Stratigraphy of the 

Morrison and Related 

Formations, Colorado 

Plateau Region 

A Preliminary Report

GEOLOGICAL SURVEY BULLETIN 1009-E

A CONTRIBUTION TO THE GEOLOGY OF URANIUM

STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS, COLORADO PLATEAU REGION, A 

PRELIMINARY REPORT

By LAWRENCE C. CRAIG and OTHERS *

ABSTRACT

Three subdivisions of the Jurassic rocks of the Colorado Plateau region are: 

the Glen Canyon group, mainly eolian and fluvial sedimentary rocks; the San 

Rafael group, marine and marginal marine sedimentary rocks; and the Morrison 

formation, fluvial and lacustrine sedimentary rocks.

In central and eastern Colorado the Morrison formation has not been differentiated into members. In eastern Utah, northeastern Arizona, northwestern 

New Mexico, and in part of western Colorado, the Morrison may be divided 

into a lower part and an upper part; each part has two members which are 

differentiated on a lithologic basis.

Where differentiated, the lower part of the Morrison consists either of the 

Salt Wash member or the Recapture member or both; these are equivalent 

in age and intertongue and intergrade over a broad area in the vicinity of the 

Four Corners area of New Mexico, Colorado, Arizona, and Utah. The Salt 

Wash member is present in eastern Utah and parts of western Colorado, northeastern Arizona, and northwestern New Mexico. It was formed as a large 

alluvial plain or "fan" by an aggrading system of braided streams diverging 

to the north and east from an apex in south-central Utah. The major source 

area of the Salt Wash was to the southwest of south-central Utah, probably in 

west-central Arizona and southeastern California. The member was derived 

mainly from sedimentary rocks. The Salt Wash deposits grade from predominantly coarse texture at the apex of the "fan" to predominantly fine texture at 

the margin of the "fan".

The Salt Wash member has been arbitrarily divided into four facies: a conglomeratic sandstone facies, a sandstone and mudstone facies, a claystone and 

lenticular sandstone facies, and a claystone and limestone facies.

The Recapture member of the Morrison formation is present in northeastern 

Arizona, northwestern New Mexico, and small areas of southeastern Utah 

and southwestern Colorado near the Four Corners. It was formed as a large

"This report is based on -work done jointly by Lawrence C. Craig, Clifford N. Holmes, 

Robert A. Cadlgan, Val. L. Freeman, Thomas B. Mullens, and Gordon W. Weir.

125
126 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

alluvial plain or "fan" by an aggrading system of braided streams. The Recapture deposits grade from predominantly coarse texture sedimentary rocks to 

predominantly fine texture and have been arbitrarily divided into three fades: 

a conglomeratic sandstone facies, a sandstone facies, and a claystone and 

sandstone facies. The distribution of the facies indicates that the major source 

area of the Recapture was south of Gallup, N. Mex., probably in west-central 

New Mexico. The Recapture was derived from an area of intrusive and 

extrusive igneous rocks, metamorphic rocks, and sedimentary rocks.

The upper part of the Morrison formation consists of the Westwater Canyon 

member and the Brushy Basin member. The Westwater Canyon member forms 

the lower portion of the upper part of the Morrison in northeastern Arizona, 

northwestern New Mexico, and places in southeastern Utah and southwestern 

Colorado near the Four Corners, and it intertongues and intergrades northward 

into the Brushy Basin member. The Westwater Canyon member was formed 

as a large alluvial plain or "fan" by an aggrading system of braided streams. 

The Westwater deposits grade from predominantly coarse-textured sedimentary 

rocks to somewhat finer textured sedimentary rocks, and have been arbitrarily 

divided into two facies: a conglomeratic sandstone facies and a sandstone 

facies. The distribution of the facies indicates that the major source area 

of the Westwater was south of Gallup, N. Mex., probably in west-central New 

Mexico. The Westwater was derived from an area of intrusive and extrusive 

igneous rocks, metamorphic rocks, and sedimentary rocks. The similarity of 

the distribution and composition of the Westwater to the Recapture indicates 

that the Westwater represents essentially a continuation of deposition on the 

Recapture "fan"; the Westwater contains, however, considerably coarser 

materials.

Whereas the Salt Wash, Recapture, and Westwater members of the Morrison 

formation are characterized by sequences of interstratifled sandstone and red or 

green claystone, the Brushy Basin member consists mainly of variegated claystone with a few lenticular conglomeratic sandstone strata. The Brushy Basin 

member is present in eastern Utah and parts of western Colorado, northeastern 

Arizona, and northwestern New Mexico. It consists of sediments formed in 

fluvial and lacustrine environments and contains large amounts of clay, part

of which is bentonitic and was probably derived from falls of volcanic ash. The 

source area for many of the fluvial deposits of the Brushy Basin member may 

have been the same as that for the Salt Wash member. No lithologic facies with 

restricted areal distribution can be distinguished in the Brushy Basin member. 

At .the conclusion of deposition of the conglomeratic sandstone and sandstone of 

the Westwater member, deposits of the Brushy Basin were spread southward

over at least part Of the Westwater. The original extent of the Brushy Basin

to the south ana west is not known, for it has been removed by pre-Dakota erosion 

from most of northeastern Arizona.

The wnaiffereatiafced Morrison formation of eastern and central Colorado has

lithologic characteristics similar to those of the Brushy Basin member. It is

thought to contain beds equivalent to both the upper and lower parts of the 

Morrison to the west, but these parts cannot be distinguished, and no Other lithologic units have sufficient continuity to warrant member status.

iCovrer Cretaceous beds, mainly of fluvial and lacustrine character, have been 

recognized overlying the Morrison formation throughout most Of the Colorado 

Plateau region. In places the beds are so similar to the beds of the Morrison 

that the formations are difficult or impossible to separate. Upper Cretaceous 

formations consist of intertonguing continental and marine beds which mark 

widespread transgressions and regressions of the strand line. The Dakota sand-
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 127

stone, at the base of the Upper Cretaceous, overlies an erosional unconformity; 

in western New Mexico and. northeastern Arizona the Dakota progressively overlies older and older formations.

Most of the carnotite deposits of the Morrison formation are in the Salt Wash 

member. They are found entirely within the sandstone and mudstone facies of 

the Salt Wash member. Lithofacies studies have delimited an area relatively 

favorable for the occurrence of ore within the area of this facies. Most of the 

carnotite deposits occur in areas where sandstones of the Salt Wash are relatively well sorted and probably have a relatively high permeability. The resultants of dip directions of cross-laminae in the sandstones of the Salt Wash and 

the trends of ore "rolls" show similar radial patterns and may indicate that the 

shapes of carnotite deposits were influenced by primary sedimentary structures; 

however, the ore deposits show little.detailed control by sedimentary structures, 

for in many places the ore cuts across the bedding and lamination.

Three distinct possible sources for the uranium of the carnotite deposits may 

be postulated: 1) the rocks of the source area of the Salt Wash member of the 

Morrison formation, 2) a post-Salt Wash hydrothermal source in the Colorado 

Plateau region, and 3) disseminations in post-Salt Wash sedimentary rocks.

INTRODUCTION

PURPOSE AND METHODS

In July 1947, a program of stratigraphic studies was begun by the 

Colorado Plateau project of the U. S. Geological Survey on behalf 

of the Atomic Energy Commission. The general purpose of the 

stratigraphic studies has been (1) to determine the paleogeography 

of the uranium-bearing formations of the Colorado Plateau, with the 

ultimate goals of establishing possible sources of the ore minerals, 

their means and routes of transportation, and controlling factors for 

their localization in ore bodies as an aid to guiding exploration for 

these deposits; and (2) to provide a sound foundation for stratigraphic nomenclature within the areas of the geologic mapping and 

exploration programs.

, The first phase of the stratigraphic studies has been concerned with 

the Morrison formation of Late Jurassic age, which contains most of 

the carnotite deposits of the Colorado Plateau and has shown the 

most promise for development of ore reserves. Study of the Morrison 

is nearing completion. This report summarizes the results and interpretations warranted at this stage of the work. Many of the ideas 

resulting from this work are new. This is due to the development 

of new methods, to a more widespread application of old methods, 

and to standardization of descriptions and techniques.

The work has been divided into four studies, two of which deal 

with the Morrison and adjacent formations, and two of which deal 

mainly with the carnotite-bearing Salt Wash member of the Morrison 

formation, as follows:

j 1. Eegional stratigraphic study, concerned with establishing and 

interpreting the stratigraphic sequence, physical continuity, color,
128 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

composition, texture, structure, and thickness variations of the members of the Morrison and adjacent formations.

2. Sedimentology, concerned with the laboratory analysis of samples of the Morrison and adjacent formations to determine detailed 

lithologic characteristics and variations. Particular emphasis has 

been placed on the Salt Wash member to determine not only the 

regional variations but also any relation of the carnotite deposits to 

these variations.

3. Lithof acies study, concerned with determining the distribution 

and variation of the sedimentary rocks formed in the two main depositional environments of the lower part of the Morrison formation.

4. Study of sedimentary structures, concerned with determining the 

current directions during deposition of the Salt Wash member of the 

Morrison formation and the relation of the resulting sedimentary 

structures to ore structures.

The region of study includes more than 5,000 linear miles of outcrop of the Morrison formation. Outcrops are so extensive that it was 

necessary to resort to sampling methods in all the phases of the stratigraphic studies. All the studies yielded quantitative as well as qualitative results, and all except the regional stratigraphic study supplied 

data which can be studied statistically.

Work was begun in the carnotite-producing area of westernmost 

Colorado and was extended radially from this area with decreasing 

concentration. The region of study extends sufficiently beyond the 

limits of recognizable Salt Wash member of the Morrison formation

to permit a thorough understanding of the geologic history of the 

member.

REGION OP STUDY AND GEOLOGIC SETTING

The region of study includes the western two-thirds of Colorado, 

the northwestern quarter of New Mexico, the eastern half of Utah, 

and the northeastern quarter of Arizona (fig. 19). This region includes all except the southwestern margin of the Colorado Plateau 

province, all the Southern Rocky Mountain province, and the western 

edge of the Great Plains province, as these physiographic provinces

are outlined by Fenneman (1931),

In the Colorado Plateau, sedimentary beds are flat-lying or gently 

warped except where intruded by laccoliths, pierced by volcanic plugs, 

and Warped in Salt anticlines, or where sharply folded along large 

monoclines. The Morrison formation crops out in long, COntinUOUS 

Serrate patterns (fig, 1$), In the Southern Rocky Mountain part of 

the region the rocks exposed are dominantly igneons or metamorpnic 

and are faulted, folded, and uplifted to form mountains of complex 

structure. In this area the Morrison crops out in short disconnected
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 129

'-.MIDDLEi I--_.._W Y 0 M I N G

NWYOMING 

BASIN

' . \1FORT COLLIN 1

LOVEL4NO

BASIN AND RANGE':

EXPLANATION 

'Outcrop of Morrison formotion Boundory of physiogrophic province

FIGURE 19. Index map of the Colorado Plateau region, showing the outcrop pattern of

the Morrison formation.

belts that form sinuous or straight patterns. In the Great Plains 

province, sedimentary beds are nearly flat-lying, and, where exposed, 

the Morrison crops out in long, continuous serrate patterns.

The rocks exposed in the region of study range in age from preCambrian to Cenozoic. Igneous and metamorphic -rocks constitute 

the pre-Cambrian, whereas younger rocks are predominantly sedimentary. The early Paleozoic is represented by relatively thin marine limestones and elastics. These grade upward to the thick terrestrial and marginal-marine elastics and evaporites of the late Paleozoic. 

