' * **f. »> -* *-.- .*.. -

**. -'-..>?-* J*&%&&.- +: £** '^ : >

*. <^-v^>^^r^|^ ,'^s~, t^;J^:^ ^F-" ^ v

 ^^'^^^^^.i^^M^^^.^ ^

FIGURE 10. Deformed beds of the Arapien Shale. A, Crumpled and 

contorted light-gray to gray mudstone and shaly siltstone beds 

of the Arapien Shale exposed in Salt Creek canyon along north 

side of Utah Highway 132, about 5 km (3 mi) east of Nephi. B, 

Overturned beds of the Arapien Shale exposed along Utah Highway 132, about 5 km (3 mi) east of Nephi. C, Overturned fold 

(dashed line) in the Arapien Shale exposed in the White Hills

near Mayfield. Photograph by Mathis Zimmermann, ElfAquitaine Oil Company. D, Intricate deformation within the 

crumpled mudstone and siltstone beds of the Arapien Shale. 

Comparable large- and small-scale deformation is common 

throughout the Sanpete Sevier Valley area, implying that the 

Arapien Shale is more or less deformed in central Utah.

suggest repeated compression from the east. Examples are the many minor "thrust faults" in which 

older, overturned units have been shoved westward 

onto younger right-side-up beds (Weiss, 1982), and 

the Z-fold in Dry Canyon (along the east flank of the 

Gunnison Plateau) (Spieker, 1949, p. 75), which 

reflects westward-directed compression.

The Arapien mudstone beds have been deformed so 

many times by their contained salt that their present 

attitude merely reflects the last episode of salt movement. The next diapiric episode will distort them 

once more into new and different attitudes.

Evidence of the mobile and intrusive nature of the 

Arapien Shale is widespread. On a small scale are 

minor structures, such as "dikes" and "sills" of 

Arapien Shale in country rock (figs. 11 and 46), that 

seem reasonably explained only by visualizing the 

Arapien Shale as an intrusive unit. On a large scale 

are the steeply tilted to overturned sedimentary beds 

that not only extend along strike for long distances 

but also flank those Arapien outcrops that I interpret 

as the cores of the major diapiric folds. This is perhaps most dramatically shown near Sterling (F-4), 

where to the west, in and near the Red Rocks (F-3)
DIAPIRIC STRUCTURES 29

area (fig. 19), those conglomerate beds in the 

Indianola Group that form the southeast flank of the 

Gunnison Plateau stand vertical or are overturned. 

East of Sterling, in Sixmile Creek canyon (F-4) 

(fig. 21), Indianola equivalents are also vertical or dip 

steeply eastward. Between these two sequences of 

steeply tilted beds, which I interpret as the west and 

east flanks respectively of the Sanpete-Sevier Valley 

diapiric fold, are the contorted shale and mudstone 

beds of the Arapien Shale the core of the fold.

The plastic and mobile aspects of the Arapien were 

noted by previous workers. So, for example, Spieker 

(1949, p. 68), impressed by the fact that the soft 

Arapien Shale formed hills even as the more resistant units were planed off, commented: "* * *the 

cheese-like shale rose under pressure while the more 

resistant sandstones stood firm." It is clear from 

Spieker's discussion, however, that, in his mind, the 

responsible forces were orogenic in nature, and 

wholly unrelated to the salt in the Arapien. Gilliland 

(1963, p. 122), also impressed by the high mobility of 

the Arapien Shale, attributed the development of the 

Sanpete-Sevier Valley anticline (my Sanpete-Sevier 

Valley diapiric fold) to flowage of the Arapien into the 

axial part of the anticline. He attributed the flowage 

to a combination of compressional forces and geostatic load, and noted: "* * *although salt and gypsum certainly must have aided in the growth of the 

anticline, their role was minor."

In the following pages, I first describe several 

minor structures that display the intrusive characteristics of the Arapien Shale (p. 29-37), then describe 

the huge diapiric folds that dominate this sector of 

central Utah (p. 37-102), and finally suggest how I 

believe the diapiric folds grew and collapsed (p. 117- 

132).

MINOR STRUCTURES

THISTLE AREA

The intrusive aspects of the Arapien Shale are well 

shown in the Thistle (A-5) area. As a result of the 

disastrous Thistle landslide of April 1983 (Duncan 

and others, 1986; Kaliser and Fleming, 1986), a new 

segment of U.S. Highway 6 and 89 had to be cut 

through a large hogback known locally, and erroneously, as Billies Mountain.3 The hogback, in sec. 28, T. 

9 S., R. 4 E., is east of the landslide and consists of

3The crews involved in the conversion of the Thistle landslide into an earthfilled dam (Thistle dam), and in the construction of the new segment of U.S. 

Highway 6 and 89, incorrectly called the ridge "Billies Mountain." In fact, 

Billies Mountain is some 3 km (2 mi) northeast of the ridge. Continued incorrect usage has transferred the name Billies Mountain to the hogback.

the Navajo Sandstone overlain by Twin Creek Limestone, both of which dip steeply eastward. These 

units are part of the eastern mass of the CharlestonNebo thrust plate, and an erosional escarpment has 

been cut across them (Witkind, 1988, p. 86 and fig. 2). 

The escarpment is partly concealed beneath a series 

of Cretaceous and Tertiary units, chiefly beds of the 

North Horn, Flagstaff, and Colton Formations that 

unconformably overlie the Navajo and Twin Creek 

strata. The new segment of U.S. Highway 6 and 89, 

that cuts through the Twin Creek beds, exposed large 

and small irregular wedgelike masses of Arapien 

Shale that not only intrude and deform the limestone 

beds of the Twin Creek (fig. 1LA), but also follow the 

unconformable contact between the Twin Creek and 

the overlying Colton Formation (fig. 1LB).

DOME NEAR ANCESTRAL WILLOW CREEK

A small, elongate dome about 8 km (5 mi) northeast of Salina (G-3), occupies the SEV4 sec. 33, T. 20 

S., R. 1 E. (fig. 14A). The core of the dome, north of 

an ancestral course of Willow Creek (G-3), consists 

of deformed beds of the Arapien Shale (fig. 12). Salt 

was once mined from these Arapien beds, and even 

now salt bloom mantles many of the Arapien mudstones. Green River strata overlie these Arapien 

mudstones along the margins of the dome, and in 

places, Crazy Hollow beds overlie the Green River 

strata.

About 3 km (2 mi) east of the dome the Green 

River beds dip westward toward the dome at angles 

of about 30°. At the east edge of the Arapien outcrop 

the westward-dipping Green River beds flex up 

sharply and dip eastward at about 30°. On the opposite side of the dome, at the west edge of the Arapien 

outcrop, Green River beds dip steeply (60°) northwestward. They are overlain by semiconsolidated 

sands and gravels, probably the Axtell Formation of 

Pliocene and (or) Pleistocene age, that dip northwestward at about 20°.

I interpret these exposures to mean that the 

Arapien Shale intruded and deformed this area 

twice. During the first intrusive event (late Eocene(?) 

or Oligocenef?) i the Green River was bowed up. Subsequently, these upturned beds were beveled and 

then buried by near-horizontal sand and gravel beds 

of the Axtell Formation. During the second intrusive 

event (Pliocene(?)-Pleistocene(?)) the Green River 

beds were bowed up once again to a still steeper 

angle, and the newly deposited, near-horizontal sand 

and gravel beds were tilted to an attitude considerably steeper than their former angle of repose.
30 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

FIGURE 11. Intrusive aspects of the Arapien Shale. Exposures 

are near Thistle, Utah. A, Beds of the Arapien Shale intrude 

and deform tilted beds of the Middle Jurassic Twin Creek 

Limestone, part of the erosional escarpment formed on the 

Charleston-Nebo thrust plate. B, View looking northward in 

roadcut where a segment of U.S. Highway 6 and 89, relocated 

following the Thistle landslide of April 1983, crosses the crest 

of "Billies Mountain." A dikelike mass of Arapien Shale is intruded between the Twin Creek Limestone (which here forms 

part of the erosional escarpment cut on the Charleston-Nebo 

thrust plate) and the Colton Formation, one unit in a mantle 

of younger Cretaceous and Tertiary rocks that partly overlies 

the thrust plate.

Elsewhere in this general area, an isolated outcrop 

of the semiconsolidated beds of sand and gravel (the 

Axtell Formation) has been warped into a syncline 

above an even more pronounced syncline in the 

Arapien (Gilliland, 1963, p. 121, and pi. 3, fig. 2). The 

evidence attests to the recency of the upward movement of the Arapien, and strongly suggests that similar movements have occurred repeatedly during the 

Tertiary and Quaternary.

RED KNOLLS AREA

At the three Red Knolls, along the west side of 

Sevier Valley near the small community of Redmond 

(G-3), the Arapien Shale appears to have intruded 

and bowed up the toe of an alluvial fan (fig. 13). The 

knolls coalesce to form a low ridge that trends about 

N. 30° E. and that rises some 35 to 70 m (110 to 230 

ft) above the adjacent ground surface. The ridge, 

which extends through parts of sec. 35, T. 20 S., R. 1 

W., and sec. 2, T. 21 S., R. 1 W., is underlain by soft 

reddish-brown mudstone and shaly siltstone of the 

Arapien Shale; the surrounding terrain by sand and 

gravel. The gravel is unusually rich in volcanic 

clasts, possibly derived from the Osiris Tuff (Willis, 

1986). The volcanic clasts are so plentiful that the 

gravel has a gray to dark-gray hue; Gilliland (1948, 

p. 103), impressed by the volcanic detritus, referred 

to the gravels as the "volcanic gravels." These gravels 

are inclined away from the ridge.

Comparable volcanic clasts are widespread in the 

uplands near Salina (G-3), but are not found in the 

nearby Valley Mountains (G-2) west of the Red 

Knolls. Thus, it would seem that the volcanic-rich 

gravel deposits near Redmond may represent part of 

an old alluvial fan that spread northwestward from 

the Salina area. Since the development of the fan, 

erosion has removed the bulk of the fan, leaving only 

the remnant near Redmond. This remnant, which I 

view as the toe of the fan, is split into two parts by 

the northeast-trending ridge formed by the coalescence of the Red Knolls. One cannot help but be 

impressed by the contrast between the soft mudstones that form the Red Knolls, and the unconsolidated, lower, more durable sand and gravel deposits 

that flank them. It seems unreasonable to assume 

that these soft mudstone knolls could have remained 

high when more durable units were being eroded and 

removed. The knolls must have been elevated at 

some time in the recent past. This bifurcation of a 

former unified mass can only mean that at some time 

after the fan was formed, the Arapien Shale intruded 

the fan, bowed it up, and effectively split the toe of 

the fan into two parts. Since then, erosion has 

removed the former gravel cap from the knolls and 

now is rapidly lowering the knolls.

I am uncertain just when the Arapien intruded the 

fan. The sand and gravel mantle probably was 

formed during the Pleistocene; hence, a reasonable 

assumption is that the uplift began and ended during 

the late Pleistocene or early Holocene.

Others have also noted the intrusive nature of the 

Arapien Shale in the Redmond area, and they, too,
DIAPIRIC STRUCTURES 31

111°48'30 EXPLANATION

1000 2000 3000 FEET

A'

FEET

5000- -5000

FIGURE 12. Geology of an area near an ancestral course of 

Willow Creek, in which Arapien Shale mudstones (T(Ja)) have 

intruded and bowed up younger sedimentary rocks to form an 

elongate dome. Along east edge of area. Green River strata 

(Tg) dip westward, but farther west, at east edge of the intrusive mass, they flex up sharply, reverse dip, and dip eastward 

at angles of about 30°. Green River strata (Tg) that overlie 

west edge of intrusive mass (near center of map area) dip

Holocene and > QUATERNARY

Coalesced alluvial fans

Colton Formation

?

T(Ja)

i 

Arapien 

Shale

Pleistocene

- Pliocene(?)

 Eocene

Middle 

Jurassic

.

>- TERTIARY

JURASSIC

Contact

Intrusive contact Oblongs on intrusive unit

Fault Dashed where inferred; bar and ball on 

downthrown block

25

Strike and dip of inclined beds 

 ^Sa Abandoned salt mine 

X U Uranium prospect

northwestward at high angles. Semiconsolidated sands and 

gravels, here mapped as pediment mantle (QTpm) but probably part of the Axtell Formation, overlie these steeply tilted 

Green River strata. These surficial deposits also dip northwestward at angles greater than their normal angle of repose. 

Fig. 14A gives a photographic overview of the intrusive dome. 

Base modified from U.S. Geological Survey 1:24,000 Redmond 

(Utah), 1966. Topographic contour interval 100 ft.

attributed that movement to salt (Pratt, Heylmun, 

and Cohenour, 1966, p. 52; Picard, 1980, p. 145).

CUESTA NORTH OF REDMOND

A small north-trending cuesta that occupies the 

SEV4 SWV4 sec. 12, T. 20 S., R. 1 W., just north of 

Redmond (G-3), illustrates still another example of 

the intrusive nature of the Arapien Shale. The cuesta 

is underlain by beds of the Green River(?) Formation. 

The strata dip eastward (valleyward) at about 35°, 

and rise above an even surface underlain by Arapien 

Shale mudstone and siltstone. A small mound, about 

8 m (25 ft) high, formed by the Arapien Shale, bulges

above the ground surface and abuts the south end of 

the ridge (fig. 14B).

I interpret the cuesta as a remnant of the east flank 

of the Redmond diapiric fold. Presumably, the Green 

River(?) beds were bowed up by upward movement of 

the Arapien Shale, which in this area is part of the 

diapiric core of the fold. The Arapien mudstones in the 

small mound probably did not break through to the 

surface during this intrusive stage; if they had, they 

would have been removed long ago. More likely, in 

view of their soft and easily eroded nature, they broke 

through at some time late Pleistocene or early 

Holocene after the erosion surface that encircles the 

ridge was formed.
32 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

1H°52'3D'

39°00' ^

I

1 MILE

2 KILOMETERS

J

R 1 W R 1 E

EXPLANATION

Q(Ja)

Qal

Alluvium

$$$£?

Older alluvialfan deposits 

Coal

is

 - 0

esced all 

n deposi

HOttS 1 ^ Holocene

Slope wash 1

1 

^ Pleistocene 

1 

j^ Pliocene(?)

nvial- 1 

ts ! Middle 

1 Jurassic

TERTIARY

JURASSIC

Arapien Shale

Contact Approximately located or inferred
DIAPIRIC STRUCTURES 33

FIGURE 13 (facing page). Geology of the Red Knolls area near 

Redmond, Utah. Base modified from U.S. Geological Survey 

1:24,000 Redmond Canyon and Redmond (1966). Contour interval 40 ft. Each of the Red Knolls is composed of red mudstones of the Arapien Shale (Q(Ja)), and all are part of a

{ northeast-trending ridge formed of the same material. The 

older alluvial-fan deposits (Qof) are rich in basaltic fragments 

not found in the Valley Mountains west of Redmond. Presence 

of these older fan deposits (Qof) on both sides of the northeast-trending Arapien ridge suggests that they were once a 

continuous deposit that has since been separated by the upthrust mass of the Arapien Shale.

HOGBACKS IN EASTERN SEVIER VALLEY

The moderately to steeply inclined beds that form 

the hogbacks in the eastern Sevier Valley (between 

Mayfield (F-3) and Salina (G-3)) also strongly imply 

upward movement of the Arapien Shale. The hogbacks consist of Green River beds unconformably 

overlying the Arapien Shale; the Green River beds, 

in turn, are conformably overlain by beds of the

NORTH SOUTH

NORTH SOUTH

Eastward-tilted beds of 

the Green River Formation

Sand and 

gravel deposit

Red mudstones of the Wasatch Plateau 

AraPien Shale \

WEST EAST

Green Rived?) Formation 

4^ -^ Arapien Shale

<-*">* **,

FIGURE 14. Small-scale features throughout the San pete Sevier 

Valley area that suggest intrusive movement by the Arapien 

Shale. A, Small intrusive dome near an ancestral course of Willow Creek. The red mudstones of the Arapien Shale have bowed 

up the overlying Green River strata to form an elongate, northeast-trending dome. See figure 12 for geologic map of area. B, 

Small mound composed of mudstones of the Arapien Shale that 

abut, deform, and probably intrude units of the Green River(?) 

Formation. Because the mudstones are soft and easily eroded, 

their presence in the mound suggests that they probably broke 

through to the surface only in late Pleistocene or even Holocene

Wasatch Plateau

Steeply dipping beds of 

the Green River Formation

Steeply dipping beds of 

Crazy Hollow Formation 

concealed beneath slope 

wash

NORTH

Eastward-dipping beds of 

Green River Formation

SOUTH

Wasatch Plateau,

time. C, One of several large northeast-trending hogbacks north 

of Salina in which Green River beds, dipping steeply to the 

west and that form the back slope of the hogback, overlie 

Arapien mudstones (not shown). View is eastward. These relations have been interpreted by Billings (1933) to be the result 

of strip-thrusting. I suggest instead that they stem from the 

intrusive action of the Arapien mudstones that were forced 

upward by upwelling salt. D, View looking southeastward 

across Sanpete Valley at the face of a small knoll south of Ninemile Reservoir that displays upward tilting of the Green River 

Formation by the underlying Arapien Shale. See figure 15 for 

geologic map of area.
34 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

Arapien Valley Tg (shale unit)

19 _ Tg (shale unit) Tg Qsw

Sanpete-Sevier Valley diapiric fold

T 19 S

39"07 30

4000- : : '-4000
DIAPIRIC STRUCTURES 35

Qal

Alluvial fan Alluvium

Qoa

Older alluvium

Qsw

Slope wash I

I

EXPLANATION

Holocene Q[JATERNARY 

Pleistocene

North Horn Formation

Price River Formation

Indianola Group and 

Cedar Mountain Formation

FIGURE 15 (above and facing page). Geology of an isolated, 

unnamed hill directly south of Ninemile Reservoir. Strata of 

the Green River Formation (Tg) dip west as part of the 

Wasatch monocline. West of Arapien Valley the Green River 

directly overlies the Arapien Shale and dips east, reflecting

T(Ja)

Arapien 

Shale

->

-<

 <

* Eocene

" Paleocene

-<

Upper 

Cretaceous

y Lower 

Cretaceous

i Middle 

| Jurassic

TERTIARY

 Contact Approximately located or inferred; 

dashed in cross section where 

speculative

- - - Intrusive contact Approximately located or

inferred; oblongs on intrusive unit 

Fault Dashed where approximately located; 

dotted where concealed; bar and ball on 

downthrown block; barb shows 

downthrown block in cross section 

Strike and dip of inclined beds

Strike and dip of overturned beds

CRETACEOUS

JURASSIC

upward movement of the Arapien mudstones, which have been 

forced upward by the upwelling of the Sanpete Sevier Valley 

salt diapir under Sanpete Valley. Base modified from U.S. 

Geological Survey 1:24,000 Sterling (1966). Contour interval 

200 ft.

Crazy Hollow Formation of Eocene age. The Green 

River and younger beds dip westward at moderate to 

steep angles, and in a few places are near-vertical 

(fig. 14C). Commonly, the contact between the Green 

River and Arapien beds is even and regular, but 

locally it is ragged and irregular. In one or two 

places the Green River strata are broken to form an 

imbricate sheet, and here and there these strata dip 

into the contact at angles of 30° to 60° (Billings, 

1933, p. 153-154). Billings interpreted these relations to be the result of thrusting during which 

younger beds (the Green River and overlying strata) 

were shoved eastward along a preexisting unconformity onto older Jurassic shales (Arapien Shale). The 

term "strip-thrust" was coined by Billings to describe 

these thrust relations.

It is difficult to visualize, however, how the steep 

to vertical dip of these beds could have been formed 

solely by strip-thrusting. A more reasonable

explanation, it seems to me, involves the bowing up 

and folding back of the Green River and younger 

strata by the upward movement of the Arapien 

Shale. Some support for this intrusive concept is 

given by the age relations. If the Green River Formation overlies the Arapien mudstones as a result of 

strip-thrusting, this thrusting must have begun at 

some time following deposition of the Crazy Hollow 

Formation of Eocene age, presumably during either 

the late Eocene, Oligocene, or later. This, however, 

raises vexatious problems. The thrusting that marks 

the Sevier orogeny began in either Late Jurassic 

(Armstrong, 1968) or Early Cretaceous (Heller and 

others, 1986) time, continued as episodic pulses 

throughout much of Cretaceous time, and seems to 

have ended during the Late Cretaceous or early Paleocene (Armstrong, 1968, p. 449). This lengthy episode 

of thrusting was followed by one of extensional tectonism that began during either the late Oligocene or
36 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

40 KILOMETERS

20 MILES
DIAPIRIC STRUCTURES 37

Miocene and that has persisted to the present. If 

strip thrusts were indeed formed during the Oligocene, or later, as Billings suggested for this sector 

of the Sevier Valley, this Tertiary thrusting would 

have begun long after thrusting ended elsewhere, 

and even as block faulting was beginning in this area 

in response to the widespread episode of crustal 

extension. The pattern of crustal deformation, so 

widespread throughout the Western Interior of the 

United States, argues against thrusting in this area 

after Paleocene time. In my view, the most plausible 

explanation for the structural deformation of these 

hogbacks involves the upward tilting of the Green 

River beds by the upward, rising movement of the 

Arapien Shale.

SMALL HILL NEAR NINEMILE RESERVOIR

A small hill directly south of Ninemile Reservoir 

(F-3) displays upward tilting of Green River beds by 

the Arapien Shale. Directly east of the hill, Green 

River limestone beds, dipping west as part of the 

Wasatch monocline, pass below the east edge of 

Arapien Valley (fig. 15). These Green River limestone 

beds reappear along the west side of the valley, but 

dip east, and thus form a small north-trending 

syncline whose axis has determined the trend of 

Arapien Valley. These limestone beds, part of the 

upper unit of the Green River Formation, directly 

overlie the Arapien Shale. The fact that units commonly found below these limestone beds, such as the 

shale unit that makes up the lower part of the Green 

River Formation, fail to crop out implies that these

FIGURE 16 (facing page). Major diapiric folds in central Utah. 

Thick dark lines represent approximate position of fold crests; 

dashed lines represent inferred position. Query reflects 

uncertainty as to whether mapped structure is a diapiric fold. 

Encircled numbers identify folds. Page numbers refer to 

description of fold in text.

1 Sanpete-Sevier Valley diapiric fold (p. 38).

2 Redmond diapiric fold (p. 57).

3 Levan diapiric fold (p. 69).

4 Sevier Bridge Reservoir diapiric fold (p. 57).

5 West Hills diapiric(?) fold (p. 100).

6 Valley Mountains diapiric(?) fold (p. 101).

7 Fairview diapiric(?) fold (p. 98).

8 Little Clear Creek diapiric fold (p. 96).

9 Hjorth Canyon diapiric fold (p. 93).

10 Dry Hollow diapiric fold (p. 83).

11 Thistle Creek diapiric(?) fold (p. 83).

12 Pole Creek diapiric fold (p. 77).

13 Footes Canyon diapiric(?) fold (p. 81).

older units pinched out against a rising paleo-high 

the core of the Sanpete-Sevier Valley diapiric fold 

(cross section, fig. 15). The abrupt reversal of the 

Green River beds to an eastward dip must reflect the 

upward push of Arapien beds. The relations between 

the intrusive Arapien and the upward tilted Green 

River beds are well exposed along the west flank of 

the knoll (fig. 14D).

MAJOR STRUCTURES (DIAPIRIC FOLDS)

I recognize 13 diapiric folds in and adjacent to the 

Sanpete-Sevier Valley area (fig. 16), and believe that 

other comparable folds are still to be found. The folds 

appear as elongate, narrow, linear to faintly sinuous 

upwarps whose trend and extent reflect the underlying salt diapirs. The folds are much like the "salt 

anticlines" (salt-cored anticlines) of the Paradox 

Basin in southwestern Colorado and northeastern 

Utah (Cater, 1955, p. 125), and the "elongate salt 

structures" of northern Germany (Trusheim, 1960, 

fig. 3). Although the folds in central Utah have been 

deeply eroded, one is impressed by the similarities 

between the central Utah folds and those exposed in 

the Paradox Basin. These central Utah diapiric folds 

extend for tens of kilometers. In places, the position 

and trend of individual folds are expressed by outcrops of the calcareous mudstones of the Arapien 

Shale, which I interpret as the "diapiric core" of the 

fold (fig. 5). Elsewhere, the Arapien Shale is concealed beneath surficial deposits, and the fold is 

expressed by elongate, linear belts of steeply dipping 

to vertical and overturned sedimentary beds (the 

deformed country rocks of fig. 5). I interpret these 

complexly deformed sedimentary beds to be the 

eroded flanks of the fold. I believe that the strike of 

these vertical or overturned beds precisely reflects 

the trend of the diapiric fold and its underlying causative salt diapir.

The contorted beds of Arapien Shale that underlie 

the White Hills (G-3), along the east side of Sevier 

Valley, are an excellent example of the exposed core 

of a north-trending diapiric fold; the vertical to overturned beds that delineate much of the east flank of 

the Gunnison Plateau are an outstanding example of 

the eroded west flank of the same north-trending 

fold the Sanpete-Sevier Valley diapiric fold.

These vertical to overturned beds of the deformed 

country rock (fig. 5) are typically confined to a narrow zone. In place after place, these beds, traced 

perpendicular to strike, abruptly lessen in dip away
38 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

from the diapiric core and conform to the regional dip 

in distances as short as several kilometers. If these 

steeply tilted beds were concealed beneath surficial 

deposits, it would be almost impossible from surface 

exposures to recognize the presence of one of these 

folds (fig. 64).

The 13 diapiric folds trend generally northward 

through the Sanpete-Sevier Valley area (fig. 16), 

more or less parallel to the many grabens and highangle normal faults that break the crest of the 

Wasatch Plateau. Most of the folds trend northeast; a 

few mainly those that flank the Gunnison Plateau 

trend north; a single fold, the Sevier Bridge Reservoir 

fold, trends northwest. Their spatial distribution suggests that most are interrelated, each branching off 

another much as distributary streams branch off a 

master stream.

The Sanpete-Sevier Valley fold (fig. 16, 1) appears 

to be the master fold. Branching off its south end is 

the Redmond fold (2), which extends at least from 

Redmond (possibly Sigurd) to near Gunnison and 

may continue northward to join the Levan fold (3). 

Near Fayette, the Sevier Bridge Reservoir fold (4) 

may branch off the Redmond fold. The West Hills 

fold (5), trending north, has been drilled and much 

salt found in its core. The Valley Mountains fold (6) 

also may once have had a salt core; recent drilling 

failed to penetrate any salt. A north-trending graben 

in the Valley Mountains, Japanese Valley, suggests 

that the salt core of the fold may have been dissolved 

and removed, with subsequent collapse of the overlying strata to form the graben. The Fairview 

diapiric(?) fold (7) may branch off the master 

Sanpete-Sevier Valley fold near Ephraim and extend 

northeastward to near Indianola. The Little Clear 

Creek fold (8) trends northeastward; its crest has 

determined the position of Little Clear Creek. The 

northeast end of the Little Clear Creek fold passes 

directly into the Dairy Fork graben, implying dissolution of the salt core with subsequent collapse of the 

overlying beds to form a graben. The Hjorth Canyon 

fold (9) appears as an elongate northeast-trending 

dome. The Dry Hollow fold (10) is collinear with and 

may be the north end of the northeast-trending Pole 

Creek fold (12). The Thistle Creek fold (11) and the 

Footes Canyon fold (13) seemingly have deformed 

part of the Charleston-Nebo thrust plate.

SANPETE-SEVIER VALLEY DIAPIRIC FOLD

The Sanpete-Sevier Valley diapiric fold (the 

Sanpete-Sevier Valley anticline of Gilliland (1963)) 

appears to be the longest of the 13 folds so far recognized (fig. 16, 1). On the basis of diverse geologic evidence (such as exposures of the Arapien Shale,

steeply tilted to overturned sedimentary beds, testwell data, and collapse phenomena), I believe that 

the fold extends northward from near Richfield (1-1) 

to at least Moroni (D-4). Gravity data (fig. 52) imply 

that the fold extends northward beyond Moroni, possibly reaching Fountain Green (C-4). If so, the fold 

has a minimum length of at least 95 km (60 mi), and 

may be as much as 125 km (75 mi) long. In general, 

the fold trends about N. 30° E., although its course is 

faintly sinuous.

The exposed diapiric core of the fold, expressed as 

an unbroken belt of Arapien mudstone, extends from 

near Richfield on the south to near Manti (E-4) (fig. 

8). Northward, beyond Manti, the core is completely 

concealed beneath the surficial deposits that floor 

Sanpete Valley Between Richfield and Salina (G-3), 

the core clings to the east side of Sevier Valley, where 

volcanic flows mantle both flanks. Those volcanic 

rocks along the east flank of the core dip eastward; 

those along the west flank dip westward. Locally, 

these volcanic rocks are overturned (Gilliland, 1963, 

p. 121). Farther north, between Salina and Mayfield 

(F-3), the core of the fold still hugs the east side of 

Sevier Valley, but here the core's west flank is overlain by Green River strata that dip moderately to 

steeply westward. The core's east flank, presumably 

eroded, is concealed beneath the surficial deposits 

that floor Arapien Valley (G-3). Near Sterling (F-4), 

the core fills the narrow mouth of Sanpete Valley; 

both flanks of the fold are exposed as near-vertical to 

overturned beds of Cretaceous rocks (figs. 19 and 21).

The vertical to overturned Indianola beds along the 

east flank of the Gunnison Plateau (D-3) represent 

the partly eroded west flank of the fold (fig. 17). 

These strata are unconformably overlain either by 

the Price River Formation, or, where Price River 

strata pinch out presumably against the flanks of the 

fold, by the North Horn Formation. Invariably, these 

younger Price River and North Horn strata dip away 

from the crestal part of the fold at moderate angles 

(20° to 30°). In the Sterling area, where both flanks 

of the fold are exposed, Indianola beds east of the 

core are overlain by North Horn strata that dip east 

20° to 30°. West of the core, North Horn strata dip 

west at comparable angles.

I believe that the Sanpete-Sevier Valley diapiric 

fold abuts the east side of the Gunnison Plateau as far 

north as Freedom (D-4); beyond Freedom the crestal 

part of the fold trends northward toward Fountain 

Green (C-4), even as the front of the Gunnison 

Plateau bends to the northwest. In this sector, thus, 

the crest of the fold may be about 2.5 km (1.5 mi) east 

of the steep slopes and cliffs that mark this part of the 

plateau front. I suspect that the fold curves near
DIAPIRIC STRUCTURES 39

WEST

-Westward-dipping beds 

of Flagstaff Limestone

EAST

Westward-dipping beds 

'of North Horn Formation

Westward-dipping beds 

of Flagstaff Limestone

FIGURE 17. Aerial views along east flank of Gunnison Plateau. Vertical to overturned beds 

of the Indianola Group and Price River Formation form a striking reef along part of the 

plateau's east front. In most places, gently to moderately inclined Price River strata unconformably overlie vertical and overturned beds of the Indianola Group. A, In the view 

shown here (looking northward), the Price River beds, along with the underlying Indianola 

strata, have been tilted upward to vertical and overturned attitudes. These vertical and 

overturned beds flatten westward and underlie the westward-dipping, reddish-brown mudstones and brown sandstone beds of the North Horn Formation, which form the steep 

escarpment. The North Horn Formation, in turn, is overlain conformably by westwarddipping beds of the Flagstaff Limestone. B, View looking westward, showing reef formed 

by vertical and overturned beds of the Price River and Indianola Group (center of photograph), and still farther west, the westward-dipping North Horn strata conformably overlain by the Flagstaff Limestone (on horizon). See cross section A A', figure 24, for details. 

Photographs by D.A. Sprinkel, Placid Oil Company.
40 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH
DIAPIRIC STRUCTURES 41

Fountain Green and trends northwestward, conforming to the trend of the west fork of Sanpete Valley.

In my view, the 620 m (2,038 ft) of salt and interlayered subordinate mudstone penetrated by the 

Price "N" well (fig. 9), which was about 2.8 km (1.7 

mi) east of the Gunnison Plateau front, reflects the 

east flank of the causative salt diapir. Had the well 

been drilled farther to the west, in essence, closer to 

the plateau front, I believe that thicker deposits of 

salt would have been found. The Hanson Oil Company's Moroni wells, drilled about 5 km (3 mi) east of 

the Price "N" well, penetrated great thicknesses of 

Arapien mudstone, but found no salt. Seemingly, the 

Moroni wells are substantially east of and beyond the 

flanks of the salt diapir.

Unusual geologic and structural relations at four 

discrete localities along the flanks of the fold demonstrate how this fold repeatedly grew and collapsed. 

These localities are: (1) the Red Rocks (F-3)-Sixmile 

Canyon area (F-3), (2) Wales Gap (D-4), (3) the 

ancestral Willow Creek area (also known as the Willow Creek gap), and (4) the Gunnison Reservoir (F-3) 

area. For each area, I discuss the salient features 

and propose a sequence of diapiric events to explain 

the present configuration of the strata.

RED ROCKS-SIXMILE CANYON AREA

The Red Rocks (Christianburg) and Sixmile Canyon areas represent the west and east flanks, respectively, of the Sanpete-Sevier Valley fold. In these two 

areas the exposed rocks demonstrate not only depositional thinning but also how diapiric folds grew and 

collapsed.

FIGURE 18 (facing page). Red Rocks area, north of U.S. Highway 

89, between Gunnison (F-3) and Sterling (F-4). A, Distant view, 

looking north at the Red Rocks area. As the open syncline 

(along skyline), in conglomerate beds of the Indianola Group, is 

traced southward (toward camera), the syncline closes to become an isoclinal fold whose axial plane dips steeply eastward. 

The eastward-dipping conglomerate ledges (slightly to right of 

center) are part of the west flank of that fold. These conglomerate beds are overlain with striking angular unconformity by

f both Price River and North Horn strata. B, Close-up view of 

Red Rocks exposure showing unconformable relations between 

eastward-dipping beds of the Indianola Group (right side of photo), and westward-dipping beds of the Price River and North 

Horn Formations. C, Detailed view of angular unconformity between Indianola Group and the overlying North Horn strata. 

Geologist stands on eastward-dipping Indianola strata; dog 

stands on westward-dipping North Horn. D, Sketch illustrating 

details of photograph shown in B.

RKD ROCKS AREA

The southeast end of the Gunnison Plateau, north 

of U.S. Highway 89 between Gunnison (F-3) and 

Sterling (F-4), is known locally as the "Red Rocks 

area" because of the well-exposed reddish conglomerate beds that here make up the undivided Indianola 

Group (fig. 18A, and fig. 19). Spieker (1949, p. 76) 

referred to the site as the Christianburg area; I have 

not used that name because Christianburg is not on 

modern highway maps. The critical exposures occupy 

parts of sees. 12 and 13, T. 19 S., R. 1 E., and sec. 7, 

T. 19 S., R. 2 E.

Among the oldest units exposed in the Red Rocks 

area are the steeply inclined and overturned, coarse 

conglomerate beds of the Indianola Group (fig. 18A, 

B). These beds dip eastward, and are flexed to form 

an isoclinal syncline whose axial plane dips steeply 

to the east. An angular unconformity that dips about 

25° W (fig. 18A-D) truncates the conglomerates, and 

an unusually thin section of the Price River Formation (0.5 to 1.5 m (2 to 5 ft) thick) overlies the unconformity. The Price River is, in turn, conformably 

overlain by about 40 m (135 ft) of North Horn strata. 

The Price River and North Horn sequence dips 

northwestward at about 30°. The North Horn strata 

are overlain by beds of the Flagstaff Limestone, 

which also dip northwest at about 30°. These limestone beds belong to a zone in the Flagstaff Limestone that is "some distance above the North Horn" 

(Spieker, 1949, p. 76). Thus, the structural relations 

between the North Horn and Flagstaff are uncertain. 

Spieker (1949, p. 76), referring to these relations, 

commented: "The question is whether or not there is 

an angular relation at the contact between the Flagstaff and North Horn formations, and it is not settled. The contact is concealed* * *." I suspect that an 

unconformity separates the North Horn beds from 

the Flagstaff, and that this unconformity, too, is 

tilted northwestward.

In gross aspect, then, the exposed sequence is broken by an angular unconformity between the Indianola beds and the Price River and North Horn 

sequence, and a disconformity(?) between North Horn 

and Flagstaff strata.

All units exposed in the Red Rocks area, from the 

Price River to the Flagstaff, are anomalously thin 

compared with their thicknesses some 13 km (8 mi) 

to the east along the flanks and crest of the Wasatch 

Plateau.

Figure 20, which schematically depicts the west 

limb of the Sanpete-Sevier Valley fold, illustrates the 

sequence of events that I believe led to the present
42 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

Red Rocks 

in figure 20 \ area

3000-

-4000

-3000

FIGURE 19 'above and facing page). Geology of Red Rocks area (F-3). Strata represent part of the west flank of the Sanpete-Sevier Valley 

diapiric fold. Base modified from U.S. Geological Survey 1:24,000 Sterling and Gunnison (1966). Contour interval 200 ft.

geologic relations; the following discussion is keyed to 

that figure.

The isoclinal fold in the Indianola conglomerates 

(fig. 20, I) suggests that major movement of the 

Sanpete-Sevier Valley diapir first occurred after

consolidation of the Indianola, probably during Late 

Cretaceous (Campanian?) time. The Indianola beds 

were bowed up and then steeply tilted or overturned 

as the diapiric fold developed. Probably, Indianola 

strata on both sides of the fold were overturned
DIAPIRIC STRUCTURES 43

Alluvial fan 

deposits

T(Ja)

Arapicn Shale

EXPLANATION

Landslide Older alluvial Older alluvialHolocene f QUATERNARY

I I

deposits fan deposits I

Arapien Shale

Eocene

Paleocene

Upper 

Cretaceous

Lower 

Cretaceous

Middle 

Jurassic

TERTIARY

>- CRETACEOUS

JURASSIC

20

80

-yContact Approximately located or inferred

Intrusive contact Approximately located or 

inferred; oblongs on intrusive unit

Fault Dashed where approximately located; 

dotted where concealed; bar and ball 

on downthrown block

Strike and dip of inclined beds

Strike and dip of overturned beds

Overturned syncline Approximately located; 

showing direction of dip of limbs

111 C43'

Modified somewhat from 

original mapping by 

M.P. Weiss, Northern 

Illinois University

SOURCES OF GEOLOGIC DATA
44 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

EAST

WEST EAST

EXPLANATION

~ZI \ Ground surf ace __- - f ~\ 

^ ^^ - /

Indianola Group and 

Cedar Mountain Formation

Eocene

TERTIARY

Paleocene

Upper 

Cretaceous

Lower 

Cretaceous

CRETACEOUS

Contact
DIAPIRIC STRUCTURES 45

FIGURE 20 (facing page). Diagrammatic cross sections suggesting 

how the Red Rocks area evolved. All sketches depict part of the 

west flank of the Sanpete-Sevier Valley diapiric fold. Ground 

surface in I-V speculative, not shown.

I. At some time during the Late Cretaceous (Campanian?), beds 

of the Indianola Group and the underlying Cedar Mountain Formation (Kic) were folded and locally overturned as a result of 

upward movement of the Sanpete-Sevier Valley salt diapir. A 

small isoclinal syncline, whose axial plane dips steeply eastward, was formed in the Red Rocks area.

II. As rate of upward movement decreased, erosion cut a surface 

of low relief across the diapiric fold. Price River strata (Kpr), 

deposited on this surface, thin eastward (toward the diapir) and 

locally pinch out, reflecting the diapir's slow persistent upward 

movement. North Horn strata (TKn), deposited conformably on 

the Price River (Kpr), also thin eastward; both North Horn and 

Price River were warped upward in response to the slowly rising 

diapir.

III. A renewed upward surge of the salt diapir warped up and 

deformed the Price River (Kpr) and North Horn (TKn) sequence, 

and Flagstaff Limestone (Tf) deposited above. Underlying 

Indianola and older strata (Kic) were tilted to more recumbent 

positions.

IV Again a surface of low relief was cut across the fold; this 

time, however, the surface beveled both the Price River (Kpr) 

and North Horn (TKn) sequence and some of the underlying 

Indianola and Cedar Mountain strata (Kic). Flagstaff sediments 

(Tf), deposited on this surface, thin eastward and were warped 

up in response to the slow, persistent upward movement of the 

diapir. Younger sediments (Colton (Tc), Green River (Tg), and 

probably Crazy Hollow (Teh)) also thin eastward and also were 

warped by movement of the diapir.

V As in the Sixmile Creek canyon area to the east, two alternatives can explain what occurred next. The first suggests that the 

newly deposited Tertiary strata (Flagstaff to Crazy Hollow strata) were warped up to form a diapiric fold by a renewed upward 

surge of the diapir. A second alternative is that the newly deposited strata subsided, presumably as a result of removal of salt, 

to form the eastward-facing East Gunnison monocline that has 

since been destroyed by erosion.

For the Red Rocks area, as for the Sixmile Creek canyon area 

to the east (fig. 22), the first alternative would seem to be correct, based on the vertical attitudes of the Flagstaff and younger 

strata in the ancestral Willow Creek area, just some 11 km 

(7 mi) south of the Red Rocks area.

After this new fold was destroyed and much of the underlying 

salt was removed, the upwarped strata subsided to form the 

eastward-facing East Gunnison monocline.

VI. Erosion has since destroyed the monocline, removed much of 

the younger sedimentary cover, and exposed part of the intensely folded underlying Indianola and older strata (Kic). Compare 

this illustration with the photographs and sketch of figure 18 

and with that part of the cross section indicated in figure 19.

during this intrusive stage: those in the Red Rocks 

area were overturned to the west (and so dipping 

east), those in the Sixmile Canyon area were overturned to the east (and so dipping west).

I suspect that the fold failed shortly after it was 

formed and the remnants then quickly eroded.

Erosion beveled the tilted beds to a broad surface of 

low relief. As Price River strata unconformably 

overlie this erosional surface, the surface must have 

been formed during the Late Cretaceous, presumably during middle Campanian time, assuming that 

Price River beds are correctly dated as late Campanian (Fouch and others, 1982, chart, p. 270-271).

