2007

U.S. Department of the Interior

U.S. Geological Survey

Prepared in cooperation with the National Park Service, the Navajo Nation, and the Hopi Tribe

Geologic Map of the Cameron 30’ x 60’ Quadrangle,

Coconino County, Northern Arizona

By George H. Billingsley, Susan S. Priest, and Tracey J. Felger

Pamphlet to accompany

Scientific Investigations Map 2977

Adeii Eechii Cliffs showing Jurassic and Triassic strata. Photograph by George H. Billingsley.

1

Introduction

This geologic map is the result of a cooperative effort of 

the U.S. Geological Survey and the National Park Service in 

collaboration with the Navajo Nation and the Hopi Tribe to 

provide regional geologic information for resource management officials of the National Park Service, U.S. Forest Service, 

Navajo Indian Reservation (herein the Navajo Nation), the Hopi 

Tribe, and for visitor information services at Grand Canyon 

National Park, Arizona as well as private enterprises that have 

lands within the area. Funding for the map was initiated by 

the Grand Canyon Science Center, Grand Canyon National 

Park and provided by the Water Rights Branch of the Water 

Resources Division of the National Park Service, Ft. Collins, 

Colorado. Field work on the Navajo Nation was conducted 

under a permit from the Navajo Nation Minerals Department. 

Any persons wishing to conduct geologic investigations on 

the Navajo Nation must first apply for, and receive, a permit 

from the Navajo Nation Minerals Department, P.O. Box 1910, 

Window Rock, Arizona 86515, telephone # (928) 871–6587. 

Permission to publish a small portion of the Hopi Moenkopi 

District at the north-central edge of the map was granted by the 

Department of Natural Resources. Any person wishing to conduct geological investigations within this area, must submit for 

permission to the Department of Natural Resources, The Hopi 

Tribe, P.O. Box 123, Kykotsmovi, Arizona 86039, telephone # 

(928) 734–3601.

The Cameron 30’ x 60’ quadrangle encompasses approximately 5,018 km2 (1,960 mi2) within Coconino County, 

northern Arizona and is bounded by longitude 111° to 112° 

W., and latitude 35°30’ to 36° N. The map area is within the 

southern Colorado Plateaus geologic province (herein Colorado 

Plateau). The map area is locally subdivided into six physiographic areas: the Grand Canyon (including the Little Colorado 

River Gorge), Coconino Plateau, Marble Plateau, Little Colorado River Valley, Moenkopi Plateau, and the San Francisco 

Volcanic Field as defined by Billingsley and others, 1997 (fig. 

1). Elevations range from about 2,274 m (7,460 ft) at the south 

rim of Grand Canyon along State Highway 64 to about 994 m 

(3,260 ft) in the Grand Canyon, northeast quarter of the map 

area.

Settlements within the map area include Cameron and 

Gray Mountain, Arizona. The small community of Coal Mine 

Canyon, Arizona is about 1.5 km (1 mi) east of the northeast 

corner of the map (fig. 1). U.S. Highway 180 provides access to 

the southwest corner of the map area, U.S. Highway 89 to the 

central part, State Highway 64 to the northwest half, and State 

Highway 264 to the far northeast corner of the map area.

The roads and trails in the Kaibab and Coconino National 

Forests are maintained by the National Forest Service, and 

several dirt roads on the Babbitt Ranches provide limited access 

to remote areas within the central region of the map. Travel is 

restricted to paved roads in the Wupatki National Monument 

area. Four-wheel drive vehicles are recommended in the Navajo 

Nation area northeast of the Little Colorado River due to sandy 

conditions. Extra water and food is highly recommended for 

travel in this remote region.

Land ownership forms a checkerboard pattern in the central 

region of the map area between private and State land. Kaibab 

National Forest and Grand Canyon National Park manage lands 

in the northwest third of the map area, the Coconino National 

Forest manages land in the southwest portion, the National Park 

Service manages the Wupatki National Monument area, and the 

Navajo Nation and local Navajo Chapter governments manage 

lands of the Navajo Nation in the eastern part of the map, and 

the Hopi Tribe and Moenkopi Village governments manage the 

Hopi Moenkopi District in the north-central edge of the map 

(fig. 1).

The Cameron quadrangle is one of the few remaining 

areas near the Grand Canyon where uniform geologic mapping 

was needed for geologic connectivity of the regional geologic 

framework that will be useful to federal, state, and private land 

resource managers who direct environmental and land management programs such as range management, biological studies, 

flood control, and water resource investigations. The geologic 

information presented will support future and ongoing local 

geologic investigations and associated scientific studies of all 

disciplines within the Cameron quadrangle area.

Previous Studies

Wilson and others (1969) compiled an early reconnaissance photogeologic map (1:500,000-scale) of this area as 

part of a geologic map of Coconino County and the State of 

Arizona. The map was later recompiled at 1:1,000,000 scale by 

Richard and others (2000). Cooley and others (1969) produced 

an excellent photogeologic map of the Navajo Nation area but 

the map was not registered to a topographic database because 

a topographic base larger than 1:250,000 scale did not exist at 

the time. A geologic map of the Cameron 15’ quadrangle was 

mapped by Akers and others (1962); a geologic map of the 

Flagstaff 1° x 2° quadrangle (1:250,000 scale) was produced 

by Ulrich and others (1984); a geologic map of the Coconino 

Point and Grandview Point (15’) quadrangles was produced 

by Billingsley and others (1985); a geologic map of the S P 

Mountain part of the San Francisco Volcanic Field was produced by Ulrich and Bailey (1987); a geologic map of the 

southwestern Moenkopi Plateau and southern Ward Terrace was 

produced by Billingsley (1987a); a preliminary map of Wupatki 

National Monument was produced by McCormack (1989); and 

a small part of the Grand Canyon in the northwest corner of 

the map area was mapped by Huntoon and others (1996). The 

Quaternary geology of all previous maps has been modified 

and updated for this map to match consistency and detail of the 

adjoining Valle 30’ x 60’ quadrangle (Billingsley and others, 

2006). A geologic map of the Grand Canyon 30’ x 60’ quadrangle (Billingsley, 2000), adjoins the northwest corner of this map 

and a geologic map of the Valle 30’ x 60’ quadrangle (Billingsley and others, 2006) is adjacent to the west edge of the map.

Mapping Methods

This map was initially compiled at 1:24,000 scale from 

1958 and 1968 black and white aerial photographs; the initial 
2

Figure 1. Index map of the Cameron 30’ x 60’ quadrangle showing physiographic, cultural, and geologic 

locations mentioned in the text.

compilation was extensively field checked. Many of the Quaternary alluvial and eolian deposits, which have similar lithology 

and geomorphic characteristics, were mapped almost entirely by 

photogeologic methods. In most areas, the lithology, stratigraphic position, and the amount of erosional degradation were 

used to correlate relative age of alluvial deposits. Field studies 

insured accurate location and description of several map units 

and structures.

Susan S. Priest and Tracey Felger (U.S. Geological 

Survey), Flagstaff Science Center, compiled the map in digital 

format using Arc/Map techniques. Thirty-two detailed 1:24,000 

scale maps that were initially compiled to produce this map 

can be seen as view maps in the USGS web site address. This 

map is the 6th of a series of digital geologic maps of the Grand 

Canyon region.

Geologic Setting

The map area is characterized by nearly flat-lying to gently 

dipping Paleozoic, Mesozoic, and Cenozoic strata. Miocene, 

Pliocene, and Pleistocene volcanic rocks of the San Francisco 

Volcanic Field form a protective caprock over weak strata of 

Paleozoic, Mesozoic, and Cenozoic rocks in the southern part 

of the map area. The southeastern part of the Kaibab upwarp 

or anticline elevates the northwest part of the Kaibab National 

Forest. Within elevated highlands, the Grandview and East 

Kaibab Monoclines extend east and southeast to Gray Mountain, partially within the Navajo Nation. South and southwest 

of Gray Mountain, the Paleozoic and Mesozoic strata have a 

regional southwesterly dip averaging 2° toward the Dog Knobs 

area of the Coconino Plateau (fig. 1). The highlands in the 
3

northwestern part of the map are separated from the highlands 

in the southern part of the map by the northeast-trending Cedar 

Ranch and Mesa Butte Faults (fig. 1). These closely associated 

fault structures form a major subsurface divide of the Coconino 

Plateau between the Little Colorado River to the east and Cataract Canyon of the Grand Canyon west of the map area (Don 

Bills, oral comun., 2005).

The Mesozoic and Paleozoic strata under the volcanic 

rocks of the San Francisco Volcanic Field, the eastern part of the 

Coconino Plateau, Little Colorado River Valley, and the Moenkopi Plateau have an average regional dip of about 2° northeast. 

The Little Colorado River and its tributary systems eroded 

much of the Mesozoic strata from the highland areas of the 

Gray Mountain and Coconino Plateau areas before volcanism 

began. In the eastern half of the map area, the Little Colorado 

River is eroding a strike valley parallel to the northeast-dipping 

Mesozoic strata. The Little Colorado River meandered within 

this strike valley for much of Miocene to Holocene time and 

maintained a position mostly on the Triassic Chinle Formation. 

Along the northern edge of the map area, the Little Colorado 

River eroded into and became entrenched in the resistant 

Permian Kaibab Formation and incised a meandering canyon 

downstream of Cameron, Arizona. Here the valley is subsequent 

to and controlled by the highland areas of the Coconino Point 

and East Kaibab Monoclines.

The southern margin of the Marble Plateau is characterized 

by gently dipping Paleozoic and Mesozoic strata that generally dip less than 2° to the south and east. The Little Colorado 

River eroded deeply into Paleozoic strata exposing nearly 580 

m (1,900 ft) of Mississippian to Permian strata and is physiographically part of the Grand Canyon area, which begins about 

11 km (7 mi) west of Cameron, Arizona.

From east of Cameron, Arizona, to the southeast corner 

of the map area, the Little Colorado River Valley is characterized by gently northeast dipping Paleozoic and Mesozoic strata. 

These strata form the Ward Terrace and Red Rock Cliffs area 

below the Adeii Eechii Cliffs of the Moenkopi Plateau. The 

Adeii Eechii Cliffs form the southwest edge of the Moenkopi 

Plateau where Jurassic and Cretaceous strata are largely covered 

by extensive fluvial and eolian surficial sand deposits of Late 

Cenozoic age.

Paleozoic and Mesozoic Sedimentary Rocks

Paleozoic Rocks

Erosion of the Grand Canyon in the northwest corner of 

the map area has exposed about 994 m (3,260 ft) of Paleozoic 

rock strata. The Paleozoic rock strata in the subsurface of the 

Coconino and Marble Plateaus in the western two-thirds of the 

map area are, from oldest to youngest, the Muav Limestone 

(Middle Cambrian), the Temple Butte Formation (Upper and 

Middle Devonian), the Redwall Limestone (Upper and Lower 

Mississippian), the lower part of the Supai Group, undivided 

(Upper, Middle, and Lower Pennsylvanian and Upper Mississippian), the Esplanade Sandstone (Lower Permian) in the 

upper part of the Supai Group, the Hermit Formation, Coconino 

Sandstone, Toroweap Formation, and the Kaibab Formation (Lower Permian). These rocks of unknown thickness are 

likely in the subsurface of northeast third of the map area. The 

Redwall Limestone, Supai Group of rocks, Hermit Formation, 

Coconino Sandstone, Toroweap Formation, and the Kaibab Formation are exposed in the Grand Canyon and in the walls of the 

Little Colorado River Gorge. The Kaibab Formation forms the 

surface bedrock of most of the western two-thirds of the map 

area except for a few isolated exposures of the Moenkopi and 

Chinle Formations (Triassic) beneath volcanic rocks of the San 

Francisco Volcanic Field and in the Wupatki National Monument area.

Based on exposed rocks in Grand Canyon and in the 

Verde Valley 65 km (40 mi) south of the map area, the Muav 

Limestone gradually thins eastward and southeastward in the 

subsurface of the map area and may locally pinch out onto Precambrian basement rocks. The Temple Butte Formation unconformably overlies the Muav Limestone and is correlative to the 

Devonian Martin Limestone of the Verde Valley and gradually 

thins or pinches out east and south of the map area. The Redwall Limestone gradually thins eastward in the subsurface of the 

map area and unconformably overlies either the Temple Butte 

Formation or overlies the Muav Limestone where the Temple 

Butte is locally missing. The Redwall Limestone is 170 m (560 

ft) thick in the west part of the map and gradually thins eastward 

to about 122 m (400 ft) in the subsurface of the eastern part of 

the map area. The lower Supai Group, undivided, unconformably overlies the Redwall Limestone and thins eastward in the 

subsurface of the map area but probably maintains a general 

thickness of about 244 m (800 ft) in the subsurface of the map 

area. The Esplanade Sandstone of the upper Supai Group gradually thins eastward and southward in the subsurface of the map 

area averaging about 107 m (350 ft) thick or less. The Hermit 

Formation unconformably overlies the Esplanade Sandstone in 

the Little Colorado River Gorge and Grand Canyon area; north 

and east of the map area, channels have eroded into the Esplanade Sandstone as much as 9 m (30 ft) (Huntoon and others, 

1996; Billingsley, 2000). The Hermit Formation is about 25 m 

(80 ft) thick in Grand Canyon and thins eastward to less than 

about 6 m (20 ft) in the Little Colorado River Gorge and gradually pinches out under the Cameron area. The Hermit Formation may extend to the southern part of the map area because it 

is present in the Verde Valley 65 km (40 mi) south of the map 

area. In the Grand Canyon in the northwest quarter of the map 

area, a sharp planar erosional contact separates the Hermit Formation from the overlying Coconino Sandstone.

The Coconino Sandstone forms a shear buff-white cliff in 

the Grand Canyon and Little Colorado River Gorge area and 

maintains a relatively constant thickness of about 183 m (600 

ft) or less in the subsurface throughout most of the map area. 

Subsurface well logs suggest that the basal part of the Coconino 

Sandstone is a red sandstone that is likely the northern extent 

of the Schnebly Hill Formation of the Verde Valley as defined 

by Blakey (1990; Ronald C. Blakey, oral commun., 2005). The 

Coconino Sandstone (not the Schnebly Hill Formation) is basically a tongue of the Seligman Member of the Toroweap Formation in the western and northern part of Grand Canyon (Fisher, 

1961; Schleh, 1966; Rawson and Turner, 1974; and Billingsley 

and others, 2000; Billingsley and Wellmeyer, 2003) but the 
4

Coconino Sandstone is a well established term in Grand Canyon 

nomenclature and does form a distinct mappable unit throughout the Grand Canyon region. Therefore, the name Coconino 

Sandstone is herein maintained as a map unit and the lower 

red sandstone is the Schnebly Hill Formation that thickens 

southward in the subsurface of the map area to about 60 m (200 

ft) along the southwest edge of the map. The Coconino Sandstone gradually thins north, east, and west of the map area but 

thickens south of the map area, and the Schnebly Hill Formation 

gradually thickens south and southeast of the map area. Both 

the Schnebly Hill Formation and the Coconino Sandstone form 

an important ground water bearing unit in the map area locally 

known as the “C” aquifer.

The Toroweap Formation unconformably overlies the 

Coconino Sandstone and undergoes a substantial west to east 

facies change in the subsurface of the map area. In Grand 

Canyon, in the northwest corner of map area, the three recognized members of the Toroweap Formation, in ascending order, 

are the Seligman, Brady Canyon, and Woods Ranch Members 

but are too thin to show at map scale, thus the Toroweap Formation is mapped as one unit (Sorauf and Billingsley, 1991). These 

three members change from a thin lower sandstone, middle 

limestone ledge, and upper gypsiferous siltstone slope to a general cliff-forming calcareous sandstone facies of the Toroweap 

Formation in the Little Colorado River Gorge, Gray Mountain, 

and subsurface of the entire map area. The Toroweap Formation 

gradually thins from about 60 m (200 ft) in the Little Colorado 

River Gorge to less than about 9 m (30 ft) in the subsurface in 

the southeast corner of the map based on recent well log interpretations near Leupp, Arizona, about 32 km (20 mi) southeast 

of the map area (Don Bills, oral commun., 2005).

The Kaibab Formation forms the surface bedrock for much 

of the Coconino Plateau and the western two-thirds of the map 

area where not covered by volcanic rocks or surficial deposits. 

The Kaibab Formation is divided into, in ascending order, 

the Fossil Mountain Member (lower part) and the Harrisburg 

Member (upper part) as defined by Sorauf and Billingsley 

(1991). The Fossil Mountain Member is a gray, cliff-forming, 

cherty, sandy limestone about 70 m (230 ft) thick in the west 

half of the map area and forms narrow canyon drainages on 

the Coconino Plateau and the main cliff at the rim of Grand 

Canyon and Little Colorado River areas. A gradational and 

arbitrary boundary separates the ledge- and cliff-forming Fossil 

Mountain Member from the overlying slope- and ledge-forming 

Harrisburg Member of the Kaibab Formation. The Fossil 

Mountain Member contains brachiopod, sponge, and trilobite 

fossils preserved mostly in chert nodules and chert lenses, 

whereas the Harrisburg Member contains only a mollusk fossil 

fauna.

The Harrisburg Member of the Kaibab Formation forms a 

ledge-slope topography above the cliff-forming Fossil Mountain Member at the rim of Grand Canyon and the rim of the 

Little Colorado River Gorge where the sandy limestone beds 

are often weathered or stained dark gray or black by manganese 

oxide. The Fossil Mountain and Harrisburg Members undergo 

a west to east facies change from fossiliferous ledges of cherty 

limestone to cliff-forming, calcareous sandstone that is largely 

devoid of fossils and becomes increasingly difficult to distinguish one member from the other east of U.S. Highway 89 and 

are mapped collectively as the Kaibab Formation (Pk) in the 

southeast corner of the map area. Deposits of gray gypsum and 

light-red gypsiferous siltstone and sandstone of the Harrisburg 

Member have been subjected to modern erosion and dissolution weathering resulting in the development of several internal 

drainage basins and local sinkhole depressions on the Coconino 

Plateau southwest of Gray Mountain.

A regional unconformity with a general relief of less than 

3 m (10 ft) separates the Permian Kaibab Formation from the 

overlying Triassic Moenkopi Formation. The unconformity is 

easily recognized by a lithologic and color change from the 

grayish-white sandy limestone of the Kaibab Formation to the 

light-red and red, thin-bedded sandstone and siltstone beds of 

the Moenkopi Formation. The erosional depressions and channels in the upper Kaibab were subsequently filled with angular 

and subangular chert and sandstone conglomerate deposits 

derived from the Kaibab Formation that forms the basal part of 

the Moenkopi Formation. The Kaibab Formation isopachs demonstrate substantial thinning over the Gray Mountain area prior 

to deposition of the Moenkopi Formation (Barnes, 1989).

Mesozoic Rocks

In the northeast half of the map area, erosion by the Little 

Colorado River has exposed about 707 m (2,320 ft) of Mesozoic 

rock strata. The Mesozoic rock strata are in the Little Colorado 

River Valley and Moenkopi Plateau areas but undergo rapid 

facies and thickness changes beneath the Moenkopi Plateau. 

