Structural and Igneous Geology of the La Sal Mountains, Utah

68 Pages·2012·6.45 MB·English

Structural and Igneous
Geology of the
La Sal Mountains, Utah
By CHARLES B. HUNT
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY
GEOLOGICAL SURVEY PROFESSIONAL PAPER 294-1
With collaboration by Aaron C. Waters on the
North La Sal stock and the origin and
evolution of the magmas
UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1958
UNITED STATES DEPARTMENT OF THE INTERIOR
FRED A. SEATON, Secretary
GEOLOGICAL SURVEY
Thomas B. Nolan, Director
For sale by the Superintendent of Documents, U. S. Government Printing Office
Washington 25, D. C.
CONTENTS
(cid:9)Page Page
Abstract__._______._.__._..___.__________ 305 Intrusions and intrusive structures—Continued
Introduction _______________________________________ 305 Intrusions on North Mountain—Continued
Previous investigations._________________________ 306 Diorite porphyry laccoliths and related intru
Present investigation and acknowledgments______ 307 sions—Continued
General setting of the mountains _________________ 307 Laccoliths southwest of the stock — _—__ 320
Haystack Mountain laccolith____ — — _ 322
Stratigraphy--- ———— ____ — ____.__________ 309
Mill Creek sill_-_._-------_________ 322
Concealed formations.__________________________ 311
Laccoliths northwest of the stock_______ 322
Precambrian complex_______________________ 311
Laccoliths northeast of the stock.________ 323
Carboniferous systems____________________ 311
Intrusions between Willow Basin and Bear
Pennsylvanian system_____________________ 311
Creek......___________-... 323
Paradox member of the Hermosa forma
Beaver Creek laccolith---.-.-...-------- 323
tion—____________________ 311
Round Mountain bysmalith________-_-_. 323
Hermosa and Rico formations_________ 312
Monzonite porphyry sills and dikes_____-----_ 324
Exposed formations_____-_______________________ 312
Petrography. __--_-_---_--_----_---_-_- 324
Pennsylvanian and Permian systems________ 312
Placer Creek sill_______ ______—— 324
Cutler formation_____________________ 312
Other dikes and sills.______________ — __ 324
Triassic system_______________________________ 312
North La Sal stock, by Charles B. Hunt and
Lower and Middle(?) Triassic series________ 312
Aaron C. Waters..-..-_—_———————— 325
Moenkopi formation.___________________ 312
General features.----.---------.--—____ 325
Upper Triassic series____________________ 312
Diorite porphyry._____-__-._____.._.— 325
Shinarump conglomerate and Chinle for
Monzonite porphyry______________-----_ 326
mation. _____________________________ 312
Dike-swarm complex___-_-______-__---_- 326
Triassic and Jurassic systems__._-___--________. 312
Feldspathoidal and other soda-rich dikes— 328
Glen Canyon group and Entrada sandstone_ _ 312
Soda syenite porphyry——————— ———— 328
Jurassic system_______________________________ 313
Explosion breccias and associated aegirine
Upper Jurassic series__-___________._________ 313
granite porphyry and aphanitic sheets. __ 331
Morrison formation.....________________ 313
Soda rhyolite porphyry dikes.____-_-----_ 333
Cretaceous system______________________________ 313
Summary of the structural history of the
Lower(?) and Upper Cretaceous series_______ 313
North La Sal stock...._______... 333
Dakota sandstone____________________ 313
Rock alteration on North Mountain_„___—__-_ 334
Upper Cretaceous series.____________________ 313
Structural control of altered zones. _--____ 334
Mancos shale._________________________ 313
Degree of alteration....-----.----------- 335
Tertiary(?) system____________________ 314
Alteration minerals.___--_-_-___-_------ 335
Pliocene(?) series_____-______ —__- — _______- 314
Distribution of metals____-------_------- 338
Conglomerate in Castle Valley_________ 314
Source of the alteration products______--_ 339
Quaternary system____________________________ 314
Middle Mountain_____ _ _________————— 339
Pleistocene and Recent deposits ______________ 314
Brumley Creek laccolith___-_________--_---_- 340
Structural geology____________-_____________________ 314
Dorry Canyon laccolith.——________-_-_-._-- 341
Structural features surrounding the mountains. ____ 314
Mount Tukuhnikivatz laccolith________.---- 341
Details of folds adjacent to the mountains..... 315
Intrusions at head of La Sal Creek_______--_ 341
Castle Creek anticline_____-____.________ 315
Mount Peale laccolith-__-_-_---____--------- 342
Moab anticline and the Spanish Valley-Pack
Mount Mellenthin laccoliths.__________----.- 343
Creek synclines_______________________ 315
Blue Lake laccolith-..-.-_-.-_—————— 343
Area adjacent to Middle Mountain.______ 316