Even as Price River sediments were spread across 

this erosion surface, the slow, imperceptible upwelling 

of the diapir gradually arched the surface, effectively 

restricting deposition of these sediments. In places, 

Price River sediments pinched out against this rising 

barrier (fig. 20, II). In time, North Horn sediments 

were deposited, conformably overlying Price River 

units. As North Horn strata also thin in this general 

area, I assume that the slow, continuous upwelling of 

the salt persisted into North Horn time. In central 

Utah the North Horn ranges in age from Late Cretaceous (Maastrichtian) to Paleocene, possibly early 

Eocene (Fouch and others, 1982, chart, p. 270-271), so 

deposition must have continued uninterrupted during 

this interval.

Reactivation of the salt diapir during the Paleocene 

resulted in a new daughter fold that appears to have 

occupied the same site and had the same trend as 

the earlier parent fold. The recently deposited Price 

River and North Horn sequence was bowed up to 

form a fan-shaped diapiric fold (fig. 20, III), even as 

the older, underlying Indianola strata were tilted to 

still steeper angles. Again the fold failed, presumably 

as a result of renewed removal of salt from the 

underlying causative salt diapir. The fold partially 

collapsed; its remnants were then once again quickly 

eroded to form a surface of low relief one, however, 

that truncated both the upturned Price River and 

North Horn sequence as well the near-vertical Indianola strata. Even as sediments of the Flagstaff 

Limestone began to be deposited upon this newly 

formed erosion surface, the persistent slow upwelling 

of the salt forced up the crestal part of the fold, and 

the lower and medial parts of the Flagstaff Limestone wedged out against this rising barrier. The 

younger (upper) parts of the Flagstaff extended 

across the crest of the fold, but they, too, were greatly 

attenuated by the rising fold. In time, still younger 

sediments (now represented by the Colton and Green 

River Formations) were deposited. The anomalous 

thinness of these units near the crestal part of the 

diapir suggests that the salt continued its persistent 

upward movement even as these units were being 

formed (fig. 20, IV).
46 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

111 °3B'

39°14

FIGURE 21 (above and facing page). Geology of Sixmile Creek canyon area. Map and cross section show geology of part of area. 

Base modified from U.S. Geological Survey 1:24,000 Sterling 

(1966). Contour interval 200 ft. Area includes sectors north of 

Sterling, including part of Sanpete Valley, Palisade State Park, 

and the mouth of Sixmile Creek canyon. Strata represent part 

of east flank of Sanpete-Sevier Valley diapiric fold. When all or 

part of the Sanpete-Sevier Valley salt diapir was removed, the 

late Oligocene(?) version of the fold collapsed. Arapien mudstones, which I believe underlie the entire area, subsided into 

the newly formed void; this effectively removed the support for 

the overlying sedimentary strata which then collapsed, in part 

along high-angle faults and in part by gradual subsidence. Most 

of the crustal blocks were downthrown (western part of cross 

section) toward core of fold. Westward tilt of the Flagstaff

Limestone (Tf) defines the Wasatch monocline, which formed in 

response to this subsidence of the mudstones. Fault "F" marks 

west margin of Wasatch monocline.

Sketch shows north valley wall at mouth of Sixmile Creek 

canyon. Two angular unconformities are exposed: The older is 

between the Sixmile Canyon Formation of the Indianola Group 

and the overlying Price River and North Horn Formations. The 

younger is between the Flagstaff Limestone and underlying 

strata. Near center and right edge of sketch, the Flagstaff Limestone truncates both North Horn and Price River strata. Left 

side of sketch shows Flagstaff strata cutting across steeply dipping beds of the Sixmile Canyon Formation of the Indianola 

Group. Compare this sketch with figure 31, which displays relations near the mouth of Red Canyon in the Valley Mountains, 

some 20 km (12 mi) west.
DIAPIRIC STRUCTURES 47

WEST EAST

Flagstaff Limestone

\ Sixmile * Canyon Formation^of Indianola ~ Group

EXPLANATION

Older alluvium Mass-wasting Landslide 

deposits deposits

Indianola Group

£Kg3M«(*<fc^e£

:. I

: GTof 1 

Coalesced

S

g»~|

i iQsW; j

lope wash

?

; Otd?-,

Terrace 

deposits

lluvial fans

 ? 

T(Ja)

( Holocene

1 

} Pleistocene 

1 

f- Pliocene?

 

,

'

" Eocene

y Paleocene

Upper 

Cretaceous

AfllJ Jl«

Contact Approximately located or inferred 

Intrusive contact Oblongs on intrusive unit

Fault Dotted where concealed; bar and ball 

on downthrown block; barb shows 

downthrown block in cross section; dashed 

in cross section where reconstructed above 

eroded surface

Strike and dip of inclined beds

Strike and dip of vertical beds

Arapien 

Shale Jurassic

The salt diapir may have reactivated a third time to 

form still another daughter fold that again occupied 

the same site and had the same trend as the previous

two folds (fig. 20, V). This reactivation is suggested by 

the westward dip of the Flagstaff strata exposed in 

the Red Rocks area (fig. 20, VI). Subsequently, the
48 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

diapiric fold failed again, as salt was removed from 

the underlying diapir, and the overlying beds subsided 

into the resultant void. The end result was the development of the Wasatch monocline along the west flank 

of the Wasatch Plateau, even as another opposing 

monocline probably developed along the east flank of 

the Gunnison Plateau. This second monocline along 

the east flank of the Gunnison Plateau has been 

destroyed by erosion, and its remnants are now concealed beneath the alluvial floor of Sanpete Valley.

SIXVIII.K CRKHK CANYONI ARKA

The Sixmile Creek canyon (F-4) area, east of Sterling, is some 10 km (6 mi) northeast of the Red Rocks 

area; the critical exposures underlie parts of sees. 25, 

26, 35, and 36 of T. 18 S., R. 2 E.

The exposures here closely resemble those of the 

Red Rocks area. The Indianola Group, exposed at and 

near the mouth of Sixmile Creek canyon, consists of 

vertical to steeply tilted beds that dip eastward 

(fig. 21). Near the east edge of its exposure, the 

uppermost unit of the Indianola Group the Sixmile 

Canyon Formation dips southeastward 30° to 60°, 

and is truncated by an angular unconformity that 

also dips eastward but at about 10°. This unconformity is overlain by a thin sequence of Price River 

strata, which, in turn, is conformably overlain by a 

thin North Horn sequence. The Price River and North 

Horn sequence dips about 30° E., and totals about 

20 m (65 ft). This sequence is cut out near the western part of the exposure by Flagstaff Limestone, some 

10 to 15 m (35 to 50 ft) thick, which dips westward at 

about 35°. Thus, the upturned edges of both the Price 

River and North Horn are unconformably overlain by 

Flagstaff Limestone. West of the pinchout of the Price 

River and North Horn sequence, the down warped 

Flagstaff Limestone unconformably overlies the 

steeply tilted to vertical beds of the Sixmile Canyon 

Formation.

In summary, the stratigraphic sequence at the 

mouth of Sixmile Creek canyon is broken by two distinct unconformities: the first truncates the Indianola 

beds and is overlain by the Price River and North 

Horn sequence. The second not only truncates the 

upturned Price River and North Horn beds but also 

extends across the steeply inclined Indianola beds; 

west-dipping Flagstaff beds overlie this unconformity. 

Figure 22 depicts, in a series of diagrammatic 

sketches, how I visualize the relations in Sixmile 

Creek canyon to have formed. Subsidence of the sedimentary units, as shown in the last sketch, resulted 

in the development of the Wasatch monocline.

FIGURE 22 (facing page). Diagrammatic cross sections suggesting 

how Sixmile Creek canyon area evolved, with resultant formation of the Wasatch monocline. All sections represent part of 

east limb of Sanpete-Sevier Valley diapiric fold. In views I VII, 

ground surface speculative, not shown.

I. Geologic relations at the mouth of Sixmile Creek canyon. See 

figure 21 for geologic map of the area and sketch of north valley wall at the mouth of Sixmile Creek canyon. The geologic 

pattern is almost a mirror image of that exposed in the Red 

Rocks area to the west (assumed to be west limb of Sanpete 

Sevier Valley diapiric fold); in essence, steeply dipping beds of 

the Sixmile Canyon Formation of the Indianola Group (Kis) are 

unconformably overlain by a Price River (Kpr) and North Horn 

(TKn) sequence, which in turn is unconformably overlain by the 

Flagstaff Limestone (Tf).

II. During the first diapiric episode, an upward surge of the 

Sanpete-Sevier Valley salt diapir warped rocks of the Sixmile 

Canyon Formation (Kis) into a diapiric fold, mushroom-shaped 

in cross section.

III. The rate of uplift decreased and the fold was eroded to a 

surface of low relief. A Price River (Kpr) and North Horn (TKn) 

sequence was deposited on this surface.

IV The beginning of the second diapiric episode was marked by 

a second upward surge of the salt diapir, which raised and 

deformed all strata. The newly deposited Price River and North 

Horn sequence was warped to form a diapiric fold, and the 

previously tilted beds of the Sixmile Canyon Formation were 

rotated to still steeper angles.

V This second diapiric fold also was eroded to a near-horizontal surface. Flagstaff (Tf) was deposited across this surface, and 

in time still younger units (at least the Colton (Tc), and Green 

River (Tg) Formations) accumulated.

VI. Two alternative interpretations for what occurred next are 

possible: In the first, a renewed upward surge of the salt 

warped these newly deposited Tertiary units into a new diapiric 

fold. The second alternative suggests that as part of the salt 

diapir was removed, the overlying sedimentary units subsided 

into the resultant void to form a westward-facing monocline. I 

sketch the first alternative here, chiefly because the westward 

tilt of the Flagstaff and younger strata in the Red Rocks area to 

the west imply that a new fold was formed shortly after deposition of these younger Tertiary strata.

VII. Subsequent removal of salt from the Sanpete-Sevier 

Valley diapir resulted in failure of the fold. The mudstones of 

the Arapien sank into the newly created void, and the upturned 

country rocks, lacking the support of the mudstones, subsided 

to form the westward-facing Wasatch monocline.

VIII. Erosion and removal of younger units (Green River (Tg), 

and Colton (Tc)) expose the westward-dipping Flagstaff Limestone (Tf) overlying eastward-dipping strata (Kis, Kpr, TKn).

The Red Rocks and Sixmile Creek canyon exposures are unusual in two respects: (1) Most of the 

units are much thinner in these areas than in the 

Wasatch Plateau to the east, and (2) strata that are 

conformable only a kilometer or two away are separated here by striking angular unconformities. In the 

Sixmile Creek canyon area, for example, where exposures are good and easily traceable, the Price River 

and North Horn strata thicken gradually eastward, 

and attain thicknesses of hundreds of meters just a
DIAPIRIC STRUCTURES 49

WEST EAST

EXPLANATION

Sixmile Canyon Formation 

(of Indianola Group)

WEST

Eocene

!*Paleocene

Upper 

Cretaceous

Middle 

/ Jurassic

EAST

Tg

VII

EAST WEST EAST

TUa) 

VIII
50 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

few kilometers to the east. The North Horn and Flagstaff beds, unconformable at the canyon mouth, are 

conformable about 2 km (1.2 mi) to the east.

I interpret the exposures in the Red Rocks area to 

be remnants of the west limb of the Sanpete-Sevier 

Valley diapiric fold, and the similar exposures in 

Sixmile Creek canyon to be remnants of the opposite 

(east) limb of the same fold.

WALES GAP

Wales Gap (D-4), at the mouth of Wales Canyon, is 

along the east flank of the Gunnison Plateau, some 

37 km (23 mi) north of the Red Rocks area. Essentially the same stratigraphic units are exposed at 

Wales Gap as at Red Rocks, but the Wales Gap rocks 

have been more intensely deformed.

At Wales Gap, overturned conglomerate beds of 

both the Indianola Group and the Price River Formation form a steep, narrow ridge (figs. 23A, 24). The 

structural relations between the two units are somewhat masked by their similar lithologies and by the 

low angular discordance between them (Spieker, 1946, 

pi. 24B). The overturned Indianola conglomerate beds 

form the eastern part of the ridge and dip eastward at 

about 50° (fig. 235). They abut, and stratigraphically 

underlie, overturned conglomerate beds of the Price 

River Formation that form the western part of the 

ridge. These Price River beds also dip eastward, but 

at about 80° (fig. 25). Just west of the ridge the gray 

and red mudstone and brown sandstone beds of the 

North Horn Formation are right-side-up and dip 

gently westward. East of the ridge, overturned palered and orange mudstone, siltstone, and sandstone 

beds of the Cedar Mountain Formation, which dip 

about 60° E., stratigraphically underlie the Indianola 

beds. The Cedar Mountain strata, in turn, are stratigraphically underlain by overturned light-brown and 

gray thin sandstone beds of the Twist Gulch Formation, which also dip about 60° E. All units for which 

an upper and lower contact can be found are anomalously thin compared with their thicknesses elsewhere in the area.

I attribute the anomalous thinness of the sedimentary units to the gradual upwelling of the SanpeteSevier Valley diapir, and the deformation to repeated 

upward surges of the diapir.

In figure 25 I suggest a sequence of events to 

explain these structural relations. At some time after 

Indianola strata were deposited, the Sanpete-Sevier 

Valley diapir surged upward and forced the Arapien 

mudstones to bow up and fold back the Twist Gulch, 

Cedar Mountain, and Indianola beds, forming a fanWEST EAST

 Flagstaff Limestone (Tf)

s North Horn Formation (TKn)

/Price River Formation 

/ (Kpr)

^»n

SHf,

&a"4^§^'t*i- N

6£ £<. jw; ". _-

*- 

' - "-

FIGURE 23. East front of Gunnison Plateau near Wales. A, Aerial 

view, looking north along east flank of the Gunnison Plateau. 

Wales Gap (D-4) is just beyond skyline. Overturned to vertical 

conglomerate beds of the Price River Formation (Kpr) and the 

Indianola Group (Ki) form the narrow, elongate, north-trending 

ridge. These upturned conglomerate beds abruptly flatten 

westward (left) in the subsurface, and in a distance as short as 

several kilometers assume the gentle westward dip suggested 

by the overlying North Horn (TKn) and Flagstaff (Tf) strata 

that form the steep, imposing front of the Gunnison Plateau 

(left side of photo). Photograph by D.A. Sprinkel, Placid Oil 

Company. B, View northward of the Indianola and Price River 

relations as exposed in a road cut (Wales Gap) through the 

north-trending ridge shown in A. Price River strata (left side of 

photograph) are vertical to overturned; Indianola beds (right 

side) are overturned and dip about 50° E.

shaped fold (only the west flank of this fold is shown 

in fig. 25, sketch I). Although no evidence is available 

to indicate how the fold failed, most likely, removal of 

the salt caused collapse of the crestal part of the fold. 

Erosion then beveled the area to a surface of low 

relief. Price River sediments were deposited on this
DIAPIRIC STRUCTURES 51

surface, and in time, these were covered by North 

Horn sediments (fig. 25, II). The sequence, thus, is 

identical to that postulated for the Red RocksSi xmile Creek canyon area.

At some time during or after North Horn time the 

salt diapir welled upward once more, and again 

forced the Arapien mudstones to bow up and fold 

back the overlying strata. The Price River and North 

Horn sequence was probably warped into a fanshaped fold, and the underlying Indianola beds were 

rotated into overturned attitudes (fig. 25, III). Subsequently, this newly formed fold failed, presumably 

when the supporting salt was removed. On the basis 

of exposures elsewhere in the area (as in the Red 

Rocks area), I assume that the area was again 

reduced to a surface of low relief. Flagstaff sediments 

were deposited on this surface, and these, eventually, 

were covered by a sequence of still younger Tertiary 

beds. Subsequently, when salt was removed from the 

causative salt diapir, the overlying Tertiary beds 

were let down to form an eastward-facing monocline the East Gunnison monocline comparable to 

and paired with the westward-facing Wasatch monocline. Erosion has since removed all traces of the 

East Gunnison monocline, leaving only the structurally complex west flank as evidence of the diapiric 

activity (fig. 25, sketch IV).

ANCESTRAL WILLOW CREEK AREA

GEOLOGIC SETTING

The ancestral Willow Creek (G-3) area, also 

known as the Willow Creek gap, is some 8 km (5 mi) 

northeast of Salina (G-3) astride an ancestral course 

of Willow Creek. Two low cuestas that trend about 

N. 30° E. dominate the area (fig. 26). The cuestas 

are collinear and the resulting ridge extends for 

some 4.5 km (2.7 mi) through parts or all of sections 

26, 27, 34, and 35 of T. 20 S., R. 1 E. The aligned 

cuestas parallel the crest of the White Hills, composed of deformed mudstone beds of the Arapien 

Shale, which is about 1.6 km (1 mi) to the northeast.

Sedimentary rocks exposed in and near the cuestas 

range from the Arapien Shale (Middle Jurassic) to 

the Crazy Hollow Formation (Eocene). All units 

exposed in the cuestas are anomalously thin compared to their thicknesses in and near the Wasatch 

Plateau some 8 km (5 mi) to the east. So, for example, the Flagstaff Limestone is about 30 m (100 ft) 

thick here, but more than 365 m (1,200 ft) thick 

where it caps the plateau.

In detail, the cuestas consist of steeply dipping to 

vertical beds of the Colton Formation and the underlying Flagstaff Limestone (fig. 26). Some uncertainty 

and differences of opinion exist as to just what units 

should be included in the Flagstaff. Spieker (1949, 

p. 56) considered the Flagstaff in the Willow Creek 

area to be a composite unit consisting of a light-gray, 

fine-grained limestone bed plus some conglomerate 

beds that crop out on both sides of the near-vertical 

to vertical limestone. The conglomerate beds dip 

steeply and appear to conform to the attitude of the 

limestone bed. G.E. Moore, Jr., and K.E. Stanley 

(Ohio State University, written commun., 1979) considered only the limestone bed to be Flagstaff. They 

interpreted those conglomerate beds west of the limestone bed to be basal units of the Colton Formation, 

and those east of the limestone bed to be uppermost 

North Horn strata in essence, a normal stratigraphic sequence. I offer a third interpretation. I concur with Moore and Stanley that the limestone bed is 

Flagstaff and that the conglomerate beds west of the 

limestone bed are basal Colton. I believe, however, 

that the conglomerate beds east of the limestone bed 

are part of a block of the Colton Formation that was 

downthrown along a high-angle normal fault that 

delineates the east side of the steeply inclined bed of 

Flagstaff Limestone. The fault, which follows the 

crests of the two cuestas, is marked in many places 

by vertical slickensides. Small steps, or heels, along 

the slickensides suggest that the crustal block east of 

the fault has been downthrown. The fault is best 

exposed along the north end of the northern cuesta, 

where beds of the Twist Gulch Formation, east of the 

fault, dip westward at 35° to 65° and abut vertical 

beds of the Flagstaff Limestone west of the fault 

(fig. 6A).

DISCUSSION

Figure 27 is a geologic map of the ancestral Willow 

Creek area. I include a series of diagrammatic 

sketches and cross sections that illustrate how I 

believe the ancestral Willow Creek area evolved. In 

my interpretation the welt of contorted Arapien 

Shale mudstones that makes up the White Hills is 

part of the exposed core of the Sanpete-Sevier Valley 

diapiric fold, and the two northeast-trending, aligned 

cuestas are the broken and dissected remnants of the 

fold's west flank. The east flank of the fold is not 

exposed; apparently it was obliterated by collapse 

and erosion, and now is concealed beneath surficial 

deposits. Its former position is followed approximately by the Cedar Mountain road (fig. 27).

I propose that the Sanpete-Sevier Valley salt diapir 

surged upward at some time after deposition of the 

Crazy Hollow Formation (Eocene), presumably during
52 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

111°41'

2 KILOMETERS

J

1/2 1 MILE

FEET

7000-

6000 -: :-: : : 

5000-

West flank of the SanpeteSevier Valley diapiric fold

Kcm GUNNISON FAULT 

/ QTcf

FEET

-7000

-6000

-5000

FIGURE 24 (above and facing page). Geology of an area near 

Wales, Utah. A small area along the east flank of the Gunnison 

Plateau, centered on Wales Gap, displays well the unusual 

structural and stratigraphic relations that characterize the 

plateau's east flank. Geology by M.P. Weiss, modified by I.J. Witkind. Base modified from U.S. Geological Survey 1:24,000 Wales 

(1965). Contour interval 200 ft.

Vertical and overturned beds of the Price River Formation and 

Indianola Group form an elongate, narrow, north-trending ridge. 

These clastic units are stratigraphically underlain by overturned 

beds of both the Cedar Mountain and Twist Gulch Formations.

I interpret the vertical and overturned Price River and older 

strata to be part of the west flank of the Sanpete-Sevier Valley 

diapiric fold; surficial deposits that floor Sanpete Valley conceal 

the bulk of the fold. The attitude of these upturned Price River 

and older beds resulted from repeated upward movements of 

the Arapien Shale. See figure 25 for a diagrammatic explanation.

The Gunnison fault, a much younger feature, likely formed 

when the salt in the core of the Sanpete-Sevier Valley fold dissolved, resulting in collapse of the crestal part of the fold and 

subsidence of the overlying strata.
DIAPIRIC STRUCTURES 53

TUa)

EXPLANATION

Landslide 

deposits

Holocene

QUATERNARY

Colton Formation

Arapien Shale

Twist Gulch Formation

Contact Approximately located or inferred

Fault Dashed where approximately located; 

dotted where concealed; bar and ball on 

downthrown block; barb shows downthrown 

block in cross section

Cretaceous and 

Jurassic rocks, 

undivided

Eocene

Paleocene

Upper Cretaceous

Lower Cretaceous

Middle Jurassic

TERTIARY

CRETACEOUS

JURASSIC

25

_l_

65

Strike and dip of inclined beds 

Strike and dip of overturned beds

-| Strike and dip of vertical beds

U Angular unconformity

post-Eocene time. During this upward surge the salt 

forced the mudstone beds of the Arapien Shale to bow 

up the overlying sedimentary strata and thus form a 

fan-shaped diapiric fold. Only the west limb of this 

fold is shown in stage I of cross sections A-A, B-B', 

and C-C", figure 27. Upon removal of the salt, the 

crest of the fold collapsed unevenly between highangle faults that developed along the flanks of the 

fold (stage II of cross sections A-A', B-B', and C-C', 

fig. 27). The western fault developed adjacent to and 

east of the vertical bed of Flagstaff Limestone. 

Depending upon the amount of stratigraphic throw, 

different units, east of the fault, were downthrown 

and juxtaposed against the Flagstaff Limestone. As 

shown in cross section A-A, Twist Gulch beds, part of 

the downthrown crest, were dropped against vertical 

Flagstaff beds. In cross section B-B', steeply dipping 

to near-vertical beds of the Colton were downthrown 

against the Flagstaff. The geologic relations shown in 

interpretation B-B' form the basis for my suggestion

that the correct stratigraphic sequence at Willow 

Creek gap involves near-vertical to vertical Flagstaff 

beds flanked by near-vertical Colton strata. Colton 

strata west of the Flagstaff Limestone conformably 

overlie the Flagstaff; Colton strata east of the Flagstaff are in fault contact with that unit ('stage III of 

cross section B-B'}.

Other unusual geologic relations in the same area 

can also be explained by invoking different amounts 

of downthrow along the same vertical fault. So, for 

example, about 365 m (1,200 ft) east of the cuesta 

south of the Willow Creek road, beds of the Flagstaff 

Limestone crop out along a small knoll (fig. 27). 

These limestone beds are overturned and dip about 

85° E. Stratigraphically, they underlie overturned 

beds of the Colton Formation that also dip eastward. 

As shown in cross section C-C', figure 27, these 

unusual stratigraphic relations are readily explained 

by again invoking downthrow of the west limb of the 

diapiric fold.
54 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

EAST WEST

Graveled road connecting Wales, east of Gunnison Plateau, with Levan, west of the plateai

EXPLANATION

Holocene and 

Pleistocene

Paleocene

Upper 

Cretaceous

Indianola Group, 

undivided

QUATERNARY 

> TERTIARY

- CRETACEOUS

EAST WEST EAST WEST
DIAPIRIC STRUCTURES 55

At the north end of the cuesta north of the Willow 

Creek Road, where Twist Gulch beds abut vertical 

Flagstaff beds, the amount of downthrow along the 

fault is somewhat less than the amount of throw 

involved in the juxtaposition of Colton beds against 

the Flagstaff. As all units, however, are anomalously 

thin in this locality, the differences in amount of 

throw between the two areas are not excessive. Here, 

as in the Red Rocks-Sixmile Canyon area, the 

crustal blocks adjacent to a fault are downthrown 

valleyward (eastward in the ancestral Willow Creek 

area) toward the core of the collapsed fold.

I stress that these geologic relations in the ancestral Willow Creek area represent but one episode in 

the many that mark the repeated growth and collapse of the Sanpete-Sevier Valley salt diapir. 

Because Tertiary units Flagstaff, Colton, Green 

River, and Crazy Hollow are steeply tilted, the 

deformation must have occurred at some time after 

Crazy Hollow strata (Eocene) were deposited long 

after Sevier thrusting had come to an end. It would

FIGURE 25 (facing page). Wales Gap (D-4), along east flank of the 

Gunnison Plateau. Diagrammatic field sketch, looking south, 

shows exposures along south wall of Wales Gap. Both the Indianola Group (Ki) and the Price River Formation (Kpr) are overturned and dip eastward (left) but at different angles. Both 

units consist of coarse conglomerate beds that are very much 

alike. Sketches I to IV suggest how these relations may have 

formed as a result of repeated episodes of salt diapirism. Area is 

part of west flank of the Sanpete Sevier Valley diapiric fold; 

Sanpete Sevier Valley salt diapir (not shown) is concealed to 

the east (left) beneath alluvial floor of Sanpete Valley.

I. Conglomerate beds of the Indianola Group (Ki) were deformed 

into a fan-shaped fold as a result of an upward surge of the 

Sanpete-Sevier Valley salt diapir.

II. Subsequently, the fold collapsed, and was eventually eroded 

to a broad surface of low relief. On this newly formed surface, 

sediments of the Price River Formation (Kpr) were deposited, 

and in time these were mantled by sediments of the North Horn 

Formation (TKn). Although not shown in these diagrammatic 

sketches, both the Price River (Kpr) and North Horn (TKn) Formations thin in this area, presumably as a result of a slow but 

persistent upwelling of the Sanpete-Sevier Valley salt diapir.

III. Another rapid upward surge of the Sanpete Sevier Valley 

salt diapir deformed the area once again. The newly deposited 

Price River (Kpr) and North Horn (TKn) Formations were deformed into a fan-shaped fold whose general trend and position 

coincide closely with that of the previously formed diapiric fold. 

The tilted Indianola strata (Ki) were overturned.

IV. Collapse of the most recently formed fold and subsequent 

erosion have almost obliterated all evidence of the two diapiric 

folds. Remnants of the deformed rocks are exposed only along 

the east flank of the Gunnison Pleateau. (Compare with field 

sketch.) About 0.8 km (0.5 mi) to the west (right), both the Indianola (Ki) and Price River (Kpr) strata flex sharply in the subsurface and conformably underlie the North Horn (TKn) .

seem, therefore, that of the three major diapiric episodes recognized in the Red Rocks-Sixmile Canyon 

area, only the third episode, (late(?) OligocenePliocene(?)), is represented in the ancestral Willow 

Creek area. All evidence of the first and second diapiric episodes is still concealed.

GUNNISON RESERVOIR AREA

The previous areas discussed demonstrate that 

consolidated sedimentary strata were repeatedly 

deformed during the Cretaceous and Tertiary, 

presumably as a result of the recurrent growth and 

collapse of the Sanpete-Sevier Valley salt diapir. In 

my opinion, the results of these diapiric episodes can 

be recognized throughout much of central Utah, and 

I believe that they determined the structural pattern 

of central Utah. Deformation was extensive and, 

although localized in specific belts, extends along 

strike for tens of kilometers. By contrast, in several 

small areas evidence suggests that diapirism may 

have persisted into the late Tertiary or Quaternary. 

In one such area, along the east shore of the Gunnison Reservoir (F-3), semiconsolidated sediments 

have been warped into a deformational pattern that 

is strikingly like those discussed previously.

Beds of semiconsolidated gravels, tilted on end, 

crop out along the east side of Gunnison Reservoir, 

chiefly in the SEV4 sec. 21, T. 18 S., R. 2 E. (fig. 28). 

Near-horizontal beds of younger gravels overlie these 

vertical gravels, and the angular unconformity 

between the two gravels is as spectacular as any of 

the angular unconformities exposed in the SanpeteSevier Valley area. The discordant relations between 

the two gravels does not extend for more than 1 km 

(1/2 mi) and has been found only near the reservoir.

The age of the vertical gravels is unknown, but 

their lack of consolidation and their thin caliche rinds 

imply that they were probably formed during the late 

Tertiary (Miocene or Pliocene) or Pleistocene. I tentatively correlate these vertical gravels with the Axtell 

Formation (Spieker, 1949, p. 38), which Spieker (1949) 

believed may be of "late Tertiary" age. Elsewhere in 

this general area several small deposits of sand and 

gravel, correlated with the Axtell Formation, have 

been warped into synclines with dips as high as 45° 

(Gilliland, 1963, p. 121 and plate 3, fig. 2; Hardy, 

1952, p. 60). One of these localities is near a small 

dome in the ancestral Willow Creek area (p. 29) 

where a pediment mantle of sand and gravel dips 

northwestward at about 20° (fig. 14A).
56 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

WEST EAST

Westward-dipping beds 

of Green River Formation

Near-vertical beds of 

Flagstaff Limestone

Near-vertical beds of 

Colton Formation

EAST WEST

Detachment slide block composed 

chiefly of beds of Green River 

Formation

Near-vertical beds of 

Flagstaff Limestone

High-angle normal fault

 - -

Near-vertical beds of 

Colton Formation

w r »-* >- -. «. jm, - .^i^Sr^ *-* «? ^» ^f*

> .A^- S^fe ^ ^^ ^^^» 

*^Kk » "^ ^^k> . jJK ^ ^:»'a^..^«^P' - - '" . ^«*^»* *w.

How the lowermost gravels exposed near Gunnison 

Reservoir were tilted to a vertical position is not 

clear. Although it is possible that they are part of a 

slump block that was tilted to steeper and steeper 

angles during successive valleyward rotational 

slumps, their vertical attitude suggests that this origin is unlikely. A more reasonable explanation, it 

seems to me, is that they were bowed up and folded 

back to form a diapiric fold by the upward movement

of part a cell of the much larger Sanpete-Sevier 

Valley salt diapir, the crest of which underlies the 

reservoir, directly west of the vertical gravels. If so, 

these vertical gravels represent the east flank of a 

reactivated segment of the north-trending SanpeteSevier Valley diapiric fold.

Prof. M.P. Weiss, of Northern Illinois University, 

has suggested (oral commun., 1987) that the gravels 

may have been tilted to their vertical position as a
DIAPIRIC STRUCTURES 57

FIGURE 26 (facing page). Views of ancestral Willow Creek area. 

These exposures are part of west flank of the Sanpete-Sevier 

Valley diapiric fold. Structural relations reflect collapse of the 

crest of the fold between two high-angle normal faults (a graben), 

of which only the western fault is shown here. (U, relatively 

upthrown block; D, relatively downthrown block.) See geologic 

map and cross sections, figure 27, for additional details. A, View, 

looking northward, of the cuesta north of Willow Creek road. 

West (left) of the near-vertical Flagstaff Limestone, stratigraphic 

sequence is normal, extending through the Colton Formation 

into the Green River Formation. A high-angle fault, however, 

flanks east (right) edge of the Flagstaff Limestone, and Colton 

strata are downthrown against the Flagstaff Limestone. (See 

geologic map, fig. 27.) B, View, looking southward, of the cuesta 

south of the Willow Creek road. Colton strata west (right) of the 

high-angle fault are part of the normal stratigraphic sequence; 

those Colton strata east (left) of fault are downthrown, along a 

high-angle normal fault, against vertical beds of Flagstaff Limestone. (Compare with cross section C-C" (III), fig. 27. Note that 

view shown here is reversed with respect to that cross section.) 

As these vertical and near-vertical strata are traced southward, 

they pass below a westward-inclined slide block composed of 

Green River strata.

result of upward movement by an unrecognized diapir that underlies that sector of Sanpete Valley north 

of Sterling and directly east of the upturned, vertical 

gravels. In Weiss' interpretation, the tops of the 

upturned gravels would be to the west. In my interpretation, the tops would be to the east.

I do not know how the diapiric fold was destroyed. 

Presumably it collapsed, much as postulated for 

those diapiric folds previously discussed, and the fold 

remnants were then eroded during the late Pliocene 

or early Pleistocene to form an even surface of local 

extent.

Younger sands and gravels, carried either by Pleistocene(?) streams or by Holocene descendants of 

those streams, were spread across this newly formed 

surface. Subsequent erosion by the San Pitch River 

exposed this remnant.

Seemingly, the driving salt has moved throughout 

much of the late Mesozoic and Cenozoic, and probably is continuing to well upward slowly today. Pediment gravels that overlie Arapien Shale exposures, 

near the junction of Twelvemile Creek with the San 

Pitch River (the northeast corner of sec. 24, T. 19 S., 

R. 1 E.), dip about 25° NW. (M.P. Weiss, Northern 

Illinois University, written commun., 1989). These 

gravel exposures, as well as the vertical gravels 

exposed near Gunnison Reservoir, imply that the 

underlying salt diapirs are still active; if so, they 

pose a potential threat to man-made structures (Witkind, 1981).

REDMOND DIAPIRIC FOLD

The surface evidence for the Redmond diapiric fold 

(fig. 16, 2), originally named the Redmond Hills 

anticline by Gilliland (1963, p. 121), consists of a 

string of Arapien Shale outcrops that begins at 

Redmond (G-3) and extends as far north as Gunnison (F-3) (fig. 8). A gravity low coincides with the 

string of Arapien outcrops, and in my view this low 

reflects the crest of the diapiric fold (fig. 52). Gravity 

data (fig. 52) imply that the Redmond fold branches 

off the Sanpete-Sevier Valley fold near Salina (G-3), 

and then extends northward to some indefinite point 

beyond Gunnison, possibly joining the Levan fold 

(fig. 16, 3).

On the assumption that the Redmond fold does 

extend, at least, from near Salina to Gunnison, the 

fold has a minimum length of about 49 km (30 mi), 

and trends almost due north. I interpret a small 

east-dipping (valleyward) exposure of Green River(?) 

beds (p. 31) (in the SV2 sec. 12, T. 20 S., R. 1 W), 

about 8 km (5 mi) north of Redmond, to be a remnant of the east flank of the fold (fig. 14B).

SEVIER BRIDGE RESERVOIR DIAPIRIC FOLD

Generally, Arapien Shale outcrops flanked by 

upturned, commonly vertical to overturned beds of 

consolidated sedimentary rock identify many diapiric 

folds. In places, however, the Arapien beds, being soft 

and easily eroded, are concealed beneath surficial 

deposits and only the upturned beds reflect the presence of the fold. Thus, for example, at the south end 

of the Sanpete-Sevier Valley fold (fig. 16, 1), west of 

Mayfield (F-3), the Arapien Shale forms the White 

Hills (G-3). I interpret these Arapien outcrops to be 

the core of the Sanpete-Sevier Valley fold, and the 

adjacent upturned beds (along the west flank of these 

exposures) to be part of the west limb of the fold. As 

these Arapien exposures are traced northward they 

pass below the alluvial fill of Sanpete Valley, and 

only upturned vertical to overturned Indianola beds, 

as, for example, at Wales Gap (D-4), indicate the 

position and trend of the fold.

By contrast, in the Sevier Bridge Reservoir (E-2) 

area, Arapien beds are not exposed, and only a narrow band of steeply tilted to overturned conglomerate 

beds of the Indianola Group exposed along the northeast flank of the Valley Mountains suggests the presence of a diapiric fold (fig. 16, 4; fig. 29A). Additional 

evidence, including both the complex structural relations and the anomalous depositional thinning best 

displayed at Red Canyon (E-2) along the northeast
58 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

11T45'

39°02

39°01'~

R 1 E

2 KILOMETERS

_\

1/2 1 MILE

FIGURE 27 (above and following pages). Geology of ancestral Willow Creek area, plus cross sections, 

across part of west limb of the late(?) Oligocene version of the Sanpete-Sevier Valley diapiric fold. 

Base modified from U.S. Geological Survey 1:24,000 Redmond (1966). Contour interval 100 ft.

In the three schematic cross section panels labeled I, reactivation of the Sanpete-Sevier Valley 

salt diapir (not shown) forced up the mudstones of the Arapien Shale (T(Ja)), which in turn bowed 

up (arrows) the overlying sedimentary strata to form a diapiric fold, roughly mushroom shaped in 

cross section. In places, the beds were folded back and overturned; cross-sectional shape of the fold 

differs from place to place along the fold's length. The three schematic cross-section panels labeled

II represent failure of fold along a high-angle normal fault. The three cross-section panels labeled

III show present-day configuration. 

Cross section A-A':

I. The beds were bowed up and folded back to form a fan-shaped fold. Only the west flank of that 

fold is shown.

II. Upon partial removal of the salt core (not shown) the fold collapsed between two high-angle 

faults. Only the west fault is shown. Crest of fold was dropped down against the vertical to overturned beds of the relatively upthrown limb.

III. After erosion, only remnants (Jtg) of the downthrown limb are preserved, juxtaposed by a 

fault against vertical beds of the Flagstaff Limestone (Tf).
DIAPIRIC STRUCTURES 59

EXPLANATION

Slope wash

Tertiary units, undivided

TJu

QTcf

Coalesced alluvial 

fan deposits

Crazy Hollow Formation Green River Formation 

(Detachment blocks)

Pediment mantle

Unconformity

Paleocene, Cretaceous and 

Jurassic units, undivided Twist Gulch Formation

___ r -y ___^

TUa)

__ 7 

Arapien 

Shale

? Holocene 

f- Pleistocene

\- Pliocene?

J -<

> Miocene?

'

\

^ Eocene

" Paleocene 

- Upper Cretaceous

* Middle Jurassic

> QUATERNARY

>- TERTIARY

- CRETACEOUS

> JURASSIC

Contact Approximately located or inferred 

Intrusive contact Oblongs on intrusive unit 

Fault Bar and ball on downthrown block 

 Detachment fault

85

Strike and dip of inclined beds 

Strike and dip of vertical beds 

Strike and dip of overturned beds

Cross section B-B':

I. The beds were bowed up but not overturned. Only the west flank of the fold is shown.

II. Upon partial removal of the salt core (not shown), the fold collapsed between two high-angle faults (only the faults that are 

part of the west fault zone are shown), and the crest of the fold dropped down against vertical to steeply tilted beds of the 

relatively upthrown limb.

III. After erosion, beds of the Colton Formation (Tc) (of the downthrown limb) are preserved, juxtaposed along one of the west 

faults, against vertical beds of the Flagstaff Limestone (Tf). In this area, then, the Flagstaff Limestone (Tf) is both overlain and 

underlain by the Colton Formation (Tc). 

Cross section C-C":

I. The beds were bowed up and folded back. Only the west flank of the fold is shown.

II. Upon partial removal of the salt core (not shown), the fold collapsed along a high-angle fault and the overturned limb of the 

fold dropped down against vertical to overturned beds of the relatively upthrown limb.

III. After erosion, overturned beds of the Colton Formation (Tc) are preserved, juxtaposed by a fault, against steeply dipping to 

vertical beds of the Flagstaff Limestone (Tf). In this area, the Colton Formation (Tc) (east of the high-angle fault) is both overlain 

and underlain by the Flagstaff Limestone (Tf). A photograph of this area, fig. 26B, shows these units as viewed from the north 

(so that, in essence, the view is reversed).
60 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

Cuesta north of Willow Creek road north end 

(Cross section A-A ')

Cuesta north of Willow Creek road central part 

(Cross section B-B')

W

Units omitted for 

cartographic purposes

-Proposed fault 

T(Ja)

T(Ja)

"Units omitted for 

cartographic purposes

W Units omitted for 

cartographic purposes

Units omitted for 

^cartographic purposes

TUa)

W

III

FIGURE 27 (above and facing column) Continued. How the ancestral Willow Creek area may have evolved.
DIAPIRIC STRUCTURES 61

Cuesta south of Willow Creek road 

(Cross section C-C')

NW SE

NW

T(Ja) T(Ja)

NW

4500 T(Ja)

SE

III

WEST EAST

FIGURE 28. Deformed gravels exposed along east shore of Gunnison Reservoir. Near-vertical gravels of late Tertiary(?) age are 

truncated and overlain by near-horizontal gravels of HoloceneC?) 

age. It seems likely that the older gravels were bowed up into 

their present position when salt in the underlying Arapien 

Shale welled upward. Outcrop is viewed by eminent U.S. Geological Survey geologist C.B. Hunt, who has mapped extensive 

areas throughout Utah.

flank of the mountains, supports the existence of this 

fold (Witkind and Page, 1984).

GEOLOGIC SETTING 

COMPLEX STRUCTVRAL RELATIONS

An eastward-facing monocline extends all along the 

northeast and east flank of the Valley Mountains. 

Downwarped beds of the Flagstaff Limestone express 

the general configuration of the monocline. Locally,
62 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

WEST EAST EAST

Westward-dipping beds of Overturned beds of

Price River and North Horn Indianola Group

Formations \

\ \ ^

 u.* JL.-J

FIGURE 29. Exposures along northeast flank of the Valley Mountains near Yuba Dam. A, Eastward-dipping, overturned beds of the 

Indianola Group. Locally these beds are vertical or right-side-up and dip steeply to the south and southwest. Price River strata, 

exposed on distant hillside behind geologist, dip moderately westward and unconformably overlie the overturned Indianola. B, Beds 

of the Green RiverC?) Formation are downthrown along a high-angle normal fault and juxtaposed against overturned to steeply 

dipping beds of the Indianola Group. U, relatively upthrown block; D, relatively downthrown block.

these downwarped beds are overlain conformably by 

younger strata, chiefly units of the Colton, Green 

River, and Crazy Hollow Formations. Near Yuba 

Dam, the monocline has been breached for a length 

of almost 8 km (5 mi), with the breached area 

extending from the NV2 sec. 8, T. 17 S., R. 1 W. on 

the north, to C sec. 29, T. 17 S., R. 1 W. on the south. 

The strata exposed in the breached area, rather than 

conforming in attitude to the downwarped beds that 

form the monocline, are tilted at unusual and varying angles. So, for example, the basal beds exposed, 

part of the Indianola Group, are vertical or overturned, and strike between N. 10° W. and N. 20° W. 