Rocks of Mesozoic age are mainly elastics; they were deposited under 

terrestrial conditions throughout the Triassic, Jurassic, and Early Cretaceous with the exception of two marine units of Middle and Late

319582 55 2
130 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Jurassic age. The Late Cretaceous is represented by thick, dominantly marine elastics. Tertiary sedimentary rocks are mainly nonmarine elastics; Tertiary igneous activity is represented in many 

forms in places in the region studied.

STRATIGRAPHY OF JURASSIC AND CRETACEOUS

ROCKS

The Jurassic rocks (table 1) of the Colorado Plateau are subdivided 

into three major units. In ascending order these are: the Glen

TABLE 1. Generalized section of the Winffate sandstone and, Jurassic and 

Cretaceous strata in part of southwestern Colorado and adjoining parts of 

Utah

System

Cretaceous

Jurassic

Jurassic(?)

Triassic

Group

Rafael Sn group

Glen Canyon group

Formation

Mesaverde formation

Mancos shale

Dakota sandstone

Burro Canyon formation

Morrison formation

Summerviile formation

Curtis formation

Entrada sandstone

Carmel formation

Navajo sandstone

 Kayenta formation

wmgate sandstone

Thickness 

(feet)

1, 000±

2, 000-5, 000

0-200

50-250

300-500

200-400

0-400

0-250

50-1, 000

0-600

0-2,000

0-300

0-400

Character and distribution

Light-colored sandstone and gray shale; 

coal-bearing; cliff -forming; wide-spread.

Gray shale; forms valleys and steep slopes; 

widespread.

Gray and brown sandstone and shale; 

mesa-capping; widespread.

Light-colored conglomeratic sandstone and 

maroon and green mudstone; mesacapping.

Brushy Basin member: varicolored shale 

(or mudstone), some sandstone lenses; 

forms slopes; widespread.

Salt Wash member: light-colored sandstone and red mudstone; forms cliff 

and benches; widespread; carnotitebearing.

Red and gray shale, thin sandstone; forms 

slopes; thickens westward.

Giauconitic sandstone, greenish shale, 

gypsum; present only in central Utah.

Light-colored, massive, cliff-forming sandstone in Colorado and eastern Utah; 

thickens westward and becomes red, 

earthy sandstone. Vanadium-bearing.

Bed, earthy sandstone in Colorado and. 

eastern Utah; thickens westward and 

becomes gray and red shale; limestone 

and gypsum.

Light-colored, massive sandstone; cliffforming; thins to extinction in western 

Colorado; thickens westward.

Red sandstone, irregularly bedded; benchforming; absent In eastern part Of region.

Red, massive sandstone; cliff-forming; 

absent in eastern part of region.

Canyon group, the San Rafael group, and the Morrison formation. 

This classification may be applied throughout the region of study. 

Baker, Dane, and Reeside (1936, 1947) have discussed the Jurassic 

stratigraphy of the Colorado Plateau, and their papers cite most of the 

basic references dealing with this subject.
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 131 

PRE-MOBRISON FORMATIONS ' ' 

G1LEN CANYON GBOUP

The Glen Canyon group consists in ascending order of the Wingate 

sandstone, Kayenta formation, and Navajb sandstone. Assignment 

of the group to the Jurassic is tentative because of the lack of diagnostic fossils.1 The Wingate sandstone forms a broad lens-shaped deposit extending throughout southeastern Utah, and into southwestern 

Colorado and the Four Corners. In the center of this area the Wingate is mostly of eolian origin but to the north and east shows increasing characteristics of deposition in a standing body of water and to 

the southeast, of fluvial deposition.

The Kayenta formation forms a broad lens-shaped deposit throughout southeastern Utah, and extends into western Colorado and part of 

northeastern Arizona. The Kayenta is of fluvial 'origin. The marginal relations of the Wingate sandstone and the Kayenta formation 

are poorly understood.

The Navajo sandstone forms an irregular wedge of sandstone, predominantly eolian in origin, extending throughout southern and eastern Utah into western Colorado and part of northeastern Arizona. 

The Navajo is thickest in southwestern Utah and is represented by the 

Aztec sandstone of even greater thickness in southern Nevada. The 

eastern limit of the Navajo is along an irregular north-south trending 

line through western Colorado and northeastern Arizona.

In Colorado and Utah the Glen Canyon group is generally conformable on the underlying Upper Triassic Chinle formation, but 

in parts of New Mexico and Arizona an erosional disconformity is 

indicated at the base of the Glen Canyon (Harshbarger, Repenning, 

and Jackson, 1951, p. 96) . The formations of the Glen Canyon group 

are separated in most places by gradational contacts.

The Glen Canyon group reflects a period of aridity during which terrestrial elastics accumulated over the region of the Colorado Plateau. 

The dominant eolian deposition characterizing the group was interrupted by a period of widespread stream deposition in Kayenta time. 

Data as to source areas of the formations are incomplete. The Wingate sandstone was probably derived from areas to the west in Utah 

and eastern Nevada. Baker, Dane, and Keeside (1936, p. 44) suggest 

that the Kayenta formation had an important local source from the 

east, the Ancestral Uncompahgre Highland of western Colorado, 

but no major source area has been recognized. The Navajo sandstone 

probably was 'derived from a source area in western and southern 

Nevada. Analyses of the orientation of sedimentary structures in

Geological Survey now treats the Wingate sandstone as Triassic In age, the 

Kayenta formation as Jurassic(?), and the Navajo sandstone as Jurassic. See table 1.
132 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

the Navajo indicate that the sands were deposited by winds blowing 

from the west and northwest across eastern Utah and northeastern 

Arizona.

SAN RAFAEL. GROUP

The San Raf ael group is divided into four formations: the Carmel 

formation, Entrada sandstone, the Curtis formation, and the Summerville formation, in ascending order. The Carmel has been dated 

as Middle and early Late Jurassic and the Curtis as middle Late 

Jurassic from marine invertebrate fossils. The Entrada and Summerville lack diagnostic fossil remains.

The Carmel formation was deposited throughout southern Utah 

and northeastern Arizona. It thins to the northeast to a feather edge 

in southwestern Colorado. In central and southwestern Utah a partly 

marine sandstone and shale facies containing limestone and gypsum 

has been distinguished from a marginal marine red shale facies in 

northeastern Arizona and a marginal marine red silty sandstone 

facies in eastern Utah. The extent of the Carmel in New Mexico has 

not been determined. This problem can be solved only by detailed 

studies of facies relations in southeastern Utah.

The Entrada sandstone was deposited throughout southern and 

eastern Utah, most of Colorado, and all northeastern Arizona and 

northern New Mexico. A red earthy sandstone facies in central and 

southwestern Utah has been distinguished from a clean sandstone 

facies in Colorado, eastern Utah, northeastern Arizona, and northern 

New Mexico. The earthy sandstone facies is largely of subaqueous 

origin, and the clean sandstone facies was deposited in an environment of alternating subaerial and subaqueous marginal marine conditions. The Entrada is absent in parts of central Colorado over the

Ancestral Highlands.

The interval between the top of the Entrada sandstone and the base

of the Morrlson formation is complicated bj many facies changes and

by a number of formation and member names. The Curtis and Summerville formations are the main units occupying the interval. The

Curtis is grayish to greenish glauconitic sandstone and shale; the

Summerville is red silty shale with minor light-colored sandstone. The

Curtis has been recognized in southwestern, central, and northeastern

Utah and. in northwestern Colorado, Thin-bedded sandstones and

shales along the northern part of the Front Range in Colorado and

limestone and gypsum deposits in southwestern Colorado and northwestern ISTew Mexico may be equivalent to the Curtis. The Curtis

and these possible equivalents are regarded as predominantly marine 

in origin. The Summerville formation has been recognized throughout south-central and southeastern Utah, and parts of southwestern 

Colorado, northeastern Arizona, and northwestern New Mexico.
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 133

Where both formations are present, the Summerville overlies the 

Curtis. In northeastern Utah and northwestern Colorado the Curtis 

occupies the entire interval between the Entrada and the Morrison.. 

The Summerville is regarded as a marginal marine deposit formed 

in relatively quiet shallow water. It contains the Moab tongue of the 

Entrada sandstone in part of southeastern Utah.

In the vicinity of the Four Corners and as far west as south-central 

Utah a prominent sandstone unit is present at the top of the Summerville formation and at the base of the Morrison formation. This unit 

has received various assignments in the geologic literature. Gregory 

(1938, p. 58) designated the sandstone unit as the Bluff sandstone 

member of the Morrison formation in southeastern Utah. Goldman 

and Spencer (1941, p. 1750) defined it as the Junction Creek sandstone 

member of the Morrison in southwestern Colorado. The Junction 

Creek has been treated as a separate formation (Eckel, 1949, p. 29) 

and, most recently, has been treated as a member of the Wanakah 

formation (Eead, Wood, Wanek, and McKee, 1949), a unit that occupies the stratigraphic position of the Summerville formation in parts 

of Colorado and New Mexico.

Goldman and Spencer (1941, p. 1759) suggested that the Junction 

Creek correlates with the Bluff. This correlation seems certain on the 

basis of similarity of lithology, stratigraphic position, and detailed 

stratigraphic sequence, but the outcrops of this sandstone in southwestern Colorado are separated from those of the Bluff in adjacent 

states, and the unit is treated here as a separate formation, the Junction 

Creek sandstone of southwestern Colorado.

The Bluff sandstone has been traced southward from the Four 

Corners area into northeastern Arizona and northwestern New Mexico. 

In the area west of Gallup, N. Mex., the Bluff constitutes an inseparable part of the Cow Springs sandstone (Harshbarger, Repenning, 

and Jackson, 1951, p. 97-98). The Cow Springs occupies the entire 

stratigraphic interval of the Summerville formation and part of the 

Morrison formation. Inasmuch as the Bluff of the Four Corners area 

has been identified as an extension of the thicker and more complete 

sandstone section to the south, the Bluff is recognized as a tongue of 

the Cow Springs sandstone.

The Bluff has been observed to tongue and grade into the Summerville formation in southeastern Utah, and a part of the Bluff has been 

observed to tongue with the overlying Salt Wash member of the 

Morrison formation in northeastern Arizona a short distance west of 

the Four Corners. Thus the sandstone unit is related to both the 

Summerville and Morrison formations. Both the Bluff sandstone and
134 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

the correlative Junction Creek sandstone are assigned here arbitrarily 

to the San Rafael group. This is appropriate, for the Bluff and 

Junction Creek exhibit bedding and lithologic characteristics quite 

similar to those found in the San Eafael group and quite dissimilar 

to those of the bulk of the Morrison of the Colorado Plateau region.

Southward from the Four Corners the rocks in the stratigraphic 

interval of the Summerville formation, as well as most of the Morrison 

formation, grade into the Cow Springs sandstone. In places west and 

south of Gallup, the Entrada and Cow Springs sandstones are essentially inseparable. Similarly, to the northwest of the Four Corners, 

in south-central Utah, the stratigraphic interval of the Summerville 

formation becomes sandstone and constitutes the Winsor formation 

(Gregory, 1951, p. 30-53).

The base of the San Rafael group is marked by an erosional break, 

probably of little time duration. The irregularities of the underlying 

Glen Canyon group were beveled and the uppermost deposits were 

reworked into the basal few feet of the Carmel formation. The 

remainder of the San Rafael group is essentially conformable. Local 

angular unconformities are common in central and south-central Utah 

as well as in the Four Corners area at various horizons in the San 

Rafael group, and are regarded as minor breaks of little importance.

