Isopach Mapping by 

Photogeologic Methods 

as an Aid in the Location 

of Swales and Channels in the 

Monument Valley Area, Arizona

By TRYING J. WITKIND, WILLIAM R. HEMPHILL, CHARLES L. PILLMORE, and 

ROBERT H. MORRIS

PROCEDURES AND STUDIES IN PHOTOGEOLOGY

GEOLOGICAL SURVEY BULLETIN 1043-D

Prepared in part on behalf of the U.S. 

Atomic Energy Commission and published with the permission of the Commission

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1960
UNITED STATES DEPARTMENT OF THE INTERIOR 

FRED A. SEATON, Secretary

GEOLOGICAL SURVEY 

Thomas B. Nolan, Director

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

Washington 25, D.C.
CONTENTS v:

Page

Abstract_ __________________j________- __________-_-____-_-_______ 57

Introduction. -______--_________-___--____________-_-:__.___ 11 _____ 57

Swales and channels in the Monument Valley area, Arizona, by I. J. Witkind- 60

Geology---------- _'_-_ ....'_ .'...._____. -_. 60

Relation between swales and channels..___________________________ 62

Photogeologic methods used to compile isopach maps, by W. R. Hemphill

and C. L. Pillmore..__ _ _-_-____.__.__._..._.___..... 63

Stratigraphic interval represented by the isopachs-_---___----_-_-. 65

Kelsh plotter..______._._-------___-------_____... 65

Base-map compilation___._____---_.__._____.__._._._________. 67

Kelsh-plotter notation of geologic data___-__-_-_-___-_-_______--_ 69

Computation of stratigraphic thickness_._--_____---_--__-___-__-_ 70

Appraisal of photogeologic isopach maps of areas in the Monument Valley

area, Arizona, by I. J. Witkind and R. H. Morris__________________ 73

Monument No. 2 area___-_-_-_-______--_-___-___-_______-____ 73

East Cane Valley area_________________________________________ 75

Hunts Mesa area_-----__------_-_-------______________________ 76

Unnamed mesa southwest of Hunts Mesa_______________________ 78

West Cane Valley area.________________________________________ 80

General appraisal...___----__-__-_-_________-___._-____________ 81

Advantages-._______---_----_-______-_____--______-_______ 82

Disadvantages _______--_-__---_____-___________-___-______ 82

Conclusion__ _______-___-__--_-_-_______-___---_-___-______-_ 83

Literature cited___________________________________________________ 83

Index..________-______-_---_-----_----_-__-______-----__-_-----_- 85

ILLUSTKATIONS

Page 

PLATE 3. Isopach maps of the Monument No. 2 area, compiled by

photogeologic and field methods._______________________ In

pocket

4. A, View of part of a channel exposed on the north rim of

Hunts Mesa. B, The Kelsh plotter._________________ Facing 60

5. A, Annotated stereopair of vertical aerial photographs showing part of the Monument No. 2 channel. B, Ground view 

of part of the area shown in .A_______________________ Facing 61

FIGURE 18. Index map of parts of northeastern Arizona and southeastern

Utah showing area selected for photogeologic study______ 59

19. Stratigraphic section of consolidated sedimentary rocks exposed in the Monument No. 2 area..___________________ 61

20. Map showing area selected for isopach mapping by photogeologic methods.__-__----____-__--_---___-_-________ 64

ni
IV CONTENTS

Page

FIGURE 21. Diagram showing spatial positions, with respect to the terrain, 

of two overlapping vertical aerial photographs at the instant each photograph was taken__--_-__-_-___________ 66

22. Stereotemplet of a single stereoscopic model_________--___ 68

23. Preliminary isopach-map manuscript of part of the Monument No. 2 area, plotted with the Kelsh plotter._________ 71

24. Isopach map of the east Cane Valley area, compiled by photogeologic methods---_____-_-__-___----______-_---_____ 75

25. Isopach and geologic maps of parts of the Hunts Mesa area,

including area Q_______._________-_-_----_-__-__--_. 76

26. Isopach map of unnamed mesa southwest of Hunts Mesa,

compiled by photogeologic methods___._----_--__----___ 79

27. Isopach map of the west Cane Valley area, including area P,

compiled by photogeologic methods._---____---_-_---___ 80
PROCEDURES AND STUDIES IN PHOTOGEOLOGY

ISOPACH MAPPING BY PHOTOGEOLOGIG METHODS AS AN

AID IN THE LOCATION OF SWALES AND CHANNELS

IN THE MONUMENT VALLEY AREA, ARIZONA

By IRVING J. WITKIND, WILLIAM R. HEMPHILL, CHARLES L. PILLMORE, 

and ROBERT H. MORRIS

ABSTRACT

In the Monument Valley area of northeastern Arizona, uranium-vanadium 

deposits are localized in strata of the Shinarump member of the Chinle formation of Triassic age that fill ancient scour channels, some of which are along 

the axes of broad, shallow, elongate troughs known as swales.

Commonly the swales are not visible from the ground but are apparent on 

isopach maps of selected strata that underlies the Shinarump. To determine 

whether maps prepared from aerial photographs would be equally useful, a test 

area previously mapped in the field was mapped by photogeologic methods.

The strata in the interval represented by the isopach maps are distinctive 

both in the field and on the aerial photographs. Both the base and top of this 

interval are unconformities. As the unconformity at the base of the interval is 

smooth and even, however, the isopachs reflect irregularities at the top of the 

interval, the most prominent of which are the channels and swales at the 

base of the Shinarump.

Isopach maps made by photogeologic methods were compared with one isopach 

map and one channel map that were prepared by field methods. The photogeologic isopach maps delineated both the swales and the channels. This suggests that photogeologic methods are adequate for use in defining swales similar 

to those in the Monument Valley area. Furthermore, photogeologic methods 

are independent of weather and logistics problems, and can conveniently precede 

geologic fieldwork. Many isopach readings can be easily taken in a relatively 

short time. On the other hand, limitations are imposed by the need for aerial 

photographs from which suitable photogrammetric measurements can be made. 

If such photographs are not already available, the cost of obtaining them may 

be prohibitive. Also, the top and base of the interval to be measured must be 

discernible on the photographs. Accuracy is reduced where observations are 

widely spaced or where the top and base are widely separated horizontally.

INTRODUCTION

Geologic Avork in the Monument Valley area of northeastern Arizona and southeastern Utah by both the U.S. Geological Survey and 

the U.S. Atomic Energy Commission has indicated that uranium57
58 PROCEDURES AND STUDIES IN PHOTOGEOLOGY

vanadium deposits are localized in Triassic sedimentary rocks 

(Shinarump member of the Chinle formation) that fill ancient stream 

channels. During a Geological Survey mapping program in northeastern Arizona, it became apparent that some of the channels are 

along the axes of wide elongate shallow troughs known as swales 

(Witkind, 1956a). It is unknown at this time (1958) whether all 

channels are associated with swales.

In at least one area a swale continues beyond the channel. This 

suggests that some channels, at least, may be confined within, and 

irregularly spaced along, the swales.

Because of their great width and relative shallowness, the swales are 

not discernible on the ground. However, isopach maps of selected 

strata directly beneath the swales aid in determining their extent, 

width, depth of scour, and trend.