(fig. 29A). Unconformably overlying these Indianola 

beds is a sequence of Price River and North Horn 

strata that dips gently to moderately westward 

(toward the mountains) (fig. 29A). In this area, thus, 

two striking angular unconformities break the stratigraphic sequence: an older unconformity between the 

vertical Indianola and the inclined Price River and 

North Horn sequence, and a younger unconformity 

between the upturned Price River and North Horn 

sequence and the downwarped Flagstaff Limestone 

that forms the monoclinal slope. Much the same 

stratigraphic relations can be seen in the Sixmile 

Canyon (F-4) area (along the east side of Sanpete 

Valley) exposed in a breached sector of the Wasatch 

monocline.

Along the northeast flank of the Valley Mountains, 

near Yuba Dam, beds of the North Horn, Flagstaff, 

Colton, and Green River are downthrown along a 

high-angle normal fault, against the overturned 

Indianola strata (figs. 29B, 30). These downthrown 

units are much disrupted, and most dip at various 

angles both into and away from the fault. In a few 

places, where exposures are good, Green River(?)
DIAPIRIC STRUCTURES 63

beds dip northeastward away from the fault at about 

35°. Locally, these Green River(?) beds are overlain 

by light-gray and pale-red mudstones and shaly siltstones that I correlate with the Colton Formation, 

and that Prof. J.L. Baer of Brigham Young University has stated are indurated surficial deposits of 

Pliocene or Pleistocene age (oral commun., 1980). If 

these varicolored mudstones and siltstones are part 

of the Colton Formation, the Green River beds must 

be overturned (first alternative, fig. 30). If the mudstones and siltstones are surficial deposits, as 

suggested by Prof. Baer, the Green River beds are 

probably right-side-up (second alternative, fig. 30). 

Conclusive evidence to resolve this problem was not 

found. These varicolored beds have also been considered to be part of the Arapien Shale (D.A. Sprinkel, 

Placid Oil Company, oral commun., 1983).

I interpret these exposures to mean that at some 

time after deposition of the Crazy Hollow Formation 

(of Eocene age) the Sevier Bridge Reservoir salt 

diapir reactivated and bowed up the overlying strata 

to form a diapiric fold. Subsequently, dissolution of 

salt caused the crestal part of the fold to fail along 

high-angle normal faults that developed along the 

flanks of the fold. As a result, the crest of the fold, 

consisting of the North Horn to Green River 

sequence, was downthrown and juxtaposed against 

the Indianola conglomerate beds that form part of 

the northwest limb of the fold. This interpretation 

satisfies both alternatives offered in figure 30; the 

amount of downthrow determines which part of the 

folded limb of the fold abuts the Indianola.

ANOMALOUS DEPOSITIONAL THINNING

Sedimentary units exposed in and near this 

breached sector of the Valley Mountains monocline 

are anomalously thin. So, for example, near the north 

end of the breached area, in the center of sec. 8, T. 17 

S., R. 1 W., the North Horn Formation is about 38 m 

(125 ft) thick, the Flagstaff but 11 m (37 ft), the Colton only 61 m (200 ft), and the Green River Formation but 35 m (115 ft) thick. I interpret this sector as 

being adjacent to the crest of the fold. As one moves 

away from the crestal part of the fold, the units 

increase in thickness rapidly. Thus, some 600 m 

(2,000 ft) away, still in the southwest quarter of section 8, the North Horn is in excess of 100 meters 

thick (its actual thickness is uncertain because its 

base is concealed beneath debris), the Flagstaff has 

increased in thickness to 49 m (162 ft), the Colton is 

about 83 m (270 ft) thick, and the Green River is 

about 95 m (310 ft) thick. Although exposures are 

poor and stratigraphic control is uncertain, I believe

that the lower the older parts of the units pinch 

out, and only the upper and younger parts of the 

units are preserved.

This depositional thinning, of not one but a 

sequence of units, must reflect the imperceptible, 

continuous upward movement of an active diapir. 

The anomalous thinness of the sedimentary units 

suggests that this part of the southwest flank of the 

fold is close to the crest of the concealed fold. The 

fact that many sedimentary formations thin implies 

that a dynamic, ancestral topographic high was 

slowly rising as the sediments that form these formations were being deposited. Were the high not active, 

but rather a static buried hill, only one or two of the 

lowermost formations would thin or pinch out 

against the flanks of the hill. Once the hill was buried, younger formations would pass over the buried 

hill with their thicknesses unchanged.

Possibly, most of the sediments that now form the 

basal and middle parts of any one formation were 

deposited against the flanks of this rising dynamic 

high; only those sediments that now make up the 

upper part of that specific formation were able to 

surmount the rising high. This suggests several 

alternative interpretations: (1) the diapir rose at different rates during its growth, (2) sedimentation 

rates differed from time to time, or (3) some combination of the first two alternatives. I favor the third 

interpretation, in which changes in rate of both diapiric growth and sedimentation are responsible for 

this thinning of sedimentary units near the crestal 

part of the fold.

Thus, I attribute both the structural complexity 

and the depositional thinning to the recurrent reactivation of a major diapiric fold, one that lay directly 

east of the monocline. I refer to this fold as the Sevier 

Bridge Reservoir diapiric fold. Presumably, recurrent 

upward surges of the salt part of the core of the diapiric fold repeatedly deformed the Indianola and 

overlying beds; subsequent removal of the salt from 

the concealed diapir resulted in differential subsidence of the overlymg younger consolidated sedimentary units to form the monocline (Witkind and Page, 

1984, p. 147-156). In this interpretation, the bulk of 

the fold underlies the pediment mantle that fringes 

the mountains and that extends northeastward 

toward the southwest shore of the reservoir (fig. 30).

RED CANYON AREA (VALLEY MOUNTAINS)

Red Canyon (E-2), near the south end of the 

breached area, trends about N. 70° E. as a deep, 

narrow gorge. The mouth of the canyon, in C sec. 29, 

T. 17 S., R. 1 W., exposes older rocks whose attitudes
64 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

39°21'

T 17 S

KILOMETER

EXPLANATION

Quaternary 

Pliocene(?)

Indianola Group

QUATERNARY

Eocene

Paleocene

Upper Cretaceous

TERTIARY

CRETACEOUS

1/2 MILE

20

45

Contact Approximately located or inferred

Fault Bar and ball on downthrown block; barb 

shows downthrown block in cross section; 

dashed in cross section where reconstructed 

above eroded surface

Strike and dip of inclined beds 

Strike and dip of vertical beds 

Strike and dip of overturned beds

FIGURE 30 (above and facing page). Geology of northeast flank of Valley Mountains, and diagrammatic 

sketches suggesting how the southwest flank of the 

Sevier Bridge Reservoir diapiric fold may have 

grown and then collapsed during the third diapiric 

episode (late(?) Oligocene-Pliocene). Base modified 

from U.S. Geological Survey 1:24,000 Hells Kitchen 

Canyon SW (1965). Contour interval 200 ft.

Two alternative explanations are offered reflecting 

my uncertainty as to whether downthrown beds east 

of the northwest-trending fault are overturned or 

right-side-up. I favor the first alternative (that shown 

on the geologic map) that a small patch of light-gray 

and pale-red mudstones above the Green River Formation is part of the Colton Formation. This implies 

that the beds east of the fault are overturned. 

First alternative beds are overturned: 

I. Late(?) Oligocene intrusive stage. Renewed movement of the northwest-trending Sevier Bridge Reservoir salt diapir forced the mudstones of the Arapien 

Shale (not shown) to raise and fold back the overlying 

sedimentary strata and so form a fan-shaped fold. Section is drawn across part of the southwest limb of the 

fold.

II. Late(?) Oligocene-Pliocene(?) erosional stage. Upon 

removal of the salt core (not shown) the fold collapsed 

and the overturned limb of the fold was downthrown 

along a high-angle fault.

III. Cross section A-A' . Erosion has removed much of 

the collapsed fold leaving the overturned, down-thrown 

beds of the Green River Formation (east of the fault) 

juxtaposed against the vertical to overturned beds of 

the Indianola Group (west of the fault). 

Second alternative beds are not overturned:

I. Late(?) Oligocene intrusive stage. It is assumed, in 

this interpretation, that the crest of the fan-shaped 

fold, formed by the intrusive action of the Arapien 

Shale (not shown) is flattened and flexed into an undulatory pattern. Section is drawn across part of the 

southwest limb of the fold.

II. Late(?) Oligocene-Pliocene(?) erosional stage. As 

the fold collapsed, due to removal of salt, the crest of 

the fold was downthrown along a high-angle fault. 

Amount of stratigraphic throw postulated is greater 

than that shown in first alternative.

III. Cross sectionA-A'. Erosion has removed much of the 

collapsed fold, leaving the right-side-up, downthrown 

beds of the Green River Formation (east of the fault) juxtaposed against the vertical to overturned beds of the Indianola Group (west of the fault).
DIAPIRIC STRUCTURES 65

First alternative beds are overturned Second alternative beds are not overturned

HI TKn III
66 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

EAST

jHKjf^**^

FIGURE 31 (above and facing page). Exposures near 

the mouth of Red Canyon, Valley Mountains. A, View 

southward of exposures near mouth of Red Canyon. I 

interpret these exposures to be part of the west flank 

of the Sevier Bridge Reservoir diapiric fold formed 

above a salt diapir concealed to east (left) beneath 

Sevier Valley. B, Sketch of view A. Indianola strata 

dip steeply westward (right). These are unconformably overlain by a Price River and North Horn sequence that also dips westward but at much lower 

dips. The North Horn, in turn, is unconformably 

overlain by Flagstaff Limestone that dips gently 

eastward (left) to form part of the Valley Mountains 

monocline. Long-dashed lines represent approximate 

attitude of bedding planes. Just to south, beyond 

area shown in this photograph, the deformed older

rocks (Indianola, Price River, and North Horn) are 

concealed beneath an unbroken mantle of eastward-dipping beds of the Flagstaff Limestone that 

define the Valley Mountains monocline.

Compare this photograph with the sketch in figure 21, of an area near the mouth of Sixmile Creek 

canyon along the west flank of the Wasatch Plateau, some 20 km (12 mi) to the east. In both photograph and sketch, steeply upturned beds of the 

Indianola Group are unconformably overlain by a 

Price River and North Horn sequence, which dips 

toward the mountains. This sequence, in turn, is 

unconformably overlain by downwarped beds of the 

Flagstaff Limestone, which dip valleyward toward 

the causative salt diapirs. In both localities, the 

downwarped Flagstaff defines major monoclines.

mimic those found elsewhere within the breached 

sector of the monocline. So, the Indianola beds are 

near vertical, and these are overlain with profound 

angular unconformity by Price River beds that dip 

westward (toward the mountains) at about 15°. 

North Horn strata overlie the Price River beds conformably, and this westward-dipping Price River and 

North Horn sequence is truncated by the downwarped eastward-dipping Flagstaff Limestone to 

form a second, younger angular unconformity (fig. 

31).

Here, too, all strata are remarkably thin at the 

mouth of Red Canyon, near the crest of the postulated Sevier Bridge Reservoir diapiric fold, but they 

thicken rapidly to the west. The North Horn Formation, for example, is about 15 m (50 ft) thick near the

canyon mouth, but more than 180 m (600 ft) thick 1.5 

km (1 mi) to the west near the head of Red Canyon.

As shown in figure 32,1 interpret the relations in 

Red Canyon to reflect three episodes of salt diapirism.

DISCUSSION

FIRST DIAPIRIC EPISODE

During the first diapiric episode, Indianola Group 

and older rocks (KJu), were bowed up and warped into 

a diapiric fold by the upward surge of a salt diapir 

contained within the Arapien Shale (K(Ja); sketch II of 

fig. 32). With removal of salt from the core of the fold, 

the fold collapsed (the collapsed axial part of the fold
DIAPIRIC STRUCTURES 67

EAST

West flank of 

Gunnison Plateau

 Approximate conformable contact

Beds of Indianola Group (Ki) 

dipping steeply to west

is eastward (left) beyond area covered in this hypothetical sketch), and its remnants were then eroded to 

a surface of low relief (III of fig. 32). Sediments of the 

Price River Formation were deposited on this surface, 

and in time North Horn sediments were conformably 

deposited on Price River strata (IV of fig. 32).

SKCOND DIAPIRIC EPISODF

A second upward surge of the diapir, marking the 

beginning of the second diapiric episode, deformed all 

strata (V of fig. 32). The newly deposited Price River 

and North Horn sequence was deformed into a diapiric fold, and the previously tilted Indianola beds 

were tilted to still steeper angles. When this second 

fold failed, its remnants were eroded to a nearhorizontal surface (VI of fig. 32). Flagstaff (Tf) 

sediments were deposited across the erosion surface, 

and in time still younger units (at least Colton (Tc), 

and Green River (Tg) strata), also accumulated (VII 

of fig. 32). Subsequently, volcanic units assigned to 

the Eocene and Oligocene Goldens Ranch Formation 

(Tgr) mantled the sedimentary stack.

THIRD DIAPIRIC; EPISODE

I am uncertain as to the precise sequence of events 

that occurred during the third diapiric episode. Two 

alternatives are feasible; the first suggests that a

renewed upward surge of the diapir deformed the 

near-horizontal Tertiary strata into a new diapiric 

fold. The exposures in the ancestral Willow Creek 

(G-3) area (p. 51), where similar Tertiary units, part 

of the west flank of the Sanpete-Sevier Valley fold, 

are preserved as vertical and overturned beds, favor 

this interpretation. Subsequently, at some time after 

this new diapiric fold was formed, removal of salt 

from the causative diapir resulted in failure of the 

fold, and the upturned beds were let down to form an 

eastward-facing monocline (VIII of fig. 32).

The second alternative, which I tend to favor, suggests that the near-horizontal Tertiary beds, rather 

than being warped up to form a diapiric fold, subsided, presumably in response to removal of the 

salt, to form an eastward-facing monocline (VTII of 

fig. 32).

On the basis of the exposures along the east and 

northeast flanks of the Valley Mountains, I suggest 

that the fold trends about N. 55° W, and is at least 

24 km (15 mi) long. I am uncertain how this fold 

relates to the Redmond fold (fig. 16); possibly the two 

are joined to form a compound fold that extends for 

at least 48 km (30 mi) from near Redmond, on the 

south, to near Yuba Dam, on the north. I am also 

uncertain how far to the northwest this diapir 

reaches. On the basis of the strike of the overturned 

to near-vertical Indianola beds exposed at the northwest end of the breached sector of the monocline, the 

diapir turns to the north, east of Yuba Dam, and
68

EAST

SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

WEST EAST WEST EAST WEST

K(Ja)

KJu

KJu

K(Ja)

K(Ja)

K(Ja)

III

T(Ja)

T(Ja)

IV T(Ja)

T(Ja)

T(Ja)

Tgr

Tgc

T(Ja)

Tf

FIGURE 32. Diagrammatic sketches of the Red Canyon area, 

Valley Mountains, suggesting how structural relations in 

Red Canyon formed as a result of two episodes of salt diapirism. View is southward to conform with photograph shown in 

figure 31. Sketches illustrate west limb of diapiric fold. 

Causative salt diapir is concealed to east (left) beneath floor 

of Sevier Valley. Tgr, Goldens Ranch Formation; Tgc, Green 

River and Col ton Formations, undivided; Tf, Flagstaff Limestone; TKn, North Horn Formation; Kpr, Price River Formation; Ki, Indianola Group; KJu, Indianola Group, Cedar 

Mountain, and Twist Gulch Formations, undivided; J(Ja), 

K(Ja), T(Ja), emplacement ages of the Middle Jurassic Arapien Shale (see text for discussion). U, angular unconformity.

I. Twist Gulch, Cedar Mountain, and Indianola strata (KJu) 

were deposited along the west flank of a slowly rising diapiric 

fold. All units thin toward the crest of the fold (left, not shown) 

in response to the slow upward movement of the salt diapir.

II. An upward surge of the salt diapir bowed up the Jurassic 

and Cretaceous units (KJu) to form a fan-shaped fold.

III. As a result of removal of salt the fold collapsed; subsequent erosion formed a surface of low relief across the fold's 

remnants.

IV. Price River sediments (Kpr) were deposited on the newly 

formed surface, and in time these were conformably overlain 

by North Horn sediments (TKn). Both formations thinned toward the crest of the fold in response to the slowly rising salt 

diapir.

V A renewed upward surge of the salt diapir warped up all 

overlying strata to form a new fan-shaped diapiric fold that 

occupied the same site and had the same trend as the previous fold.

VI. Collapse of the fold and subsequent erosion reduced the 

area to a surface of low relief.

VII. Flagstaff Limestone sediments were deposited across this 

surface, and these in turn were overlain by successively 

younger units-the Green River and Colton (Tgc), and Goldens 

Ranch (Tgr) Formations. All units thin toward the crest of the 

fold in response to the slowly rising salt diapir.

VIII. Removal of salt resulted in subsidence of overlying 

units to form the eastward-facing Valley Mountains monocline.

I.. Erosion removed most of the younger units, and locally 

breached the Flagstaff Limestone (Tf), exposing the complex 

structural sequence imposed on the older rocks.
DIAPIRIC STRUCTURES 69

extends into a broad flat known as The Washboard. 

The 60 m (200 ft) of intermixed salt and mudstone 

cut by Placid Oil Company's Monroe 13-7 well (sec. 

13, T. 16 S., R. 2 W.) (fig. 9), which was sited north of 

the Sevier Bridge Reservoir and northeast of Yuba 

Dam, essentially in The Washboard, implies that the 

well penetrated part of the diapir.

I believe that the Arapien Shale is concealed 

beneath both the reservoir and the surficial deposits 

that floor this sector of Sevier Valley.

LEVAN DIAPIRIC FOLD

The Arapien Shale crops out extensively along the 

west flank and around the north end of the Gunnison 

Plateau (D-3) (fig. 8). Along the west flank of the 

plateau, east of Levan (C-3), consolidated sedimentary strata overlie Arapien exposures. Those sedimentary beds that overlie the east edge of the 

Arapien exposures dip eastward, those that overlie 

the west edge dip westward I interpret these relations to mean that the Arapien exposures are part of 

the core of the Levan diapiric fold (fig. 16, 3), and the 

overlying sedimentary strata the eroded flanks of 

that same fold.

On the basis of Arapien exposures, the core of the 

Levan fold extends about N. 15° E. for some 40 km 

(25 mi) from Little Salt Creek (D-3) on the south to 

Salt Creek (B-3) on the north. I believe, however, 

that the diapiric core is much longer, extending perhaps as far south as the south end of the Gunnison 

Plateau where it may join the Sevier Bridge Reservoir diapir. If so. the diapir is about 50 km (32 mi) 

long. I project the diapir to the south chiefly on the 

basis of the westward-facing West Gunnison monocline, perceiving this monocline to have been formed 

as the result of the removal of salt from the causative salt diapir, in much the same fashion as the 

Wasatch and Valley Mountains monoclines.

At the north end of the diapiric fold near Salt 

Creek the fold seemingly divides to form three 

branches (fig. 16). The western fold, for which I 

retain the name Levan fold, extends northward 

beyond Salt Creek, and passes below and deforms 

the upper plate of the Charleston-Nebo thrust fault 

(Witkind, 1983, p. 51-54). The eastern fold, the Pole 

Creek diapiric fold (fig. 16, 12), extends northeastward into Salt Creek where it seemingly deforms the 

north end of the Gunnison Plateau, as well as those 

strata that lap onto the eastern margin of the 

Charleston-Nebo thrust plate. The middle fold, the 

Footes Canyon (B-3) fold (fig. 16, 13), may extend 

northward beneath the Charleston-Nebo thrust plate, 

and deform part of that plate.

Gravity data (fig. 52) show part of a deep linear 

low that seemingly follows the centerline of Juab 

Valley. This low may reflect either a thick valley fill 

of surficial material or Arapien mudstone. If the low 

does indeed stem from Arapien mudstone, one would 

have to assume that still another diapiric fold underlies Juab Valley (Witkind and Marvin, 1989). The 

crest of such a fold would be about 8 km (5 mi) west 

of the Levan fold.

A series of unusual geologic relations exposed 

along the flanks of the diapiric fold demonstrate the 

upward movement of the Levan diapir. Of these exposures, perhaps the most striking is along Pigeon 

Creek (C-3).

PIGEON CREEK AREA

East of Levan (C-3), in Pigeon Creek along the 

west flank of the Gunnison Plateau (fig. 2), Arapien 

mudstones that form the core of the Levan diapiric 

fold have intruded and warped an overturned anticline. Pigeon Creek, flowing westward, cuts through 

a northward-trending anticline, which is formed, in 

part, by the thin, dark-gray beds of the Twin Creek 

Limestone. A test well, the Levan Unit, in the NEV4 

NWVi sec. 17, T. 15 S., R. 1 E., drilled by Standard 

Oil of California, demonstrated that the fold is overturned (Ritzma, 1972, p. 78).

Near the mouth of Pigeon Creek the limestone 

beds that form the west flank of the fold dip gently to 

moderately westward (fig. 33). Eastward, toward the 

crest of the fold, the beds become nearly horizontal, 

and then beyond the crest, the beds dip eastward. 

Near the center of the fold, red mudstone beds of the 

Arapien Shale and several gypsum beds are intercalated in the thin limestone beds of the Twin Creek. 

Locally, these lenses and seams of gypsum separate 

the limestone beds to form elongate, near-horizontal 

pods that conform to the bedding. Elsewhere, the 

gypsum forms vertical pods that cut across the 

bedding. These relations imply that the lenses and 

seams of gypsum are intrusive, and not interbedded.

At the east edge of the fold, the eastward-dipping 

beds flex up sharply and dip westward (fig. 34A), 

then become vertical, and finally are overturned 

(fig. 345, C). These overturned beds abut Arapien 

mudstone beds that form the west flank of the diapiric core of the Levan fold (fig. 16). Locally, these 

beds of the Arapien Shale overlie the overturned 

Twin Creek beds.

I interpret these geologic relations to mean that 

the Levan diapiric fold invaded and warped this 

overturned fold long after the fold was emplaced. The
70 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

1/2 MILE

EXPLANATION

Holocene

Alluvium

QUATERNARY

JtC

S Oligocene? . 

Middle

win Creek | Jurassic 

Jmestone J

\ TERTIARY 

>- JURASSIC

Arapien 

Shale

 Contact Approximately located or inferred; dotted 

where concealed; in cross section, queried 

where speculative

- "- Intrusive contact Approximately located or inferred; oblongs on intrusive unit

 ' Strike and dip of inclined beds

35 

(j Strike and dip of overturned beds

® Horizontal beds

-Approximate trace of synclinal axis Dashed 

where inferred; dotted where concealed

FIGURE 33. Geology across the Pigeon Creek area showing relations between an overturned anticline (composed of limestone beds of 

the Twin Creek Limestone) and intrusive mudstone and gypsum beds of the Arapien Shale. As the Arapien Shale deforms volcanic 

units of middle Tertiary age in this general area, I suspect that the time of major movement of the Arapien is middle Tertiary, 

hence the symbol "T(Ja>". Base modified from U.S. Geological Survey 1:24,000 Levan (1983). Contour interval 200 ft.

intruding and deforming nature of the Arapien Shale 

is shown by the intercalated and vertical beds and 

pods of gypsum and mudstone in the center of the 

anticline. The eastward-dipping Twin Creek beds, 

along the east flank of the anticline, that were 

warped into westward dips, overturned, and eventually torn off, demonstrate the upward thrust of the 

Arapien (cross section A-A', fig. 33).

I believe that this overturned anticline is an erosional remnant of the much larger overturned 

Charleston-Nebo thrust plate so well exposed some 

20 km (12 mi) to the north near Nephi (B-3).

GARDNER CANYON-RED CANYON AREA

The deformation of the Charleston-Nebo thrust 

plate by the Levan fold is best seen in Gardner and 

Red Canyons (B-3), a rugged area about 4 km (2.5 

mi) northeast of Nephi (fig. 2).

The Gardner Canyon-Red Canyon area consists of 

two deep canyons cut into the west flank of the 

southern Wasatch Range (fig. 35). Both canyons 

trend southwest and expose, in a series of outcrops, 

the relations between the Arapien Shale and various

sedimentary units that form part of the CharlestonNebo thrust plate. In this sector of the southern 

Wasatch Range, the thrust plate appears as the 

lower limb of an overturned, almost recumbent anticline. This lower limb consists of strata that range in 

age from Jurassic (Twin Creek Limestone) to Permian and Pennsylvanian (Oquirrh Group). All units 

are overturned.

GARDNER CANYON AREA

In Gardner Canyon (B-3), which is about 1.3 km 

(0.8 mi) north of Red Canyon, the overturned beds of 

the thrust plate are disrupted by a small mass of 

intensely contorted Arapien mudstones. These mudstone beds, exposed along the lower flanks of the valley walls, are locally overlain by beds of light-gray to 

gray thin limestone, part of the Twin Creek Limestone, that, in striking contrast to the overturned 

beds that form the thrust plate, are right-side-up. 

These Twin Creek beds form two distinct exposures.

The southern Twin Creek exposure, about 0.8 km 

(0.5 mi) wide, is encircled by Arapien mudstones, and
DIAPIRIC STRUCTURES 71

EAST Bedding of 

,- Twin Creek strata

k »^ ** 

: * -:S?> >/r-*E

EAST

appears as a northeast-trending syncline (fig. 35). In 

detail, those limestone beds along the south edge dip 

northward at about 40°, but in one place where they 

directly abut the Arapien mudstones, they are overturned and form a tight anticline (fig. 36) that is 

much like the overturned fold formed along the east 

margin of the north-trending anticline in Pigeon 

Creek (C-3). As these north-dipping beds are traced 

northward, they lessen in dip and then reverse dip

FIGURE 34. Folding of the Twin Creek Limestone in Pigeon Creek 

as a result of upward movement of the Arapien Shale. A, View 

of south canyon wall of Pigeon Creek showing east limb (right 

side of photo) of north-trending anticline exposed along Pigeon 

Creek. Twin Creek Limestone dips eastward as part of the east 

limb of the anticline. At their juncture with the Arapien Shale 

the beds are warped up and dip westward (left side of photograph). A small, distinct syncline, exposed in a side canyon 

south of Pigeon Creek, marks abrupt reversal of dips. On the 

opposite (north) canyon wall, outcrops (views B and C) demonstrate that the warped-up Twin Creek Limestone becomes vertical and is eventually overturned. B. View of north canyon wall 

of Pigeon Creek showing the warped-up Twin Creek Limestone 

beds exposed along east flank of the north-trending anticline. 

Vertical beds of Twin Creek Limestone are overturned at top of 

the small knoll (above head of geologist) but the overturned 

beds are concealed behind the trees. View C shows relations on 

top of knoll. The Arapien Shale crops out beneath scree-covered 

slope directly behind geologist. C, As the vertical beds shown in 

B are traced onto crest of the knoll they are overturned, become 

almost recumbent and dip about 30° eastward. The Arapien 

Shale crops out on the scree-covered slope on which dog lies.

FIGURE 35 (following pages). Geology of Gardner Canyon-Red 

Canyon-Birch Creek area showing relations between the upper 

plate of the Charleston-Nebo thrust fault (lower limb of an 

overturned anticline) and the north end of the Levan diapiric 

fold. Base modified from U.S. Geological Survey 1:24,000 Mona 

(1979) and Nephi (1983). Contour interval 200 ft.

As interpreted, the Arapien Shale (T(Ja)) intruded and bowed 

up the upper plate of the thrust fault. Probably the Arapien 

Shale simultaneously bowed up the edge of the thrust plate as 

well as beds of the Indianola(?) Group (Ki) that are exposed 

east of the Rees Flat area. |

The upper plate was further deformed, in the Gardner 

Creek-Birch Creek area, when an intrusive mass of the Arapien Shale forced up a small wedge of the Navajo Sandstone (Jn) 

and the overlying Twin Creek Limestone (Jtc) and juxtaposed 

these units against overturned beds of the Permian and Pennsylvanian Oquirrh Group (PPo). As the Navajo and Twin Creek 

are right-side-up, they probably represent part of the lower 

plate of the Charleston-Nebo thrust.

I am uncertain when this uplift of the Navajo-Twin Creek 

wedge occurred, but possibly both intrusive events the deformation of the thrust plate and the uplift of the wedge 

occurred at the same time, during the second diapiric episode.
72 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH
Part of upper plate of Charleston-Nebo thrust fault 

All beds are overturned

Uplifted diapiric structure

Part of upper plate of 

FEET Charleston-Nebo thrust fault 

All beds are overturned

A'

FEET

7000-

6000-

4000-

3000-

Possible sole of Charleston-Nebo thrust fault

EXPLANATION

QTcf .

Coalesced

alluvial-fan

deposits

Colluvium

Cedar Mountain Formation

Twin Creek Limestone

-? i

T(Ja)

moloceneI( PleistoceneI I

!>Pliocene(?)I Upper 

J Cretaceous

I Lower 

J Cretaceous

Ara'pien < 

Shale J

Middle

Navajo Sandstone

1 Lower 

J Jurassic

Upper 

Trias sic

Lower 

Trias sic

Diamond Creek Sandstone 

and Kirkman Limestone

Lower 

Permian

Oquirrh Group

I Permian and 

j Pennsylvanian II2 <

UJ >

45

30

Contact Approximately located or inferred; dotted where 

concealed; dashed and queried in cross section to reflect speculative relations

Intrusive contact Dashed where inferred; queried where 

uncertain; oblongs on intrusive unit

Fault Bar and ball on downthrown block; barb shows 

upthrown block in cross section; dashed in cross section where reconstructed above eroded surface

Strike and dip of inclined beds

Strike and dip of vertical beds 

Strike and dip of overturned beds

- -+- Inferred position of axial trace of 

Levan diapiric fold

O

%S3 Cl 

O 

H Cl 

S3 H CCCO
74 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

and are inclined southward at about 25° where they 

abut the Arapien mudstones.

The northern Twin Creek exposure, also about 0.8 

km (0.5 mi) wide, is separated from the southern 

exposure by about 300 m (1,000 ft) of Arapien mudstone. This northern exposure is subparallel to and 

about 1 km (0.7 mi) east of the mountain front 

(fig. 35). Both the east and west edges of this Twin 

Creek exposure are in near-vertical fault contact with 

overturned, northwest-dipping beds of the Oquirrh 

Group of Permian and Pennsylvanian age. At the 

north end of this narrow Twin Creek exposure, Birch 

Creek has eut a deep, narrow canyon and exposed 

the underlying Navajo Sandstone. This band of 

Navajo and Twin Creek strata extends for more than 

1 km (0.75 mi) north of Birch Creek before it 

disappears, near Ingram Canyon, beneath Paleozoic

FIGURE 36. Overturned beds of the Twin Creek Limestone as 

exposed in Gardner Canyon. The Arapien Shale crops out just 

to the right of beds exposed in this photograph. I believe this 

fold, much like the overturned fold in Pigeon Creek (fig. 34), is 

the result of intrusion and upwarp by the Arapien Shale.

strata that form part of the Charleston-Nebo thrust 

plate.

The Arapien mudstones exposed in Gardner Canyon appear to be a northward outcrop of similar 

Arapien units exposed to the south near Red Canyon, 

and I interpret both Arapien exposures to be part of 

the diapiric core of the Levan fold.

Although these geologic relations between the 

Arapien, Twin Creek, and the Oquirrh may represent 

a window in a folded thrust sheet, much as interpreted by Black (1965, cross section C-C"), I believe 

that the steep to near-vertical contacts between the 

Arapien Shale and the Oquirrh Group, and between 

the Twin Creek Limestone and the Oquirrh, are more 

reasonably explained by vertical uplift. Although it is 

possible that thib vertical compression was induced 

during southeastward-directed emplacement of the 

Charleston-Nebo thrust plate (Black, 1965, p. 80), the 

lack of uniformity in the axial trends of the folds 

formed in the contorted Arapien strata suggests that 

the compression, more likely, stems from the later, 

upward vertical movement of the Arapien Shale as it 

was forced upward by its salt component. Consequently, as suggested by cross section A-A', figure 35, 

I interpret the Arapien strata to be a plug of the 

Levan diapiric core that lifted, tilted, and juxtaposed 

this band of Navajo Sandstone-Twin Creek Limestone against overturned Oquirrh strata, part of the 

main body of the Charleston-Nebo thrust plate. During the upward movement, the Arapien broke the 

Navajo-Twin Creek mass into two parts, and folded 

the southern part into a syncline.

As the Navajo Sandstone and the overlying Twin 

Creek Limestone are right-side-up and in a normal 

stratigraphic sequence, rather than being overturned 

as one might expect if they were a part of the overturned beds that form the upper plate, this upthrust 

mass is probably part of the lower plate of the 

Charleston-Nebo thrust fault.

Exposures to the east, near Rees Flat (fig. 35), support the concept that the Arapien Shale has intruded 

and deformed part of the thrust sheet. As the contact 

between the overturned beds of the thrust plate and 

the Arapien mudstones is traced eastward up Red 

Canyon, the contact eventually disappears beneath a 

pediment mantle of sand and gravel that floors Rees 

Flat. The east edge of Rees Flat is bounded, on the 

north, by overturned rocks of the thrust plate, and 

on the south, by a small hill formed by upturned conglomerate and sandstone beds that have been 

warped to form an irregular-shaped basin. The 

Arapien Shale underlies these conglomerate beds 

along the east and south edges of the basin; because 

of the pediment mantle (fig. 35), I have not identified
DIAPIRIC STRUCTURES 75

the unit underlying the conglomerates along the west 

and north edges of the basin. The basin, although of 

somewhat irregular shape, is about 1.2 km (3k mi) in 

diameter. The conglomerate beds nearest the thrust 

plate are vertical or overturned; those along the east 

flank of the basin dip westward, even as those along 

the south flank dip northward. In the past, Johnson 

(1959) assigned the reddish-brown conglomerate and 

sandstone beds that form the basin to the Price River 

Formation; subsequently, Black (1965) assigned them 

to the Indianola Group; and still later I (1983) also 

assigned them to the Indianola Group.

Biek (1988b), however, has decided that the beds in 

question are part of the Cedar Mountain Formation. 

Whether the beds are Indianola or Cedar Mountain 

stems from uncertainty as to just what units should 

be included in the Cedar Mountain Formation. Witkind, Standlee, and Maley (1986, p. 4), studying 

exposures in the Red Rocks area, along the southeast 

flank of the Gunnison Plateau, included two units in 

the Cedar Mountain Formation: "* * *an upper unit 

that consists primarily of beds of reddish-brown 

coarse conglomerate, and a lower unit that consists 

of variegated mudstone* * *." As the upper conglomeratic unit is much like the conglomerate beds that 

make up the bulk of the Indianola Group, the two 

units are difficult to separate. Co-authors Witkind 

and Maley (in Witkind, Standlee, and Maley, 1986, 

p. 5), influenced by the fact that the change from 

mudstone to conglomerate is an easily recognizable 

contact, proposed that the "* * *upper unit be provisionally assigned to the undivided Indianola Group." 

For mapping purposes, therefore, I have considered 

the upper conglomeratic unit to be part of the Indianola. Biek (1988b), however, included both the conglomerate and mudstone units in his Cedar 

Mountain Formation. In figure 35 I show the beds as 

Indianola but add a query to reflect my uncertainty 

as to the correct assignment of these conglomerate 

beds.

I suspect that the basin is encircled and underlain 

by the Arapien Shale with much of the Arapien 

concealed beneath the surficial deposits that form the 

floor of Rees Flat (Witkind and Weiss, 1991). It is possible that some of the deformation of the north end of 

the basin is attributable to the southeastwarddirected movement of the Charleston-Nebo thrust 

plate, with some deformation due to the upward 

thrust of the Arapien. The vertical to overturned beds 

that mark the north edge of the basin imply that a 

strip of Arapien, confined between the edge of the 

thrust plate and the once near-horizontal Indianola(?) 

beds, pushed up and bowed back the Indianola(?) 

beds. The westward dip of the beds that form the east

edge of the basin probably reflect the west flank of the 

Footes Canyon diapiric fold, one of the three folds 

formed when the Levan fold trifurcated.

If this deformation of the basin is due, in part, to 

vertical uplift of the Arapien Shale as well as to 

eastward movement of the thrust plate (Black, 1965, 

p. 80), the mudstones of the Arapien not only underlie the basin but also underlie the toe of the thrust 

plate. By their upward movement the Arapien 

mudstones may have bowed up part of the plate even 

as they deformed the basin (east half of cross section 

A-A', fig. 35).

RED CANYON AREA (SOUTHERN WASATCH RANGE)

Basal thrust plate strata are exposed in and near 

Red Canyon (B-3) where overturned beds of the Twin 

Creek Limestone, part of the thrust plate, rest on 

contorted mudstones of the Arapien Shale. These 

mudstones and their contained evaporites are 

severely deformed and give every sign of intense 

compression. Near the mouth of Red Canyon, the 

Twin Creek beds that directly overlie the Arapien 

Shale mudstones are overturned and dip northwestward (45°), thus conforming to the attitude of the 

overlying (stratigraphically older) strata. As these 

Twin Creek beds are traced northeastward along 

strike, they become vertical, and then right-side-up 

and dip 80° SE. (fig. 37). It is much as if vertical 

upward movement of the Arapien Shale has pushed 

up the overturned beds and bowed them back into 

their normal right-side-up sequence.

SKINNER PEAKS AREA

The extent of the Levan fold south of Little Salt 

Creek is speculative, being based chiefly on sparse 

outcrops of the Arapien Shale, and on the development of the westward-facing West Gunnison monocline. Near Skinner Peaks (D-3), about 6 km (3 V2 mi) 

south of Little Salt Creek, the Arapien Shale crops 

out beneath westward-dipping (20°) volcanic rocks, 

part of the Goldens Ranch and Moroni Formations 

(Witkind and Marvin, 1989). I attribute this westward dip of the volcanic rocks to the upward movement of the underlying Arapien Shale. As these 

Arapien exposures are directly south of and collinear 

with those Arapien beds that crop out at Little Salt 

Creek, it seems reasonable to conclude that all are 

part of the core of the Levan diapiric fold.

Witkind and Marvin (1989), using potassium-argon 

techniques, have dated these volcanic rocks as 

having been formed during an interval that extended
76 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

o i-!%"^-~* >&* 

F ^rwsrv^!

". ..**»vv- v*W

> '*> » *i. * "IK'>- 

:'->x^- .5^' ^ ^v;^..-r *

» *, *'- -iX

 i ' _, ^" *i_';-*J>«a" 'C* ?«' »' "

ft*."^-^^-^^* "-*^"^v4* i

^t'-.t«f :-V^«c^-Ai:.%^ ^* 

2.4H-^ * ^....fc4 ,"* -,;^' ,** %.***, = .<";^^- J-^*'" A-. :^,v 2iV^^, ^->..^ .v?\.--? 

v \\ \'^>r

\^\>V^

v*s^;i

FIGURE 37. View eastward along south wall of Red Canyon showing Twin Creek Limestone dipping steeply to the southeast. 

Mudstones, which I interpret to be part of the Arapien Shale, 

are exposed to the right of this view.

The rocks exposed along Red Canyon are part of the upper 

plate of the Charleston-Nebo thrust fault, which in central 

Utah appears as the lower limb of an overturned anticline. As 

a result, all strata are overturned and dip moderately to the 

northwest. In this specific locality, however, near the edge of 

the thrust plate, the beds of the Twin Creek are right-side-up 

and dip steeply to the southeast, exactly opposite to the dips of 

all other units in the area.

I interpret these relations to mean that the adjacent Arapien 

mudstones, part of the Levan diapiric fold, have locally bowed 

up and flexed back the formerly overturned beds of the Twin 

Creek Limestone, which once dipped northwest, so they now 

appear right-side-up dipping to the southeast.

from the late Eocene to the middle Oligocene. If the 

volcanics were indeed tilted as a result of upward 

movement of the Arapien, as I propose, then that 

movement must have occurred at some time after the 

middle Oligocene, long after the compressive events 

of the Sevier orogeny ended at the close of the 

Paleocene.

Mattox and Weiss (1987, p. 60), studying the 

southwest flank of the Gunnison Plateau, directly 

south of Skinner Peaks, have stated that salt diapirism has not "played a major role in the structural 

development of the study area." To support their contention they noted that Indianola beds east of and 

adjacent to the Chriss-Mellor graben dip gently eastward (Mattox, 1987) rather than being vertical or 

overturned as one might expect next to a diapiric 

upwarp. Seemingly, Mattox and Weiss have failed to 

grasp Witkind and Page's (1984) suggested explanation of the relations between salt diapirs and the 

monoclines in the Sanpete-Sevier Valley area. Witkind and Page proposed that partial removal of salt 

from a causative salt diapir resulted in subsidence of 

the overlying sedimentary beds to form a monocline. 

The causative diapir, thus, is at the toe the distal 

end of the downwarp. The large north-trending 

Chriss-Mellor graben of Mattox and Weiss (1987), 

which breaks the flank of the West Gunnison monocline, is at least 3 km (2 mi) east of the crest of the 

Levan diapir. One would not expect vertical or overturned beds this distant from the diapir.

Mattox and Weiss (1987, p. 58) described a distinctive thinning and pinch-out of the North Horn Formation along the southwest flank of the Gunnison 

Plateau and attributed it to the gradual uplift of a 

topographic and structural high west of one of the 

major faults the Escarpment fault in their area 

(1987, p. 60). I propose an alternative interpretation, 

that this thinning of the North Horn Formation is 

much like the depositional thinning that marks the 

various diapiric folds throughout the area (p. 107). If 

so, it strongly suggests that salt diapirism has played 

a significant role in this sector of the Gunnison 

Plateau.

The westward-facing position of the West Gunnison 

monocline implies that the crest of the Levan diapiric 

fold is concealed beneath those surficial deposits that 

fringe the west flank of the Gunnison Plateau.

In many respects, the north-trending ChrissMellor graben is similar to the many north- and 

northeast-trending grabens that break the west 

flank and crest of the Wasatch Plateau. These grabens appear to be salt derived; seismic reflection 

profiles across the Wasatch Plateau suggest strongly 

that the faults that bound the grabens do not 

extend below Jurassic strata, in essence, below 

Arapien and below Carmel beds. The implication is 

strong that dissolution of bedded salt resulted in the 

development of those grabens.
DIAPIRIC STRUCTURES 77

POLE CREEK DIAPIRIC FOLD

GEOLOGIC SETTING

The Pole Creek diapiric fold (fig. 16, 12) extends 

northeastward from near the north end of the Gunnison Plateau (D-3), where the Levan fold trifurcates, 

to its disappearance beneath young volcanic rocks, 

some 11 km (7 mi) away, near the head of the Middle 

Fork Pole Creek (B-4) (fig. 38).