MORRISON FORMATION

The Morrison formation (Cross, 1894, p. 2) has been recognized 

over most of the western interior of the United States; except where

removed by erosion, it is present over all of Colorado, eastern Utah, 

northwestern New Mexico, and part of northeastern Arizona (fig. 19).

The Morrison consists of lenticular strata of variegated mudstoneS 

and ClajStones and light-gray, cross-laminated sandstones. Over most

of the western interior of the United States the Morrison has not 

been divided into members. In western Colorado, eastern Utah, northeastern Arizona, and northwestern New Mexico, however, the Morrison

can be separated into a lower and an upper part, each of which has

two members, differentiated on lithologic criteria (fig. 20). An arbitrary line separating the undifferentiated Morrison of central Colorado 

from the subdivided Morrison to the west extends irregularly from

HOrtll"?vester-n Oolorsxclo to soutK-centra-l Colorado. In figure £21 fl-»ig

line is shown as the limit of recognizable Salt wash,

The base of the Morrison formation is defined in the Colorado

Plateau region as the base of the terrestrial, fluvial Jurassic deposits 

OYerljing DeClS Of tne marine or marginal marine San Hafael group.

Detailed criteria for selecting the contact vary from one area to 

another.
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 135 

LOWER PART OF THE MORRISON FORMATION

The lower part of the Morrison consists solely of the Salt Wash 

member in most of eastern Utah and western Colorado and solely of 

the Kecapture member in most of northeastern Arizona and northwestern New Mexico. These members interfinger and grade into 

each other over a broad area in the vicinity of the Four Corners 

(% 20).

REGIONAL STRATIGRAPHY

Salt Wash member. The Salt Wash member (Lupton, 1914, p. 127; 

Gilluly and Keeside, 1928, p. 82) constitutes the lower part of the 

Morrison formation over the large fan-shaped area shown in figure 21. 

The blunt apex of the fan lies along the northwest-southeast trending 

line in south-central Utah and north-central Arizona. This line is a 

limit of preservation; southwest of it the Salt Wash has been removed 

by erosion. The south side of the fan-shaped area is a limit of deposition. South of Monticello, in southeastern Utah, the upper part of 

the Salt Wash intertongues with and grades into the Recapture member. In northeasternmost Arizona lower parts of the Salt Wash 

intertongue with the Recapture, and farther south a basal tongue of 

Salt Wash reaches to the limit of deposition, a feather edge of the 

Salt Wash along the zero isopach. The western edge of the fanshaped area is a poorly defined limit of deposition trending almost 

north-south along the zero isopach in south-central Utah. The 

rounded margin of the fan is the irregular line extending from northwestern to south-central Colorado, beyond which the Salt Wash cannot be distinguished from the upper part of the Morrison.

Gregory (1938, p. 58-59) did not recognize the Salt Wash member in the southeastern corner of Utah, but subsequently Stokes (1944, 

p. 963-964) recognized the member in the lower part of Gregory's 

Recapture member in this area as well as in the Carrizo Mountains 

area of northeastern Arizona. The extension of the Salt Walsh member as a recognizable unit through southeastern Utah and into northeastern Arizona and northwestern New Mexico constitutes a restriction 

of Gregory's original definition of the Recapture member.

The Salt Wash member is composed dominantly of interstratified 

units of sandstone and claystone. The sandstone intervals consist of 

grayish-yellow, very pale orange, and white (Goddard, et al., 1948), 

fine- to medium-grained sandstones, which locally contain stringers 

of pebbles. The sandstone may form strata composed of a single, 

lensing bed, 1 to 20 feet thick, or it may form strata composed of many 

lensing beds, which may have a total thickness of 80 feet or more.
136 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

fry.

--.-J^/T- EXPLANATION *<&-&!0o *£*%!o

600 T FEET 

*$ 300f

Morrison formotion.undifferentioted

Solt Wash member 

FIGURE 20. Fence diagram of the Morrison formation of the Colorado Plateau region.

The beds are cross-laminated and generally show a slightly irregular

to sharply channeled scour surface at the base. The sandstone strata 

form cliffs on steep ledgy slopes.

The claystone stratca consist of interbedded claystones and minor

clayey sandstones. The claystones are variably silty and sandy and in

much of the area studied can properly be called mudstones. They are

pale reddish brown, grayish red, and light greenish gray. The thin 

sandstone interbeds are pale red to light gray ana fine grained, in

some places the claystone intervals contain thin nodular ZOneS Or plflty

to slabby beds of gray limestone which locally contain remains of 

algae, fresh-water mollusks, and ostracods. Bedding within the clayStone Strata is gently to sharply lenticular, and scour features are

uncommon.

The base of the Salt Wash member of the Morrison formation is the

base of terrestrial, fluvial beds above the marine and marginal marine 

deposits of the San Eaf ael group, The top of the Salt Wash is characterized by a change of lithology and composition that reflects a minor 

variation in the fluvial environment.
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 137

Areal changes in the texture and composition of the Salt Wash 

.member permit the separation of four major facies (fig. 21). A conglomeratic sandstone facies, confined to south-central Utah, consists 

mainly of scour-fill sandstones containing chert pebbles as much as 4 

inches in diameter. A sandstone and mudstone facies, consisting of 

interstratified scour-fill sandstones and variably impure clay stones, 

surrounds the conglomeratic sandstone facies on the northwest, north, 

and east. A claystone and lenticular sandstone facies, consisting of 

sparse lenses of sandstone in a dominant matrix of claystone, is present in northeastern Utah and part of northwestern Colorado. The 

fourth facies, a claystone and limestone facies, lies east of the limit of

-recognition of the Salt Wash and, thus, strictly is not a facies of the 

.member. However, the gradual decrease in sandstone content and 

increase in claystone and limestone content indicate that beds continuous and essentially contemporaneous with the typical Salt Wash 

were deposited east of the limit of recognition. The difficulty of distinguishing these claystones and limestones from similar lithologies 

in the upper part of the Morrison formation prevents eastward extension of the Salt Wash member as a recognizable unit.

The thickness distribution of the Salt Wash member is shown on 

figure 21. From a maximum thickness of more than 600 feet in south-

 central Utah, the Salt Wash in general thins radially to the north 

.and east. The thinning is fairly regular except in several marginal 

areas. In the Vernal area of northeastern Utah the Salt Wash is 

moderately thick, reaching a maximum thickness of 285 feet. This 

thickening is poorly understood but may represent an accumulation 

of sediment from a source unrelated to the main source of the Salt 

Wash- In westernmost Colorado the isopach lines show irregularities thought to represent irregular independent sinking of the basement. The irregularity cannot be related to either the variation of 

thickness or to differential compaction of underlying formations. A 

thin area of Salt Wash in southeastern Utah is related to the thickness of the underlying Bluff sandstone, for, in general, as the Bluff 

thickens, the Salt Wash thins in this area. However, the complementary thickness relations are inexact; they probably result both from 

rsimple depositional thickness changes within the Salt Wash and the 

Bluff and, as observed in northeastern Arizona, from intertonguing

 of the two units.

Recapture member. The Recapture member (Gregory, 1938, p.

-58) forms the lower part of the Morrison formation over a part of 

northeastern Arizona and northwestern New Mexico (fig. 22). To the 

north it intertongues with and grades into the Salt Wash member; the 

nipper part is the most extensive and is recognized to the south of

319572 55 3
138 CONTRIBUTIONS .TO THE GEOLOGY OF URANIUM ; :

COLORADO.

NEW MEX."

EXPLANATION

Conglomeratic sandstone facies Sandstone and mudstone, facies

Claystone and lenticular sandStone facies

Approximate boundary between

facies __

Claystone and limestone facies

Location of measured section

Isopach, dashed where inferred, 

interval 50 feet

FIGURE 21. Isopachous and facies map of the Salt Wash member of the Morrison formation.

Monticello in southeastern Utah, To the southwest the Recapture

pincKes out along the zero isopach line passing south of G-allup,

N, lex, Both at the northwestern and southeastern extremities of

this zero isopach the line marks the apparent limit of deposition of 

the Kecapture, but in the middle, south of Gallup, beds equivalent 

to the Recapture have been removed by subsequent erosion, and, thus,
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 139

L____ WYOMING

COLORAD.Q_ 

NE'W M'EX

50'MILES

EXPLANATION

Conglomerate sandstone 

facies

Sandstone facies Claystone and sandstone 

facies

Approximate boundary between facies Location of 'measured section

 200 

Isopqch, dashed where inferred,

interval 50 feet

FIODEB 22. Isophachous and facies map of the Recapture member of the Morrison

formation.

this unit originally may have been more extensive in this area. The 

eastward extent of the Eecapture in north-central New Mexico is not 

yet known.

The recognition of the Eecapture member as a distinct lithplogic 

unit through much of northeastern Arizona (Harshbarger, Eepenning, and Jackson, 1951, p. 98), and northwestern New Mexico constitutes an appreciable areal extension of the member beyond its 

previously known limits.
140 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

The Recapture member is composed of interstratified sandstone 

and claystone. The sandstone strata consists of pinkish-gray to lightbrown, fine- to medium-grained sandstone, which, locally, contains 

granules and pebbles disseminated in the sand matrix or concentrated 

in stringers along the laminations. The sandstones are uniformly 

quite friable, and sedimentary structures are poorly displayed. However, where structures are preserved, the sandstone strata are seen to 

comprise lenticular, cross-laminated, scour-fill beds similar to those 

of the sandstone strata of the Salt Wash member. In Arizona, west 

and northwest of Gallup, N". Mex., the Recapture member is gradually replaced southward by sandstone strata that exhibit sweeping, 

wedging, cross-lamination and lack the scour-fill structures. These 

sandstones constitute an upper part of the Cow Springs sandstone 

(Harshbarger, Repenning, and Jackson, 1951, p. 97-98). The claystone strata of the Recapture member consist of pale-red, grayish-red, 

and very dusky red, variably silty and sandy claystone. The bedding 

in the claystone strata exhibit the same lensing shown in the bedding 

in the claystone strata of the Salt Wash. The friable character of' the 

sandstone of the Recapture causes the member to weather to a steep 

earthy slope; a bench is developed at the foot of the slope on the more 

resistant sandstones of the Salt Wash in most places where that 

member is present.

Three distinctive facies, based on variations in texture and composition, have been recognized in the Recapture member (fig. 22). A conglomeratic sandstone facies occupies a narrow lobate area north of 

Gallup. The pebbles occur in rare stringers and consist mainly of 

QUartZ. feldspar, granite, and minor black and gray chert. These 

pebbles are as much as 1 inch in diameter. A sandstone facies surrounds the conglomeratic sandstone facies on the west, north, and, 

possibly, on the east, and differs from it mainly in the absence of pebbles. The third and most extensive facies of the Recapture is the claystone and sandstone facies. It surrounds the sandstone facies on the 

W6St IlOrth. and eaSt) and Consists Of interstratified variably impure

claystone and nonconglomeratic sandstone.

The thick part of the Recapture member occupies an elongate curving area from northeastern ^Vri^ona, into northwestern New Mexico

(fig. 22). A maximum thickness of 680 feet was measured m northeastern AriZOna, The Recapture is erratically thin in tllG arQft 01

the congioxrx^tio sandstone iacies north of Gallup. The variations in thickness are regarded as a result of differential sinking of **«»*>^oment. The northward thinning shown in figure 22 results frOfll ifltertonguing with the Salt Wash and the southward thinning 

depositional convergence, and, near Gallup, from later erosion.
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 141 

LITHOFACIES

The lower part of the Morrison formation consists of cross-laminated sandstone and conglomeratic sandstone lenses, which were de*- 

posited in a stream environment, and of claystones and horizontally 

bedded sandstones, which accumulated in a floodplain environment. 