If some rapid method could be devised for finding the swales along 

the outcrop, it might be possible to trace the swales, possibly by 

geophysical methods, where they are buried beneath younger strata. 

Subsequently, drilling along the axes of the swales might be of use in 

locating completely concealed channel sediments. Among the techniques considered for the rapid location of the swales was the use of 

photogeologic methods.

The purpose of this study was to locate and delineate swales and 

channels by means of isopach maps compiled by photogeologic methods. A test area was selected.in the Monument Valley area (fig. 18) 

for several reasons: A well-defined swale was known to be present 

in the area; good, aerial photography was available; and, most important, the strata are well exposed and are readily identifiable on 

the aerial photographs. This test area had been mapped previously 

in the field, and the geologic map. and data were given to the photogeologists before they began their study. Both the photogeologic 

methods used in the experimental isopach study and the resulting 

isopach map are the responsibility of W. R. Hemphill and C. L. 

Pilhnore. The geologic interpretation of the results is the responsibility of I. J. Witkind and R. H. Morris.

This report presents the results of the work in three parts. The 

first part describes the geologic setting in the Monument Valley area 

and the relation between channels and swales; the second deals with 

the photogeologic methods used to compile isopach maps; and the 

third compares the results obtained by photogeologic methods with 

those obtained from fieldwork.

This work was done on behalf of the Division of Raw Materials of 

.the U.S. Atomic Energy Commission.

60 PROCEDURES AND STUDIES IN PHOTOGEOLOGY

SWALES AND CHANNELS IN THE MONUMENT VALLEY

AREA, ARIZONA

By IBVING J. WITKIND

In 1951 and 1952 the U.S. Geological Survey undertook a program 

of geologic mapping and uranium investigation in the Monument 

Valley area of northeastern Arizona. The geologic data presented 

in this report were gathered during that study.

The Monument Valley area is a desert; vegetation is sparse and 

only a few people, principally Navajo Indians, inhabit the area. 

Roads are poor and travel by vehicles is almost impossible during 

sandstorms or the sudden, unexpected summer thunderstorms. 

Broad sand-filled valleys separate towering mesas, buttes, and rock 

monuments. The ore-bearing strata are all well exposed, and prospecting is relatively simple, although getting to, and moving along

the outcrops is arduous.

GEOLOGY

Consolidated sedimentary strata exposed in the test area (fig. 20) 

range in age from Permian (De Chelly sandstone member of the Cutler formation) to Late Triassic (Shinarump member of the Chinle 

formation) (fig. 19). These strata form the southeast limb of the 

Agathla anticline, a south westward-plunging minor fold that is superimposed on the much larger Monument upwarp. Dissection of the 

Agathla anticline has been severe, and its core has been eroded to 

form a broad valley with mesas, buttes, pinnacles, and isolated crags 

in its center. The southeast limb of the anticline now appears as a 

serrated ridge that strikes northeastward and dips southeastward. 

This limb occupies the major part of the area.

Of the strata that were involved in the photogeologic study the 

De Chelly sandstone is the lowermost exposed in the test area (fig. 19). 

It is a light-tan massive crossbedded fine-grained sandstone that 

commonly stands as a vertical cliff (pi. 4A). Unconformably overlying the De Chelly is a series of dark-reddish-brown and chocolatebrown shaly siltstone, shale, and ripple-marked fine-grained 

sandstone that contrast conspicuously in color with the overlying and 

underlying strata, as seen both in the field and on the aerial photographs. These strata include the Hoskinnini member and the upper 

part of the Moenkopi formation (Triassic? Lower and Middle? Triassic) . They are treated here as one lithologic unit and their combined thickness is referred to as the undifferentiated Moenkopi formation. The unconformity at the top of the De Chelly sandstone is 

remarkably even and free of relief and, therefore, is used as the base 

of the interval represented on the isopach maps.
GEOLOGICAL SURVEY BULLETIN 1043 PLATE 4

"Res Hunts Mesa NO 1 channel "Res

A, View of part of a channel exposed on the north rim of Hunts Mesa. Symbols: Trcs, Shinarump member 

of the Chinle formation; Trmu, upper part of the Moenkopi formation; Trmh, Hoskinnini member of the 

Moenkopi formation; and Pcd, De Chelly sandstone member of the Cutler formation.

B, The Krlsh plotter, showing sourres of liglil, -'' a»d I*>', cliupusitives of overlapping aerial photographs, 

C and D; platen, E; tracing table, F; metric scale, G; and variable-ratio pantograph, P.
GEOLOGICAL SURVEY BULLETIN 1043 PLATE 5

A, Annotated stereopair of vertical aerial photographs showing part of the Monument No. 2 channel. 

Symbols: Trcs, Shinarump member of the Chinle formation; Trmu, upper part of the Moenkopi formation; 

Trmh, Hoskinnini member of the Moenkopi formation; Trm, combined Hoskinnini member and tipper 

part of the Moenkopi formation; and Pcd, DC Chelly sandstone member of the Cutler formaton. The 

trend of the Monument No. 2 channel is indicated by the centerline, C, which is dotted where the channel 

is eroded. Point Y shows the position from which the ground view below (pi. 55) was photographed.

Monument No 2 channel

B, Ground view looking southwestward from part of the area shown in plate 5/4, showing the Monument 

No. 2 channel as it crops out on South Ridge. The debris from the construction of the access road 

has fallen across and partly obscures the contact.
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photogeologic methods. Interval represented by isopachs extends from the base of t

the top of the upper part of the Moenkopi formation.
62 PROCEDURES AND STUDIES IN PHOTOGEOLOGY

Overlying the Moenkopi are the light-gray massive crossbedded 

sandstone, conglomerate, conglomeratic sandstone, and mudstone beds 

that make up the Shinarump member of the Chinle formation. The 

Moenkopi- Shinarump contact is an erosional unconformity marked by 

swales and channels, and it is the top of the interval represented on 

the isopach maps (fig. 19). As the unconformity between the De 

Chelly and the Hoskinnini is even and free of relief, any irregularities 

apparent on the isopach maps reflect swales, channels, and other 

erosional features at the top of the undifferentiated Moenkopi 

formation.

RELATION BETWEEN SWALES AND CHANNELS

Channels of different trend, length, width, and depth are exposed 

in the Monument Valley area (pi. 4A). These channels contain, in 

their fill of basal sediments of the Shinarump, all the uraniumvanadium ore deposits. Some of the channels can be traced for many 

miles, others for only 1 or 2 miles. Many of the channels are exposed 

on only one face of a mesa and do not crop out elsewhere; geophysical 

studies indicate that the bottom of these channels curves upward near 

the ends of the channels (R. A. Black and W. H. Jackson, 1954, written communication). Some channels are symmetrical in cross section, 

and others are asymmetrical. They range in width from 15 feet to 

as much as 2,300 feet and in depth, from 5 feet to as much as 150 

feet. Details about the channels are given elsewhere (Bain, 1952; 

Witkind, 1956a, 1956b), and no attempt is made here to describe them 

fully.