KOA CAMPGROUND ARF.A

About 8 km (5 mi) east of Nephi (B-3), where the 

scenic Nebo Loop Road joins State Highway 132 

(near a KOA Campground (C-3)), amorphous, earthy, 

reddish-brown Arapien mudstones crop out between 

extensive exposures of volcaniclastic rocks (southwest 

corner of area shown in fig. 38). Where these volcaniclastics, part of the Moroni Formation of late Eocene 

to middle Oligocene age, overlie the northwest flank 

of the Arapien exposures, they dip about 25° NW.; 

where they overlie the southeast flank they dip 

southeastward about 30°. About 1.6 km (1 mi) northeast of the aforementioned road junction, Indianola 

conglomerates, unconformably underlying the volcaniclastic rocks and overlying the Arapien Shale, crop 

out along the west valley wall of Pole Creek. The 

conglomerates dip about 60° NW. Directly across the 

valley, which is floored with alluvium but is most 

likely underlain by the Arapien Shale, comparable 

Indianola beds, also unconformably interleaved 

between the volcaniclastics and the Arapien Shale, 

are vertical or dip steeply to the southeast. Thus, 

both Moroni and Indianola units unconformably overlie and dip away from the Arapien exposures.

In places, these Moroni volcaniclastics are overlain 

unconformably by semiconsolidated sands, gravels, 

and boulders of the Salt Creek Fanglomerate (Eardley, 1933a), which also dip away from the Arapien 

exposures but not as steeply as the underlying volcaniclastics.

I interpret the Arapien beds to be the crest of the 

diapiric core of the northeast-trending Pole Creek 

fold, and the upturned beds that flank the Arapien 

exposures to be segments of the upturned flanks of 

the fold. From the road junction, the crest of the fold 

trends about N. 45° E. and can be traced into the 

Middle Fork Pole Creek (fig. 39A).

The fact that units of the Indianola Group, the 

Moroni Formation, and the Salt Creek Fanglomerate 

conform in direction of dip but differ greatly in 

amounts of dip implies several episodes of deformation. Presumably, one episode occurred after the Indianola beds (of Late Cretaceous age) were consolidated;

| a second deformational episode must have occurred 

after the volcaniclastic sediments (of mid-Tertiary 

age) were emplaced and partly consolidated, and a 

third occurred during early(?) Quaternary time, at 

some time after the Salt Creek Fanglomerate was 

formed.

As shown in cross section A-A' (center) of figure 

38, I propose that the units commonly present 

between the Arapien and the Indianola the Twist 

Gulch and Cedar Mountain Formations pinch out 

against the flanks of the diapiric core. Farther to the 

northeast, in the Middle Fork Pole Creek, both the 

Twist Gulch and the Cedar Mountain Formations are 

exposed between the Arapien and the Indianola but 

as extremely thin remnants.

MIDDLE FORK POLE CREEK

The core of the Pole Creek fold and the sedimentary rocks that form its southeast flank crop out in 

the Middle Fork Pole Creek (fig. 39A). Best exposures are in C sec. 13, T. 12 S., R. 2 E. The Arapien 

Shale, part of the core of the fold, forms the northwest bank of Middle Fork; vertical units of the Twist 

Gulch are exposed in the narrow stream bottom (fig. 

39B, C), and Cedar Mountain beds form the eastern 

stream bank. The Twist Gulch and Cedar Mountain 

Formations are extremely thin; determining their 

exact thicknesses is difficult, for much of the area is 

mantled with colluvium and shrubs. I estimate the 

Twist Gulch to be about 60 m (200 ft) thick, and the 

Cedar Mountain to be about 250 m (800 ft) thick. 

Elsewhere in the Sanpete-Sevier Valley area, the 

Twist Gulch is about 915 m (3,000 ft), and the Cedar 

Mountain about 550 m (1,800 ft) thick.

These exposures in the Middle Fork Pole Creek are 

flanked on the southeast by beds of the Indianola 

Group that are vertical, or dip steeply southeastward. To the northwest these Middle Fork exposures 

are flanked by volcanic beds of the Moroni Formation

FIGURE 38 (following pages). Geology across Pole Creek-Hop 

Creek area, Cedar Hills. Base modified from U.S. Geological 

Survey 1:100,000 Nephi (1981). Contour interval 250 m. The 

broad geologic pattern of the Cedar Hills has been determined by 

the Pole Creek diapiric fold, whose crest on this map is delineated by a dashed line. The fold trends approximately N. 45° E. 

through the area, and probably joins the Dry Hollow diapiric fold 

(fig. 16, 10). Arapien mudstones are exposed beneath volcaniclastic sediments at the stream junction shown in the lower left 

corner of the map, and in Middle Fork Pole Creek. Strata west of 

the Arapien exposures dip westward, strata east of those exposures dip eastward. Crest of the fold is well exposed in Middle 

Fork Pole Creek. (See fig. 39.)
78 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

111°40'

3 MILES

METERS

Possible sole of Charleston-Nebo thrust fault

-1000-
DIAPIRIC STRUCTURES 79

EXPLANATION

OTprrr

*,"-.*. $ > *&.- ;'

Pediment deposits

Alluvium

Moroni Formation

Park City Formation

Diamond Creek Sandstone 

and Kirkman Limestone

PPo

Oquirrh Group

Alluvial fan deposits OTcf

^ Holocene

T(Ja)

Coalesced alluvialfan deposits

 ^ __i 

Earthflow deposits ^ Pleistocene

y Pliocene

QUATERNARY

Dike

Mancos Shale

Arapien Shale

Triassic strata, 

undivided

- Contact Approximately located or inferred

1 Intrusive contact Approximately located or inferred; oblongs on intrusive unit

-^ Fault Dotted where concealed; bar and ball on downthrown block

-^ A High-angle reverse fault Dashed where approximately located; queried where

uncertain; sawteeth on upthrown plate; barb shows upthrown plate in cross section

\

Oligocene

Eocene

Paleocene

Upper Cretaceous

Lower Cretaceous

>- TERTIARY

CRETACEOUS

Middle Jurassic

Lower Jurassic

Upper and 

Lower Triassic

Lower Triassic

JURASSIC

TRIASSIC

Lower Permian > PERMIAN

70

PERMIAN AND 

PENNSYLVANIAN

Strike and dip of inclined beds 

Strike and dip of vertical beds 

Strike and dip of overturned beds
CO

o

WEST EAST

> , J

Moroni volcanics Hop Creek Ridge 

dipping westward Chiefly Indianola Group strata

Middle Fork Pole Creek dipping eastward ^-, ' <M

- - . . __^_^^^M / , > \ ^ai^^H

' ' '

.

'. Twist Gailch Formatioh ' , ;!' ?'- ' ' ' 

I* ^

tfSr- -&V

fc*

'&-

- v VKIKT'- " /«*b 4 i^ft^f¥%< ^asS^s^T^^^/r *& -Si8?f % ^P 5^^%^; ; ^^^p^' f% ; - 

.; I j " y» '-^ / ^ , ^f**?;-

FIGURE 39. Geologic relations in and near Middle Fork Pole Creek. A, View northeastward along crest of Pole Creek diapiric fold. Fold trends about N. 45° E., 

and Middle Fork Pole Creek (left of center) essentially follows crest of fold. Beds 

east of the crest generally dip eastward; those west of the crest generally dip 

westward.

Volcanics of the Moroni Formation (left side of photograph), of late Eocene to 

middle Oligocene age, form the west flank of the fold. As these volcanics are 

tilted westward along with the underlying sedimentary strata, the suggestion is 

strong that the tilting occurred at some time after middle Oligocene time. Tilting 

of the Moroni thus implies that compression stemming from the Sevier orogeny, 

which ended in the Paleocene, could not have been a factor in the tilting. I 

believe the responsible forces are salt generated.

B, Vertical beds of the Twist Gulch Formation exposed in floor of Middle Fork 

Pole Creek. Arapien strata form west valley wall, and Cedar Mountain beds form east valley wall. The Twist Gulch and Cedar Mountain Formations are 

anomalously thin in this locality, which flanks the crest of the fold. C, Close-up view of vertical beds of the Twist Gulch as exposed in east valley 

wall of Middle Fork Pole Creek.
DIAPIRIC STRUCTURES

that dip moderately northwestward. In places, this 

volcanic cover has been breached to expose Indianola 

beds that are vertical or dip steeply northwestward. 

Near the head of the Middle Fork Pole Creek, these 

vertical Indianola beds are overlain by North Horn 

strata that dip away from the crest of the fold beds 

east of the crest dip about 45° SE., beds west of the 

crest dip 10° to 20° NW.

DISCUSSION

These exposures, in Pole Creek and in the Middle 

Fork Pole Creek, imply that the Arapien mudstones 

were slowly rising, presumably as an ancestral 

northeast-trending ridge, even as Twist Gulch sediments were being deposited. This dynamic paleo-high 

impeded the deposition of Twist Gulch and successive 

younger sediments. The fact that Twist Gulch sediments thin is most significant, for the Twist Gulch is 

the next younger unit deposited after the Arapien. 

This must mean that the salt began its slow upward 

movement shortly after it was deposited.

This slow upwelling of the salt apparently was disrupted at least twice by more rapid upward surges of 

the salt: once during the Late Cretaceous when the 

Indianola beds were bowed up, and again when the 

volcanic rocks were bowed up. As the volcanic and 

volcaniclastic rocks are part of the Moroni Formation, tentatively dated as having been formed during 

the late Eocene to middle Oligocene (Witkind and 

Marvin, 1989), this second deformational episode 

must have occurred at some time after the middle 

Oligocene. These age relations reemphasize the fact, 

noted from structural relations near Skinner Peaks, 

that the forces responsible for this second deformational episode, whatever their origin, could not have 

stemmed from the Sevier orogeny, for that orogeny 

came to an end at the close of Paleocene time (Armstrong. 1968, p. 449).

The deformational sequences in the Middle Fork 

Pole Creek, thus, are similar to those in the KOA 

Campground area, and to those in the Skinner Peaks 

area along the west flank of the Levan diapiric fold.

The Pole Creek fold has determined the structural 

pattern of the Cedar Hills. West of Pole Creek, all 

strata, volcanic as well as sedimentary, are vertical 

or dip northwestward toward the Charleston-Nebo 

thrust plate. East of Pole Creek, most strata are 

either vertical or dip steeply southeastward; in a few 

places these beds are overturned to the southeast 

and so dip steeply to the northwest. These steeply 

dipping to vertical strata, all part of the Indianola 

Group, are well exposed along Hop Creek Ridge and 

in Hop Creek (fig. 40).

The Pole Creek fold not only has determined the 

pattern of the Cedar Hills, but it seemingly has also 

modified the north end of the Gunnison Plateau and 

the exposed east edge of the Charleston-Nebo thrust 

plate. So, the north end of the Gunnison Plateau is 

tilted southeastward, presumably bowed up by the 

rising diapiric core. I believe the northwestward tilt of 

the Charleston-Nebo thrust plate, near Nephi (B-3), 

reflects the northwest flank of the Pole Creek fold and 

stems, in part, from the same upward movement of 

the core.

Apparently, the Pole Creek fold continues northeastward concealed beneath the volcanic mantle, and 

eventually reappears east of Thistle in Dry Hollow to 

form the Dry Hollow diapiric fold (fig. 16, 10).

FOOTES CANYON DIAPIRIC(?) FOLD

The trifurcation of the Levan diapiric fold, at the 

north end of the Gunnison Plateau, resulted in three 

major diapiric folds. I have discussed both the western (Levan) and eastern (Pole Creek) folds, and in 

this section I describe the sparse surface evidence 

that hints at the existence of the middle, Footes Canyon (B-3) fold (fig. 16, 13).

In general, I believe that the Footes Canyon fold 

trends about N. 15° E., extending from the north end 

of the Gunnison Plateau to some indefinite point 

beneath the Charleston-Nebo thrust plate. Footes 

Canyon, a minor tributary that breaks the north wall 

of Salt Creek, probably follows the crest of the fold, 

for Arapien strata are exposed all along the canyon's 

length, and the consolidated strata that overlie these 

Arapien mudstones appear to be tilted away from the 

crest. Thus, Indianola(?) conglomerates that form 

part of the northwest valley wall of Footes Canyon 

are tilted northwestward. These conglomerates seemingly define the northwest flank of the fold. The 

southeast flank of the fold is indistinct, chiefly 

because of thick forest cover and the debris shed by 

the disintegrating volcanic units that overlie the 

Arapien exposures. On the basis of a few poor exposures, I believe that these volcanic units of the 

Moroni Formation dip southeastward. At the north 

end of Footes Canyon the Arapien mudstones pass 

below the Charleston-Nebo thrust plate.

Although only sparse surface data are available to 

establish the existence of the Footes Canyon fold, 

considerable evidence along the eroded flank of the 

Charleston-Nebo thrust plate implies that the plate, 

and a mantle of sedimentary rocks that once overlay 

the plate, were bowed up at some time after the plate 

was emplaced (Witkind, 1987). As the trend of the 

Footes Canyon fold, projected northeastward, is
82 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH
DIAPIRIC STRUCTURES 83

adjacent and parallel to the eroded margin of the 

thrust plate, I attribute the bowing up of the plate to 

movement along the Footes Canyon fold. The 

detailed evidence, involving the deformation of the 

Charleston-Nebo plate, is summarized elsewhere in 

this report (p. 104-107).

DRY HOLLOW DIAPIRIC FOLD

Vertical to overturned beds of the Indianola Group, 

striking about N. 40° E., crop out southeast of Thistle 

(A-5) in a deep canyon known as Dry Hollow (A-5) 

(fig. 41). The canyon, tributary to northwest-flowing 

Lake Fork (A-5), trends northeastward, its course 

seemingly determined by the strike of the steeply 

dipping Indianola beds. These vertical to near-vertical 

strata are overlain with striking angular unconformity by gently dipping reddish-brown conglomerate, 

sandstone, and mudstone beds of the North Horn Formation (fig. 42). North Horn beds that overlie the 

northwest flank of the fold dip northwestward at 

about 25°; those that overlie the southeast flank dip 

southeastward at about 10°.

These exposures represent the crest and flanks of 

the northeast-trending Dry Hollow diapiric fold (fig. 

16, 10), of which only part crops out in Dry Hollow. 

The fold extends to the northeast across both Lake 

Fork and Soldier Creek (A-5) and passes below 

inclined North Horn beds exposed along the north 

valley wall of Soldier Creek. On the basis of these 

limited exposures the fold trends about N. 40° E. for 

some 6 km (4 mi), reaching from the head of Dry 

Hollow to the north wall of Soldier Creek Canyon. 

The extent of the fold to the southwest is uncertain; 

it may connect with the Pole Creek fold (fig. 16, 12).

North Horn and Flagstaff strata near the upturned 

Indianola beds are unusually thin compared to their 

thicknesses elsewhere in the area.

As shown in figure 43, I interpret these exposures 

to represent deformation of part of the CharlestonNebo thrust plate by a rising mass of the Arapien 

Shale. The thrust plate the lower limb of an anticline overrode a mass of the Arapien Shale, probably during the Late Cretaceous (fig. 43, I). 

Subsequently, Arapien Shale, forced upward by 

slowly upwelling salt, bowed up the thrust plate to 

form a paleo-high that restricted deposition of sediments (fig. 43, II). Price River sediments, deposited 

against the flanks of this rising high, locally pinch 

out (fig. 43, III). Younger sediments, such as the 

North Horn and Flagstaff Formations, both pinch out 

against the flanks of the high and locally bury it. The 

Arapien probably continued to rise until well into the 

Tertiary, judging by the fact that volcanic units

tentatively dated as late Eocene to middle Oligocene 

have been deformed along with the underlying sedimentary rocks. At some time after the upward movement of the rising Arapien ceased, erosion removed 

the volcanic cover as well as many of the underlying 

younger Tertiary sedimentary units. In time, erosion 

effectively breached the crest of the rising high to 

expose the vertical and overturned Indianola beds of 

the thrust plate (fig. 43, IV).

In several other areas where diapiric folds are 

exposed, erosion has been extensive enough to break 

through those sedimentary units that form the crest 

of the fold and expose the Arapien core. Seemingly, 

erosion has not been as extensive in the Dry Hollow 

area, and the upturned Indianola beds have not, as 

yet, been completely breached to expose the Arapien 

core (cross section A-A', fig. 41).

THISTLE CREEK DIAPIRIC(P) FOLD

The Thistle area (A-5), some 40 km (25 mi) southeast of Prove, is perhaps best known for the disastrous landslide of April 1983 that effectively blocked 

the major road and rail connections between Price, 

east of the Wasatch Plateau, and Prove, west of the 

plateau. Geologic aspects of the slide, its multiple 

impacts on the economic life of central Utah, and the 

potential geologic hazards near the slide have been 

described and discussed elsewhere (Duncan, Fleming, 

and Patton, 1986; Kaliser and Fleming, 1986; Witkind, 1986; Willis, 1987).

GEOLOGIC SETTING

In the Thistle area, arched Cretaceous and Tertiary 

strata overlie the Charleston-Nebo thrust plate and 

suggest the presence of a diapiric fold (fig. 16, 11; 

cross section A-A', fig. 44).

Two major elements dominate the geologic framework of the Thistle area: the eroded east margin of 

the major Charleston-Nebo thrust plate, and a 

sequence of younger Cretaceous and Tertiary sedimentary and volcanic rocks that unconformably overlies and partly buries the thrust plate.

CHARLESTON-NEBO THRUST PIATE

The basic elements of the Charleston-Nebo thrust 

plate have been described on pages 8 to 9. In the 

Thistle area, the easternmost exposed rocks of the 

thrust plate form a high ridge that trends slightly 

east of north. It is unclear whether this ridge is at 

the distal margin of the thrust plate (fig. 4A) or
84 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

whether the distal margin is farther east buried 

beneath younger strata (fig. 4jB). If the latter, the 

plate margin in the Thistle area is an erosional 

escarpment cut on the thrust plate (fig. 4.B). Because 

of uncertainty as to which of these two alternatives 

is correct, I refer to this eastern part of the thrust 

plate as an "erosional escarpment," and delineate it 

on figure 44 by hachures.

Spanish Fork River and its tributaries, westflowing Soldier Creek (A-5) and north-flowing Thistle 

Creek (A-4), have cut a deep canyon, shaped somewhat like a T on its side, through the ridge. That 

part of the ridge north of the confluence of Soldier 

and Thistle Creeks is unnamed; in the past, crews 

involved in the construction of Thistle dam and the 

new segment of U.S. Highway 6 and 89 incorrectly 

called it "Billies Mountain," but in fact, Billies Mountain is some 3 km (2 mi) to the northeast. Continued 

incorrect usage, however, has transferred the name 

Billies Mountain to the north part of the ridge, and 

in this report I follow that custom but alert the 

reader to this misusage by placing the name in 

quotes, thus, "Billies Mountain."

In the Thistle area, the rocks in the thrust plate 

range in age from Pennsylvanian to Jurassic (table 

2). Most of them dip eastward at moderate to high 

angles; in the ridge, along the eastern part of the 

thrust plate, Navajo (Jn on the map) and Twin Creek 

(Jtc) strata dip eastward at about 60°. Farther west, 

toward the main mass of the thrust plate, successively older strata dip east but at about 40°,

SEDIMENTARY SEQUENCE OF YOUNGER ROCKS

The deeply eroded plate is partly buried by 

younger sedimentary rocks of Late Cretaceous to 

Eocene age. Locally, these rocks are mantled by pyroclastic volcanic rocks of the Moroni Formation (late 

Eocene to middle Oligocene). East of the erosional 

escarpment, the younger sedimentary and volcanic 

rocks dip eastward at low to moderate angles (10°- 

30°). By contrast, the same strata west of the escarpment dip westward at moderate angles (fig. 45A). 

Wherever exposed, these younger sedimentary and 

volcanic rocks unconformably overlie the eastwarddipping rocks of the thrust plate.

These younger sedimentary rocks thin markedly 

toward the erosional escarpment. This is perhaps 

best shown in a diagram prepared by Young (1976, 

fig. 5), which shows a westward thinning of all 

strata, extending from the North Horn to the Green 

River Formation.

STRATA NORTH OF SPANISH FORK CANYON ("BILLIES MOUNTAIN" AREA)

Most of these younger Cretaceous and Tertiary 

strata are well exposed where they mantle the thrust

m°30 28'

R4E

1 2 KILOMETERS

J_________I

1 MILE

FIGURE 41 (above and facing page). Geology of Dry Hollow area. 

Base modified from U.S. Geological Survey 1:24,000 Thistle 

(1967). Contour interval 200 ft. In Dry Hollow, which follows 

the crest of the Dry Hollow diapiric fold, vertical beds of the 

Indianola Group, possibly part of the Charleston-Nebo thrust 

plate, pass below and unconformably underlie beds of the 

North Horn Formation. North Horn strata east of the crest of 

the fold dip gently eastward; similar strata west of the fold's 

crest dip gently westward. Near the west edge of the map area 

these westward-dipping North Horn strata abruptly reverse dip 

and dip eastward, reflecting a small intrusive mass of Arapien 

Shale.
DIAPIRIC STRUCTURES 85

EXPLANATION

Valley-fill 

deposits

Qcl1 Qnw Qal

Colluvium and Alluvium

mass -was ting

deposits

TUa)

Arapien Shale

Alluvial-fan deposits 

(locally coalesced)

Landslide and 

earthflow deposits Sand and

gravel deposits I

QUATERNARY

Navajo Sandstone

Contact Approximately located or inferred;

dashed and (or) queried in cross section

to reflect speculative relations 

Intrusive sedimentary contact Approximately

located or inferred; oblongs on intrusive

unit 

Fault Dashed where approximately located;

dotted where concealed; bar and ball

on downthrown block

Eocene

Paleocene

Upper 

Cretaceous

Lower 

Cretaceous

Middle 

Jurassic

Lower 

Jurassic

Strike and dip of inclined beds 

Strike and dip of vertical beds 

Strike and dip of overturned beds 

Angular unconformity

> TERTIARY

CRETACEOUS

JURASSIC

plate south and west of Spanish Fork Canyon, but 

they have largely been eroded from much of the 

thrust plate north and east of the canyon. Some 

units do crop out north of the canyon as a series of 

eastward-dipping strata that lap onto the east margin of the plate.

This general pattern of eastward-dipping strata is 

interrupted, however, north of Soldier Creek directly 

east of "Billies Mountain." There, the Flagstaff Limestone (Tf) abuts the east flank of "Billies Mountain" 

at an eastward dip of about 20° (fig. 44). About 150 

m (500 ft) east of the ridge, the Flagstaff gradually 

flattens, and then reverses and dips moderately to 

steeply westward; locally these strata are almost 

vertical (fig. 45.B). Although the Flagstaff Limestone

is underlain by the North Horn Formation throughout most of central Utah (table 1), in this specific 

locality the near-vertical beds of the Flagstaff are 

underlain by the Arapien Shale. These Arapien 

strata, chiefly calcareous mudstones. are severely 

contorted and broken.

The deformed Arapien strata, and the relations 

between the Flagstaff and the Arapien, suggest that 

the Arapien, driven by its contained salt, has raised 

and tilted back the Flagstaff Limestone.

Elsewhere in this general area, other exposures 

indicate the intrusive nature of the Arapien. Thus, 

during excavation, the earth-moving equipment time 

and again exposed wedgelike masses of Arapien 

Shale that intrude and deform the steeply tilted beds
86 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

EAST WEST

Figure 42. View southward near head of Dry Hollow showing angular unconformity. Vertical light-gray beds of the Indianola 

Group unconformably underlie reddish-brown North Horn strata that dip gently southeast.

of Twin Creek in the thrust plate (fig. 1LA). At the 

east edge of "Billies Mountain" a dike-like mass of 

the Arapien separates the Twin Creek strata of the 

thrust plate from the tilted units of the Colton Formation that lap onto the erosional escarpment of the 

plate (fig. 1LB). Sills of the Arapien, containing both 

nodules and masses of gypsum and clasts of the Twin 

Creek Limestone, intrude the Twin Creek Limestone 

(fig. 46).

East of "Billies Mountain," where the steeply tilted 

beds of Flagstaff Limestone are underlain by the 

intensely contorted Arapien strata (fig. 45B), the 

deformed Arapien beds pass eastward into noncontorted but nearly vertical Arapien strata. These 

Arapien beds are right-side-up and lack the crumpled 

and contorted aspect of the profoundly disturbed 

Arapien beds. As these steeply dipping Arapien 

strata are traced eastward, they seem to conformably 

underlie the Twist Gulch Formation, which in turn 

underlies the Cedar Mountain Formation. The unbroken progression of beds, in normal stratigraphic 

sequence east from the disturbed mass of Arapien, 

implies that the thrust plate extends eastward 

beyond the erosional escarpment. Two alternatives 

are possible: (1) the mass of disturbed Arapien 

punched up through Arapien beds that were part of 

the plate, or (2) the disturbed Arapien beds, integral 

elements of the thrust plate, became mobile and then 

deformed the overlying strata. Of the two interpretations, I prefer the former: I believe that an underlying overridden mass of Arapien Shale punched up 

and deformed the thrust plate (cross section A-A', 

fig. 44). Intrusive fingers of the Arapien invaded both 

the plate and the adjacent younger strata. In this 

interpretation, the contorted Arapien strata and the

less deformed Arapien beds of the thrust plate are 

fortuitously juxtaposed.

Other examples of Arapien deformation are 

exposed elsewhere in the general area. So, for example, a small mass of Arapien Shale (labeled T(Ja) in 

fig. 44) crops out along the east valley wall of Thistle 

Creek about 0.8 km ( Vz mi) south of the confluence of 

Soldier and Thistle Creeks. West of that outcrop, 

North Horn (TKn) beds dipping eastward, off the erosional escarpment cut on the thrust plate, flatten and 

then reverse attitude to assume a steep westward dip 

directly adjacent to the west flank of the Arapien 

exposure. East of the Arapien mass, the North Horn 

beds dip eastward. These opposing dips in North 

Horn strata that flank the Arapien lead to the inference that consolidated North Horn strata have been 

arched by an intrusive mass of the Arapien Shale 

(cross section A-A', fig. 44).

STRATA SOUTH AND WEST OF SPANISH FORK CANYON

Younger sedimentary and volcanic rocks mantle 

parts of the thrust plate exposed south and west of 

Spanish Fork Canyon. Indeed, detritus from these 

younger rocks, chiefly the North Horn Formation,

FIGURE 43 (facing page). Diagrammatic sketches suggesting how 

the Dry Hollow diapiric fold developed. All views are oriented in 

same compass directions.

I. During the Late Cretaceous, the Charleston-Nebo thrust 

plate the lower limb of an overturned anticline overrode 

units of the Arapien Shale (K(Ja)). In this schematic cross section only some of the units that make up the thrust plate are 

shown.

II. After the thrust plate ground to a halt, the overridden 

Arapien Shale began to well upward slowly, gradually intruding 

the plate and bowing it upward. In this sketch erosion has 

beveled the bowed-up thrust plate to produce a surface of low 

relief.

III. Price River sediments (Kpr) began to be deposited on this 

surface of low relief. Incessant slow upwelling of the Arapien 

(T(Ja)) continued to bow up the plate, thus restricting deposition 

of Price River sediments, which locally pinched out against the 

flanks of the rising high. The Price River units unconformably 

overlay units of the thrust plate. In time, North Horn sediments 

(TKn) were deposited on the Price River sediments, and 

although some units of the North Horn pinched out against the 

flanks of the rising high, other North Horn units continued 

across the high and buried it. Ever younger sediments (representing, at the least, the Flagstaff (Tf), and later the Colton and 

Green River Formations) were deposited across the rising upwarp, and these units too were bowed up by slow upwelling of 

the Arapien.

IV. At some stage, probably after deposition of an Eocene and 

Oligocene volcanic mantle, erosion removed many of the younger volcanic and sedimentary units deposited across the crest of 

the fold, and exposed part of the bowed-up thrust plate, represented here by near-vertical and overturned Indianola (Ki).
DIAPIRIC STRUCTURES 87

WEST EAST WEST EAST

K(Ja) 

1

T(Ja)

TUa)

III

 ? 

TUa)

K(Ja)

EXPLANATION

Eocene

Upper Cretaceous

Flagstaff Limestone y Paleocene TERTIARY

CRETACEOUS

Lower Cretaceous

Middle Jurassic > JURASSIC

Arapien Shale

Arapien Shale

-U Angular unconformity
STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

111°28'

3000-
DIAPIRIC STRUCTURES 89

EXPLANATION

. CU

Old landslide deposits

Deposits of ancestral 

Lake Bonneville(?)

T(Ja)

Pediment mantle

Moroni Formation Volcaniclastic sediments

Colton Formation Green River and Colton

North Horn Formation

Price River Formation

mi

Indianola Group

Arapien Shale

Nugget Sandstone (north of Thistle); Navajo Sandstone (south of Thistle)

Ankareh Formation

Paleozoic rocks, undivided

Holocene

Pleistocene

Pliocene

Middle Oligocene

Eocene

Paleocene

Upper Cretaceous

Lower Cretaceous

Middle Jurassic

Lower Jurassic

Upper and 

Lower Triassic

QUATERNARY

TERTIARY

CRETACEOUS

JURASSIC

TRIASSIC

PALEOZOIC

Contact Approximately located or inferred;

dashed and queried in cross section to

reflect speculative relations 

Intrusive sedimentary contact Approximately

located or inferred; oblongs on intrusive

sedimentary unit 

Fault Dashed where approximately located;

dotted where concealed; bar and ball on

downthrown block

80

-1 - Edge of erosional escarpment Hachures point

in general direction of inclination 

Strike and dip of inclined beds

 Syncline Approximately located; trace of

axial plane

Crest of diapiric fold Approximately located; 

trace of axial plane; dotted where concealed

FIGURE 44 (above and facing page). Geology of Thistle area. (Caption continued on p. 90.)
90 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

FIGURE 44 (previous pages). Geology of Thistle area. Base modified from U.S. Geological Survey 1:24,000 Billies Mtn (1967), Birdseye 

(1979), Spanish Fork (1949), and Thistle (1967). Contour interval 200 ft. The Charleston-Nebo thrust plate, formed in part by units of 

the Twin Creek Limestone (Jtc), Nugget Sandstone (Jn) (called the Navajo Sandstone south of Thistle), and the Ankareh Formation 

("fia), is partly concealed beneath a cover of younger sedimentary rocks. These younger rocks include, in ascending order, the North 

Horn Formation (TKn), the Flagstaff Limestone (Tf), the Colton Formation (Tc), the Green River Formation (Tg), and the Moroni

. Formation (Tm).

At one time the thrust plate was completely concealed beneath this younger sedimentary and volcanic mantle. Since then, however, 

the mantle has been partly breached, exposing parts of the thrust plate, chiefly in and near the valley of Thistle Creek. This younger 

sedimentary and volcanic cover and the underlying thrust plate appear to have been warped into a northward-trending asymmetric 

fold. The crest of the fold (shown by a dotted and dashed line) essentially follows the west valley wall of Thistle Creek. West of the 

crest the younger Tertiary and Cretaceous mantle dips gently westward; east of the crest the beds dip eastward at slightly greater 

dips. The presence of Arapien exposures (T(Ja)) along the east valley wall of Thistle Creek and along the north valley wall of Soldier 

Creek suggests that the Arapien both underlies the thrust plate and is responsible for the upwarp of the thrust plate and its overlying 

mantle of younger sedimentary rocks (cross sections A A' and B B'). Cross section C C" is in figure 47.

WEST EAST

FIGURE 45. Photographs of Thistle area. See figure 44 for corresponding geologic map. A, View northward of the west valley 

wall of Thistle Creek. The Nugget Sandstone (Jn), part of the 

Charleston-Nebo thrust plate, dips steeply eastward. The North 

Horn Formation (TKn), dipping gently westward as part of a 

mantling younger sequence of rocks, unconformably overlies the 

Nugget. The North Horn Formation, in turn, is conformably 

overlain by a Tertiary sequence comprising the Flagstaff (Tf), 

Colton (Tc), and Green River (Tg) Formations. B, View looking 

northeastward at beds of the Flagstaff Limestone that dip 

steeply westward. Exposure is north of Soldier Creek and 

directly east of "Billies Mountain." Light-gray Flagstaff Limestone, commonly underlain by the North Horn Formation, is 

underlain, in this specific locality, by reddish-brown contorted 

and crumpled beds of the Arapien Shale (T(Ja)). I attribute the 

upwarp of the Flagstaff Limestone and the absence of units commonly found beneath the Flagstaff to intrusion of the Thistle 

Creek salt diapir.
i*pr^^:^^ '^^'' '^

Sk^* "&* s^^m_ » .%-

 ^; : '; ; i^m^^

itV&O'l J *< < *.' AJ ^ .-..L. *«. ..-.. 

. > ^ *, *:.^«<. ^"

I "^^^ ^

"X ""'^ '" .~-'Av..«.,- ..»,"»« \, % * ^-m^ ' *% .' '-. ' -«A vJ^K:"* .- ,.- . - __ w^.

*

..-^, ^?" «rapi^t:S^< | ,

 M

~_ *" 

FIGURE 46. Arapien sill intruded into the Twin Creek Limestone. Exposure is in 

new roadcut for U.S. Highway 6 and 89 through "Billies Mountain," Thistle Creek area. A, Arapien sill that intrudes the Twin Creek Limestone. Gypsum 

masses and Twin Creek Limestone clasts are scattered through Arapien matrix. 

Dashed lines delineate part of contact between sill and Twin Creek Limestone. 

B, Twin Creek Limestone clasts within the Arapien Shale. C, Close-up view of the contorted and crumpled beds of Arapien Shale that form the sill.

a

o

CO1

o
92 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

forms the bulk of the Thistle landslide. Directly east 

of the escarpment cut on the thrust plate, these 

younger sedimentary and volcanic rocks dip eastward; the same units exposed west of the escarpment 

dip westward (fig. 45A). Relations between the thrust 

plate and these overlying sedimentary rocks are well 

exposed along the west valley wall of Thistle Creek 

some 6 km (3.5 mi) north of the small community of 

Birdseye (A-4). One of the best exposures occupies 

parts of sees. 5, 6, and 7, T. 10 S., R. 4 E. near the 

junction of Crab and Thistle Creeks (fig. 44). There, 

the thrust plate is represented by beds of Nugget 

Sandstone (Jn) (called Navajo Sandstone south of 

Thistle, Utah (A-5)) and Twin Creek Limestone (Jtc) 

that dip eastward about 60°. These beds are unconformably overlain to the east by the North Horn Formation (TKn), which also dips eastward, but at about 

20°. A small wedge of eastward-dipping Flagstaff 

Limestone (Tf) (in the NEV4 sec. 7, T. 10 S., R. 4 E.) 

conformably overlies the North Horn.

Farther south, near the junction of Aggie and 

Thistle Creeks, volcanic rocks, part of the Moroni Formation, unconformably overlie the North Horn strata; 

the Moroni also dips eastward at this point but at 

about 30°. West of this exposure (as shown on cross 

section B-B', fig. 44), the North Horn (TKn) passes 

over and conceals the thrust plate, and then dips 

westward. The North Horn is overlain conformably by 

the Flagstaff Limestone (Tf), which passes westward 

beneath ever younger sedimentary beds that also dip 

westward. This sedimentary sequence is overlain to 

the west, beyond the area shown in the cross section, 

by westward-dipping volcanic rocks of the Moroni 

Formation. It seems clear that the sedimentary rocks 

were originally overlain by an unbroken blanket of 

volcanic rocks, now much eroded, that was arched 

along with the sedimentary rocks.

Structurally, then, the sedimentary and volcanic 

rocks appear to have been warped into a northtrending asymmetric anticline marked by a steep 

east flank and a gentle west one. After the beds 

were arched, erosion removed many of them and in 

the process exhumed part of the buried thrust plate.

DISCUSSION OF ALTERNATIVE INTERPRETATIONS

FAULTED TERRAIN

Although all workers in the area agree that the 

basic structural pattern involves an eroded thrust 

plate partly buried beneath younger sedimentary 

rocks, their explanations for the tilted strata differ. 

Baker (1976), Harris (1954), and Pinnell (1972) concluded that a high-angle, down-to-the-east normal

fault, named the Thistle Canyon fault by Harris 

(1954), separates the younger Cretaceous and Tertiary rocks from the thrust plate (fig. 47A). Presumably the eastward tilt of the younger rocks, east of 

and juxtaposed against the erosional escarpment, is 

the result of drag as the east block dropped along the 

fault. Downthrow to the east is also suggested by the 

difference in altitude between Flagstaff (Tf) strata 

astride the thrust plate west of the escarpment and 

those Flagstaff strata east of the escarpment. West of 

the escarpment, the Flagstaff beds are at an altitude 

of about 6,500 ft; east of the escarpment about 2.5 

km (1V2 mi) away they are at an altitude of about 

5,300 ft, some 1,200 ft lower.

To the best of my knowledge, no worker has offered 

any explanation for the westward tilt of those strata 

that overlie and are west of the erosional escarpment 

formed on the thrust plate (fig. 45A). A possible 

explanation involves westward tilting of a discrete 

fault block as a result of downthrow along a northtrending normal fault, as yet unrecognized, that may 

extend along the east flank of Loafer Mountain (A-4) 

(about 1.6 km (1 mi) west of the area shown in fig. 

44). Nor have previous workers offered any explanations for the many localized structural complexities 

that seem related to intrusive masses of the Arapien 

Shale. These complexities seem to be products of 

plastic intrusion.

DIAPIRIC DEFORMATION

I view most of the structural complexity in the 

Thistle area as a direct result of diapiric deformation that occurred after emplacement of the 

Charleston-Nebo thrust plate. The localized upwarp 

of those Flagstaff Limestone beds north of Spanish 

Fork River (fig. 45.B), and the arching of the 

Tertiary strata, both on a small and on a large 

scale, seem reasonably explained only by assuming 

that masses of the Arapien Shale deformed the 

country rocks long after those rocks were emplaced 

and consolidated.

The fact that a sedimentary sequence, extending 

from the North Horn Formation to the Green River 

Formation, thins toward the crest of the fold 

essentially the erosional escarpment implies that a 

dynamic, ancestral paleo-high continued to rise 

slowly, impeding sedimentary deposition throughout 

much of the Late Cretaceous and early Tertiary. As 

the Moroni Formation is involved in the arching, 

the high must have persisted at least through 

middle Oligocene time.

These structural and stratigraphic relations must 

mean that even as the younger sediments
DIAPIRIC STRUCTURES 93

WEST EAST

(Triassic, Permian, and Pennsylvanian strata, undivided)

WEST

(Triassic, Permian, and Pennsylvanian strata, undivided)

B

2 KILOMETERS 

J

0 1 MILE

FIGURE 47. Two alternative interpretations of geologic relations in Thistle area. Line of cross section C-C' is shown 

in figure 44, geologic map of the Thistle area. Contacts are 

dashed and (or) queried where relations are speculative. 

Quaternary units: Old, landslide deposit; Qcl, colluvium; 

Qf, alluvial fan; Qal, alluvium. Jtg, Jurassic Twist Gulch 

Formation. A, The Thistle Canyon fault, downthrown to 

the east, separates the younger Cretaceous and Tertiary 

sedimentary rocks (represented by the Flagstaff Limestone 

(Tf)) from the Charleston-Nebo thrust plate, represented 

by beds of the Twin Creek (Jtc), Nugget (Jn), and Ankareh 

("6a) Formations. B, A mass of Arapien Shale (T(Ja)) intruded and raised part of the Charleston-Nebo thrust 

plate, and in so doing arched the overlying younger Cretaceous and Tertiary sedimentary and volcanic rocks into a 

north-trending asymmetric fold. The eastward-dipping 

Flagstaff (Tf) strata, directly east of the erosional escarpment, are part of the fold's east flank. The westwarddipping North Horn strata (TKn), west of the escarpment, 

are part of the fold's west flank.

The thinning of all younger sedimentary units (here represented by the North Horn (TKn) and Flagstaff (Tf) Formations) toward the crest of the fold suggests that a 

diapiric fold, concealed beneath the thrust plate, has been 

growing at a slow, almost imperceptible rate impeding sedimentary deposition.

accumulated, a diapiric fold the Thistle Creek diapiric fold began to move upward beneath the 

thrust plate.

Many of the diapiric folds in central Utah are 

readily recognizable by the juxtaposition of contorted 

Arapien Shale masses against vertical to overturned 

beds, commonly of the Indianola Group. In the Thistle 

area, by contrast, a diapiric fold is indicated by strata 

arched asymmetrically over the escarpment cut on the 

Charleston-Nebo thrust plate. The eastward-dipping 

North Horn (TKn) ? Flagstaff (Tf), and Moroni (Tm) 

strata east of the erosional escarpment are in the east 

flank of the fold; the same strata west of the escarpment are in the west-dipping flank. In my view, the 

opposing dips of the strata and the difference in altitude between Flagstaff strata west and east of the 

escarpment merely reflect the configuration and 

asymmetry of the fold draped across the escarpment 

(fig. 47£).

I suggest that the erosional escarpment, formed on 

the thrust plate, was originally buried beneath 

nearly horizontal North Horn and younger strata. 

As a diapiric fold developed beneath the thrust plate, 

it raised the plate, and in so doing arched the overlying younger rocks. Erosion has since removed the 

crestal part of the arched sheet of North Horn and 

younger rocks and exhumed part of the escarpment.

HJORTH CANYON DIAPIRIC FOLD

Part of a northeast-trending diapiric fold (fig. 16, 9) 

is exposed in Hjorth Canyon (A 5) (sees. 15, 16, 21, 

and 22, T. 11 S. ; R. 4 E.), some 6 km (3V2 mi) north of 

Indianola (B-5) (fig. 2). This fold was first recognized 

and called the "Hjork Creek dome" by Runyon (1977b, 

p. 76), who noted that the structure "is actually an 

elongated dome rather than a circular one* * *and is 

illustrated * * *as a plunging anticline."