The areal variation of thickness, relative proportion, and continuity 

of the stream deposits and floodplain deposits is the subject matter 

of the lithof acies study of the Morrison.

The lithofacies studies have been restricted mainly to the lower 

part of the Morrison formation, for the Salt Wash and Recapture 

members are particularly amenable to ratio studies. The usual practice in ratio studies of comparing the thickness of one or more rock 

types to the thickness of different rock types has not been followed, 

because of the complete gradations between sandstone and claystone 

that are common in the lower part of the Morrison, and because of the 

possibilities of paleogeographic reconstruction offered by a classification based on environment of deposition.

The areal variations in lithofacies were determined by measuring 

the thickness of the stream and floodplain deposits at 64 localities. 

Five sections were measured through the lower part of the Morrison 

formation at each locality, in order to permit computation of average 

data on the thickness and relative proportions of the two types of deposits and to allow a measure of the continuity of the stream deposits. 

Isolith maps showing the areal variations of these aspects were prepared from the collected data.

The areal distribution of the total thickness of the stream deposits 

in the lower part of the Morrison formation is shown by figure 23.

The areal distribution of the relative proportions of the stream and 

floodplain deposits is shown by figure 24. A high ratio indicates a 

high proportion of stream deposits.

The areal variation in the relative continuity of the stream deposits 

is shown by figure 25. The relative continuity at each locality is determined by computing for each locality the average of the deviation 

of the total thickness of the stream deposits in each section from the 

average thickness for the five sections and expressing the deviation as 

a percentage. A low percentage of deviation is interpreted to indicate high continuity of the stream deposits.

The three maps are remarkably similar. The pattern of the isoliths 

show that the total thickness of stream deposits, relative proportion, 

of the stream deposits to the floodplain deposits, and relative continuity of the stream deposits decrease rather uniformly away from 

two centers, one in south-central Utah and one along the northern part 

of the Arizona-New Mexico state line. Values of all .three factors
142 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

EXPLANATION

Locoiion of lithofocies 

section

-100 

Isopoch, doshed where inferred, 

interval 50 feet

FIGURE 23. Isopachous map of stream deposits In the lower part of the Morrlson

formation.

decrease to the north and east of the Utah center, and the isolith lines

concentric to this area form an asymmetric fan-shaped pattern -with a

prominent lobe extending eastward, Thickness of stream deposits,

proportion of stream to floodplain deposits, and continuity of the

stream deposits decrease to the north, south, and west of the northern 

Arizona-New Mexico area. The isolith lines concentric to this area

form a fan-shaped or ellipsoidal pattern, with the long axis trending 

slightly west of north. All three maps show that the two areas of high

values are separated, by an area of lo'w values tliat trencls mor-tlioo-stsouthwest through southeastern Utah, In southwestern Colorado and 

eastern Utah irregularities in the isolith lines interrupt the uniformity

of the major fan-shaped pattern extending outward from southcentral Utah.
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 143

EXPLANATION

 

Locotion of lithofocies study Isolith, dashed where inferred,

interval 0.5

PIGDHB 24. Isollth map of the ratio of thickness of stream deposits to thickness of floodplain deposits In the lower part of the Morrison formation.

SEDIMENTARY STRUCTURES

Sedimentary structures in the lower part of the Morrison formation 

include cross-lamination, current lineatiori, contorted bedding, ripple 

marks, and mud cracks. Horizontally bedded and structureless units 

are also common in.the lower part of the Morrison. Emphasis of 

the sedimentary structure study was on the Salt Wash member.

Sedimentary structures are amenable to two types of analysis 

description and measurement. A brief description of the important 

sedimentary structures of the lower part of the Morrison formation 

follows:

Cross-lamination in the Salt Wash member is a complex of several 

types. Classified according to the terminology of McKee (1948), as
144 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

W Y 0 M I N G

SALT LAKE CITY

UTAH 

ARIZ.

EXPLANATION

Locotion of lithofocies study Isolith, doshed where inferred,

intervol5 percent

FIGURE 25. Isolith map of percentage mean deviation'of stream deposit thickness in the

lower, .part of the Morrison formation.

illustrated, by Kiersch. (195O), the most prevalent types are festoon

cross-lamination, wedge "torrential" cross-lamination, and low-angle

compound cross-lamination. Festoon cross-lamination, the most common type in the Salt Wash, is produced by channeling action and subsequent deposition. In plan view, festoons are semiellipsoid.a.1, re-'

sembling half a canoe, Dips are highest near the closed end, or

"prow": away from the closed end the laminae gradually flatten. 

Tli© closed end is interpreted to be in the upstream direction; the open

end to be in the downstream direction, Wedge "torrential" crosslamination is formed bJ deposition of crossbeds that are subsequently

beveled by scour surfaces. Low-angle compound cross-lamination
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 145

is the result of simple accumulation of crossbeds with cross-laminae 

of moderate to low dip without any truncating surfaces.

Current lineation (Stokes, 1947) is the result of a streaming effect 

of sand particles to form low ridges parallel to the current. Current 

lineation is generally perpendicular to ripple marks where both are 

present in the same depositional unit. Current lineation has not been

WYOMING 

T

EXPLANATION

Arrow represents resultant .dip azimuth, of cross -laminae.

Length is^proportional'to consistency factor.

' . . -Tail1 of arrow marks location of cross-lamination/ 

study.

FIGURE 26. Map of resultant dip directions of cross-laminae In sandstones of the Salt Wash 

member of the Morrlson formation.
146 . ; CONTRIBUTIONS T0x THE GEOLOGY OF -URANIUM-, :: ;,

observed directly superimposed on ripple marks. Ripple marks occur 

in both the sandstone and the mudstone of the Salt Wash member. 

They are always of the current type. Rarely, superposed sets of 

ripple marks in the mudstone form a false cross-lamination the 

"ripple cross-lamination" of McKee (1939). Contorted laminae occur 

locally in the cross-laminated sandstone and represent the slumping 

of water-saturated sand. Mud cracks are rare in the Salt Wash but 

have been noted on the surfaces of mudstone partings.

Sedimentary structures in the Recapture member are similar to those 

described for the Salt Wash member. However, festoon cross-lamination appears to be less common in the Recapture; horizontally lamif 

nated units, and units with low-angle compound cross-lamination are 

more common.

I Directional features of sedimentary structures that may be measured 

with precision include the strikes and dips of cross-laminae, the plunge 

directions of festoon axes and of current lineation, and the strikes of 

ripple marks. If adequately sampled, the average of measurements 

of trends of any of these structures will give an approximate indication of the main current direction. Cross-lamination is the sedimentary structure most amenable to statistical analysis, because it is 

the only structure that can be measured in areas of poor to fair 

eippsure.

' In the field study of cross-lamination, a measurement is made of 

the azimuth dip of one cross-lamina, in each separate cross-laminated

unit conformable within itself. The study is made along the outcrop 

of a single sandstone stratum. 

The statistical methods of treatment of the field data are adapted

from Reiche (1938). Each dip azimuth may be considered a unit 

vector; the vector sum of a number of dip azimuths gives a resultant 

dip azimuth. The resultant dip azimuth is the vectoral "average"

of the directions of dip of all cross-laminae measured at a locality.

A numerical expression for the consistency of direction of the individual di,p azimuth vectors is obtained by dividing the resultant length

by the number of measurements. If all observations were identical, 

the consistency factor would be unity; if the vectors were disposed at

random, the consistency factor -would be zero.

Figure 26 shows the pattern of cross-lamination in the Salt Wash

member. Arrows show the resultant dip azimuths of cross-laminae 

:£or studies at 55 localities. The length of the arrow is proportional to the consistency factor, The map shows a pattern of arrows that

-diverges to the north. -and east from. an. apex in south-central XJtah.

Based on the premise that each cross-lamina has a component of 

<lip azimuth down-current, the resultant dip azimuth.is interpreted
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 147

as the average drainage direction. The consistency factor is regarded 

as a measure of the relative persistency of direction of drainage at the 

place of study. , . .- The resultant dip azimuths of cross-laminae indicate that the 

streams depositing the Salt Wash member flowed north, east, and 

southeast from the south-central part of Utah. No contemporaneity 

of deposition is implied by the map. It is a "multiple exposure" of 

drainage directions throughout the time of deposition of the Salt 

Wash. Studies at different horizons in the Salt Wash were made 

at each of four localities. These show that the resultant dip azimuths 

are about the same regardless of stratigraphic position in the member 

and imply that about the same drainage directions prevailed throughout Salt Wash deposition.

Kegional study of cross-lamination orientations in the Recapture 

member are incomplete.

SEDIMENTARY PETROGRAPHY

The sedimentary petrography contained in this preliminary report 

is based on the results of the study of 202 sandstone samples from the 

Salt Wash member of the Morrison formation. An investigation of 

the claystones and siltstones of the Salt Wash and other members of 

the Morrison was made by 2 A. D. Weeks (1953). 

, Methods used in the laboratory study of the sandstones of the Salt 

Wash member may.be divided into two groups: preparation and 

measurement. Preparation includes the use of standard methods of 

disaggregation of consolidated sedimentary rocks, separation of heavy 

mineral fractions, and the preparation of mineral grain slides for 

petrographic examination/ . Measurement includes the determination 

of grain-size. distribution for each sample by means of graduated 

sieves and pipette elutriation, computation of the statistical analysis 

of the grain-size distribution of each sample, determination of the 

proportions of light (sp gr < 2.90) and heavy (sp gr > 2.90) 

minerals, and determination of amounts of cements and soluble detrital 

fractions.

Averages of the analytical results show that sandstones of the Salt 

Wash member may be classified as fine-grained, quartzitic sandstones. 

The average modal diameter of the sand is 0.176 mm. Of the detrital 

grains, 93 percent are of sand size, and Y percent are of silt or clay size. 

The average composition of the sandstones is: calcite (cement), 13 

percent; secondary silica (cement and overgrowths), 4 percent; detrital grains, 83 percent. Of the detrital grains, quartz (grains and over1 Weeks, A. D., 1953, Mlneraloglc study of some Jurassic and Cretaceous claystones and 

slltstones from western Colorado and eastern Utah: U. S. Geol. Survey Trace Elements 

Investigations Kept. 285.
148 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

growths) comprises 86 percent; feldspar (orthoclase to albite), 7 percent; chert (silicified tuff and chert), 7 percent. Only a small suite 

of light and heavy minerals is present. Light detrital minerals other 

than quartz are chert, feldspar, gypsum, calcite, and dolomite. Heavy 

minerals are zircon, tourmaline, garnet, rutile, anatase, staurolite, biotite, spinel, and apatite.

The statistical analysis of the grain-size distribution of each of the 

samples yielded a number of measurements, of sorting, average grainsize, asymmetry of the distribution, and other properties of petrologic 

interest. The results of the statistical analysis showed that the most 

significant measurements of the grain-size distribution are the logarithmic standard deviation and the percentile skewness, the former 

is a coefficient of sorting, and the latter a measure of the deviation of 

the distribution of the grain sizes from a symmetrical bell-shaped 

curve.

The logarithmic standard deviation of a. perfectly sorted sand is 

0.000. The averages of the samples of Salt Wash taken at each locality studied vary between 0.500 and 1.500. Figure 27 shows that there 

are regional differences in the sorting of the sands of the Salt Wash 

member and that the differences fall into a distinct pattern as outlined 

by isopleths of the 1.000,1.100 and 1.200 values.

