i 

The Upper Part of the Upper 

Triassic Chinle Formation 

and Related Rocks, 

. Southeastern U tab and 

Adjacent Areas 

By ROBERT B. O'SULLIVAN 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 644-E I 

Prepared in cooperation with the Bureau of 

Indian Affairs and the Navajo Tribe 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970 
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary 

GEOLOGICAL SURVEY 

William T. Pecora, Director 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 40 cents {paper cover) 
CONTENTS 

( Pa~ 

Abstract----------------------------------------------------------------------------------- E1- Introduction _____________________________________________ -·-'-·- _ _ _ _ _ _ _ __ _ _ _ _ __ _ _ _ _ _ _ __ _ _ _ _ _ _ _ 1 

StratigraphY------------------------------------------------------------------------------- 1 

Stratigraphic relations in southern Monument Valley________________________________________ 3 

Stratigraphic relations in northeastern Monument Valley_____________________________________ 4 

Owl Rock Member_._ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 5 

Reddish-orange siltstone member_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 5 

Mule Ear ledge_____________________________________________________________________ 5 

Hite Bed--------------------------------------------------------------------------- 5 

Unconformity at the base of the Hite Bed_____________________________________________ 9 

Division A------------------------------------------------------------------------- 10 

Stratigraphic relations in north we& tern Monument Valley____________________________________ 10 

Regional relations____ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 11 

Grain size__________________________________________________________________________________ 12 

Clay minerals----------------------------------------------------------------------------~- 13 

Fossils------------------------------------------------------------------------------------- 13 

Chinle Formation-Glen Canyon Group contact__________________________________________________ 13 

PaleogeographY----------------------------------------------------------------------------- 17 

Conclusions________________________________________________________________________________ 21 

References cited____________________________________________________________________________ 21 

ILLUSTRA'TIONS 

Pa~ 

FIGURE 1. Map of northeast Arizona and adjacent areas_________________________________________ E2 

2. Nomenclature of Chinle Formation and related rocks of Gregory (1917) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 3 

3. Graphic sections and stratigraphic diagram showing correlation ·of upper part of Chinle 

Formation and related rocks along Comb Ridge__________________________________ 6 

4. Photograph of Upper Triassic rocks along Comb Ridge________________________________ 8 

5. Photograph of west wall of Comb Ridge_____________________________________________ 8 

6. Generalized diagram showing stratigraphic relations of Chinle Formation and related rocks_ 12 

7. Generalized fence diagram of Chinle Formation and related rocks_______________________ 14 

8. Paleogeographic map of northeast Arizona and adjacent areas __________ .:._______________ 19 

III 

J., 
-.' 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

THE UPPER PART OF THE UPPER TRIASSIC 

CHINLE FORMATION AND RELATED ROCKS, 

SOUTHEASTERN UTAH AND ADJACENT AREAS 

BY RoBERT B. O'SULLIVAN 

ABSTRACT 

In northeastern Arizona the Owl Rock Member of the Chinle 

Formation is overlain by a unit of reddish-orange very fine 

grained sandstone and siltstone. Previously, this reddish-orange 

unit has been referred to informally as division A of the Chinle 

Formation. Division A is rerognized throughout northeastern 

Arizona; stratigraphic studies show that the unit extends not 

more than 8 miles into southeastern Utah. In different parts of 

northeastern Arizona, division A is named the Rock Point Member of the Wingate Sandstone or the Church Rock Member of 

the Chinle Formation. In southeastern Utah and parts of northeastern Arizona a fluviatile sandstone-the Hite Bed-is at the 

top of the Chinle Formation, and stratigraphic studies show it 

to be equivalent to division A. In much of southeastern Utah a 

unit of reddish-orange very fine grained sandstone and siltstone 

is present below the Hite Bed and is also called Church Rock 

Member of the Chinle Formation. However, the stratigraphic 

relations, grain-size analyses, clay minerals, and fossil content 

show that it is a separate unit equivalent to the Owl Rock Member of the Chinle Formation. It is the author's opinion that rocks 

formerly assigned to division A of the Chinle Formation be 

everywhere called the Rock Point Member of the Wingate Sandstone and that the so-called Church Rock of southeastern Utah 

be renamed. 

A widespread unconformity that separates the Chinle Formation, as here defined, from overlying rocks extends from southern Nevada across southwestern Utah and northeastern Arizona 

to northwestern New Mexico. The unconformity overlies the 

Owl Rock Member in most of northeastern Arizona and overlies 

older parts of the Chinle Formation to the west in Nevada and 

to the east in northwestern New Mexico. In southeastern Utah 

the unconformity probably lies at the base of rocks equivalent 

to the Hite Bed, where present, or .at the base of the Wingate 

Sandstone. 

INTRODUCTION 

Part of the Upper Triassic rocks of northeastern Arizona and adjacent areas (fig. 1) includes the Chinle 

Formation and the overlying Wingate Sandstone. The 

uppermost subdivision of the Chinle Formation, in the 

Monument Valley area, is the same unit that, in the Defiance Plateau area, is assigned to the basal part of the 

Wingate Sandstone. Geologic studies by the author in 

parts of southeastern Utah and northeastern Ariz·ona 

have yielded some new information on the stratigraphic 

relations of these rocks. The purpose of this report is 

to review the nomenclature and to summarize the a vailable information about' the Upper Triassic stratigraphy 

of the area. This report proposes no changes in the existing nomenclature, but the information presented herein 

may help .to resolve this conflict in nomenclature. 

The. author is grateful to R. A. Cadigan, M. E. 

Cooley, L. C. Craig, J. H. Stewart, J.D. Strobell, and 

D. G. Wyant for helpful suggestions and comments 

about terminology and regional geology made during a 

field conference in Monument Valley. The author expresses particular thanks to D. G. Wyant, who first 

recognized the significance of an important unconformity within the rock units discussed in this report. J. H. 

Stewart aided in measuring a stratigraphic section and 

examined some of the stratigraphic relations herein 

described, but he does not necessarily agree with any of 

the conclusions in this report. 

The work on which this report is based is part of a 

continuing study of the geology of the Navajo Indian Reservation and was done on behalf of the U.S. 

Bureau of Indian Affairs in cooperation with theN avajo 

Trilbe. 

STRATIGRAPHY 

Stratigraphic subdivisions recognized by Gregory 

(1917, p. 37-50) in northeastern Arizona and adjacent 

parts of' southeastern Utah include, in ascending order, 

the Shinarump Conglomerate, the Chinle Formation, 

and the Wingate Sandstone. Gregory (1917, p. 42-43) 

distinguished four units (fig. 2)' of the Chinle Formation, which he .referred to as divisions D, C, B, and 

A in ascending order. Gregory later (1950, p. 67) used 

the name Petrified Forest Member in the Zion Park 
E2 

37" 

SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

I I 

I 

.......... I ..-r---- __j ........_ __ j_r0 Paria (abandoned) 

oTuba City 

oF!agstaff 

0 50 

/Line of generalized 

diagram 

oBlanding 

1l 

r 

)> 

-1 

fT1 

)> 

c 

100 MILES 

Delta 0 

oCortez 

oGallup 

0 Fort Wingate 

Thoreau 0 

Fence Lake 

FIGURE 1.-Map of northeastern Arizona and adjacent areas showing approximate outcrop distribution of division A 

(solid). Compiled in part from Dane and Bachman (1957); Cooley, Harshbarger, Akers, and Hardt (1004); and 

M. E. Cooley (written commun., 1966). Hase from U.S. Geological Survey, 1: 1,000,000 State base maps. 
..,. 

I 

.... 

CHINLE FORMATION AND RELATED ROCKS, SOUTHEASTERN UTAH AND ADJACENT AREAS E3 

Wingate Sandstone 

Chinle 

Formation 

Division 

A 

Division 

B 

Division 

c 

Division 

D 

Shinarump Conglomerate 

Reddish-orange and reddish-brown 

massive crossbedded sandstone 

Reddish-orange sandstone and 

siltstone 

Pale-red shale and interbedded reddishorange siltstone and conglomeratic 

gray, light-green, and pink limestone 

and pale-red sandstone 

Gray, pale-blue, pale-red, and brown 

shale and variegated siltstone and 

shale 

Dark-gray and red shale and light-gray 

crossbedded and conglomeratic sandstone 

Light-gray conglomeratic sandstone 

<: .·; 

--

~ -~-~~() --

- --

1-- - -

--

---( - -- ---1 --

---

FIGURE 2.-Nomenclature of Chinle Formation and related 

rocks of Gregory ( 1917) . 

area -of southwestern ·utah, and this name is now applied to his division C. In a series of reports describing 

the geology of southeastern Utah and the Monument 

Valley area of Arizona ( Stewrurt, 1957; Stewart and 

others, 1959; Witkind and Thaden, 1963), formal member names were-given to the other lettered subdivisions 

of the Chinle. The name Owl Rock was applied to division B, and Monitor Butte, to division D. The Shinarump Conglomerate was reduced to member status and 

assigned to the Chinle Formation. 

The uppermost unit of the Chinle .Formation or division A of Gregory, however, has been given two different names and assigned to two different formations. 

Division A was originally defined by Gregory (1917, 

p. 42) as the highest strata of the Chinle, and the type 

localities were given as Mesa de Ventana (now Ventana Mesa) and Todilto Park in the Defiance Plateau 

area. Harshbarger, Repenning, and Irwin (1957) removed division A from the Chinle Formation and 

assigned it as the lower member of the Wingate Sandstone (Rock Point Member) at Little Round Rock in 

the Defiance Plateau; the remaining upper part of the 

Wingate was named the Lukachukai Member. At this 

locality the base of the Wingate was placed at the 

top of division B (Owl Rock Member). Witkind and 

Thaden in a later report (1963, p. 22) named division 

~ the Church Rock Member in, the Monument Valley 

·:trea of Arizona and left it in the Chinle Formation. 

As a result of the different assignments of division 

A, an arbitrary decision was made. "North of Laguna 

Creek * * *, division A (of the Chinle) is known as 

the Church Rock Member of the Chinle Formation. 

South of Laguna Creek the same sequence of strata is 

to be known as the Rock Point Member of the Wingate 

Sandstone" (Witkind and Thaden, 1963, p. -34). Although two different names are used for division A, 

there appears to be no dispute about the correlation of 

the unit across Laguna Creek (fig. 1) in northeastern 

Arizona . 

Stewart, Williams, Albee, and Raup (1959, p. 518) 

recognized, in addition to these formal members, another unit-the Rite Bed-at the top of the Chinle and 

below the Wingate Sandstone over a large part of southeastern Utah. The Rite Bed in much of Utah is 10-50 

feet thick and consists of pale-~red and light-greenishgray very fine grained sandstone and interbedded lenses 

of pale-reddish-brown siltstone. It locally contains 

trough sets of cross-strata and conglomeratic sandstone 

lenses which are composed of granules, pebbles, cobbles, 

and boulders. Previously a sandstone bed similrur to the 

Rite Bed was noted in part of the Monument Valley 

area, but the-relation of this sandstone to the Rite Bed ·as 

recognized to the north in southeast Utah was unknown 

(Stewart and others, 1959, p. 518). Work described 

here indicates that the Rite Bed is wide·ly distributed 

in Monument Valley and consists of recognizably different upper and lower parts. The upper part of the 

Rite Bed is probably present everywhere in the Monument Valley area below the cliff-forming Wingate 

Sandstone. The lower part of the Rite Bed is only 

locally present. 