Some of the channels are along the axes of broad, shallow, elongate 

troughs known as swales. These swales have been formed in the 

uppermost strata of the Moenkopi, and their widths are measured 

in miles in contrast to the relatively narrow channels whose width is 

measured in feet. In general, they range in length from 1 to 4 miles, 

in width from Vz mile to 3 miles, and in relief from 20 to about 60 

feet. Fieldwork indicates that at least one swale is exposed in the test 

area; other swales are visible elsewhere in the Monument Valley 

area.

A good example of a channel along the axis of a swale (pi. 3Z?) is in 

the area of the Monument No. 2 mine, Apache County, Ariz. (fig. 18). 

The Monument No. 2 channel is about 1% miles long, about 700 feet 

wide at its center, and about 50 feet deep. The swale is about 3 miles 

wide, has about 50 feet of relief, and can be traced for 3 to 4 miles 

(Witkind, 1956b, p. 236). Here, the swale extends beyond the channel. 

Similar channel-swale relationships are found elsewhere in the Monument Valley area.

Most of the channels exposed at the outcrops can be detected either 

from the air or by field observation on the ground. However, it is
LOCATING CHANNELS BY PHOTOGEOLOGIC MAPPING 63

especially difficult to locate channels which do not crop out at the 

surface and which are generally deeply buried beneath younger strata. 

It is unknown how many channels are so concealed. In the relatively 

small Monument Valley area, Arizona, only about 40 square miles of 

the Shinarump is exposed. The Shinarump is generally deeply buried, 

however, for about 360 square miles. During the fieldwork, about 

60 channels were found in the 40 square miles where the Shinarump 

is exposed. If it is assumed that the channels are distributed at random and that the same ratio of 60 channels for each 40 square miles 

persists, about 540 channels are buried in the 360 square miles where 

the Shinarump is concealed. The major problem is how to locate 

some of these 540 channels. As of 1957, elaborate drilling programs 

following surveyed grids have been relatively successful. Some channels are within swales, and this relationship may assist in the location 

of concealed channels. If swales can be detected at the outcrop, geophysical or other methods might be used to delineate their extent, 

width, and depth along the projection of their trend. Drilling along 

the axes of the swales might result in the location of some channels. 

Clearly, the delineation of the swales would reduce the size of the 

areas where drilling would be necessary.

A test area (figs. 18 and 20) that had previously been mapped in the 

field was selected for isopach mapping by photogeologic methods. 

The area includes the Monument No. 2 channel with its accompanying 

swale. Photogeologists of the Geological Survey prepared isopach 

maps of the test area by photogeological methods, and from these 

maps an attempt was made to delineate the swales and channels. 

Their results are compared with field results shown in plate 3 and 

figure 25.

PHOTOGEOLOGIC METHODS USED TO COMPILE ISOPACH

MAPS

By WILLIAM R. HEMPHILL and CHARLES L. PILLMOBE

In order to compile an isopach map by photogeologic methods, the 

contacts defining the stratigraphic interval to be measured must be 

distinguishable on aerial photographs. Contacts may be distinguished by direct observation of bedrock exposure or, in some poorly 

exposed areas, by indirect evidence, such as changes in soil, vegetation, 

and topography that reflect contacts between partly or completely 

buried bedrock units.

Furthermore, instruments must be available that provide a stereoscopic model from which the stratigraphic interval can be measured 

with an accuracy commensurate with the purpose of the map. To 

date, such instruments as the stereometer, multiplex aeroprojector, 

and the Kelsh plotter have been used.
FIGURE 20 Map showing area selected for isopach mapping by photogeologic methods. 

the Monument No. 2 area (pi. 3), east Cane Valley area (fig. 24), Hunts Mesa (fig. 25

and west Cane Valley area (fig. 27).
LOCATING CHANNELS BY PHOTOGEOLOGIC MAPPING 65

In the Monument Valley study, the thickness of the undifl'erentiated 

Moenkopi formation was measured with the use of a Kelsh plotter; an 

isopach map of the test area, which includes about 40 square miles, 

was completed in about 45 man-days. This includes time for basemap compilation, notation and computation of data, and drafting.

STRATIGRAPHIC INTERVAL REPRESENTED BY THE ISOPACHS

On aerial photographs of the test area the undifferentiated Moenkopi formation appears as dark slopes between the light-toned cliffs 

of the underlying De Chelly sandstone member and the overlying 

Shinarump member (pi. 5A) .

Generally the same criteria are used to distinguish these rock units 

in the field (pi. 55). Because preliminary inspection of the photographs showed that the contact between the Hoskinnini and the upper 

part of the Moenkopi is difficult to discern, the combined thickness 

of the Hoskinnini and the upper part of the Moenkopi is included 

in the measured interval. The De Chelly-Hoskinnini contact is an 

unconformity; however, as previously mentioned (p. 60), this contact 

is remarkably even and free of relief. Although a small amount of 

local relief, probably less than 3 or 4 feet per mile, is suggested by the 

subsequent photogeologic work (p. TO), it is believed to be too slight 

to affect the study significantly. Furthermore, at least part of this 

inferred relief may be due to error in photograrnmetric measurement. 

Therefore, it is assumed that the De Chelly-Hoskinnini contact can 

be used as a reference datum and that significant variations in thickness of the undifferentiated Moenkopi can be attributed to irregularities in the erosion surface at the base of the overlying Shinarump 

member.

KELSH PLOTTER

A Kelsh plotter was used to plot the photo control points necessary 

for base-map compilation, to plot both the planimetry and the basal 

contact of the Shinarump member, and to measure stratigraphic intervals. The Kelsh plotter is a photogrammetric projection-type measuring and mapping instrument that duplicates in the office the relative 

positions of the camera stations in space with respect to the terrain at 

the instant the photographs were taken (fig. 21). The relation of the 

geometry of the aerial photograph to the Kelsh plotter is shown in 

plate 45. Two sources of light, A and 5, one equipped with a blue 

filter, the other with a red filter, optically project a metrically correct 

stereoscopic model of the terrain from two overlapping vertical aerial 

photographs, C and Z>, onto a viewing screen or platen, E. The 

projected image is viewed stereoscopically through blue and red
()6 PROCEDURES AND STUDIES IN PHOTOGEOLOGY

FIGURE 21. Diagram Illustrating spatial positions, with respect to the terrain, of two 

overlapping vertical aerial photographs at the instant each photograph was taken.

spectacles, the lens color for each eye corresponding respectively to 

the filters in the left and right light sources, A and B. . The platen is mounted on a mobile support called a tracing table 

(F, pi. 4JB). An illuminated dot at the center of the platen may be
LOCATING CHANNELS BY PHOTO-GEOLOGIC MAPPING 67

made to appear to float or to rise and fall in the stereoscopic model by 

raising and lowering the platen. Once the photographs are oriented 

properly in the Kelsh plotter, a particular feature, such as a geologic 

contact, may be traced on the manuscript map in its correct position by manipulating the horizontal and vertical position of the 

dot, whose position must be made to correspond to that of the feature's 

image in the stereoscopic model. Similarly, the difference in altitude 

between two or more selected features may be determined from the 

stereoscopic model by positioning the dot at the altitude of each feature ; a height-finding scale, G, is used to measure the vertical distance 

traveled by the "floating" dot between the features. The data and 

position of the measurements taken from the stereoscopic model can 

be plotted at a reduced compilation scale by means of a scale-reduction 

pantograph, P, which is linked mechanically to the tracing table.