GEOLOGIC SETTING

Critical exposures, along the north wall of Hjorth 

Canyon, consist of a narrow band of highly contorted 

Arapien Shale that trends about N. 40° E., bounded 

on each flank by beds of the Twist Gulch Formation 

(fig. 48). Exposures are poor, but I suspect that beds 

of the Cedar Mountain Formation are stratigraphically above the Twist Gulch beds; in figure 48 I have 

mapped these Cedar Mountain(?) beds with Twist 

Gulch strata.

The Twist Gulch and Cedar Mountain(?) strata are 

anomalously thin; the thickness of the Twist Gulch 

Formation in the Hjorth Canyon area is less than 450 

m (1,500 ft). Elsewhere in this general area the Twist 

Gulch is about 915 m (3,000 ft) thick (Khin, 1956, 

p. 34). This unusual thinning has been recognized by
94 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

: ::.:. T 11 s

6000

5000 5000
DIAPIRIC STRUCTURES 95

EXPLANATION

Holoccne

North Horn Formation

Price River Formation 

(only on cross section)

Indianola Group

Twist Gulch Formation (Units of the 

Cedar Mountain 

Formation (Kcm) of 

Early Cretaceous 

age may be present)

Arapien 

Shale

TUa)

Arapien 

Shale

J -i

1 Middle Oligocene to 

J lower Eocene

:

 >

* Paleocene ^

- Upper Cretaceous

J

- Middle Jurassic

QUATERNARY

TERTIARY

CRETACEOUS

JURASSIC

40 _i_ 

85

Contact Approximately located or inferred; dashed and queried in cross 

section to indicate speculative relations

Intrusive sedimentary contact Approximately located or inferred; oblongs 

on intrusive unit

Strike and dip of inclined beds

Strike and dip of overturned beds

Crest of diapiric fold Dotted where concealed

FIGURE 48 (above and facing page). Geology of Hjorth Canyon 

area showing part of northeast-trending Hjorth Canyon diapiric 

fold. Base modified from U.S. Geological Survey 1:24,000 Indianola (1967). Contour interval 200 ft. Beds of the Twist Gulch 

Formation flank the core a northeast-trending mass of 

Arapien Shale of the diapiric fold. Twist Gulch strata on both 

flanks of the fold dip steeply southeast; those on the northwest 

flank are overturned. Overlying North Horn strata reflect the 

general configuration of the fold, as do the volcanics of the Moroni Formation (cross section A-A'). Arapien Shale as unit Ja is 

listed for completeness but is not shown, as such, on the map.

previous workers. Thus, Runyon (1977b, p. 67) 

attributed this "drastic thinning" to "drag faulting 

caused by the diapiric upwelling of the underlying 

Arapien* * *." Pinnell (1972, p. 97), however, attributed it to "* * *rapid facies changes in* * *environments of deposition or of Laramide thrusting."

Those Twist Gulch beds that form the northwest 

flank of the fold strike about N. 40° E., are vertical 

or overturned to the northwest, and so dip about 85° 

to the southeast. Twist Gulch beds that form the 

southeast flank of the fold are right-side-up and dip

southeastward between 80° and 85°. The outermost 

flanks of the fold are formed by units of the Indianola Group that dip about 20° NW. along the northwest flank, and about 85° SE. along the southeast 

flank.

All beds that form the fold are unconformably overlain either by moderately dipping strata of the North 

Horn Formation or by volcanic units of the Moroni 

Formation. Here too, as in the Dry Hollow (A-5) fold, 

these younger beds appear to have been arched during one or more upward movements of the underlying fold. Thus, those North Horn beds that overlie 

the northwest flank of the fold dip about 10° W.; 

those North Horn beds that overlie the southeast 

flank dip 30° to 50° SE. These southeast dips persist 

southeastward for about 1.6 km (1 mi), after which 

the North Horn beds pass beneath volcanic units of 

the Moroni Formation. Although attitudes of the 

Moroni beds are difficult to determine, I believe that 

they, too, reflect the configuration of the fold. Southeast of the exposures already described, near Little 

Clear Creek (B-5), Moroni beds dip northwest. This 

northwest dip of the Moroni strata reflects the northwest flank of the Little Clear Creek diapiric fold, 

which also trends northeast, and thus is parallel to 

and about 3 km (2 mi) southeast of the Hjorth 

Canyon fold (fig. 16).

DISCUSSION

I attribute the anomalous thinning of the Twist 

Gulch, Cedar Mountain(?), and most likely the Indianola strata, in the Hjorth Canyon area, to the 

imperceptible upward movement of the salt diapir 

during much of the time these units were being 

deposited.

The deformed rocks in Hjorth Canyon suggest 

three distinct diapiric episodes. During the first episode, once near-horizontal Twist Gulch, Cedar Mountain, and Indianola strata were bowed up and locally 

turned over as the Hjorth Canyon salt daipir surged 

upward to form a mushroom-shaped diapiric fold. 

This upward surge must have occurred at some time 

after Indianola strata were deposited and consolidated, in essence, during the Late Cretaceous, possibly after Santonian but before Campanian time. 

Subsequently, removal of salt partly destroyed this 

fold, and erosion then reduced it to a surface of low 

relief on which Price River sediments were deposited; 

these were subsequently overlain by North Horn sediments. As Price River strata are missing from this 

specific locality, I assume that they pinched out 

locally against the flanks of the slowly rising fold.
96 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

The second diapiric episode, represented by the 

arched beds of the North Horn, must have occurred 

at some time during the early Tertiary, for North 

Horn deposition continued at least into the Paleocene. The fact that the arched North Horn dips 

away from the crest of the fold, represented by the 

northeast-trending band of Arapien strata (fig. 48), 

implies that the upward surge of the diapir occurred 

in the same place and had the same trend as the previous fold. As North Horn strata are unconformably 

overlain by the volcanic rocks of the Moroni Formation, I assume that whatever younger Tertiary sedimentary strata were deposited, following the 

formation of the North Horn, either pinched out 

against the flanks of the rising fold or were eroded 

before volcanics of the Moroni spread across the area.

The arched Moroni represents the third diapiric 

episode. Presumably, a renewed upward surge of the 

salt diapir bowed up these once near-horizontal 

flows. Again, the attitudes of the Moroni rocks, 

dipping away from the crest of the fold, indicate that 

this renewed surge must have occurred in the same 

place and with the same trend as the two ancestral 

folds. This third surge must have come at some time 

after middle Oligocene time for the Moroni is of late 

Eocene to middle Oligocene age.

LITTLE CLEAR CREEK DIAPIRIC FOLD

GEOLOGIC SETTING

Little Clear Creek (B-5) has cut a deep, narrow 

canyon into the crest of a major diapiric fold (fig. 16, 

8) that trends about N. 45° E. The fold can be traced 

from the center of sec. 26, T. 11 S., R. 4 E. to the 

northwest corner of sec. 5, T. 11 S., R. 5 E., where it 

passes into a large graben known as the Dairy Fork 

(A-5) graben (fig. 49).

Twist Gulch strata form the crest and part of both 

flanks of the fold. The flanks dip steeply away from 

the crest for much of the fold's exposed length. Thus, 

those Twist Gulch rocks that are part of the fold's 

northwest flank dip about 80° NW.; comparable dips, 

but to the southeast, mark the fold's southeast flank. 

Only a narrow segment of Twist Gulch strata crops 

out along the fold's northwest flank; much of that 

flank is concealed beneath beds of either the North 

Horn or Moroni Formations that dip northwestward 

at moderate angles, and that unconformably overlie 

the steeply dipping Twist Gulch strata. The wellexposed southeast flank of the fold includes units of 

the Twist Gulch and Cedar Mountain Formations 

and the Indianola Group. All these strata dip at high 

angles, commonly to the southeast, but locally some

beds are vertical or are overturned and so dip northwestward. These steeply inclined units are unconformably overlain by Price River and North Horn 

strata that dip about 35° SE.

Exposures are inadequate to determine whether 

any of the units involved thin toward the crest of the 

fold.

DISCUSSION

I interpret the geologic relations in Little Clear 

Creek, as in Dry Hollow, and Hjorth Canyon, to indicate three distinct episodes of diapiric deformation.

During the first episode an upward surge of the 

causative salt diapir bowed up the Twist Gulch, 

Cedar Mountain, and Indianola strata to form a 

mushroom-shaped fold. Collapse of that fold, presumably as a result of withdrawal of salt, and subsequent erosion left a surface of low relief on which the 

Price River and North Horn were deposited.

During the second episode a second upward surge 

of the causative diapir arched this Price River and 

North Horn sequence. Inadequate exposures hinder 

any clear interpretation of what followed. Perhaps 

the arched Price River and North Horn sequence was 

eroded to a surface of low relief on which Flagstaff 

sediments were deposited. In time, these Flagstaff 

strata were buried beneath younger beds, possibly 

Colton and Green River strata. Erosion, after Green 

River time, resulted in a moderately dissected surface onto which volcanic flows of the Moroni Formation were extruded.

At some time after volcanics of the Moroni were 

emplaced, the salt diapir surged upward for a third 

time and warped up the volcanic rocks. The beds 

deformed by the diapir during this third episode 

occupy the same site and have the same trend as 

those older beds deformed during the previous 

episodes, implying that once again the diapir moved 

up the same conduit it followed in the previous two 

episodes.

As volcanic rocks of the Moroni Formation (formed 

between late Eocene and middle Oligocene time) are 

involved in this last episode of diapirism, the diapiric

FIGURE 49 (facing page). Geology of Little Clear Creek area. Base 

modified from U.S. Geological Survey 1:100,000 Nephi (1981). 

Contour interval 250 m. Little Clear Creek and West Lake Fork 

follow the crest of the Little Clear Creek diapiric fold. At its 

north end, the fold passes into the Dairy Fork graben. These 

relations suggest that part of the causative salt diapir was removed, and the overlying beds then subsided into the resultant 

void or voids to form the graben. Arapien Shale as unit Ja is 

listed for completeness but is not shown, as such, on the map.
DIAPIRIC STRUCTURES 97

111°25'

' EXPLANATION

Alluvial-fan 

deposits

Alluvium

Holocene 

Landslide ^ Pleistocene 

deposits ^ Pliocene

QUATERNARY

Coalesced

alluvial-fan

deposits

Indianola Group

Cedar Mountain 

Formation

T(Ja)

Oligocene

Eocene

Paleocene

Upper 

Cretaceous

> TERTIARY

Lower 

Cretaceous

Middle 

Jurassic

CRETACEOUS

Arapien Shale Arapien Shale

Contact Approximately located or inferred

JURASSIC

Fault Bar and ball on downthrown block; barb shows downthrown block 

in cross section; dashed in cross section where reconstructed above 

eroded surface

Strike and dip of inclined beds

Strike and dip of vertical beds 

Strike and dip of overturned beds 

Dry hole
98 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

folds presumably developed at some time during or 

after middle Oligocene time.

Near Smiths Reservoir (where Side Canyon joins 

Lake Fork), the fold passes northeastward into a 

northeast-trending graben, the Dairy Fork graben of 

Merrill (1972, p. 79), that is collinear with the fold. 

Seemingly, the graben represents collapse of the 

crestal part of the Little Clear Creek fold as a result 

of salt dissolution (cross section B-B', fig. 49).

Union Oil Company drilled its well, No. G-24, along 

the crest of the fold in the NEV4 sec. 24, T. 11 S., R. 4 

E. (fig. 49). The well drilled into the Arapien Shale 

but did not pass through it.

FAIRVIEW DIAPIRIC(P) FOLD

The east fork of Sanpete Valley, essentially that 

sector of Sanpete Valley that extends from Ephraim 

(E-4) northeastward to and beyond Milburn (B-5), is 

flanked on the east by the imposing, westward-facing 

Wasatch monocline. I believe that the Wasatch monocline (E-5), much like the Valley Mountains monocline (G-2), was formed when salt was removed from 

a major salt diapir that lies at the foot of the monocline. Removal of the salt resulted in near-horizontal 

beds being let down to form the monocline (Witkind 

and Page, 1984).

Much evidence, in the form of upturned Cretaceous 

and Jurassic beds, and Arapien exposures, suggests 

that a major diapir, the Sanpete-Sevier Valley diapir, 

underlies the southern part of Sanpete Valley. Near 

Ephraim, the diapir appears to bifurcate, with one 

branch extending northward into the west fork of 

Sanpete Valley, and the other extending northeastward into the east fork of Sanpete Valley. The structural complexity along the east flank of the Gunnison 

Plateau near Wales Gap (D-4) supports the presence 

of the west branch of the diapir, for which I have 

retained the name Sanpete-Sevier Valley diapir. By 

contrast, mainly the downwarp of strata to form the 

north end of the Wasatch monocline suggests the 

presence of the east branch of the diapir, which I call 

the Fairview diapir(?) (fig. 16, 7). These downwarped 

strata dip westward at about 20°. At the\ north end of 

the Wasatch monocline, near the head\of the east 

fork of Sanpete Valley east of Indianola, the strata 

are flexed up and dip eastward as part of the east 

flank of the Little Clear Creek (B-5) diapiric fold. 

These upwarped strata mark the northernmost 

extent of the Wasatch monocline.

The south half of the Wasatch monocline, thus, 

may have been formed by the removal of salt from 

the Sanpete-Sevier Valley diapir, whereas the north

half may have been formed by the removal of salt 

from the Fairview diapir(?).

I propose that the Fairview diapiric(?) fold extends 

in a generally northeastward direction from Ephraim 

(E-4), through Mount Pleasant (D-5), Fairview fC-5), 

Oak Creek (C-5), and Milburn (B-5), to end near the 

head of the east fork of Sanpete Valley. The fold, thus, 

is about 52 km (32 mi) long, and, in detail, trends 

about N. 30° E. from Ephraim to Mount Pleasant, 

and then bends to trend almost due north from 

Mount Pleasant through Fairview and Milburn to its 

end east of Indianola.

GEOLOGIC SETTING

Much of the following discussion about the Fairview diapiric(?) fold is speculative; the available 

ground evidence is sparse and contradictory. Some 

evidence hints at the existence of a diapiric fold 

beneath the east fork of Sanpete Valley. Thus, for 

example, test wells and seismic reflection profiles 

indicate that near Mount Pleasant (D-5) an inordinately large mass of Arapien Shale underlies the 

surficial deposits that floor Sanpete Valley. Furthermore, the downwarp of the Cretaceous and Tertiary 

sedimentary strata that form the north end of the 

Wasatch monocline, essentially near and north of 

Milburn (B-5), seems most readily explained by dissolution of salt from a diapir the Fairview diapir 

concealed beneath the surficial deposits.

At the north end of the east fork of Sanpete Valley, 

coalesced alluvial fans partly bury westward-dipping, 

cuesta-like masses of Green River strata that have 

been much broken. Many of the smaller Green River 

masses are intensely brecciated, and locally appear 

as chaotically disrupted masses. A few of the larger 

masses, however, although greatly disrupted, still 

appear as entities. Runyon (1977b, p. 76) interpreted 

these disrupted masses to be part of a collapsed, 

dome-shaped diapir, which he called the "North San 

Pitch River Valley diapir."

Strata exposed west of the east fork of Sanpete 

Valley also dip westward at angles that range from 

about 15° to 20°.

Directly west of the north end of the east fork of 

Sanpete Valley, North Horn, Flagstaff, Colton, and 

Green River strata are warped to form a southplunging syncline best exposed east of Indianola 

(B-5) along the north side of Indian Hollow.

DISCUSSION

At the north end of the Wasatch monocline the 

Cretaceous and Tertiary beds flex down, and this
DIAPIRIC STRUCTURES 99

NORTH

FIGURE 50. Landslide and earthflow phenomena along Wasatch 

front. A, View eastward of earthflow (dashed outline), typical 

of those exposed along base of Wasatch monocline; about 6 km 

(4 mi) southwest of Ephraim. Detritus derived chiefly from the 

Colton Formation forms earthflow. The earthflow was emplaced at some time after the Wasatch monocline was formed. 

As salt was removed from the causative Sanpete-Sevier Valley 

salt diapir, which underlay Sanpete Valley, those sedimentary 

strata that overlay the diapir subsided into the resultant 

voids. The Wasatch monocline formed as a result of this

subsidence; probably the earthflow occurred shortly after in 

response to that downwarp. B, View northward near mouth of 

north valley wall of Manti Canyon. This exposure, about 0.8 

km (V2 mi) south of Temple Hill the large detachment block 

composed of Green River and Crazy Hollow strata on which 

the Mormon temple at Manti is constructed shows westwardinclined drag folds (directly beneath the colluvium) that probably stem from the valleyward movement of comparable slide 

blocks that have since been eroded.

downwarp, in my opinion, is the most telling bit of 

evidence supporting the existence of the Fairview 

diapiric(?) fold. Elsewhere, as in the Sixmile Canyon 

(F-4) area of the Wasatch Plateau, where the toe of 

the monocline has been breached, or in the Red Canyon area (E-2) of the Valley Mountains, where the 

Valley Mountains monocline has been breached, the 

complex structural relations exposed in the breached 

areas seem reasonably explained only by invoking 

the repeated growth and collapse of causative salt 

diapirs (Witkind and Page, 1984, p. 152-155). Those 

causative diapirs, now concealed beneath surficial 

deposits, were once concealed beneath near-horizontal beds. Dissolution of salt from the diapirs resulted 

in subsidence of the Arapien mudstones into the 

newly formed voids, thus removing support from the 

near-horizontal beds. Inevitably, these strata failed 

and flexed down to form the monoclines. In my view, 

then, the process that formed the Wasatch and Valley 

Mountains monoclines was not differential uplift but 

rather subsidence, stemming from dissolution of salt 

in a system of diapirs including the proposed Fairview diapir(?).

Runyon (1977b, p. 76), discussing his North San 

Pitch River Valley diapir, also attributed its formation 

to subsidence as a result of dissolution of salt. I agree 

with Runyon about the existence of a diapir in the 

east fork of Sanpete Valley, but disagree with his 

interpretation that the jumble of disrupted Green

River rocks at the north end of the east fork of Sanpete Valley marks the site of a dome-shaped collapsed 

diapir. I believe rather that these brecciated Green 

River masses are ancestral landslide blocks that slid 

valleyward as the Wasatch monocline developed.

The many large earthflows (fig. 50A), landslides, 

detachment blocks, and other mass-wasting deposits 

that mantle and flank the lower slopes of the 

Wasatch monocline probably stem from this downwarp. Most of these deposits consist of a chaotic jumble of fragmented rocks, derived chiefly from the 

breakup of the Colton Formation, which slid valleyward off the tilted beds of the Flagstaff Limestone. 

Locally, however, large unbroken detachment blocks 

slid westward and came to rest at or near the base of 

the monocline. Perhaps the best example is Temple 

Hill, in Manti (E-4), on which the town's striking 

Mormon temple is built. This block slid westward off 

the monocline, crossed steeply inclined Flagstaff and 

Colton strata (fig. 505), and came to rest on the valley floor 150 m (500 ft) west of the monocline (fig. 

51). The block, a crude oblong, trends west, and is 

about 1.4 km (0.9 mi) wide. It rises some 105 m (350 

ft) above the adjacent valley floor, and is composed 

almost wholly of limestone beds of the Green River. 

These beds of Green River are overlain, along the 

north face of the block, by conglomerate beds of the 

Crazy Hollow Formation that were obviously carried 

"piggyback" on the Green River.
100 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

FIGURE 51. Stereographic vertical aerial photographs of the Temple Hill area, Manti, Utah. Temple Hill, a detachment block composed 

of Green River and Crazy Hollow strata, slid valleyward (westward) off the Wasatch monocline. From 1877 to 1888, early Mormon 

pioneers quarried oolitic limestone from the Green River Formation and constructed the temple at Manti. Some of the quarries 

used as a source of building stone are shown on the photograph; others are farther north near Ephraim.

Still another detachment block, also composed of 

Green River and Crazy Hollow strata, is near the 

ancestral Willow Creek (G-3) area (Witkind, 1981). 

The presence of Crazy Hollow strata on these slide 

blocks implies that the downwarp responsible for the 

monocline and the accompanying sliding occurred 

during or after the late Oligocene.

Some ground evidence, however, seemingly contradicts my view that a diapiric fold is concealed 

beneath the east fork of Sanpete Valley So, Green 

River strata west of the east fork of Sanpete Valley 

dip westward (Witkind and Weiss, 1991). If, as I propose, dissolution of salt from a concealed diapir 

caused subsidence of overlying near-horizontal strata 

to form the westward-facing Wasatch monocline, one 

would expect that strata west of the diapir would dip 

eastward and so form an eastward-facing monocline: 

in essence, paired, facing monoclines should result 

from the partial failure of the causative diapir. Such 

is not the case in this specific locality, and the westward dip of those rocks west of the east fork of Sanpete Valley puzzles me. One possible explanation is

that these strata west of the east fork of Sanpete Valley were tilted up to a westward dip at some time 

after the monocline was formed. Some support for 

this view is given by the south-plunging syncline 

near Indian Hollow. As Green River strata occupy the 

center of the syncline, the implication is strong that 

the deformation responsible for the development of 

the syncline occurred at some time after Green River 

strata were flexed down to form the Wasatch monocline.

WEST HILLS DIAPIRIC(P) FOLD

West Hills (D-2), and Long Ridge (B-2) to the 

north, are low, narrow, north-trending ridges composed of sedimentary and volcanic rocks that form 

the west side of Juab Valley (C-2). I suspect that a 

major salt diapir underlies the West Hills (fig. 16, 5).

GEOLOGIC SETTING

Structurally the West Hills are an elongate upwarp 

that trends about N. 20° E. and is about 24 km (15 mi)
DIAPIRIC STRUCTURES 101

long by 5 km (3 mi) wide. The fold extends from near 

Mills Gap (D-2) on the south, to near Utah State 

Highway 132 on the north (fig. 16), where it abuts an 

erosional remnant of the Charleston-Nebo overthrust. 

The fold is composed of Cretaceous and Tertiary strata 

(North Horn), and Tertiary strata (Flagstaff, Colton, 

and Green River Formations) that are unconformably 

overlain by volcaniclastic beds of the Eocene and Oligocene Goldens Ranch Formation. The volcanic units 

of the Goldens Ranch have been warped and faulted 

along with the underlying sedimentary units. In general, both flanks dip away from the crest of the fold at 

about 20° to 30°.

In several places, elongate veins of banded calcite 

intrude the volcanic units. One of these veins, about 

850 m (2,800 ft) long and 8 m (25 ft) wide, trends 

about N. 75° E. through C sec. 16, T 13 S., R. 1 W. 

Other small calcite seams and veins, most of 

unknown length but ranging from 0.5to2.0m(2to6 

ft) in width, intrude volcaniclastic sediments that are 

exposed in small knolls in the EV2 sec. 26, T. 13 S., R. 

2 W.

DISCUSSION

Although the Arapien Shale is nowhere exposed in 

the West Hills, recent drilling by Placid Oil Company 

on the crest of the fold (Howard Well No. 1-A WXC, 

NWV4NWV4 sec. 5, T. 14 S., R. 1 W) (fig. 9) indicates 

that the fold has a core of Arapien Shale that contains many beds of both salt and anhydrite scattered 

through calcareous mudstone.

The fact that the volcanics of the Goldens Ranch 

are deformed along with the underlying sedimentary 

rocks of Cretaceous and Tertiary age suggests that 

the folding must have occurred at some time after 

the middle Oligocene, the youngest age assigned to 

the Goldens Ranch Formation (Witkind and Marvin, 

1989). As much salt is contained in the Arapien core 

of the fold, it seems reasonable to surmise that the 

folding may stem from movement of the salt.

The calcite veins that intrude the volcanic mantle 

would seem to support the view that the deformation 

is the result of movement of the Arapien core. 

Presumably some of the evaporites of the buried 

Arapien were dissolved and then reprecipitated at 

some time after the volcanics were extruded, consolidated, and warped. Such dissolution and reprecipitation would seem most likely during episodes of 

diapiric deformation.

VALLEY MOUNTAINS DIAPIRIC (?) FOLD

The Valley Mountains (G-2) are a low, northtrending, oval mass about 45 km (28 mi) long and

some 11 km (7 mi) wide (fig. 2), bounded on the west 

by Scipio (E-l) and Round Valleys (F-2) and on the 

east by Sevier Valley (G-2). Sevier River, flowing 

north through Sevier Valley, bends around the north 

end of the Valley Mountains and is then impounded 

behind Yuba Dam (E-2) to form the Sevier Bridge 

Reservoir (Yuba Lake). On the south, the Valley 

Mountains end in a small saddle formed near a 

southeastward bulge of the Pavant Range (H-l). 

Highway U.S. 50 follows the west flank of the Valley 

Mountains southward from Scipio to Salina (G-3). 

The Valley Mountains may be the site of a diapiric 

fold (fig. 16, 6).

GEOLOGIC SETTING

The Valley Mountains, composed chiefly of Cretaceous and Tertiary units, are an eastward-tilted fault 

block bounded on the west by a high-angle normal 

fault that trends north and dips steeply to the west. 

The crustal block west of the fault (greater Scipio 

Valley) is downthrown. The strata that form the crest 

of the mountains are nearly horizontal, and these are 

broken by many northward-trending high-angle normal faults. Comparable fault patterns are found in 

the Wasatch Plateau (Gilliland, 1951, p. 61). Locally, 

several of these faults in the Valley Mountains are 

paired to form grabens; one of the larger grabens so 

formed is an unusually straight north-trending 

depression expressed topographically for part of its 

length as Japanese Valley. Japanese Valley is about 

13 km (8 mi) long and 2 km (1V4 mi) wide. I believe, 

however, that the graben extends beyond the ends of 

Japanese Valley, possibly reaching from South Valley 

(G-2) northward almost to Red Canyon (E-2), a distance of about 19 km (12 mi).

As the nearly horizontal strata that form the crest 

of the Valley Mountains are traced eastward they 

gradually flex downward to form the eastward-facing 

Valley Mountains monocline. As in the Wasatch monocline, far to the east, beds of the Flagstaff Limestone form much of the monoclinal slope. Younger 

beds, chiefly Colton, Green River, and Crazy Hollow 

strata, have been almost completely removed from 

this slope, but are preserved along and near the 

slope's base where they appear as small eastwarddipping cuestas. Eastward-flowing consequent (but 

intermittent) streams have cut deep valleys that 

reach far back toward the crest of the mountains.

Along the northeast and east edges of the Valley 

Mountains, the monocline has been breached to 

expose a structurally complex sequence of Cretaceous 

and Tertiary beds. I describe these exposures elsewhere in this Professional Paper (p. 62-66), and
102 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

attribute the structural complexity to recurrent 

movement of the Sevier Bridge Reservoir diapir, and 

the monoclinal downwarp to dissolution of salt from 

that diapir.

DISCUSSION

Although mudstones of the Arapien Shale are 

nowhere exposed in the Valley Mountains, they have 

been found in the Anschutz Corporation's Monroe 

Fee No. 1 well (SEV4 SEV4 sec. 14, T. 20 S., R. 2 W.), 

and Placid Oil Corporation's WXC-USA 1-2 well 

(NWV4SWV4 sec. 24, T. 19 S., R. 2 W.) (fig. 9). The 

Placid well is along the west flank of the mountains, 

and the Monroe well is in Round Valley. Although 

both wells penetrated the Arapien Shale, neither well 

cut beds of salt.

Several factors hint that the mountains are a diapiric fold somewhat similar to other diapiric folds in 

the area. Thus, the elongate shape of the mountains, 

the linear, collapsed graben (Japanese Valley) that 

follows the mountain crest, and the presence of 

Arapien mudstones in the core all favor the concept 

that the Valley Mountains are, or once were, underlain by a salt diapir. The graben, in particular, suggests subsidence as a result of withdrawal of salt 

from a causative diapir. The many north-trending 

faults, so much like those that break the crest of the 

Wasatch Plateau, also favor dissolution of salt as an 

explanation for their origin.

Although the two test wells failed to penetrate salt, 

this in itself does not necessarily mean that salt does 

not, or did not, underlie the Valley Mountains. Both 

wells, along the west flank of the fold, are considerably west of the crest of the fold, and thus could have 

missed the causative salt core. Previously, I have 

suggested (p. 12 and fig. 5) that most of the salt 

diapirs are long, narrow ridges of salt. Trusheim 

(1960, fig. 4), studying the Zechstein salt of northern 

Germany, has referred to comparable diapirs as "salt 

walls." Wells drilled along the flanks of a diapiric fold 

could easily miss such thin salt ridges.

GRAVITY DATA

Gravity data are available for parts of the SanpeteSevier Valley area as a result of a Bouguer gravity 

survey completed between 1968 and 1974 by Brown 

(1975, fig. 5). Brown's data were subsequently reevaluated by Brown and Cook (1982), but this new 

appraisal included no new data.

The gravity data reveal the general distribution 

pattern of the diapiric folds (fig. 52). The trends of

most folds closely coincide with the gravity lows, but 

the trends of a few folds seemingly diverge somewhat 

from the determined gravity lows. Such divergence 

may stem from the low density contrast between the 

Arapien Shale and the valley fill; the contrast seemingly is just too small to be easily recognized. Brown 

and Cook (1982, p. 123) commented: "The expected 

density contrast between it [the alluvium] and the 

Arapien Formation is too small to be detailed in this 

study. Hence, alluvium will be included with the 

Arapien in quantitative interpretations."

The gravity map shows three elongate, faintly sinuous lows more or less coincident with the Sevier (G-3), 

Sanpete (E-4), and Juab valleys (C-2). Farthest south 

is a narrow, deep trough that trends about N. 30° E., 

and that coincides with that part of Sevier Valley 

between Richfield (1-1) and Gunnison (F-3). Near 

Gunnison, the trough bifurcates to form two narrow 

lows an eastern one that trends about N. 20° E. and 

that follows Sanpete Valley, and a western one that 

trends about N. 20° W. and that persists beneath 

Sevier Valley to underlie the Sevier Bridge Reservoir 

(E-2) sector. The third low, which follows Juab Valley, 

trends about N. 20° E.; the low's south end joins the 

northwest-trending low beneath the Sevier Bridge 

Reservoir.

All three gravity lows are remarkably alike 

narrow, deep, and faintly sinuous, almost straight. 

Locally, as in the Sevier (Salina (G-3)-Redmond (G-3) 

area) and Sanpete Valleys, intense gravity lows 

closely coincide with exposures of the Arapien Shale, 

strongly suggesting that at least in those areas the 

lows directly reflect the salt-rich diapiric cores. Elsewhere, however, the belts of Arapien mudstone, which 

I interpret to be the cores of the diapiric folds, are 

disturbingly distant from the gravity lows. For 

example, near Richfield (1-1) the gravity low follows 

the center of Sevier Valley, but the Arapien Shale 

exposures are some 10 km (6 mi) to the east, where

FIGURE 52 (facing page). Bouguer gravity anomaly map of part of 

central Utah on which are plotted the estimated traces of several 

major diapiric fold crests, which generally follow the trend of 

three major gravity lows. The Redmond diapiric fold follows the 

northern part of the low underlying Sevier Valley, between Richfield and Gunnison. The Sanpete-Sevier Valley diapiric fold follows the eastern lobe of the low extending northeast from 

Gunnison. The Sevier Bridge Reservoir diapiric fold follows part 

of the western low extending northwest beneath Sevier Bridge 

Reservoir. From data in Witkind and Marvin (1989), another 

diapiric fold as yet unrecognized may coincide with the branch of 

the low beneath Juab Valley. Fold crests dashed where inferred, 

queried where speculative. Gravity data from Brown, 1975. 

Contour interval 10 mGal; dashed where inferred; hachured to 

indicate area of closed low.
DIAPIRIC STRUCTURES 103

38°45

39°00' -

\ 

10 MILES

20 KILOMETERS 

_J
104 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

they form part of the eastern reaches of Sevier Valley. 

Brown and Cook (1982, p. 130) recognized this inconsistency and attributed it to an anticline formed in 

pre-Arapien strata and concealed beneath the 

Arapien. Seemingly, the Arapien over the buried anticline is relatively thin; away from the anticline the 

Arapien thickens and forms definitive gravity 

troughs.

A similar lack of agreement between a gravity low 

and the Arapien exposures is apparent in the Levan 

(C-3) area to the north. The gravity low follows the 

center of Juab Valley; the north-trending Arapien 

Shale outcrops, which mark the core of the Levan 

diapiric fold, are some 7.2 km (4.5 mi) to the east, 

where they form part of the west flank of the Gunnison Plateau. Possibly, another diapiric mass underlies Juab Valley (Witkind and Marvin, 1989).

Furthermore, two major postulated diapiric folds, 

the Fairview and the Valley Mountains folds, seemingly are not shown at all by the gravity data. This 

lack, however, may be due to the sparsity of gravity 

data in those localities.

DIAPIRIC DEFORMATION OF THE

EAST FLANK OF THE 

CHARLESTON-NEBO THRUST PLATE

Most of the diapiric folds discussed previously are 

distinctive and readily recognized. A causative salt 

diapir has warped up the surface rocks into nearvertical attitudes, and these upwarped rocks precisely reflect the trend of the underlying diapir. By 

contrast, in this section I discuss how several of 

these diapirs, and their overlying diapiric folds, 

overridden by and concealed beneath the CharlestonNebo thrust plate, subsequently deformed the overriding plate and its mantle of younger rocks.

I am convinced that both the Levan and the Thistle 

Creek diapirs have broken and warped the thrust 

plate (p. 69-75 and 83-86). Here, I summarize material that originally appeared in USGS Professional 

Paper 1170-F (Witkind, 1987), which described a 

series of geologic exposures along the eastern margin 

of the thrust plate that seemed most reasonably 

explained by diapiric uplift of the thrust plate and its 

sedimentary and volcanic cover.

In brief, Cretaceous and Tertiary sedimentary and 

volcanic strata unconformably overlie the sinuous erosional escarpment (p. 83 and fig. 4) formed along the 

eastern margin of the thrust plate. Wherever these 

strata abut and overlie the escarpment they invariably dip away from it, regardless of the escarpment's 

trend. For example, remnants along that part of the 

escarpment that trends northward dip generally east

or northeast; elsewhere, where the escarpment trends 

eastward the remnants dip south or southwest. 

Within short distances from the escarpment, however, 

the beds reverse dip and consistently dip toward the 

escarpment. A narrow to broad, ill-defined, sinuous 

syncline thus rims the escarpment. In my view, the 

tilted strata adjacent to the escarpment are the remnants of an upwarp formed when the east edge of the 

thrust plate was lifted up and arched long after the 

plate was emplaced, eroded, and buried beneath these 

younger Cretaceous and Tertiary strata. I attribute 

this uplift and warpage to upward movement of one or 

more diapiric folds concealed beneath the plate. I 

believe that the width of the marginal syncline at any 

one place is determined by the distance between the 

escarpment and one or another of several diapiric 

folds, described previously, that crop out east of the 

escarpment.

In my earlier report (Witkind, 1987), I described 

nine localities marked by these upturned Cretaceous 

and Tertiary beds. Eight of these nine localities are 

alike, in that tilted beds of mudstone and clastic rocks 

of the North Horn Formation unconformably overlie 

Paleozoic and Mesozoic beds that form the escarpment cut on the thrust plate. In the ninth locality, the 

tilted beds that overlie the escarpment are volcanic 

rocks of the Moroni Formation. Of the nine localities 

marked by tilted strata, three Salt Creek (fig. 54), 

Taylor Fork (fig. 56), and Red Lake (fig. 57) are 

characterized by strata that dip eastward. In another 

three localities Black Canyon (fig. 55), Payson Canyon (fig. 58), and Thistle Creek (fig. 44) the strata 

dip southeastward; and in two localities Bennie 

Creek (fig. 58), and Loafer Mountain the strata dip 

southwestward. In Santaquin Canyon (fig. 59), the 

North Horn strata dip northward. In all localities, no 

matter what the direction of dip, the strike of the 

overlying younger strata parallels the escarpment. 

This parallelism, coupled with these divergent directions of dip, implies some structural relationship 

between the thrust plate and its mantle of younger 

Cretaceous and Tertiary rocks.

For brevity, I omit descriptions of these localities in 

the present report, but do include a geologic map and 

cross section for eight of these localities. Photographic overviews of various of these localities are 

given in figure 53, and figure 3 shows the locations of 

all nine.

IMPLICATIONS OF THE TILTED STRATA

Seemingly, four alternative interpretations reasonably explain the deformation:
DIAPIRIC DEFORMATION OF THE EAST FLANK OF THE CHARLESTON-NEBO THRUST PLATE 105

1. The tilt of beds in the North Horn Formation is 

the result of drag along one or more high-angle normal faults that separate the North Horn from the 

escarpment.

2. Movement along the Wasatch fault zone has 

raised and tilted the Charleston-Nebo thrust plate 

eastward, resulting in eastward tilting of the overlying mantle of North Horn and younger rocks.

3. Uneven compaction, at time of deposition, of 

unconsolidated North Horn and younger sediments 

that were deposited across the eroded thrust plate 

resulted in the development of a pseudo-arch that 

reflected the buried plate. Erosion of the arch left 

tilted remnants of North Horn and younger beds.

4. One or more salt-generated structures 

diapiric folds developed beneath the thrust plate 

and arched parts of the plate and its overlying mantle of younger rocks.

DRAG ALONG NORMAL FAULT OR FAULTS

I could find no evidence of normal faults separating 

the North Horn from the escarpment. Possibly such 

faults do exist, but if so they are concealed beneath 

debris and foliage. It seems unlikely, however, that a 

single unbroken fault extends along the length of the 

entire escarpment; such a fault would be marked by 

an extremely complex and sinuous trace having several right-angle bends.

MOVEMENT ALONG THE WASATCH FAULT ZONE

Clearly all sorts of attitudes are possible along a 

large, complex fault zone. Still, if the thrust plate 

was raised and tilted eastward as a result of movement along the Wasatch fault zone, all North Horn 

strata draped across the plate should dip eastward. 

In fact, some North Horn beds that are along the 

west side of the southern Wasatch Range (near Santaquin), but east of the Wasatch fault zone, dip westward (fig. 59). Moreover, although the North Horn 

along the east flank of the escarpment does dip eastward, comparable units dip northward near the head 

of Santaquin Canyon, and southward in the Payson 

Canyon and Bennie Creek areas.

UNEVEN COMPACTION OF UNCONSOLIDATED NORTH HORN 

FORMATION AND YOUNGER SEDIMENTS

Uneven compaction of unconsolidated sediments 

deposited across the exposed, sloping, and eroded 

escarpment would result in beds of sedimentary 

rocks that dip away from the buried plate. As 

younger sediments were deposited on these rocks and

then unevenly compacted, the new units would have 

still lower dips. The end result would be a stack of 

sedimentary units with each younger unit marked by 

somewhat lower dips. This pattern is not apparent 

in the exposures discussed. The impression created 

is that all units in the sedimentary stack are parallel 

and were tilted concurrently.

UPLIFT AS A RESULT OF SALT DIAPIRISM

One or more diapiric folds, concealed beneath the 

thrust plate, raised and warped parts of the plate, 

and in so doing arched the overlying North Horn and 

younger strata. I believe that the Thistle Creek diapiric(?) fold deformed the northern sector of the erosional escarpment cut across the plate, even as the 

Footes Canyon diapiric(?) fold (the middle fold of the 

three formed when the Levan fold trifurcated) 

deformed the southern sector.

Although all four alternatives seem reasonable, it 

seems to me that only two differential compaction 

of unconsolidated sediments, and salt diapirism are 

acceptable alternatives. Inadequate exposures preclude complete acceptance of either. I believe, however, that salt diapirism is the best explanation, and 

point to the deformation near Thistle as an example 

of such warpage of younger beds by uplift of the 

thrust plate.

DISCUSSION

Almost all the structural complexity in the SanpeteSevier Valley area is most reasonably and simply 

explained as the result of the repeated growth and 

collapse of salt-generated diapiric folds. These recurrent episodes of salt diapirism, which began during 

the Mesozoic and have persisted into the Quaternary, 

have stamped a unique geologic pattern on this sector 

of central Utah. It seems unreaonable to assume that 

these diapiric folds are restricted only to that part of 

the area that lies in front of the thrust plate. The folds 

must be impressed on that part of the area overlain by 

the thrust plate; if so, the folds must have deformed 

the thrust plate, too. Still, some relationship must 

exist between the thickness of the "mother bed" of salt, 

the amount of overburden, and the degree of diapirism. Where the overburden is thick, as in those localities overlain by the thrust plate, possibly the 

diapirism is restricted and diapiric features are few in 

number; where the overburden is thin, the diapirism 

is more active and as a result its features are 

widespread.
106 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

WEST

SOUTHWEST NORTHEAST

EAST Santaquin 

Canyon

NORTHWEST NORTHEAST

Tf
DEPOSITIONAL THINNING 107

FIGURE 53 (facing page). Photographic overviews of localities adjacent to the erosional escarpment bordering the CharlestonNebo thrust plate. In all localities, clastic beds of the North 

Horn Formation unconformably overlie the escarpment formed 

on the Charleston-Nebo thrust plate. Dashed lines delineate angular unconformity between the North Horn and underlying 

units. The North Horn invariably dips away from the escarpment. A, View northward in Salt Creek Canyon showing eastward-dipping sandstone beds of the North Horn Formation 

(TKn) unconformably overlying overturned beds of the Navajo 

Sandstone (Jn) and Twin Creek Limestone (Jtc). The Navajo 

and Twin Creek dip northwestward (away from viewer) and are 

part of the escarpment. The eastward dip of the North Horn 

strata lessens and is almost horizontal near the right (east) 

edge of the photograph. Farther to the east, beyond the right 

edge of the photograph, the North Horn reverses dip and is inclined westward toward the escarpment. See figure 54 for geologic map of this locality. B, View northward along the east 

flank of Dry Mountain in Taylor Fork near the head of Santaquin Canyon. Clastic beds of the North Horn Formation 

(TKn), which strike northward and dip eastward, unconformably 

overlie beds of the Great Blue Limestone (Mgb), which is part of 

the erosional escarpment formed on the Charleston-Nebo thrust 

plate. Volcanic units of the Moroni Formation (Tm) unconformably overlie the North Horn Formation, and seemingly are deformed along with it. See figure 56 for geologic map of this 

locality. C, View southward along east flank of Dry Mountain, 

near Red Lake, showing eastward-tilted clastic beds of the 

North Horn Formation (TKn) unconformably overlying eastward-tilted undivided Mississippian strata (Mu) that are part of 

the escarpment on the Charleston-Nebo thrust plate. See figure 

57 for geologic map of this locality. D, View eastward at exposures near head of Payson Canyon. In this locality, the escarpment bends sharply to the northeast along a reentrant cut into 

the thrust plate. As a result, the clastic beds of the North Horn 

Formation (TKn), which unconformably overlie the escarpment, 

strike northeast and dip southeast. The escarpment is formed 

on the Oquirrh Group (PPo), which also strikes northeast and 

dips southeast. See figure 58 for geologic map of this locality. E, 

View looking northwestward at a small hogback, near the head 

of Bennie Creek, along south flank of Loafer Mountain. The 

hogback is formed by southward-dipping clastic beds of the 

North Horn Formation (TKn) that are capped by a thin lightgray bed of the Flagstaff Limestone (Tf). The North Horn rests 

unconformably on the Oquirrh Group (PPo), which strikes 

northwestward and dips northeastward, and forms part of the 

east-trending escarpment. See figure 58 for geologic map of this 

locality. F, View northward along west valley wall of Thistle 

Creek. The escarpment formed on the Charleston-Nebo thrust 

plate is exposed in a small gap eroded in a mantle of folded 

younger Cretaceous and Tertiary units. The escarpment is represented by steep eastward-dipping beds of the Navajo Sandstone (Jn) and the Twin Creek Limestone (Jtc). The folded 

Cretaceous-Tertiary mantle is represented by sedimentary beds 

of the North Horn Formation (TKn) and the Flagstaff Limestone 

(Tf), and by volcanic units of the Moroni Formation (Tm). Only 

remnants of the sedimentary cover are preserved along the base 

of the west valley wall of Thistle Creek, but the cover is extensively exposed on the uplands both east and west of the creek. 