The Wingate Sandstone is the oldest formation of 

the Glen Canyon Group, which includes, in addition, 

the Moenave and Kayenta Formations of Triassic ( ~) 

age and the Navajo Sandstone of Triassic( n and 

Jurassic age. Harshbarger, Repenning, and Irwin 

(1957) described these units in detail. 

STRATIGRAPHIC RELATIONS IN SOUTHERN 

MONUMENT VALLEY 

The southern Monument Valley area of Arizona has 

been mapped and described by Witkind and Thaden 

( 1963). The Chinle Formation in this area consists of 

five members, but only the upper two member~the 

Owl Rock and overlying Church Rock-are discussed 

here. 

The Ow 1 Rock Member ranges in thickness from 120 

to 166 feet (Witkind and Thaden, 1963, p. 30-32} and 

is characterized by pale-red shale and minor ledges of 

limestone and sandstone. At the type locality the member is 166 feet thick (Witkind and Thaden, 1963, p. 31) 

and is made up of six limestone beds, 2-19 feet thick, 

that form ledges; these ledges are separated by slopeforming beds of mudstone or shale as much as 30 feet 

thick. 
E4 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

In the same area the overlying Church Rock Member 

(Witkind and Thaden, 1963, p. 32-34) consists 

dominantly of a slope-forming sequence of reddishorange to reddish-brown siltstone and some sandstone. 

The following section measured by Witkind and Thaden 

( 1963, p. 33) is c~msidered to be typical. 

Section of Church Rock Member of Chinle Formation measttred 

on Comb Ridge about 6% miles northeast of Kayenta, Ariz. 

Wingate Sandstone. 

Chinle Formation: Thickness 

Church Rock Member: (feet) 

11. Siltstone, reddish-brown, fissile, even-bedded; 

weathers to form nodular ledges_________ 12 

10. Siltstone, reddish-brown, crossbedded; locally 

interbedded lenses of fissile shaly siltstone_ 11 

9. Sandstone, grayish-brown, crossbedded, 

coarse-grained; includes granules as much 

as a quarter of an inch in diameter; thin 

discontinuous seams of chocolate-brown 

siltstone along bedding planes____________ 4 

8. Siltstone, reddish-orange altering locally to 

light-gray ; interbedded lenses of coarsegrained sandstone_______________________ 20 

7. Siltstone, reddish-orange, massive; weathers 

to form blocks about 2 ft on a side________ 3 

6. Siltstone, reddish-orange to reddish-brown, 

even-bedded ; slightly fissile; mottled surface covered with light-gray spots about 2 

in. across_______________________________ 75 

5. Siltstone, reddish-brown, even-bedded ; locally 

discontinuous ; gray spots irregularly distributed over surface____________________ 5 

4. Siltstone, reddish-orange, even-bedded, extremely fissile ; locally interbedded with 

massive crossbedded siltstone beds_______ 52 

3. Siltstone, reddish-orange, fissile ; locally discontinuous ----------------------------- 6 

2. Siltstone, reddish-brown ; . even-bedded 'although locally crossbedded; weathers as 

blockyledges---------------------------- 52 

1. Sandstone, light-tan to light-brown, thinbedded, platy, faintly ripple-marked______ 6 

Tota,l Church Rock Member_____ 246 

Owl Rock Member. 

For purposes of correlation the author recognizes a 

tripart subdivision in this section. The upper 47 feet in 

part consists of course-grained crossbedded sandstone, 

which contains granules as much as a quanter of an inch 

across. Tllis upper sequence (units 8 through 11) is here 

assigned to the upper part of the Rite Bed. The medial 

silty part of the Church Rock Member underlies the 

upper part of the Rite Bed and is 193 foot thick (units 

2 through 7). The ripple-marked 6-foot sandstone bed 

(unit 1) at the ha.se is tentatively assigned to the lower 

part of the Rite Bed. 

The name Rite Bed was not used hy Witkind and 

Thaden (1963) for rocks in the southern Monument 

Valley area of Arizona. The Rite Bed, however, can 

be recognized in their description of the upper part of 

the Church Rock Member. They (Witkind and Thaden, 

1963, p. 33) described the contact with the Wingate 

Sandstone as a change from "a parallel ;and crossbedded 

deposit with depositional features typical of fluvial depoeits, to a massive deposit marked hy large sweeping 

cross-laminae commonly attributed to eolian deposits." 

The fluvial deposirts below the Wingate are considered 

to be the Rite Bed. 

In southern Monument Valley the thickness of the 

upper part of the Rite Bed varies. It. is 11 feet thick 

at the Arizona-Utah State line on Cornlb Ridge, 47 feet 

thick where typically exposed 61h miles northeast of 

l(ayenta, Ariz., and ·about 42 feet thick at Ow'l Rock, 

Ariz. (M. E. Cooley, written commun., 1967). The Rite 

Bed thins westward from Owl Rock, and a thickness of 

only 2 feet was measured by the author at the north tip 

of Tyende Mesa on the east side of Oljeto Wash about 

11h miles southwest of Boot Mesa. 

The f:ilty part of the Church Rock Member forms a 

reddish-brown to. reddish-orange ledgy slope below the 

upper part of the Rite Bed. The silty part constitutes 

most of the Church Rock Member and is 193 feet thick 

where typically exposed 61j2 miles northeast of Kayenta. 

It is 191 feet thick at Owl Rock (M. E. Cooley, written 

commun., 1967). The silty part of the Church Rock 

Member is equivalent to division A as recognized by 

Gregory at his type locality in the Defiance Plateau area 

and is therefore equivalent to the Rock Point Member 

of the Wingate Sandstone. For convenience and simplicity, the silty part of the Church Rock and the 

equivalent Rock Point Member of the Wingate will 

generally be referred to as division A in· this report. 

In most of southern Monument Valley the lower part 

of the Rite Bed is not conspicuous, and the unit 3ippears 

to be restricted w the outcrops along Comb Ridge. The 

lower part of the Rite Bed is 3Jbout 20 feet thick from 

the Arizona-Utah State line to the Monumelllt No. 2 

mine area. It possibly is 6 feet thick where exposed 61h 

miles northeast of Kayenta. 

STRATIGRAPHIC RELATIONS IN NORTHEASTERN 

MONUMENT VALLEY 

North of the lJtah State line in northeastern Monument Valley the Chinle Formation is complicated by 

additional lithologic units that wedge into the upper 

part of the formation. The correlation of these units, as 

shown on the accompanying line of sections (fig. 3), 

is based pri·marily on geologic mapping (O'Sullivan, 

1965) of the area but incorporates some1ater, more detailed studies of the rocks so well exposed along Comb 

-! 
: 

.. , 

1_ 

CIDNLE FORMATION AND RELATED ROCKS, SOUTHEASTERN UTAH AND ADJACENT AREAS E5 

Ridge in this part of Monument Valley. From the vicinity of the Monument No. 2 mine, the line of sections 

trends northward along Comb Ridge for a ·distance of 

about 29 miles. A section (fig. 3, No. 16) near Church 

Rock in Arizona is also included. 

OWL ROCK MEMBER 

Along Comb Ridge, in northeastern Monument Valley, the Ow I Rock Member consists mainly of pale-red 

shale. Delicate pastel pink and reds of the Ow I Rock 

contrast sharply with the darker blue and gray of the 

underlying Petrified Forest Member and with the reddish orange of the overlying units. The shale is generally silty and calcareous, and much of it is spotted 

light greenish gray. Interspersed with the shale are 

several ledge-forming beds of limestone, sandstone, and 

siltstone. The limestone, in beds from less than 1 foot 

to 8 feet thick, is light greenish gray to light gray and 

at places is mottled pale red. The sandstone, in beds from 

1 to 10 feet thick, is brown and pale red, fine to coarse 

grained, and at places contains pebbles of limestone and 

shale as much as 4 inches across. A tentative correlation of some of these beds for a distance of about 8 miles 

north of Monument No.2 mine in an area mostly covered 

by windblown sand is shown in figure 3 (sections 15-

10) 0 

Where best exposed at a locality about 21h miles 

north of Moses Rock (fig. 3, section 4), the Owl Rock 

Member is 414 feet thick and contains five ledges. The 

ledges in this area, however, tend to be nonpersistent 

and lenticular, and, as a result, the number and arrangement of the ledges vary from place to place. The base 

of the Owl Rock Member is arbitrarily placed below 

the lowest prominent ledge of sandstone or limestone. 

REDDISH-ORANGE SILTSTONE MEMBER 

The upper part of the Owl Rock Member in the 

area north of Moses Rock grades laterally into a sequence of reddish-orange siltstone beds (fig. 3). These 

beds are recognized by Stewart (1957, p. 459) as part 

of his Church Rock Member of the Chinle over wide 

areas of southern Utah. For reasons that will be discussed, this so-called Church Rock in Utah is not a cor-· 

relative of the type Church Rock in Arizona. In this 

report, for convenience, this sequence of beds will be 

referred to ·as the reddish-orange siltstone member. 

The reddish -orange siltstone member forms a banded 

slope due to the alternation of hard and soft layers. 

The member is composed mainly of coarse silt-sized 

quartz grains, but it contains some grains of very fine 

sand size. At places, beds of pale-red and !brown shale 

similar to the main part of the Ow I Rock Member are 

interbedded with the siltstone. This interbedding is interpreted as an interfingering of lithology typical of 

375-048 0-7o-2 

the reddish-orange siltstone member to the north with 

lithology typical of the Owl Rock Member to the south. 

Although most of the reddish-orange siltstone member passes laterally southward into the upper part of 

the Ow I Rock near Moses. Rock, some ledges of reddishorange siltstone or sandstone persist farther south. A 

reddish-orange ledge at Moses Rock may represent a 

southern extension of the reddish -orange siltstone 

member, or it may represent a separate lentil within the 

Ow I Rock. The ledge, which is 6 feet thick and consists 

of very fine grained silty sandstone, is 64 feet below the 

top of the Owl Rock Member. Similar beds have been 

noted elsewhere in the Owl Rock Member at a few 

places to the south. 

MULE EAR LEDGE 

A prominent cliff-forming sandstone bed overlies the 

reddish-orange siltstone member throughout most of the 

area, but it also rests on the Owl Rock Member for a 

short distance near Moses Rock. This sandstone bed has 

previously been called the lower ledge (O'Sullivan, 

1965, p. 59), hut in this report it is referred to as the 

Mule Ear ledge of local usage. The Mule Ear ledge is 

reddish orange, massive, and generally very fine grained 

and is commonly stained with a black manganese coating. Its base is marked by a sharp topographic break 

from the slope-forming underlying unit-either the 

reddish-orange siltstone member or the Owl Rock Member-to the cliff-forming Mule Ear ledge. 