Intrusions in Horse Canyon._________________ 344
Other folds nearby,.______.____.__ 316
Brumley Ridge noselite syenite porphyry. _____ 344
Structure of the La Sal Mountains.______________ 316 Middle Mountain stock——_________ — ___-_ 344
Relation between the La Sal Mountains and the South Mountain—___-__________--_ — -.-_------- 345
regional structures.-..-.__________________ 318 Pack Creek laccolith. ________———— 345
Intrusions and intrusive structures__________________ 318 Laccolith southeast of the stock——— _________ 345
Intrusions on North Mountain..-..__...___ 318 Intrusions south and west of the stock——_____ 346
Diorite porphyry laccoliths and related intru Intrusions northeast of the stock—— __________ 346
sions. ___________________________________ 319 South Mountain stock____________ —— __— 346
Petrography.-.________________ 319 Summary comparison of the volumes and positions of
Laccoliths southeast of the stock _________ 320 the intrusions______._____--_.__.__._.__-_---- 346
in
IV CONTENTS
Page Page
Origin and evolution of the magmas, by Aaron C. Waters Economic geology—Continued
and Charles B. Hunt____________________ 348 Placer deposits__________-__..____-_--______.____ 355
Inadequacy of crystallization differentiation of Metalliferous deposits in the intrusions-___________ 355
basalt_______________________ 348 Mine descriptions_-_-__-___-______-__-__________ 356
Evidence from inclusions...-_-___--______-_______ 349 Dillon adit.._.__.________________ 356
Palingenesis of amphibolite______________________ 352
M. I. F. adit_____________________ 356
Some physical-chemical deductions._______________ 352
High Ore adit__._________________ 357
Field evidence________________________________ 353
Dewey adit. _____________________________ 357
Origin of the quartz-rich differentiate _____________ 353
McCoy adit__.__________________ 357
Summary. _____________________________________ 354
Economic geology_________-____-_________-_-_______- 355 Selected bibliography______________________________ 359
General__ ____________________________________ 355 Index. _________.______________________ 361
ILLUSTRATIONS
[Plates 41-44 follow page 332}
PLATE 39. Geologic map of La Sal Mountains______________________--_-_--___--___---_-_-_--_-_------_ — __ In pocket
40. Geologic map of the North La Sal stock, La Sal Mountains._---_-- — ________________________________ In pocket
41. Aerial view of North and Middle Mountains.
42. Green Mountain vent breccia. A. Northwest edge. B. East side.
43. View northwest along the vertically sheeted joints in the south part of Beaver Basin.
44. Aerial view of Middle Mountain.
45. Maps of adits in North La Sal Mountain._______________________________________________________ In pocket
Page
FIGUKE J 05. Index map showing location of the La Sal Mountains, Utah, and other igneous centers on the Colorado Plateau.- 306
106. Sketch of the La Sal Mountains; view from west------------------------------------------------------ 307
107. Generalized map of part of eastern Utah and western Colorado showing relation of the La Sal Mountains to
other structural features._________________________________________________________________________ 308
108. Structure contour map of the La Sal Mountains.-- —___----------_--------_----------------------___-- 317
109. Thin sections of diorite porphyry and metadiorite____________________________________________________ 319
110. Thin sections of rocks from the dike-swarm complex in the North La Sal stock-___________________________ 327
111. Filter-press relations at contact between soda syenite porphyry and metadiorite in Snowslide Gulch, Mineral
Mountain___________________.___________-----_-----_________-______-___ 329
112. Thin sections of soda syenite porphyry and feldspathoidal rocks, North Mountain.-__--__-__-____________- 330
113. Sketch of Precambrian schist partly replaced by soda syenite porphyry___________________________________ 331
114. Vesiculated syenite porphyry from vent breccia on Green Mountain_-__-_-_---_-__-_-_-__-_-_-___________ 332
115. Thin sections of soda rhyolite and aegirine granite porphyries.________-_______-_-_____-_-_-_-_-___-_-__- 333
116. Thin sections of altered rocks_ ________________________-_-__--___-_----____-_-_---_-_-_-----__----_-_ 336
117. Thin sections illustrating alteration of feldspar.___________________-_-_______-_-___-_--__-_-____--_____ 338
118. View west in Gold Basin______________________-___________---_-___---_-----_-------_--------_-----_- 340
J19. View west across cirque at head of North Fork of La Sal Creek______---_____-_-__--____________--____- 342