The Mesozoic rocks exposed are, in ascending order, the Moenkopi Formation, (Upper(?) and Lower Triassic), the Chinle 

Limestone (Upper Triassic), the Moenave Formation (Upper 

Triassic(?) and Lower Jurassic), the Kayenta Formation (Lower 

Jurassic), the Kayenta Formation-Navajo Sandstone transition 

zone (Lower Jurassic), the Navajo Sandstone (Lower Jurassic), the Entrada Sandstone-Cow Springs Sandstone, undivided 

(Middle Jurassic), the Dakota Sandstone (Upper Cretaceous), 

and the Mancos Shale (Upper Cretaceous).

Moenkopi Formation

Overlying the Permian Kaibab Formation is a sequence of 

red sandstone ledges and siltstone slopes of the Triassic Moenkopi Formation that is unconformably overlain by a light-brown 

cliff of sandstone and conglomerate of the Shinarump Member 

of the Chinle Formation. The Moenkopi Formation is partly 

preserved as isolated outcrops under Quaternary and Tertiary 

volcanic rocks in the western and southern margins of the map 

area and as extensive outcrops in the Marble Plateau and Little 

Colorado River Valley. Prior to Cenozoic erosion, the Moenkopi 

Formation covered the entire map area as much as 300 m (1,000 

ft) thick just west of the map area at Red Butte south of Grand 

Canyon Village (Billingsley and others, 2006). The Moenkopi 

gradually thins eastward to about 107 m (350 ft) near Cameron, 

Arizona (Repenning and others, 1969), and thins to less than 67 

m (220 ft) at Wupatki National Monument (McKee, 1954). An 

unknown amount of the upper Moenkopi Formation was eroded 

prior to deposition of the overlying Triassic Chinle Formation.
5

The Moenkopi Formation is not subdivided in the Dog 

Knobs area along the west edge of the map. Elsewhere, there 

are four members of the Moenkopi Formation as defined by 

McKee (1954) that are recognized and mapped in the Little 

Colorado River Valley. In ascending order they are the Wupatki 

Member, the lower massive sandstone member, and the undivided Holbrook and Moqui Members. The Moenkopi Formation in northwestern Arizona and southern Utah, as defined 

by Stewart and others (1972), was mapped by Billingsley and 

Workman (2000). McKee (1954) tentatively correlates all of 

the Moenkopi Formation in the Little Colorado River Valley 

to parts of the middle red member, Shnabkaib Member, and 

upper red member of the Moenkopi Formation of northwestern 

Arizona. The nomenclature used for the Moenkopi Formation 

by McKee (1954) is used for this map area with a proposed new 

correlation to the Moenkopi Formation in northwest Arizona 

based on regional mapping, tracing of stratigraphic units, and 

observation of facies changes over distance. It is proposed here 

that the Wupatki Member is approximately equivalent to the 

lower red and middle red members of the Moenkopi Formation 

of northwestern Arizona; the lower massive sandstone member 

is correlative to the Shnabkaib Member; and the Holbrook and 

Moqui Members are approximately correlative to an undetermined amount of the upper red member that may be Middle(?) 

Triassic age.

The Wupatki Member thins east and southeast from 27 m 

(90 ft) on the east flank of Gray Mountain and Little Colorado 

River Gorge west of Cameron, Arizona, to 23 m (75 ft) thick 

at Wupatki National Monument, and to less than 4.5 m (15 ft) 

thick in the southeast corner of the map area. South of Leupp, 

Arizona, about 32 km (20 mi) southeast of the map area, the 

Wupatki Member gradually pinches out and the lower massive 

sandstone member of the Moenkopi Formation unconformably 

overlies the Kaibab Formation. The lower massive sandstone 

member, according to McKee (1954), is stratagraphically above 

the Shnabkaib Member of the Moenkopi Formation of northwestern Arizona and southern Utah. Field mapping observations at the Vermilion Cliffs northwest of Marble Plateau and 

the Colorado River north show that the Shnabkaib Member 

undergoes a facies change south and east from a white siltstone, 

gypsiferous sandstone, and limestone to a yellowish-white 

crossbedded, ledge-forming, fine-to coarse-grained calcareous 

sandstone and thin limestone along the Echo Cliffs and Marble 

Plateau north of the Little Colorado River Gorge, then rapidly 

continues a facies change to a light red, fine-grained, cliffforming, crossbedded fluvial sandstone southeast of the Little 

Colorado River Gorge to the Wupatki National Monument area 

where McKee (1954) describes the unit as the lower massive 

sandstone member. Thus, the lower massive sandstone member 

and the Shnabkaib Member are one and the same at the same 

stratigraphic horizon and represent a northwest to southeast 

shoreward facies change.

The lower massive sandstone is 12 to 15 m (40 to 50 ft) 

thick at the Little Colorado River Gorge and thins to less than 3 

m (10 ft) in the vicinity of the town of Gray Mountain, Arizona, 

and gradually thickens southeast along the Little Colorado 

River Valley to as much as 26 m (53 ft) in the Wupatki National 

Monument area.

The Holbrook and Moqui Members of the Moenkopi 

Formation are defined by McKee (1954) and Hager (1922). 

The slope-forming Moqui Member is defined by McKee (1954) 

from exposures along Moqui Wash 13 km (8 mi) west of Winslow, Arizona, and is 26 m (85 ft) thick and is a lighter shade 

of reddish-brown than the underlying Wupatki or overlying 

Holbrook Member. The Moqui Member erodes into a uniform, mostly covered slope below the cliff-forming Holbrook 

Member. The sandstone beds of the Holbrook Member of the 

Moenkopi Formation were originally defined by Hager (1922) 

and form an irregular line of bluffs north of the Little Colorado 

River Valley between Holbrook, Arizona (about 64 km (40 mi) 

east of the map area) and Cameron, Arizona. The Holbrook 

and Moqui Members are mapped together as an undivided unit 

because both members are difficult to identify in some areas of 

the map. The Holbrook and Moqui Members are approximately 

correlative to the upper red member of the Moenkopi Formation in northwestern Arizona and southern Utah (McKee 1954; 

Repenning and others, 1969) and may, in part, be Middle(?) Triassic age. The Holbrook and Moqui Members are unconformably separated from the overlying Triassic Chinle Formation.

A regional uplift terminated the deposition of the Moenkopi Formation and caused a general withdrawal of the Triassic 

tidal flats and floodplains northwest into Utah, followed by a 

general northwest flowing drainage system toward the sea. The 

drainages that eroded into the Moenkopi Formation averaged 

about 10 m (30 ft) deep and locally as much as 46 m (150 ft) 

deep. This unconformity is known as the T-3 unconformity 

(Blakey, 1994). The eroded streams and valleys began to accumulate mud, sand, gravel, and conglomerate that formed the 

basal deposits of the Shinarump Member of the Chinle Formation.

Chinle Formation

The Triassic Chinle Formation is the most colorful formation in the map area and is subdivided into three mappable 

units along the Little Colorado River Valley. In ascending order 

they are the Shinarump Member and sandstone and siltstone 

member, undivided; the Petrified Forest Member; and the Owl 

Rock Member as defined by Repenning and others (1969).

The Shinarump Member and sandstone and siltstone 

member, undivided, is thickest northwest of Cameron in and 

around Shadow Mountain where accumulations are between 

55 and 60 m (180 and 200 ft) thick. The upper sandstone and 

siltstone sequence of strata is predominantly a lenticular maze 

of thin to thick interbedded stream channel and flood-plain 

deposits of light-brown conglomerate, and lenticular crossbedded units of purple, gray, and red siltstone and sandstone. The 

sandstone and siltstone member as defined by Repenning and 

others (1969) forms a transitional unit between the Shinarump 

Member and Petrified Forest Member of the Chinle Formation; 

the sandstone and siltstone member erodes forming irregular 

and covered slopes of lenticular beds of mudstone, siltstone and 

silty sandstone.

Locally and just north of the map area, the sandstone 

and siltstone member is divided into two conspicuous units 

(Akers and others, 1958), a lower slope-forming mudstone and 
6

siltstone unit and an upper sandstone cliff-forming unit (these 

subdivisions are not mapped for this map). The sandstone 

and siltstone member sequence is not as crossbedded or as 

conglomeratic as the underlying Shinarump Member. The upper 

cliff-forming sandstone forms an irregular ledge between the 

lower slope-forming unit and the overlying Petrified Forest 

Member. The lower slope-forming unit thins southeastward 

resulting in a pinch out where the upper sandstone combines 

with the Shinarump Member near Cameron, and is often 

mistaken for the Shinarump. For this reason and for mapping 

purposes, the Shinarump Member and sandstone and siltstone 

member are combined as an undivided map unit. West of 

Cameron at Red Butte (west of map area) and in a few 

exposures near the Coconino Point Monocline at the base of 

Gray Mountain, the sandstone and siltstone member overlies the 

Moenkopi Formation where the Shinarump Member is absent 

(Repenning and others, 1969).

The conglomeratic sandstone beds of the Shinarump 

Member contain numerous petrified logs and wood fragments. 

Some of the petrified logs and carbonaceous sandstone deposits 

became enriched with uranium minerals. Several open-pit mines 

were developed in the 1950’s to mine the uranium along the 

Little Colorado River area. Today all of the mines are abandoned and many have undergone restoration. The thickness of 

the Shinarump Member and sandstone and siltstone member, 

undivided, is variable due to widespread local channel erosion 

and local pinch out and thinning of the siltstone unit. The map 

unit generally thins southeastward to between 9 and 18 m (30 

and 60 ft) thick along the Little Colorado River. The contact 

between the Shinarump Member and sandstone and siltstone 

unit, undivided, and the overlying Petrified Forest Member is 

gradational and highly variable.

The Petrified Forest Member of the Chinle Formation is the 

colorful middle part of the Chinle Formation and forms the multicolored blue, red, and grayish-green mud hills of the “Painted 

Desert” badlands along and north of the Little Colorado River 

and is the most widespread member of the Chinle Formation. 

The upper and lower parts of the Petrified Forest Member are 

separated by the Sonsela Sandstone Bed in the upper Little 

Colorado River Valley east of the map area. In the map area, the 

upper and lower parts of the Petrified Forest Member cannot be 

differentiated with certainty because the Sonsela Sandstone Bed 

is absent; therefore the Petrified Forest Member is mapped as 

one unit.

Locally, the Petrified Forest Member can be subdivided 

into three units based on slight lithologic and color differences 

according to Akers and others (1958), but these units are herein 

mapped together as the Petrified Forest Member of the Chinle 

Formation because the gradational boundaries between them are 

highly variable. The three units are, in ascending order, a blue 

mudstone, a gray mudstone and sandstone, and a red mudstone 

and sandstone. The blue mudstone unit is a continuous band of 

strata within the lower part of the Petrified Forest Member and 

the two overlying units gradually thin and grade eastward of the 

map area into the interval occupied by the Sonsela Sandstone 

Bed and upper part of the Petrified Forest Member. The Petrified Forest Member generally maintains a thickness between 

122 and 153 m (400 and 500 ft).

Gradationally overlying the Petrified Forest Member of 

the Chinle Formation is the Owl Rock Member of the Chinle 

Formation. The Owl Rock Member consists of a sequence of 

gray interbedded ledge-forming siliceous limestone and lightred and yellowish-gray, slope-forming, calcareous siltstone 

beds that form Ward Terrace northeast of the Little Colorado 

River (fig. 1). The contact between the Petrified Forest and Owl 

Rock Members is generally marked between the pastel pale-red 

mudstone and siltstone beds of the lower Owl Rock Member 

and the lenticular varicolored mudstone, siltstone, and sandstone beds of the Petrified Forest Member about 12 m (40 ft) 

below the lowest gray limestone bed of the Owl Rock Member. 

The upper contact of the Owl Rock Member with the overlying 

Moenave Formation is unconformable and marked by a sharp 

contrast in color and lithologic change from the blueish-gray 

mudstone of the Owl Rock to the orange-red fluvial sandstone 

of the Moenave. This regional unconformity is known as the 

J-O unconformity (Pipiringos and O’Sullivan, 1978; Peterson 

and Pipiringos, 1979) and separates the Triassic rocks from the 

overlying Jurassic rocks. The Owl Rock Member is about 82 m 

(270 ft) thick north of Cameron, Arizona, and gradually thins 

southeastward along the Little Colorado River to less than 60 m 

(200 ft) in the southeast corner of the map area.

Moenave Formation

The Owl Rock Member of the Chinle Formation is overlain by the orange-red sandstone and silty sandstone sequences 

of the Moenave Formation. The type section of the Moenave 

Formation is about 13 km (8 mi) north of the map area near 

the community of Moenave, Arizona. The Moenave Formation 

includes, in ascending order, the Dinosaur Canyon Member 

(Colbert and Mook, 1951) that is exposed 30 km (19 mi) south 

of the type locality and within this map area; and the Springdale 

Sandstone Member, originally described by Gregory (1950) as 

part of the Chinle Formation and redefined as the upper member 

of the Moenave Formation by Harshbarger and others (1958). 

The Dinosaur Canyon and Springdale Sandstone Members 

are not mapped separately on this map because the Springdale Sandstone, although present at the north edge of the map, 

undergoes a facies change from sandstone to siltstone and silty 

sandstone in the upper part of the Dinosaur Canyon Member. 

East of the map area, the Moenave Formation intertongues 

with the Wingate Sandstone. The environmental and regional 

correlations and paleogeographic reconstructions of the fluvial 

and eolian systems of the Moenave Formation and the Wingate Sandstone are described by Edwards (1985), Clemmensen 

and others (1989), Blakey and others (1992), Riggs and Blakey 

(1993), and Nation (1990). Overall, in the map area the Moenave Formation is between about 84 to 98 m (275 to 320 ft) 

thick and gradually thins east of the map area.

Cooley and others (1969) mapped the Rock Point and 

Lukachukai Members of the Wingate Formation (Sandstone) 

on the Ward Terrace area northeast of the Little Colorado River, 

as did Billingsley (1987a) using data by Cooley and others 

(1969). However, the Rock Point and Lukachukai Members of 

the Wingate Sandstone are not mapped in this map area because 

of the correlation of these units east of the map area is not 
7

stratagraphically correct. The Wingate Sandstone members as 

mapped by Cooley and others (1969) is between the Moenave 

Formation and the Chinle Formation, but east and north of the 

map area, the Wingate Sandstone is correctly mapped between 

the Moenave Formation and the Kayenta Formation. A thin 

white sandstone at the top of the Moenave Formation forms 

a hard caprock at the top of the Red Rock Cliffs resulting in 

the development of the Red Rock Cliffs (fig. 1). This white 

sandstone is likely the western extent of the Wingate Sandstone 

but is not shown on this map because it is too thin (less than 1 m 

[3 ft]) to show at map scale. The Wingate Sandstone increases 

to 12 m (40 ft) thick as a light-red and white massive, lowangle crossbedded sandstone in the western part of the Hopi 

Buttes area about 60 km (37 mi) southeastward into the western 

part of the Hopi Buttes area southeast of the map area (current 

mapping by the author). Most of the Moenave Formation, 

Wingate Sandstone, and Kayenta Formation interval is covered 

by surficial alluvial and eolian deposits about 72 km (45 mi) 

east of the map in the Hopi Buttes area. However, regional and 

local trends suggest that some of the upper fluvial-dominated 

cycles of the Moenave Formation correlate with eoliandominated cycles of the Wingate Sandstone east and northeast 

of the map area (Blakey, 1994). The Rock Point and Lukachukai 

Members of the Wingate Formation (Sandstone) at the base of 

the Red Rock Cliffs, as mapped by Cooley and others (1969), 

are lithologically and locally similar to the overall Moenave 

Formation and are herein mapped as the basal part of the 

Moenave Formation.

Kayenta Formation and Navajo Sandstone

Contact of the purplish-red, slope-forming siltstone and 

sandstone sequence of the Kayenta Formation (Jk) unconformably overlies the brick-red sandstones of the Moenave Formation (Jm) in the Red Rock Cliffs and Ward Terrace areas. The 

unconformity is marked by a sharp, white to purplish-white 

silica-cemented sandstone bed that is the western extent of 

the Wingate Sandstone at the base of the Kayenta Formation. 

This unconformity is the sub-Kayenta Formation unconformity 

(J-sub-K) as defined by Riggs and Blakey (1993) and Blakey 

(1994) and the unconformity extends across the Colorado 

Plateau wherever the Kayenta Formation and the Springdale 

Sandstone Member of the Moenave Formation are present. The 

erosional relief is generally less than 2 m (6 ft) in the map area 

but the relief is as much as 15 m (50 ft) north of the map area 

(Nation, 1990).

The Kayenta Formation (Jk) grades upward into a 

sequence of interbedded red and white crossbedded sandstone 

ledges and cliffs and purplish-red mudstone and siltstone slopes 

mapped as the Kayenta Formation-Navajo Sandstone transition 

zone (Jkn). The white and red crossbedded sandstone ledges 

and cliffs within the upper Kayenta Formation are tongues 

of the Navajo Sandstone and the purplish-red mudstone and 

siltstone slopes are tongues of the Kayenta Formation. North 

of the map area, the tongues of Navajo Sandstone change 

southward from cliff-forming eolian deposits to slopeforming fluvial deposits of the “silty facies” of the Kayenta 

Formation (Blakey, 1994). Blakey (1994) subdivided the 

Navajo Sandstone of this region into two parts, as suggested by 

Marzolf (1983); the lower part is equivalent to and intertongues 

with eolian and fluvial deposits of the Kayenta FormationNavajo Sandstone transition zone, and the upper part is the 

eolian cliff-forming Navajo Sandstone above the youngest 

documentable horizon of intertonguing. This subdivision of the 

Navajo Sandstone is recognized by Marzolf (1983) as the “wet 

lower part” and the “dry upper part.”

The Kayenta Formation thins from about 122 m (400 

ft) thick in the northeast corner of the map area to less than 

about 98 m (320 ft) at the east edge. The Kayenta FormationNavajo Sandstone transition zone gradually thickens from 

about 37 m (120 ft) at the northeast corner of the map area to 

about 73 m (240 ft) thick at the southeast edge. In the zone 

of facies change, the associated succession of fluvial, eolian, 

and lacustrine strata become more frequent southeastward 

of the Adeii Eechii Cliffs, and the Kayenta Formation thins 

(Middleton and Blakey, 1983; Sargent, 1984). Several springs 

and seeps are associated with the base of the Navajo Sandstone 

(Jn) along the Adeii Eechii Cliffs and this horizon is used as 

the map contact between the Kayenta Formation and Navajo 

Sandstone transition zone.

The Navajo Sandstone consists of red and white, cliffforming, crossbedded eolian sandstone and is the upper part 

of the Navajo Sandstone as proposed by Blakey (1994). The 

Navajo Sandstone includes several horizons and intervals of 

local wadi lake deposits as thin-bedded, silica-cemented sandy 

limestone beds (0.5 to 1.2 m [1 to 2 ft]) thick that are highly 

lenticular and are of limited lateral extent. These resistant limestone beds are at various levels within the Navajo Sandstone 

and form local cherty limestone ridges or hills on the Moenkopi 

Plateau surface. The limestone ledges are frequently exposed 

along the Adeii Eechii Cliffs and increase in number southeastward as the Navajo Sandstone decreases in thickness from 76 to 

48 m (250 to 160 ft) on the Moenkopi Plateau.