The Mule Ear ledge forms an easily recognized 

marker bed high on the west wall of Comb Ridge for 

a distance of about 27 miles north ward from Moses 

Rock. In this distance it varies so mew hat in thickness. 

It is thickest, 130 feet, at Moses Rock, hut within 1 

mile southward it is beveled out by an unconformity at 

the base of the next overlying unit. The Mule Ear ledge 

is 92 feet thick 2lh miles north of Moses Rock and 63 

feet thick about 2 miles north of the San Juan River. 

At a point about 18 miles north of the San Juan River 

and beyond the limits of the area studied in detail by 

the author, equivalents of the Mule Ear ledge weather 

to a slope that merges with the underlying reddishorange siltstone member. 

HITE BED 

At Moses Rock (fig. 3, section 6) and in areas to 

the north, the Rite Bed is about 50 feet thick and consists of a uniform pale-red very fine grained cross bedded 

sandstone that forms a prominent cliff above the Mule 

Ear ledge. In color, composition, and bedding features 

the Rite Bed strikingly resembles the Kayenta Formation of Late Triassic(?) age, a unit that overlies the 

Wingate Sandstone. Because of this ·resemblance, the 

field term "Kayenta-like" has been applied to the Rite 
E6 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

Bed by some geologists. The Rite Bed is 62 feet thick 

about 2 miles north of the San Juan River and a;bout 

30 feet thick in the area 21h miles north of Moses Rock. 

South of Moses Rock the Rite Bed contains .thin 

lentils of reddish-orange sandstone or siltstone. Between 

sections 6 and 7 (fig. 3) the base of the Rite Bed unconformably channels down acr'oss the underlying Mule 

Ear ledge. At section 7 the Rite Bed is split into upper 

and lower parts by an intervening sequence of reddish· 

orange siltstone, 27 feet thick, that represents the wedge 

NORTHEAST 

11 2 3 4 

edge of the silty part of the Church Rock Member or 

division A. 

The upper part of the Rite Bed south of Moses Rock 

is similar ·to all the Rite Bed to the north but is somewhat coarser grained. It commonly consists of fine- to 

medium-grained crossbedded. pale-red sandstone. Locally, the Rite Bed contains beds of reddish-orange and 

pale-reddish-brown crossbedded sandstone. At places, 

reddish-brown siltstone pebbles and thin beds of ,reddish-brown siltstone or shale are also present. Individual 

Moses Rock 

5 6 7 8 9 

4.7 MILES 4.8 MILES 4.5 MILES ·I· 1.2 MILES ·I· 1.4 MILES 1.7 MILES ,,0.7 MIL~,, 1.7 MILES 

0 10 20 MILES 

INDEX MAP 

Bed 

ledge of 

Location of sections 

1. Sec. 13, T. 40 S., R. 20 E. 

2. Sec. 2, T. 41 S., R. 20 E. 

3. 0.7 mile south of San Juan River 

4. 2.6 miles north of Moses Rock 

5. 1.4 miles north of Moses Rock 

6. At Moses Rock 

7. 0.7 mile south of Moses Rock 

8. 2.4 miles southwest of Moses Rock 

9. 3.1 miles southwest of Moses Rock 

10. At the road crossing Comb Ridge 

11. 1.9 miles north of Utah-Arizona State line 

12. 0.9 mile north of Utah-Arizona State line 

13. Utah-Arizona State line 

14. 2 miles south of Utah-Arizona State line 

15. East of Monument No.2 mine 

16. 6.5 miles northeast of Kayenta 

1 Section measured by L. C. Craig and 

T. E. Mullens, 1951 

z Section measured by J. H. Stewart 

and R. B. O'Sullivan, 1967 

3 Section from Witkind and Thaden 

(1963, p. 33) 

0 

Owl 

NORTHEAST 

4 

Member 

EXPLANATION 

~ 

~ 

Sandstone, fine- to coarse-grained 

Siltstone and very fine grained sandstone 

Shale 

Limestone 

Conglomerate 

5 

-·-·-

Reddish-orange 

siltstone member FEET 

[,~ 2 

VERTICAL EXAGGERATION X 6.336 

FEET 

0 

25 

50 

100 

150 

6 

3 MILES 

FIGURE 3.~Graphic sections and stratigra.phic diagram showing correlation 

, • .l
I 

I 

....., 

.. ( 

CJnNLE FORMATION AND RELATED ROCKS, SOUTHEASTERN UTAH AND ADJACENT AREAS E7 

sandstone beds tend to be lenticular and commonly fill 

channe·ls cut into under lying units. 

The lower part of the Hite Bed consists of a more 

heterogeneous assemblage of rocks than the upper part. 

One important reference bed (l•abeled "unit r" on fig. 3) 

can be traced for about 5 miles along Comb Ridge. Between sections 9 and 10 it forms a prominent ledge and 

bench. The ledge dips eastward and is capped by spires 

and remnants of division A (fig. 4). The main outcrop 

of division A is eroded !back to the east. U ni't r is genUTAH I ARIZONA 

10 11 12 13 14 

10.4 MILE I 1 MILE I' 0,9 MILE I· 2 MILES 3 MILES 

erally pale red, typical of the color of the Hite Bed elsewhere in this area, but at places it is pale red brown and 

light greenish gray. It is crossbedded and flat bedded, 

consists of fine- to very coarse- grained sandstone, and is 

locally conglomeratic. The conglomerate at section 10 

(fig. 3) consists of pebbles 3-4 inches across which are 

limestone and sandstone and subordinate amounts of 

siltstone. Unit r apparently terminates abruptly between 

sections 10 and 11; a thin conglomeratic sandstone at 

SOUTHWEST 

152 163 

·I . 19 MILES 

Sandstone 

of 

Member 

GRAPHIC SECTIONS 

7 8 9 

Wingate Upper part of Hite Bed 

Owl 

STRATIGRAPHIC DIAGRAM 

of upper pa·rt of Obinle Formation _;and related rocks along Oomib Ridge. 

division A of 

10 11 

•• 0 ...... _;... ·: • 

Gregory 

12 

SOUTHWEST 

13 
E8 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

FIGURE ·4.-Upper Triassic rocks along Comb Ridge. View north along road leading to Monument No. 2 mine. Owl Rock Member 

of Chinle Formation ("Reo); unit r of the lower part of Hite Bed (hr); division A (A); upper part of Hite Bed (hu); and Wingate 

Sandstone (liw). 

section 11 may, however, represent a further continuation of unit r to the south. (See fig. 3.) 

From section 9 (fig. 3) northward to a point about 

1lj2 miles north of section 8, unit r weathers back into a 

cliff that includes overlying rocks; but farther north 

toward Moses Rock, unit r again forms a bench. Between section 9 and Moses Rock (section 6) unit r consists of a complex assemblage of channeling sandstones. 

The sandstone beds are generally fine to very fine 

grained, pale red, grayish yellow, and dark yellowish 

brown with some interbedded reddish-brown shale or 

siltstone. Cobbles as much as half a foot across were 

noted near the middle of unit r at section 7; these cobbles resemble the conglomerate in unit r at section 10. 

The part of the Hite Bed below unit r consists of a 

heterogeneous sequence of dark-reddish-brown, moderate-orange-pink, pale-red, and pale-reddish-brown siltstone and shale and some very light gray and pale-red 

sandstone. Much of the lower part of the Hite Bed 

below unit r appears to be material reworked from the 

Owl Rock Member of the underlying Chinle Formation. 

This part of the Hite Bed is characterized by great 

swales or channels (fig. 5) as much as half a mile wide 

and an estimated 30-40 feet deep. These great swales 

are filled with smaller overlapping sets of channel deposits arranged in an intricate manner suggestive of 

large-scale crossbedding. The deposits in these smaller 

channels, which are as much as 100 feet across, consist 

of moderately cemented beds 3 inches to 3 feet thick 

separated by thin interbeds of softer rock. 

At a point midway between sections 9 and 10 (fig. 3) 

and directly below unit r is a group of beds of deltaic 

origin which measure about 42 feet in thickness. The 

FIGURE 5.-West wall of Comb Ridge about 4 miles south of Moses Rock. Unit r of lower part of Hite Bed (hr); division A (A); 

and Wingate Sandstone (liw). Note large channel (C) below unit r. 
\.. 

CIDNLE FORMATION AND RELATED ROCKS, SOUTHEASTERN UTAH AND ADJACENT AREAS E9 

foreset beds strike N. 87° E. and dip as much as 30° S. 

From areas of maximum dip the beds flatten rapidly 

into gently dipping bottomset beds in a distance of 

about 100 feet. Topset beds have been truncated by the 

overlying unit r. Similar deltaic beds were noted below 

unit r in the area between sections 7 and 8. 

The lower part of the Hite Bed thickens in a small 

area between sections 10 and 11 (fig. 3) at the expense 

of the overlying division A. At section 11 the lower 

part of the Hite Bed is about 102 feet thick and consists 

dominantly of reddish-brown and reddish-orange siltstone and shale and some thin sandstone beds. The overlying division A at section 11 is 85 feet thick, compared 

to 141 feet thick at section 10 about 0.4 mile to the north 

and 125 feet thick at section 12 about 1 mile to the south. 

The lower part of the Hite Bed thins from section 11 

('fig. 3) southward. It is 15-19 feet thick in the area from 

section 12 to section 15, in the vicinity of Monument 

No. 2 .mine. In this area it consists mainly of darkreddish-brown to reddish-orange sandstone and siltstone 

and some thin light-gray to brown lenticular and platy 

limestone beds. A·t section 13 the lower part of the Hite 

Bed consists of beds 1-2 feet thick separated by shaly 

niches; at the base is a white and light-tan very finegrained to fine-grained sandstone, which contains some 

thin interbeds of shale. The basal sandstone is both 

crossbedded and flatbedded, forms a ledge, and contains 

pebbles of chert as much as 1 inch across in ·the lower 

part. Southward, at section 16 (fig. 3), the lower part 

of the Hite Bed may be represented by a 6-foot ripplelaminated sandstone bed at the base of division A. 

UNCONFORMITY AT THE BASE OF THE HITE BED 

Everywhere along Comb Ridge, between sections 1 

and 15 (fig. 3) , the Hite Bed is separated from the 

underlying rocks by an unconformity. Within the Hite 

Bed are numerous minor channeling erosional surfaces 

as would be expected in a fluviatile deposit. These minor 

erosional surfaces, however, cannot be traced regionally 

as can the widespread unconformity at the base of Hite 

Bed, as shown in figure 3. 

North of Moses Rock the unconformity separates very 

fine grained massive sandstone of the Mule Ear ledge 

from crossbedded pale-red fine- to medium-grained 

sandstone of the Hite Bed. South of Moses Rock the 

unconformity at the base of the Hite Bed cuts across 

the underlying rocks, and the Hite Bed overlies the 

Owl Rock Member. In this area the Owl Rock Member 

is characterized by persistent units of uniform thickness 

than can be traced for a considerable distance. The beds 

just above the unconformity, particularly in the area 

between sections 8 and 10, are a heterogeneous sequence 

of channeling lenticular units of sandstone and siltstone. 