The Kelsh plotter was selected to be used in the compilation of the 

isopach map for three reasons: (a) It provides a practicable method 

of obtaining the necessary isopach data in areas for which reliable 

base maps are not available; (b) it provides a stereoscopic model of 

higher resolution than that provided by other types of projection-type 

stereoscopic-plotting equipment available when the project was 

begun; and (c) compared to similar projection-type instruments, it 

provides the largest enlargement ratio (X 5) between original photograph scale and projected stereoscopic-model scale.

BASE-MAP COMPILATION

Photo control points are readily identifiable features, such as small 

shrubs or stream and road intersections, that are located and encircled 

on aerial photographs for use in construction of base maps. A Kelsh 

plotter was used to plot the orthographic positions of the photo 

control points in each of the 30 stereoscopic models covering the test 

area; the base map was constructed with the aid of these control 

points and a stereotemplet layout. A stereotemplet layout employs 

slotted cardboard templets and is used to triangulate mechanically 

the horizontal positions of photo control points at a constant scale in 

much the same manner that a planetable intersection is used to triangulate the horizontal positions of ground-control points. Briefly, 

construction of a stereotemplet of a single stereoscopic model includes 

plotting on paperboard or other suitable material the orthographic 

positions of a minimum of 4 photo control points, located near the 

corners of the stereoscopic model, and cutting slots radiating from 1 of 

these points, called the radial center, through the other 3 (or more) 

points. A second cardboard templet of the same area is prepared in a 

similar manner, except that a different radial center, usually located 

diagonally opposite from the first, is selected. The two templets are 

fastened together with studs as shown in figure 22. The radial centers
68 PROCEDURES AND STUDIES IN PHOTOGEOLOGY

Templet material

r Duplicate material

Stud

Slot

Radial center 

on duplicate

Rodiol center

FIGURE 22. Stereotemplet of a single stereoscopic model.

are analogous to the instrument stations in planetable intersection; 

similarly, the line between the two radial centers, known as an expansion base, is analogous to the base line in planetable intersection. 

The scale of the Stereotemplet can be varied as desired; the slots and 

two radial centers enable the studs representing the photo control 

points to slide a distance proportional to the change in scale along the 

expansion base. Photo control points common to two adjacent stereo-
69

scopic models are used to "tie" stereotemplets of the two models 

together. Scher (1955) describes sterotemplets thoroughly.

In this manner stereotemplets of each of the 30 stereomodels covering the test area were tied together. The position of the photo control 

points was then transferred to a separate sheet called a point-control 

base map.

Because ground control was not available when the area was studied, 

the vertical and horizontal scale of the map is based upon an assumed 

height of the aerial camera. Therefore, the stated horizontal scale, 

although constant throughout the map, is only approximate. Comparison with field data indicates that the units of measurement of 

thickness are approximately equivalent to feet. In the following discussion the measured thicknesses are described in terms of feet.

KELSH-PLOTTEB NOTATION OF GEOLOGIC DATA

The scale of the aerial photographs is about 1:20,000; using the 

X 5 enlargement capability of the Kelsh plotter the stereoscopic-model 

scale is approximately 1:4,000. Each stereoscopic model was reoriented in the Kelsh plotter and scaled to the photo control points on the 

base map. The image of the Moenkopi-Shinarump contact was traced 

on each model by means of the tracing table and "floating" dot. Simultaneously with tracing, the orthographic position of the MoenkopiShinarump contact was plotted on the point-control base at a scale 

of about 1:10,000 by means of the pantograph. Streams and roads, 

additional information to aid orientation in the field, were traced and 

plotted in the same manner.

Next, altitude readings were made all along the part of the Moenkopi-Shinarump contact shown on the stereoscopic model. The location and the value of each reading was noted on the base map. The 

horizontal ground distance along the outcrop between each reading 

was about 500 feet; however, in areas where the contact was not clear 

in the stereoscopic model, as in areas covered by talus, the horizontal 

distance between readings was as much as 1,000 feet.

In the same manner readings were made and noted along the 

basal contact of the Hoskinnini member (fig. 19). Locally, one or two 

light-toned resistant beds appear to lie above the massive sandstone of 

the De Chelly; commonly dark slope-forming beds lie between the 

resistant beds and the massive sandstone of the De Chelly. In these 

areas it is difficult to discern which horizon is the basal contact of the 

Hoskinnini or, specifically, which horizon is nearest the reference 

datum, located in adjacent areas where the base of the Hoskinnini is 

distinct. In several areas, readings made with the Kelsh plotter 

suggest that the upper contact of the massive sandstone of the De 

Chelly may be stratigraphically below the reference datum picked in

551404 60 3
70 PROCEDURES AND STUDIES IN PHOTOGEOLOGY

adjacent areas. If this is true, it could be due to some slight relief 

at the De Chelly-Hoskinnini unconformity which is expressed so 

gradually along the outcrop that it is difficult to detect in the field 

without detailed study.

In these local areas, readings were taken both at the top of the 

massive sandstone and at one or both light-toned resistant beds. 

These readings were noted separately on the manuscript map and distinguished by assigning code letters (A and B) to each of the alternate horizons (fig. 23).

COMPUTATION OF STRATIGRAPHIC THICKNESS

Altitude readings made with the Kelsh plotter at the base of the 

Hoskinnini vary from place to place because the contact is not horizontal. They may also vary a few feet owing to slight relief on the 

unconformity at the base of the Hoskinnini and human error in 

making and recording the altitude readings.

In order to minimize the effect of local relief and human error in 

establishing the position of the reference datum, the following procedure was used: First, the manuscript map was divided into areas 

small enough to be used to visualize local changes in strike and dip 

throughout (fig. 23). Second, the strike of the reference datum, the 

De Chelly-Hoskinnini contact, within each local area was established 

by drawing straight lines between all equal altitude readings at the 

base of the Hoskinnini (see dashed lines in fig. 23). Third, anomalous strike lines were assumed to be based upon inaccurate altitude 

readings, and such strike lines (X-X', fig. 23) were not used in correcting thickness computations. Likewise, isolated altitude readings 

(I7, fig. 23) that were not in accord with adjacent readings or nearby 

strike lines were not used in correcting thickness computations.

In each area, the strike lines were used to interpolate the relative 

altitude of the reference datum directly beneath each altitude reading at the base of the Shinarump member. For example, in figure 23 

the number in smaller print at Z is an altitude reading at the base 

of the Shinarump. The altitude of the datum directly beneath the 

reading at Z is interpolated to be 497 feet.

The thickness is computed as the difference between the altitude 

reading at the base of the Shinarump and the altitude of the reference datum beneath. Thus, as shown on figure 23, the approximate 

thickness of the undifferentiated Moenkopi formation at Z is 42 feet. 

Correction for dip is unnecessary because it is less than 3°.

After all the thicknesses had been computed in this manner for 

each local area, isopachs were added at 10-foot intervals. The isopachs are solid where their direction or trend is reasonably certain; 

in areas where more than one interpretation is feasible they are dashed.
611

587-11^^ *^wsr>

eiatf600 

.563

492.; 512^^dlllill...........