The beveled upper surface of the Navajo Sandstone is an 

erosional unconformity known regionally as the J-1 and J-2 

unconformity (Pipiringos and O’Sullivan, 1978; Blakey, 1994). 

At Appaloosa Ridge and at the west end of Coal Mine Mesa of 

Moenkopi Plateau, as much as 9 m (30 ft) of erosional relief 

separates the Navajo Sandstone from the overlying Jurassic 

Entrada Sandstone-Cow Springs Sandstone, undivided. The 

erosional channels are filled with conglomerate and sandstone 

sediment that may be the southernmost extent of the Carmel 

Formation. At Middle Mesa about 26 km (16 mi) north of the 

northeast corner of the map area, about 12 m (40 ft) of the 

Carmel Formation overlies the Navajo Sandstone at Tohnali 

Mesa and just north of the northeast edge of the map the Carmel 

Formation is 1.5 to 2 m (5 to 7 ft) thick. The Carmel Formation pinches out in the subsurface of Coal Mine Mesa and is 

included in the lower part of the Jurassic Entrada Sandstone 

(Je), but is too thin to show at map scale.

Entrada Sandstone and Cow Springs Sandstone, undivided

The interval of sedimentary strata between the Jurassic 

Navajo Sandstone (Jn) and the overlying Cretaceous Dakota 

Sandstone (Kd) consists mostly of white crossbedded sandstone 
8

of the Entrada Sandstone (Je) and the yellowish sandstone 

of Cow Springs Sandstone in the upper part, undivided. This 

sandstone sequence includes thin red beds of the Carmel Formation at the base of the unit that pinches out southward into the 

subsurface of Coal Mine Mesa and is too thin to show at map 

scale. The Carmel Formation thickens north of the map area 

forming the J-1 and J-2 unconformity (Blakey, 1994) at the top 

of the Navajo Sandstone.

The lower massive white, very fine-grained cliff- and 

slope-forming sandstone that weathers steel gray is the Entrada 

Sandstone (Je) and contains multiple small-scale trough 

crossbeds. The middle part of the Entrada Sandstone sequence 

contains a few thin, flat bedded, red siltstone and sandstone beds 

that may be equivalent to the Summerville Formation at Black 

Mesa northeast of the map area but pinch out into this part of 

the map area (Harshbarger and others, 1958). The upper part 

of the sandstone sequence is yellowish-white, cliff and slope 

of planar crossbedded sandstone that is a southern extension of 

the Cow Springs Sandstone (Harsbarger and others, 1958). The 

Entrada Sandstone and Cow Springs Sandstone, undivided, is 

unconformably overlain by the Cretaceous Dakota Sandstone 

(Kd). The Jurassic-Cretaceous unconformity is regionally widespread east and southeast of the map area.

Dakota Sandstone and Mancos Shale

The Cretaceous Dakota Sandstone (Kd) crops out at Appaloosa Ridge and Coal Mine Mesa of the Moenkopi Plateau, 

northeast corner of the map area. The Dakota Sandstone is 

subdivided into three units, in ascending order, the lower sandstone member, middle carbonaceous member, and the upper 

sandstone member; all are present at Coal Mine Mesa and have 

gradational contacts (O’Sullivan and others, 1972). All three 

members are too small to show at map scale and are collectively 

mapped as the Dakota Sandstone.

The lower sandstone member forms a pale-orange lenticular conglomeratic sandstone cliff that occupies shallow channels 

of a regional unconformity eroded into the underlying Jurassic 

Entrada Sandstone and contains abundant small iron-rich concretions. The lower sandstone member is generally less than 6 

m (20 ft) thick and is missing in parts of the eastern Coal Mine 

Mesa area where the middle carbonaceous member unconformably overlies the Entrada Sandstone. The middle carbonaceous 

member is a brown, grayish-black, and black carbonaceous 

mudstone and siltstone and that averages about 9 m (30 ft) 

thick. Coal beds are locally several feet thick at the eastern part 

of Coal Mine Mesa and in the early 1900’s coal was mined from 

this unit at Coal Mine Canyon just north of the northeast corner 

of the map area for use at Tuba City, Arizona. The Dakota Sandstone has a gradational and arbitrary contact with the overlying 

Mancos Shale.

Only the lower part of the Mancos Shale is present at Coal 

Mine Mesa of the Moenkopi Plateau in the northeast corner of 

the map area. During the Cenozoic, most of the bluish-gray, 

thin-bedded, slope-forming Mancos Shale was eroded from 

Coal Mine Mesa; the Mancos Shale is now largely covered by 

extensive surficial deposits of eolian and fluvial sand, silt, and 

mud eroded from remnants of the Mancos Shale.

San Francisco Volcanic Field

The Tertiary and Quaternary volcanic rocks of the San 

Francisco Volcanic Field form a protective caprock over the 

Permian Kaibab Formation and the Triassic Moenkopi Formation in the southwest quarter of the map area. The volcanic 

rocks are Pliocene, Pleistocene, and Miocene in age (table 1) 

as mapped by Ulrich and Bailey (1987) and Wolfe and others 

(1987). The oldest volcanic rock in the map area is the basalt 

flow of Cedar Ranch Mesa (K-Ar age, 5.62±0.19 Ma) east of 

U.S. Highway 180 and the youngest is the basalt flow of Merriam Crater (optical-luminescence age, 19.6±1.2 ka; Duffield 

and others, 2004) in the Little Colorado River channel, southeast corner of map area. The volcanic rocks range in composition from basalt to rhyolite. The volcanic rocks were mapped 

on the basis of lithology and morphology and are grouped into 

map units delineated on the basis of magnetic polarity, radiometric age, and field relations by Ulrich and Bailey (1987) and 

Wolfe and others (1987). Within these chronostratigraphic units, 

boundaries are shown between adjacent basalt flows because 

their individual lithologic characteristics and stratigraphic relations are important to the magnetic history of the individual 

units of the field as a whole. The K-Ar ages indicated for some 

of the map units were determined by Paul E. Damon and Edwin 

H. McKee (Ulrich and Bailey, 1987), and recently by Duffield 

and others (2004), but most were originally reported by Damon 

and others (1974).

Surficial Deposits

Quaternary fluvial and eolian deposits cover parts of 

the southwestern two-thirds of the map area and much of the 

northeastern third of the map area. Extensive black volcanic 

cinder ash has been deposited by southwesterly winds as eolian 

cinder sand sheet and dune deposits in the Wupatki National 

Monument area and at nearby volcanic pyroclastic cones and 

basalt flows southwest of Wupatki National Monument. Alluvial deposits are largely unconsolidated thin surface deposits 

in much of the west and central part of the map area. The 

Little Colorado River, which flows towards the Grand Canyon 

northwest of the map area, is the principal drainage in the map 

area. The Little Colorado River and all of the tributaries on 

the northeast side of the river are the main source and supply 

for extensive eolian sand sheet and sand dune deposits that are 

transported by southwesterly winds to the northeast toward 

Moenkopi Plateau. Eolian sand sheet and dune deposits have 

accumulated on Ward Terrace and thick deposits have piled up 

against the Red Rock Cliffs area (fig.1; fig. 3. on map). These 

eolian deposits are gradually eroded and transported as sandy 

alluvium down the tributary drainages back to the Little Colorado River where some of the sand is recycled by the southwesterly winds and blown back to the Red Rock Cliffs to be eroded 

again. Eventually, the sand is transported down the Little Colorado River to the Colorado River and through Grand Canyon. 

Extensive and older sand sheet and dune deposits blanket the 

Moenkopi Plateau northeast of the Adeii Eechii Cliffs (Hack, 

1941; Billingsley, 1987b) and are largely stabilized by grassy 

vegetation. However, in recent years (1990 to 2006) drought has 

caused some of these deposits to become reactivated and strong 
9

Table 1. Geochron ages for volcanic rocks within the map area

Unit label General geographic Location Rock type Calculated age Polarity, 

locality Latitude (N) Longitude (W) (K-Ar unless noted) Chronozone age

Qmcb Merriam Crater flow 35.34° 111.28° Basalt 19.6±1.2 ka ––– 

in Little Colorado River (optical-luminescence)

Qyab S P Mountain 35.62° 111.61° Basaltic andesite 0.071±0.004 Ma Brunhes 

Qb Arrowhead Sink 35.50° 111.55° Basalt 0.22±0.05 Ma Brunhes Qb S P Tank 35.72° 111.62° Basalt 0.46±0.05 Ma Brunhes 

Qbt Tappan Wash 35.89° 111.46° Basalt 0.53±0.079 Ma Brunhes 

Qsb Shadow Mountain 35.99° 111.38° Basalt 0.649±0.23 Ma ––– 

Qb Southwest of S P Mountain 35.54° 111.74° Basalt 0.66±0.11 Ma Brunhes Qb Campbell Francis Wash 35.69° 111.55° Basalt 0.74±0.08 Ma Brunhes Qb S P Tank 35.66° 111.59° Basalt 0.77±0.04 Ma Brunhes 

Qwb Southwest of Woodhouse Mesa 35.82° 111.65° Basalt 0.786±0.14 Ma Matuyama 

Qsfp San Francisco Mountain 35.51° 111.55° Pumice 0.80±0.11 Ma Matuyama 

(fission-track) 

Qwb Woodhouse Mesa, 35.48° 111.37° Basalt 0.812±0.059 Ma ––– 

south of map area

Qmb Mesa Butte Fault fissure vent 35.66° 111.75° Basalt 0.83±0.04 Ma Matuyama 

near Lockwood Canyon 

Qwb Kellam Ranch, south of map area 35.37° 111.30° Basalt 0.874±0.13 Ma ––– Qwb Wupatki National Monument 35.50° 111.00° Basalt 0.897±0.14 Ma ––– 

south of visitor center

Qmlp Lava Point 35.69° 111.53° Basalt 1.01±0.13 Ma Matuyama 

Qmb East of Mesa Butte 35.63° 111.74° Basalt 1.04±0.04 Ma Matuyama Qmb Northeast of S P Mountain 35.66° 111.54° Basalt 1.04±0.14 Ma Matuyama Qmb Large Whiskers Tanks 35.74° 111.56° Basalt 1.09±0.03 Ma Matuyama 

Qmbi East of U.S. Highway 89 and 35.64° 111.51° Basalt 1.20±0.05 Ma Matuyama 

north of S P Mountain

Qmb East of Mesa Butte 35.68° 111.72° Basalt 1.38±0.16 Ma Matuyama 

Qslr Slate Mountain 35.49° 111.84° Rhyolite dome 1.54±0.02 Ma Matuyama 

complex 

Tbpb Black Point 35.63° 111.35° Basalt 2.43±0.32 Ma ––– 

Tbi Dike in ampitheater 35.66° 111.58° Basalt 3.13±0.39 Ma Gauss or Gilbert 

Tocb Cedar Ranch Mesa 35.52° 111.75° Basalt 5.62±0.19 Ma ––– 
10

dry winds redeposit the sand as a fresh thin sand veneer over the 

older deposits in some areas, especially where large stock tanks 

and windmills are present.

Other surficial deposits are comprised of landslide, talus, 

and rock fall deposits that are exposed mainly around and 

below the edges of volcanic rock outcrops such as at Black 

Point. Several landslide and associated deposits are present on 

Gray Mountain and in the Little Colorado River Gorge. Manmade diversion dams, stock tanks, gravel pits, and old open-pit 

uranium mine operations are also mapped to show the human 

impact on the landscape.

Structural Geology

High-angle to nearly vertical normal-fault separation of 

Paleozoic and Mesozoic strata and northeast and east-dipping 

sinuous and intersecting monoclines are the characteristic structures of the map area. Compressional folding of the Paleozoic 

and Mesozoic rocks along reactivated Proterozoic high-angle 

faults began in Late Cretaceous and early Tertiary time (about 

65 Ma) causing erosion to begin removing Mesozoic strata that 

once covered the entire map area (Huntoon, 1990). The Laramide erosional period began to transform the landscape to its 

general configuration, but the late Tertiary and Pleistocene erosion developed the Little Colorado River Valley as a subsequent 

stream that became an established tributary to the Colorado 

River in Grand Canyon northwest of the map area (Ranney, 

2005). A meandering Little Colorado River appears to have 

been superimposed as a subsequent stream onto the southern 

part of Marble Plateau within a synclinal strike valley between 

the East Kaibab/Coconino Point Monoclines and Marble 

Plateau. The Little Colorado River and its tributaries became 

firmly established as an integrated tributary river system to the 

Grand Canyon sometime in late Miocene or early Pliocene time, 

between about 6 to 9 million years (Lucchitta, 1979; 1990). 

Headward erosion of the Little Colorado River, caused by the 

deepening Colorado River in Grand Canyon, gradually extended 

the Little Colorado Canyon upstream toward Cameron, Arizona, 

as demonstrated by the 500 thousand year-old Tappan Basalt 

flow (Qbt) that forms a ridge or inverted valley within the Little 

Colorado River drainage downstream of Cameron, Arizona (fig. 

2 on map).

The north- and east-dipping monoclines in the map area 

overlie deep-seated reverse faults that displaced strata up-tothe-west and south during Late Cretaceous and early Tertiary 

time. During Pliocene and Pleistocene time, east-west extension 

reactivated the deep-seated faults along parts of some monocline folds, producing normal fault separation that reversed the 

Cretaceous and Tertiary offset as well as accentuating the dip 

of the monoclines by reverse drag along the faults (Huntoon, 

1990; 2003). Cenozoic extensional faulting that produced many 

grabens began during late Pliocene time, less than 3 million 

years ago, based on similar extensional faulting evidence and 

conditions along the Hurricane and Toroweap Faults west of 

the map area (Billingsley and Workman, 2000; Billingsley and 

Wellmeyer, 2003).

The northwest-trending grabens and faults in the Gray 

Mountain, S P Mountain, Little Colorado River Gorge, and 

Wupatki National Monument areas seem to be the most tectonically active structures based on minor offset of Pleistocene and 

Holocene(?) alluvial deposits and Pleistocene volcanic deposits. 

Numerous sinkhole depressions have developed along fractures 

and joints associated with the faults and grabens and have temporarily interrupted runoff in several tributary drainages to the 

Little Colorado River in the area from the Little Colorado River 

Gorge southeast to Wupatki National Monument. The basalt 

flow of Tappan Wash (0.51±0.079 Ma) is offset a few meters by 

two grabens in two areas along the Little Colorado River below 

Cameron, Arizona (Rice, 1977), and is offset by minor grabens 

southwest of Cameron, Arizona, and is offset by the Cedar 

Ranch Fault at the southwest edge of the map (Shoemaker and 

others, 1974).

The Coconino Point Monocline is the largest monocline 

in the map area and it forms the topographic prominent highland of Gray Mountain (fig. 1). Paleozoic and Mesozoic strata 

dip sharply north, northeast, east, and southeast along the 

Coconino Point Monocline and at some places on the north side 

of Gray Mountain, the dip of strata is nearly vertical to slightly 

overturned. Southwest of the Gray Mountain prominence, the 

regional dip of strata is generally between 1° and 2° southwest. Small, normal, high-angle, down-to-the-west faults have 

reversed some of the Laramide offset of strata along short segments of the Coconino Point Monocline on Gray Mountain. The 

western segment of the Coconino Point Monocline terminates at 

the T-shaped intersection of the northwest-trending East Kaibab 

Monocline and the west-trending Grandview Monocline (Doty, 

1982).

The East Kaibab Monocline extends northwest into the 

eastern Grand Canyon area northwest of the map and forms a 

major structural feature of the eastern Grand Canyon (Huntoon 

and others, 1996). The East Kaibab Monocline continues 

northward into Utah. Strata along the East Kaibab Monocline 

within the map area dip northeast between 20° and 40° with the 

steepest dip in the lower part of the fold. The vertical relief of 

Paleozoic strata averages about 305 m (1,000 ft) up-to-the-west.

The Grandview Monocline extends west from the intersection of the East Kaibab and Coconino Point Monoclines to 

a northwest bend in the structural trend and continues into the 

Grand Canyon at the northwest corner of the map. The Permian and Triassic strata along the east trending segment of the 

Grandview Monocline are mostly Permian age, highly folded 

to a near vertical position, and partly faulted, generally with 

less than 30 m (100 ft) of offset. The folding has elevated the 

Coconino Plateau an average of 275 m (900 ft) up-to-the-south. 

South of the Grandview Monocline the elevated highlands form 

the western part of Gray Mountain of the Coconino Plateau. 

From the northwest bend of the Grandview Monocline to the 

Grand Canyon, the dip of Paleozoic and Mesozoic strata in the 

upper part of the monocline averages 20° to 30° northeast, and 

the dip of strata increases to as much as 75° northeast in the 

lower part of the fold. West and southwest along the northwest 

segment of the Grandview Monocline to the Grand Canyon, the 

elevated highlands are between 122 and 153 m (400 and 500 ft) 

high.

West of the bend in the Grandview Monocline, a small east 

striking scissors fault indicates a probable structural connection 
11

at depth with the Skinner Ridge Anticline 3 km (2 mi) farther 

west. The east trending Skinner Ridge Anticline and associated 

syncline is a similar structure north of the Red Horse Anticline 

and Red Horse Syncline.

The Red Horse Anticline and Red Horse Syncline are 

generally east trending and parallel to Red Horse Wash southwest of Gray Mountain. Between the anticlinal and synclinal 

hinges the Paleozoic and Mesozoic strata dip as much as 7° 

north with an average dip of 3° to 4° north. Strata on the south 

limb of the Red Horse Anticline dip less than 2° south. The Red 

Horse Anticline and Syncline gradually terminate southwest of 

Gray Mountain and west of the Mesa Butte Fault and appear to 

control the stream patterns in their vicinity.

South of Gray Mountain, the Coconino Point Monocline 

extends to what was mapped as the Additional Hill Monocline 

described by Barnes (1974) and mapped by Billingsley and 

others (1985). Upon closer inspection of aerial photographs and 

additional field checking, it is determined that the Coconino 

Point Monocline and the Additional Hill Monocline are really 

one and the same structure that makes a southeasterly bend at 

its intersection with the Mesa Butte Fault. The Coconino Point 

Monocline gradually turns to a southwesterly trend parallel to the Mesa Butte Fault (fig. 1). The name Additional Hill 

Monocline is herein dropped from usage and is replaced by the 

Coconino Point Monocline on this map.

Gray Mountain

The trapezoidal shape of Gray Mountain northeast of the 

Burro Canyon Graben System is the highest block of Gray 

Mountain; its surface is cut by three prominent joint sets that 

form perfect equilateral triangles. This area is also distinguished 

by two dome structures separated by a sharp synclinal flexure. 

This structurally complex area has produced an epidermal landslide block (labeled as Ql, cross section B–B’) that consists of a 

relatively coherent sheet of the Kaibab Formation derived from 

a steeply dipping source near the crest of Gray Mountain. This 

landslide block horizontally preserves the synclinally folded 

younger Triassic strata at the base of the northeast face of Gray 

Mountain (Marshall, 1972).