Farther south, between sections 12 and 15, pebbles 

of chert and limestone commonly are present just above 

the unconformity in the ba.Se of the lower part of the 

Hite Bed. In the vicinity of sections 14 and 15 a conspicuous hackly-weathering limestone, which contains 

nodules of chert (fig. 3, unit 1), marks the top of the 

Owl Rock Member of the Chinle Formation. At 

several localities the unconformity cuts into or through 

unit 1. The relations near section 13 are obscured by 

windblown sand, but the distinctive unit 1 cannot 

be recognized at section 13. At section 14 the unconformity cuts through unit 1 and into underlying 

beds of the Owl Rock Member in a channel ·about 20 

feet deep. Boulders of rounded and angular limestone, 

many as much as 2 feet across, partly fill the south side 

of the channel. One slab of limestone about 4 feet across 

was found in the channel. The lithology of the boulders 

suggests that the boulders were derived from unit 1. 

For some distance to the south of section 14, small 

channels cut into or through unit 1. The unconformity 

at the base of the lower part of the Hite Bed, however, 

gradually becomes less noticeable father south near section 15. At section 15, and from there for some distance 

to the south, the contact between unit 1 (the top of the 

Owl Rock Member) and the overlying beds is not 

ma:rked by any channeling or by the presence of ronglomerate. On the contrary, unit 1 appears to be 

a continuous bed that may extend over wide wreas of 

Monument Valley as the highest· limestone of the· Ow 1 

Rock Member. · 

Witkind and Thaden (1963) regarded the Owl Rock 

and overlying Church Rock Members as partly intertonguing in southern Monument Valley. They have 

described stratigraphic relations they regarded as intertonguing in the vicinity of Monument No.2 m.ine (fig. 

3, section 15), where the limestone that marks the top 

of the Owl Rock (unit 1 of this report) is "underlain by * * * reddish-brown * * * typical Church 

Rock strata" (Witkind and Thaden, 1963, p. 32). Siltstone, similar to that in the Church Rock Member ( division A), is also present near Moses Rock in a 6-foot bed 

that is 64 feet below the unconformity at the top of 

the Owl Rock Member. Beds of similar siltstone have 

also been noted within the Ow 1 Rock Member in the 

Chinle Valley a;rea by the author, and in the Carrizo 

Mountains area, by Strobell ( 1956). These siltstone beds 

are not ·tongues that connect with the Church Rock, 

but they are either discrete lentils within the Owl Rock 

or southward-extending tongues of the reddish-orange 

siltstone member. 

Although Witkind and Thaden ( 1963) described 

neither an erosional surface nor 'pebbles at the contact 

between the Ow 1 Rock Member and overlying ·beds, such 
ElO SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

features are present at least locally in other parts of 

northern Arizona. In the Echo Cliffs area, Callahan 

(1951) reported that the Chinle Formation is in contact with overlying beds along an unconformity that is 

marked by conglomerate that consists of granules and 

pebbles of chert, limestone, siltstone, and mudstone. He 

stated (1951, p. 51) that the conglomerate "has also 

been observed at Kayenta, Arizona, in the same stratigraphic position." The "same stratigraphic position" 

would be at the top of the Owl Rock Member, for the 

Owl Rock is the uppermost member of the Chinle in the 

Echo Cliffs area and near Kayenta. Beaumont and 

Dixon (1965, p. A6) have also noted reworked limestone pebbles locally at the contact of the Owl Rock 

Member and overlying beds in the Kayenta area. In 

southern Monument Valley, as already noted, a conglomerate unconformably overlies the Owl Rock Member for several miles between Monument No. 2 mine 

(fig. 3, section 15), and the Arizona-Utah State line. 

Thickness relations suggest that the top of the Owl 

Rock in the southern Monument Valley area south 

of section 15 (fig. 3) is erod~d. Regionally, the Owl 

Rock Member thins westward across northeastern Arizona. The Owl Rock is thickest, about 300 feet, along 

a line that trends from Round Rock southwestward to 

Castle Butte in the Hopi Buttes area (Akers and 

others, 1958, p. 94). It is 120-166 feet thick in the southern Monument Valley area of Arizona (Witkind and 

Thaden, 1963, p. 31). At Lees Ferry on the Colorado 

River, the Owl Rock Member is about 100 feet thick 

(M. E. Cooley, written commun., 1967). In southwestern 

Utah the Owl Rock is absent, largely owing to progressive westward erosional truncation at the top of the 

o Chinle Formation (Wilson, 1965, p. 35-36). Some of 

the differences in reported thicknesses of the Owl Rock 

Member may ·be due to disagreements by different geologists in placing the contacts, but a general thinning 

westward does seem apparent. The thinning of the Owl 

Rock Member across the Monument Valley area of 

Arizona is explained by a regional unconformity, even 

though the unconformity may not be evident at all outcrops in the Monument Valley area. 

DIVISION A 

Witkind and Thaden (1963, pl. 1) mapped their 

Church Rock Member, which includes division A (or 

the silty part of the Church Rock) and the upper and 

lower parts of the Rite Bed, around the east side 

of southern Monument Valley in Arizona to the Arizona-Utah State line. At the State line (fig. 3, section 

13), division A is 166 feet thick and consists mainly of 

reddish-orange siltstone .locally spotted light greenish 

gray. The unit forms a slope interrupted by ledges 

as much as 4 feet thick. Northward in Utah, division 

A thins between the upper and lower parts of the Rite 

Bed and is 77 feet and 27 feet thick, 3 miles and 1 mile 

south of Moses Rock, respectively. Division A wedges 

out into the Rite Bed just south of Moses Rock (fig. 3, 

section 6). Near the pinchout, siltstone beds of division 

A contain lentils of pale-red sandstone, lithologically 

like the Rite Bed, which make more abrupt the rapid 

lateral gradation of division A into Rite Bed. Vertical 

gradation has been noted at section 8 (fig. 3). At that 

locality the top of the lower part of the Rite Bed includes siltstQne beds like those in division A, which are. 

'interbedded with sandstone beds like those that make 

up the main body of the Rite Bed. 

STRATIGRAPHIC RELATIONS IN NORTHWESTERN 

MONUMENT VALLEY 

The Church Rock Member, including the Rite Bed 

and the silty part or division A, was mapped around 

the south end of Monument Valley by Witkind and 

Thaden ( 1963, pl. 1) to Skeleton Mesa at the west 

edge of their area. From there northwestward, as shown 

on a geologic map accompanying a report 'by Cooley, 

Harshbarger, Akers and Hardt (1964), an equivalent 

unit labeled the Rock Point Member of the Wingate 

Sandstone has been traced as far as No Mans Mesa in 

Utah. M. E. Cooley (written commun., 1966) indicated, 

however, that division A does not extend this far north 

but disappears probably near the Utah-Arizona State 

line. 

In Utah at the place where the Wetherill trail 

crosses Piute Creek about 6 miles north of the Utah-Arizona State line, division A is absent. At that locality 

the Rite Bed rests unconformably on the Owl Rock 

Member (D. G. Wyant, written commun., 1967). Hence, 

division A disappears between Wetherill trail and 

Skeleton Mesa. The reason for its disappearance has not 

been determined, but it may possibly grade into the Rite 

Bed in this area in much the same manner as division 

A grades into or pinches out in the Rite Bed along 

Comb Ridge on the east side of Monument Valley. 

An approximate northern limit can be drawn for 

division A (fig. 1). The limiting line passes near the 

Utah-Ar~zona State boundary on the west side of Monument Valley and near Moses Rock on the east side of 

Monument VaHey. As thus defined, division A extends 

not more than 8 miles into southeastern Utah. 

In northwestern Monument Valley between the northern limit of division A and the San Juan River, the 

Rite Bed is present above the Owl Rock Member and 

below the Wingate Sandstone. The Rite Bed is 68.5 

' 

r 
-<, 

CIDNLE FORMATION AND RELATED ROCKS, SOUTHEASTERN UTAH AND ADJACENT AREAS Ell 

feet thick in San Juan Canyon near the mouth of Piute 

Creek (M. E. Cooley, written commun., 1966). In a 

measured section (Mullens, 1960, p. 320-321) at Monitor Butte, it is 38 feet thick ( J. H. Stewart, written 

commun., 1966). North of the San Juan River, the Rite 

Bed is locally present at least as far north as the junction of the Colorado and Green Rivers (J. H. Stewart, 

written commun., 1966). 

The Chinle Formation has been mapped in the Clay 

Hills area near the San Juan River on the west side of 

Monument Valley (Mullens, 1960). In that area, 

Mullens ( 1960, p. 280-290) recognized three units of 

the Chinle above the Shinarump Member. The middle 

unit contains equivalents of the Owl Rock Member and 

most of the Petrified Forest Member. According to 

Mullens (1960, p. 287), the upper unit of the Chinle 

Formation 

is as much as 190 feet ~thick and consists mainly of reddishorange interbedded· siltstone and very fine-grained sandstone. 

Dense gray limestone and limestone-pellet conglomerate beds 

are sparsely distributed in the upper division, and locally the 

upper 10 to 40 feet of the upper unit consists of a pale-red 

medium-coarse to coarse-grained sandstone. 

The pale-red sandstone just below the Wingate Sandstone and at the top of the upper unit of Mullens contains red mudstone pebbles. As described by Mullens 

( 1960, p. 288), the pa!le-red sandstone "occurs in lenticular beds and is cross-laminated with the type of 

cross-laminations attributed to stream deposits." This 

sandstone is prob~bly the Rite Bed (M. E. Cooley, oral 

commun., 1967). 

Mullens ( 1960, p. 288-289) believed tha;t the upper 

unit 

correlates in general with ~the Church Rock member. However, 

the presence of limestone in the upper unit indicates gradation 

of Church Rock and Owl Rock members, and precludes an exact 

correlation of the upper unit with the Chureh Rock membe:r. * * * The upper unit * * * grades southwestward into an 

interbedded limestone and calcareous sandy siltstone sequence 

that cannot be separated from the middle unit of the * * • 

Chinle in the southwest part of the map area. 

The correlation of the upper unit with the Church 

Rock Member seems inappropriate inasmuch as ·the 

silty part of the Church Rock or division A has not 

been mapped as far north as the Clay. Hills area. The 

author interprets the upper unit of Mullens, excluding 

the locally present Rite Bed, to be equivalent to the 

reddish-orange siltstone member of this report .and to 

grade to the southwest into the upper part of the Owl 

Rock Member of the Chinle Formation. 

The stratigraphic relationships in the Clay Hills area 

in northwestern Monument Valley thus appear to be 

analogous to the strrutigraphic rel~tionships in northeastern Monument Valley. Along Comb Ridge in 

northeastern Monument Valley, as described previouSly ' 

(fig. 3), the reddish-orange siltstone member or the 

Church Rock Member as used by Stewart grades south· 

ward into the Owl Rock Member which is stratigraphically below division A. 