SB! 

467^||^toll|^ 1 '^ iV.ig :'f - - >: ;-'-->?>' y' :^^ jin jl 494

1000 1000 2000 FEET

APPROXIMATE SCALE

EXPLANATION

Shinarump member of the Chinle formation

539 ^_ _^

 ' -^

Relative altitude,in feet, of basal contact of the Shinarump 

member, determined with the Kelsh plotter

497

Relative altitude,in feet, of basal contact of the Hoskinnini member, determined 

with the Kelsh plotter( A and B refer to two resistant beds distinguishable locally 

in stereoscopic model at or near base of the Hoskinnini member)

Line of strike of the reference datum, based on the altitude reading at the base of the Hoskinnini member

FIGURE 23. Preliminary Isopach manuscript map of the undifferentiated Moenkopi In 

part of the Monument No. 2 area, plotted with the Kelsh plotter. X-X' is an 

example of an anomalous strike line; Y is an example of an isolated altitude reading 

not used in correcting thickness computations; and Z is an example of a point at 

which the thickness of the undifferentiated Moenkopi, 42 feet, was computed from 

altitude readings (531 497 ft).
72 PROCEDURES AND STUDIES IN PHOTOGEOLOGY

Unreliable thickness measurements are noted on the manuscript map 

followed by a question mark, and the isopachs that are positioned 

according to questionable readings are either both dashed and 

questioned or omitted.

Because the Shinarump member commonly crops out as a vertical 

cliff in the Monument Valley area it was necessary in some places to 

question the reliability of both the altitude readings made with the 

Kelsh plotter at the basal contact of the Shinarump and the thickness 

determinations based on these readings. Where the cliff exposure 

faces away from the center of either of the photographs making up 

the stereoscopic model, the base of the Shinarump cannot be seen 

clearly, owing to the perspective of vertical aerial photographs. Also, 

in some areas the cliff of the Shinarump casts a shadow which obscures the base of the Shinarump in the stereoscopic model. However, such conditions rarely exist for more than a few hundred feet 

along the outcrop of the Shinarump; therefore, reliable altitude readings and thickness determinations usually were obtained either 

in areas nearby, where the basal contact of the Shinarump can be 

seen clearly, or on adjacent stereoscopic models that offered a more 

favorable perspective of the same area. Where the cliff of the Shinarump is low, less than 30 feet, the vertical position of the contact can 

be determined with reasonable reliability by projecting the Moenkopi 

slope to intersect with the cliff of the Shinarump and making an 

altitude reading at that intersection.

Thickness determinations also were questioned in areas where reliable strike and dip readings on the reference datum could not be 

obtained sufficiently near the Kelsh altitude readings at the base of 

the Shinarump. This situation exists along the north side of Cane 

Valley where the Shinarump crops out as a series of dissected dip 

slopes and the base of the Hoskinnini member appears only northwest of the Shinarump outcrop (pi. 3.4, figs. 24 and 27). In order to 

obtain thickness determinations in this area it was necessary to project 

the reference datum as much as 2,000 feet, the distance depending 

upon the location of altitude readings at the base of the Shinarump 

relative to the nearest exposure of the De Chelly-Hoskinnini contact. 

Reliability of thickness determinations in this area depends upon the 

accuracy of the dip used to project the reference datum.

A similar situation exists in the broad area of Shinarump outcrop 

south-southwest of Hunts Mesa (fig. 26). In the northern and northwestern parts of this area, the strike is believed to change over a short 

distance along the outcrop of the undifferentiated Moenkopi formation. Strike and dip could not be determined by the three-point 

method from aerial photographs of this area because the base of the 

Hoskinnini either is locally obscured by talus or else crops out in a 

linear pattern unbroken by stream reentrants.
LOCATING CHANNELS BY PHOTOGEOLOGIC MAPPING 73

In areas Q (fig. 25) and P (fig. 27) the capping bed was identified 

in the field as Shinarump. However, stereoscopic inspection and 

thickness determinations in these areas suggest that this bed may be 

within the undifferentiated Moenkopi formation. In order to call 

attention to this possibility the capping bed in areas P and Q, previously mapped in the field as Shinarump, is here mapped as Shinarump ( ?) and the isopachs are omitted.

APPRAISAL OF PHOTOGEOLOGIC ISOPACH MAPS OF 

AREAS IN THE MONUMENT VALLEY AREA, ARIZONA

By IRVING J. WITKIND and ROBERT H. MORRIS

In the test area (fig. 20) the photogeologic data were taken from 

five specific localities in which the Shinarump member is most extensively exposed. These areas are the Monument No. 2 area (pi. 3), 

east Cane Valley area (fig. 24), Hunts Mesa area (fig. 12), unnamed 

mesa southwest of Hunts Mesa (fig. 2§), and west Cane Valley area 

(fig. 27). This appraisal is confined entirely to the isopach maps of 

these localities.

Such factors as the type of photogrammetric instruments used and 

the quality of the aerial photography available have not been considered in this appraisal. Consideration was given only to the study 

of the geologic features shown on the photogeologic isopach map and to 

the comparison of these features with similar features shown on maps 

prepared from field work.

For comparison each of the five localities is described separately 

according to (a) geologic setting as determined in the field, (b) known 

channels and swales, and (c) photogeologic results.

MONUMENT NO. 2 AREA

The Monument No. 2 area, near the east margin of the test area 

(fig. 20), consists of a series of isolated buttes, mesas, and hogbacks 

formed by the dissection of a monoclinal ridge. The strata that form 

the ridge range from the De Chelly sandstone member at the base to 

the Shinarump member at the top. These strata strike approximately 

northward and dip 3° to 5° E. In this general area the maximum 

thickness of the undifferentiated Moenkopi formation is about 80 

feet (pi. 3^).

Relation between swale and channels. Two channels are exposed 

in the Monument No. 2 area (pi. 35). The largest and most prominent is the Monument No. 2 channel, which trends about N. 18° W., 

is about 1% miles long, about 700 feet wide at its center, and is about 

50 feet deep. About half a mile northeast of the Monument No. 2 

channel is a second smaller channel, known as the Cuesta channel. 

The Cuesta channel trends about N. 25° W., is about three-fourths of 

a mile long, about 300 feet wide, and is about 20 feet deep.
74 PROCEDURES AND STUDIES IN PHOTOGEOLOGY

The swale in the Monument No. 2 area, as determined by field measurements, is shown in plate 3B. The trend of the swale is parallel to 

that of the two channels; the Monument No. 2 channel is along the 

axis of the swale and the Cuesta channel is along the east flank of the 

swale. The swale is estimated to be about 3 miles wide, has about 50 

feet of relief, and can be traced for 3 to 4 miles.

Photogeologic results. The photogeologic isopach map of the 

Monument No. 2 area (pi. 3A) shows a trough, interpreted as a swale, 

whose location and trend of axis is nearly identical with that found 

on the map compiled by field methods (pi. 3B). Both axes can be 

traced for about the same distance (3^ to 4 miles) and the isopach 

maps by both methods show about the same thicknesses in each area. 