The map shows a .central area of relatively well sorted sand on the 

boundary between southwestern Colorado and- southeastern Utah. 

Extensions radiate outward to the north, east, south, and- west from the 

' central area.

These zones of better sorted sand may represent areas in which the

stream-deposited sand had'been reworked more than in adjacent areas. 

A map of percentile skewness is similar to the map of sorting as 

shown by the logarithmic standard deviation (fig. 27). In general, 

tlie areas of better sorted sand have low positive skewness values; 

areas of poorer sorted sands have either high positive values or low

negative values, that is, a lack of symmetry due to the presence either

of too many fine grains or too many coarse grains respectively. Negative skewness values were obtained mainly along the southwestern

margin of the Salt TVash member in south-central Utah and northeastern Arizona. These negative values indicate that sandstones of

this area tend to have an excess of coarse material and are probably 

proximal to the source area of the Salt Wash.

Sandstones of the Salt "Wash member contain a. relatively KISK pr-oportion of feldspar in northern Arizona and New Mexico in an elongate area along the southern part of the Colorado-Utah border, and 

in northwest Colorado and northeast Utah. The sandstones in southwest Colorado and southeast Utah outside of the elongate area contain less feldspar. Some samples from south -of the Four Corners
STRATIGRAPHY Ot1 MORRISON AND RELATED FORMATIONS 149

COLORAJLQN~EW ~MEX.

EXPLANATION

-/.zooLocation of sampled 

section

Isopleth, dashed where inferred,

interval 0.100

Only the 1.000, 1.100, ana

1.200 isopleths are shown

FIGURE 27. Isopleth map of logarithmic standard deviation of grain-size distribution in 

sandstones of the Salt Wash member of the Morrison formation.

area contain substantial fractions of fresh angular feldspar and 

quartz, which indicates the presence of a local granitic source. The 

decrease in the amount of the fresh material northward suggests that 

the source was to the south.

Samples from several localities on the extreme western edge of the 

Salt Wash member in central Utah contain large amounts (as much 

as 86 percent of the detrital fraction) of fresh, angular to rounded, 

opaline tuff. The grains are much less weathered and show less 

sphericity than the silicified tuff and chert characteristic of the Salt 

Wash to the east and suggest a local source to the west, possibly quite 

close to the region of investigation.
150 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Garnet is absent from most of the samples from western Colorado, 

but is present in almost all samples from west of ..the Colorado-Utah 

border. Owing to the high specific gravity of garnet and the tendency to fracture into grains of high sphericity, it tends to settle out in 

the placer-type concentrations, which, in an aggrading system, are 

soon buried. Thus, the distribution indicates that the source of the 

garnet was to the west or southwest.

Staurolite has an areal distribution similar to that of garnet. The 

general absence of the mineral from the sandstones of Colorado is 

probably the result of attrition, for the splintery cleavage makes 

staurolite vulnerable to abrasion and solution. A western or southwestern source is indicated.

Apatite is present throughout the sandstones of the Salt Wash 

member in northeastern Utah and in a relatively narrow belt extending diagonally southeastward to south-central Colorado. A possible 

source to the northwest is suggested.

INTERPRETATION

The collected data of the stratigraphic investigations yield a welldefined concept of the paleogeography of the lower part of the Morrison formation.

Two major source areas are indicated by the facies and isopachous 

maps of the lower part of the Morrison formation. One major source 

area was southwest of south-central Utah, probably in west-central 

Arizona and southeastern California. It furnished most of the sediments comprising the Salt Wash member. The other major source 

area was south of Gallup, probably in west-central New Mexico. It 

furnished most of the sediments comprising the Recapture member. 

The mineralogy of the members of the lower part of the Morrison 

indicate that the rocks exposed in the source area of the Salt Wash

were quite different from those exposed in the source area of the 

Recapture. The Salt Wash was derived mainly from older sedimentary formations and received only minor contributions from

igneous and metamorphic rocks. Fossils in chert pebbles from the

conglomeratic sandstone facies of the Salt "Wash Have been identified

as late Paleozoic in age. These were derived either directly from 

upper Paleozoic beds or from younger beds formed by reworking 

of the upper Paleozoic formations. The Recapture was derived from

an area of preexisting sedimentary, igneous, and metamorphic rocks.

The abundance of feldspar, quartz, and granite pebbles found in the

conglomeratic sandstone facies indicates that acid ipeous rocks comprised a large part of the rocks exposed in the source area. The

erratic distribution of opaline tuff, feldspar, and apatite in the Salt 

Wash represent contributions from minor sources to the west and
STRATIGRAPHY' OF'"MORRISON" -AND "RELATED" "FORMATIONS 151

northwest of central Utah; similarly the Recapture member may have 

had contributions from minor sources oast and west of the major 

source in west-central New Mexico. The presence of angular fresh 

feldspar and quartz in the Salt Wnsii of the Four Corners area 

suggests that material from the Recapture source may have mixed 

with materials of the Salt Wash in this area. r !

Structures and textures of the lower part of the Morrison formation 

indicate that both the Salt Wash and Recapture members were deposited in a dominantly fluvial environment and are composed of 

alternations of stream-deposited sediments and floodplain-deposited 

sediments.' Slight epeiric uplift probably caused northward retreat 

of the marine and marginal marine deposition which characterizes 

the San Rafael group. Moderate orogenesis in the source areas of 

the Salt Wash and'Recapture members initiated the spread of elastics 

northward and eastward across the Colorado Plateau region. 

Streams of low gradient transported and deposited detritus on the 

almost flat surface of the San Rafael group. Although some time is 

required to transport detritus from one locality to another, the spread 

of the lower part of the Morrison across the region is thought to have 

been essentially synchronous geologically.

The Salt Wash and Recapture members are regarded as two broad 

fan-shaped alluvial plains or "fans"'constructed simultaneously by 

deposition from two separate aggrading stream systems. The two 

fans coalesced along a common margin which passes as a wide belt 

through the Four Corners area.! In this belt .the two members intertongue and intergrade. ' . :" . 

- The isopachous and isolith maps of the Salt Wash member (figs. 

21, 23, 24, 25) show similar fan-shaped patterns. The sedimentary 

structure orientations (fig. 26) show a pattern of drainage directions 

which diverges northward and eastward from the apex of the Salt 

Wash fan in south-central Utah. During the time of Salt Wash 

deposition, streams probably formed an aggrading distributary system of braided channels which changed position on the fan by lateral 

migration.

The distribution of facies (fig. 21) and the distribution of the 

stream-deposit thickness relative to floodplain-deposit thickness (fig. 

24) indicate a decrease in transporting capacity of the streams outward from the apex of the fan. Either decrease in gradient or decrease in volume of the streams or both would produce the decrease in 

transporting capacity.. The uniform distribution of facies (fig. 21) 

and the gradual change from one facies to another suggest that any 

decrease in stream gradient must have been quite gentle. Loss of volume of the streams could have resulted from evaporation, absorption 

by the sediments, or from subdivision of streams to form successively
152 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

smaller distributaries outward across the surface of the fan. The 

thick. Salt Wash member (fig. 21) at the apex of the fan is thought to 

represent an accumulation of sediments near the source area. Irregular thick and thin areas in the vicinity of Four Corners probably reflect topographic features of the top of the San Rafael group; the 

Salt Wash streams locally impinged on, beveled, and reworked the 

sands of the upper part of the Bluff and Junction Creek sandstones, 

and only relatively thin deposits of Salt Wash were formed in areas 

where these underlying sandstones are thick. The lack of uniform 

thickness in the Salt Wash in the area south of Grand Junction, Colo., 

probably resulted from local subsidence and filling of the consequent 

depressions. The poorly defined thickening of the Salt Wash in Utah 

and Colorado near the Wyoming boundary also may have resulted 

from local subsidence; however, it may represent an accumulation of 

sediment from a source area unrelated to the major source area of the 

Salt Wash. '

The isopachous and isolith maps of the Recapture member (figs. 

22-25) do not show as prominent a fan-shaped pattern as do the maps 

of the Salt Wash member. However, the facies distribution (fig. 22) 

supports the concept of an alluvial plain or fan with an apex near 

Gallup, N. Mex. The irregular distribution of Recapture thickness 

is thought to result from differential subsidence. During Recapture 

deposition, streams probably formed an aggrading distributary system 

of braided channels, similar to the streams on the fan of the Salt Wash.

The climate during deposition of the lower part of the Morrison is 

difficult to define with much certainty from evidence in the rocks. A

semiarid climate is suggested by the preservation of sand dunes in the 

Recapture member in northeastern Arizona. Stokes 3 has reported 

remains of thorny plants from the Salt Wash member of east-central 

Utah, a discovery which supports the concept of semiaridity. How*-

ever, sufficient moisture was present to support growth of grasses,

reeds, and large trees, at least along the stream courses, and to permit 

the existence of small bodies of standing water in which thin beds of 

limestone were deposited. Casual observation suggests a greater

aburxcLano© of fossil tree remains near the apex of the fan O± the Salt

Wash than away from it, This distribution may reflect a greater

abundance of vegetation in this area resulting from a slightly higher 

elevation than the rest of the fan and proximity to o. e-rea.t©r water 

supply in the uplands of the

UFFER PART OF THE MORRISON FORMATION

The upper part of the Morrison formation consists of the Westwater Canyon member and the Brushy Basin member. The West8 Stokes, W. L., 1945, unpublished U. S. Geol. Survey report.
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 153

water Canyon member constitutes the lower unit of the upper part of 

the Morrison in the southern part of the region of study. The Brushy 

Basin member is present over most of the region of study (fig. 20).

REGIONAL STRATIGRAPHY

Westwater Canyon member. The Westwater Canyon member 

(Gregory, 1938, p. 59) is present over a part of northeastern Arizona 

and northwestern New Mexico (fig. 28). To the north the Westwater 

Canyon intertongues with and grades into the lower part of the 

Brushy Basin member along a limit of recognition that passes just 

south of Monticello in southeastern Utah. In most of northwestern 

New Mexico and a small part of northeastern Arizona the upper part 

of the Brushy Basin member overlies the Westwater Canyon, but to 

the southwest, post-Morrison erosion has removed the Brushy Basin, 

and the Westwater Canyon is the only part of the upper part of the 

Morrison preserved. The Westwater Canyon and equivalent beds thin 

to extinction along the zero isopach on the south and southwest, mostly 

as a result of increasing magnitude of the post-Morrison erosion. 

True depositions! convergence may also contribute to this thinning. 

The eastern limit of the Westwater Canyon in north-central New 

Mexico is not yet known.

The recognition of the Westwater Canyon member as a distinct 

lithologic unit through much of northeastern Arizona (Harshbarger, 

Repenning, and Jackson, 1951, p. 98) and northwestern New Mexico 

constitutes an appreciable areal extension of the member beyond its 

previously known limits.

The Westwater Canyon member is composed of interstratified sandstone and minor amounts of claystone. The sandstone is yellowish 

gray, pale yellowish orange, or light brown, fine to medium-coarse 

grained, and locally contains stringers and lenses of pebbles. The 

sandstone forms strata composed of many, lensing cross-laminated 

beds, which exhibit slightly irregular to deeply channeled scour surfaces at their base. South and west of Gallup in a narrow belt along 

the margin of the member the scour-fill sandstones are replaced 

gradually by sandstone strata that exhibit sweeping, wedging, crosslamination and lack the scour-fill characters. These sandstones constitute the uppermost part of the Cow Springs sandstone (Harshbarger, Repenning, and Jackson, 1951, p. 97-98). The claystone strata 

of the Westwater Canyon member consist of light-greenish-gray or 

pale-red to grayish-red, variably silty and sandy claystone and have 

a gently lensing subparallel bedding similar to that observed in the 

claystone strata of the Salt Wash member. The sandstones of the 

Westwater Canyon member are more resistant than those of the underlying Recapture member and form nearly vertical cliffs or very steep
154 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

.COLORADO,.