In general, the beds that form the cover west of the exposed 

escarpment dip westward; those that form the cover east of the 

escarpment dip eastward. See figure 44 for geologic map of this 

locality.

I propose that the Footes Canyon diapiric(?) fold 

(fig. 16, 13) and the Thistle Creek diapiric fold (fig. 16, 

11) raised parts of the thrust plate after the plate was 

emplaced, eroded, and then covered by North Horn 

and younger strata. As a result, the overlying North 

Horn and younger beds were more or less uniformly 

arched.

I do not know how far to the north the Footes Canyon fold continues beneath the plate. Possibly the 

concealed fold extends as far north as Santaquin 

Canyon, as suggested by isolated outcrops of tilted 

North Horn beds exposed on both sides of the thrust 

plate. Along the east flank of the southern Wasatch 

Range, in the Taylor Fork and Red Lake areas, the 

North Horn and younger beds dip eastward (fig. 59). 

Directly to the west, on the opposite side of the 

mountains, patches of the North Horn Formation 

overlain by small eroded remnants of the Flagstaff 

Limestone dip westward. These opposing dips developed in North Horn and younger strata exposed on 

opposite sides of the mountains suggest that an anticlinal fold was formed in these younger beds above 

an arched thrust plate, much as in the Thistle area. 

And, as in the Thistle area, the deformation of the 

rocks within the thrust plate obscures the simple, 

later upwarping.

The attitudes assumed by the bowed-up North 

Horn and younger beds were determined by the configuration of that part of the erosional escarpment on 

which they rested. This would explain the general 

eastward tilt of those North Horn and younger beds 

that rest on that part of the escarpment that trends 

north, the northward dip of North Horn strata in 

Santaquin Canyon where these beds overlie the 

north flank of an eastward-directed protuberance of 

the escarpment, and the southward and southwestward dips of similar strata exposed along the south 

flank of Loafer Mountain, where North Horn and 

younger beds overlie the sinuous south flank of the 

east-trending escarpment.

DEPOSITIONAL THINNING

Sequences of sedimentary units thin and locally 

pinch out near the crests of the diapiric folds. Some 

units wedge out by onlap against the flanks of the 

fold; other units thin but continue across the crests of 

the folds. Both the pinchouts and the thinning presumably result from impeded deposition. This depositional thinning appears to influence sequences of 

units rather than just one discrete unit in a
108 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

111°44'

£:8S111

T 12 S

39°4E'

R2 E

2 KILOMETERS

J

1 MILE

FIGURE 54 (above and facing page). Geology of Salt Creek area. 

Geology slightly modified from Witkind (1987, fig. 6). Base 

modified from U.S. Geological Survey 1:24,000 Nebo Basin 

(1979). Contour interval 200 ft. Overturned Paleozoic and 

Mesozoic strata that strike northeast and dip northwest mark 

the erosional escarpment formed on the Charleston-Nebo

thrust plate. These beds are mantled by beds of the North 

Horn (TKn) and Moroni (Tm) Formations. The North Horn 

strata that overlie the escarpment dip eastward; a short distance away from the escarpment the strata reverse dip and 

are inclined toward the escarpment. See figure 53A for photographic overview of this locality.

sequence. This thinning affects beds that range in 

age, at the least, from Middle(?) Jurassic to early 

Tertiary.

This widespread pattern of depositional thinning 

involving sequences of sedimentary units near the 

crests of folds provides some of the most compelling 

evidence that diapirism has played a significant role 

in the structural evolution of this part of central

Utah. If but one unit thinned as a result of onlap 

onto a static topographic high, younger sediments 

would, in time, bury the ancestral high. This is not 

the case in central Utah. All stratigraphic units near 

the crests of the folds thin, implying that a dynamic 

ancestral high the diapiric fold continued to move 

upward slowly even as the younger sediments were 

being deposited.
DEPOSITIONAL THINNING 109

T(Ja)

Arapien Shale

Park City Formation

Diamond Creek Sandstone 

and Kirkman Limestone

Oquirrh Group

Holocene

I Oligocene 

\ and Eocene

EXPLANATION

QUATERNARY

TERTIARY

Contact Approximately located or inferred

- - Intrusive sedimentary contact Oblongs

on intrusive sedimentary unit 

J ' ' ' L- Edge of erosional escarpment Hachures point

in general direction of inclination

30

i" Paleocene and

> Upper Cretaceous V CRETACEOUS

Strike and dip of inclined beds 

Strike and dip of overturned beds

1 Middle 

\ Jurassic

I Lower 

\ Jurassic

I Upper and 

J Lower Trias sic

Lower 

Triassic

JURASSIC

TRIASSIC

PERMIAN

> PENNSYLVANIAN

39°46'

Unpublished

reconnaissance

mapping by

J.J. Witkind

Black 

(1965)

SOURCES OF GEOLOGIC DATA

Good examples of this depositional thinning are 

widespread; several are discussed following.

SANPETE-SEVIER VALLEY DIAPIRIC FOLD

In Wales Gap (D-4) (along the east flank of the 

Gunnison Plateau), near the crest of the SanpeteSevier Valley diapiric fold, the Indianola Group, 

which is thousands of meters thick elsewhere, is but 

35 m (115 ft) thick. Similarly, the Cedar Mountain 

Formation at Wales Gap is only 18 m (60 ft) thick 

but is almost 430 m (1,400 ft) thick away from the 

diapiric core of the fold.

The Sixmile Canyon (F-4) area (along the west 

margin of the Wasatch Plateau) is just east of the 

crest of the Sanpete-Sevier Valley diapiric fold. The 

Price River, North Horn, and Flagstaff Formations 

are all extremely thin near the mouth of Sixmile 

Canyon but thicken markedly eastward away from 

the diapiric crest. The Flagstaff Limestone, for example, is about 30 m (100 ft) thick at the canyon mouth 

but at least 365 m (1,200 ft) thick some 10 km (6 mi) 

to the east along the top of the Wasatch Plateau.

In various localities in Sanpete Valley, such as near 

ancestral Willow Creek (G-3), and in place after 

place along the west flank of the Gunnison Plateau, 

uppermost Green River strata unconformably overlie 

the Arapien Shale (Witkind, Weiss, and Brown, 

1987). These localities are along the flanks of the diapiric folds, and I interpret the stratigraphic relations 

to mean that units below the Green River, such as 

the North Horn, Flagstaff, and Colton, have pinched 

out against the flanks of the rising fold. The fact that 

uppermost Green River strata, unbroken but anomalously thin, mantle the fold's crest, implies that lower 

Green River and older sediments pinched out against 

the fold's flanks. Seemingly, during late Green River 

time deposition was rapid enough to surmount the 

rising mass of Arapien.

SEVIER BRIDGE RESERVOIR DIAPIRIC FOLD

Along the northeast flank of the Valley Mountains 

(G-2), the North Horn, Flagstaff, Colton, and Green 

River Formations are anomalously thin where they 

form part of the southwest flank of the Sevier Bridge
110 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

42' 41' 40' 111°39'

39°52' 

39°50

Estimated.-trace'-of syricltha) 'f 

Jjxte :formed .to. NOrth.;Hoirr>: arid,/ .. 'i^ 

'younger .. .........................y strata-.<q.ueried^ wherjp^7' %Q -t'4

T 11 S

R2 E

2 KILOMETERS

I

1 MILE

FEET

EXPLANATION

6000

I

Oligocene 

and Eocene

Upper 

Cretaceous

39°50'

SOURCE OF GEOLOGIC DATA

Oquirrh 

Group

TERTIARY

CRETACEOUS

PERMIAN AND 

PENNSYLVANIAN

20

Contact Approximately located 

or inferred; queried in cross section where speculative

Edge of erosional escarpment 

Hachures point in general direction of inclination

Strike and dip of inclined beds

Strike and dip of vertical beds
DEPOSITIONAL THINNING 111

Reservoir diapiric fold. So, for example, the North 

Horn is about 38 m (125 ft) thick, the Flagstaff about 

11 m (37 ft), the Colton about 61 m (200 ft), and the 

Green River about 53 m (175 ft) thick. As these units 

are traced perpendicularly away from the crest of the 

fold, they thicken rapidly; within about a kilometer 

(0.6 mi) the North Horn has increased in thickness to 

about 91 m (300 ft), the Flagstaff to about 49 m (160 

ft), the Colton to 82 m (270 ft), and the Green River 

to about 95 m (310 ft).

The same pattern of depositional thinning is 

apparent in Red Canyon (E-2) (in the Valley Mountains) along the west flank of the Sevier Bridge Reservoir fold. The North Horn Formation, for example, 

is about 15 m (50 ft) thick near the canyon mouth, 

but more than 180 m (600 ft) thick 1.5 km (1 mi) to 

the west near the head of Red Canyon.

Both along the northeast flank of the Valley Mountains and in Red Canyon, as far as I can determine, 

only the younger, upper parts of the formations are 

represented, implying that the older, lower parts of 

the formations pinched out against the flanks of the 

diapiric folds.

POLE CREEK DIAPIRIC FOLD

Units that are part of the southeast flank of the 

Pole Creek diapiric fold crop out in the Middle Fork 

Pole Creek (B-4) (fig. 39). These units, which include 

the Middle Jurassic Twist Gulch Formation and the 

Lower Cretaceous Cedar Mountain Formation, are 

vertical and anomalously thin. The Twist Gulch is 

only about 60 m (200 ft) thick; elsewhere in the 

Sanpete-Sevier Valley area, the Twist Gulch is about 

915 m (3,000 ft) thick. The Cedar Mountain, east of 

and conformably overlying the steeply dipping Twist

FIGURE 55 (facing page). Geology of an area along and near Black 

Canyon. Geology slightly modified from Witkind (1987, fig. 7). 

Base modified from U.S. Geological Survey 1:24,000 Nebo Basin 

(1979). Contour interval 200 ft. Clastic beds of the North Horn 

Formation (TKn), which are juxtaposed against the escarpment 

formed on the thrust plate, strike northeast and dip southeast, 

and unconformably overlie units of the Oquirrh Group (PPo) of 

similar strike and dip. These North Horn units reverse dip west 

of Nebo Creek, reflecting the west flank of a diapiric fold (possibly a segment of the Thistle Creek fold (fig. 16, 11), part of 

which is exposed in sections 24 and 25. Cross section is not deep 

enough to include the Charleston-Nebo thrust fault, which is the 

sole of the thrust plate.

Gulch strata, is only about 245 m (800 ft) thick; elsewhere, the Cedar Mountain is as much as 430 m 

(1,400 ft) thick.

THISTLE CREEK DIAPIRIC FOLD

In the Thistle area, various of the Cretaceous and 

Tertiary units thin westward toward the crest of the 

Thistle Creek diapiric fold. This is perhaps best 

shown in Young's (1976) figure 5, which shows that 

all units from the North Horn to the Green River 

Formation thin westward toward Thistle.

DISCUSSION

Gundersen and Gilliland (1967) recognized this pattern of depositional thinning in various localities 

throughout the Sanpete-Sevier Valley area. As the 

most striking examples are near their Sanpete-Sevier 

Valley anticline (my Sanpete-Sevier Valley diapiric 

fold), their article concentrated on that part of the 

area. In a series of isopach maps, they demonstrated 

that three formations the Price River and North 

Horn Formations, and the Flagstaff Limestone thin 

anomalously toward the crest of the Sanpete-Sevier 

Valley fold; they commented (1967, p. 688): "* * * each 

formation thins markedly towards the anticline * * *." 

Their isopach maps for the Price River (1967, fig. 2), 

North Horn (1967, fig. 3), and Flagstaff Limestone 

(1967, fig. 4) show that, on both flanks of the fold, the 

formations thin toward the fold crest. The Flagstaff 

Limestone, for example, thins westward from about 

460 m (1,500 ft) along the top of the Wasatch Plateau 

to about 75 m (250 ft) near Sterling (F-4), which is 

along the east flank of the Sanpete-Sevier Valley diapiric fold. Gundersen and Gilliland's isopach map of 

the North Horn Formation demonstrates a similar 

pattern of thinning. The North Horn, about 460 m 

(1,500 ft) thick along the top of the Wasatch Plateau, 

thins westward to only about 75 m (250 ft) near 

Manti (E-4), along the east flank of the SanpeteSevier Valley fold.

Farther west, in and near the Valley Mountains 

(G-2), Gundersen and Gilliland's isopach map (1967, 

fig. 3) shows the North Horn to be about 610 m 

(2,000 ft) thick near Scipio Lake (F-2) (west of the 

Valley Mountains), but to thin eastward to about 

230 m (750 ft) near Redmond (G-3), which is along
112

39°5G

SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

43' 111°42'

39°53

T10S

T11 S

R2E

2 KILOMETERS

J

1 MILE
DEPOSITIONAL THINNING 113

Colluvium Landslide deposits

Upper Cambrian rocks, undivided

Middle Cambrian rocks, undivided

Holocene

Oligocene 

and Eocene

Paleocene 

Upper Cretaceous

EXPLANATION

[ QUATERNARY

TERTIARY

CRETACEOUS

PERMIAN

PENNSYLVANIA

25

Contact Approximately located or inferred

Edge of erosional escarpment Hachures 

point in general direction of inclination

Fault Approximately located; bar and ball

on downthrown block 

Strike and dip of inclined beds

Horizontal beds

39°5B'

Upper 

Mississippian

Lower 

Mississippian

Upper Devonian

t MISSISSIPPIAN

39°53'

Unpublished

reconnaissance

mapping by

I.J. Witkind

SOURCES OF GEOLOGIC DATA

DEVONIAN

Middle Cambrian Tintic Quartzite

Late Proterozoic 

Big Cottonwood Formation

7000-

FIGURE 56 (above and facing page). Geology of Taylor Fork area 

near head of Santaquin Canyon. Geology slightly modified 

from Witkind (1987, fig. 8). Base modified from U.S. Geological Survey 1:24,000 Payson Lakes (1979). Contour interval 

200 ft. In Taylor Fork, the escarpment formed on the Charleston-Nebo thrust plate trends north, and the overlying North 

Horn Formation (TKn) thus trends northward and dips east-

-7000

ward (see fig. 53B for photographic overview of these relations). As these beds of the North Horn are traced 

southeastward into Santaquin Canyon, they gradually assume 

an eastward strike and a northward dip reflecting an eastward 

bulge of the escarpment. Cross section is not deep enough to 

include the Charleston-Nebo thrust fault, which is the sole of 

the thrust plate.

the flank of their Redmond Hills anticline (my Redmond diapiric fold).

Willis (1986), working in the Salina Canyon area, 

astride the south end of the Sanpete-Sevier Valley 

diapiric fold, noted that North Horn and Flagstaff 

strata thin and locally pinch out near the crest of a 

north-trending "paleo-high," essentially the SanpeteSevier Valley "anticline" (Willis, 1986, p. 9). Willis 

indicated that Colton and Green River strata also 

thin toward the axis of the paleo-high.

Gundersen and Gilliland (1967, p. 686) suggested 

that this anomalous thinning stemmed from the 

Sanpete-Sevier Valley and Redmond anticlines being 

topographically positive elements through much of 

Late Cretaceous and early Tertiary time. They attributed the development of the Sanpete-Sevier Valley 

anticline to: "* * * compression during the early Laramide orogeny."

I disagree somewhat with Gundersen and Gilliland's interpretation. I suggest instead that the
114 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

111"41'

39°55

T10S

1 MILE
DEPOSITIONAL THINNING 115

EXPLANATION

Holocene

Oligoccne 

and Eocene

_V Paleocene 

y Upper Cretaceous

QUATERNARY

TERTIARY

CRETACEOUS

> PERMIAN

\ PENNSYLVANIAN

 Contact Approximately located or inferred; 

queried in cross section where speculative

 * Fault Approximately located; bar and ball 

on downthrown block

 Fault Indeterminate type; approximately

located 

Edge of erosional escarpment Hachures

point in general direction of

inclination 

Strike and dip of inclined beds

Horizontal beds

Upper 

Mississippian

I Lower 

J Mississippian

MISSISSIPPIAN

111044- 

39°58'| 

Middle Cambrian 

Tintic Quartzite

39°55'

Unpublished 

Metter I reconnaissance 

(1955) \ mapping by

I.J. Witkind

SOURCES OF GEOLOGIC DATA

A

FEET 

10,000-]

9000-

8000-

7000-

DRY MOUNTAIN 

Md

.tff&y.'. Vr-". ..-;

Erosional escarpment

-7000

FIGURE 57 (above and facing page). Geology of an area near Red 

Lake. Geology slightly modified from Witkind (1987, fig. 9). 

Base modified from U.S. Geological Survey 1:24,000 Payson 

Lakes (1979). Contour interval 200 ft. Clastic beds of the North 

Horn Formation (TKn) strike northward and dip eastward, and 

unconformably overlie a series of Mississippian strata that also

strike northward and dip eastward. These Mississippian strata 

are part of the escarpment formed on the Charleston-Nebo 

thrust plate. Cross section is not deep enough to include the 

Charleston-Nebo thrust fault, which is the sole of the thrust 

plate. See figure 53C for general photographic overview of this 

locality.

depositional thinning so evident in the SanpeteSevier Valley area is due to slowly rising, dynamic, 

salt-cored diapiric folds that probably began rising in 

Middle Jurassic time and continued to rise slowly 

throughout the Cretaceous and into the middle Tertiary. Seemingly, Gundersen and Gilliland viewed

their Sanpete-Sevier Valley anticline as a dynamic 

feature they demonstrated depositional thinning for 

at least three units. The conclusion seems inescapable depositional thinning is reasonably explained 

only by invoking a dynamic, rising body. As noted 

above, sediments deposited against the flanks of a
116 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

 T10S

39°56 R2E R 3 E

I , I , L -r i i i

2 KILOMETERS

J

1 MILE

A'

FEET

111°41' 

39°5fl'i 

7000 -7000

Metter (1955)

Unpublished

reconnaissance

mapping by

I.J. Witkind

39 "56' 1 

SOURCES OF GEOLOGIC DATA

FIGURE 58 (above and facing page). Geology of an area near 

head of Payson Canyon and Bennie Creek. Geology slightly 

modified from Witkind (1987, fig. 10). Base modified from U.S. 

Geological Survey 1:24,000 Payson Lakes (1979). This area 

encompasses the north edge of the broad, eastward-facing Santaquin embayment. As a result, the escarpment formed on the

Charleston-Nebo thrust block trends eastward, and the overlying North Horn Formation dips southward. Cross section is not 

deep enough to include the Charleston-Nebo thrust fault, which 

is the sole of the thrust plate. See figure 53D for a photographic 

overview of the exposure at the head of Payson Canyon, and 

figure 53E for an overview of the Bennie Creek exposure.
DIAPIRIC PROCESSES 117

Gardison Limestone

EXPLANATION

Holocene

Oligocene 

and Eocene

Eocene

Paleocene

Upper 

Cretaceous

I Upper

J Mississippian

I Lower

J Mississippian

QUATERNARY

TERTIARY

CRETACEOUS

PERMIAN AND 

PENNSYLVANIAN

MISSISSIPPIAN

Middle Cambrian 

rocks, undivided

Contact Approximately located or inferred

Fault Indeterminate type; approximately

located 

Edge of erosional escarpment Hachures

point in general direction of

inclination 

Strike and dip of inclined beds

static "anticline" would eventually bury that anticline. Younger strata, unchanged in thickness, would 

then pass over the buried anticline and show no pattern of depositional thinning.

This anomalous thinning of the sedimentary units, 

although extremely localized, being confined to and 

near the crests of the diapiric folds, is found throughout the area. I have recognized it in the Valley 

Mountains (G-2) near the west end of the study 

area, throughout the center of the area, and to the 

east near Thistle (A-5). I interpret this widespread 

(but localized) depositional thinning to be evidence of 

the slow, continuous upwelling of salt in discrete diapiric folds. Seemingly, the rate of upwelling was 

comparable to the rate of deposition; the folds kept 

coming up just about as fast as the sediments kept 

trying to bury them. In those places where the sedimentary beds wedge out against the flanks of the 

fold, the fold's growth rate must have slightly 

exceeded the depositional rate of the sediments. 

Where thinned sediments overlie the crest of the fold

the depositional rate must have exceeded the fold's 

growth rate.

Sannemann (1968, p. 357), discussing the saltstock families of northwestern Germany, suggested 

that salt, as it forms a salt stock (salt diapir), moves 

about 0.3 mm per year. Such movement would be difficult to detect, but would be rapid enough to form a 

growing barrier that would impede the comparably 

slow deposition of sediments. The result would be 

wedgeout and thinning of sedimentary units along 

the flanks of the growing fold.

It seems reasonable to conclude that as the folds 

grew they impeded sedimentary deposition throughout much of the Middle and Late Jurassic, Early and 

Late Cretaceous, and early Tertiary. Incomplete 

exposures prevent a definitive statement as to which 

units show this depositional thinning, but probably 

they include, at the very least, the sequence from the 

Twist Gulch Formation of Middle Jurassic age up to 

and including the Green River Formation of Eocene 

age.

Two factors seem very significant: (1) Sequences 

of stratigraphic units thin near the crest of a diapiric 

fold, and (2) invariably, where criteria are adequate 

to permit determination, as in the Red Rocks area (p. 

41), the beds that overlie the crest of the fold are the 

younger and uppermost parts of the formations 

involved; the older and lower beds of the formations 

pinch out against the flanks of the fold.

DIAPIRIC PROCESSES

GROWTH AND COLLAPSE OF DIAPIRIC FOLDS

In place after place throughout central Utah, the 

structural complexity seems most reasonably 

explained by the repeated growth and collapse of diapiric folds.

GROWTH OF DIAPIRIC FOLDS

The salt within the Arapien Shale has probably 

been moving since shortly after it was deposited. Some 

of this movement has been a slow upwelling that has 

resulted in the development of ancestral, linear to 

faintly sinuous topographic highs paleo-highs that 

impeded sedimentary deposition. At times, however, 

the salt, in the form of a linear, narrow salt diapir, 

seemingly has surged upward rapidly (in a geologic 

sense), and forcefully. These recurrent upward surges 

of the causative salt diapir have forced the overlying 

Arapien mudstone repeatedly to bow up and fold back
118 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

39°55' v

T10S

R 1 E

1

2 MILES

4 KILOMETERS

J

Foutz 

(1960)

Metter 

(1955)

SOURCES OF GEOLOGIC DATA

(Modified somewhat on basis of

unpublished reconnaissance mapping

by I.J. Witkind)

METERS

DRY 7 

MOUNTAIN -S 

(2

1000-

Tm

A'

METERS

-3000

-2500

-2000

-1500

-1000

Earthflow 

deposits

Deposits of Lake Bonneville cycle

Coalesced alluvial-fan deposits

Laguna Springs 

Volcanic Group

Flagstaff Limestone

Mass-wasting 

deposits

EXPLANATION

f- Holocene

Pleistocene 

Pliocene(?)

Ar

TUa) ;

__ 7 __ : 

apien Shale

Oligocene 

and Eocene

- Paleocene

Upper 

Cretaceous 

Middle 

Jurassic

QUATERNARY

TERTIARY

CRETACEOUS 

JURASSIC

25

Contact Approximately located or inferred; in cross section, dashed where 

inferred, queried where speculative

Edge of erosional escarpment 

Hachures point in general direction of 

inclination

Fault Approximately located; bar and 

ball on downthrown block; dotted 

where concealed; hachures indicate 

modem fault scarp; barb shows 

downthrown block in cross section; 

dashed in cross section where 

reconstructed above eroded surface

Strike and dip of inclined beds

Paleozoic rocks, undivided
DIAPIRIC PROCESSES 119

the overlying sedimentary units into mushroomshaped diapiric folds.

SLOW UPWELLING

The slow, upward movement of the salt diapir is 

expressed by the anomalous thinning of sedimentary 

units near the crests of the ancestral highs, much as 

discussed previously (p. 107-117). Locally, some of 

the units pinch out against the flanks of the high. 

Those units that continue unbroken across the crests 

of the highs, however, are the uppermost and 

younger parts of the formations. The lower and older 

parts of the formations presumably have pinched out 

against the slowly rising high. The fact that 

sequences of units thin must mean that the high was 

a dynamic feature growing continuously throughout 

lengthy episodes of geologic time. Were the paleohigh merely a static feature, the first units deposited 

against the flanks of the high might thin, but once 

the high was surmounted, subsequent units would 

pass over the crest of the high unchanged in thickness. This depositional thinning near the crests of 

the highs, found throughout the area, seems reasonably explained only as the result of slowly rising salt 

diapirs.

RAPID, UPWARD, FORCEFUL SURGES

In contrast to the slow, continuous movement, it is 

the repeated, forceful upward surges of the causative 

salt diapirs that appear to have determined the 

structural pattern of this part of central Utah. Salt is 

the motive force: It forces up the Arapien mudstones, 

which, in turn, force up and deform the overlying 

sedimentary units. These deformed sedimentary 

units, and their contained folded angular unconformities, reflect the repeated upward surges of the causative salt diapir. Expectably, the Arapien mudstones 

show many signs of extreme deformation; their 

present attitudes, however, merely reflect the last 

diapiric episode. Subsequent episodes will deform 

them once a Tain.

FIGURE 59 (facing page). Geology of an area near Dry Mountain. 

Geology slightly modified from Witkind (1987, fig. 12). Base 

modified from U.S. Geological Survey 1:100,000 Nephi (1981). 

Contour interval 250 m. An underlying diapir appears to have 

arched the Charleston-Nebo thrust plate. North Horn (TKn) 

strata that flank north-trending Dry Mountain, part of the 

Charleston-Nebo thrust plate, dip eastward east of the range 

and westward west of the range. These opposing dips in the 

younger strata suggest that the Charleston-Nebo thrust plate 

was arched by an underlying diapir (cross section A A').

COLLAPSE OF DIAPIRIC FOLDS

After the major folds were bowed up by the intrusive action of the Arapien Shale, they failed when 

salt was removed from the core of a diapiric fold. As 

the salt was removed, as a result of either extrusion 

or dissolution, the Arapien mudstone subsided into 

the newly formed void or voids. The failure probably 

occurred in small spasmodic movements, and not as 

a single catastrophic event.

Failure of the folds seems to have occurred either 

by collapse of the crestal part of the fold between 

high-angle normal faults, or by gradual subsidence of 

strata (outside the normal faults) to form monoclines 

(fig. 60). In some places both modes of failure may 

have occurred downthrow along a high-angle marginal fault on one flank of a fold and downwarp on 

the opposite flank. Invariably, the downthrow or 

downwarp was toward the core of the fold.

In the ancestral Willow Creek (G-3) area (fig. 27), 

and along the northeast border of the Valley Mountains (G-2) (fig. 30), the crestal part of the fold probably collapsed between high-angle faults that formed 

along the fold's flanks (fig. 6QA). A long, linear graben most likely resulted, probably much like those 

grabens that break the rocks along the crest and 

west flank of the Wasatch Plateau. This concept 

implies that the marginal faults that bound the graben extend to the base of the Arapien Shale but do 

not cut through the underlying Twin Creek Limestone on which the Arapien rests. My examination 

(through the courtesy of Chevron, USA) of seismic 

reflection profiles that cross the Wasatch Plateau 

convinces me that those faults that bound large grabens, such as the Joes Valley graben, do not, in fact, 

extend below the base of the Middle Jurassic Arapien 

Shale or its correlative, the upper part of the Carmel 

Formation.

Elsewhere, as near the mouth of Sixmile Creek 

canyon (F-4), along the west flank of the Wasatch 

Plateau (fig. 21), and in Red Canyon (E-2), along the 

east flank of the Valley Mountains (fig. 31), the folds 

appear to have failed by gradual subsidence and so 

formed monoclines (fig. 60S; and Witkind and Page, 

1984). Thus, I interpret the westward-facing Wasatch 

monocline, and the much smaller, unrelated, eastward-facing Valley Mountains monocline, along the 

east flank of the Valley Mountains, to stem from such 

subsidence.

As the diapiric core subsided, in response to the 

removal of salt, the overlying sedimentary and 

volcanic strata subsided into the resultant void to 

form a broad V, forming, thus, a pair of facing monoclines. The resultant feature is best visualized as a
120

WEST

SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

EAST WEST EAST

T(Ja)

EXPLANATION

Tertiary rocks, undivided Includes, in

descending order, Crazy Hollow Formation. Green River Formation, and Colton Formation, and Flagstaff Limestone

undivided Includes, in descending order,

North Horn Formation and Price River

Cretaceous and Jurassic rocks, 

undivided Includes, in descending order, 

the undivided Indianola Group, Cedar 

Mountain Formation, and Twist Gulch 

Formation

T(Ja)

Arapien Shale

Holocene

Eocene and 

Paleocene

Upper 

Cretaceous

Middle 

Jurassic

B

QUATERNARY

TERTIARY

CRETACEOUS

JURASSIC
DIAPIRIC PROCESSES 121

collapse structure, for the formerly continuous strata 

that overlay the diapir were broken and disrupted as 

they subsided. The structure, thus, differs from a 

syncline, which is formed by downwarped but essentially unbroken strata. Doelling (1988, p. 45, figs. 46 

and 49) referred to somewhat comparable collapse 

features developed in the Paradox Basin, and essentially similar in size to those within the SanpeteSevier Valley area, as "* * * v-shaped dissolution 

synclines * * *," or "V-synclines."

PAIRED, FACING MONOCLINES

If the monoclines in the Sanpete-Sevier Valley area 

are indeed the result of subsidence stemming from 

removal of salt, one would expect to find paired, facing monoclines one facing east even as its opposite 

number faces west. In places, that appears to be the 

case. So, the eastward-facing Valley Mountains monocline is paired with the westward-facing West Gunnison monocline developed along the southwest flank of 

the Gunnison Plateau. Sevier Valley separates the 

two monoclines (fig. 61). In like fashion, the eastward-facing West Hills monocline, which delineates 

the east flank of the West Hills, is paired with the 

northern part of the westward-facing West Gunnison 

monocline. Juab Valley separates the two monoclines.

Farther to the east, the westward-facing Wasatch 

monocline then should be paired with another monocline across Sanpete Valley, one that faces east and

FIGURE 60 (facing page). Diagrammatic sections illustrating two 

alternative interpretations of how diapiric folds may fail. In 

each view, west is at left, east is at right. 

A, The crest of a fold collapses and a linear graben is formed.

I. Fan-shaped diapiric fold is formed as a result of the upward 

thrust (large arrow) of Arapien mudstones a direct result of 

the upward movement of a salt diapir (not shown).

II. With gradual removal of salt, by either extrusion or dissolution, the underlying support for the Arapien mudstones is removed, and they and the overlying strata collapse (large arrow) 

along high-angle faults formed along both flanks of the fold's 

crest. (Barbs show relative movement along faults.) The end 

result is a long, linear graben comparable to those that break 

the rocks along the crest and west flank of the Wasatch Plateau. 

B, The central part of a fold gradually subsides, and facing 

monoclines are formed.

I. A fan-shaped diapiric fold is formed.

II. With gradual removal of salt, the Arapien mudstones, lacking support, sink into the newly created voids; the overlying 

sedimentary strata founder and break into large masses. Erosion quickly destroys these fragmented blocks.

III. Continued removal of salt and the concurrent subsidence of 

the Arapien mudstones eventually cause downward flexing of 

previously upturned beds to form paired, facing monoclines.

that delineates the east flank of the Gunnison Plateau. Rather than a monocline, however, a northward-trending belt of upturned and locally 

overturned Cretaceous and Jurassic rocks marks the 

lower flank of the plateau.4 All sedimentary units 

within this distinctive belt are anomalously thin. 

Analogous structures elsewhere in the area imply 

that this belt may once have lain beneath a former 

monocline. Similar, anomalously thin Cretaceous and 

Jurassic rocks are exposed in both the Wasatch and 

Valley Mountains monoclines, where the downwarped 

Tertiary beds have been breached (Witkind, 1992). In 

both those areas, the upturned "Cretaceous" rocks 

are complexly deformed, and all strata, upturned 

"Cretaceous" and downwarped Tertiary, are anomalously thin compared with their thicknesses elsewhere in the area. Specifically, where the foot of the 

Valley Mountains monocline is breached at its north 

end, the sedimentary units exposed at Red Canyon 

are both structurally complex and remarkably thin. 

Similarly, where the foot of the Wasatch monocline is 

breached at the mouth of Sixmile Creek canyon, the 

exposed rocks are both unusually complex structurally and atypically thin.

Locally, this same pattern downwarped Tertiary 

beds overlying upturned "Cretaceous" rocks is 

exposed along the West Gunnison monocline. In that 

sector, too, the Cretaceous and Tertiary rocks display 

the anomalous thinness seen elsewhere, but not the 

striking structural complexity. I attribute this apparent absence of structural complexity to the fact that 

erosion has not cut deeply enough to expose the 

underlying vertical to overturned beds (fig. 62A). 

Weiss (in Witkind, Weiss, and Brown, 1987) and Mattox and Weiss (1987) have assigned the clastic beds 

beneath North Horn strata and exposed along the 

southwest flank of the Gunnison Plateau to the Indianola Group. I believe that the beds in question, 

rather than being part of the Indianola, are more correctly part of the Price River Formation. In lithology, 

appearance, and attitude, the beds in question are 

very much like the Price River strata that overlie vertical to overturned beds of the Indianola Group 

exposed along the east flank of the Gunnison Plateau 

north of Wales (fig. 625, and fig. 17). Thus, in my 

view, erosion has not cut deeply enough along the 

west flank of the Gunnison Plateau to expose the

4The bowed up strata include, in various localities, Middle Jurassic (Twist 

Gulch Formation), Lower Cretaceous (Cedar Mountain Formation), Upper 

Cretaceous (Indianola Group, Price River Formation), and Upper Cretaceous 

and Paleocene units (North Horn Formation). For ease of discussion I group 

these beds and refer to them as "Cretaceous" in this discussion.
122 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

112°00' 45' 30' 11T15'

39°45

H. I

I

V

7

.-ao 1

^

39°00'

30 KILOMETERS

, I

20 MILES
DIAPIRIC PROCESSES 123

FIGURE 61 (facing page). Paired, facing monoclines in the 

Sanpete-Sevier Valley area formed as the result of removal of 

salt from an underlying diapir. East-facing Valley Mountains 

monocline is paired with the west-facing West Gunnison monocline, across Sevier Valley. East-facing West Hills monocline is 

paired with north end of the west-facing West Gunnison monocline. A now completely eroded and removed monocline markI ing the east flank of the Gunnison Plateau the East Gunnison 

monocline is postulated to pair with the Wasatch monocline. 

Of major Neogene monoclines trending northward through the 

Sanpete-Sevier Valley area, only the Wasatch and Valley monoclines are essentially whole and only slightly eroded. Only 

remnants of the West Gunnison monocline are left to indicate 

its former extent, and the East Gunnison monocline, completely 

eroded, can only be inferred. Base modified from U.S. Coast 

and Geodetic Survey 1:500,000 Grand Junction (T-3) Sectional 

Aeronautical Chart (1954; rev).

underlying Indianola strata. Were those Indianola 

strata exposed, I believe their attitudes vertical or 

dipping steeply toward the east would mimic those 

exposures along the east flank of the plateau (fig. 62).

Seemingly, the monoclines in the Sanpete-Sevier 

Valley area differ from most monoclines. A section 

through any monocline within the Colorado Plateau 

displays a sequence of stacked, layered beds that conform in attitude to those beds that form the monoclinal slope. It is much like a section through an 

onion. By contrast, a section through a monocline in 

central Utah does show the characteristic layered 

aspect in the upper and middle parts of the monocline, 

but not in the distal end the foot of the monocline. 

Those beds exposed at the foot of the monocline, 

beneath the downwarped Tertiary strata that define

FIGURE 62. Diagrammatic cross sections showing suggested geologic relations along both east and west flanks of Gunnison 

Plateau, a southward-plunging syncline. A, West flank of the 

Gunnison Plateau. In general, Cretaceous strata that dip eastward along the west flank of the plateau are overlain with angular unconformity by westward-dipping Tertiary strata. These 

Tertiary beds form the much-dissected westward-facing West 

Gunnison monocline. Units here labeled Price River(?) Formation 

have been called the Indianola Group by Mattox and Weiss 

(1987). B, East flank of the Gunnison Plateau. In general, Cretaceous strata dip westward along the east flank of the plateau. I 

contend that these strata were once overlain with angular unconformity by eastward-dipping Tertiary strata that formed the East 

Gunnison monocline, now completely eroded. C, East flank of the 

Gunnison Plateau. Locally, the Cretaceous beds that crop out 

along the east flank of the plateau have been warped up into 

vertical and overturned attitudes. Near Wales (D-4), for 

example, Price River strata, which dip gently westward near the 

mouth of Maple Canyon (E-3), are overturned and form a prominent ridge that parallels the front of the plateau. See figure 17, 

and figure 23A. For an explanation of how these relations 

developed, see figure 25.

the monoclinal slope, are both anomalously thin and 

unusually complex structurally.

It seems more than fortuitous that in three widely 

separated areas (1) Red Canyon in the Valley 

Mountains, (2) Sixmile Canyon along the west flank 

of the Wasatch Plateau, and (3) the lower flanks of 

the east side of the Gunnison Plateau the exposed 

rocks display both unusual structural complexity and 

atypical thinness. The one great difference among 

the three areas is the absence of a monocline along

WEST EAST

Suggested configuration of the 

West Gunnison monocline

Angular unconformity

\ \ Indianola Group, Cedar Mountain,

\ \ and ai Twist Gulch Formations,, 

undivided

WEST EAST

Suggested configuration of the 

East Gunnison monocline

Riverl?) Formation

Indianola Group, Cedar Mountain,

and Twist Gulch Formations,

1 undivided \

B

WEST

Flagsta« Limestone\ _^

EAST 

Angular unconformity

. 

Indianola Group, Cedar Mountain,^

and Twist Gulch Formations, undivided
124 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

the east flank of the Gunnison Plateau; that absence 

can be attributed to erosion. It is this similarity 

between the beds exposed in the breached sectors of 

recognizable monoclines and comparable beds 

exposed along the east flank of the Gunnison Plateau 

that has led me to propose that the near-horizontal 

Tertiary units that cap the Gunnison Plateau once 

flexed down along the east flank of the plateau to 

form an eastward-facing monocline (fig. 62B). I refer 

to this monocline as the East Gunnison monocline, 

and it must have been every bit as impressive as the 

Wasatch monocline.

During middle and late Tertiary time, then, the 

geomorphic pattern of the Sanpete-Sevier Valley 

area was probably dominated by at least four major 

north-trending monoclines (fig. 61). From east to 

west, these were (1) the Wasatch monocline, facing 

west; (2) the East Gunnison monocline, facing east;

(3) the West Gunnison monocline, facing west; and

(4) the Valley Mountains and West Hills monoclines, 

facing east. The Wasatch-East Gunnison monoclines 

formed a facing pair separated by Sanpete Valley; the 

West Gunnison-Valley Mountains and West Hills 

monoclines formed a second facing pair separated by 

the lowland formed by the collinear alignment of 

Sevier and Juab Valleys.

DIAPIRIC STAGES AND EPISODES

The diapiric folds have grown and collapsed 

repeatedly. Figure 63 illustrates this repeated 

growth and collapse of diapiric folds. In this figure, I 

have, for ease of understanding, assumed that the 

folds collapse between parallel crestal faults. As 

noted in figure 6GB, the folds may also fail by gradual subsidence.

A diapiric fold grows and collapses in three successive, interrelated stages, which together make up a 

diapiric episode. The first stage-the intrusive stageis characterized by the rapid upwelling of a salt 

diapir that forces up the mobile mudstones of the 

Arapien Shale. These, in turn, acting much like a 

viscous magma, intrude, bow up, and fold back the 

overlying sedimentary beds (fig. 63, II). The resultant 

fan-shaped diapiric fold is probably partly destroyed, 

even as it rises, by gravity sliding and other forms of 

mass-wasting. Nevertheless, the end result is a topographic high.

This stage is followed almost immediately by the 

onset of the second stage, during which the fold fails, 

presumably owing to removal of the salt (fig. 63, III). 

The remnants of the collapsed fold are then eroded to 

form a broad, even-surfaced plain of low relief (fig. 63, 

IV). During this second stage the erosional stage 

the salt diapir probably resumes its slow upwelling,

but its upward movement must be so slight that erosion is able to keep pace with whatever doming 

occurs.

The third stage begins with the deposition of sediments on this newly formed erosion surface (fig. 63, 

V). During this stage the depositional stage the 

salt diapir wells upward rapidly enough to restrict 

the amount of sediment deposited across the crest of 

the rising fold, resulting in depositional thinning. 

This third stage ends with a renewed upward surge 

of the salt diapir the intrusive stage in yet another 

episode of salt diapirism (fig. 63, VI).

I term each cycle of growth and collapse a diapiric 

episode; thus, each episode comprises three distinguishable diapiric stages. Three such major diapiric 

episodes are well shown in the Red Rocks (F-3)- 

Sixmile Canyon (F-4) area along the east flank of the 

Gunnison Plateau, and in the Red Canyon (E-2) area 

of the Valley Mountains.