The relief at the top of the isopach interval is virtually the same on 

both maps. Although the area covered by the photogeologic map is 

smaller and the swale appears narrower than that shown on the field 

map, the width of the swale indicated on each map is probably similar.

To the geologist familiar with the Monument No. 2 area, several 

minor errors are apparent on the photogeologic isopach map. The 

most striking of these is the failure of the map to indicate places where 

the strata of the undifferentiated Moenkopi formation have been removed by pre-Shinarump erosion. For example, along most of South 

Ridge and the Monument No. 2 cuesta, the channel fill rests disconformably on the De Chelly sandstone member. This is clearly shown 

in the field where the channel crops out along the valley walls formed 

by the Monument No. 2 cuesta and the north side of South Ridge 

(pi. 35). On South Ridge, the debris from the construction of an 

access road has fallen across and partly obscured the contact (pi. 5B). 

The points along the cuesta rims where the undifferentiated Moenkopi 

formation is absent are shown as circled zeros (pi. SB). In contrast, 

the photogeologic isopach map of the swale (pi. 3A) indicates that 

the corresponding interval on Monument No. 2 cuesta is less than 15 

feet, and on South Ridge as much as 18 feet.

Except for minor errors, the swale is correctly depicted on the 

photogeologic isopach map (pi. 3A). If the only exploration aid 

available was this map of the swale, the location of the channel and its 

trend could be predicted accurately. A series of drill holes along the 

swale axis, as shown in plate 3J., could penetrate the Monument No. 2 

channel fill.

The closely spaced readings on the photogeologic map (pi. 3A) 

provide much data which can be used to position the isopachs. About 

16 man-hours was expended in gathering these readings. In contrast, 

about 80 man-hours was expended in gathering the data needed for 

the construction of the field map of the swale (pi.
LOCATING CHANNELS BY PHOTOGEOLOGIC MAPPING 75

EAST CANE VALLEY AREA

The east Cane Valley area is a part of Cane Valley near the east 

edge of the test area (fig. 20). In the east Cane Valley area (fig. 24) 

the exposed rocks form part of the east limb of an anticline. The 

strata strike northeastward and dip southeastward. Dips range from 

about 6° SE. near the north and west edges of the area to about 22° 

SE. near the east edge. Dissection has been severe and many small 

irregularly shaped buttes, mesas, and cuestas have been formed. Exposures are moderate to good in the center of the east Cane Valley 

area, but are poor along the east edge. The undifferentiated Moenkopi 

formation, as determined in the field, is about 80 feet thick.

Channels. It is unknown whether any channels are present in the 

east Cane Valley area. No channel exposures were observed during 

the field examination.

2000 2000 4000 FEET 

I_______I

APPROXIMATE SCALE

EXPLANATION

Shinarump member 

of the Chinle formation

Basal contact of the 

Shinarump member

Photogrammetrically measured 

thickness, in feet, of the 

combined Hoskinnini and 

upper part of the Moenkopi 

formation

Strike and dip of beds

Isopach lines

Dashed where trend is uncertain; 

queried where both trend and 

thickness determinations are 

uncertain. Isopach interval is 

10 ft

FIOOEB 24. Isopach map of the east Cane Valley area, compiled by photogeologic methods.
76 PROCEDURES AND STUDIES IN PHOTOGEOLOGY

Photogeologic results. Many of the data on the photogeologic 

isopach map of the east Cane Valley area (fig. 24) are uncertain and, 

therefore, are followed by a question mark, indicating the difficulty of 

projecting the base of the Hoskinnini (p. 72). The isopachs indicate 

a northwestward thinning of the undifferentiated Moenkopi formation. Although there is a slight indication that the interval thickens 

again still farther to the west, more data cannot be gathered because 

erosion has removed most of the Shinarump, the upper part of the 

Moenkopi, and the Hoskinnini from this area. Therefore, the feature 

shown by isopachs on the map cannot be recognized as a swale (fig. 

24).

HUNTS MESA AREA

The Hunts Mesa area includes a large area near the center of the 

test area (fig. 20). Hunts Mesa (fig. 25), which is difficult to reach 

and is distant from all sources of supply, is typical of the many 

isolated mesas common in the Monument Valley area.

2000 

1_L

2000 

I

4000 FEET 

__I

APPROXIMATE SCALE

Shinarump member 

of the Chinle formation

Basal contact of the 

Shinarump member

61 s

Photogrammetrically measured 

thickness, in feet, of the 

combined Hoskinnini and 

upper part of the Moenkopi 

formation

Strike and dip of beds

.6°

Isopach lines

Dashed where trend is uncertain; 

queried where both trend and 

thickness determinations are 

uncertain. Isopach interval is 

10 ft

FIGURE 25. Isopach (above) and geologic (facing page) maps of parts of the Hunts Mesa 

area, including area Q. The isopach map was compiled by photogeologic methods. 

The geologic map, compiled by field methods, shows the location and estimated trend of 

the known channels.
LOCATING CHANNELS BY PHOTOGEOLOGIC MAPPING 77

Hunts Mesa is at the junction of several minor structural features 

in the Monument Valley area. As a result the strata along the east 

edge of the mesa dip about 2° NW., along the southwest edge they dip 

about 3° S., and on the north edge they are either nearly horizontal or 

dip slightly northward.

Exposures in the Hunts Mesa area are good, although locally rockslides conceal the base of the Shinarump.

The undifferentiated Moenkopi formation, as determined in the 

field, is about 70 feet thick near the center of the Hunts Mesa area.

Channels. Two channels are exposed on Hunts Mesa. The larger 

one, known as the Hunts Mesa No. 1 channel, crops out near the middle

110°04' 110°03' 110°02'

36°54'

EXPLANATION

Hoskinnini member of the 

Moenkopi formation

De Chelly sandstone member 

of the Cutler formation

Contact 

Dashed where approximately located

Centerline of strike of known channel

Dashed where concealed or inferred; dotted

where removed

Strike and dip of beds

FIGURE 25. Continued
78 PROCEDURES AND STUDIES IN PHOTOGEOLOGY

of the mesa. It is believed to trend eastward, is about 300 feet wide, 

and is about 50 feet deep, its length is unknown. A second smaller 

channel, known as Hunts Mesa No. 2, is about half a mile west of the 

larger channel and is exposed on the north edge of the mesa. It trends 

about N. 85° E., is about 50 feet wide, and is about 20 feet deep; its 

length is unknown. No other channels are known in the Hunts Mesa 

area.

The Hunts Mesa No. 1 channel is so poorly exposed that when the 

channel was first found it was believed to.trend northward. Later, 

during a short geophysical program on Hunts Mesa, the trend of 

the channel was believed to be southeastward (L. C. Pakiser, 1953, 

written communication). More recent examination of the limited 

channel exposures indicates that the true trend is eastward.

Photogeologic results. The photogeologic isopach map of Hunts 

Mesa shows a narrow elongate trough which trends northeastward 

(fig. 25). This trough is interpreted as a swale that is collinear with 

Hunts Mesa No. 1 channel. The swale curves broadly. At its west 

edge it trends about N. 46° E., near its east edge it curves slightly 

to trend about N. 70° E. The swale can be traced for about 2 miles, 

is about % of a mile wide, and has about 30 feet of relief. It extends 

beyond the known limits of the channel.