120. Graphs showing variations in alkali and silica content of the differentiation sequence in North Mountain. _____ 349
TABLES
Page
TABLE 1. Chemical analyses of diorite porphyry from the laccolithic mountains on the Colorado Plateau-_____-___--_--__ 321
2. Chemical analyses of monzonite porphyry from the laccolithic mountains on the Colorado Plateau___-__-_- — ___ 324
3. Dimensions, volume, and stratigraphic positions of intrusions in the La Sal Mountains._______________________ 347
4. Estimated volumes of intrusive rock in the Henry Mountains..___________________ — _______________________ 348
5. Statistical study of 85 inclusions in diorite porphyry float in the La Sal Mountains.-____-_______-----__-_--___ 350
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY
STRUCTURAL AND IGNEOUS GEOLOGY OF THE LA SAL MOUNTAINS, UTAH
BY CHARLES B. HUNT
ABSTRACT ones. These explosion breccias undoubtedly mark the roots
The La Sal Mountains, in central-eastern Utah, comprise 3 of of volcanoes. Associated with the breccias are intrusions of
the 15 laccolithic mountain groups on the Colorado Plateau. aegirine granite porphyry and soda rhyolite porphyry.
The mountains include 3 masses that are distinct topo The field evidence and the inferred physical-chemical condi
graphically and geologically; each of the 3 consists of a stock tions can be interpreted to mean that the La Sal magmas did
surrounded by a cluster of laccoliths that radiate from the stock. not evolve from a primary basalt by crystal differentiation. It
Sedimentary rocks exposed in the La Sal Mountains are is suggested that the magmatic sequence and hydrothermal
mostly of Mesozoic age, but some are late Paleozoic. The effects could be derived by the following sequence of events:
rocks of late Paleozoic age include the highly incompetent or 1. Partial fusion of amphibolite or related heteromorphous
even plastic salt beds of the Paradox member of the Hermosa metamprphic rocks to a dioritic melt containing unfused horn
formation. The intrusives are Tertiary. blende-rich remnants of the original metamorphic series.
The intrusions are in the midst of a series of salt anticlines 2. Physical injection upward of the palingenetic melt, carry
and synclines whose axes trend northwest. Although the fold ing suspended unfused fragments.
ing and attendant faulting in the area around the La Sal Moun 3. Continued melting of the leftover hornblende remnants
tains are chiefly the result of late Late Cretaceous or early Terti in the substratum, changing the composition of the melt to a
ary deformation, the structural history is complicated because more alkalic and more femic liquid which, rising in the stock
there has been repeated plastic deformation of the salt beds and with attendant filtration and other differentiation, produced
the strata arched over them. These structures antedate the intru injections first of monzonite and then of syenite.
sions and are not believed to be causally related to them. 4. As activity waned and crystallization progressed the in
North La Sal Mountain is located on an anticline, South La crease in gas pressure in the stock blasted a series of diatremes
Sal Mountain is in a faulted syncline, and Middle La Sal Moun through the arched roof.
tain is in an area of gentle homoclinal dips between these two 5. Retrograde boiling of the rest magma as a result of this
structures. The North La Sal Mountain forms a dome 10 miles release of pressure developed a gaseous diffusion column in the
long and 5 miles wide, and the uplift on it exceeds 6,000 feet. stock and produced a silica-rich liquid represented by the
This dome is greatly elongated northwesterly, parallel to the aegirine granite and soda rhyolite porphyries.
axis of the anticline in which it is located. The Middle Mountain
dome is nearly circular in plan, about 5 miles in diameter, and INTRODUCTION
about 3,500 feet high. South Mountain dome is 6 miles long, The La Sal Mountains, in eastern Utah, include 3 of
4 miles wide, and about 6,000 feet high. At the center of each
the 15 laccolithic mountain groups on the Colorado
of these domes is a stock, and radiating from each stock are
Plateau (fig. 105). These 15 igneous centers seem to
laccoliths. The domes are attributed to the physical injection
of the stocks. In the North and South La Sal Mountains the represent one general intrusive process that operated
laccoliths spread in the salt beds of late Paleozoic age; in the under very similar physical and chemical environments
Middle La Sal Mountain the laccoliths spread in shale of late but was arrested at different stages of development in
Cretaceous age.