The Clay Hills-San Juan Canyon area has been 

mapped by M. E. Cooley (written commun., 1966), and 

a summary description of the Chinle Formation and 

rela·ted rocks and a unit called the Church Rock Mem· 

her of the Chinle Formation, which were mapped by 

Cooley, is ·contained in a report by Repenning, Codley, 

and Akers ( 1965). They stated ( Repenning and others, 

1965, p. 133-134) that "the member is ~om posed of two 

units, which are separated roughly by a line trending 

west-southwestward through Monitor Butte." North of 

this line, "The rocks most typical of the Church Rock 

Member * * * are pale red-purple * * * to grayish· 

orange pink * * * .sandy siltstone and silty sandstone 

beds which form a broken ledge-and-slope topography 

similar to that of the Owl Rock Member." South of the 

line, "the rocks assigned to the Church Rock Member 

are similar and stratigraphically equivalent to 

those of the Rock Point Member of the Wingate 

Sandstone * * *." 

The rocks north of the line that trends through 

Monitor Butte are equivalent to the reddish-orang-? 

siltstone member of this report. The rocks south of the 

line are stratigraphically higher and 3/re equivalent to 

the Church Rock Member (that is, division A and the 

Rite Bed) as defined by Witkind and Thaden ( 1963, 

p. 32-34). 

REGIONAL RELATIONS 

A generalized diagram (fig. 6) shows the author's 

interpretation of the stratigraphy of the· Chinle Formation in parts of northeastern Arizona and southeastern 

Utah. The diagram represents the area that extends 

from Moab, Utah, southward along Comb Ridge in the 

area just described, to Round Rock, Ariz. The reddishorange siltstone member that replaces the upper part 

of the Owl Rock along Comb Ridge, together with the 

Mule Ear ledge1 is a southward-extending tongue of a 

thicker unit that is present over wide -areas of southeastern Utah. The reddish-orange siltstone member 

thickens northward below the Rite Bed or the Wingate Sandstone. In the Moab, Utah, area the reddishorange siltstone member is called the Church Rock 

Member and at places constitutes the entire Chinle Formation (see Stewart, 1957, fig. 4). As clearly shown by 

figures 3 and 6, the reddish-orange siltstone member lies 

below the Rite Bed in the Monument Valley area and 
E12 .SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

NORTH 

Moab area, Utah 

r 500 

[1000 

Wingate 

Pre-Chinle Formation rocks 

SOUTH 

Round Rock area, Arizona 

Sandstone 

Owl Rock Member 

Petrified Forest Member and older member 

FIGURE 6.-Generalized diagram showing stratigraphic relations of Chinle Formation and related rocks from the Moab, Utah, area 

to the Round Rock, Ariz., area. Diagram in part from Stewart (1957, fig. 4; written commun., 1966) and Repenning, Cooley, 

and Akers (1965, fig. 5). 

is, therefore, stratigraphically lower and older than 

Gregory's division A. The reddish-orange siltstone 

member is confined to southeastern Utah and apparently is best developed north of the San Juan River, 

although along Comb Ridge the southward-extending 

tongue of the member can be recognized as far southward as the vicinity of Moses Rock. 

Although division A superficially resembles much of 

the reddish-orange siltstone member-the Church Rock 

l\fember as used by Stewart-the grain-size distribution, fossil content, clay mineralogy, paleogeography, 

and othe-r regional relations of the two members 

strongly support the conclusion that the two are different units. · 

GRAIN SIZE 

Outcrop samples have been collected from sedimentary rock ·units in much of the Colorado Plateau by 

many geologists during an intensive program of field 

mapping and stratigraphic studies by the U.S. Geological Survey. These samples were examined by R. A .. 

Cadigan, of the U.S. Geological Survey, for measurable 

characteristics of texture and composition. The analytical methods have been described by Cadigan (in 

Stewart and others, 1959; Cardigan, 1~61). The author 

and R. A. Cadigan examined the results of the grainsize analyses for those samples from the upper part of 

the Chinle and related rocks, and some preliminary 

interpretations are presented here. 

The samples have been rearranged (by the author) 

into two· groups. One group comprises all the samples 

from division A (including the Rock Point Member and 

the equivalent silty part of the Church Rock Member 

of the southern part of Monument Valley). The other 

group contains the samples from the reddish-orange 

siltstone member of this report from southeastern Utah 

north of the San Juan River. The results are as follows: 

Number Mean Standard Skewness Kurtosis 

Stratigraphic unit of grain size deviation 

samples (millimeters) (phi units) 

Division A _______ 37 0. 056 1. 527 1. 241 7. 308 

Reddish-orange 

siltstone 

member _______ 42 . 053 2. 054 . 765 2. 33 

The reddish-orange siltstone member is, on the average, a coarse siltstone that is poorly sorted, slightly 

skewed, and moderately peaked. Division A is, on the 

average, a coarse siltstone that is moderately well 

sorted, moderately skewed, and moderately peaked. According to R. A. Cadigan (written commun., 1966) "On 

the basis of analysis of variance of the standard deviation of the grain-size distributions, the difference in 

sorting between the two groups of samples is significant 

at the 99-percent confidence level. Although untested, 

similarly significant differences probably exist also in 

grain size, skewness, and kurtosis." 

The differences in sorting (derived from the standard 

deviation) and in skewness and kurtosis would be explained if division A accumulated at a slower rate than 

the reddish-orange siltstone member and was more 

thor~mghly reworked (perhaps because of a slower rate 

of subsidence during deposition). In addition, division 

A probably accumulated in an environment of lower 

fluid velocities than the reddish-orange siltstone member. This probability is suggested by bedding features 

that indicate division A is a quiet-water deposit 

(Harshbarger and others, 1957, p. 9-10), whereas the 

reddish-orange siltstone member is partly fluviatile 

(Baker, 1933, p. 40; Schultz, 1963, p. C40; Witkind, 

1964, p. 16-17). 

-. 

.... 

,J 
CHINLE FORMATION AND RELATED ROCKS, SOUTHEASTERN UTAH AND ADJACENT AREAS E13 

CLAY MINERALS 

The clay minerals in Triassic rocks of the Colorado 

Plateau including the rocks described in this report, 

are disc~ssed by Schultz ( 1963). The clay-mineral distribution presented by Schultz indicates a difference in 

both source and composition of the clays in the reddishorange siltstone member (Church Rock Me.m~~r as us~d 

by Stewart) in Utah as compared to diVISIOn A In 

northeast Arizona. 

Schultz (1963, p. C40-C43) showed that the 0~1 

Rock and the-overlying division A in northeastern Arizona are predominantly montmorillonitic in comp~sition and in this respect closely resemble the underlying 

Petrified Forest Member. Moderate amounts of illite 

and chlorite are also present. Schultz (1963, p. C42) indicated that the principal source for the montmorillonitic clays was to the south. 

Montmorillonitic rocks of the upper p.art of the 

Chinle Formation, including the reddish-orange siltstone member, _become increasingly illitic in composition from Arizona northward into Utah (Schultz, 1963, 

p. C42 and pl. 4). In the Moab area, illitic clays are 

dominant in the reddish-orange siltstone member 

(Church Rock Member as used by Stewart). Intermixed 

with the illitic rocks in the Moab area are a few percent 

of chlorite, generaHy to the east, and a few percent kaolinite, generally to the west. The distribution of the accessory kaolinite and chlorite indicates a source to the 

east (Schultz, 1963, p. C42). The theory of an e~stern 

source for the illitic clays is supported by the thickening of these rocks eastward and by studies of crossbeds 

(Schultz, 1963, p. C42). 

FOSSILS 

The distribution and relative abundance of fossils in 

the Chinle and related rocks give some help in differentiating division A. Camp (1930, p. 3) noted that ~he 

lower part of the Chinle (divisions C, D) contains 

abundant fossil wood and vertebrate remains, but 

that such organic remains are sparse in the upper part 

of the Chinle (divisions A, B). In the Carrizo Mountains area, J. D. Strobell, Jr. (oral commun., 1966), 

pointed out that this relationship can be carried further 

and that organic remains are common in divisions C 

and D, less common in division B, and are not found 

in division A. . 

Organic remains have bee.n reported from division A 

on the southeast flank of the Carrizo Mountains 

(Harshbarger and others, 1957, p. 10) in an area where 

divisions A and B intertongue. According to Strobell, 

however ( 1956; oral commun.,_ 1966), the lithology of 

these fossiliferous beds indicates that they should be. 

classified as Chinle Formation (division B). Fragmentary vertebrate fossils have also been found at the base 

of division A near Lupton, Ariz.- (Harshbarger and 

others, 1957, p. 10, 23), but these are in conglome:~tic 

lenses of fluviatile origin that represent ·depositiOn 

marginal to the more typical facies of division A. 

No fossils, except worm trails (Harshbarger ~nd 

others, 1957, p. 23), have been found so far in the siltstone facies typical of division A. This suggests that 

the area of deposition of division A (the Rock Point 

Lagoon, see fig. 8) was an inhospitable area for ~he 

growth or preservation of organisms. It has been Inferred (Harshbarger and others, 19'57, p. 23) that the 

water in which division A was deposited "was abnor- · 

mal" and that "it may have been highly saline and of an 

oxidizing nature." 

In southeastern Utah, fossils have been reported 

(Baker 1933, p. 41; McKnight, 1940, p. 69-70; ·Mullens, 

1960, p~ 288) from throughout the Chinle Formation, 

including the upper part that contains the reddishorange siltstone member or Church Rock Member. as 

used by Stewart. The fossils found in the red~is~­

orange siltstone member of southeastern Utah are Similar to the fossils found in the Owl Rock Member of 

northeastern Arizona. In summary, the presence of 

similar fossils in both the Owl Rock and the reddishorange siltstone member contrasts with the general absence of fossils from division A. 

CHINLE FORMATION-GLEN CANYON GROUP 

CONTACT 

In a large area that includes parts of Arizona, Utah, 

and New Mexico, the author places the contact between 

the Chinle Formation and ~Glen Canyon Group at a 

well-defined horizon that probably everywhere is an 

unconformity, which marks an important regional 

break in sedimentation in the Upper Triassic Series. In 

northeastern Arizona and adjacent areas this contact is 

at the top of the Owl Rock Member. In southeastern 

Utah, beyond the limits of the Owl Rock Mem~er, the 

contact is placed at the top of the laterally equivalent 

reddish-orange siltstone member. In the southwestern 

Utah and in parts of northwestern New Mexico, it is at 

the top of the Petrified Forest Member. Different units 

of the ·Glen Canyon Group ·overlie the Chinle Formation. The relationships of the various units above and 

below the unconformity at the top of the Chinle Formation are shown in figure 7. 