N'EW "MEX.

EXPLANATION

Conglomeratic sandstone fades

Approximate boundary between 

facies

Sandstone facies

Location of measured section

-too 

Isopach, dashed where inferred, 

interval 50 feet

28. Isopachous and facies map of tfie Westwater Canyon member of the Morrison

formation, 

ledgy slopes "with, small reentrants or narrow benches marking the

position of the thin and less resistant claystone strata,

The Westwater Canyon member maj bo separated Into two fades

(fig. 28), mainly based on textural differences. A conglomeratic sandstone facies occupies a wide lobate area north of Gallup, N. Mex. 

The pebbles are predominantly quartz, feldspar, granite, and quartzite with minor amounts of gray and black chert. This facies may be 

subdivided into a central area, where pebbles as muck as 4 inches in 

diameter are common, and a peripheral area, where pebbles are generally less than 1 inch in diameter. The second facies, a sandstone 

if acies, surrounds the conglomeratic sandstone facies on the west, north,
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 155

and east. It differs from the conglomeratic facies mainly in the absence of pebbles. Both facies contain thin strata of claystone, but the 

sandstone facies generally contains a greater percent of claystone 

(10-40) than does the conglomeratic sandstone facies (5-20).

The Westwater Canyon member forms an arcuate belt of relatively 

thick sedimentary rocks extending from northwestern New Mexico 

through the northeastern corner Arizona into southeastern Utah (fig. 

28). A maximum thickness of 330 feet was measured 30 miles north 

of Gallup, N. Mex. Studies of the orientation of sedimentary structures and sedimentological analyses of the Westwater Canyon member 

are incomplete.

Brushy Basin member. The Brushy Basin member (Gregory, 1938, 

p. 59) is present in western Colorado, eastern Utah, northern New 

Mexico, and part of northeastern Arizona (fig. 29). To the southL____ W Y 0 M I N G

COLORADO.. N'EW "MEX"

EXPLANATION

Locolion of meosured section , Isopoch, dashed where inferred,

intervalSO feet

FIGURE 29. Isopachous map of the Brushy Basin member of the Morrlson formation.
156 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

west it has been removed by post-Morrison erosion, leaving only the 

partly equivalent Westwater Canyon member. The eastern and northeastern boundary is an arbitrary line drawn where the Salt Wash 

member loses its identity and cannot be distinguished from the upper, 

part of the Morrison formation. East of this arbitrary line the Morrison is not differentiated into members.

The Brushy Basin member is composed predominantly of variegated 

claystone containing varying amounts of silt and sand. Fissile shale. 

is rare. Impure bentonitic clay forms much of the Brushy Basin and 

is, in part, volcanic in origin. Lenses of conglomeratic sandstone are 

common. The pebbles consist mainly of red, green, white, and black 

chert and are as much as 2 inches in diameter. The lenses are rarely 

more than several hundred feet wide, and pinch out laterally in the 

main mass of claystone. A few thin-bedded, discontinuous beds of 

limestone occur in the Brushy Basin and were probably deposited in 

temporary fresh-water lakes.

A lensing conglomeratic sandstone containing red, green, and white 

chert pebbles has a wide distribution at the base of the Brushy Basin 

member in western Colorado and eastern Utah. The base of this 

bed has been used as the basal contact of the member in this area. 

Where the basal conglomerate is absent in western Colorado, the top 

of the uppermost scour-fill sandstone of the Salt Wash member is used 

as the contact between the Brushy Basin and the underlying Salt 

Wash member.

Distinct f acies with limited areal distribution have not been recognized in the Brushy Basin member, for the lithologic components 

show no regularity. Colors of red, purple, and gray predominate in 

northeastern Utah and western Colorado and light greenish gray and 

pink predominate in southeastern Utah, northeastern Arizona, and

northwestern New Mexico.

Petrified dinosaur bones and wood are common in the Brushy Basin

member, Other fossils are rare; fresh water gastropods and algae

have been found at only a few localities.

The thickness of the Brushy Basin member varies considerably

over the Plateau (fig, 28), More than 600 feet of Brushy Basin has

been measured at Vernal. Utah. In southwestern Colorado 450 feet

considerably in thickness in contrast to the more gradual thickness

changes elsewhere,

The members of the upper part of the Morrison formation form 

two relatively distinct groups of sedimentary rocks. The facies distribution of the Westwater Canyon member (fig. 28) indicates a 

major source south of Gallup, probably'in west-central New Mexico.
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 157

The feldspar, quartz, granite, quartzite, and chert pebbles in the 

conglomeratic sandstone facies indicate as the source an area of 

preexisting sedimentary, igneous, and metamorphic rocks. The 

source area of the Brushy Basin member is not clearly indicated from 

.any of the collected data. The coincidence in distribution of the 

basal conglomeratic sandstone of the Brushy Basin with the distribution of the sandstones of the Salt Wash member suggests that the 

Brushy Basin may have been derived from essentially the same source 

area as the Salt Wash. Similar conglomeratic sandstone higher in 

the Brushy Basin may also have had the same source area. The 

area of thick Brushy Basin in northeastern Utah may reflect a source 

area to the north or northwest, but the conglomeratic sandstones in 

that area have lithologic similarities to those to the south. The 

prevalence of chert pebbles and the almost complete absence of other 

varieties suggest that at least the sandstones were derived mainly 

from a source area of sedimentary rocks.

Structures and textures in the Westwater Canyon member and in 

the sandstones of the Brushy Basin member indicate that they were 

deposited in a fluvial environment. Much of the bentonitic clay of 

the Brushy Basin accumulated from falls of volcanic ash. Limestone, 

as well as some of the clay, may have been deposited in a lacustrine

 environment.

The facies distribution in the Westwater Canyon member (fig. 28) 

indicates that it formed as a broad fan-shaped alluvial plain or "fan" 

similar to that of the Recapture member. It was formed by an alluviating distributary system of braided channels and represents essentially a continuation of Recapture deposition. The Westwater 

differs, however, in that it consists predominantly of much coarser material than the Recapture. This is thought to reflect a rejuvenation 

of the source area, in west-central New Mexico. As the source area 

was reduced and ceased furnishing coarse material, Brushy Basin 

sediments were spread southward over the area of deposition of the 

Westwater. The original southern limit of the Brushy Basin is not 

known, for the member has been removed by pre-Dakota erosion

 south of a line (the zero isopach) extending from northwestern New 

Mexico to south-central Utah (fig. 29).

Greater abundance of fossil plant and dinosaur remains suggests 

that the climate was more humid during deposition of the upper part

 of the Morrison formation than during deposition of the lower part

 of the Morrison. In contrast to the Recapture member, the Westwater Canyon member contains much less extensive windblown deposits in northeastern Arizona. This may also support a concept of 

increased humidity during late Morrison time.
158 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

REGIONAL STRATIGRAPHY

The Morrison formation has not been separated into members east 

and north of the arbitrary line marking the limits of recognizable 

Salt Wash member. Lithologic units do not have sufficient continuity 

in central and eastern Colorado to warrant member status. The area 

of undifferentiated Morrison includes all central and eastern Colorado 

and extends eastward into western Kansas to a subsurface pinch-out of 

the formation. This area includes the type section of the Morrison 

formation near the town of Morr,ison in central Colorado.

Eldridge's (Emmons, Cross, and Eldridge, 1896) original definition 

of the formation included an upper sandstone and shale unit that is 

now assigned to the Lower Cretaceous and excluded a basal sandstone 

now assigned to the basal part of the Morrison. The beds near Morrison form a typical section of undifferentiated Morrison formation. 

At the new type section, described by Waldschmidt and LeKoy (1944, 

p. 1097-1114), a basal lenticular sandstone, 17 to 30 feet thick, is overlain by 55 feet of gray and red shale with Aclistocham and fresh water 

gastropods, 50 feet of gray clay and limestone, 52 feet of gray shale 

and sandstone with dinosaurian remains, 37 feet of red shale, and 77 

feet of variegated shale and sandstone. The total thickness is approximately 300 feet.

Northward from the type section, along the Front Range near Loveland, Colo., and into Wyoming the Morrison formation can be 

divided roughly into three units: a lower unit of thin-bedded gray 

shale and limestone with charophyte oogonia and ostracods, a medial 

unit of crossbeclded sandstone and conglomerate with dinosaurian

remains, and an upper unit of variegated shale. Overlying the variegated shale unit are sandstones and conglomerates of Early Cretaceous 

age.

West of the type section, in the central Colorado basin the Morrison

formation consists of claystone beds with thin intercalated limestone 

and sandstone beds. Dense limestones are abundant in the basal part 

of the Morrison in this area, but these are lenticular and cannot be individually correlated from section to section. The ancestral Uncompahgre uplift, which has a northwesterly trending axis through. Gunnison, Colo,, may have served as a barrier, retarding the easterly

flowing streams during Salt Wash deposition so that only the finer

sediments were carried eastward across the highland into the central 

DaSln( Xfte Morrison tliins appreciably over ine crest oi ttfiis uplift

(fig. 80).

The isopachous map of the Morrison formation of the ColoradoPlateau region (fig. 30) shows the combined thickness of the separate
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 159

EXPLANATION

Locotion of meosured 

section

Isopoch, dashed where inferred, 

interval 50 feet

FIGURE 30. Isopachous map of the Morrison formation.

members of the "western" differentiated Morrison; the thickness variations of the western part of the map are, in some areas, known 

to result from more than one factor. In central and eastern Colorado,, 

the map shows thickness of the undifferentiated Morrison; here, variations may be the result of a complex history, which cannot be interpreted because distinctive units in one area cannot be recognized ,in 

others.

INTERPRETATION

The undifferentiated Morrison formation is lithologically similar 

to the Brushy^Basin member of the "western" Morrison and the depositional environment is thought to have been the same. The structures.
160 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

of the sandstones suggest fluvial deposition; limestones and some of 

the clays were probably deposited in shallow temporary lakes; some 

of the clay is bentoniticj recording falls of volcanic ash. The main 

source areas of the undifferentiated Morrison were probably to the 

south and to the west, the same source areas as those of the members 

of the "western" Morrison.

POST-MORBISON FORMATIONS 

LOWER CRETACEOUS FORMATIONS

Lower Cretaceous beds overlie the Morrison formation in Colorado,

 eastern Utah, a small corner of northeastern Arizona, and northern 

New Mexico. In the past, these beds have been included in either the 

Morrison formation or the Dakota sandstone, depending On the basis 

of their characteristics and affinities in different areas. In southeastern Colorado and northeastern New Mexico the Purgatoire formation separates the Morrison and Dakota. In north-central Colorado, 

beds usually called Dakota probably contain equivalents of the Lower

 Cretaceous Cloverly formation of Wyoming. In the Four Corners 

:area and northward through western Colorado and easternmost Utah, 

the Burro Canyon formation has been recognized as a separate 

formation of Early Cretaceous age. In central Utah the Cedar Mountain formation of Stokes (1944, p. 965) forms a widespread Lower 

Cretaceous unit. These formations are composed of interstratified conglomeratic sandstone and variegated claystone in varying 

proportions and sequence. The basal contact is conspicuous only 

in those areas where basal channel sandstones are present. Where 

these are absent it is exceedingly difficult or impossible to differentiate 

the variegated shales of the Lower Cretaceous from those of the upper

part of the Morrison. No field evidence for a major disconformity has 

"been recognized at the base of the Lower Cretaceous strata. The sandstones and claystones are thought to represent various combinations

 of fluvial and lacustrine deposition.