1. Late Cretaceous-early Paleocene episode:

The first clearly recognized diapiric episode probably began during the Late Cretaceous, after deposition of the Indianola Group, and probably ended in 

the early Paleocene after deposition of the North 

Horn Formation but before deposition of the Flagstaff 

Limestone.

The Twist Gulch and Cedar Mountain Formations, 

and the Indianola Group, bowed up during this first 

intrusive stage (fig. 63, II), were subsequently eroded 

to form a surface of low relief during the first erosional stage (fig. 63, IV). Later, the Price River and 

North Horn Formations were deposited on this 

surface of low relief during the first depositional 

stage (fig. 63, V).

2. Early Paleocene-late Oligocene(?) episode:

The second episode probably began in early Paleocene time, after deposition of the North Horn Formation, and ended after deposition of the Crazy 

Hollow Formation, possibly during the late Oligocene 

or Miocene.

The North Horn and Price River Formations were 

bowed up during a second intrusive stage (fig. 63, VI). 

Subsequently, erosion reduced the newly formed diapiric folds to a surface of low relief by the end of the 

second erosional stage (fig. 63, VIII). A sequence of 

Tertiary units, extending from the Flagstaff Limestone to at least the Crazy Hollow Formation, was 

deposited on this surface during the second depositional stage (fig. 63, IX).

3. Late(?) Oligocene-Pliocene(?) episode:

The third episode probably began during the late 

Oligocene or Miocene, after deposition of the Goldens 

Ranch and Moroni Formations, and may have ended 

during the Pliocene or Pleistocene. The evidence as to
DIAPIRIC PROCESSES 125

when this episode ended is fragmentary and inconclusive.

Locally, the Tertiary units (Flagstaff, Colton, Green 

River, and Crazy Hollow) were bowed up during a 

third intrusive stage (fig. 63, X). The folds failed in 

various ways, some by collapse (fig. 63, XI), and some 

by subsidence. Erosion, however, has not as yet 

completely beveled the diapiric folds, and most now 

appear in varying stages of dissection (fig. 63, XII).

I believe that each of these three episodes was 

regional in extent, and that during each episode all 

the salt diapirs in central Utah reactivated and 

deformed the overlying beds. The evidence in the 

Gunnison Reservoir (F-3) area (fig. 28) suggests that 

a fourth, localized diapiric episode began and may 

have ended during the Pleistocene or Holocene.

Although all three stages of all three episodes are 

clearly shown in some exposures, elsewhere erosion 

has not cut deeply enough. Thus, in the ancestral 

Willow Creek (G-3) area (fig. 27), only that vestige of 

the Sanpete Sevier Valley diapiric fold formed during 

the third diapiric episode (late Oligocene-Pliocene(?)) 

is exposed; erosion has not yet uncovered the earlier 

versions of the fold formed during the first (Late 

Cretaceous-early Paleocene) and second (early 

Paleocene-late(?) Oligocene) episodes.

GEOLOGIC PATTERN

The three major episodes of diapirism have 

stamped a geologic pattern on the area that is 

repeated in place after place. In its simplest form 

this pattern is represented by upturned conglomerate

FIGURE 63 (following pages). Schematic sections suggesting how 

the repeated growth and collapse of diapiric folds have determined the structural pattern of central Utah. All sections represent part of the west limb of a typical diapiric fold.

I. Jurassic and Cretaceous sediments (KJu) were deposited on 

the Arapien Shale. Slow upwelling of the salt diapir (just east of 

area of section shown) pushed up the Arapien mudstones to 

form an elongate, north-trending arch, which impeded deposition of the sediments. As the arch continued to rise, all sediments that were deposited against its flanks or across its crest 

thinned or pinched out. 

First diapiric episode (Late Cretaceous to early Paieocene):

II. Late Cretaceous intrusive stage. A sudden upward surge of 

the salt diapir (not shown) pushed up the mudstones and shales 

of the Arapien Shale (K(Ja)), which in turn bowed up and folded 

back (arrow) the overlying sedimentary strata (KJu) to form a 

fan-shaped fold. (Much of the overturned limb was soon destroyed by gravity sliding and other forms of mass-wasting.)

III. Late Cretaceous erosional stage. Removal of the salt core 

(chiefly by solution) caused the central part of the fold to collapse, forming a graben between high-angle normal faults. 

Only the western fault (A) is shown here.

IV. Late Cretaceous erosional stage. Erosion of fold remnants 

produced a surface of low relief. Persistent slow upwelling of the 

salt diapir arched the deformed strata (KJu) slightly. The fault 

(A), formerly vertical, is tilted. The rate of erosion either exceeded or at least kept pace with the rate of arching.

V. Late Cretaceous-early Paleocene depositional stage. Upper 

Cretaceous sediments deposited on the eroded surface subsequently were buried beneath lower Paleocene sediments (TKu). 

The continued slow upwelling of the salt diapir warped up the 

deformed strata (KJu), further tilting the previously vertical 

fault (A), and thinning those sediments (TKu) deposited across 

the crest of the fold.

Second diapiric episode (early Paleocene-late Oligocene(?) 

episode):

VI. Early Paleocene intrusive stage. Reactivation of the salt diapir during the early Paleocene resulted in a renewed diapiric 

fold, whose general trend and position followed that of the earlier fold (II). The recently deposited Cretaceous and Paleocene 

strata (TKu) were flexed into a fan-shaped fold, and the older 

strata (KJu) were tilted to still steeper angles. Fault (A) was 

probably destroyed by the renewed movements of the mobile 

mudstones and shales of the Arapien Shale (T(Ja)); it is shown

here to emphasize the tilting of the strata. Here too, as for the 

earlier fold, the overturned limb of the developing fold was 

probably destroyed in great part by gravity sliding.

VII. Middle(?) Paleocene erosional stage. Removal of the salt 

core, possibly during the middle Paleocene, resulted in collapse 

of the crest of the fold along high-angle normal faults. Only the 

western fault (B) of those faults that bound the graben thus 

formed is shown here. The pattern of collapse of the parental 

fold (III) is repeated. Near the core of the fold, the undivided 

Tertiary and Cretaceous strata (TKu) overlay the overturned undivided Cretaceous and Jurassic strata (KJu) with profound angular unconformity. A short distance to the west the two units 

are disconformable, and still farther away they are conformable.

VIII. Middle(?) Paleocene erosional stage. Erosion again reduced the area to a widespread surface of low relief. The slow 

upwelling of the salt diapir resumed and the strata were again 

arched. Erosion kept pace with the upward bowing of the consolidated units.

IX. Late(?) Paleocene to late(?) Eocene depositional stage. The 

pattern recurs. Beginning in the late(?) Paleocene and continuing through the late Eocene and probably even into the Oligocene, sediments (Tu) were deposited on the newly formed 

erosion surface. The slow rise of the salt diapir arched the consolidated strata (KJu, TKu), tilted the faults (A, B), and thinned 

the sequence of those sedimentary units being deposited across 

the axis of the fold. 

Third diapiric episode (late(?) Oligocene-Pliocene episode):

X. Late(?) Oligocene intrusive stage. The salt diapir reactivated 

for a third time; again a new fold formed, and again it lay along 

the same site and had the same trend as that of the previous 

folds. The time of this reactivation may have been during the 

late(?) Oligocene or possibly even the Miocene. The newly deposited Tertiary strata (Tu) were raised and folded back by the remobilized mudstones of the Arapien Shale to form a fan-shaped 

fold. The overturned limb of the fold was concurrently destroyed 

by gravity sliding and mass wasting.

XL Late(?) Oligocene-Pliocene erosional stage. The newest 

formed fold was destroyed by collapse of the crest of the fold 

along high-angle normal faults. Fault C is the westernmost of 

the faults that bounded the newly formed graben. 

XII. Late(?) Oligocene-Pliocene erosional stage; ancestral topography. Erosion began to reduce the fold, even as the sedimentary beds were raised and arched by continued slow upwelling of 

the salt diapir.
126 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

WEST EAST WEST

Late Cretaceous-early Paleocene episode 

EAST WEST EAST

KJu - -

K(Ja)

- KJu

KUa)

A B

VII VIII IX

Early Paleocene-late Oligocenel?) episode

EXPLANATION

Tertiary rocks, undivided Includes, in descen

ding order, Crazy Hollow Formation, Green

River Formation, Colton Formation, and

Flagstaff Limestone

Tertiary and Cretaceous rocks, undivided 

Includes, in descending order, North Horn and 

Price River Formations

1 KJu

Cretaceous and Jurassic rocks, undivided 

Includes, in descending order, Indianola 

Group, undivided, Cedar Mountain Formation, and Twist Gulch Formation

Ar

T(Ja)

KUa)

J(Ja)

apien Sh

 >

ale

Eocene and Paleocene

Upper Cretaceous

Middle Jurassic

TERTIARY

CRETACEOUS

JURASSIC

beds of the Indianola Group unconformably overlain 

by thin Price River and North Horn Formations, 

which in turn are unconformably overlain by the

Flagstaff Limestone. The two angular unconformities 

commonly are folded, and they are distinctive in the 

stratigraphic sequence. This geologic pattern is well
DIAPIRIC PROCESSES 127

WEST

-Late Cretaceous-early Paleocene episode 

EAST WEST EAST WEST EAST

K(Ja)

K(Ja) IV

"TKu

Late(?) Oligocene-Pliocenel?) episode

exposed at the mouth of Sixmile Creek canyon (F-4), 

in Red Canyon (E-2) (along the northeast flank of 

the Valley Mountains), and not quite as easily recognizable along the east and west flanks of the 

Gunnison Plateau.

How much of this geologic pattern is exposed 

depends to a great extent upon how deeply an area 

has been eroded. As exemplified in figure 64, if erosion has cut a deep valley through the "ancestral surface," the geologic pattern is easily recognized 

upturned beds of the Indianola Group and older rocks 

(KJu) unconformably overlain by thin Price River and 

North Horn sequences (TKu), which in turn are 

unconformably overlain by the Flagstaff Limestone 

and younger Tertiary strata (Tu). If, however, erosion 

has cut deeper and reached the "modern surface," 

much of the structural complexity has been 

removed the geologic pattern can only be inferred.

The angular unconformities, in which near-vertical 

beds are overlain by near-horizontal beds, appear to 

be present only near the core of a diapiric fold. As 

one moves away from the core, the near-vertical beds

lessen in dip and several kilometers (a mile or so) 

away are conformable with the overlying units. So, 

for example, in the Red Rocks (F-3) area, which is 

about 1 km (0.5 mi) west of the core of the diapiric 

fold, the lower angular unconformity (between the 

Price River and North Horn and the Indianola) is 

well exposed, but the upper unconformity (between 

the Flagstaff and North Horn strata) is not easily 

recognized (Spieker, 1949, p. 76). Here, the FlagstaffNorth Horn contact appears as a disconformity; erosion has removed that part of the fold in which the 

angular unconformity between the Flagstaff and the 

North Horn was well displayed.

By contrast, in the Sixmile Creek canyon (F-4) 

area, which is about 4 km (2.5 mi) east of the crest of 

the fold, the lower unconformity is not as impressive 

as it is in the Red Rocks area, for the Price River and 

units in the Indianola (Sixmile Canyon Formation, in 

particular) are separated by only a slight angular 

unconformity; the beds flatten rapidly eastward and 

are conformable only about 1 km (0.5 mi) away. The 

upper unconformity, however, does catch the eye, for
128 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

EXPLANATION

FIGURE 64. Cross section of typical diapiric fold in central Utah, 

illustrating how the extent of erosion can influence interpretation of a geologic pattern. Vertical and overturned beds of the 

Indianola Group and older units are unconformably overlain by 

a Price River and North Horn sequence, which in turn is unconformably overlain by a Tertiary sequence of which the Flagstaff Limestone is the oldest. Two distinctive angular

Tertiary rocks, undivided 

Includes, in descending 

order, Crazy Hollow Formation, Green River Formation, 

Colton Formation, and 

Flagstaff Limestone

Tertiary and Cretaceous rocks, 

undivided Includes, in 

descending order, North 

Horn and Price River 

Formations

Cretaceous and Jurassic rocks,

undivided Includes, in 

descending order, Indianola 

Group, undivided, Cedar 

Mountain Formation, and 

Twist Gulch Formation

fHolocene

Eocene and 

Paleocene

T(Ja)

QUATERNARY

Arapien -« 

Shale

^TERTIARY

Upper 

Cretaceous

Middle 

Jurassic

^CRETACEOUS

JURASSIC

U Unconformity

Fault Dashed where reconstructed toward ancestral 

surface: barb shows direction of relative movement

unconformities are produced. If erosion is at the "ancestral surface" level, both unconformities are exposed and geologic relations are unequivocal. If erosion has cut to the "modern surface" 

level shown, only one unconformity can be recognized, and the 

younger unconformity is removed or masked. Compare this illustration with figure 63, XII, and with photograph of the Red 

Rocks area, figure 18B.

the westward-tilted Flagstaff Limestone rests upon 

the upturned eastward-tilted beds of the Price River 

and North Horn sequence (fig. 21).

The same geologic pattern is clearly visible in Red 

Canyon (E-2) along the northeast flank of the Valley 

Mountains. Near-vertical beds of the Indianola Group 

are overlain with angular unconformity by the North 

Horn Formation that dips west at a moderate angle. 

The North Horn, in turn, is overlain by beds of the 

Flagstaff Limestone that dip eastward (fig. 31). The 

exposure is a mirror image of the one in Sixmile 

Creek canyon (F-4) (Witkind and Page, 1984).

Only part of the pattern is exposed along the east 

flank of the Gunnison Plateau. At and near the 

mouth of Maple Canyon (C-4), Price River strata, 

dipping gently to moderately westward, unconformably overlie vertical to overturned Indianola beds, 

duplicating stratigraphic relations found in the Red 

Rocks (F-3) area, and in the Red Canyon area of the 

Valley Mountains. Erosion, however, has removed 

much of the North Horn and all of the Flagstaff

Limestone from the Maple Canyon area; the Flagstaff now crops out along the top of the plateau about 

1.6 km (1 mi) to the southwest, far back from the 

crest of the diapiric fold. The Flagstaff, expectably, 

conformably overlies North Horn strata. Here too, 

then, much as in the Red Rocks area, that part of the 

fold (near the diapiric crest) where the Flagstaff and 

the North Horn were once separated by an angular 

unconformity has been removed by erosion.

In a few localities, an additional complexity, stemming from the collapse of a diapiric fold, has somewhat modified this geologic pattern. Along the 

northeast flank of the Valley Mountains, northwest of 

Painted Rock Canyon (E-2), younger beds are 

downthrown along a range-front, high-angle normal 

fault and abut the much older Indianola beds. Relations are confused, but in general, it appears that 

elements of the North Horn, Flagstaff, Colton, and 

Green River formations are juxtaposed against the 

conglomerates of the Indianola Group (fig. 29B). I 

interpret these relations to result from the collapse of
LOCALIZATION AND CAUSATIVE FORCES 129

the crestal part of the Sevier Bridge Reservoir diapiric fold.

CYCLICAL ASPECTS

The fact that the three diapiric episodes are represented in single outcrops at several different localities implies that ever-younger diapiric folds were 

formed time and again in the same structural zones 

and had the same trends as the earlier diapiric folds. 

In essence, the "parental" diapiric folds that were 

formed in Late Cretaceous time (and that are represented by the beveled, steeply inclined beds of the 

Indianola Group) were the precursors of other folds 

formed still later, once during the Paleocene, and 

again during the late(?) Oligocene or Miocene. It is 

much as if the salt was confined to specific conduits 

and repeatedly used these conduits each time it 

surged upward.

LOCALIZATION AND CAUSATIVE FORCES

The diapiric folds in central Utah, the "salt anticlines'"' (salt-cored anticlines) of the Paradox Basin, 

the elongate salt-cored structures of northern 

Germany (Trusheim, 1960; Sannemann, 1968), and 

northern Tunisia (Perthuisot, 1981), to select but a 

few examples, are all alike in that they are strikingly 

regular in distribution and orientation. This regularity of the salt structures in northern Germany was 

attributed by Trusheim (1957) to autonomous, isostatic salt movement, for which he coined the term 

"halo-kinesis." In brief, he proposed that as soon as 

deeply buried salt begins to flow, it forms a low, 

swelling salt mass (Trusheim, 1960, p. 1524-1527). 

Adjacent salt from the "mother bed" of salt moves 

inward toward the salt mass, which begins to expand 

and forms a mound. Even as this occurs, the sedimentary rocks adjacent to these areas of inflowing 

salt subside to form rim synclines. Sedimentary 

material, deposited in these rim synclines, adds 

weight, which augments the inflow of the salt toward 

the salt mass. As the salt mass swells, it arches the 

overlying strata, and in time, the swelling salt mass, 

fed by a continuous supply of mother salt, intrudes 

the overlying sedimentary beds, starting the diapiric 

stage. With continued addition of salt, the diapir may 

breach the sedimentary cover, and flow out across the 

surface. A new rim syncline, formed adjacent to this 

diapir, is gradually filled as sediments accumulate in 

it. In time, these sediments are thick and dense 

enough to force the mother salt adjacent to the original "parent" diapir to migrate away from it and form

a new salt mass some distance away. With continued 

addition of mother salt, this new salt mass eventually becomes a diapir; in essence, a second generation 

of salt structures develops. This process is repeated 

again and again with ever-younger generations of 

diapirs forming away from the parental diapir until 

the mother bed of salt is depleted.

The cause of the initial movement of the salt is 

uncertain. It may be an inhomogeneity in the roof of 

the salt layer, a gentle warp in the basement rocks, 

or a tectonic impulse (Trusheim, 1960, p. 1523-1524; 

Sannemann, 1968, p. 268). In Trusheim's interpretation, autonomous, isostatic movement of the salt is 

the fundamental reason the salt diapirs developed.

In a series of uniformly oriented, subparallel salt 

diapirs, then, the oldest is the central "parental" one. 

On each side, a second generation of daughter diapirs 

flanks this parental diapir; beyond these the succeeding diapirs represent ever-younger generations with 

the outermost diapirs being the youngest.

This age sequence, however, is not apparent in 

central Utah The oldest beds deformed (tilted vertically or overturned) as part of the westernmost 

diapiric fold (the Sevier Bridge Reservoir diaipiric 

fold (fig. 16, 4)) are conglomerate beds of the Indianola Group. Correlative beds of the Indianola Group 

have been tilted vertically or overturned in a central 

diapiric fold (the Sanpete-Sevier Valley diapiric fold 

(fig. 16, 1)) as well as in the easternmost diapiric 

fold exposed (Little Clear Creek diapiric fold (fig. 16, 

9). Apparently, all the diapiric folds, no matter what 

their position in the diapiric cluster, were formed at 

the same time.

The stratigraphic sequence at several localities 

indicates that the area has been deformed during at 

least three distinct diapiric episodes. And in each of 

these widely separated localities, the geologic evidence suggests that each of the three episodes began 

and seemingly ended at the same time. There is no 

evidence of progressive change of age from one diapir 

to another during any one of the three episodes.

Moreover, the repetition of extremely localized 

angular unconformities, exposed in single outcrops at 

different localities, suggests repeated reactivation 

and destruction of ever-younger diapiric folds, which 

always occupied the same structural zones and had 

the same trends. As each reactivated salt diapir 

welled upward (seemingly using the same conduit as 

the previous diapir), a new diapiric fold was formed, 

at the same site and along the same trend as the 

previous fold. Each time the newly emplaced salt was 

removed, the newly formed fold collapsed. If, as suggested by the halokinetic hypothesis, the salt diapirs 

continuously form away from the parental diapir, it
130 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

is difficult to see how this central Utah pattern of 

diapiric folds being formed repeatedly and simultaneously in all localities can be explained solely by 

halo-kinesis. Some other factor, or factors, must be 

involved.

Although the central Utah salt diapirs may have 

been formed in part by halo-kinesis, I believe that 

tectonic forces are probably responsible for their 

development, and propose, therefore, that halotectomsm (another term proposed by Trusheim (1957) 

to imply development of salt diapirs in response to 

tectonic forces) is a more plausible explanation.

The diapiric folds are elongate, narrow, faintly sinuous features that extend for many kilometers. This 

linearity suggests some form of structural control 

that determined not only the trends of the folds but 

also their distribution. The linearity of the folds plus 

the fact that they grew and collapsed repeatedly 

along the same axes suggests that well-established 

fault planes may have served as conduits for the salt 

and intermixed mudstones as they repeatedly welled 

upward toward the surface. This concept is supported 

by the fact that two of the diapiric folds align with 

major fault zones, and a third parallels such a zone 

(fig. 65). The Sanpete-Sevier Valley diapiric fold is 

collinear with the northeastward projection of the 

Sevier fault zone, and the Redmond fold aligns with 

the southward projection of the Wasatch fault zone. 

The Levan fold, which may be a northern segment of 

the Redmond fold, parallels the south end of the 

Wasatch fault zone.

The Sevier fault zone extends northeastward from 

southwestern Utah into central Utah. Southeast of 

Richfield (1-1) it appears as a series of small scarps 

that break surficial deposits along the east side of 

Sevier Valley. The scarps end near Richfield; northeastward beyond Richfield neither scarplets nor other 

features suggestive of the fault zone can be found. 

Even as the fault zone apparently ends, the elongate, 

narrow welt of Arapien mudstone beds, which marks 

the core of the Sanpete-Sevier Valley diapiric fold, 

begins and extends northeastward along the east 

side of Sevier Valley. The trend of the fault zone and 

the core of the fold are collinear.

A similar alignment appears to exist between the 

trend of the Wasatch fault zone and the Redmond 

diapiric fold. The Wasatch fault zone can be traced 

southward from northern Utah into this area as a 

series of small scarps that break surficial deposits. 

The zone ends near Fayette (F-3) (Cluff, Brogan, and 

Glass, 1973), but about 6 km (4 mi) farther south, 

near Gunnison (F-3), a line of Arapien Shale outcrops the core of the Redmond diapiric fold begins 

and extends southward along the west valley wall of

Sevier Valley to Redmond (G-3). Here, too, even as 

the fault zone ends, the line of Arapien Shale outcrops begins and is collinear with the trend of the 

fault zone.

Finally, from Nephi (B-3) southward, the Wasatch 

fault zone, marked by a series of small scarps, closely 

parallels the northward-trending welt of Arapien 

mudstone that crops out along the west flank of the 

Gunnison Plateau (fig. 65), and that I consider to be 

the core of the Levan diapiric fold.

Possibly this collinearity between major fault zones 

and diapiric folds is fortuitous, but I do not think so. 

I believe the alignment is meaningful and propose 

that the position and extent of each parental diapiric 

fold was originally determined by a preexisting, deepseated, fundamental structure. Other workers have 

commented on this apparent structural control of 

salt-generated structures. So, Stokes (1948, p. 14), 

discussing the salt structures in the Paradox Basin, 

noted: "This regional uniformity of trend is evidently

114° 

42°rr-- r

113° 

 ~i~

112° v " 

\

Brigham

"1

4,.u

V,

Great Salt Lake

50

 '-r1 'i ! i i 

]

1° ____

100 Kl

I

50 MILES

110°

40

i

;

Utah Lake 

WASATCH FAULT ZONE

Core of the 

Levan diapiric fold

39'r

38

I 

37°l .

/v i^ore of the ^ 

/Sanpete-Sevier Valley 

diapiric fold

^Fayette^j 

_ Gunnison^ 

Seoier 

Lake

I Core "of the 

I Redmond diapiric fold 

I Richfielr

' SEVIER FAULT ZONE

|O I 

Cedar City o

_j____i / \-^ EXPLANATION i

Major outcrops of the j 

Arapien Shale (

Fault zone Dashed where 1 

approximately located I

FIGURE 65. Alignment of several diapiric cores with major 

fault zones in central Utah. The core of the Sanpete-Sevier 

Valley diapiric fold begins where the Sevier fault zone ends 

and extends northeastward, collinear with the fault zone. In 

much the same fashion, the core of the Redmond diapiric 

fold begins where the Wasatch fault zone ends, near Fayette, 

and continues the southward trend.
LOCALIZATION AND CAUSATIVE FORCES 131

a reflection of important deep-seated breaks in the 

basement rocks* * *." Cater (1955, p. 125), also 

impressed by the regularity of distribution of the 

salt-cored anticlines in the Paradox Basin, similarly 

speculated that deep-seated structures were responsible for their parallelism. Cater and Elston (1963), on 

the basis of well data from the Paradox Basin, proposed that the larger diapirs were underlain by 

major pre-salt breaks. Baars and Stevenson (1981, p. 

28) noted that past and recent seismic surveys in the 

Paradox Basin area "have left no doubt as to the 

existence of pre-salt faulting* * *," which dictated the 

trend of the salt structures. Perthuisot (1981, p. 233), 

discussing the elongate salt diapirs of northern Tunisia, called upon deep movement of large basement 

blocks as an explanation for the preferred orientation 

of the diapirs. And Trusheim (1960, p. 1524) noted 

that the pattern of the northern German salt structures may reflect "a network of faults in the presaline basement."

I suggest that in central Utah such basic deepseated structures have continued to control and localize the younger reactivated versions of the diapiric 

folds. This would explain why these younger folds 

occupy the same sites and have the same trends as 

the older folds. Possibly each occurrence of crustal 

disturbance caused movement on one or more faults. 

Repeated movements along these faults have persisted at least from late Mesozoic time to the late 

Tertiary-Quaternary; each major movement has 

resulted in a major diapiric episode.

It may be that the salt, under confining pressure 

as a result of static load, finds relief when movement 

along a fault opens a passageway The salt, using the 

fault plane as a conduit, flows upward to form a long, 

near-linear salt diapir. In its upward movement the 

salt pushes up the overlying mudstones and shaly 

siltstones of the Arapien Shale and these, in turn, 

intrude and bow up the overlying sedimentary rocks. 

The end result is a faintly sinuous, near-linear, fanshaped diapiric fold whose general trend, determined 

by the core of salt, reflects the fault plane now obliterated by the transported mudstones and siltstones. 

Repeated reactivation of the same fault results in 

repeated renewal of the same causative salt diapir. 

This would explain the near-linear shape of the 

major folds, the collinearity between known fault 

zones and several of these major folds, and the fact 

that similar folds have formed repeatedly in the 

same sites and with the same trends during all three 

major diapiric episodes.

I suggest, therefore, that each of the major diapiric 

folds marks the position of a zone of weakness a 

preexisting fundamental fault that may have

formed in Precambrian time and that has been intermittently active ever since. These faults represent 

major flaws in the Earth's crust. The fact that the 

hingeline (the east margin of the Cordilleran geosynclinal basin), the Jurassic Arapien basin in which the 

salt accumulated, the transition zone, and the zone of 

diapiric activity all, at one time or another, occupied 

the same geographic area must be more than mere 

coincidence. Movement along these fundamental 

faults during Paleozoic time led to the development 

of the hingeline, and, during much of Early and 

Middle Jurassic time, to the development and subsequent growth of the saline basin of deposition in 

which the Arapien Shale with its contained salt and 

other evaporites accumulated. The striking break 

between the Colorado Plateaus and Basin and Range 

provinces probably reflects such fault movement.

If this interpretation is valid, each intrusive stage of 

each of the three major diapiric episodes reflects reactivation of these deep-seated faults. As all the diapiric 

folds display a similar pattern of development the 

postulated sequence of geologic events is the same for 

the Sanpete-Sevier Valley fold as it is for the Sevier 

Bridge Reservoir fold movement probably occurred, 

more or less in concert, along all the faults in the area 

in response to the regional stresses applied.

Presumably these faults first moved at some time 

after the Middle Jurassic, and were then used as 

conduits by the salt and intermixed mudstones of 

the Arapien Shale, which effectively obliterated the 

conduits. Subsequent tectonic pulses, probably once 

during the Late Cretaceous (post-Indianola Grouppre-Price River Formation), again during the Paleocene (post-North Horn Formation-pre-Flagstaff 

Limestone), and still again during the late(?) Oligocene or Miocene (post-Goldens Ranch Formation 

and post-Moroni Formation), triggered renewed 

movement along these faults, resulting in reactivation of the salt diapirs; this renewed diapiric movement further masked any evidence of the former 

faults.

Prior to the Paleocene, compressive forces from the 

west presumably caused movement along the faults. 

During the Late Cretaceous an eastward-directed 

thrust fault (stemming from the Sevier orogeny) may 

have triggered movement along these deep-seated 

faults and thus given rise to a diapiric episode. This 

may also explain the early Paleocene movement of 

the diapirs. Any movement along the faults since the 

Paleocene, however, must stem from the episode of 

crustal extension that began probably during late(?) 

Oligocene and Miocene time and that has persisted 

to the present.
132 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

ECONOMIC IMPLICATIONS

The combination of multiple episodes of salt intrusion and the resultant repeated upward movements 

of the Arapien Shale may have created a series of 

structural traps in which oil and gas could accumulate, and in which mineral-rich, possibly saline, solutions could deposit their mineral content.

OIL AND GAS

The likelihood of finding economic pools of oil is 

enhanced if an area contains source rocks, reservoir 

beds, and suitable structural and stratigraphic traps. 

These three required elements appear to exist in this 

part of central Utah, and all seemingly have been 

influenced or modified in one way or another by the 

recurrent episodes of diapirism.

SOURCE BEDS

At least three major stratigraphic units in the area 

are potential source rocks the Mancos Shale of Late 

Cretaceous age, the Manning Canyon Shale of Pennsylvanian and Mississippian age, and the Arapien 

Shale of Middle Jurassic age.

MANGOS SHALE

The Mancos Shale is widely exposed along the east 

flank of the Wasatch Plateau, in Castle Valley (E-7) 

(between the Wasatch Plateau and the west flank of 

the San Rafael Swell), and in the barren lowlands 

that lie at the base of the curving mass of the Book 

Cliffs. The shale extends westward beneath the 

Wasatch Plateau and, although not exposed, underlies 

much of Sanpete Valley. Kale's proposal (1972, p. 33) 

that Mancos sediments were deposited in a Sanpete 

Valley embayment of a shallow epicontinental seaway 

seems valid, and recent drilling has begun to give 

some indication of the thickness and extent of Mancos 

beds beneath Sanpete Valley

The Mancos forms a thick sequence in central Sanpete Valley, but it probably thins rapidly westward 

and southward; I suspect that it does not extend 

much farther west than a north-trending line through 

Wales (D-4) (along the east flank of the Gunnison 

Plateau), nor much farther south than Manti (E-4). 

Three exploratory test wells drilled in the central 

part of Sanpete Valley, near Moroni (D-4) (fig. 9), 

penetrated black marine sedimentary rocks of the 

Mancos Shale. Together the well data indicate that 

the Mancos thins rapidly westward. The easternmost

test (fig. 9), Hanson Oil Corporation's well Moroni 

AX-1 (SEV4 NWV4 sec. 14, T. 15 S., R. 3 E.) penetrated 

about 2,135 m (7,000 ft) of Mancos strata. About 2.4 

km (1V2 mi) to the west the Tennessee Gas Transmission Company's J.W Irons well No. 1 (C, SEV4NEV4 

sec. 16, T. 15 S., R. 3 E.) penetrated only about 1,070 

m (3,500 ft) of Mancos. The westernmost well, the 

Phillips Petroleum Company's well Price "N" (SEV4 

SEV4 sec. 29, T. 15 S., R. 3 E.), penetrated only about 

610 m (2,000 ft) of Mancos Shale. These data emphasize this westward shoaling of the Mancos sea.

The two westernmost wells also demonstrate the 

westward rise of the top of the Mancos. In the J.W. 

Irons well the Mancos top is at 6,268 ft, but in the 

next well to the west, the Phillips Price "N" well, the 

top is at 3,058 ft. Possibly this westward rise of the 

top of the Mancos may reflect the upward movement 

of the Sanpete-Sevier Valley salt diapir, which is 

west of the three wells and hugs the east flank of the 

Gunnison Plateau.

Witkind and Sprinkel (1982, p. 317) interpreted 

these well data to mean that the Mancos sea occupied much of the present site of Sanpete Valley and 

probably had its shoreline close to what is now the 

east flank of the Gunnison Plateau.

The Mancos penetrated by the test wells appears 

to be lithologically similar to its exposures to the 

east a series of black marine and paludal shales 

and brown sandstones seemingly an excellent 

source of hydrocarbons.

MANNING CANYON SHALE

The Manning Canyon Shale is a dark-gray to 

brownish-gray marine shale that contains interleaved 

lenses of brown quartzitic sandstone and bluish-gray 

limestone. It crops out in the Charleston-Nebo thrust 

plate; good exposures are east of Mona (B-3).

Although the Manning Canyon, like the Mancos, is 

rich in an oil-generative type of organic material, it 

may be an unsuitable source rock because it has been 

subjected to high temperatures and is thermally 

supermature. Poole, Claypool, and Fouch (1983), discussing episodes of petroleum generation in the 

northern Great Basin, indicated on their figure 5 that 

many of the Paleozoic rocks in central Utah have 

been subjected to temperatures of 300 °C (571 °F) or 

higher. Virtually all surface exposures of the Manning 

Canyon are included within the area of these elevated 

temperatures, which coincides, in general, with the 

extent of the Charleston-Nebo thrust plate.

On the east flank of the Lake Mountains, along the 

west side of Utah Lake, several quarries have been 

opened in the Manning Canyon, and several clay
ECONOMIC IMPLICATIONS 133

beds in the shale are quarried extensively for the 

manufacture of brick and other ceramic products. 

The high-temperature clay minerals pyrophyllite and 

rectorite are principal constituents in these Manning 

Canyon exposures (Hall and Schnabel, 1985), and 

their presence reemphasizes the possibility that the 

Manning Canyon Shale is too mature, at least in that 

specific locality, for consideration as a promising 

source rock.

ARAPIEN SHALE

The calcareous mudstones that make up the bulk 

of the evaporite-rich Arapien Shale may also be 

potential source rocks for oil. Many geologists have 

noted the close association between evaporites and 

petroleum. Halbouty (1967), for example, discussing 

the salt domes along the Gulf Coast, demonstrated 

that large amounts of petroleum are associated with 

these domes. Weeks (1961) listed a multitude of 

basins in which petroleum accumulations are closely 

related to evaporite deposits. Kirkland and Evans 

(1981) proposed a new explanation for this close relation. They suggested that although most organisms 

cannot survive high-saline (mesosaline) conditions 

characterized by brines in which the saline content 

ranges from 4 to 12 percent some algae not only can 

exist under these circumstances but literally thrive. 

Vast amounts of such algae, for example, are found 

in present-day basins marked by such mesosaline 

conditions. Upon death, the algae sink into the 

deeper waters of the basin, where they are buried by 

fine sediments and preserved as fine-grained carbonates rich in organic matter. These carbonates are 

immature source rocks which, upon maturation, produce petroleum.

It seems probable that the calcareous mudstones 

that make up most of the Arapien Shale developed 

under such mesosaline conditions. Presumably, 

marine waters from an open sea flowed periodically 

into the broad and extensive land-locked saline 

Arapien basin, which overlay much of central Utah 

during Middle Jurassic time. Continued evaporation 

resulted in increased salinity of the brines, and in 

time mesosaline conditions prevailed. If large 

amounts of organic matter did flourish in the Arapien 

basin, much of that organic matter must have been 

preserved in the bottom sediments, implying that the 

Arapien Shale is a possible source rock. Regrettably 

for the hydrocarbon potential, total organic carbon in 

the Arapien is low (R.J. Coskey, Forest Oil Company, 

oral commun., 1982); despite this, probably the one 

factor that detracts from the Arapien as a promising

source rock is its low maturation level (D.A. Sprinkel, 

Placid Oil Company, oral commun., 1983).

RESERVOIR BEDS

Of the various units suitable for the accumulation 

of oil and gas, the most promising would be those 

sandstone beds that make up the Ferron Sandstone 

Member of the Mancos Shale. The Ferron produces 

both hydrocarbon and carbon dioxide gas in the Clear 

Creek area to the east along the crest of the Wasatch 

Plateau (Walton, 1963). Comparable reservoir beds, 

however, could be any of the sandstone beds of the 

Emery Sandstone Member of the Mancos Shale. 

Likely, some of the units in the stratigraphic section 

may be good reservoir beds because they are highly 

fractured and not because of any inherent primary 

porosity.

POTENTIAL TRAPS

The stratigraphic column in this sector of central 

Utah can be visualized as consisting of two parts: the 

salt-bearing and younger beds, which extend from 

the base of the Arapien Shale to the surface, and the 

pre-salt beds, which include the Twin Creek Limestone and older strata. The salt-bearing and younger 

beds are locally intensely warped and form the many 

diapiric folds described in the previous sections of 

this Professional Paper. By contrast, the pre-salt 

units, although deformed, may not be as severely 

contorted as the overlying younger units. I believe 

that structural traps suitable for the accumulation of 

commercial amounts of oil and gas are in both 

sequences of rocks.

SALT-BEARING AND YOUNGER STRATA

The upward thrust of the salt diapirs may have 

resulted in a series of structural traps, the most 

favorable of which would be those confined to areas 

underlain by the Mancos Shale. I recognize four 

types of traps related to the diapiric folds: (1) those 

that are along the flanks of a diapiric fold, (2) those 

that are along the crest of a fold, (3) those that are 

wholly within a diapiric fold, and (4) those that 

resulted from the collapse of a fold.

Traps along the flanks of the folds. It seems probable that any diapirs formed beneath the Mancos 

Shale would have intruded and bowed up the Mancos. Such up warped beds, juxtaposed against the 

intrusive Arapien mass, would seem to be ideal 

structural traps for the accumulation of oil and gas.
134 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

The Arapien, in most localities a somewhat impervious mudstone, would serve as a barrier, trapping the 

oil and gas migrating up the upturned Mancos beds.

Traps along the crest of a fold. PL second type of 

potential trap may be those sedimentary beds that 

are draped across the crests of the diapiric folds. 

Examples are common in the Gulf Coast (Halbouty, 

1967), but there, the draped, deformed beds directly 

overlie the salt core of the salt domes. In central 

Utah, the salt has pushed up the mudstones and 

shales of the Arapien Shale and these, in turn, have 

bowed up the overlying sedimentary beds. I consider 

these domed sedimentary beds likely targets. 

Although they have been extensively eroded and 

almost completely removed from the crests of many 

of the major diapiric folds, in several places, the 

crests of some of the larger folds (such as the north 

end of the Sanpete-Sevier Valley fold) are still mantled by surficial deposits. Suitable targets may 

underlie these surficial deposits.

Traps wholly within a diapiric fold. Other potential oil traps may be wholly within a diapiric fold. 

The salt core of the diapir penetrated by the Argonaut-Federal well consisted almost completely of salt; 

little or no anhydrite was found. By contrast, various 

oil tests in this part of central Utah have drilled 

through an alternating sequence of salt and 

anhydrite. If the anhydrite beds in a diapiric fold 

were much fractured as a result of the repeated 

growth and collapse of that fold, they would have 

become quite porous. The salt, however, being more 

plastic and mobile, would retain its nonporous character. The result would be porous zones of anhydrite 

sealed by nonporous salt.

Traps resulting from collapse of a diapiric fold. 

Other structural traps may have formed as a consequence of the collapse of the diapiric folds. Although 

it is clear that some of the folds collapsed by gradual 

subsidence, much as shown in figure 60S, others 

appear to have collapsed along high-angle faults 

(fig. 6QA). These latter folds are ones that may be 

worthy of investigation, for the dpwnthrown limbs, 

either overturned or right-side-up (as, for example, in 

the ancestral Willow Creek (G-3) area, fig. 27), are 

probably sealed against the marginal faults, and thus 

become suitable traps for the accumulation of oil and 

gas. An inherent uncertainty in this type of trap, 

however, is how much the downthrown limb was 

fragmented. The limb was probably dropped thousands of meters, and most likely this occurred as 

many small spasmodic events; each event may have 

fractured and offset the once-continuous beds. 

Although the offset during each event may have been

minor, the cumulative effect of many such offsets 

may be sizeable.

Previously, I have suggested that the zero line of 

the Mancos Shale is approximately along a northtrending line through Wales (D-4) essentially along 

the east flank of the Gunnison Plateau and that the 

Mancos thickens eastward (p. 132). In my view, then, 

those diapiric folds that are east of the Gunnison 

Plateau are the most favorable; they underlie the 

Mancos Shale, a good source rock, which also contains adequate reservoir rocks. By contrast, those 

folds west of the plateau are probably somewhat less 

favorable; they are distant from suitable source 

rocks.

PRE-SALT STRATA

Although the most feasible oil traps appear to be 

related in one way or another to the salt diapirs, 

other traps, concealed beneath the masking blanket 

of diapirically folded rocks, may have formed in the 

older pre-s alt-bearing strata. Such traps seemingly 

would be unrelated to the diapiric deformation, 

which is confined to the salt-bearing and younger 

strata.

OVERTHRUST BELT AND SALT DIAPIRS

Salt diapirism may have had a profound effect on the 

position of oil pools, for whatever oil pools did form 

may have been displaced as a result of intrusion by the 

Arapien Shale. Much of the search for oil has centered 

on the overthrust belt, and overturned folds have been 

prime targets. In this sector of central Utah, for example, an overturned fold (possibly a remnant of the 

Charleston-Nebo thrust plate) well exposed along the 

west flank of the Gunnison Plateau in Chicken (D-2) 

and Pigeon (C-3) Creeks (east of Levan), was tested by 

Standard Oil of California's Levan Unit 1 (fig. 9) and 

by American Quasar's Chicken Creek Fed. No. 16-34. 

Ample evidence, however, demonstrates that the fold, 

after it was emplaced, was deformed and intruded by 

both gypsum beds and mudstones of the Arapien Shale 

(figs. 33, 34).

It seems clear that diapirism, throughout central 

Utah, has modified the thrust-related features. In the 

Gardner Canyon-Red Canyon (B-3) area, for example, the Arapien Shale broke, raised, and locally tilted 

the overturned fold that forms the upper plate of the 

Charleston-Nebo thrust (fig. 35). In the Thistle area, 

a northeast segment of the same overturned fold, plus 

its overlying mantle of Cretaceous and Tertiary units, 

has been arched to form an elongate north-trending 

upwarp (fig. 44). The causative agent appears to have
SUMMARY 135

been the Arapien Shale. If oil pools did form in overturned strata in this part of central Utah, they have 

probably been displaced during one or more episodes 

of salt diapirism. In essence, displacement of an oil 

pool may be a simple migration because of secondary 

deformation imposed on the original overturned fold.