At many places in northeastern Arizona the contact 

between division A and the Owl Rock Member appears 

to be conformable, but the author believes that the con-
E14 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

/ 

0 '"" /·" Hurric/ 

oHanksville 

0 Escalante 

0 Cameron 

0 Farmington 

FEET 

r 50: 

[1000 

' ' 

0 10 20 30 40 MILES 

"' ' ' "' ' 

'""' 

FIGURE 7.-Generalized fence diagram of Chinle Formation and related rocks. In part from Stewart (1957); Harshbarger, Repenning 

and Irwin (1957); Akers, Cooley, and Repenning (1958); Wilson and Stewart (1967). 

tact is sharp and that it records an abrupt change in 

lithology. At other places the basal contact of division 

A and basal units of the Glen Canyon Group, where 

they rest on the Chinle, is marked by an erosional surface, which generally shows minor relief and which is 

overlain by a thin conglomerate composed of pebbles 

reworked from the Chinle Formation. The basal conglomerate has been noted locally in the Chinle Valley 

area and near Round Rock (Akers and others, 1958, 

p. 94). In the Ward Terrace-Echo Cliffs area (see fig. 

1 for geographic location), the ·Moenave Formation 

overlies the Owl Rock Member. The basal contact of the 

Moenave is described as an unconformity, which shows 

minor relief. The basal bed of the Moenave is a thin 

conglomerate 2-3 inches thick, which consists of ·pebbles 

derived from the Chinle Formation (Harshbarger and 

others, 1957, p. 13, 15). Along Echo Cliffs the unconformity, overlain by the basal conglomerate, is represented by a gently rolling surface on the Owl Rock 

Member commonly with as much as 2 feet of 'relief 

within a few feet laterally (Callahan, 1951, p. 51). Near 

Tuba City the unconformity at one place is the base of 

a stream channel12 feet deep ·and 40 feet aoross, which 

is filled with large cobbles ·and pebbles of reworked 

Chinle (Callahan, 1951, p. 51). 

In the Lees Ferry area an unconformity between the 

Owl Rock Member of the Chinle Formation and the 

Glen Canyon Group has been described by Phoenix 

(1963, p. 23-27). Basal beds of the Glen Canyon Group, 

which contain small chips of green and red chert and 

flakes of mudstone probably derived from the Chinle 

Formation, fill scour structures along the unconformity. 

At places, a zone of sandstone as much as 10 feet thick 

above the unconformity is bleached white. Locally, beds 

in the Owl Rock Member directly below the unconformity have been silicified to light-pink chert, which contains masses of grayish-green chalcedonic chert and 

stringers and veinlets of red jasper. 

Northwest of Lees Ferry in southwestern Utah, in a 

large area extending £,rom Paria town site (now abandoned) on the east to St. George on the west, the uncon-. 

formity between the Glen Canyon Group and the Chinle 

Formation has been discussed by Wilson ( 1965). In describing the unconformity, Wilson ( 1965, p. 35-36) 
.. 

CHINLE FORMATION AND RELATED ROCKS, SOUTHEASTERN UTAH AND ADJACENT AREAS E15 

states,: "Higher members of the Chinle, such as the 

Owl Rock and Church Rock Members of southeastern 

Utah, are absent in southwestern Utah, largely as the 

result of a progressive westward truncation of the 

Chinle along an unconformity at the base· of the overlying Glen Canyon Group." 

The Church Rock Member of southeastern Utah 

mentioned by Wilson is the reddish-orange siltstone 

member of this report and the Church Rock Member as 

used by Stewart. 1\tlost of the reddish -orange siltstone 

member, as discussed, disappears by grading out southward and westward into the Owl Rock Member in the 

Clay Hills area rather than by erosional truncation. 

Any erosional t:vuncation of the reddish-orange siltstone member would be at the base of the Hite Bed. The 

unconformity at the base of the Hite Bed probably is 

the same one as the unconformity at the base of the Glen 

Canyon Group discussed by Wilson. 

According to Wilson ( 1965, p. 39), there is as much 

as 10 feet of erosional relief locally on the unconformity 

at the base of the Glen Canyon Group in southwestern 

Utah. The basal beds of the Glen Canyon Group commonly contain coarse grains and granules of quartz, 

quartzite, and chert and, at places, contain lag gravels, 

which were derived f,rom the Chinle Formation and 

which consist of pebbles of quartz, quartzite, and chert. 

The unconformity in an area that extends from the 

Hurricane Cliffs of Utah westward to southern Nevada 

has also been described by Wilson and Stewart (1967). 

They desoribed the Chinle Formation and Glen Canyon 

Group contact as "an erosion surfa·ce that marks * * * 

an important stratigraphic break in the Upper Triassic 

Series" ("\,Vilson and Stewart, 1967, p. D13). In describing this contact or erosional surface and tlie basal beds 

of the Glen Canyon Group directly over the unconformity, Wilson and Stewart (1967, p. D13, D14) 

stated: 

the basal bed of the Glen Canyon Group or its probable equivalents consists of conglomeratic sandstone or of lenses of conglomeratic sandstone in a sandstone matrix. This bed ranges 

from 1 inch to 18 feet in thickness, and seems to be persistent 

unit. The conglomeratic material contains granules to cobbles 

of chert and lesser amounts of quartzite and quartz. Siltstone 

and limestone pebbles are common. In the Spring :i\lountains, a 

considerable amount of the conglomeratic material in this bed 

consists of volcanic rock fragments * • *. 

The pebbles in the basal bed of the Glen Canyon Group probably accumulated as lag gravel deposits on the erosion surface 

at the top of the Chinle Formation. * * • the pebbles probably 

were derived by reworking from the underlying Chinle Formation . 

Topographic relief along the contact • * • is not particularly noticeable * * *. The contact surf·ace is almost fiat, and 

t~e a vera.ge relief is not more than a few inches. 

The Chinle Formation and the Glen Canyon Group 

have also been mapped and desoribed west of Lees Ferry 

along the Vermilion Cliffs and in the House Rock Valley area of Arizona (Wells, 1960; Petersen and Wells, 

1960; Petersen, 1959, 1961). In the House Rock Valley 

area the Owl Rock Member is as much as 53 feet thick 

and pinches out southward (Wells, 1960, p. 123-124, 

pl. 4). The contact between the Glen Canyon and the 

Chinle Formation at the few places where it is exposed 

is conspicuous and sharp, but, because there is no apparent truncation of underlying beds and no channeling 

or basal conglomerate, the ·contact was considered by 

Wells (oral commun., 1969) to be conformable. In the 

adjacent Lees Ferry area to the east, however, the contact is better exposed, and it is described by Phoenix 

(1963) as an unconformity. The contact is also an unconformity to the north and west (Wilson, 1965 ; Wilson 

and Stewart, 1967). These relations strongly suggest 

that the base of the Glen Canyon Group is also an unconformity in the Vermilion Cliffs-House Rock VaHey 

area of Arizona. The pinchout of the Owl Rock in the 

House Rock Valley, which is described by Wells (1960, 

p. 123-124), may be due to this unconformity. More 

work, however, needs to be done in this area to clarify 

the relationships. 

Southeast of Monument Valley along the ArizonaNew Mexico State line, the Owl Rock Member of the 

Chinle Formation is overlain by division A. The contact between the two units is marked by a thin granule 

conglomerate, and near Lupton, Ariz., basal beds of 

division A contain several thick conglomeratic lenses 

(Harshbarger and others, 1957, p. 5). East of Gallup, 

N. Mex., in the Fort Wingate area, the Lukachukai 

Member of the Wingate Sandstone overlies the Ow 1 

Rock Member, and the basal contact of the Wingate 

is a channeled surface overlain by a 6-inch granule 

conglomerate (Harshbarger and others, 1957, p. 11). 

Farther east near Thoreau, conglomerate occurs above 

the unconformity in channels that, have a relief of as 

much as 3 feet (Harshbarger and others, 1957, p. 5). 

In the Thoreau area the Owl Rock Member is overlain 

by a unit assigned to the Wingate ( ? ) Formation 

(Smith, 1954). The basal beds of the Wingate ( ? ) Formation are from a few inches to 8 feet thick and consist 

of siltstone reworked trom the Chinle Formation; these 

beds contain coarse angular fragments of white chert 

and include channel deposits that fill a ·scour zone that 

is cut on the underlying Chinle (Smith, 1954, p. 11). 

Farther east, at a locality 9 miles northeast of Grants, 

N. Mex., the Wingate Sandstone rests unconformably 

on the Chinle Formation, and large mud cracks as much 
E16 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

as 3 feet wide at the top of the Chinle are filled to a 

depth of at least 9 feet with sandstone from the overlying Wingate (R. E. Thaden, oral commun., 1969). 

Still farther east in the Laguna area, New Mexico, the 

Entrada Sandstone rests unconformably on the Petrified Forest Member. Basal beds of the Entrada locally 

include a quartz-pebble conglomerate that fills scours 

cut into the Chinle Formation (Moench, 1964b). 

Post-Chinle erosion beveled the uplifted Chinle Formation in southwestern Utah and in the area east of 

Gallup, N.' Mex. The Owl Rock Member of the Chinle 

Formation thins eastward from about 300 feet in 

northeastern Arizona to about 40 feet near Thoreau, 

Mex. ; it also thins westward to a pinchout in the House 

Rock Valley area of Arizona. Some of the thinning may 

be depositional, but most of it is probably due to erosion 

beneath the overlying unconformity. A measure of the 

amount of truncation is indicated by the relation of 

the unconformity to the Correo Sandstone Bed of the 

Petrified Forest Member of the Chinle Formation. According to Smith (1954, p. 10), a reddish-brown crossbedded sandstone in the Thoreau area may correspond 

to the Correo. The questionable Correo ·in the Thoreau 

area is 364 feet below the unconformity at the top of the 

Chinle Formation (Cooley, 1959, p. 71). In the Laguna 

area the Correo is locally present directly below the unconformity at the top of the Chinle Formation 

(Moench, 1964a). The Correo is not present at places in 

- the Laguna area, and its absence may be due to preEntrada erosion. If the Chinle was deposited uniformly 

across the ·area~ and if the correlation of the Correo is 

correct between the Thoreau and Laguna areas, then 

about 360 feet of the Chinle Formation is beveled out 

between the two localities. 

In southeastern Utah, units overlying the unconformity as herein described are either the Rite Bed or the 

massive Wingate Sandstone (equivalent to the Lukachukai Member of the Wingate in northeastern Arizona). 

The Rite Bed is a distinctive unit that is present in 

much of southeastern Utah. The lower contact of the 

Rite Bed is a channeling surface of erosion. The upper 

contact with the massive Wingate Sandstone is generally sharp. The Rite Bed, however, intertongues with 

the overlying Wingate Sandstone in the Elk Ridge area. 

In describing the upper part of the Chinle Form·ation, 

Lewis ~and Campbell ( 1965, p. B19) stated, "The upper 

most 40 feet commonly includes from one to three beds 

of maroon medium- to coarse-grained sandstone, at 

least partly of fluvial origin, which locaHy intertongues 

with the lowermost part of the overlying Wingate Sandstone." The name Rite Bed was not used by Lewis and 

Campbell (1965), but the presence of this bed as the 

"maroon medium- to coarse-grained sandstone" is cJear· 

from their description . .Similar relations between the 

Rite Bed and the Wingate Sandstone have been noted 

elsewhere. According to D. G. Wyant (oral commun., 

1968), the Rite Bed grades upward into the Wingate 

Sandstone in the Rite, Circle Cliffs, and Clay Hills 

areas. 