UPPER CRETACEOUS FORMATIONS

DAKOTA SANDSTONE

The Dakota sandstone is recognized as a lithologic unit throughout

most of the region of .study and forms a sequence of interstratified 

conglomeratic sandstone, gray carbonaceous shale, and coal. These

reflect deposition in alternating stream and swamp enyironments,

The Late Cretaceous age of the Dakota sandstone has been established 

in southwestern Colorado (Brown, 1950, p. 45), but faunal evidence 

indicates that the lithologic unit called the Dakota sandstone in parts

 of central Utah is Early Cretaceous in age (unpublished thesis by
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 161

P. J. Katich, 1951, Ohio State University). Throughout western 

Colorado and eastern and central Utah the Dakota sandstone is 

separated from underlying Lower Cretaceous formations by an erosional disconformity, but in New Mexico and northeastern Arizona 

pre-Dakota warping and subsequent erosion have removed Lower 

Cretaceous formations, the Morrison formation, and part of the San 

Rafael group along the southern and southwestern margin of the 

region of study. Consequently the Dakota sandstone progressively 

overlies older and older formations to the south and west.

MANGOS SHALE

The Mancos shale consists of gray calcareous and gypsiferous 

marine claystones and minor sandstones. Marine invertebrate fossils 

are common. The Mancos lies conformably on the Dakota sandstone; 

the contact is gradational and in many places is only arbitrarily 

located.

RELATION OF ORE DEPOSITS TO MORRISON 

STRATIGRAPHY

Information concerning the relation of carnotite deposits to the 

stratigraphy of the Colorado Plateau region and particularly to 

that of the Morrison formation has been collected during the regional 

studies as well as during a number of detailed studies in the vicinity 

of ore deposits. Many of the results are negative but are of value in 

that some lines of research can be eliminated.

The distribution of major groups of carnotite deposits is shown in 

figure 31. Most of the carnotite deposits of the Morrison formation 

are confined to the Salt Wash member. The carnotite deposits of the 

Salt Wash member lie almost entirely within the sandstone and mudstone facies (fig. 21); most are in areas where the Salt Wash member 

is more than 240 feet thick (fig. 21). The lithofacies studies show that 

most of the carnotite deposits are in areas where the stream deposits 

(essentially the channel sandstones) constitute from 40 to 55 percent of the thickness of the Salt Wash member; that most of the carnotite deposits are in areas where the total thickness of the stream 

deposits in the Salt Wash is from 90 to 200 feet (fig. 23); and that most 

of the carnotite deposits are in areas where the thickness of the stream 

deposits shows a percentage mean deviation of from 5 to 18 percent.

These observations suggest that an area of relative favorability for 

ore localization may be defined (fig. 31) within the area of the sandstone and mudstone facies (fig. 21). It is generally agreed that most 

of the ore was introduced by mineral-bearing solutions that percolated 

through the more permeable layers at sometime after the accumulation
162 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

I WYOMING

EXPLANATION

 

Location of major carnotite deposit

by lithofacies criteria: Salt Wash member more than 2^0

feet thick. Stream lithotope comprises 40 to 55 percent 

or thickness oT member. Total thicKness or stream lithotope 

in member is 90 to 200 feet. Percentage mean deviation 

of stream lithotope is 5 to 18 percent.

[FIGURE 31.-Map showing the location of major capaotite digits In the Salt Wash mewbe?

of the Morrison formation and the areas of favorable environment for ore deposition, as 

delimited by lithofacies criteria.

of the sediments. Before the Salt Wash member was regionally deformed, it must have varied areally in its quality as an aquifer. Near

the apex of the fan in south-central Utah it must have been an excellent

.aquifer, for it is relatively thick and contains a high percentage of

 continuous, permeable, stream-deposited sandstone. To the north and 

east, in the areas of the claystone and lenticular sandstone fac.ies and 

the limestone and claystone facies, the Salt Wash must have been a
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 163

poor aquifer, for it is thin and contains a very low percentage of 

stream-deposited sandstone beds, which are mostly discontinuous. 

Within the area of the sandstone and mudstone f acies, the Salt Wash 

must have had intermediate properties as an aquifer. If ore-bearing 

solutions were introduced prior to regional deformation, they might 

have "flushed" through the highly permeable part of the Salt Wash 

without appreciable opportunity for deposition and concentration of 

the ore minerals. In the marginal f acies of the Salt Wash, ore-bearing 

solutions perhaps would have moved too slowly to have brought in 

much uranium and vanadium in solution. Optimum conditions of 

supply and movement of mineral-bearing solutions could have 

occurred within the sandstone and mudstone f acies.

The petrography of the Salt Wash member of the Morrison formation shows no detailed or regional relation between ore deposits and 

the heavy-mineral distribution or between any of the parameters of 

.grain-size distribution except the sorting as measured by the logarithmic standard deviation (fig. 27). Most of the carnotite deposits occur 

in areas where the sandstones of the Salt Wash are relatively wellsorted (low logarithmic standard deviation). In general, well-sorted 

sands have greater permeability than those that are poorly sorted. A 

greater permeability of the Salt Wash member may have influenced 

migration of ore-bearing solutions and contributed to the development and localization of deposits in the area of relatively well-sorted 

sandstone.

Detailed control for the localization of ore deposits is probably the 

Tesult of the interplay of a number of environmental factors. The

 coincidence of several physical features of the Salt Wash member 

with the ore deposits has been studied and summarized by Weir 

(1952). The variations of the Salt Wash in the vicinity of the 

TJravan mineral belt (Fischer and Hilpert, 1952), "A narrow, elongate area in southwestern Colorado in which the carnotite deposits 

. . . have a closer spacing, larger size, and higher grade than those 

in adjoining areas," have been studied and summarized by McKay.4 

The parallel orientation of the long axes of ore "rolls" with the elongation of ore deposits and the orientation of fossil logs has been noted

 by Fischer (1942, p. 387) and indicates a large-scale controlling influence by primary sedimentary features on the shape of ore bodies. 

However, sedimentary structural studies show considerable divergence between the resultant dip direction of cross-laminae in some 

mineralized areas and the orientation of ore "rolls" in the mines of 

the same areas. This may be a result of sampling technique, for the

* McKay, B. J., 1955, Large-scale geologic guides to camotite deposits In the Uravan and 

-Gateway districts, Montrose and Mesa Counties, Colorado: U. S. Geol. Survey Bull. 

1009J (in press). :
164 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

sedimentary structural study may average the orientation of many 

different stream channels and the orientation of ore deposits may be 

influenced by only a few channels in the area studied. Nevertheless, 

the resultant dip directions of cross-laminae (fig. 26) and the trends 

of ore "rolls" show about the same radial regional pattern. Ore 

deposits show little detailed control by sedimentary structures, for 

in many places the ore cuts across the bedding and lamination.

Three possible distinct sources of the uranium in the carnotite deposits may be postulated: the sedimentary rocks of the source area 

of the Salt Wash member; a post-Salt Wash hydrothermal source m 

the Colorado Plateau region; or post-Salt Wash sedimentary rocks,, 

possibly tuffaceous beds, either in the immediate vicinity of or away 

from the present ore deposits. The stratigraphic studies of the Morrison formation have furnished little evidence for determining the 

most probable original source.

The pre-Morrison sedimentary rocks have been entirely removed 

from the probable area of the major source of the Salt Wash member of 

the Morrison formation in west-central Arizona and evidence for preexisting uranium deposits in these rocks is lacking. Evidence for the 

origin of such hypothetical uranium deposits might be found in the 

pre-Cambrian rocks of this area. Two deposits of moderate uranium 

content have been cited in the pre-Cambrian of Arizona (Kaiser B 6 ), 

One of these, the Jim Kane mine in Mohave County, is in the area 

considered as the probable source area of the Salt Wash member. 

Uranium deposits have been reported .in the Triassic Chinle formation of Arizona not far from the probable source area of the Salt 

Wash. Both the upper Paleozoic Kaibab and Madison limestones of

Utah have "strong traces" of uranium (Webber 7, 1947, p. 234) and 

might have formed a low-grade source of the uranium concentrated

in the Salt Wash. Argall (1943, p. 19) suggests that the uranium of

the Salt Wash might have been derived from the vanadiferous beds 

of the Permian Phosphoria formation, a phosphate-bearing formation of northern Utah, southern Idaho, and southwestern Wyoming. 

In Wyoming and Idaho this formation contains low percentages of

uranium and might liave yielded uranium that, by concentration,,

formed the relatively rich deposits of the Salt Wash. However, this

WOUld have involved migration of uranium-bearing solutions from

the west and northwest to the south and southeast across the grain

of the Salt Wash Structures (fig. 26). Such migration seems im8 Kaiser, m P., 1951a, Uraniferons quartzite, Red Bluff prospect, Gila County, Arizona: 

U. S. Geol. Survey Trace Elements Mem. Kept. 120.

« Kaiser, E. P., 1951b, Radioactivity at the Jim Kane Mine, Mohave County, Arizona: 

U. S. Geol. Survey Trace Elements Mem. Kept. 216.

7 Webber, B. N., 1947, Geology and ore resources of the uranlum-vanadiumi deposltlonal 

province of the Colorado Plateau region: Union Mines Development Corp. unpublished! 

report, p. 234, p. 177-178.
STRATIGRAPHY OF MORRISON AND RELATED FORMATIONS 165

probable unless a regional tilting to the southeast forced ground-water 

movement across the structures. Evidence for this postulated tilting 

is lacking. The absence of phosphatic material in the Salt Wash 

suggests that the Phosphoria was neither an .important source during 

the accumulation of the Salt Wash sediments nor an important source 

of mineral-bearing solutions during formation of the carnotite deposits.

Much field evidence has been cited as supporting a hydrothermal 

origin of the carnotite deposits of the Morrison formation. Much of 

this evidence is inconclusive. Perhaps the greatest support to the 

hypothesis rests in age determinations (Stieff, Stern, and Milkey, 

1953) that indicate the uranium was emplaced at about the beginning 

of the Tertiary.

Migration of uranium into the Morrison from minerals disseminated in overlying sediments, particularly tuffaceous clays, is possible. 

However, it appears unlikely: first, because these overlying beds 

are quite impervious, and second, because they generally do not seem 

to contain more metal than is normal in a sedimentary rock.

Regardless of the source of the carnotite deposits of the Colorado 

Plateau region, mineral-bearing solutions must have migrated laterally through the sandstone beds to emplace most, if not all, deposits. 

The migration of these solutions through the Morrison formation and 

the emplacement of the deposits were undoubtedly affected by the 

orientation and character of the sedimentary structures and the f acies 

variations of the Salt Wash member. These stratigraphic features 

serve to focus attention on broad areas favorable for carnotite deposits and may serve to provide expectable orientations of the ore 

bodies within the Salt Wash member.

LITERATURE CITED

Argall, G. O., Jr., 1943, The occurrence and production of vanadium: Colorado

School of Mines Quart, v. 38, no, 4. 

Baker, A. A., Dane, O. H., and Reeside, J. B., Jr., 1936, Correlation of Jurassic

formations of parts of Utah, Arizona, and Colorado: U. S. Geol. Survey Prof.

Paper 183. 

Baker, A. A., Dane, C. H., and Reeside, J. B., Jr., 1947, Revised correlations of

Jurassic formation of parts of Utah, Arizona, New Mexico, and Colorado:

Am. Assoc. Petroleum Geologists Bull., v. 31, p. 1664-1668. 