the mountain groups. Evidence indicates that the
At each of the mountains the earliest intrusions were diorite
differences in structure and paragenesis between the
porphyry and most of the laccoliths are diorite porphyry. As
five Henry Mountains, and between them and the
in the Henry Mountains, these dioritic rocks contain many
amphibolite inclusions. At the North La Sal Mountain the La Plata and Navajo Mountains, are due to differences
diorite porphyry was followed by monzonite porphyry, mostlj in the stage reached by the intrusive process and not
in the form of dikes and sills. In the North La Sal stock the to differences in depth of erosion (Hunt, C. B., 1953).
monzonite porphyry was followed successively by a dike-swarm
Development of this concept suggested the desir
complex of dominantly syenitic rocks, a series of feldspathoidal
ability of mapping all the laccolithic mountains on the
dikes, and an irregular mass of soda syenite. These intrusions
were accompanied by hydrothermal activity that extended out Colorado Plateau in order to determine if they repre
ward from the stock along zones of vertically sheeted joints sent working models illustrating different stages in the
that had been developed in the earlier diorite porphyry laccoliths. igneous process. Comparison of the stages then would
At this stage in the history of the North Mountain the roof
lead to .better understanding of the process and perhaps
over the intrusions became breached and explosion breccias
provide information helpful in interpreting igneous
developed in four major pipelike masses and in several lesser
305
306 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY
I""-"——1
Cenozoic igneous rocks
Outline of Colorado Plateau
FIGURE 105.—Index map showing location of the La Sal Mountains, Utah, and other igneous centers on the Colorado Plateau.
and hydrothermal phenomena in areas where the composed of porphyry intrusions that deformed the
geology is more complex. This report on the La Sal adjacent strata.
Mountains is a part of that larger program. In 1905 the mountains were visited briefly by L. M.
PBEVIOUS INVESTIGATIONS Prindle, Whitman Cross, W. H. Emmons, G. F. Kay,
The first geologic studies in the La Sal Mountains and L- H- Woolsey of the U. S. Geological Survey. No
were made during the seventies under the auspices of formal report of their findings was published, but
the Hayden Survey (Peale, 1877b and 1878). This Prindle sampled some of the intrusive rocks and deter-
examination disclosed that the La Sal Mountains are mined the presence of alkalic rocks.
STRUCTURAL AND IGNEOUS GEOLOGY OF THE LA SAL MOUNTAINS, UTAH 307
The general geology and mineral deposits of the La
Sal Mountains were summarized by Hill (1913) and
later by Butler (1920).
The first comprehensive study of the mountains was
by Gould (1925, 1926) who confirmed the earlier
inference that the mountains are laccolithic, and
therefore similar to the others on the Colorado Plateau.
Other reports describing the geology of surrounding
areas, or discussing problems related to the La Sal
Mountains, are listed in the bibliography.
PRESENT INVESTIGATION AND ACKNOWLEDGMENTS
The fieldwork on which this report is based was
done during parts of the summers of 1947, 1949, 1950,
and 1952. The mapping was done on contact prints of
airplane photographs and transferred to a mosaic that
was used for the planimetric base. The planimetry of
the mosaic was corrected in part by locating about
50 land corners and comparing the surveyed distances
with those measured from the mosaic.
The topographic contours for plate 39 were sketched
by hasty planetable methods. Vertical angles to known
points on the mountainsides were measured by alidade, * 2 . § £d
and horizontal distance was measured on the mosaics as
corrected in the field. The topography on the map of the
North La Sal stock (pi. 40) was prepared by multiplex
methods by the Topographic Division of the U. S.
Geological Survey, using vertical control provided by
me. The topographic survey of the La Sal Mountains
represented by the topographic quadrangle maps was
made after this report and accompanying maps had
been prepared.
The general mapping of the mountains was completed
in 1949. The seasons of 1950 and 1952 were devoted
to mapping and studying the North La Sal stock.
In these studies it was my good fortune to have had
visits and helpful suggestions from many colleagues.
Earl Ingerson visited me in the field in 1950. Aaron
Waters spent most of the 1952 field season helping to
map and to interpret the North La Sal Stock.