In most of the Circle Cliffs area of south-central 

Utah (Davidson, 1967), the Wingate Sandstone rests on 

the Ow 1 Rock Member of the Chinle Form~tion. 

Davidson (1967, p. 36) described the contact between 

the Wingate Sandstone and the Chinle Formation as 

sharp and well deifined with little or no relief, except in the 

Long Canyon area in the northwestern part of the Circle Cliffs 

area' where 15-25 foot of poorly sorted fluvial sandstone beds 

forms the base of the Wingate and fills erosional pockets in the 

top of the Ohinle. 

So mew hat similar relations were noted at a measured 

section by Davidson (1967, p. 106) in the west-central 

part of the Circle Cliffs area. In that area, a basal conglomeratic sandstone of the Wingate rests unconformably on the Owl Rock Member of the Chinle. The conglomeratic sandstone is grayish red to pale greenish 

yellow and crossbedded and contains pebbles of gray 

chert as much as 1 inch across. The basal contact of the 

Wingate, below the conglomeratic sandstone, bevels 

across the "Owl Rock Member disconformabiy, cutting 

out as much as 5 feet of beds in 15 feet along contact" 

(Davidson, 1967, p. 106). These conglomeratic sandstone beds, which are assigned to the Wingate Sandstone, may be equivalents of the Rite Bed. 

The contact between the Rite Bed and the massive 

Wingate Sandstone at many places in southeastern 

Utah is sharp and conspicuous and, according to J. H. 

Stewart and R. A. Cadigan (oral commun., 1968), it 

may be disconformable. It seems apparent that a contact 

between fluviatile deposits (Rite Bed) and eolian deposits (Wingate Sandstone) should be sharp, for it 

marks an abrupt change in bedding structures which reflects an abrupt change in environment of deposition. As 

noted, however, some geologists describe the contact, 

at least locally in central southeastern Utah, as gradational or intertonguing; the locally sharp contact does 

not necessarily record a; significant hiatus. In addition, 

the stratigraphic relations to the south indicate that 

the Rite Bed and the Wingate Sandstone are contemporaneous in part. In northeastern Arizona and in 

extreme southeastern Utah, the Rite Bed grades into 

division A, which, in turn, intertongues extensively with 

the Lukachukai ~{ember of the Wingate Sandstone. 

Where the Rite Bed is not present in southeastern 

Utah, the massive Wingate Sandstone overlies the reddish-orange siltstone member (Church Rock Member 

... 
CHINLE FORMATION- AND RELATED ROCKS, SOUTHEASTERN UTAH AND ADJACENT AREAS E17 

as used by Stewart) of the Chinle Formation. The contact between the formations represents a hiatus that in-

.volves a considerable time lapse. 

In southeastern Utah the contact between the Chinle 

Formation and Wingate Sandstone has been variously 

interpreted as indicated by the quotation below : 

"The contact between the Wingate and the underlying Chil,lle is unconformable and quite sharp over most 

of the mapped area, though in part it appears conformable." (Smith and others, 1963, p. 23); "A widespread 

unconformity separate_s the Wingate sandstone from the 

Chinle formation * * *" (Gilluly, 1929, p. 94); 

"There is a marked unconformity at the top of the 

Chinle in the San Rafael Swell" and this unconformity 

is shown extending from the San Rafael Swell to" the 

junction of the Dolores and Colorado Rivers ( Gilluly 

and Reeside, 1928, p. 68, and pl. 15) ; "At the top of the 

Chinle is an erosional unconformity, * * *" (Hunt and 

Miller in Hunt and others, 1953, p. 56); "The writer 

regards the Wingate-Chinle contact as markip.g a widespread rather abrupt change in conditions of sedimentation, of almost identical nature everywhere but not 

necessarily contemporaneous." (Dane, 1935, p. 74); 

"The writer believes that the Wingate is essentially conformable on the Chinle with a zone of lithologic transition between them." (McKnight, 1940, p. 75); "The 

bedded sandstone indicates continuous deposition and a 

gradual change from the conditions under which the 

Chinle sediments accumulated to those under which the 

Wingate sediments accumulated." (Baker, 1933,.p. 41); 

"The writer believes the contact is conformable." 

(Baker, 1946; p. 63); "The contact between * * * the 

Chinle and the overlying ·Wingate is arbitrarily selected * * *" (Witkind, 1964, p. 16) ; "The contact between the Chinle and Wingate has a local relief of a few 

inches except where the formations intertongue." 

(Thaden and others, 1964, p. 69). 

An examination of the various reports suggests that 

the discrepancies may be due to an attempt to include all 

fluvial-bedded sandstone deposits in the Chinle Formation and, conversely, to include in the Wingate only massive crossbedded sandstone. The relationship in the 

Green River Desert area of Utah was described by 

Baker (1946, p. 62), who stated, 

The contact with the overlying Wingate is sharp and marks an 

abrupt change in Uthology at most places in the area, but at 

other places there is a gradation from typical Chinle Utihology 

through a series of irregularly bedded sandstones into the massive Wingate sandstone, and the contact is placed more or less 

arbitrarily at the top of the bedded s•andstone. 

Similarly in the Elk Ridge area (see Lewis and 

Campbell, 1965, p. B19, columnar section, pl. 1) and in 

the Clay Hills area (Mullens, 1960, p. 288, 290), fluvialbedded .sandstones are present at the top of the Chinle 

Formation. In the Elk Ridge area the fluvial-bedded 

sandstones intertongue with the massive Wingate Sandstone and the contact is therefore conformable (Lewis 

and Campbell, 1965, p. B19). In the Clay Hills area the 

conformable contact between the bedded sandstones at 

the top of the Chinle and the Wingate is shown by the 

"even character of the contact ·and the close resemblance 

in texture and composition of uppermost beds of the 

Chinle to Wingate Sandstone" (Mullens, 1960, p. 290). 

The fluvial-bedded sandstones at the top of the Chinle 

Formation in the Clay Hills and Elk Ridge areas are 

now known to be the Rite Bed. The bedded sandstones 

in the Green River Desert area, which were described 

by Baker ( 1946), are· also proba~ly the Hite Bed or 

equivalents of it. The author would place the contact 

between the Glen Canyon Group and the Chinle Formation at the channeling erosion surface at the base of the 

bedded sandstones or the Rite Bed. 

In the Green River Desert area of Utah, a sharp contact was also described by Baker (1946, p. 62), who 

stated, "Where the contact is sharp the top of the Chinle 

shows slight relief, and streaks of grit and chunks of 

shale and sandstone are occasionally present in the base 

of the Wingate." The author believes that the Hite Bed 

is absent from areas where Baker described a sharp contact and that in those areas massive Wingate Sandstone 

lies on the Teddish-orange siltstone member. 

In summary, the regional relations in southeastern 

Utah and adjacent areas strongly suggest that a widespread unconformity separates the Chinle Formation 

from the Glen Canyon Group. Discrepancies in picking the contact are mostly in the areas where the Hite 

Bed is present and variously assigned to the overlying 

or underlying sequence. In view of the different interpretations of the Chinle-Wingate contact in southeastern Utah, however, it is apparent that more detailed 

lvork needs to be done in this area before the contact 

relations can be clarified. 

PALEOGEOGRAPHY 

The Chinle Formation accumulated in a large irregularly shaped basin whose axis lay somewhere east of 

Gallup. The Chinle is about 1,600 feet thick in the Fort 

"\Vingate area about 12 miles east of Gallup (Callahan 

and Cushman, 1955, p. 4). On a summary isopach map 

of Triassic rocks (McKee and others, 1959, pl. 4), a 

control point about 50 miles east of Gallup shows 1,820 

feet for an interval that includes the Wingate Sandstone and the Chinle Formation. The unit assigned to 

the Wingate is about 50-80 feet thick in that area; the 

total Chinle is, therefore, more than 1,700 feet thick. In 

this area the upper part of the Chinle has been removed 
El8 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

by erosion, and the total original thickness of the Chinle 

Formation may have been as much as 2,000 feet. 

From this area, the Chinle thins northward to about 

1,200 feet in the vicinity of Chinle Valley and to about 

400 feet near Moab, Utah. Much of this decrease in 

thickness :results from the northward thinning of the 

Petrified Forest and older me·mbers. (See fig. 6.) The 

Petrified Forest and older members 1Vere probably derived for the most part from a volcanic sou~ce (Schultz, 

1963, p. C37-C39). Hayes, Simons1 and Raup (1965) 

outlined a Triassic volcanic terrane in southern Arizona 

that is probably this source area. According to R. A. 

Cadigan (oral commun., 1967), the poor internal sorting and lack of alteration of the contained tuffaceous 

material indicate rapid deposition of the Petrified 

Forest and older members in a sinking basin. 

After deposition of the Petrified Forest Member, 

rates of deposition slowed, and th~ large basin was filled 

by the Owl Rock Member and laterally equivalent reddish-orange siltstone member. The illitic reddish-orange 

siltstone member in southeastern Utah was derived 

from a source area to the east. In the San Rafael Swell 

area of Utah, stream directions in the reddish-orange 

siltstone member are west and northwest (Stewart and 

others, 1959, p. 519-520). These directions suggest that 

a slight divide separated west-flowing streams from the 

main Chinle basin to the south. Interfingering relations 

of the illitic reddish-orange siltstone member, however, 

and the dominantly montmorillonitic content of the 

Owl Rock Member indicate that from time to time some 

streams from the eastern source were diverted south 

into the main basin. 

In northeastern Arizona and adjacent areas the Owl 

Rock Member was deposited in alternating flood-plain 

and lacustrine environments. During periods of slow 

deposition, lakes were formed in which limestone was 

deposited. Some individual limestone beds have been 

traced in outcrops for 20 miles (Akers and others, 1962, 

p. B5) . At least one limestone bed has been traced for 

40 miles (M. E. Cooley, oral commun., 1967); these 

distances indicate rather extensive lakes. Montmorillonitic clay suggests a southern volcanic source area for 

much of the Owl Rock Member. In southeastern Utah 

the increasingly illitic composition of the Owl Rock 

Member in areas where it grades northward into the 

reddish-orange siltstone member (Church Rock Member as used by Stewart) .indicates commingling of sediments from different source areas. 

Apparently, widespread erosion and nondeposition 

began at the end of Ow 1 Rock time ; this indicates a 

period of tectonic adjustment and uplift in southeastern 

Utah. Uplift is indicated in Utah hy a disconformity 

at the top of the reddish-orange siltstone member of 

this report (Church Rock Member as used by Stewart). 