Brown, R. W., 1950, Cretaceous plants from southwestern Colorado: U. S. Geol.

Survey Prof. Paper 221-D. 

Cross, Whitman, 1894, Description of the Pikes Peak sheet: U. S. Geol. Survey

Geol. Atlas, folio 7. 

Eckel, E. B., 1949, Geology and ore deposits of the La Plata district, Colorado:

U. S. Geol. Survey Prof. Paper 219. 

Emons, S. F., Cross, Whitman, and Eldridge, G. H., 1896, Geology of the Denver

Basin in Colorado: U. S. Geol. Survey Mon. 27.
166 CONTRIBUTIONS TO THE GEOLOGY OF URANIUM

Fenneman, N. M., 1931, Physiography of western United States, McGraw-HilL 

Book Co.

Flscher, R. P., 1942, Vanadium deposits of Colorado and Utah; U. S. Geol. SurveyBull. 936-P.

Fischer, R. P., and Hilpert, L. S., 1952, The Uravan mineral belt: U. S. Geol, 

Survey Bull. 988-A.

Gilluly, James, and Reeside, J. B., Jr., 1928, Sedimentary rocks of the San Rafael 

Swell and some adjacent areas in eastern Utah: U. S. Geol. Survey Prof. 

Paper 150.

Goddard, E. N., and others, 1948, Rock-color chart: National Research Council.

Goldman, M. I., and Spencer, A. C., 1941, Correlation of Cross' La Plata sandStone, southwestern Colorado: Am. Assoc. Petroleum Geologists Bull., v. 25r 

p. 1745-1767.

Gregory, H. E., 1938, the San Juan Country: U. S. Geol. Survey Prof. Paper 188, 

p. 58-59.

Gregory, H. E., 1951, The geology and geography of the Paunsaugunt region. 

Utah: U. S. Geol. Survey Prof. Paper 226.

Harshbarger, J. W., Repenning, C. A., and Jackson, R. L., 1951, Jurassic stratigraphy of the Navajo country: New Mexico Geol. Society Guidebook of the 

San Juan Basin, New Mexico and Arizona, p. 95-99.

Kiersch, G. A., 1950, Small scale structures and other features of Navajo sand-' 

stone, northern part of the San Rafael Swell, Utah: Ainer. Assoc. Petroleum 

Geologists Bull., v. 34, p. 923-942.

Lupton, C. T., 1914, Oil and gas near Green River, Grand County, .Utah: U. S. 

 Geol. Survey Bull. 541.

McKee, E. D., 1939, Some types of bedding in the Colorado River delta: Jour. 

Geology, v. 47, p. 64-81.

McKee, E. D., 1948, Classification and interpretation of cross-lamination (abstract) : Geol. Soc. America Bull., v. 59, p. 1378.

Moore, R. C. 1949, Meaning of facies: Geol. Soc. America Mem. 39, p. 8-16.

Read, C. B., Wood, G. H., Wanek, A. A., and MacKee, R. V., 1949, Stratigraphy 

and geologic - structure in the Piedra River Canyon, Archuleta County, 

Colorado: U. S. Geol. Survey Oil and Gas Inv. Prelim. Map 96.

Reiche, Parry, 1938, An analysis of cross-lamination; Coconino sandstone: Jour;

Geology, v. 46, p. 905-932.

stieff, L. R., stem, T. w., and Milkey, R. G., 1953, A preliminary determination 

Of the age of some uranium ores of the Colorado Plateaus by the leaduranium ratio: U. S. Geol. Survey Circular 271.

stokes, w. L., 1944, Morrison ana related deposits in and adjacent to the Colorado Plateau: Geol. Soc. America 'Bull., v. 55, p. 951-992. '

Stokes, W. L,.; 1947; Primary lineation in fluvial sandstones: A criterion of current directions: Jour. Geology, v. 55, p. 52-54.

WaldSCbmidt, W. A., and LeRoy, L. W., 1944, Reconsideration of the 'Morrison

formation in the type area, Jefferson County, Colorado: Geol. Soc. America 

Bull., v. 55, no. 9, p. 1097-1114. ... 

Weir, T>.' B.,: 1952, Geologic guides to prospecting for carnotlte deposits .on Colorado Plateau : U. S. Geol. Survey Bull, 988-B,' "
INDEX

Page 

Abstract................................... 125-127

Age, carnotite deposits.... ............... 162

Alluvial fans....................... 151-152,157,162

Ancestral Uncompahagre Highland....... __ 131

Angular unconformities......... .... . 134

Apatite................................. ... 150

Area of studies...._..... .____..._ 128

Areal variations, lithofacies...__.._ ... 141 

ratio of stream to floodplain deposits._. 142 

relative continuity._ ...___.__ 141 

total thickness.......................... 141,142

Bedding... ........................... .. 136

Bibliography ......... . ..... 165-166

Bluff sandstone..._____.._..__.... 133-134

Boundary between differentiated and undifferentiated Morrison formation.__... 134 

Brushy Basin member... _________ 155-156

Carmel formation..._____-____._... 132 

Carnotite deposits, criteria of favorable areas

of deposition.._______. _____ 161,162 

local controls.___... ..__....._. 163

' origin._.________._________ 165 

sources of uranium.... ..-...-_.... 164-165

Character, Morrison formation__._---.. 134 

Chert... 153,156,157

Claystone.. . ..... .- 136,140,153,156,160

Claystone and lenticular sandstone facies... 138,162 

Claystone and sandstone facies... . .. 140 

Climate, Morrison time___- _ _.. _ 152,157 

Colorado Plateau....... ___......... 128

Conditions of deposition....--.___..-. .. 131

Conglomeratic sandstone facies........... 137,

140,150,154,155,157

derived from acid igneous rocks...___.. 151 

Consistency factor___________.__ 146-147 

Contorted bedding.__._...___...._ 145

Correlations_____._____.._..__ 133,134 

Cow Springs sandstone... ..___....... 133,140

Cross-laminated beds.................. 136,141,153

Cross lamination, false.... ...........__ 146

festoon.......___........._....._ 144,145

field study................................ 146

low angle compound-_-___.... 144-145,146

relation to ore rolls..........._....... 163-164

wedge torrential..._........_....... 144,153

Current lineation......._.___....... 145

Curtis formation....._____..______ 132-133

Dakota sandstone.__......_____ . 160-161

Dip direction (azimuth) of cross lamina. 146-147,164 

Drainage directions..___..._......... 147

Entrada sandstone...._______....._ 132

Environment of deposition......___.........131,

132,133,141,151-152,157,160 

carnotite deposits.........__.._.. 161,162

stream and floodplain....- __.... 141,151

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Eolian deposition. . ................ __ 131,132

Facies................... 132,135,140,151,152,154-155

Pans, alluvial......._.................... 151-152

Feldspar........................... 149,150,151,154

Fluvial deposition.......................... 131,151

Fossils............._..... 132,136,150,156,157,159

Friable sandstone......._______..___ 141

Garnet______.__.__________.. 150 

Glen Canyon group.__.____._____ 130-1321 

Gradational contacts..____________ 131 

Great Plains province..___.________ 129

Heavy minerals... .. __ _... 148 

Isoliths........................................ 141

Junction Creek sandstone......______ 133-134

Keyenta formation....._..^___..__ 130,131

Laboratory study methods. _________ 146 

Lacustrine origin_______________ 131 

Lenses, conglomeratic sandstone.... . 141

Lensing nature of claystone beds.... ..._ 140

Light minerals.___..___________ 148- 

Limestone..-......!.. .. . 136,152,156,157,158

Limit, of deposition... ___. ________ 135,138

erosional....__1.___..__ _.... 135 

Lithofacies, areal variations....... -. .. 141

study............................... 128,141,161

Logarithmic standard deviation..__-__ 148,163 

Lower Cretaceous strata, character...... 160

Lower part of Morrison formation___..... 135-152

Mancos shale..._ .. - 161 

Mcsozoic rocks__ ............ .. .. 129

Mineral suite.._. ..._.._.. _ 148

Mineralizing solutions. __ _ . 161-162,164-165

Modal diameter, average.. .. 147

Morrison formation, base...-.....-.- 134

general description.... _ 134

outcrop pattern..-._______..__ 128-129

type section....--..-.... 158

undiflerentiated part..- 1 ".8-160

Mud cracks....__ __........ 145

Orerolls...... . .... . . -- 163,164

Orientation, stream channels.... -- 164

Origin, carnotite deposits ............ 165

Kayenta sandstone..--.......... .. 131

lower part of Morrison formation..-...-... 151 

Navajo sandstone..... . 132

San Rafael group....-..-.-....------.-- 132-133

undifferentiated Morrison_........ . 159-160

upper part of Morrison formation... ... 157

Wingatc sandstone_... _ . - ... ,131

Outcrops.-..--...------..--------.--------- 128-129

167
168 INDEX

Page 

Paleogeography.... __.____... 150-152

Paleozoic rocks..........____........ 129,150,164

Pebbles in conglomerate, composition__.... 138,

140,150,153,156,157

significance_ -..._________ 157 

Percentileskewness......__.________ 148

Phosphoria formation..___________ 164-165 

Purpose of studies_......________._ 127

Recapture member, character....-...-.- .. 140 

extent.................................. 137-138

origin...... -. . -- --- isi

Regional studies -. - 127-128

Resultant dip azimuths of cross laminae... 146-147,

164 

Ripple marks_...... .... ..... 145-146

Rock types.___.___._..____ .. 129

Salt Wash member............. 128,133-137,143-147

average grain size_..-_...__... . 147-148 

average mineral composition..... _ 147-148

base .- - .. 136

carnotite deposits of..._....._--...- 161-165

character__________________ 135-136 

conglomeratic sandstone fades.__ ._ 137 

origin____ _ 151 

permeability.... 161-163

Sandstone .. . 135,137,141,153,157,163 

composition.. i....................... 147

Sandstone facies. 140,154 

Sandstone and mudstone facies____ 137,161,163 

carnotite deposits in . .. 161 

San Rafael group - ... 130,132-134 

Scour-fill beds. 137,140,153

Sedimentary structures_._ . _ 140,143,165 

orientation_..__________ 151 

study................................... 128,163

Page 

Sedimentology.........._..________ 128

Source areas__..______...______ 131,152

Source area, Brushy Basin member______ 157

Recapture member........._____ 150,151

Salt Wash member...... 148-149,150,152,157,164

Westwater Canyon member._______ 156 

Statistical analysis_._____.________ 148 

Staurolite............__....________ 150

Stratigraphic section_____________ 130 

studies............................. 127-128,164

Structures, Colorado Plateau province____ 128 

Summerville formation___________ 132-133

Tertiary rocks__________________ 130

Thickness, Brushy Basin member.._____ 156

irregularities in______________ 138,152

Recapture member..._________ 140

stream deposits.________ 141,142,151,161

Salt Wash member...___________ 138

undifferentiated Morrison_______ 158

Westwater Canyon member...._____ 155

Topographic expression of strata.___ 136,140,153

Triassic rocks. See Wingate sandstone.

Tuff, opaline and silicified._________ 149,150

Undifferentiated part of Morrison formation. 158-160 

Upper Cretaceous strata, character. ... 160,161 

Upper part of Morrison formation.... ... 152-157 

Uranium deposits. See Carnotite deposits.

Vegetation_.. . 152

Wanakah formation... ....._ .. 133

Well-sorted sands, area............. .. 148,163

Westwater Canyon member._ ... 153-154 

Wingate sandstone_....._ 130,131