Southwest of Gray Mountain, the Burro Canyon Graben 

System parallels the regional joint pattern and other north-bynorthwest oriented grabens exposed on the top of Gray Mountain and are parallel to the north on the upper limb of the East 

Kaibab Monocline. The East Kaibab Monocline intersection 

with Coconino Point Monocline marks an abrupt shift from 

monoclinal folding to marked extension along the trend of the 

East Kaibab Monocline axis southeast across Gray Mountain, 

forming the Burrow Canyon Graben System (Barnes, 1974; 

Lufholm, 1975).

On the southwest face of Gray Mountain the intersection 

of the East Kaibab-Burro Canyon structures with the Coconino 

Point Monocline marks an abrupt shift from extension across 

Gray Mountain back to monoclinal folding along the Coconino 

Point Monocline. The area of strain transfer coincides with 

the intersection of the Mesa Butte Fault (a graben in this area). 

Offset along the Mesa Butte Fault is right oblique slip, southeast 

side down. These geometric relations suggest that a northeasterly oblique shift in the strain pattern along the Mesa Butte 

Fault formed the Gray Mountain Prominence (Pettengill, 1970; 

Barnes, 1974).

The Coconino Point Monocline extends southwest and 

parallel to the southwest strike of the Mesa Butte Fault and 

Mesa Butte Graben for about 19 km (12 mi) and dies out near 

the Mesa Butte volcano about 3 km (2 mi) north of Mesa Butte. 

The Mesa Butte Fault and the Cedar Ranch Fault intersect at 

the north side of Mesa Butte volcano. The Cedar Ranch Fault 

offsets Paleozoic and Mesozoic strata down-to-the-southeast 

about 85 m (280 ft). The Mesa Butt Fault combines with the 

Cedar Ranch Fault for a short distance for a total offset of strata 

about 110 m (360 ft) down-to-the-southeast. East and south of 

Mesa Butte, the Cedar Ranch Fault strikes southwest east of and 

parallel to the Mesa Butte Fault. The Cedar Ranch Fault continues southwest to Cedar Ranch where the fault is buried by large 

landslide deposits and Tertiary basalt flows. The Cedar Ranch 

Fault likely extends to the south edge of the map, but extensive 

basalt flows of the San Francisco Volcanic Field cover the fault 

trace.

The Mesa Butte Fault offsets strata generally less than 30 

m (100 ft) down-to-the-southeast along the Mesa Butte Graben 

section that forms a linear depression along the southeast side 

of Mesa Butte Fault. However, southwest of Gray Mountain, 

Permian strata has been down-dropped into the graben as much 

as 80 m (260 ft) and forms an impressive linear feature about 

0.5 km (0.25 mi) wide and about 20 km (12 mi) long. This 

linear feature forms a prominent “crack” or linear depression 

on the landscape that is easily seen on aerial photographs and 

satellite images. The Mesa Butte Fault and Graben intersect 

the northeast structural trend of the Coconino Point Monocline 

along its eastern face; oblique shift along that fault progressively elevated Paleozoic and Mesozoic strata up-to-thenorthwest forming a hinge-faulted monocline along its trend 

northeast of the Mesa Butte Graben. This structural pattern of 

northeasterly oblique slip, up-to-the-northwest is paralleled by a 

similar but smaller scale fault, the Doney Mountain Fault in the 

south-central part of the map area (Barnes, 1974).

The Coconino Point Monocline, a short segment of the 

Mesa Butte Fault, and the Cedar Ranch Fault, form a major 

structural barrier to ground water flow between groundwater 

flowing west to Havasu Spring in the central Grand Canyon 

region and groundwater flowing north into Blue Spring about 

14.5 km (9 mi) north of the map area in the Little Colorado 

River Gorge. The divide between east and west flowing surface 

drainages is generally a few miles west of the Mesa Butte and 

Cedar Ranch Faults. Dog Knobs Lake is an area of internal 

drainage within the southwest part of the map, but in general the 

surface runoff west of the Dog Knobs and Gray Mountain areas 

flows west to Cataract Canyon and into the central part of Grand 

Canyon, and the surface runoff east of the Dog Knobs and Gray 

Mountain areas flows northeast toward the Little Colorado 

River.

The Black Point Monocline and Coconino Point Monocline intersect about 6.5 km (4 mi) south of the Gray Mountain 

Prominence (fig. 1). The Black Point Monocline is a broad 

northeast-dipping structure where Permian and Triassic strata 

dip between 15° and 30° northeast and the fold averages about 
12

1.6 km (1 mi) wide. The Black Point Monocline trends southeast from its intersection with the Coconino Point Monocline 

at Gray Mountain to Black Point (fig. 1 on the map) and to 

about 8 km (5 mi) southeast of Black Point where it intersects 

the northeast strike of Doney Mountain Fault. The Black Point 

Monocline abruptly bends to the southwest in a series of rightstepping en echelon faults and parallels the Doney Mountain 

Fault southwest to the Wupatki National Monument area 

(McCormack, 1989). The Black Point Monocline gradually dies 

out south of Wupatki National Monument and is offset downto-the-southeast by the Doney Mountain Fault. The Doney 

Mountain Fault offsets Permian and Triassic strata as much as 

67 m (220 ft) north of Doney Mountain and 92 m (300 ft) at 

Doney Mountain volcano. Doney Mountain volcano erupted 

along the east side of and parallel to the strike of the Doney 

Mountain Fault in Wupatki National Monument. The Black 

Point Monocline and Doney Mountain Fault gradually die out 

just southwest of Wupatki National Monument and are covered 

by basalt flows of the San Francisco Volcanic Field.

The Echo Cliffs Monocline is a broad southeast-dipping 

monocline that forms the eastern boundary of Marble Plateau 

where the dip of Permian and Triassic strata is generally less 

than 3° to 4° southeast in the vicinity of Shadow Mountain and 

where the monocline gradually terminates. This monocline 

forms a prominent structural fold north of the map area and parallels U.S. Highway 89 for several miles. The southern terminus 

of the monocline seems to intersect a structurally complex area 

where the Little Colorado River Gorge begins. The southwesterly trending Echo Cliffs Monocline intersects a northeasterly 

trending syncline that may be a continuation of the northeast 

strike of the Mesa Butte Fault at depth. The syncline and Mesa 

Butte Fault are separated by a nearly perpendicular structure 

called the Blue Spring Monocline.

The Blue Spring Monocline just north of Gray Mountain 

is a northwest trending structure of northeast-dipping Paleozoic 

and Mesozoic strata. The relief along this monocline is generally less than 60 m (200 ft) and the average dip of strata is about 

5° northeast. Several collapse breccia pipe structures are generally aligned along the northwest trend of the Blue Spring Monocline. The Blue Spring Monocline is perhaps the most important 

hydrological structure in the map area. Its northwesterly trend 

gradually terminates into a down-to-the-northeast fault that 

extends to Blue Spring in the bottom of the Little Colorado 

River Gorge just northwest of the map area. Associated with 

the Blue Spring Monocline and Fault are numerous northwest 

trending joints and fractures from which Blue Spring and several smaller springs issue at the top of the Redwall Limestone. 

The structural faults, fractures, and joints associated with the 

Blue Spring Monocline form a major hydrological avenue for 

ground water transport; groundwater from most regions northeast, east, southeast, and south of Gray Mountain flows through 

karst caverns and open joints in the Redwall Limestone to Blue 

Spring north of the map area. Blue Spring is the largest natural 

flowing spring in Arizona; daily discharge is nearly 200 cubic 

feet per second.

Circular bowl-shaped depressions in the Kaibab Formation, characterized by inward-dipping strata, are likely to be 

the surface expression of collapse-formed breccia pipes that 

originate from the dissolution of limestone of the deeply buried 

Mississippian Redwall Limestone. The dissolution of gypsum 

in the Woods Ranch Member of the Toroweap Formation may 

enhance some of these collapse features (Wenrich and Huntoon, 

1989). Collapse features are indicated by a black dot on the 

map and may or may not represent breccia-pipe structures at 

depth. Exposed breccia in breccia pipes are indicated by a red 

dot. Drilling methods are needed to confirm breccia pipes that 

originate at depth in the Redwall Limestone. Large-scale collapse depressions may be the result of several interconnecting 

smaller collapse features or breccia pipes, such as the depressions north of the Little Colorado River on Marble Plateau and 

on the Coconino Plateau southwest of Gray Mountain. Breccia 

pipes have the potential for uranium-mineralization and other 

minerals at depth, but not all breccia pipes are mineralized (Sutphin and Wenrich, 1989; Wenrich, 1992). Only circular collapse 

features that have inward dipping strata are marked on the map 

as potential breccia pipes at depth.

Gypsum dissolution within the Harrisburg Member of 

the Kaibab Formation has resulted in several sinkholes on the 

Coconino Plateau. The sinkholes are likely Pleistocene and 

Holocene age because they disrupt local drainages and are 

commonly filled with local ponded fine-grained sediments. The 

deposits of gypsum in the Kaibab and Toroweap Formations are 

thickest along the west edge of the map area as reflected by the 

numerous sinkholes.

Internal drainage areas in the volcanic rocks of the San 

Francisco Volcanic Field may reflect large sinkhole depressions 

in the underlying Harrisburg Member of the Kaibab Formation 

in the southwest quarter of the map area. During wet climatic 

conditions these depressions form intermittent lakes such as 

Dog Knobs Lake and Babbitt Lake, southwest quarter of map 

area (fig.1). However, because Dog Knobs Lake is underlain 

by a small graben structure along which small sinkholes have 

developed that quickly drain any water, the lake is almost 

always dry.

Acknowledgments

We are gratefully appreciative of the cooperation and support of William R. Hansen of the Water Right Branch, Water 

Resource Division of the National Park Service, Fort Collins, 

Colorado, and John Rihs, hydrologist at the Grand Canyon Science Center, National Park Service at Grand Canyon National 

Park, Arizona. We also appreciate the advice, revisions, and 

geologic information provided by Ronald C. Blakey and Charles 

W. Barnes of Northern Arizona University, Flagstaff, Arizona. 

We are indebted to Dr. Charles L. Powell, II, and Theresa Iki, of 

the U.S. Geological Survey, Menlo Park, California, and Scott 

E. Graham, of the U.S. Geological Survey, Vancouver, Washington, for their technical advice and assistance in the preparation of this map and report. 
13

DESCRIPTION OF MAP UNITS

[Some unit exposures on the printed map are too small to distinguish the color for unit identification. These 

units are labeled where possible, and unlabeled units are attributed in the geodatabase.]

SURFICIAL DEPOSITS

Holocene, Pleistocene, and Pliocene(?) surficial deposits are differentiated from one another chiefly on the 

basis of differences in morphologic character and physiographic position illustrated on 1:24,000 scale 1968 

black and white aerial photographs and from field observations. Older alluvial and eolian deposits generally 

exhibit extensive erosion and have greater topographic relief. On Moenkopi Plateau, extensive sand sheet 

and dune deposits are relatively stabilized by vegetation and are the oldest eolian deposits within the map 

area (Billingsley 1987a; Hack, 1941). These deposits are partially reactivated on surfaces during severe 

drought or storm conditions, especially along the Adeii Eechii Cliffs of the Moenkopi Plateau. Surficial 

map contacts of eolian units are provisional and arbitrary. Young surficial deposits are actively accumulating material and often subject to moderate erosion.

Qaf Artificial fill and quarries (Holocene)—Excavated alluvium and bedrock material removed 

from bar-pits and trenches to build livestock tanks, drainage diversion dams, roads, and other 

construction projects (not all highway road excavations are mapped). Include uranium mine 

excavations, tailing deposits, and mine restoration sites in the Little Colorado River Valley 

area

Qs Stream-channel deposits (Holocene)—Poorly sorted, interlensing silt, sand, pebbles, and gravel. 

Intertongue with or inset against young alluvial fan (Qay), young terrace-gravel (Qgy), and 

upper part of valley alluvial (Qv) deposits, overlaps flood-plain (Qf) and ponded sediment 

(Qps) deposits. Stream channels subject to high-energy flows and flash floods. Little or no 

vegetation in stream channels, except for salt cedar (tamerisk), Russian olive, and cottonwood trees along Little Colorado River and some of its tributaries. Contact with other 

alluvial deposits merge laterally and are approximate. Stream-channel deposits of Little 

Colorado River mapped as shown on 1968 black and white aerial photographs and do not 

necessarily reflect stream-channel deposits of today due to extensive low-gradient channel 

changes caused by yearly flooding events. Little Colorado River stream channel meanders 

within its wide valley from upstream of Cameron to southeast corner of map area where 

the channel is confined within bedrock strata of Kaibab Formation. Downstream of Cameron, the Little Colorado River is largely confined within alternating hard and soft rocks of 

the Moenkopi and Kaibab Formations for about 11 km (7 mi), then becomes confined and 

strikingly meandering within narrow walls of Permian and older Paleozoic strata that form 

the Little Colorado River Gorge (fig. 1) and is part of the Grand Canyon physiographic area. 

About 2 to 9 m (6 to 30 ft) thick

Qf Flood-plain deposits (Holocene)—Gray, brown, and light-red clay, silt, sand. Include some 

lenticular gravel. Unit is partly consolidated by gypsum and calcite cement. Intertongue or 

overlap stream-channel (Qs), valley alluvial (Qv), young terrace-gravel (Qgy), and young 

alluvial fan (Qay) deposits. Subject to stream-channel erosion or overbank flooding in lateral 

and vertical sense. Similar to valley alluvial (Qv) deposits in small tributary drainage valleys 

that form broad, flat, valley floors subject to widespread and frequent overbank flooding 

along Little Colorado River and in highland valleys west of Gray Mountain. Tamerisk trees 

in Little Colorado River valley commonly occupy floodplain or low-lying terrace areas. In 

broad floodplains on Coconino Plateau and northeast of Little Colorado River, minor arroyo 

development may occur at downstream drainage outlets due to headward erosion of streams. 

Support thick growths of sagebrush, grass, cliffrose bush, and sagebrush at high elevations 

over 1,524 m (5,000 ft) that help trap and accumulate fine-grained sediment on floodplains 

of Coconino Plateau; sagebrush, tumble weed plants, desert shrubs, and grass in and along 

Little Colorado River area. Subject to temporary ponding and often mixed with ponded sediments (Qps) or young mixed alluvium and eolian (Qae) deposits in broad drainage floodplains on Coconino Plateau. About 2 to 9 m (6 to 30 ft) thick

Qd Dune sand and sand sheet deposits (Holocene)—Coconino Plateau and Gray Mountain area: 

White, gray, fine- to coarse-grained, wind-blown sand composed mainly of quartz and chert 

grains derived from Harrisburg Member of the Kaibab Formation west and south of Gray 

Mountain; accumulates on stream-channel (Qs) or valley alluvial (Qv) deposits. Form 
14

lumpy, undefined geometric sand dunes or sand sheet deposits on flood-plain (Qf) and young 

terrace-gravel (Qgy) deposits of local washes in west and southwest quarter of map area. 

Small sand sheet and dune deposits are mostly hidden or covered by forest growth in Kaibab 

National Forest south of Grand Canyon; support moderate growth of grass, sagebrush, 

pinion pine, juniper, and ponderosa pine woodlands. Little Colorado River and Moenkopi 

Plateau area: White, gray to light-red, fine- to coarse-grained sand composed mainly of 

quartz, chert, and minor feldspar grains derived from pre-existing Triassic and Jurassic 

sedimentary strata east of Little Colorado River. Include topographically controlled climbing 

and falling dunes and sand sheets that mantle gentle slopes of bedrock at Ward Terrace and 

Red Rock Cliffs and within tributary drainages northeast and east of Little Colorado River 

below Moenkopi Plateau. Sand is originally transported by fluvial erosion down tributary 

drainages from southwestern edge of Moenkopi Plateau to Little Colorado River is re-transported upstream by southwesterly winds onto Triassic and Jurassic bedrock surfaces forming 

significant deposits on Ward Terrace and against Red Rock Cliffs (Billingsley, 1987a), 

but does not reach Moenkopi Plateau except in the southeast corner of map area; includes 

topographically controlled climbing and falling dunes, complex dunes, parabolic dunes, 

and barchan dunes as mapped by Billingsley (1987a). Arbitrary and gradational lateral and 

vertical contacts between other alluvial or eolian deposits, especially along southwestern 

edge of Moenkopi Plateau at Adeii Eechii Cliffs where southwesterly winds actively erode 

bedrock of Navajo Sandstone and distribute sand as a thin veneer of white quartz sand over 

red old dune (QTd) and old eolian sand sheet and dune (QTes) deposits. Support moderate 

growth of grass and high desert shrubs that stabilize extensive sand sheet and dune deposits 

on Moenkopi Plateau. About 1 to 61 m (3 to 200 ft) thick

Qps Ponded sediments (Holocene and Pleistocene(?))—Gray or brown clay, silt, sand, and some 

lenses of gravel; partly consolidated by calcite and or gypsum cement. Locally include small 

chert and limestone fragments or pebbles. Similar to flood-plain (Qf) deposits but occupy 

man-made drainage depressions or natural internal drainage depressions caused by sinkhole 

development, and most commonly caused by sand dune blockages. Larger internal drainage basins, such as Dog Knobs Lake and Babbitt Lake, or smaller sinkhole depressions are 

common in west half of map area. Eolian blowout depressions, common in dune sand and 

sand sheet (Qd) deposits on Ward Terrace and below Red Rock Cliffs northeast of Little 

Colorado River area, and in old eolian sand sheet and dune (QTes) deposits on Moenkopi 

Plateau, accumulate temporary ponded sediments due to temporary sand-formed dams, 

many of which are too small to show at map scale. Desiccation cracks often develop in 

dry conditions on hardpan surfaces of larger accumulations that often restrict plant growth 

because of excessive clay content. Northeast and east of Little Colorado River and on Moenkopi Plateau, sandy ponded areas do support growths of seasonal grass and often develop a 

parabolic dune complex downwind (northeast) of sediment area. About 1.5 to 9 m (5 to 30 

ft) thick

Qae Young mixed alluvium and eolian deposits (Holocene and Pleistocene(?))—Gray, light-red, 

and brown clay, silt, and fine- to coarse-grained sand interbedded with lenses of pebbly 

gravel. Include white angular chert fragments locally derived from Permian strata on 

Coconino Plateau and Gray Mountain area; white, gray, brown, and red chert fragments 

derived from Owl Rock Member of the Chinle Formation east of the Little Colorado River in 

the Ward Terrace area, and chert fragments derived from the Navajo Sandstone on Moenkopi 

Plateau. Deposits have accumulated by combinations of alluvial or eolian processes resulting in an interbedded sequence of thin-bedded, mixed mud, silt, sand, and gravel deposits. 

Deposit subject to sheetwash erosion during wet conditions and wind-blown sand accumulations during dry conditions. Commonly accumulate on broad flatlands or gently sloping 

alluvial fans downwind (northeast) of local drainage valleys. Often overlapped by dune sand 

and sand sheet (Qd) deposits. Support light to moderate growth of grass, cactus, and high 

desert shrubs. About 1 to 12 m (3 to 40 ft) thick

Qgy Young terrace-gravel deposits (Holocene and Pleistocene)—Light-brown, pale-red, and gray, 

poorly sorted fluvial mud, silt, sand, gravel, pebbles, cobbles, and boulders. Composed 

primarily of subangular to well-rounded Paleozoic sandstone, limestone, and chert clasts 

of local origin. Include well-rounded clasts of quartzite, quartz, and assorted metamorphic 

crystalline rocks derived from terrains far south of the map area. Include well-rounded 

volcanic rocks that originate from the San Francisco Volcanic Field and may include some 
15

quartzite and chert clasts derived from the Shinarump Member of the Chinle Formation. 