As described by Stewart, Williams, Albee, and Raup 

( 1959, p. 523) : "The disconformity at the top of the 

Chinle formation in most of southeastern Utah probably represents a period of erosion of varying intensity 

in different areas .that resulted from slight upwarping 

of the region of Chinle deposition." 

After this period of uplift- and erosion, a shallow 

new basin developed in northeastern Arizona, partly · 

surrounded by land to the east, north, and west. This 

shallow depression, the Rock Point basin, widened toward central Arizona; the most rapidly sinking part 

was in northern Arizona and was occupied by the postulated Rock Point Lagoon (Harshbarger and others, 

1957, p. 23-24; fig. 8, this report). The center of· the 

Rock Point Lagoon was west of the axis of deposition 

of previously deposited Triassic units and moreover, 

as has been pointed out by Harshbarger, Repenning, 

and Irwin (1957, p. 23), younger units of the Glen Canyon Group were deposited in basins whose axes shifted 

progressively westward. As a result, the Navajo Sandstone, the youngest unit of the ·Glen Canyon Group, 

was deposited in a basin whose axis lay far to the west 

· in southwestern Utah. Each of these successive basins 

of deposition controlled the distribution and thickness 

of the contained and genetically related units. Thus, division A is restricted mainly to northeastern Arizona. 

The location of the Rock Point basin in northeastern 

Arizona is strikingly emphasized by indicators of stream 

directions in the Chinle Formation and in the Rite Bed. 

Studies of sedimentary structural features in southeasttern Utah show ~n average resultant dip direction of 

cross-sti~ata for beds in the reddish-orange siltstone.-

member (Church Rock Member as· used by Stewart) of 

N. 45° W. for one study and N. 85° W. for another 

(Stewart and others, 1959, p. 519). The Rite Bed, however, shows an average resultant dip direction of N. 60° 

E. (Stewart and others, 1959, p. 519-520). The near 

reversal in average stream directions can be explained 

by an uplift to the west during deposition of the Rite 

Bed. 

Northeast direction of transport of sediment in the 

Rite Bed in the Rite, Utah, area trends away from the 

Rock Point basin of northeastern Arizona. The stream 

directions may indicate a separate basin in southeastern 

Utah, or the directions may have been measured on 

tributaries to a master stream draining south into the 

Rock Point basin. Along Comb Ridge and near Moses 

Rock, as mentioned, foreset beds in the Rite Bed dip 

south into the Rock Point basin. 

The configuration of the basin that was formed at the 

end of Chinle time is shown by the fact that away from 

the axis of the Rock Point basin progressively younger 

i 

1 
\_ 

I 

.,., 

1. 

.J r·-. l. ~...j ( 

\ 

o F'lagstaff 

0 20 40 MILES 

0 Hoi brock 

,._... .,...... •• .;+ 

~+ 

EXPLA N ATION 

Sa

~ nd dunes 

Early de po.~its of the Lu.kaclz u kai MembPr and eolian tongue.~ in the Rork Point Member of the Wingate 

Sand.~fone; rontain re?>iile tracks 

D . 

. Alluvia l plains 

Conglmneratic fluvial deposits; contain petrified 1vood 

~ . 

...._ 

Marches 

Fine-grained fluvial deposits and 

linH!Rtone; rontain phytosmrrs and 

reed impression.'{ 

~ 

~ 

Tidal fl ats 

Ripple-marked .()Ul~lone: contain 

inrertebratt- lrail.fl 

Rock Point Lagoon 

Area in wh·ichflat-bedded siltstone and mudstone of the Rork Point Member and equ.ivafen t s werP deJJOsited 

FIGURE B.-Paleogeographic map of northeastern Arizona and adjacent areas. Map (from Harshbarger and others, 1957, fig. 18) shows hypothetical physiography of 

area during late stages of deposition of Rock Point Member of Wingate Sandstone. 

0 

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~ 1-.j 

0 

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~ 0 

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~ 

0 

0 

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~ 
E20 &HORTER CONTRIBUTIONS TO GENERAL GEOLOGY 

units of the Glen Canyon Group lie on progressively 

older units of the Chinle Formation. (See maps accompanying report by Cooley and others, 1964.) Thus, 

n~ar the axis of the Rock Point basin in northeastern 

Arizona, division A rests on the Owl Rock Member. 

(See fig. 7.) To the west, along Ward Terrace, the 

Lukachukai Member of the Wingate Sandstone rests 

on the Owl Rock Mem'ber. Along Echo Cliffs and in the 

Lees Ferry area, the Moenave Formation overlies the 

Owl Rock. Farther west in southwestern Utah, the 

Moenave Formation overlies the Petrified Forest Member (Wilson 1965). 

East of the axis of the Rock Point basin, the stratigraphic relations are somewhat similar to those west 

of the axis. Along the Arizona-New Mexico State line, 

division A rests on the Owl Rock Member. To the 

east, the rocks dip below the surface but reappear east 

of Gallup, and in the Fort Wingate area the Lukachukai Member of the Wingate Sandstone (Harshbarger and others, 1957, p. 10) overlies the Owl Rock 

Member. Farther east, between Thoreau and Laguna, 

the Owl Rock Member is beveled out by the unconformity at the top of the Chinle Formation. The Moenave 

Formation is not present in New Mexico. Either it was 

not deposited that far east, or it was eroded beneath an 

unconformity at the base of the Entrada Sandstone of 

Jurassic age. Farther east, between Grants and Laguna, the pre-Entrada unconformity bevels out the Wingate Sandstone and merges with the unconformity at 

the top of the Chinle Formation. In the Laguna, N. 

Mex., area the Petrified Forest Member of the Chinle 

Formation is unconformably overlain by the Entrada 

Sandstone (Moench, 1964b). 

The formation of the Rock Point basin must have 

been rapid. Erosion exposed the Petrified Forest Member on the uplifted edges of the basin in southwestern 

Utah and northwestern New Mexico. In northeastern 

.A!rizona, streams that drained into the Rock Point basin 

laid down a thin basal veneer of conglomerate that 

was derived from the underlying Chinle Formation; 

these streams also cut shallow channels on top of the 

underlying Owl Rock Member. These features suggest that the top of the Owl Rock was subjected to 

subaerial erosion ii1 much of northeastern Arizona during the preliminary stages of the development of the 

Rock Point basin. In the Carrizo Mountains area, however, a limestone bed of the Ow I Rock Member intertongues with division A (Strobell, 1956), and there, 

deposition was continuous. This small area of about 

24 square miles (Harshbarger and others, 1957, p. 7) 

where the units intertongue represents a possibly deeper 

part of the Rock Point basin. Here, the Owl Rock Member was not exposed to subaerial erosion, and the end 

of Owl Rock deposition was not so abrupt as it was elsewhere. In this small area, a small remnant lake or pond 

lingered on during the period of erosion that elsewhere 

preceded deposition of division A. 

Most of division A, or the Rock Point Member of 

the Wingate Sandstone (Harshbarger and others, 1957), 

represents deposition in quiet water. However, as 

pointed out by Harshbarger, Repenning, and Irwin 

(1957, p. 23) : 

The presence of a few lenses of fluviatile sandstone at the base 

of the Rock Point suggests that streams flowed into the basin 

during the initial stages of deposition. However," initial deposition of this type was of short duration throughout most of 

the area, and typical _silty flatbedded quiet-water sediments 

soon covered the basal beds·. 

At several places, marginal fluviatile deposits were 

laid down by streams that entered the Rock Point Lagoon (fig. 8). The most extensive fluvial deposits are 

on the southeast margin of the Rock Point basin where 

they are found throughout division A (or the Rock 

Point Member, Harshbarger and others, 1957, p. 23). 

Similarly, fluvial deposits are present along the Arizona-New Mexico State line and in the area west of Kayenta (Harshbarger and others, 1957, pl. 2). In northeastern Arizona such fluvial deposits have been included 

with division A (or the Rock Point Member, Harshbarger and others, 1957, p. 23). The similar, but more 

extensive, fluviatile deposits in southeastern Utah 

around the northern periphery of the Rock Point !basin 

constitute the Hite Bed. 

During the final stages of deposition of division A, 

dunes of the Lukachukai Member of the Wingate 8-andstone migrated across the Rock Point basin. In a large 

area of about 6,000 square miles (Harshbarger and 

others, 1957, p. 7) in northeastern Arizona and adjacent 

areas, the Lukachukai Member and division A interfinger, which indicates partial contemporaneity of the 

two units. In the Carrizo ~fountains area of northeastern 

Arizona, the intertonguing between division A and the 

partly overlying and partly equivalent Wingate is 

especially pronounced. Strobell ( 1956) described the 

Wingate Sandstone in this area as consisting of "two 

thick lithologic units * * * a lower siltstone and an 

upper sandstone * * * which could be mapped separately only on the basis of very arbitrary and sometimes 

inconsistent division." The dunes were transported into 

the Rock Point basin by winds from the northwest and 

probably accumulated in an interior-desert environment (Poole, 1962, p. D148). The Lukachukai Member 

of the Wingate Sandstone filled the Rock Point basin 

and overlapped the margins of the basin to the east and 

extended far to the north into Utah. To the west, the 

Lukachukai Member extends only a short distance be-
CIDNLE FORMATION AND RELATED ROCKS, SOUTHEASTERN UTAH AND ADJACENT AREAS E21 

yond the limits of division A (HarShbarger and others, 

1957, pl. 2). The westward extent of the Lukachukai 

Member was apparently controlled by the configuration 

of the Rock Point basin. 

Toward the end of the deposition of the Lukachukai 

Member of the Wingate Sandstone, the Moenave Formation began to accumulate. The axis of the Moenave 

basin of deposition shifted to the west of the Rock Point 

basin. There was, however, no halt in sedimentation, 

for the Lukachukai Member of the Wingate and the 

Moenave Formation intertongue in the Ward Terrace 

area (Harshbarger and others, 1957, p. 23 and pl. 2). 

Detailed descriptions of the Moenave Formation, as 

well as of the younger and older units of the Glen 

Canyon Group, are in the report by Harshbarger, 

Repenning, and Irwin ( 1957). 

CONCLUSIONS 

Divisions A, originally assigned to the Chinle Formation by Gregory (1917), can be recognized in a limited 

area of northeastern Arizona and southeastern Utah. 

Division A however, has been given two names and has 

been assigned to two different formations by subsequent 

workers. It seems appropriate to retain the name Rock 

Point Member of the Wingate Sandstone for division A. 

The name Church Rock Member of the Chinle Formation haR been used for division A and for the Rite Bed in 

the Monument Valley area. The Rite Bed has a much 

wider distribution than rocks more typical of division A 

and should be recognized separately. The name Church 

Rock, moreover, has been applied to units of different 

ages in different places. In southeastern Utah the name 

has been applied to the reddish-orange siltstone member of this report (Church Rock Member as used by 

Stewart) that is now known to be older than division A. 

In the author's opinion the reddish-orange siltstone 

member of most of southeastern Utah should be considered a facies of the Owl Rock Member or should be 

. renamed. 

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U.S. GOVERNMENT PRINTING OFFICE: 1970 o-375-048