My wife, Alice P. Hunt, managed the commissary • 0> O C
at the field camps and conducted a companion study
(1953) on the archeology of the area. G. M. Kichmond
is reporting on the Quaternary geology.
Fieldwork was greatly facilitated by the kindness of
the local residents, especially Mr. and Mrs. Gordon
Fowler. Mr. Q. D. Hanson, U. S. Forest Service,
rendered many favors.
GENERAL SETTING OF THE MOUNTAINS
•111
The La Sal Mountains are in the central part of the
Colorado Plateau in eastern Utah, 10 miles from the
Colorado boundary. The mountains (fig. 106) com
prise three masses that are distinct topographically
308
SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY
EXPLANATION
• Intrusive igneous rocks SPANISH VALLEY AND
PACK CREEK SYNCLINE
Outcrop of Paradox member of
Hermosa formation, generally
in graben on anticline
t____ ___
Fault, symbol shows downthrown side
20 Miles
I
FIGUKE 107.—Generalized map of part of eastern Utah and western Colorado showing relation of the La Sal Mountains to other structural
after Dane, 1935).
309
STKUCTTJRAL AND IGNEOUS GEOLOGY OF THE LA SAL MOUNTAINS, UTAH
and geologically; each of the three consists of a stock late Tertiary age. The intrusive rocks probably are
surrounded by a cluster of bulbous intrusions—lac Tertiary.
coliths whose long axes radiate from the stock. Because of poor exposures in the mountains, the
North Mountain, the largest, has several peaks bedrock sedimentary formations have not been sub
higher than 12,000 feet in altitude, and about 15 square divided as finely as they have been in the adjacent
miles of the mountain is higher than 11,000 feet. parts of the plateau where exposures generally are ex
Middle Mountain has the highest peaks in the La Sal cellent. Indeed, the 20 or so formations and members
Mountains, and two of them, Mount Peale and Mount that have been mapped in adjoining areas are grouped
Tukuhnikivatz, reach nearly to 13,000 feet. But the into only 4 mappable units in parts of the mountains.
area of Middle Mountain that is higher than 11,000 At most places the Triassic and older rocks have
feet is only about half that of North Mountain. South been grouped together for mapping. Locally individual
Mountain has a single peak higher than 12,000 feet, formations of Triassic, Permian, or Pennsylvanian age
but only about 2% square miles of this mountain is can be identified, but the boundaries between them
higher than 11,000 feet. The three mountains are cannot be distinguished consistently enough to warrant
separated by passes that are slightly above 10,000 feet mapping them over large areas.
in altitude. The Glen Canyon group and the lower part of the
Around the foot of the mountains are the mesas and San Rafael group comprise five distinguishable forma
canyons so typical of the Canyon Lands section of the tions in adjoining areas, but these have been grouped
Colorado Plateau. The Colorado Eiver, about 15 together into a single mappable unit in the mountains.
miles northwest of the mountains, is at an altitude of The Wingate, Navajo, and Entrada sandstones are
about 4,000 feet. conspicuous cliff formers in the canyons of southeastern
The higher peaks are timberless boulder fields, with Utah but they are not at all well exposed in the La
out vegetation except for scattered lichens. Below Sal Mountains. Here they are thoroughly fractured
about 11,500 feet in altitude, however, the mountainous by joints as a result of folding, and during the Pleisto
ridges and valleys are forested, with spruce-fir forest cene they were largely reduced to rubble by frost ac
at high altitudes, aspen and Douglas-fir at intermediate tion. Nowhere in the mountains do these sandstone
altitudes, oak brush below this, and pinon-juniper formations form extensive cliffs; in fact, few outcrops
woodland around the base. Most of the forests are of them are satisfactory for measuring strikes and dips.
open stands of timber interspersed with meadows. Around the base of the mountains the Morrison and
The mountains were glaciated in Pleistocene time related formations are reasonably distinctive, but in
and the Pleistocene deposits are an extensive cover. most of the La Sal Mountains these deposits are shown
Bedrock exposures are few, and most of the bedrock as a single unit, locally including, at the top of the for
mapping had to be based upon float. mation, some sandstone beds that belong to the
The La Sal Mountains are in the midst of the north Dakota.
west-trending salt anticlines (fig. 107), and in this re Overlying the Morrison formation is the Mancos
spect they are unique among the laccolithic mountains shale. A conglomerate in Castle Valley may be late
on the Colorado Plateau. The intrusions penetrated Pliocene in age.
the salt beds and apparently pushed them aside. In Only meager data are available about the thickness
the Middle La Sal Mountain they rose into and domed and kind of rocks that underlie the exposed formations.
the overlying formations of Mesozoic age in the same In adjoining areas more than 3,500 feet of sedimentary
manner as in the other laccolithic mountains of the rocks of late Paleozoic age lie between the Precambrian
Colorado Plateau. basement and the Triassic formations (Dane, 1935, p.