As shown on the isopach map (fig. 25), the deepest part of the 

swale parallels the known exposures of Hunts Mesa No. 1 channel. 

The shape of the swale suggests that the channel trends northeastward rather than eastward and that the channel is relatively short. 

No reflection of Hunts Mesa No. 2 channel is apparent on the swale 

shown on the isopach map (fig. 25).

In general the photogeologic isopach map delineates a swale that 

can be used to locate accurately the larger channel on the mesa, and 

to determine the trend of the channel. This map can be used to 

delineate the areas of major interest prior to a geologic examination 

of Hunts Mesa.

UNNAMED MESA SOUTHWEST OF HUNTS MESA

About 1 mile southwest of Hunts Mesa is a large irregularly shaped 

unnamed mesa capped by the Shinarump (figs. 20, 26). The strata 

form part of the east limb of an anticline, but locally they have been 

folded into a shallow syncline whose axis trends northeastward. 

South of this mesa the strata resume the regional northeastward 

strike, and they dip about 5° SE.

Channels. A small segment of channel fill is exposed at the south 

tip of this unnamed mesa. This channel, known as the Mike Brodie 

channel, trends about N. 85° E. It is estimated to have been about 

150 feet wide and to have been about 20 feet deep. No other channels 

are known on the mesa.
LOCATING CHANNELS BY PHOTOGEOLOGIC MAPPING 79

EXPLANATION

Shinarump member of the Chinle formation

Basal contact of the Shinarump member

Photogrammetrically measured thickness, in feet, of the 

combined Hoskinnini and upper part of the Moenkopi 

formation

Strike and dip of beds

Isopach lines

Dashed where trend is uncertain; queried where both trend and thickness 

determinations are uncertain. Isopach interval is 10 ft

APPROXIMATE SCALE

FIGURE 26. Isopach map of unnamed mesa southwest of Hunts Mesa, compiled by

photogeologic methods.

Photogeologic results. Two narrow, elongate northeastwardtrending troughs are shown on the photogeologic isopach map of 

this unnamed mesa (fig. 26), although the data are so distributed 

that isopachs can be drawn in more than one direction. Both troughs 

are interpreted as swales. The northern one trends about N. 40° E., 

can be traced for about iy2 miles, is about 14 mile wide, and has 

about 20 feet of relief. Its trend is nearly parallel to that of the 

Hunts Mesa swale, of which it may be a southward extension. The 

southern swale trends about N. 60° E., can be traced for about iy2 

miles, is about ^ mile wide, and has about 20 feet of relief. No 

channels are known within the area of either swale. The Mike Brodie 

channel is south of the southern swale, and no suggestion of its 

presence is given on the photogeologic isopach map.
80 PROCEDURES AND STUDIES IN PHOTOGEOLOGY 

WEST CANE VALLEY AREA

The west Cane Valley area is a part of Cane Valley near the west 

edge of the test area (figs. 20 and 27). Exposed consolidated strata 

form the south edge of the nose of a southwestward-plunging anti2000 0 2000

APPROXIMATE SCALE

EXPLANATION

4000 FEET 

_J

X.

Shinarump member 

of the Chinle formation

Basal contact of the 

Shinarump member

Photogrammetrically measured 

thickness, in feet, of the 

combined Hoskimrmi and 

upper part of the Moenkopi 

formation

Strike and dip of beds

Isopach lines

Dashed where trend is uncertain; 

queried where both trend and 

thickness determinations are 

uncertain. Isopach interval is 

10 ft

FIGURE 27. Isopach map of the west Cane Valley area, including area P, compiled by

photogeologlc methods.
LOCATING CHANNELS BY PHOTOGEOLOGIC MAPPING 81

cline. The beds strike eastward and dip 3° to 6° S. The area is 

drained by a few small streams which have dissected the strata into 

several cuestas, a small mesa, and two buttes. Although exposures are 

moderate to good, the width of the outcrop of the undifferentiated 

Moenkopi formation is as much as 1 mile locally. The thickness of 

the unit in this general area, as determined in the field, is about 105 

feet.

Channels. The west boundary of the test area selected (fig. 18) 

was chosen because it includes a series of channels which crops out 

along the valley walls in the western part of the west 'Cane Valley 

area (fig. 27). Regrettably the photogeologic work does not cover 

the area far enough to the west, for the westernmost readings are 

those made at the east edge of the area that contains the known 

channels. Consequently, the channel complex is beyond the limit of 

the isopachs. No channels are known in the area covered by the map 

(fig. 27).

Photogeologic results. The photogeologic isopach map of the west 

Cane Valley area (fig. 27) shows a trough that trends about N. 28° 

W., can be traced for about % mile, is about l1/^ miles wide, and has 

about 30 feet of relief. It is interpreted as a swale; however, most 

of the data used are questionable. Furthermore, the data are so 

sparse that the isopachs can be drawn in more than one direction.

Although exposures in this area are moderate to good, the relatively 

large width of the outcrop of the undifferentiated Moenkopi formation made it necessary to project the De Chelly-Hoskinnini contact 

for as much as 2,000 feet horizontally in order to obtain thickness 

readings in some places. This greatly reduces the reliability of the 

thickness data and the isopach map.

GENERAL APPRAISAL

The principal purpose of the photogeologic study was to determine 

whether swales could be detected on isopach maps prepared by the 

use of photogeologic methods. Comparison of field and photogeologic 

isopach maps of the test area indicates that most swales detected by 

using field methods can be detected with equal accuracy and with 

greater speed by using photogeologic methods. The principal requirements for obtaining photogeologic results comparable with field 

results are good photographs of a suitable scale, stratigraphic units 

which are discernible on the photographs, accurate plotting instruments, and an operator skilled in the use of the instruments and in 

making reasonable geologic interpretations from the data.

It is apparent that photogeologic methods offer both advantages 

and disadvantages. The advantages are: (a) accurate representation, 

(b) ease and speed of thickness determination, (c) freedom from 

weather and logistics problems, and (d) use of photogeologic data
82 PROCEDURES AND STUDIES IN PHOTOGEOLOGY

as a guide for subsequent field work. The disadvantages are: (a) 

necessity for many favorably distributed outcrops, and (b) difficulty 

of identification where contacts are partly or wholly concealed.

ADVANTAGES

Accurate representation. In the Monument No. 2 area the delineation of the swale is very similar on both the photogeologic and field 

isopach maps (p. 74 and pi. 3). This suggests that any swale depicted 

elsewhere in the region on a photogeologic isopach map will be a very 

close reflection of the swale determined in the field. Since the completion of this study, this conclusion has been confirmed elsewhere 

in the Monument Valley area.

Ease and speed of thickness determination. The thickness of a selected interval can be measured in a much shorter time by using photogeologic methods and instruments rather than field methods. It is 

estimated that the study of any given area can be completed five 

times faster by using photogeologic rather than field methods. Because the photogeologic readings are relatively much easier to obtain 

than are the field readings, many more can be taken and, therefore, a 

more detailed map can be constructed.