Include flood-plain (Qf) deposits and various terrace-gravel deposits in narrow canyon drainages too small to show at map scale. Clasts are partly consolidated by matrix of mud and 

sand cemented with calcium and gypsum. Form terraced benches about 1 to 12 m (3 to 40 ft) 

above stream-channel (Qs) deposits. Deposits are mixed with landslide, talus, and rock fall 

(Qtr) deposits in Little Colorado River Gorge. Unit fills erosion channels cut into bedrock, 

young alluvial fan (Qay), and flood-plain (Qf) deposits. Support moderate growth of local 

high-desert shrubs, sagebrush, and grass. About 1 to 12 m (3 to 40 ft) thick

Qay Young alluvial fan deposits (Holocene and Pleistocene)—Grayish-brown silt, sand, gravel, and 

some boulders. Pebbles, cobbles and boulders are subangular to rounded clasts of limestone, 

chert, and sandstone derived from local Paleozoic and Mesozoic strata of the Moenkopi and 

Kaibab Formations. Include medium- to coarse-grained sand and scattered well-rounded 

pebbles of quartzite and quartz and subrounded clasts and fragments of basalt derived from 

the San Francisco Volcanic Field. Unit is partly consolidated by silt, gypsum, and calcite and 

partly overlapped by ponded sediments (Qps), flood-plain (Qf), dune sand and sand sheet 

(Qd) deposits. Intertongue with upper part of valley alluvial (Qv), stream-channel (Qs), 

and young terrace-gravel (Qgy) deposits. Surfaces are partly eroded and cut by arroyo erosion. Surface has thin calcrete soil development that forms a sandy surface mixed with large 

cobbles and boulders of basalt near the Dog Knobs area of the San Francisco Volcanic Field. 

Extensively eroded and cut by arroyos in lowland areas northeast and east of Little Colorado 

River. Include coarse gravel, subangular to rounded pebbles and cobbles of limestone, chert, 

and sandstone derived from local Paleozoic and Mesozoic outcrops on Coconino Plateau. 

Subject to extensive sheetwash erosion and flash flood debris flows. Support moderate 

growths of sagebrush, cactus, and grass. About 1 to 12 m (3 to 40 ft) thick

Qec Eolian cinder deposits (Holocene and Pleistocene)—Black, gray, and red, coarse-grained fragments of angular to subangular, glassy, basaltic and andesitic cinders and scoria. Material is 

derived from nearby pyroclastic volcanic centers; airborne ash and cinders were deposited 

within a few miles of local volcanic eruptions in the San Francisco Volcanic Field in south 

part of map area, and from eruptions south and southwest edge of map area. Pyroclastic 

fragments are commonly vesicular ash fall deposits that have been transported by southwesterly winds and that have accumulated against or downslope of local topographic obstructions 

such as basalt flows, steep-walled drainages, rock ledges, and local fault scarps, especially in 

Wupatki National Monument area. Form extensive cover of eolian cinder sheet deposits over 

all terrain in south-central part of map area; many deposits too thin to show at map scale. 

Cinder fragments become smaller and more subrounded farther downwind (northeast) of 

eruptive centers. About 1.5 to 12 m (5 to 40 ft) thick

Qtr Talus and rock fall deposits (Holocene and Pleistocene)—Along Adeii Eechii Cliffs area; 

red to yellow, silt and sand mixed with angular rocks and boulders of light-red sandstone 

and dark-red siltstone; partly cemented by calcite. Form talus debris slopes in steep-walled 

canyons and lower slopes of Adeii Eechii Cliffs; often associated with, adjacent to, or below 

landslide (Ql) deposits. In Little Colorado River Gorge and Gray Mountain area; gray 

to yellow silt, sand, gravel mixed with small to large angular rocks and boulders of gray 

limestone, white chert, and white to tan sandstone derived from the Kaibab and Toroweap 

Formations and Coconino Sandstone; partly cemented by calcite and gypsum. Form talus 

debris cover on slopes below landslide (Ql) deposits. Unit often grades down slope into 

young alluvial fan (Qay) deposits or young terrace-gravel (Qgy) deposits. About 1.5 to 14 m 

(5 to 45 ft) thick

Ql Landslide deposits (Holocene and Pleistocene)—Landslides are unconsolidated to partly 

consolidated masses of unsorted rock debris. At northeast base of Gray Mountain, includes 

a horizontally bedded gravity-glide mass of Kaibab Formation that overlies Triassic beds 

of the Shinarump Member of the Chinle Formation. Include detached stratified blocks that 

rotated backward against parent outcrop and slid downslope as loose incoherent masses of 

broken rock fragments and deformed strata; often form talus and rock fall (Qtr) deposits 

adjacent to and below landslide masses on Gray Mountain, Little Colorado River Gorge, 

and Black Point areas. Some landslide blocks below edges of basalt flows at Black Point are 

unstable during wet conditions (fig. 1 on map). Landslide masses at Black Point are commonly associated with soft siltstone and claystone strata of Petrified Forest Member of the 

Chinle Formation. Include individual car- and house-size basalt boulders near base of Gray 
16

Mountain and in Little Colorado River Gorge. Clasts are mostly angular and unsorted; partly 

cemented by calcium. Gradational and arbitrary contact with young alluvial fan (Qay), 

flood-plain (Qf), young terrace-gravel (Qgy), and valley alluvial (Qv) deposits. Subject to 

extensive sheetwash erosion, flash-flood debris flows, and arroyo erosion. About 3 to 61 m 

(10 to 200 ft) thick

Qv Valley-fill deposits (Holocene and Pleistocene)—Gray and light-brown silt, sand, and lenses of 

gravel; partly consolidated by gypsum and calcite cement west and southwest of Little Colorado River; unconsolidated east and northeast of Little Colorado River. Include occasional 

rounded clasts of limestone, subrounded to angular chert, and subrounded to angular basalt 

southwest of Little Colorado River. Intertongue or overlap young alluvial fan (Qay) deposits and young terrace-gravel (Qgy) deposits. Commonly reflect low energy, low-gradient, 

shallow drainages. Subject to sheetwash flooding and temporary ponding due to vegetation 

growths of grass at lower elevations in central area of map, and sagebrush, grass, cactus, and 

some juniper trees at higher elevations above 1,830 m (6,000 ft) in west half of map area. 

About 1 to 9 m (3 to 30 ft) thick

QTd Old dune deposits, undivided (Pleistocene and Pliocene(?))—White, light-red to light-brown, 

coarse- to very fine-grained sand and silt; partly consolidated beneath veneer of active, 

reworked sand cover. Form base or internal cores of younger, reactivated linear dunes 

immediately downwind (northeast) of Adeii Eechii Cliffs (shown as active linear dunes by 

Billingsley, 1987a), on Moenkopi Plateau, Appaloosa Ridge, and Coal Mine Mesa. Contain 

at least 25% to 35% gray, fine-grained silt and clay content on Coal Mine Mesa from erosion 

of underlying Dakota Sandstone (Kd) and Mancos Shale (Km). Unit often forms complex 

linking sets of parabolic dunes along edge of Adeii Eechii Cliffs and Appaloosa Ridge of 

Moenkopi Plateau. Several individual dunes on Moenkopi Plateau have developed downwind of ponded sediments and are younger than adjacent old eolian sand sheet and dune 

(QTes) deposits. Bedrock or ponded sediments (Qps) are often exposed within interior of 

parabolic dunes. Include combinations of parabolic, barchan, dome, and dune-like thick sand 

sheet deposits that frequently coalesce downwind (northeast) to form old linear dunes (old 

dune deposits, undivided [QTd]) or old eolian sand sheet and dune (QTes) deposits northeast of Adeii Eechii Cliffs on Moenkopi Plateau. Linear dune traces are often longer than 

3 km (2 mi) and as long as 10 km (6 mi). Some linear dunes merge with other linear dunes 

and form a linear complex of parabolic or barchanoid dune trains within a short length of 

linear dune (not shown). Include topographically controlled climbing or falling dunes and 

short linear dunes below Appaloosa Ridge. Unit commonly stabilized by moderate growth 

of grass and mormon tea bush. Gradational and approximate contact with adjacent surficial 

deposits. About 2 to 12 m (6 to 40 ft) thick

QTes Old eolian sand sheet and dune deposits (Pleistocene and Pliocene(?))—Light-red to lightbrown, very fine-grained to medium-grained sand and silt. Form widespread deposits on 

Moenkopi Plateau that merges with old dune (QTd) and old mixed alluvium and eolian 

(QTae) deposits. Contacts with other map units are gradational and arbitrary based on morphologic characteristics observed on 1968 aerial photographs. Unit is overlapped by young 

mixed alluvium and eolian (Qae), stream-channel (Qs), and young alluvial fan (Qay) 

deposits below Appaloosa Ridge (southwest of ridge) and at Little Hollow Place, northeast 

corner of map area. Below Appaloosa Ridge, on Coal Mine Mesa, and at Little Hollow 

Place unit contains abundant gray clay and silt derived from underlying Dakota Sandstone 

(Kd) and Mancos Shale (Km). Unit is stabilized by thick growth of grass and mormon tea 

brush. Deposits cover Jurassic and Cretaceous bedrock and form protective cover against 

wind deflation of bedrock; where not covered, bedrock units are extensively eroded by wind 

deflation, especially along Adeii Eechii Cliffs. Unit is locally disturbed at stock tanks and 

windmill watering holes for livestock where fresh sand is actively forming new sand sheet 

and dune deposits (not mapped). About 1 to 3.6 m (3 to 12 ft) thick

QTae Old mixed alluvium and eolian deposits (Pleistocene and Pliocene(?))—Lithologically similar 

to young mixed alluvium and eolian (Qae) deposits but often capped or covered by poorly 

sorted sand, gravel, and small cobbles and boulders consolidated by calcrete soil development. Form flat mesa-like benches about 9 to 36.5 m (30 to 120 ft) above surrounding 

plateau surfaces along east-central edge of map area. About 3 to 6 m (10 to 20 ft) thick

QTg4 Older terrace-gravel deposits (Pleistocene and Pliocene(?))—Gray and light-brown silt, sand, 

gravel, cobbles, and boulders up to 30 cm (1 ft) in diameter along Tappan Wash southwest of 
17

Cameron; consists mostly of sand and gravel material derived from the Kaibab and Moenkopi Formations. Includes some volcanic clasts from the San Francisco Volcanic Field that 

may be older than 1 million years. Form terrace benches or ridges about 9 to 14 m (30 to 45 

ft) above Tappan Wash where Tappan Wash meanders over soft strata of lower Moenkopi 

Formation.

Form terrace benches about 45 to 60 m (150 and 200 ft) above modern Little Colorado 

River between Cameron, Arizona, and Black Point. Unit is extensively eroded and stratigraphically below oldest terrace-gravel (QTg5) deposits. Unit forms Baah Lokaa Ridge 

east of and lower than Black Point and an unnamed ridge northeast of Little Colorado River 

below Ward Terrace that fills 3 km (2 mi) wide old Little Colorado River channel with sandy 

gravely sediment as much as 30.5 m (100 ft) thick. Include calcrete soil horizon in upper 1 

m (3 ft) of unit. Supports light vegetation cover, mostly grass and small desert shrubs. Unit is 

extensively eroded and gullied. About 3 to 55 m (10 to 180 ft) thick

QTa Older alluvial fan deposits (Pleistocene and Pliocene)—Gray and light-brown clay, silt, sand, 

and gravel, poorly sorted, partly consolidated by calcrete soil in top 1 m (3 ft). Material is 

mostly reworked older terrace-gravel (QTg4) deposits and erosional debris from Petrified 

Forest Member (^cp) and Owl Rock Member (^co) of the Chinle Formation, southeast 

quarter of map area. Contain angular fragments of petrified wood and well-rounded quartzite 

and chert pebbles in fluvial and eolian sandy matrix. Form stabilized cover over remaining older terrace-gravel deposits (QTg4). Unit has a gentle surface gradient toward Little 

Colorado River and is extensively eroded. Support moderate cover of grasses and low desert 

shrubs. About 1 to 4.5 m (3 to 15 ft) thick

QTg5 Oldest terrace-gravel deposits (Pliocene and Miocene)—Gray to light-brown silt, sand, gravel, 

pebbles and cobbles. Contain well rounded pebbles and cobbles of gray limestone and chert 

derived from Kaibab Formation, red sandstone clasts derived from Moenkopi Formation, 

and dominated by quartzite and a few granite and metamorphic clasts derived from older 

gravel deposits of the Mogollon Rim southeast of the map area. Unit is 79 m (260 ft) above 

present Little Colorado River at Cameron, Arizona, (elevation 1,341 m [4,400 ft]). Unit may, 

in part, be equivalent to old stream-channel (Ts) deposits at Black Point because the Little 

Colorado River gradient between these high level gravels is 3 m/km (9 ft/mi), comparable to 

the modern day Little Colorado River gradient between Cameron and Black Point. About 2 

to 4.5 m (6 to 15 ft) thick

VOLCANIC ROCKS

[See table 1 for ages of volcanic rocks in the map area.]

Volcanic rocks of the San Francisco Volcanic Field (Pleistocene, Pliocene, and Miocene) are mapped 

and defined by Moore and Wolfe (1976), Ulrich and Bailey (1987), and Wolfe and others (1987). For 

a complete history of magnetic polarity determinations, Brunhes, Matuyama, Gauss, and Gilbert age 

assignments, analytical data, and classification of basalt types in this map area, see Ulrich and Bailey 

(1987).

Volcanic rocks of the San Francisco Volcanic Field (Pleistocene, Pliocene, and Miocene)

Qmcb Basalt flow of Merriam Crater (Pleistocene; Brunhes age)—Dark-gray alkali olivine basalt. 

Contains scattered phenocrysts of olivine, clinopyroxene, and rare plagioclase in groundmass of the same minerals plus opaque oxides. Basalt flow originated from Merriam Crater 

17.5 km (11 mi) southeast of the southeast corner of map area and flowed north to a small 

60 m (200 ft) deep canyon of the Little Colorado River and formed a lava dam across the 

canyon. The lava dam diverted the Little Colorado River stream flow around the north side 

of the basalt flow and back into 60 m (200 ft) deep canyon downstream of the lava dam that 

forms Grand Falls (8 km [5 mi]) southeast of map area (Moore and Wolfe, 1976, 1987). 

Basalt of Merriam Crater flowed downstream of Grand Falls in the Little Colorado River 

channel into the map area east of Wupatki National Monument. The river overflows the 

basalt flow and forms rapids known as Black Falls (fig. 1). Downstream of Black Falls, the 

Little Colorado River flows adjacent to basalt flow, but most of the basalt flow spread out 

onto abandoned stream-channel (Qs) and low flood-plain (Qf) deposits and terminates just 

south of Black Point. Optical-luminescence age, 19.6±1.2 ka (Duffield and others, 2004). 

About 2 to 4 m (6 to 13 ft) thick 
18

Qyap Pyroclastic deposits of S P Mountain (Pleistocene; Brunhes age)—Dark-gray to reddishgray basaltic andesite. Contain phenocrysts of clinopyroxene, olivine, and intensely corroded plagioclase in hypocrystalline groundmass of the same minerals, plus opaque oxide 

and glass. Same composition as basaltic andesite flow (Qyab), but less crystalline. Contains 

abundant large volcanic bombs that help form sharp rims of uneroded crest of cone (Hodges, 

1962; Ulrich and Bailey, 1987). Pyroclastic cone partially overlies older cone on west side 

and has a circular plan view; forms 287-m- (940-ft-) high cone with 60-m- (200-ft-) deep 

interior crater. About 287 m (940 ft) thick

Qyab Basaltic andesite flow of S P Mountain (Pleistocene; Brunhes age)—Dark-gray basaltic 

andesite. Flow is more crystalline than associated basaltic pyroclastic deposits of S P Mountain (Qyap). Flow has rough blocky surface and steep flow fronts. Basalt flowed northward 

about 6.5 km (4 mi) over Harrisburg Member of the Kaibab Formation and into local graben 

structures (fig. 4 on map). K-Ar age determined by Baksi (1974) is 0.071±0.004 Ma (Ulrich 

and Bailey, 1987). About 6 to 40 m (20 to 130 ft) thick

Qyp Pyroclastic deposits of five young cinder cones (Pleistocene; Brunhes age)—Grayish-black 

porphyritic basalt with abundant 1- to 3-mm phenocrysts of corroded tabular plagioclase, 

scattered olivine, and sparse clinopyroxene in a hyalophitic groundmass. Forms five young 

cinder cones overlying older cinder cones; 200 to 800 m (200 to 2,625 ft) in diameter and 25 

to 165 m (80 to 540 ft) high at south-central edge of map area. Thickness, 25 to 165 m (80 to 

540 ft)

Qyb Basalt flow of five young cinder cones (Pleistocene; Brunhes age)—Grayish-black porphyritic basalt flow with same composition as pyroclastic deposits of five young cinder cones 

(Qyp). Consists of one small flow 700 m (2,297 ft) long and 400 m (1,315 ft) wide. About 5 

to 10 m (16 to 33 ft) thick

Shadow Mountain is an isolated pyroclastic cone with associated basalt flows about 19 km (12 mi) northwest of Cameron, Arizona (fig. 1). These volcanic rocks are chemically and petrographically similar to 

rocks of the San Francisco Volcanic Field and represent the northern-most volcano of the field. The polarity 

of these rocks has not been determined. K-Ar age, 0.649±0.23 Ma (Damon and others, 1974; Condit, 1974).

Qsp Pyroclastic deposits of Shadow Mountain (Pleistocene)—Black and red scoria, cinder, and 

ash deposits of olivine-labradorite basaltic composition. Deposits overlie associated basalt 

flows and strata of Petrified Forest and Shinarump Members of the Chinle Formation. About 

183 m (600 ft) thick

Qsb Basalt flows of Shadow Mountain (Pleistocene)—Black olivine-labradorite basalt flows that 

are largely covered by associated pyroclastic (Qsp) deposits. Basalts flowed into one small 

graben north of main cone making that graben older than the basalt flow. The basalt was 

down-faulted into another graben 0.8 km (1⁄2 mi) east of the main cone suggesting this graben 

developed after the eruption (within the last half million years). This graben is aligned with 

the southwest-northeast strike of Mesa Butte Fault southwest of Shadow Mountain and is 

likely a northern extension of that structural trend. About 3 to 14 m (10 to 45 ft) thick

Qp Pyroclastic deposits (Pleistocene; Brunhes age)—Dark-gray, black, and reddish-brown indurated and oxidized pyroclastic deposits. Include ribbon and tear-shaped volcanic bombs in 

welded tuffaceous scoria and cinder deposits. Contains microscopic crystals of clinopyroxene, olivine, plagioclase, abundant clasts of vesicular basalt with dark-gray or reddish-brown 

glassy matrix, and occasional sedimentary xenoliths. Includes several eruptive vents that 

built pyroclastic or splatter cones on associated basalt flows. About 5 to 260 m (15 to 850 ft) 

thick

Qb Basalt flows (Pleistocene; Brunhes age)—Dark-gray and black porphyritic and aphyric, 

clinopyroxene-olivine and alkali-olivine basalt. Flows occur locally within present stream 

drainages, are moderately young in appearance, are locally covered by thin alluvium, eolian 

sand, or air-borne cinder deposits and have been little dissected. K-Ar age of various flows 

are 0.22±0.05 Ma, 0.46±0.05 Ma, 0.66±0.11 Ma, 0.74±0.08 Ma, and 0.77±0.04 Ma (Ulrich 

and Bailey, 1987). About 1 to 20 m (3 to 65 ft) thick

Qbt Basalt flow of Tappan Wash (Pleistocene; Brunhes age)—Dark-gray and black, dense, 

aphyric, clinopyroxene-olivine and alkali-olivine basalt. Conspicuously rich in black glassy 

plagioclase groundmass. Flow originated from Crater Lake volcano (N4536 of Wolfe and 

others, 1987); a vent 9.5 km (6 mi) south of the map area on the east side of Kendrick 

Mountain and flowed down various tributary drainages to Tappan Wash, then down Tappan 
19

Wash to the Little Colorado River, a distance of 88 km (55 mi); then down Little Colorado 

River another 11 km (7 mi) to the beginning of the Little Colorado River Gorge (see fig. 