19-20). The upper part of these formations of Paleo
STRATIGRAPHY zoic age consists of interbedded competent sandstone
and incompetent shale beds, but the lower part con
The sedimentary rocks exposed in the La Sal Moun
stitutes the thick highly incompetent gypsum and salt-
tains include units of late Paleozoic, Triassic, Jurassic,
bearing Paradox member of the Hermosa formation.
and Cretaceous age. In addition there are extensive The rock formations that were penetrated by the
surficial deposits of Quaternary age and one moderately intrusions, so far as they are known, are summarized
well consolidated gravel deposit that probably is of in the table below.
448662—58———2
310
SHOETEE CONTEIBUTIONS TO GENEEAL GEOLOGY
Rock formations cut by the intrusions in the La Sal Mountains
System Series Group Formation Member Thickness (feet) Description of rocks
500+ Lead-gray marine fossiliferous shale; some
Upper Cretaceous §5 nodular limestone in concretions as much
CJ c8 as 2 feet in diameter. Includes a poorly
Cretaceous SC3*-C cemented sandstone (Perron sandstone
member) about 60 feet thick in lower Pack
Creek. Structurally an incompetent unit.
50-120 Interbedded sandstone, shale, siltstone, and
Upper and 3o§ coal. Well-bedded sandstone; shale and
If
Lower(?) carbonaceous siltstone. Mapped with
«I
Cretaceous Morrison formation. Alternating com
petent and incompetent beds.
800 Upper part, 125 feet thick, consists of sand
stone, conglomerate, limestone, and shale.
i
Firmly cemented sandstone; in part
conglomerate with black and gray chert
pebbles; sandstone beds 25 feet thick.
Gray masssive limestone, generally a few
JUurapspsiecr fMormoraritsioonn feet thick and lenticular; abundant red
and white chert. Variegated shale. On
the map, Dakota sandstone generally is
included with these beds; the two consist
of alternating competent and incompetent
• oPi"t beds.
Middle part, 375 feet thick, is mostly shale,
variegated red, green, and purple. Some
1-9 lenticular sandstone. Incompetent unit.
Lower part, 300 feet thick, is mostly sand
stone with some interbedded shale. Sand
stone in thick firm beds. Competent unit.
a Summerville 0-50? Not mapped separately; if present, this
MUainpddpdlee r of-< formation formation has been included with the
Jurassic &C Morrison. Probably an incompetent unit.
"o
Entrada 275 Massive sandstone. Competent unit.
A08 sandstone Mapped with Glen Canyon group.
tf
a Carmel 0-25? Not recognized but probably present. Prob
08
formation ably an incompetent unit.
02
Jurassic and Navajo 300 Massive sandstone. Competent unit.
a
Jurassic (?) sandstone Mapped with Entrada sandstone and rest
oi-> of Glen Canyon group.
&D
Jurassic (?) Lower oa Kayenta 250 Bedded sandstone. Competent unit.
Jurassic (?) >, formation Mapped with rest of Glen Canyon group
a
c3 and Entrada sand stone.
U
aa> Wingate 300 Massive sandstone. Competent unit.
3 sandstone Mapped with rest of Glen Canyon group
and Entrada sandstone.
TUripaspsiecr
Chinle 300 Irregularly bedded sandstone, siltstone, and
formation shale. Alternating competent and in
competent beds. Mapped with other
Triassic and older formations.
Triassic
Shinarump Probably not Firm conglomerate; not recognized but
conglomer present in possibly present. Competent unit. Mapped
ate mountains. with other Triassic and older formations.
Moenkopi 500? Thinly bedded and well-bedded shale and
formation sandstone. Alternating competent and
Middle and incompetent beds. Mapped with other
Lower Triassic and older formations. Thickness
Triassic uncertain because of doubt regarding
boundary with Cutler formation.