Freedom from weather and logistics problems. Much of the Monument Valley area is difficult to reach; roads are poor and easily blocked 

both by sudden sandstorms and thunderstorms. Potable water is 

scarce, supplies are expensive, and sources of supply are few and 

widely separated. All these factors make fieldwork in the area difficult, expensive, and time consuming. All these difficulties and inconveniences are circumvented by the use of photogeologic methods.

Use of geologic data as a guide for subsequent fieldwork. A photogeologic isopach map indicating the swales in an area can expedite 

the geologic fieldwork by directly indicating exposures which can be 

studied. If the exposures are favorable, exploration work can be 

planned along the trend of the swale, as shown on the photogeologic 

isopach map.

DISADVANTAGES

Necessity for many favorably distributed outcrops. Good exposures are essential if an adequate photogeologic map is to be prepared. If the exposures are poor, not identifiable, or concealed on the 

vertical aerial photographs, the resulting isopach maps prepared by 

photogeologic methods will be of much poorer quality than those 

prepared from field observations.

In the test area (fig. 20) the undifferentiated Moenkopi formation 

was measured by photogeologic methods wherever exposures permitted. In a few localities exposures are excellent and the amount of 

data gathered was adequate to permit the preparation of detailed 

isopach maps. Examples of such localities are the Monument No. 2 

area, Hunts Mesa, and the unnamed mesa southwest of Hunts Mesa
LOCATING CHANNELS BY PHOTO-GEOLOGIC MAPPING 83

(pi. 3; figs. 26, 25). Elsewhere, poor exposures, few outcrops, or a 

combination of these factors have resulted in the gathering of a small 

amount of questionable data from which only isopach maps of much 

reduced accuracy can be constructed. For example, in the east Cane 

Valley area (fig. 24) the isopachs indicate what may be the east edge 

of a swale; and in the west Cane Valley area (fig. 25) the isopachs 

suggest a swale, which is about iy2 miles wide and has about 30 feet of 

relief. However, the lines indicating these troughs are of questionable 

value because of the small amount of data from which they were constructed. The scarcity of readings reflects the poor exposures in these 

well-dissected areas. Elsewhere, significant errors resulted from the 

necessity of projecting a concealed datum over long distances in order 

to obtain thickness readings required for photogeologic mapping 

(p. 72).

Difficulty of identification where contacts are partly or wholly concealed. Minor errors on the isopach map may result from contacts 

which are partly or wholly concealed on the aerial photographs and 

which cannot, therefore, be studied adequately. For example, in 

many places the contact of the Shinarump with the underlying Moenkopi, as shown on the photographs (pi. 5Z?), is concealed by debris. 

On some of the aerial photographs the contact is concealed by the dark 

shadow cast by the cliff of the Shinarump. Usually the basal contact 

of the unit to be measured is easily discerned, but near the Monument 

No. 2 mine, debris from access roads conceals the De Chelly-Hoskinnini 

contact.

CONCLUSION

In conclusion, it appears that the use of photogeologic methods can 

be very useful in the search for swales and channels. These methods 

can be used to delineate areas that warrant further exploration in the 

field, thereby reducing the amount of geophysical and geologic exploration to be done in an area. Considerable saving of money, time, 

and manpower seem assured.

LITERATURE CITED

Bain, G. W., 1952, Uranium deposits in southwestern Colorado Plateau: U.S. 

Atomic Energy Comm. RMO-982, 59 p., issued by U.S. Atomic Energy Comm. 

Tech. Inf. Service, Oak Ridge, Tenn.

Scher, M. B., 1955, Stereotemplet triangulation: Photogramm. Eng., v. 21, no. 

5, p. 655-664.

Witkind, I. J., 1956a, Uranium deposits at base of the Shinarump conglomerate, 

Monument Valley, Arizona: U.S. Geol. Survey Bull. 1030-C, p. 99-130.

 1956b, Channels and related swales at the base of the Shinarump conglomerate, Monument Valley, Arizona, in Page, L. R., Stocking, H. E., and 

Smith, H. B. (compilers), Contributions to the geology of uranium and 

thorium by the United States Geological Survey and Atomic Energy Commission for the United Nations International Conference on Peaceful Uses 

of Atomic Energy, Geneva, Switzerland, 1955: U.S. Geol. Survey Prof. 

Paper 300, p. 233-237.

INDEX

Page

Acknowledgments 58 

Aerial photographs, scale 69 

Agathla anticline._______ ... _ 60 

Anticlines 60,75,78,80-81

Base-map compilation_.._ _ . 67-69 

Bibliography___.._........... ... 83

Cane Valley area, east, channels. _ 75

east, geologic setting.. 75

photogeologic results.. . . 76

west, channels.. . 81

geologic setting- .- . . 80

photogeologic results.. . . 81

Channels, description....__ _ _ 62

distribution...... _.................. 63

relation to swales__________ 62-63,73-74 

Conclusion____... __ ... . 83 

Cuesta channel_____--__ _ _ 73,74 

Cutler formation_._ . ... 60

De Chelly sandstone member, Cutler formation, age-. . . 60 

Chinle formation, lithologic character__ 60 

De Chelly-Hoskinnini contact 65,70,72,81,83

Geography...... .. .. . 60

Geology....___........__..____.... 60-62

Hoskinnini member, Moenkopi formation,

age________________ 60

Hunts Mesa area, channels_______ 77-78, pi. 4 

geologic setting.... .. _ _.... 76 

photogeologic results.... __... 78

Hunts Mesa swale_______._______ 79

Introduction._________________ 57-58 

Investigation, purpose. . 58,81

Page

Kelsh plotter, altitude readings________ 69-73 

description___._..._...___ 65-67, pi. 4 

notation, geologic data _________ 69-70

Mesa, unnamed, channels__________ 78

unnamed, geologic setting________ 78

photogeologic results......... ._. 79

Mike Brodie channel_____________ 78,79

Moenkopi formation, channels________ 62

thickness..... .. __.___ 70

undiflerentiated........ 60,65,70,73,75,76,77,81

Moenkopi-Shinarump contact .. __. 62,69 

Monument No. 2 area, geologic setting....... 73

photogeologtc results...._________ 74

relation between swale and channels_... 73-74 

Monument No. 2 channel, description_ 62,73, pi. 5 

Monument No. 2 cuesta.. _ __....... 74

Monument No. 2 mine____________.. 62,83 

Monument upwarp ... __..__.__. 60

Photo control points..._____________ 67,68

Photogeologic methods, advantages_ ..... 81-82

disadvantages______________- 82-83

instruments used_____________ 63

Shinarump member, Chinle formation, age_ 60

Chinle formation, altitude readings___ 72

exposures_-__________...- 63

lithologic character-_..._ ..-.. 62

uranium-vanadium deposits. .. 67-58,62

South Ridge....-.-...-...-.----.-.-.-.-.-. 74,pi. 5

Stereotemplet layout.-.. ... .. . 67-69 

Stratigraphic section..... ......_ .-... 61

Swales, definition_______________ 62 

description.......-.. .. 74,78,79,81

relation to channels_______ 62-63,73-74,78

Thickness, compilation.._____.____ 70-73 

Three-point method___...._____-.... 72

Unconformity-___._...__...__ 60,62,65,70 

Uranium-vanadium deposits.. ______ 57-58,62

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85