2 on map). Geomorphology of basalt flow of Tappan Wash is described by Rice (1977) as 

the Tappan Lava Flow and mapped by Ulrich and Bailey, (1987). K-Ar age, 0.53±0.19 Ma 

(Damon and others, 1974). The flow averages about 2 m (6 ft) thick for much of its length 

and accumulated to as much as 40 m (130 ft) in the Little Colorado River where it forms an 

inverted valley within Little Colorado drainage (fig. 2 on map). Basalt flow is cut by several 

faults that form grabens north of S P Mountain and at Little Colorado River; fault offset 

generally less than about 1.5 m (5 ft). About 1 to 40 m (3 to 130 ft) thick

Qbf Fissure deposits of Lockett Tank (Pleistocene; Brunhes age)—Dark-gray to black linear 

extrusion of aphyric basalt along fault at Lockett Tank about 14 km (9 mi) north of S P 

Mountain. About 3 to 6 m (10 to 20 ft) thick

Qbmp Pyroclastic deposits (Pleistocene; Brunhes or Matuyama age)—Dark-gray to red pyroclastic cones and small rounded spatter cones on basalt flows (Qbmb). Weathers yellowish 

brown and reddish brown. Largest deposit forms Red Mountain (fig. 1). Unit is superficially 

gullied; consists of bedded cinders, agglutinated spatter with volcanic ribbon and tearshaped bombs. About 60 to 292 m (200 to 960 ft) thick

Qbmb Basalt flows (Pleistocene; Brunhes or Matuyama age)—Dark-gray to black aphyric alkali 

basalt composed of plagioclase, clinopyroxene, olivine, and magnetite. Weathers yellowish 

brown to reddish brown. Surface of flows are relatively smooth, flat and undissected. About 

10 to 60 m (30 to 200 ft) thick

Qsfp Pumice of San Francisco Mountain (Pleistocene; Matuyama age)—White to light-gray, 

poorly sorted, mantle bedding of rhyolite pumice fall. Unit is matrix free except for locally 

reworked zone in upper 1 m (3 ft). Lapilli range from several millimeters to several centimeters in size, are colorless vesicular glass, and lack visible crystals. Contains xenoliths 

of greenschist and blueish-gray dense rhyolite with feldspar and quartz phenocrysts. Unit 

overlies older basalt flows (Qmb) near US Highway 89 at south-central edge of map along 

Deadman Wash and is correlated with lower aphyric pumice deposits on San Francisco 

Mountain (Dennis, 1981) south of map area because of similarities in petrography, composition, and xenoliths. Fission-track age on zircons is 0.80±0.11 Ma (C.W. Naeser and G.A. 

Izett, in Ulrich and Bailey, 1987). About 3 to 5 m (10 to 15 ft) thick

Qmbi Basalt dike (Pleistocene; Matuyama age)—Dark-gray to black plagioclase-aphyric basalt 

with abundant 1- to 3-cm plagioclase laths in groundmass of olivine, clinopyroxene, plagioclase, and magnetite. Contains baked xenoliths of sandstone of the Moenkopi Formation 

(Ulrich and Bailey, 1987). Includes three dikes just east of US Highway 89 about 16 km (10 

mi) north of south-central edge of map area. Dike widths, 0.3 to 0.5 m (1 to 1.5 ft)

Qmp Pyroclastic deposits (Pleistocene; Matuyama age)—Dark-gray to reddish-brown plagioclase-aphyric and porphyritic basalt. Consist of intergranular groundmass of plagioclase, 

clinopyroxene, olivine, and magnetite. Contain scattered olivine and clinopyroxene phenocrysts. Include several cones of Mesa Butte volcano that are aligned with and overlie 

Mesa Butte Fault (fig. 1). Cones are in early stage of erosion, slightly eroded and gullied. 

About 25 to 230 m (80 to 750 ft) thick

Qmb Basalt flows (Pleistocene; Matuyama age)—Dark-gray plagioclase-aphyric and porphyritic 

basalt of similar composition to pyroclastic (Qmp) deposits. Weather yellow or brown. Surfaces are weathered and slightly eroded and gullied. K-Ar age of various flows, 0.83±0.04 

Ma, 1.04±0.04 Ma, 1.09±0.03 Ma, 1.20±0.05 Ma, and 1.38±1.01 Ma (Ulrich and Bailey, 

1987; Wolfe and others, 1987). Flows generally follow older drainage areas that are above 

present drainages. About 5 to 45 m (15 to 159 ft) thick

Qmlp Basalt flow of Lava Point (Pleistocene; Matuyama age)—Dark-gray to black plagioclaseaphyric basalt. Similar composition to (Qmb) basalt flows. Mapped as Lava Point flow 

(Qmb) by Ulrich and Bailey (1987) east of U.S Highway 89 but not mapped separately from 

other basalt flows of similar composition and age. Mapped herein as separate unit because 

unit forms an inverted valley for several kilometers north of an unknown source in south part 

of map area that is similar to an inverted valley formed by adjacent Black Point Basalt flow 

(Tbpb). K-Ar age, 1.01±0.13 Ma (Ulrich and Bailey, 1987). About 6 to 15 m (20 to 50 ft) 

thick

Qslr Rhyolite dome complex of Slate Mountain (Pleistocene; Matuyama age)—Light-gray 

aphanitic rhyolite. Rare microphenocrysts of pale-brown amphibole, biotite, and altered 
20

fayalite(?) occur in a felsic cryptocrystalline groundmass (Wolfe and others, 1987). Unit 

forms the north flank of a 1.5 km (1 mi) diameter cluster of domes that form Slate Mountain; 

summit of Slate Mountain is south of map area. Uplifted sedimentary rocks of Lower Permian age are exposed adjacent to east and south edge of rhyolite just south of map boundary. 

K-Ar age, 1.54±0.02 Ma (Wolfe and others, 1987). About 92 m (300 ft) thick

Qwb Basalt flows of Woodhouse Mesa (Pleistocene; Matuyama age)—Dark-gray alkali olivine 

basalt and minor alkali-rich-alumina basalt. Contain phenocrysts of olivine, clinopyroxene, 

and plagioclase in fine- to medium-grained matrix of same minerals. Contain minor gabbro 

xenoliths. K-Ar age, 0.786±0.14 Ma (Ulrich and Bailey, 1987), and south of map area 

0.874±0.13 Ma; 0.897±0.14 Ma; 0.812±0.059 Ma (Reynolds and others, 1986; Damon and 

others, 1974). About 2 to 15 m (6 to 50 ft) thick

QTi Intrusive dike or plug (Pleistocene or Pliocene; Matuyama age)—Dark-gray aphyric basalt 

and microporphyritic olivine basalt. Includes pyroclastic fragments. Source for pyroclastic 

cones (QTp) and basalt flows (QTb); Dog Knobs, southwest quarter of map area. Widths, 

1.5 to 4.5 m (5 to 15 ft)

QTp Pyroclastic deposits (Pleistocene or Pliocene; Matuyama age)—Dark-gray to red cinders, 

agglutinated spatter, bomb and ribbon fragments; yellowish brown to reddish brown where 

weathered. Form several rounded, little dissected, superficially gullied pyroclastic cones of 

Dog Knobs area, southwest quarter of map area. About 60 to 120 m (200 to 400 ft) thick

QTb Basalt flows (Pleistocene or Pliocene; Matuyama age)—Dark-gray, yellowish-brown to 

brown, aphyric and slightly porphyritic basalt and microporphyritic olivine basalt; surfaces 

mostly smooth, relatively flat, undissected. Includes thin, interbedded pyroclastic deposits 

near pyroclastic cones of Dog Knobs area. Unit is thickest near flow margins in some areas. 

Thickness ranges from about 10 to 60 m (30 to 200 ft)

QTap Basalt and andesite pyroclastic deposits (Pleistocene or Pliocene; Matuyama age)—Darkgray, glassy, basaltic andesite. Weather yellowish brown to brown, locally gullied. Cones 

composed of cinders, scoria, and spatter, southwest corner of map area. About 25 to 122 m 

(80 to 400 ft) thick

QTab Basalt and andesite flows (Pleistocene or Pliocene; Matuyama age)—Dark-gray basaltic andesite; partly blocky, hummocky surfaces, locally gullied. Weather yellowish brown 

to brown. Contain abundant phenocrysts of clinopyroxene and plagioclase, subordinate 

phenocrysts of orthopyroxene, sparse phenocrysts of olivine and hornblende and scattered 

rounded quarts grains with clinopyroxene reaction rims. Groundmass is mostly fine-grained 

or glassy and contains plagioclase microlites, opaque oxide, and small crystals of clinopyroxene and orthopyroxene. About 18 to 67 m (60 to 220 ft) thick

Tbi Dike in amphitheater (Pliocene; Gauss or Gilbert age)—Dark-gray plagioclase-phyric 

basalt and mixed pyroclastic dikes and necks. Composed of plagioclase, clinopyroxene, 

olivine, and opaque oxides. Crystal-rich basalt; occurs in 2.7 km (1.5 mi) wide basalt- and 

tuff-rimmed depression informally named the “Amphitheater” by Ulrich and Bailey (1987), 

10 km (6 mi) east of U.S. Highway 89 and about 8 km (5 mi) northeast of S P Mountain. 

Dike is 2 to 6 m (4 to 20 ft) wide and 5 to 10 m (15 to 33 ft) in height. K-Ar age, 3.13±0.39 

Ma (Ulrich and Bailey, 1987). Coarse pyroclastic debris is scattered on surrounding surface 

of Wupatki Member of the Moenkopi Formation. Thickness, 5 to 10 m (15 to 33 ft)

Tp Pyroclastic deposits (Pliocene; Gauss or Gilbert age)—Dark-gray to red cinder and spatter 

fragments; weathers yellowish brown, brown, or reddish brown. Composed of clinopyroxene and olivine phenocrysts, plagioclase, opaque oxides, and glass; partly decomposed and 

weathers light red. Mass wasting has diminished slope angles of pyroclastic cones; flanks 

are gullied to extensively eroded. Cones are elongated and aligned along a northwest trend 

north in Dog Knobs area indicating the influence of bedrock faults, fractures, and joints on 

vent positions and orientation. About 1.5 to 12 m (5 to 40 ft) thick

Tb Basalt flows (Pliocene; Gauss or Gilbert age)—Medium- to dark-gray plagioclase-phyric, 

aphyric, and slightly porphyritic basalt. Smooth surfaced, partly dissected north of Dog 

Knobs area and about 10 km (6 mi) northeast of S P Mountain. Composed of plagioclase, 

clinopyroxene, olivine, and opaque oxides. Less than 30 m (90 ft) thick

Tbpb Black Point Basalt flows (Pliocene)—Dark-gray to black plagioclase-aphyric basalt; surface 

weathers smooth and locally dissected. Contain scattered to abundant tabular plagioclase 

phenocrysts as large as 1 cm in diameter and includes abundant olivine microphenocrysts 

in feldspathic groundmass with intergranular to ophitic intergrowth of brown pyroxene and 
21

plagioclase. K-Ar age, 2.43±0.32 Ma (Ulrich and Bailey, 1987). Basalt flows form two lobes 

in map area; one extends northeast from south-central edge of map area for 26 km (16 mi) 

to the Little Colorado River, and the other lobe extends east-northeastward from Wupatki 

National Monument for 14 km (8.5 mi) referred to as the Citadel flow by Cooley (1962), 

but is mapped as the Black Point basalt flows (Ulrich and Bailey, 1987) because both lobes 

emerge from a single flow southwest of Wupatki National Monument. Basalt flows average about 12 m (40 ft) thick at Black Point where basalt filled a low-relief channel of Little 

Colorado River 1.5 km (1 mi) wide and extended down river about 5 km (3 mi). About 6 to 

40 m (20 to 132 ft) thick

Tocb Basalt flow of Cedar Ranch Mesa (Miocene)—Dark-gray, massive, olivine-phyric basalt; 

weathers brown and has a smooth surface. Contains abundant 1- to 3-mm subhedral to euhedral olivine phenocrysts rimmed with iddingsite in a distinctive holcrystalline groundmass of 

intergranular to subophitic clinopyroxene and plagioclase. K-Ar age, 5.62±0.19 Ma (Ulrich 

and Bailey, 1987). Unit overlies Petrified Forest Member of the Chinle Formation and is 

susceptible to landslide mass wasting along northern edges of flow near Cedar Ranch. Partly 

buried by younger basalt flow (Qb). About 20 to 32 m (65 to 110 ft) thick

SEDIMENTARY ROCKS

Ts Oldest stream-channel deposits (Pliocene(?) and Miocene)—Black Point area: Light-red, gray, 

and brown interbedded siltstone, sandstone, arkosic gravel, and lenticular conglomerate. 

Sediments are well sorted and consolidated beneath the Black Point Basalt flows (Tbpb) at 

Black Point, center of map area. Unconsolidated gravel sediments form rounded hill of Little 

Colorado River terrace and tributary alluvial fan deposit surrounded by the Black Point 

Basalt flows at Black Point. The Black Point Basalt (Tbpb) flowed northeast and east from 

the San Francisco Volcanic Field area down tributary drainage eroded into the lower half of 

the Moenkopi Formation to the Little Colorado River and flowed onto and around a stream 

delta or river terrace deposit and onto floodplain and channel of the Little Colorado River 

(fig. 1 on map). Basalt flowed a short distance upstream (south) and across river floodplain 

(east) about 1.5 km (1 mi) and downstream (north) about 3.5 km (2 mi); 2.43±0.51 Ma 

(Damon and others, 1974). Unit is the oldest Little Colorado terrace-gravel deposit in the 

map area. Base of deposit is 174 m (570 ft) above present Little Colorado River bed at Black 

Point at elevation 1,463 m (4,800 ft). The 207 m (680 ft) river down cutting estimate by 

Billingsley (1987b) from top the Black Point Basalt flow, not base of map unit. Similar and 

unconsolidated deposits cover floor of ancient meander channel of Little Colorado River 

superimposed and eroded into Harrisburg Member of the Kaibab Formation on Black Point 

Monocline about 1.5 km (1mi) south of Black Point; 174 m (570 ft) above present Little 

Colorado River. Sediments in small channel are mostly covered by quartzite lag gravel as is 

small terrace or alluvial fan hill surrounded by the Black Point Basalt flow. Conglomerate 

consists primarily of well-rounded quartzite, chert, and minor clasts of granite and metamorphic rocks derived from older gravel deposits of the Mogollon Rim southeast of the map 

area; and local gray limestone clasts derived from Kaibab Formation; and red sandstone 

derived from Moenkopi Formation.

East of Gray Mountain area: Light-gray to reddish-gray silt, sand, gravel, pebbles, 

cobbles, and small boulder detritus derived from erosion of local Kaibab and Moenkopi 

Formation outcrops; unsorted and partly consolidated. Clasts of gray limestone, white chert, 

red sandstone, and grayish-black basalt are subrounded to well rounded; pebble imbrications 

indicating a general flow from southwest to northeast. Meander loops are superimposed into 

Harrisburg Member of the Kaibab Formation south of Gray Mountain prominence. Includes 

some well rounded basalt clasts from San Francisco Volcanic Field area that are likely older 

than basalt flow of Tappan Wash (Qbt) because the basalt of Tappan Wash is stratagraphically below most of the channel fill deposits. Fills old abandoned meander loops of an 

ancient tributary canyon drainage to the Little Colorado that meandered across the Kaibab 

and Moenkopi Formations, perhaps as old as Miocene age (Charles Barnes, oral commun., 

2005). About 3 to 18 m (10 to 60 ft) thick

Km Mancos Shale (Upper Cretaceous)—Bluish-gray to light-gray, thinly laminated to thin-bedded, 

slope-forming, carbonaceous claystone, siltstone, and mudstone with interbedded light-gray, 

fine- to medium-grained sandstone. Includes bentonitic claystone, siltstone, and some thinbedded limestone. Locally fossiliferous with cephalopod faunas that are laterally equiva-
22

lent to the Tropic Shale Formation in the lower part of the Mancos Shale in southern Utah. 

Sediments were deposited on shallow sea floor that transgressed westward from the midcontinent area. Gradational and arbitrary contact with underlying Dakota Sandstone (Kd). 

Sediments are mostly removed by Cenozoic erosion and largely covered by old eolian sand 

sheet and dune (QTes) deposits at Coal Mine Mesa on Moenkopi Plateau, northeast corner 

of map area. About 43 to 60 m (140 to 200 ft) thick

Kd Dakota Sandstone (Upper Cretaceous)—Medium- to light-gray, slope-forming, laminated to 

thin-bedded mudstone, siltstone, and sandstone. Locally includes the lower sandstone and 

middle carbonaceous members as defined by O’Sullivan and others (1972). The upper sandstone member is not present in the map area.

Lower sandstone member is light-orange to light-gray silty sandstone and conglomeratic sandstone in lower part. Unit is well cemented and forms a cliff that fills erosional 

channels as much as 6 m (20 ft) thick and locally pinches out laterally in short distances. 

Pebble clasts in conglomeratic sandstone lenses are composed of red and gray, well-rounded 

chert and quartzite typically less than 5 cm (2 in) in diameter. Unit unconformably overlies 

white sandstone beds of the Entrada Sandstone (Je). The regional unconformity between 

the Dakota Sandstone and underlying Jurassic-Cretaceous rocks has been established 

as an angular regional unconformity, based on the Dakota Sandstone overlying younger 

rocks north of the map area and overlying older rocks south and southeast of the map area. 

Although these relationships establish the angularity of the pre-Dakota Sandstone age 

unconformity, the angularity is so small that it is not apparent at most outcrops within the 

Navajo Country (Harshbarger and others, 1958).