MINERAL DEPOSITS

Base-metal deposits appear to be localized chiefly 

along the contact between the Arapien Shale and the 

country rock. For example, in the ancestral Willow 

Creek (G-3) area, a small mine known as the "Redmond silver mine" produced zinc ore intermittently 

from the time of World War I until about 1950, when 

it was closed owing to lack of ore. The mine, about 5 

km (3 mi) east of Redmond (G-3), is in a small 

cuesta that occupies parts of sees. 4 and 5, T. 21 S., 

R. 1 E., Sevier County, Utah. The bulk of the oxidized zinc ore (chiefly hydrozincite and smithsonite) 

is concentrated in shattered Green River rocks next 

to a narrow "fault zone" (Heyl, 1963, 1978) that follows the contact between Arapien Shale on the east 

and the Green River Formation to the west.

The geologic relations near the mine (Witkind, 

1981) can be interpreted in two ways: as a fault zone 

in which the block west of the fault has been 

downthrown, or as an intrusive contact between the 

Arapien Shale and the bowed-up Green River Formation (fig. 66). Although Heyl (1963, 1978), who examined the mine when it was open, favored the fault 

interpretation, I favor the second alternative because 

the Arapien Shale and Green River Formation relations here are identical to intrusive relations between 

these two units elsewhere in the area.

The source of the mineral-rich solutions is uncertain. They may stem from a volcanic center in the 

East Tintic Mountains, essentially the site of the 

East Tintic Mining District. Morris and Levering 

(1979, p. 68-69) and Laughlin and others (1969) 

noted a significant igneous episode in that area during the Miocene. Still another possibility is that 

Arapien saline brines may have furnished the zinc 

and lead minerals. Thus, the Arapien Shale may be 

the ultimate source of these ore deposits. Whatever 

their source, these mineral-rich solutions were then 

deposited in the fractured rocks of the Green River 

Formation.

SUMMARY

Multiple episodes of salt diapirism seem the most 

reasonable explanation for the intense, localized

deformation that marks the disturbed zone between 

the Colorado Plateaus and Basin and Range provinces in central Utah. The salt (halite), as well as 

other evaporites such as gypsum and anhydrite, is in 

the Arapien Shale of Middle Jurassic age. The salt, 

in large amounts and much of it now probably in the 

form of narrow, steep-walled diapirs, welled upward 

repeatedly, and in so doing forced the calcareous 

mudstones and gypsiferous shaly siltstones of the 

Arapien Shale to intrude, arch, and fold back the 

overlying sedimentary beds. The Arapien, thus, is 

best visualized as an intrusive sedimentary unit. 

Repeatedly forced upward by the reactivated salt diapirs, the soft and mobile Arapien mudstones have 

acted much like a viscous magma. Perhaps the best 

analogy is that of a hydraulic car jack. The salt represents the hydraulic fluid, the Arapien mudstones 

and shales, the bearing platform of the jack, and the 

uplifted younger strata, the car.

Upward movement of the concealed, elongate salt 

diapirs formed a series of generally north trending, 

subparallel diapiric folds, fan-shaped in cross section. 

Removal of the salt either by dissolution or extrusion 

resulted in failure of these folds. The general structural pattern, thus, resulted from the repeated growth 

and collapse of salt diapirs and those folds formed 

over them. Each time the salt diapirs reactivated, the 

newly formed folds occupied the same sites and followed the same trends as the earlier folds. The many 

signs of tectonic unrest angular unconformities, 

steeply tilted to overturned beds emanate from this 

recurrent growth and collapse of the reactivated salt 

diapirs and their overlying folds.

As a result of these recurrent disturbances, the 

Arapien has different "ages." Its depositional age is 

Middle Jurassic; its emplacement ages the geologic 

age of movements however, have changed repeatedly. In places, the Arapien deforms Cretaceous beds, 

elsewhere Eocene or Oligocene beds, and in several 

places it probably has deformed Pliocene or Quaternary beds. If one considers the age of the Arapien 

Shale to be solely Middle Jurassic, critical structural 

and economic relations are masked.

The contact relations between the Arapien Shale 

and the overlying beds are neither unconformities 

nor strip-thrusts, but rather intrusive contacts. I 

question whether the Arapien Shale is undisturbed 

anywhere in central Utah. The Arapien mudstones 

have been pushed about so many times by the contained salt that it seems unlikely that their present 

attitudes in any way reflect the attitudes of the sedimentary units that underlie them.

This recurrent movement of the salt emphasizes the 

critical fact that the stratigraphic section is divisible
136 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

R 1 E

EXPLANATION

1 KILOMETER

I 

1/2 MILE

T(Ja)

Arapien 

Shale

Coalesced alhr 

fan deposits

lluvial-

!* J

I Holocene Pleistocene, I QUATERNARY

Crazy Hollow 

Formation

and Pliocene(?)

Eocene

Middle 

Jurassic

TERTIARY

JURASSIC

 Intrusive contact Oblongs on intrusive unit

Strike and dip of inclined beds 

Zn Abandoned mine (zinc)

5 FEET

4000

A'

REDMOND FEET 

SILVER MINE r~ GOOD

Tch QTcf L 5500

TUa)

Possible concealed 

ore (zinc) masses 4000

.5 KILOMETER

1/2 MILE

FIGURE 66. Two alternative interpretations of the geologic relations 

near the abandoned zinc-producing "Redmond silver mine," sees. 

4 and 5, T. 21 S., R. 1 E., Sevier County, Utah. Base modified from 

U.S. Geological Survey 1:24,000 Redmond (1966). Contour interval 100 ft. A, Mine is in a small, isolated cuesta about 5 km (3 

mi) east of Redmond. Geologic relations are from Witkind (1981). 

B, One interpretation suggests that the Green River Formation 

("Eocene limestone") is downthrown against the Arapien Shale 

("Jurassic red shale") along a normal fault. The ore is localized

in the Green River adjacent to the fault. Illustration from Heyl 

(1963, 1978). Barbs show direction of relative fault movement. C, 

An alternative interpretation, which I favor, is that the area was 

deformed in the late(?) Oligocene by the intrusive action of the 

Arapien Shale. At this time, mineral-rich saline solutions moved 

up a brecciated zone formed along the intrusive contact between 

the Green River and the Arapien Shale and deposited their basemetal content along that contact. Bedding dashed within units; 

contacts dashed and queried to indicate uncertainty.

into two parts an upper part consisting of the saltbearing and younger strata, and an underlying, lower 

part consisting of the pre-salt older units. The intense 

localized deformation so visible on the surface is confined solely to the salt-bearing and younger units. The 

underlying pre-salt units, although deformed, have 

not been deformed as a result of the repeated salt 

movements.

Sequences of sedimentary formations thin toward 

the crests of the diapiric folds, and discrete units 

within these sequences either pinch out against the 

flanks of the folds or are anomalously thin across the 

crests of the folds. This depositional thinning of 

sequences of units suggests that the salt diapirs 

welled upward very slowly but continuously, and in 

so doing have acted like dynamic barriers, impeding
SUMMARY 137

deposition. All units, from the Twist Gulch Formation 

of Middle Jurassic age up to and including the Green 

River Formation of Eocene age, display this depositional thinning. I believe that even younger units 

thin toward the diapiric crests, but because of inadequate exposures, I currently lack evidence to demonstrate this. Probably, these salt diapirs are rising 

today at a slow, almost imperceptible rate. Rapid 

upward surges of the salt diapirs sporadically interrupted this persistent upward movement. Each surge 

marked the beginning the intrusive stage of a new 

diapiric episode. Once the surge ended, the slow, continuous rise of the diapirs resumed.

The growth and collapse of a diapiric fold occur in 

three interrelated stages that together make up a 

diapiric episode: An intrusive stage, during which a 

salt diapir surges upward rapidly and forcibly drives 

up the overlying mudstones of the Arapien Shale, 

which in turn push up and fold back the overlying 

strata to form a diapiric fold, fan-shaped in cross section; an erosional stage, during which the diapiric 

fold fails (presumably as a result of partial removal 

of the salt) and its remnants are then eroded to an 

almost featureless plain; and a depositional stage, 

during which younger sediments are deposited on the 

newly formed erosional surface. This depositional 

stage is ended by a renewed upward surge of the salt 

diapir the intrusive stage of the next younger diapiric episode.

I recognize at least three major diapiric episodes:

1. A Late Cretaceous to early Paleocene episode. 

The first clearly recognized diapiric episode probably 

began during the Late Cretaceous, after deposition of 

the Indianola Group, and ended in the early Paleocene after deposition of the North Horn Formation 

but before deposition of the Flagstaff Limestone.

2. An early Paleocene to late(?) Oligocene episode. 

The second episode probably began in early Paleocene time, after deposition of the North Horn Formation, and ended after the Eocene (possibly during 

the late Oligocene or Miocene) after deposition of the 

Goldens Ranch and Moroni Formations (of late 

Eocene to middle Oligocene age).

3. A late(?) Oligocene to Pliocene(?) episode. The 

third episode probably began during the late Oligocene or Miocene, after deposition of the Goldens 

Ranch and Moroni Formations, and may have ended 

during the Pliocene or Pleistocene. The evidence as to 

when this episode ended is inconclusive.

Some evidence suggests that a fourth, localized 

diapiric episode began and may have ended during 

the Pleistocene or Holocene.

The crests and flanks of many diapiric folds display a distinctive structural pattern that reflects the

three episodes of salt diapirism. In its simplest form 

this pattern consists of vertical to overturned beds of 

the Indianola Group at the base of an exposure. 

These upturned Indianola beds are unconformably 

overlain by a sequence of gently to moderately 

inclined Price River and North Horn strata. The 

Price River and North Horn Formations, in turn, are 

unconformably overlain by a stack of downwarped 

Tertiary beds, consisting chiefly of the Flagstaff, 

Colton, and Green River Formations. During the first 

diapiric episode the Indianola beds were pushed up 

to vertical or overturned attitudes. During the second 

episode the Price River and North Horn sequence 

also was bowed up, but in most places not as drastically as the Indianola beds. The crest of the up warp 

formed during this second episode coincides, more or 

less, with the crest of the previous upwarp. During 

the third episode the Flagstaff and younger Tertiary 

beds were deformed. Locally, these younger Tertiary 

strata have been bowed up to vertical attitudes, but 

in most places they are warped down and define the 

great monoclines that mark the Sanpete-Sevier 

Valley area. The general geologic pattern is best 

expressed by the phrase: Upturned Cretaceous and 

Jurassic strata overlain by downturned Tertiary 

beds. (See also p. 8.)

Two major angular unconformities, thus, are 

exposed in single outcrops one between the Indianola and the overlying Price River and North Horn 

sequence, and a second between the Price River and 

North Horn sequence and the overlying Flagstaff 

Limestone. These angular unconformities represent 

the periods of erosion during which the upturned, 

deformed beds were beveled to surfaces of low relief. 

As the strata above and below these angular unconformities are traced laterally, away from the folds, 

they gradually lessen in dip, and in distances as 

short as 0.8 km (V2 mi) are conformable.

Most likely, if exposures were adequate, the same 

structural pattern would be found in all the diapiric 

folds. The repetition of this pattern it has been 

found in the western, central, and eastern sectors of 

the area suggests that during each of the three 

major diapiric episodes all the salt diapirs in the 

area were reactivated more or less concurrently. This 

implies that the causative forces were regional in 

extent.

Although all the salt diapirs apparently acted more 

or less in unison during each of the three major 

diapiric episodes, some evidence suggests that during 

the late Tertiary or Quaternary, small cells of these 

larger salt diapirs reactivated independently and 

deformed parts of the previously formed diapiric folds. 

The Red Knolls (p. 30), west of Redmond, are
138 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

composed of the Arapien Shale and form topographic 

prominences that rise above more durable units. 

These knolls of the easily eroded Arapien must have 

been pushed up in the recent geologic past or they 

would have long since been eroded.

Overturned folds, part of the Charleston-Nebo 

thrust plate, were intruded, broken, tilted, and probably arched by the intrusive action of the Arapien 

Shale. The field evidence suggests that the 

Charleston-Nebo thrust plate was emplaced at some 

time after Middle Jurassic (Bathonian) time but 

before Late Cretaceous (Maastrichtian) time. Farther 

north, south of the Uinta Mountains, Bryant and 

Nichols (1988, p. 420) concluded, based on stratigraphic evidence, "* * *that major movement on the 

Charleston thrust occurred in Campanian time* * *."

Erosion partly destroyed the thrust plate during its 

eastward movement. Subsequently, the deeply 

eroded plate was buried beneath near-horizontal 

younger Cretaceous and Tertiary rocks. Later, salt 

diapirs, overridden and concealed beneath the thrust 

plate, welled upward and arched the thrust plate and 

its overlying mantle of Cretaceous and Tertiary sedimentary rocks. Since then, erosion has removed 

many of these younger sedimentary rocks, leaving 

their tilted remnants as a reflection of the former 

arched sedimentary cover.

Whatever oil pools formed in these overturned beds 

of the Charleston-Nebo thrust plate possibly were 

displaced or dissipated as a result of this diapiric 

activity.

The salt diapirs, and the diapiric folds formed over 

them, may be structurally controlled. The folds are 

elongate, faintly sinuous, north ward-trending 

up warps that parallel the major fault systems in the 

area. Two of the largest diapiric folds are collinear 

with major fault zones. Possibly, renewed movement 

along preexisting faults reactivated the salt diapirs, 

which then forced the Arapien mudstones and shales 

into the fault planes. These planes acted as conduits 

along which the mudstone moved upward toward the 

surface; in time, the rising mudstone effectively obliterated the fault planes. In this interpretation, the 

former trace of a fault plane is now expressed as a 

northward-trending, slightly sinuous belt of Arapien 

mudstone the core of a diapiric fold.

The forces responsible for the movement of the salt 

are unknown; important factors were probably buoyancy, static load, regional lateral compression, crustal 

extension, or some combination of these. The slow 

but persistent upwelling of the salt diapirs possibly 

reflects sedimentary loading in those areas adjacent 

to the diapirs. By contrast, the rapid upward surges 

of the salt diapirs may have been in response to fault

movement that was triggered, during pre-Paleocene 

time, by pulses of compression (thrust faulting) from 

the west, and during post-Paleocene time, by crustal 

extension. Static load was important, for it kept the 

salt under compression; the reactivated faults merely 

offered avenues of escape for the tightly confined, 

mobile salt.

The emplacement of the salt diapirs and the resultant upward bowing of the intruded rocks may have 

created structural traps between the diapirs and the 

country rock in which oil and gas could accumulate. 

The most promising sites for such traps would be 

where the diapirs deformed the Mancos Shale.

Base-metal deposits, probably deposited from 

mineral-rich, possibly saline solutions, may be concentrated along parts of the contact between the 

country rock and the intrusive mudstones of the 

Arapien Shale.

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INDEX

{Italic numbers refer to illustrations]

Aerial views of east flank Gunnison Plateau 39 

Aggie Creek ......................................................92

Alignment between faults and folds............. 130

Alternative interpretations ("Redmond

Silver Mine").............................. 136

Ancestral course of Willow Creek ........... 29, 31

Ancestral San Pitch River ..............................24

Ancestral Sevier Lake .....................................24

Ancestral Sevier River ....................................24

Ancestral surface, geologic pattern ......127, 128

Ancestral Willow Creek ..................29, 109, 125

Ancestral Willow Creek area ..... 20, 41, 51-55,

67, 100, 119, 134, 135 

Ancient Ephraim fault ....................................23

Angular unconformities ..................11, 135, 137

Anhydrite .................................................18, 135

Anomalous depositional thinning .............57, 63

Anschutz Corporation's Monroe Fee

No. 1 well......................................102

Arapien basin ..................7, 11, 23, 25, 131, 133

Arapien deformation .......................................86

Arapien embayment ........................................23

Arapien salt .......................................................8

Arapien Shale ............................................ 16-27

Age..........................................................3, 25

Areal extent...............................................20

Aspects ...................................................... 17

Contact relations ...................................... 19

Contained salt ..........................................23

Deformed beds ..........................................28

Depositional age ...............................25, 135

Geologic aspects......................................... 18

Gypsum in....................................18, 19, 135

Intrusive aspects ...........................27, 30, 85

Lithology..............................................18, 23

Lower contact............................................ 19

Nomenclature............................................ 16

Oil potential............................................. 133

Thickness................................................... 25

Upper contact ............................................20

Arapien sill....................................................... .91

Arapien Valley ...........................................37, 38

Argonaut-Federal well ......................23, 24, 134

Autochthonous plate ..................................12, 13

Axtell Formation .......................................29, 55

B

Barton No. 1 well, Placid Oil Company..........25

Base-metal deposits .......................................138

Basement rocks ................................................ 11

Basin and Range province ..............2, 8, 11, 135

Bennie Creek area................. 104, 105, 106, 107

Billies Mountain...............................................84

"Billies Mountain" area.................29, 84, 85, 86

Birch Creek ......................................................74

Birdseye ............................................................92

Black Canyon ......................................... 104, 111

Block faulting ................................................... 37

Book Cliffs ...................................................... 132

Bouguer gravity anomaly map .....................103

Boundary Ridge Member of Twin Creek

Limestone ............................. 23, 25

Brines ..............................................................133

Buoyancy ........................................................138

Calcite ...............................................................18

Canyon Mountains .............................. 11, 21, 23

Carmel Formation .................................... 20, 21

Castle Valley .............................................. 9, 132

Causative forces of deformation.....................137

Cedar Hills ............................................8, 10,81

Cedar Mountain Formation ....3, 18, 50, 75, 77,

86, 93, 95, 96, 109, 111, 124 

Cedar Mountain road ......................................51

Center-field ........................................................21

Charleston thrust fault.......................................8

Charleston-Nebo overthrust ..........................101

Charleston-Nebo thrust fault .................8, 9, 69

Charleston-Nebo thrust plate ........... 12, 20, 21,

29, 38, 69, 70, 74, 75, 81, 83, 

92, 93, 104, 105, 132, 134, 138 

Chevron U.S.A.

Chriss Canyon well ........................... 24, 25

Salina Unit No. 1 well .............................24

Chicken Creek area .................... 18, 19, 20, 134

Chriss-Mellor graben .................................. 6, 76

Christianburg ...................................................41

Clear Creek area ............................................133

Code of Stratigraphic Nomenclature ..............16

Collapse of diapiric folds .................. 8, 119, 120

Collapse structure ................................. 120, 121

Colorado Plateaus province ........2, 8, 9, 11, 135

Colton Formation .........................29, 51, 63, 86,

98, 99, 109, 137 

Complex structural relations (Sevier Bridge

Reservoir diapiric fold) ................61

Conduit for diapiric sediments .....................129

Contained salt, Arapien Shale ........................23

Cordilleran geosyncline ...................................11

Crab Creek .......................................................92

Craton, Paleozoic ............................................. 11

Crazy Hollow Formation .............29, 35, 51, 55,

63, 99, 100, 124 

Cross section of typical diapiric fold ............128

Crustal extension ...........................................138

Cuesta north of Redmond ........................ 31, 33

Curtis Formation .............................................18

D

Dairy Fork graben ........................38. 96, 97, 98

Deformed gravels near Gunnison

Reservoir.................................................... ...61

Delta .......................................................... 23, 24

Depositional age (of Arapien Shale) ...............25

Depositional stage (of diapiric

episode).............................................. 124, 137

Depositional thinning .............................. 63, 76,

107-117, 119, 136

Pole Creek diapiric fold ....................... ....Ill

Sanpete-Sevier Valley diapiric fold....... 109

Sevier Bridge Reservoir diapiric

fold....................... 109-111

Thistle Creek diapiric fold ......................111

Diagrammatic cross sections of Red Rocks

area................................................. 45

Diagrammatic sketches of Red Canyon area,

Valley Mountains.......................... 68

Diapiric activity ............................................. 131

Diapiric core ......................... 12, 13, 37, 38, 130

Diapiric deformation in Thistle area.............. 92

Diapiric episodes .. 124, 126-127, 129, 131, 137 

Diapiric folds (salt-cored anticlines) ....... ...3, 12,

13, 21, 25, 28, 37, 57, 67, 93, 102, 105,

108, 117, 119, 124, 125, 129, 130,

131, 134, 135, 136, 137, 138

Collapse ................................ 119-121

Cross section.................................. 13

Distribution pattern...................... 36

Localization .......................... 129-131

Diapiric processes .......................................... 117

Causative forces................... 129-131

Cyclical aspects............................ 129

Geologic pattern................... 125-129

Diapiric shale .................................................. 12

Diapiric sheath .......................................... 12, 13

Diapiric stage ........................................ 124, 129

Diapiric stages and episodes ........................ 124

Diapiric structures .................................... 18, 27

Diapirism ................................................... 27-29

Dinoflagellate assemblages ............................ 25

Disturbed zone ........................................ 11, 135

Dixel Resources well ................................... .....25

Dog Valley .......................................................... 9

Dome near ancestral Willow Creek ............... 29

Dry Canyon ...................................................... 28

Dry Hollow ...........................................81, 83, 96

Dry Hollow diapiric fold ...............38, 81, 83, 95

Development........................................ 86, 87

Dry Mountain................................. 107, 118, 119

Dynamic ancestral high ................................ 108

Dynamic barriers .......................................... 136

E

East Fork of Sanpete Valley .....................98, 99

East Gunnison monocline .......................51, 124

East Tintic Mining District .......................... 135

East Tintic Mountains .................................. 135

Eastern Sevier Valley ..................................... 33

Economic implications of diapirism.............. 132

Elongate salt structures ................................. 37

Elsinore ...................................................... 21, 23

Emery Sandstone Member of the

Mancos Shale ........................................ 133

Emplacement ages of the Arapien

Shale.....................................................25, 135

Entrada Sandstone........................................... 18

Ephraim ..................................................... 38, 98

142
INDEX 143

Erosional escarpment ..............9, 10, 21, 29, 84,

92, 93, 104 

Erosional stage of diapiric episode....... 124, 137

Escarpment fault ............................................ 76

Evaporites ....................................................... 13

Extensional tectonism .................................... 35

Fairview ........................................................... 98

Fairview diapirf?) ..................................... 98, 99

Fairview diapirid?) fold ................... 38, 98-100

Fault plane used as conduit.................. 130, 131

Fault zone ...................................................... 130

Fayette ..................................................... 38, 130

Ferron Sandstone Member of the

Mancos Shale .......................... 133

Flagstaff Limestone ........ 20, 29, 41, 45, 51, 53,

62, 85, 92, 93, 98, 101, 107,

109, 111, 124, 128, 137

Footes Canyon ........................................... 69, 81

Footes Canyon diapirid?) fold ..........21, 38, 75,

81-83, 105, 107 

Fountain Green ......................................... 38, 41

Freedom ........................................................... 38

G-24 well (Union Oil Company) ................... 98

Gardner Canyon ....................................... 70, 74

Gardner Canyon-Red Canyon area ............. 134

General stratigraphy ................................ 12-16

Geologic maps of areas discussed in the

report................................................ 7

Geologic pattern .................................... 125-129

Geologic relations

Along both flanks of Gunnison Plateau 123 

Near Middle Fork Pole Creek.................. 80

Near "Redmond Silver Mine"................ 736

Geology near

Black Canyon................................... 770, 111

Dry Mountain.................................. 118, 119

Head of Payson Canyon.......................... 776

Head of Santaquin Canyon.....................773

Red Lake..................................................775

Wales, Utah............................................... 52

Geology of

Ancestral Willow Creek Area ................. 58

Dry Hollow area ...................................... 84

Hjorth Canyon area.................................. 95

Little Clear Creek area ..................... 96, 97

Pole Creek-Hop Creek area,

Cedar Hills......................... 77, 78

Red Rocks area ........................................ 42

Salt Creek area ...................................... 708

Sixmile Creek Canyon area .................... 46

Thistle area .................................. 88, 89, 90

Giraffe Creek Member of

Twin Creek Limestone............ 19

Goldens Ranch Formation .......67, 75, 101, 124

Gordon Creek well........................................... 21

Grabens ............................................... 11, 21, 76

Gravity data .......................................... 102-104

Great Basin Section of Basin and

Range province ...................... 11, 132

Great Salt Lake .............................................. 24

Great Western Salt Company ........................ 23

Greater Scipio Valley .................................... 101

Green River Formation .........20, 23, 29, 31, 84,

92, 96, 98, 99, 100, 109, 113, 117, 135, 137 

Growth and collapse of diapiric folds.... 117-121

Gulf Coast ................................................12, 134

Gunnison .......................21, 38, 41, 57, 102, 130

Gunnison Plateau (San Pitch Mountains)..... 10,

11, 18, 19, 21, 24, 27, 28, 29, 37, 38, 41,

4 8, 50, 69, 75, 76, 77, 81, 98, 104, 109,

121, 123, 124, 128, 130, 132, 134

Gunnison Reservoir area ..... 41, 55-57, 61, 125

Gypsum............................................................. 19

Gypsum Spring Member of Twin Creek

Limestone................................. 19, 23

H

Halite (salt).......................................................24

Halo-kinesis .............................................25, 129

Halo-tectonism .........................................25, 130

Hanson Oil Corporation's Moroni

A-l well........................................ 132

Hanson wells ...................................................25

High-saline conditions, Arapien Shale ......... 133

Hingeline (Paleozoic)................................ 11, 131

Hjork Creek dome ...........................................93

Hjorth Canyon area..............................93, 95, 96

Hjorth Canyon diapiric fold ................38, 93-96

Hjorth Canyon salt diapir ..............................95

Hogbacks in eastern Sevier Valley ................33

Hop Creek ..................................................81, 82

Hop Creek Ridge .......................................81, 82

Howard 1-A WXC well (Placid Oil

Company)............,...................24, 101

Hydraulic car jack (analogy)............................ 27

I

Index map of central Utah ...............................5

Indian Hollow ..........................................98, 100

Indianola ...............................8, 9, 21, 38, 93, 98

Indianola Group ........29, 41, 50, 57, 62, 75, 77,

81, 83, 93, 95, 96, 109, 121, 124, 129, 137 

Ingram Canyon ................................................74

Intrusive sedimentary beds ......................12, 27

Intrusive stage of diapiric episode........124, 137

Iranian diapirs .................................................24

Isoclinal fold, Red Rocks area .........................42

Isopach map of salt deposits............................ 24

J.W Irons well No. 1 ..................................... 132

Japanese Valley .......................................38, 101

Joes Valley graben ......................................... 119

Juab ......................................................8, 19, 102

Juab County .................................................... 20

Juab Valley ...........................................9, 24, 69,

100, 102, 104, 121, 124 

Jurassic marginal basin ..................................23

K

KOA Campground area ......................18, 77, 81

Lake Bonneville, ancestral.............................. 24

Lake Fork ...................................................83, 98

Lake Mountains ............................................ 132

Landslide and earthflow phenomena..............99

Leamington trans-current fault .......................9

Leeds Creek Member of Twin Creek

Limestone.................... 19, 20, 23, 25

Levan .....................................9, 21, 69, 104, 134

Levan area ..................................................... 104

Levan diapir .............................................. 69, 76

Levan diapiric core ................................... 69, 74

Levan diapiric fold .................21, 38, 57, 69-70,

74, 75, 76, 77, 81, 104, 130 

Levan Unit 1 well (Standard Oil of

California).............................. 69, 134

Linear upwarps ............................................... 12

Little Clear Creek .........................38, 95, 96, 98

Little Clear Creek diapiric fold .............. 38, 95,

96-98, 129 

Little Salt Creek .................................24, 69, 75

Loafer Mountain .............................92, 104, 107

Locality file (Index map of central Utah)..... 6-7

Localization and causative forces ................ 129

Long Ridge .................................................... 100

M

Major fault zones .......................................... 130

Major test wells in central Utah ................... 26

Mancos Shale ................................ 132, 133, 134

Oil potential............................................ 132

Manning Canyon Shale ........................ 132, 133

Oil potential............................................ 132

Manti ...........................................21, 38, 99, 132

Maple Canyon area ....................................... 128

Maturation level ........................................... 133

Mayfield .........................................18, 33, 38, 57

Mesocordilleran anticline ............................... 23

Micrite, Arapien Shale .................................... 18

Middle Fork Pole Creek .......20, 77, 80, 81, 111

Middle Jurassic (Callovian) (Twist Gulch

Formation)..................................... 18

Middle Rocky Mountains province ................... 8

Milburn ........................................................ 9, 98

Mills Gap ....................................................... 101

Mineral deposits ........................................... 135

Minor structures ............................................. 29

Mobilization of plastic mudstone beds ............ 3

Mona .......................................................... 9, 132

Monoclines ..................................... 121-124, 137

Paired, facing.................................. 121-124

Monroe 13-7 well (Placid Oil Co.)............ 25, 69

Monroe Fee No. 1 well (Anschutz Corp.)..... 102

Mormon temple in Manti................................ 99

Moroni ................................................38, 93, 132

Moroni AX-1 well (Hanson Oil Corp.)......... 132

Moroni Formation ........................75, 77, 81, 84,

92, 95, 96, 124, 137 

Moroni wells .............................................. 25, 41

"Mother bed" of salt .............................. 105, 129

Mount Nebo ...................................................... 2

Mount Pleasant ............................................... 98

Multiple episodes of orogeny ............................ 3

Multiple episodes of salt diapirism ............... 13

N

Navajo Sandstone (Nugget Sandstone)......... 19,

29,74 

Nebo Loop Road .............................................. 77

Nebo thrust fault .............................................. 8

Nephi ............................8, 9, 18, 24, 70, 81, 130

Ninemile Reservoir ................................... 35, 37

North American Stratigraphic Code ............. 16

North Fork Salt Creek ............................. 18, 24

North Horn Formation.... 29, 38, 76, 84, 85, 86,

92, 93, 95, 96, 98, 107, 109, 111, 124, 137 

North San Pitch River Valley diapir ....... 98, 99
144 SALT AND THE STRUCTURAL DEVELOPMENT OF CENTRAL UTAH

Northeast flank Valley Mountains ................. 62

Northern Tunisia, salt structures.................. 129

Nugget Sandstone (Navajo Sandstone).....19, 92

O

Oak Creek ........................................................98

Oil and gas, accumulation of ..................16, 132

Oil and gas, source beds.................................132

Oquirrh Group ...........................................70, 74

Orogenic forces .................................................29

Osiris Tuff ........................................................30

Overthrust belt ..............................................134

Painted Rock Canyon ....................................128

Paired, facing monoclines .............100, 121-124

Paleo-high ........................... 81, 83, 92, 113, 117

Paradox Basin ...................7, 121, 129, 130, 131

Paxton No. 1 test well

(Placid Oil Company).....................21

Pavant Range............................... 11, 21, 23, 101

Payson Canyon area........21, 104, 105, 107, 116

Phillips Petroleum Company's

Price "N" Well ............24, 25, 41, 132

Photographic overviews near erosional

escarpment............................106, 107

Photographs of Thistle area ...........................90

Physiographic provinces in central Utah ........3

Piercement structures .....................................12

Pigeon Creek ............................................19, 134

Pigeon Creek area ...........................................69

Placid Oil Company

Howard 1-A WXC well .....................24, 101

Monroe 13-7 well ................................25, 69

Paxton No. 1 test well...............................21

WXC-USA 1-2 well................................ 102

Pole Creek area...........................................77, 81

Pole Creek diapiric fold ............................21, 38,

69, 77-81, 83, 111 

Potential oil and gas traps............................. 134

Overthrust belt........................................ 134

Pre-salt strata.......................................... 134

Salt-bearing and younger strata............133

Salt diapirs ..............................................134

Pre-salt beds ........................... 16, 133, 134, 136

Preuss Sandstone ............................................21

Price "N" well (Phillips Petroleum

Company)...................24, 25, 41, 132

Price River and North Horn sequence .....45, 62

Price River Formation ................... 9, 38, 41, 45,

50, 67, 75, 109, 111, 121, 137 

Provo ......................................................9, 23, 83

Pyrophyllite ....................................................133

R

Rectorite .........................................................133

Red Canyon area

(Southern Wasatch Range).......... 20,

57, 63, 70, 74, 75, 101, 111, 119,

123, 124, 127, 128

Red Canyon area, Valley Mountains .............63,

66, 68, 99 

Red Knolls ................................................30, 137

Red Knolls area ................................................30

Red Lake ........................................104, 107, 115

Red Rocks area

(Christianburg) ..........28, 41, 45, 50,

51, 75, 117, 124, 127, 128

Red Rocks-Sixmile Canyon area .......41, 51, 55

Redmond .......................... 18, 21, 23, 24, 30, 31,

57, 67, 102, 111, 130, 135, 137 

Redmond diapiric fold ........................21, 31, 38,

57, 67, 113, 130 

Redmond Hills anticline ......................... 57, 113

"Redmond Silver Mine".......................... 135, 136

Rees Flat ....................................................74, 75

Regional lateral compression ....................... 138

Reservoir beds, oil and gas............................ 132

Rich Member of the Twin Creek

Limestone...................................... 19,

23,25 

Richfield .....................................21, 38, 102, 130

Rim syncline .................................................. 129

Rock salt (halite) ...................................3, 13, 18

Round Valley ...........................................21, 101

St. George........................................................... 3

Salina ..... 18, 20, 23, 24, 30, 33, 38, 51, 57, 101

Salina Canyon .................................................. 23

Salina Creek Canyon ................................ 9, 113

Saline basin ............................................. 11, 131

Saline solutions ............................................. 138

Salt (halite)............................................. 119, 135

"Salt anticlines" (salt-cored anticlines) .......... 2,

37, 129 

Salt-bearing and younger strata .......... 133, 136

Salt-cored anticlines (diapiric folds)................ 3,

12, 20, 131 

Salt cores ......................................................... 12

Salt Creek ....................... 18, 21, 24, 69, 81, 104

Salt Creek Canyon ............................18, 21, 107

Salt Creek Fanglomerate ............................... 77

Salt diapir ........................ 12, 13, 16, 23, 24, 25,

45, 117, 119, 124, 129, 131, 135, 138 

Salt diapirism ..................................3, 8, 76, 135

Salt diapirs ................. 12, 16, 25, 119, 135, 138

Salt-generated diapiric folds ............................ 3

Salt-generated structures .........................3, 105

Salt Spring Creek............................................. 24

Salt-cored dome................................................ 12

Salt-stock families.......................................... 117

Salt stock (salt diapir)................................... 117

Salt stocks......................................................... 25

Salt structures.................................................... 8

Salt structures in northern Germany........... 129

Salt structures in northern Tunisia.............. 129

Salt walls.................................................. 12, 102

San Pitch Mountains (Gunnison Plateau)..... 10

San Pitch River .....................................9, 10, 57

San Rafael Group ...................................... 18, 20

SanRafael Swell ........................................... 132

Sanpete County ............................................... 23

Sanpete-Sevier rift.......................................... 23

Sanpete-Sevier Valley and

Redmond anticlines..................... 113

Sanpete-Sevier Valley anticline............... 29, 38

111, 113, 115 

Sanpete-Sevier Valley area ...... 3, 9, 12, 20, 37,

55, 76, 111, 115, 124, 137 

Sanpete-Sevier Valley diapiric fold ........21, 29,

38-57, 67, 98, 109, 111, 113,

129, 130, 131, 134

Sanpete-Sevier Valley salt diapir.....55, 56, 132

Sanpete Valley............................ 8, 9, 21, 38, 48,

57, 62, 98, 102, 109, 124, 132 

Sanpete Valley embayment .......................... 132

Santaquin .................................................. 9, 105

Santaquin Canyon ........................ 104, 107, 113

Scipio ..............................................................101

Scipio Lake ..................................................... Ill

Scipio Valley ................................................... 101

Scofield Reservoir .............................................21

Seismic reflection profiles .................................8

Seismic surveys .................................................8

Selenite crystals in Arapien Shale..................18

Sevier Bridge Reservoir (Yuba Lake) ...........101

Sevier Bridge Reservoir area............ 57, 69, 102

Sevier Bridge Reservoir diapiric fold ............38,

57-69, 109, 111, 129, 131

Sevier Bridge Reservoir salt diapir . 63, 69, 102 

Sevier County, Utah ......................... 20, 23, 135

Sevier Desert ...................................................23

Sevier fault zone ............................................130

Sevier orogeny ...........................................35, 76

Sevier River ...............................................9, 101

Sevier thrusting ...............................................55

Sevier Valley ............................8, 19, 21, 30, 37,

38, 101, 102, 104, 121, 124, 130 

Side Canyon .....................................................98

Sigurd ...............................................................38

Sixmile Canyon .......99, 109, 119, 121, 123, 127

Sixmile Canyon area ......................... 41, 45, 48,

62, 109, 124, 127 

Sixmile Canyon Formation ...........................127

Sixmile Creek canyon ......................... 29, 48, 50

Skinner Peaks ............................................75, 76

Skinner Peaks area ...................................75, 81

Sliderock Member of Twin Creek

Limestone........................... 19, 23, 25

Small-scale features of Arapien Shale

(photographs).................................. 33

Smiths Reservoir .............................................98

Soldier Creek ............................9, 83, 84, 85, 86

Soldier Creek Canyon .....................................83

Source rocks (oil and gas)..............................132

South Valley ................................................... 101

South wall of Red Canyon (Southern

Wasatch Range)..............................76

Southern Wasatch Range .......8, 9, 70, 105, 107

Southwest flank of the Sevier Bridge

Reservoir diapiric fold ..................64

Spanish Fork Canyon ........................... 9, 85, 86

Spanish Fork River ...................................84, 92

Standard Oil of California Levan

unit 1 well...............................69, 134

State No. 1 well ...............................................25

Static load ...................................................... 138

Static topographic high .................................108

Sterling ............8, 18, 23, 28, 29, 38, 41, 57, 111

Stratigraphy ...............................................12-26

Strip-thrust fault ......................................35, 135

Structural and stratigraphic traps ...............132

Structural complexity and diapiric folds ........63

Structural pattern of central Utah ..............125

Structural traps (oil and gas)........................133

Summerville Formation ..................................18

Taylor Fork .................................................... 104

Taylor Fork area............................................. 107

Temple Hill, Manti ..................................99, 100

Tertiary thrusting ............................................37

Test wells in central Utah.............................. ..26

The Washboard ................................................69

Thickness of salt.............................................. 24

Thistle ........................................8, 9, 19, 20, 21,

23, 29, 81, 83, 111, 117 

Thistle area ...........83, 84, 92, 93, 107, 111, 134

Thistle Canyon fault .......................................92
INDEX 145

Thistle Creek .......................84, 86, 92, 104, 107

Thistle Creek diapiric(?) fold .................. 21, 38,

83-93, 104, 105, 107, 111 

Thistle landslide ....................................... 29, 86

Transition zone ................................... 2, 11, 131

Twelvemile Canyon Member of the

Arapien Shale.......................... 16, 27

Twelvemile Creek ........................................... 57

Twin Creek Limestone ................ 19, 20, 23, 29,

69, 70, 71, 74, 86, 91, 92, 119, 133 

Boundary Ridge Member......................... 19

Giraffe Creek Member ............................. 19

Gypsum Spring Member ......................... 19

Leeds Creek Member ............................... 19

Rich Member............................................. 19

Sliderock Member..................................... 19

Watton Canyon Member.......................... 19

Twist Gulch Formation .........16, 18, 20, 50, 51,

77, 86, 93, 95, 96, 111, 117, 124, 137 

Aspects (photographs).............................. 17

Thickness .................................................. 18

Twist Gulch Member of Arapien Shale.......... 16

U

Uinta Mountains ..................................... 23, 138

Union Oil Company's No. G-24 well.............. 98

Unnamed hill near Ninemile Reservoir......... 35

USGS Professional Paper 1170-F ................ 104

U.S. Highway 6 and 89 ................................... 29

Utah, central, index map .................................. 4

Utah, central, physiographic provinces............ 3

Utah Lake ..................................................... 132

Utah State Highway 132............................... 101

Utah Valley......................................................... 8

Valley Mountains ................... 10, 21, 23, 24, 27,

30, 38, 57, 61, 67, 101, 102,

109, 111, 117, 119, 123, 124, 127, 128

Valley Mountains diapirid?) fold ...38, 101-102

Valley Mountains monocline ................... 63, 69,

98, 99, 101, 119, 121 

Vertical aerial photographs of

Temple Hill area, Manti.............. 100

Views

Along east flank Dry Mountain..... 106, 107

Along west valley wall of

Thistle Creek ....................... 106, 107

In Salt Creek Canyon..................... 106, 107

Near head of Bennie Creek............706, 107

Near head of Dry Hollow.......................... 86

Near head of Payson Canyon......... 106, 107

Near Red Lake................................ 706, 107

Ancestral Willow Creek area ..................57

Volcanic gravels of Gilliland (1948) ................30

V-shaped dissolution synclines ..................... 121

V-synclines ..................................................... 121

W

Wales ..............................................121, 132, 134

Wales Canyon ..................................................50

Wales Gap .......................41, 50, 55, 57, 98, 109

Wasatch and Valley Mountains

monoclines .............................. 69, 99

Wasatch fault zone .....................9, 11, 105, 130

Wasatch monocline ........... 9, 37, 48, 51, 62, 64,

98, 99, 100, 101, 119, 121, 124 

Wasatch Plateau ........... 8, 9, 21, 23, 38, 48, 51,

76, 99, 101, 109, 119, 123, 132, 133 

Wasatch Range ............................................8, 10

Watton Canyon Member of

Twin Creek Limestone...... 19, 23, 25

West Fork of Sanpete Valley .......................... 98

West Gunnison monocline ....................... 69, 75,

76, 121, 124 

West Hills ..................... 9, 21, 24, 100, 101, 121

West Hills diapiric(?) fold ............... 38, 100-101

West Hills monocline ............................ 121, 124

Western Interior of the United States .......... 37

White Hills ....................................18, 37, 51, 57

Willow Creek ................................................... 51

Willow Creek gap ................................41, 51, 53

Willow Creek road .................................... 53, 55

Yuba Dam ..............................23, 62, 67, 69, 101

Zechstein salt .......................................... 12, 102

Z-fold ................................................................ 28

Manuscript approved for publication March 13, 1992 

Published in the Central Region, Denver, Colorado 

Edited by Lorna Carter 

Photocomposition by Marie F. Melone 

Graphic design by Patricia L. Wilber 

Cartography by Henry Williams

A U.S. GOVERNMENT PRINTING OFFICE: 1994-673-046/86056
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