Middle carbonaceous member is dark-grayish-brown, carbonaceous, flat-bedded 

mudstone, siltstone, coal, and interbedded brown, conglomeratic, crossbedded lenticular 

sandstone. Coal beds are generally less than 0.5 m (2 ft) thick and present only at east end 

of Coal Mine Mesa of map area. Coal was mined from thicker coal beds at the rim of Coal 

Mine Canyon just north of the northeast corner of map area. Gypsum is common constituent 

as thin stringers and as isolated crystals. Unit unconformably overlies the Entrada Sandstone 

in east part of Coal Mine Mesa where lower sandstone member is not present (J-2 unconformity of Pipiringos and O’Sullivan, 1978). Unit is mostly covered by extensive old dune 

deposits, undivided (QTd). Best exposures are southwest of Coal Mine Mesa at Appaloosa 

Ridge, northeast corner of map area. Overall thickness, about 3 to 12 m (10 to 40 ft)

Je Entrada Sandstone-Cow Springs Sandstone, undivided (Middle Jurassic)—Includes 

a lower interval of white, very fine-grained, trough crossbedded sandstone equivalent to 

Entrada Sandstone north of map area; a middle interval of interbedded red, flat-bedded siltstone and sandstone equivalent to Summerville Formation north of map area; and an upper 

interval of white, fine-grained crossbedded sandstone equivalent to Cow Springs Sandstone 

north of map area. The Summerville Formation and Cow Springs Sandstone are equivalent 

to the lower Morrison Formation farther north of map area at Black Mesa. Unit as a whole 

forms a cliff where protected by resistant conglomeratic, coarse-grained sandstone lenses 

of the overlying Dakota Sandstone. The Carmel Formation is 1.5- to 2-m- (5- to 7-ft-) thick 

lenses of red siltstone and sandstone near the base of the Entrada Sandstone at the west 

end of Appaloosa Ridge and is locally absent at the east end of Coal Mine Mesa; Carmel 

Formation is too thin to show at map scale. Entrada Sandstone-Cow Springs Sandstone, 

undivided, unconformably overlies the upper beveled surface of Navajo Sandstone known 

regionally as the J-2 unconformity; erosional relief is generally less than about 4.5 m (15 ft) 

but is as much as 9 m (30 ft). The unit as a whole thins from 60 m (200 ft) at the west end 

of Coal Mine Mesa and Appaloosa Ridge to less than 35 m (115 ft) at northeast corner of 

map area

GLEN CANYON GROUP

The Glen Canyon Group includes, in ascending order, the Jurassic Moenave Formation (Jm), the Kayenta 

Formation (Jk), the Kayenta Formation-Navajo Sandstone transition zone (Jkn), and the Navajo Sandstone (Jn). The Moenave Formation unconformably overlies the Triassic Chinle Formation. The boundary 

between the Triassic and Jurassic units is based on differences in lithology, topography, and color change. 

The purple and white mudstone, sandstone, and gray limestone of the Owl Rock Member of the Chinle 

Formation (^co) is overlain by the red mudstone, siltstone, and sandstone of the Moenave Formation (Jm). 

The basal red siltstone of the Moenave Formation may be the lateral equivalent of the Rock Point Member 
23

of the Wingate Formation as mapped by Cooley and others (1969), but is likely the lateral equivalent of the 

Church Rock Member of the Chinle Formation north and northeast of the map area as suggested by Repenning and others (1969); Cooley and others (1969) also mapped an orange-red silty ledge-forming sandstone 

on Ward Terrace as a tongue of the Lukachukai Member of the Wingate Formation (Sandstone) as did 

Billingsley (1987a) as suggested by Cooley and others (1969). The basal red siltstone (Rock Point Member 

of the Wingate Formation) and orange-red sandstone (Lukachukai Member of the Wingate Formation) is 

herein mapped as the lower part of the Moenave Formation because both units are lithologically the same 

as several overlying siltstone and sandstone units within the Moenave Formation and because the Wingate 

Sandstone is stratigraphically above the Moenave Formation at the New Mexico/Arizona State line. Furthermore, the Wingate Sandstone is stratigraphically between the Moenave and Kayenta Formation in the 

Hopi Buttes about 72 km (45 mi) east of the map area.

North of the map area 80 km (50 mi), the upper boundary of the Glen Canyon Group is an unconformity between the Navajo Sandstone and the Page Sandstone, but in the northeast corner of map area, the 

upper boundary of the Glen Canyon Group is an unconformity between the Navajo Sandstone (Jn) and 

Entrada Sandstone (Je) in the map area; old dune (QTd) and old eolian sand sheet and dune (QTes) deposits obscure the contact.

Jn Navajo Sandstone (Lower Jurassic)—Red, white, and tan, cliff-forming, high-angle crossbedded and massive horizontal or planar bedded, fine- to medium-grained, well-sorted, 

well-rounded frosted quartz sandstone. Crossbedded sets are as much as 11 m (35 ft) thick. 

Includes several thin lenses or beds of gray siliceous limestone, dolomite, or dark-red sandy 

siliceous mudstone that weather out as resistant ledges that form flat-topped ridges or hills 

on eroded surface of Moenkopi Plateau. These siliceous beds were formed in oases, playas, 

or ponds between eolian sand dunes and become increasingly common in southeast part 

of Moenkopi Plateau. Sandstone beds contain numerous small rounded black and reddishblack, pea-size hematite concretions in upper part near Appaloosa Ridge on Moenkopi 

Plateau and are similar to pumpkin-size concretions [25 cm to 1 m (10 in to 3 ft)] in diameter along Adeii Eechii Cliffs. Gradational and arbitrary contact with underlying Kayenta 

Formation-Navajo Sandstone transition zone (Jkn) at lowest white or red sandstone cliff of 

Navajo Sandstone. Several springs and seeps issue from the base of the Navajo Sandstone 

along the Adeii Eechii Cliffs. Unit rapidly thins eastward from Adeii Eechii Cliffs to the 

subsurface of Moenkopi Plateau. About 48 to 76 m (160 to 250 ft) thick

Jkn Kayenta Formation-Navajo Sandstone transition zone (Lower Jurassic)—Light-red and 

white, fine- to medium-grained, massive to crossbedded, cliff-forming sandstone beds of 

Navajo Sandstone lithology that intertongue with purple and light-red, slope-forming mudstone, siltstone, and sandstone beds of underlying Kayenta Formation that forms a sequence 

of red and white sandstone cliffs that alternate with purple and light-red mudstone and 

siltstone slopes. This interval is considered to be the lower “wet part” of the Navajo Sandstone by Marzolf (1983) and Blakey (1994). Unit gradually thins southeastward along Adeii 

Eechii Cliffs and in subsurface of the Moenkopi Plateau based on lithologic map contacts. 

Individual lower red sandstone units either pinch out or thicken resulting in variable thicknesses of unit and arbitrary contact with the underlying Kayenta Formation. About 37 to 73 

m (120 to 240 ft) thick

Jk Kayenta Formation (Lower Jurassic)—Purple, lavender, and light-red fluvial, crossbedded, 

fine-grained mudstone, siltstone, and silty sandstone. Weathers to steep slope. Upper part 

intertongues with Navajo Sandstone north and east of map area, but forms a mappable 

transition zone of intertonguing units within map area. Unit includes some lenticular, 

medium-grained sandstone ledges in middle and lower part. Lower part forms resistant ledgy 

interbedded siltstone and sandstone sequence commonly 6 to 12 m (20 to 40 ft) thick that 

forms a protective white cliff over Moenave Formation in the Red Rock Cliffs area. This 

white sandstone gradually thickens eastward and is correlative to the Wingate Sandstone 

(too thin to show at map scale) of the Hopi Buttes about 72 km (45 mi) east of the map area. 

Contact with underlying Moenave Formation is unconformable; erosional relief generally 

less than 2 m (6 ft) in map area and marked by lithology and color changes; the J-sub-K 

unconformity as defined by Riggs and Blakey (1993) and Blakey (1994). Laterally, the contact is slightly higher or lower in stratigraphic position over several kilometers accounting 

for variable thickness differences between the Kayenta and Moenave Formations. Overall 

the unit rapidly thins east and southeast of map area. About 122 m (400 ft) thick in the west 

to 98 m (320 ft) thick in the east
24

Jm Moenave Formation (Lower Jurassic and Upper Triassic(?))—Red and light-red, flat-bedded 

and crossbedded, fine- to coarse-grained fluvial siltstone and silty sandstone. Unit is divided 

into the Springdale Sandstone Member (upper part) and the Dinosaur Canyon Member 

(lower part) north of the map area near the town of Moenave, Arizona, the type section. The 

Springdale Sandstone Member type locality is in Springdale, Utah, and pinches out at the 

northeast edge of map area. The Dinosaur Canyon Member is informally named from an 

unnamed tributary (not shown on USGS topographic maps to help protect the fossil dinosaur track ways) to the Little Colorado River below the Adeii Eechii Cliffs. Within the map 

area the entire sequence of red fluvial sandstones of the Moenave Formation represents the 

Dinosaur Canyon Member. Formation as a whole generally weathers to form a slope except 

where overlain by resistant beds of the lower Kayenta Formation that form the Red Rock 

Cliffs. Unconformable contact with underlying Owl Rock Member of the Chinle Formation 

is known as the J-O unconformity and separates the Triassic rocks from the overlying Jurassic rocks. About 84 to 98 m (275 to 320 ft) thick

Chinle Formation (Upper Triassic)—Includes the Owl Rock Member; Petrified Forest 

Member; Shinarump Member and the sandstone and siltstone member, undivided (Repenning and others, 1969)

^co Owl Rock Member—Grayish-red and light-purple, slope- and ledge-forming nodular limestone interbedded with purple, light-blue, and light-red calcareous siltstone and sandstone. 

Limestone beds are gray, cherty, lenticular, silty, irregular bedded 0.5 to 1.5 m (1 to 5 ft) 

thick and extend laterally for several miles to form resistant ledges of Ward Terrace (fig. 

1). Black petrified logs form a unique petrified forest on Ward Terrace south of Landmark 

Wash. Unit contains abundant mud pellets and silicified clay and concretionary chert nodules 

and generally maintains constant thickness from Cameron to southeast edge of map area. 

Unconformable contact between Owl Rock Member of the Chinle Formation and overlying 

Moenave Formation commonly marked by distinct lithology and color change from purple 

and white calcareous siltstone and sandstone and limestone of the Owl Rock to dark-red or 

orange-red coarse-grained sandstone of the Moenave. Gradational and arbitrary contact with 

underlying Petrified Forest Member placed at lowest laterally continuous limestone or nodular calcareous grayish-white siltstone in slope generally about 18 to 25 m (60 to 80 ft) below 

lowest prominent limestone caprock of Ward Terrace. About 82 m (270 ft) thick in southeast 

part of map to 60 m (200 ft) thick in northeast part

^cp Petrified Forest Member—Purple, blue, light-red, reddish-purple, grayish-blue, slopeforming mudstone and siltstone and interbedded white, coarse-grained lenticular sandstone. 

Includes three informal units of Akers and others (1958), in ascending order: blue mudstone, 

gray mudstone and sandstone, and red mudstone and sandstone (not mapped). Includes large 

lenticular erosional channel structures and large-scale low-angle trough crossbedding. Petrified logs and wood fragments common in white or yellowish-white sandstone in lower part 

that may be within upper part of sandstone and siltstone member, undivided, of the Chinle 

Formation. Gradational and arbitrary contact with underlying Shinarump Member and sandstone and siltstone member, undivided, at lithologic and topographic change from sloping 

multicolored mudstone of Petrified Forest Member to coarse-grained, light-brown sandstone 

ledges and purple slopes of Shinarump Member. Weathers into rounded hills or slopes with 

a rough, puffy, popcorn texture surface due to swelling of clay content when wet. Thickness, 

122 to 153 m (400 to 500 ft)

^cs Shinarump Member and sandstone and siltstone member, undivided—White, light-brown, 

and yellowish-pink, cliff-forming, coarse-grained sandstone and conglomeratic sandstone. 

Includes cliff-forming, low-angle crossbedded sandstone interbedded with slope-forming, 

poorly sorted, purple, light-red, and blue siltstone and mudstone. Lithology is highly variable but is relatively homogeneous from a regional viewpoint; consists of about 75% sandstone, 20% conglomerate, and 5% mudstone. Pebbles are generally brown to light-colored, 

well-rounded quartzite and black siliceous composition. Petrified logs and wood fragments 

common at some localities but generally scattered throughout unit. Some petrified wood and 

associated sandstone include uranium mineral deposits that were mined for uranium along 

Little Colorado River valley during the 1950’s. All open-pit mines (Qaf) are abandoned 

and most have undergone landscape reclamation. Unconformable erosional contact with 

underlying red siltstone and sandstone of Moenkopi Formation. Thickest exposures of unit is 

northwest of Cameron, thinning southeastward along Little Colorado River Valley. About 18 
25

to 60 m (60 to 200 ft) thick

^m Moenkopi Formation, undivided (Middle(?) and Lower Triassic)—Red, slope-forming, 

fine-grained, thin-bedded, shaly siltstone and sandstone. Includes, in ascending order, the 

Wupatki Member, the Shnabkaib Member and lower massive sandstone member, and the 

Holbrook and Moqui Members, undivided. White, cliff-forming, coarse-grained, low-angle, 

crossbedded sandstone in lower part of unit in Dog Knobs area may be equivalent to the 

lower massive sandstone (^mss) member of the Moenkopi Formation east of Dog Knobs 

area. Unit is mostly eroded from southwest part of map area and commonly buried by volcanic rocks of the San Francisco Volcanic Field in Dog Knobs area. The basal Timpoweap 

Member of the Moenkopi Formation (not mapped) is composed of conglomeratic limestone 

or calcareous sandstone with small white, angular chert pebbles and fragments that occupy 

shallow depressions and channels eroded into underlying Harrisburg Member of the Kaibab 

Formation in western half of map area. Unit is distinguished from underlying red siltstone 

and sandstone beds of Harrisburg Member of the Kaibab Formation (Pkh) by its darker 

red color, thin-bedded, platy, coarse-grained, conglomeratic sandstone beds as opposed to 

massive-bedded, pale-red and gray, undulating, soft siltstone and sandstone beds of Harrisburg Member. Forms unconformable contact with underlying Harrisburg Member of the 

Kaibab Formation (Pkh) representing the regional Permian/Triassic unconformity. Overall 

thickness before Cenozoic erosion, about 300 m (1,000 ft) along west edge of map area, 

thins eastward to about 107 m (350 ft) near Cameron, Arizona, and to about 67 m (220 ft) at 

Wupatki National Monument area

Moenkopi Formation 

^mhm Holbrook and Moqui Members, undivided (Middle(?) and Lower Triassic)—Reddishbrown, slope-forming, alternating sequence of claystone, siltstone, and sandstone (McKee, 

1954). Includes large- to medium-scale trough crossbedding and abundant cusp-type ripple 

marks that testify to fluvial origin. Fossil casts of reptile tracks are often preserved on 

bottom surfaces of sandstone beds. Include interbedded, thin-bedded limestone and lenses of 

conglomeratic sandstone, and some lenses, nodules, veins, and thin-bedded gypsum. About 

25 to 37 m (80 to 120 ft) thick

^mss Shnabkaib Member and lower massive sandstone member, undivided (Lower Triassic)—

Yellowish-white and light-brown, cliff-forming, crossbedded, fine-grained, calcareous siltstone and sandstone. Shnabkaib Member and lower massive sandstone member is undivided 

on Marble Plateau north of Little Colorado River Gorge and intertongues or overlaps lower 

massive sandstone member in the vicinity of the Little Colorado River west of Cameron, 

Arizona. Unit is the Shnabkaib Member of the Moenkopi Formation on Marble Plateau 

north of map area. Unit is lower massive sandstone member of the Moenkopi Formation as 

defined by McKee (1954) from Cameron, Arizona south to southeast edge of map. Unit is 

thickest at Wupatki National Monument (15 m [50 ft]) consisting of two or more sandstone 

beds that form prominent isolated mesas or ridges in Wupatki National Monument area. Unit 

gradually thins in all directions from Wupatki and the lowermost ledge-forming sandstone 

is the most widespread part of unit. Gradational contact with underlying Wupatki Member 

marked at base of lowest sandstone cliff. About 3 to 26 m (10 to 53 ft) thick

^mw Wupatki Member (Lower Triassic)—Red and red-brown, slope-forming, thin flat-bedded, 

siltstone and sandstone and interbedded crumbly red-brown mudstone (McKee, 1954). Thin 

sandstone beds (0.5 to 1 m [1 to 3 ft]) form resistant ledges. Bedding surfaces often contain 

small-scale ripple marks, salt crystal casts, or rain drop impressions. Unconformably overlies Kaibab Formation on a regional Permian-Triassic boundary. Unit generally maintains 

constant thickness from Little Colorado River Gorge to Cameron, Arizona, then gradually 

thins southwest and southeast of Gray Mountain, Arizona. About 6 to 26 m (20 to 85 ft) 

thick

Pk Kaibab Formation, undivided (Lower Permian)—Includes, in descending order, Harrisburg 

and Fossil Mountain Members as defined by Sorauf and Billingsley (1991). Mapped as 

Kaibab Formation, undivided, east of Doney Mountain Fault and Wupatki National Monument along the Little Colorado River because of eastward shoreward facies change in both 

members that collectively forms gray to light-brown, cliff-forming, calcareous sandstone and 

sandy limestone beds that are indistinguishable from each other. Unit gradually thins southeastward. About 92 m (300 ft) thick in western part of map area, thinning to about 76 m (250 

ft) thick in eastern part
26

Kaibab Formation

Pkh Harrisburg Member (Lower Permian)—Reddish-gray and brownish-gray, slope-forming 

gypsum, siltstone, sandstone, and thin-bedded limestone. Includes yellowish-gray fossiliferous sandy limestone at top of unit that is mostly eroded from much of the map area; forms 

surface bedrock in west half of map area. Contact with underlying Fossil Mountain Member 

is gradational and arbitrarily marked at topographic break between the grayish-white, slope 

and ledge forming sandy limestone and sandstone sequence of Harrisburg Member and the 

gray, cliff-forming white to light-brown, cherty limestone of Fossil Mountain Member. Unit 

gradually thins west to east and undergoes shoreward facies change from limestone and 

sandy limestone to calcareous sandstone. About 25 to 37 m (80 to 120 ft) thick

Pkf Fossil Mountain Member (Lower Permian)—Light-gray, cliff-forming, fine- to mediumgrained, thin- to medium-bedded (0.3 to 2 m [1 to 6 ft]), fossiliferous, cherty, sandy limestone and dolomite. Weathers dark gray to black. In west half of map area unit characterized 

by abundance of gray and white, fossiliferous, chert nodules and white chert breccia beds. 

Some chert nodules contain concentric black and white bands. Breccia chert beds (1 to 3 

m [4 to 10 ft]) thick commonly form uppermost part of Fossil Mountain Member in west 

half of map area that helps establish contact between Harrisburg (Pkh) and Fossil Mountain 

(Pkf) Members of the Kaibab Formation. Chert makes up about 25% of unit in west half of 

map area, less than 5% in east half. Unit gradually thins eastward and undergoes a shoreward 

facies change from sandy marine limestone and limestone to calcareous sandstone similar 

to texture, composition, and appearance of Harrisburg Member. Generally forms cliff at rim 

of Grand Canyon and Little Colorado River Gorge overlain by ledges of sandy limestone 

of Harrisburg Member. Unconformable contact with underlying Toroweap Formation (Pt) 

attributed partly to solution erosion and mostly channel erosion; average erosional relief, 

about 3 m (10 ft). Thickness, 60 m (200 ft) in northwest quarter of map area and gradually 

thins east and southeast in subsurface of map area. About 70 m (230 ft) thick in northwest 

part of map area, thinning to about 55 m (180 ft) thick in southeast part

Pt Toroweap Formation, undivided (Lower Permian)—Includes, in descending order, Woods 

Ranch, Brady Canyon, and Seligman Members, undivided, as defined by Sorauf and Billingsley (1991). All three members are present in Grand Canyon, northwest corner of map area 

but too small to show at map scale and are mapped as the Toroweap Formation, undivided. 

All three members undergo a rapid shoreward facies change eastward from a general slope 

unit of siltstone, gypsiferous sandstone, and limestone to an indistinguishable cliff unit of 

calcareous sandstone and sandy limestone in Little Colorado River Gorge and Gray Mountain area. From Little Colorado River Gorge in subsurface of map area to southeast corner of 

map. Unit gradually thins eastward in subsurface of map from Little Colorado River Gorge 

and Gray Mountain areas to southeast corner of map where drill holes near Leupp, Arizona 

(southeast of map area) indicate that only 6 to 9 m (20 to 30 ft) of Toroweap Formation is 

present in that area (Don Bills, oral commun., July 2005). About 55 m (180 ft) thick in western part of map area, thinning to about 9 m (30 ft) thick in eastern part

Woods Ranch Member—In the Grand Canyon area unit is gray and light-red, slope-forming 

gypsiferous siltstone and silty sandstone, interbedded with thin, white laminated gypsum 

and gray thin-bedded limestone. Weathers to reddish-gray slope. Bedding locally distorted 

due to dissolution of gypsiferous siltstone. Unit undergoes shoreward facies change eastward becoming mostly cliff-forming calcareous sandstone. Contact with underlying Brady 

Canyon Member at Grand Canyon is gradational and marked at topographic break between 

slope-forming siltstone of Woods Ranch Member and cliff-forming limestone of Brady 

Canyon Member. About 20 m thick (65 ft) thick in western part of map area, thinning to 

about 6 m (20 ft) thick in eastern part

Brady Canyon Member—In the Grand Canyon area unit is gray, cliff-forming, thin- to 

medium-bedded (0.05 to 1.4 m [1 to 5 ft]), fine- to coarse-grained, sandy limestone. Weathers light-gray. Contains white and gray chert nodules that make up less than 5% of unit. Unit 

undergoes gradual shoreward facies change eastward along with overlying Woods Ranch 

Member and underlying Seligman Member making all three units indistinguishable from 

one another. Contact with underlying Seligman Member is marked at base of limestone cliff 

in Grand Canyon area. About 6 to 9 m (20 to 30 ft) thick

Seligman Member—In the Grand Canyon area unit is gray, light-purple, and yellowish-red, 

slope-forming, thin-bedded dolomite, sandstone, gypsum, and calcareous sandstone. Forms 
27

slope or recess between overlying cliff-forming Brady Canyon Member and underlying 

cliff-forming Coconino Sandstone (Pc) in Grand Canyon area. Unit undergoes eastward 

shoreward facies change similar to overlying Brady Canyon Member and appears to thin and 

pinch out before reaching Little Colorado River Gorge area. Sharp unconformable contact 

with underlying Coconino Sandstone where crossbedded sand dunes of Coconino were beveled off by marine wave erosion and sand was redistributed as flat-bedded beach sandstone 

within Seligman Member of the Toroweap Formation west of map area (Billingsley, 2000; 

Billingsley and others, 2006). Coconino Sandstone intertongues with lower part of Seligman 

Member west and north of map area (Fisher, 1961; Schleh, 1966; Rawson and Turner, 1974; 

and Billingsley and others, 2003). About 3 to 6 m (10 to 20 ft) thick

Pc Coconino Sandstone and Schnebly Hill Formation, undivided (Lower Permian)—Tan to 

white, cliff-forming, fine-grained, well-sorted, cross-bedded quartz sandstone. Includes 

the Schnebly Hill Formation of Blakey (1990) in subsurface of map area. Thin red sandstone beds at base of Coconino Sandstone cliff in Little Colorado River Gorge is likely the 

northern feather edge of the Schnebly Hill Formation (Ronald C. Blakey, oral commun., 

July 2005). Contains large-scale, high-angle, planar cross-bedded sandstone sets that average about 11 m (35 ft) thick. Locally includes poorly preserved amphibian fossil track ways 

and low-relief wind ripple marks on crossbedded planar sandstone surfaces. Lower part 

of Coconino Sandstone intertongues or grades southward into Schnebly Hill Formation in 

subsurface of southern two-thirds of map area. Type section of Schnebly Hill Formation 

(Blakey, 1990) is in Verde Valley, 80 km (50 mi) south of map area. Unit intertongues with 

lower part of Seligman Member of the Toroweap Formation west of map area (Billingsley, 

2000; Billingsley and Wellmeyer, 2003; Billingsley and others, 2006). Coconino Sandstone 

is a well established part of Grand Canyon nomenclature and is retained as a mappable 

unit because it forms a thick, regional, white sandstone cliff in Grand Canyon and Little 

Colorado River Gorge that is easily recognized and mappable. Unconformable contact with 

underlying Hermit Formation (Ph) is sharp, planar, with relief generally less than 1 m (3 ft) 

but locally as much as 2.5 m (8 ft) marked by distinct color and topographic change between 

white, cliff-forming Coconino Sandstone, light-red Schnebly Hill Formation, and dark-red, 

slope-forming Hermit Formation. Unit decreases slightly from west to east in subsurface of 

the map area. Unit is an important water-bearing sandstone east and south of map area (Don 

Bills, Water Resources Division of the U.S. Geological Survey, oral commun., 2005). About 

183 m (600 ft) thick

Ph Hermit Formation (Lower Permian)—Red, slope-forming, fine-grained, thin-bedded siltstone 

and sandstone. Upper part contains red massive, low-angle crossbedded calcareous sandstone and siltstone beds in Little Colorado River Gorge that may be equivalent, in part, 

to Schnebly Hill Formation. Siltstone beds are dark red and crumbly and fill widespread, 

shallow erosion channels. Siltstone beds form recesses between thicker sandstone beds; 

locally contains poorly preserved plant fossils in channel fill deposits in lower part of unit in 

Grand Canyon area. Sandstone is partly bleached to yellowish-white at upper contact with 

Coconino Sandstone (Pc). Unconformably overlies Esplanade Sandstone (Pe). Dark-red, 

platy, thin-bedded siltstone of Hermit Formation fills erosional channels as much as 9 m (30 

ft) deep eroded into underlying Esplanade Sandstone in Grand Canyon area (Billingsley, 

2000). Otherwise, erosional relief is generally less than 3 m (10 ft). Unit thins south and 

east of Grand Canyon to less than 12 m (40 ft) in Little Colorado River Gorge; may thicken 

southward in subsurface of map based on exposures in Verde Valley 80 km (50 mi) south of 

map area (Blakey, 1990). About 25 m (80 ft) thick in northwestern part of map area, thins to 

12 m (40 ft) thick in southeast part

Supai Group (Lower Permian, Pennsylvanian, and Upper Mississippian)—Includes in 

descending order, the Esplanade Sandstone (Pe); Wescogame Formation, Manakacha Formation, and Watahomigi Formation, undivided (*Ms)

Pe Esplanade Sandstone (Lower Permian)—Light-red and pinkish-gray, cliff-forming, fine- to 

medium-grained, medium- to thick-bedded (1 to 3 m [3 to 10 ft]), well-sorted calcareous 

sandstone. Includes intrabedded dark-red, thin-bedded, crumbly, recessive and slope-forming 

siltstone beds in upper and lower part. Crossbeds are small- to medium-scale, planar lowangle and high-angle sets. Unit gradually thins eastward and southeastward in subsurface of 

map area based on limited exposures in northwest quarter of map. Unconformable contact 

with underlying rocks (*Ms) is marked by erosion channels as much as 9 m (30 ft) deep in 
28

Grand Canyon and Little Colorado River Gorge area. Variable thickness, about 122 to 107 m 

(400 to 350 ft) thick

*Ms Wescogame (Upper Pennsylvanian), Manakacha (Middle Pennsylvanian), and Watahomigi (Lower Pennsylvanian and Upper Mississippian) Formations, undivided—

Includes, in descending order, Wescogame, Manakacha, and Watahomigi Formations as 

defined by McKee (1982). Separate formations are difficult to identify in the field and due to 

limited exposures in northwest corner of map area and in the Little Colorado River Gorge

Wescogame Formation (Upper Pennsylvanian)—Light-red, pale-yellow, and light-gray 

upper slope unit and lower cliff unit. Upper slope unit consists mainly of dark-red, finegrained siltstone and mudstone interbedded with light-red, coarse-grained, calcareous 

sandstone and dolomitic sandstone, siltstone, mudstone, and conglomerate. Lower cliff unit 

consists mainly of light-red to gray, high-angle, large- and medium-scale, tabular-planar, 

crossbedded sandstone and calcareous sandstone sets as much as 12 m (40 ft) thick. Unconformable contact with underlying Manakacha Formation marked by erosion channels as 

much as 4.5 m (15 ft) deep in Grand Canyon part of map area. Channels commonly filled 

with limestone/chert conglomerate. About 45 m (150 ft) thick

Manakacha Formation (Middle Pennsylvanian)—Light-red, white, and gray upper slope 

and lower cliff of sandstone, calcareous sandstone, dark-red siltstone, and gray limestone. 

Upper slope consists mainly of shaly siltstone and mudstone with minor interbedded, thinbedded limestone and sandstone. Carbonate content of upper slope increases westward to 

form numerous ledge-forming, thin- and medium-bedded limestone beds. Upper slope is 

about 30 m (100 ft) thick in Grand Canyon area of map. Lower cliff is dominated by grayish-red, medium- to thick-bedded, crossbedded calcareous sandstone, dolomite, and sandy 

limestone. Lower cliff is about 18 m (60 ft) thick. Carbonate content increases west of map 

area forming numerous gray limestone ledges. Unconformable contact between the Manakacha Formation and underlying Watahomigi Formation marked at base of lower red sandstone 

cliff of Manakacha; erosional relief generally less than 1 m (3 ft) as wavy unconformable 

surface. About, about 60 m (200 ft) thick

Watahomigi Formation (Lower Pennsylvanian and Upper Mississippian)—Gray and 

purplish-red, slope-forming limestone, siltstone, mudstone, and conglomerate. Forms an 

upper ledge/slope and lower slope. Upper ledge/slope consists of alternating gray, thin-bedded cherty limestone ledges interbedded with purplish-gray siltstone and mudstone; limestone beds contain Lower Pennsylvanian conodont fossils in western Grand Canyon area 

(Martin and Barrick, 1999); red chert lenses and nodules common. Includes limestone chertpebble conglomerate at base, locally containing Lower Pennsylvanian fossils. Upper ledge/

slope averages about 21 m (70 ft) thick throughout Grand Canyon area. Lower slope consists 

mainly of purplish-red mudstone and siltstone, interbedded with thin-bedded, aphanitic to 

granular limestone in upper part with red chert veins and nodules. Conodonts in lower thin 

limestone beds are Upper Mississippian (Martin and Barrick, 1999). Unit includes purple 

siltstone and gray limestone interbedded with conglomerate that fills small erosion channels cut into either the Surprise Canyon Formation (Ms) north and west of map area or into 

Redwall Limestone (Mr). Purple shale and mudstone of lower slope unconformably overlies 

gray Redwall Limestone in Grand Canyon and Little Colorado River Gorge area. Surprise 

Canyon Formation (Ms) is not present within map area but is present just north of map in 

Grand Canyon (Billingsley, 2000) and may be present in subsurface of map area. About 30 

m (100 ft) thick. Supai Group gradually thins eastward in subsurface of map area. Overall 

thickness of Supai Group ranges from about 244 to 274 m (800 to 900 ft)

Mr Redwall Limestone, undivided (Upper and Lower Mississippian)—Includes, in descending 

order, Horseshoe Mesa, Mooney Falls, Thunder Springs, and Whitmore Wash Members, 

as defined by McKee (1963) and McKee and Gutschick (1969), but these members are too 

small to show at map scale because of the sheer cliff outcrops of the Redwall Limestone in 

general. Unit overall is light-gray to dark-gray, cliff-forming, thin- to thick-bedded, fine- to 

coarse-grained, fossiliferous limestone and dolomite. Includes thin-bedded gray and white 

chert lenses and nodules. Unit is exposed as sheer cliff in Grand Canyon, and just the top 

part of the Redwall Limestone is exposed in Little Colorado River Gorge but is too thin 

to show at map scale. Unit gradually thins eastward in subsurface of map area and is an 

important subsurface aquifer because of solution-eroded caverns and bedrock joint systems. 

Variable thickness, about 137 to 122 m (450 to 400 ft)
29

Horseshoe Mesa Member—Light-olive-gray, ledge- and cliff-forming, thin-bedded, finegrained limestone. Weathers to receding ledges. Gradational and disconformable contact 

with underlying massive-bedded limestone of Mooney Falls Member marked by thinbedded, platy limestone beds of Horseshoe Mesa Member that form recess about 1 to 3 m 

(3 to 9 ft) thick near top of cliff. Fossils are locally common. Includes distinctive ripplelaminated limestone and oolitic limestone beds and some chert lenses. Unit locally absent 

where removed by Late Mississippian paleovalley erosion. About 15 to 30 m (50 to 100 ft) 

thick

Mooney Falls Member—Light-gray, cliff-forming, fine- to coarse-grained, thick-bedded to 

very thick bedded [1 to 6 m (4 to 20 ft)], fossiliferous limestone. Limestone weathers dark 

gray; chert beds weather black. Includes dark-gray dolomite beds; oolitic limestone and 

chert beds restricted to upper part. Disconformable contact with underlying Thunder Springs 

Member distinguished by lithology; massive-bedded, gray limestone of Mooney Falls 

Member overlies thin-bedded, dark-gray to brown dolomite and white chert beds of Thunder 

Springs Member. About 75 m (300 ft) thick

Thunder Springs Member—About half of member is gray, cliff-forming, fossiliferous, thinbedded limestone and about half is brownish-gray, cliff-forming, thin-bedded [2 to 12 cm (1 

to 5 in)], finely crystalline dolomite and fine- to coarse-grained limestone interbedded with 

lenses of white chert beds. Locally includes large-scale crossbedding and irregularly folded 

beds north of map area. Disconformable planar contact with underlying Whitmore Wash 

Member distinguished by distinct lack of chert in Whitmore Wash Member. About 30 m 

(100 ft) thick

Whitmore Wash Member—Yellowish-gray and brownish-gray, cliff-forming, thick-bedded, 

fine-grained dolomite. Weathers dark gray. Unconformable contact with underlying Temple 

Butte Formation (Dtb) marked by erosion channels of low relief about 2 to 3 m (5 to 10 ft) 

in depth. Contact generally recognized where major cliff of the light-gray Redwall Limestone overlies stair-step ledges of dark-gray Temple Butte Formation in Grand Canyon. 

About 25 m (80 ft) thick

Dtb Temple Butte Formation (Upper and Middle Devonian)—Purple, reddish-purple, dark-gray, 

and light-gray, ledge-forming dolomite, sandy dolomite, sandstone, mudstone, and limestone, as defined by Beus (2003). Purple and light-gray, fine- to coarse-grained, thin- to 

medium-bedded, ripple-laminated ledges of mudstone, sandstone, dolomite, and conglomerate fill channels eroded into underlying Cambrian Muav Limestone; channels are as much 

as 12 m (40 ft) deep in Grand Canyon area in northwest corner of map. Channel deposits 

are overlain by dark-gray to olive-gray, medium- to thick-bedded dolomite, sandy dolomite, 

limestone, and sandstone. Ledges weather to dark gray. Unconformity at base represents 

major stratigraphic break spanning about 100 million years in Grand Canyon that includes 

part of the Late Cambrian, all of the Ordovician and Silurian, and most of Early and Middle 

Devonian time. Dark-gray Devonian rocks are distinguished from underlying light-gray 

Cambrian rocks by color contrast. Unit thins eastward from Grand Canyon and is likely 

intermittent or discontinuous in the subsurface of the eastern two-thirds of map area. About 

0 to 30 m (0 to 100 ft) thick

Tonto Group (Middle and Lower(?) Cambrian)—Includes in descending order, Muav Limestone, Bright Angel Shale, and Tapeats Sandstone as defined by Noble (1922) and modified 

by McKee and Resser (1945). Only the Muav Limestone is exposed in the northwest corner 

of the map in Grand Canyon; the other Cambrian units are present in the subsurface of the 

map area. The age and depositional history of the Cambrian rocks in Grand Canyon are 

revised by Rose (2003). Tonto Group may overlie tilted strata of Grand Canyon Supergroup 

of Mesoproterozoic (1.4 to 1.1 billion years) age in subsurface of west and central part of 

map area and igneous and metamorphic rocks of Paleoproterozoic (1.7 to 1.6 billion years) 

elsewhere within the map area; this hiatus is known regionally as the Great Unconformity

_m Muav Limestone (Middle Cambrian)—Dark-gray, light-gray, brown, and orange-red, 

cliff-forming, fine- to medium-grained, thin- to thick-bedded, mottled, fossiliferous, silty 

limestone, limestone, dolomite, and calcareous mudstone. Includes unnamed siltstone and 

shale beds of green and purplish-red, micaceous siltstone, mudstone, and thin beds of brown 

sandstone. Contact with the underlying Bright Angel Shale is gradational and lithology 

dependent, arbitrarily marked at base of lowest prominent limestone of Muav Limestone in 

Grand Canyon just north of map area. Muav Limestone gradually thins from 107 m (360 ft) 
30

in west part of map area to an unknown thickness in subsurface of eastern two-thirds of map 

area

UNITS SHOWN ONLY IN CROSS SECTION

_ba Bright Angel Shale (Middle Cambrian)—Green and purple-red, slope-forming siltstone, 

shale, and red-brown to brown sandstone. Consists of green and purple-red, fine-grained, 

micaceous, ripple-laminated, fossiliferous shale and siltstone; dark-green, medium- to 

coarse-grained, thin-bedded, glauconitic sandstone; and interbedded purplish-red and brown, 

thin-bedded, fine- to coarse-grained, ripple laminated sandstone. Contact with underlying 

Tapeats Sandstone is gradational and arbitrarily marked at top of vertical transition zone 

from dominantly green siltstone to dominantly brown sandstone above Tapeats Sandstone 

cliff. About 60 to 90 m (200 to 300 ft) thick 

_t Tapeats Sandstone (Middle and Lower(?) Cambrian)—Brown and red-brown, cliff-forming, coarse-grained sandstone and conglomerate. Unconformable contact with underlying 

Lower Proterozoic surface forms the Great Unconformity. Tapeats Sandstone fills lowland 

areas and thins across or pinches out against Proterozoic highlands. Variable thickness, 0 to 

60 m (0 to 200 ft) 

PROTEROZOIC CRYSTALLINE ROCKS

Intrusive and metamorphic rocks as defined by Ilg and others (1996), Hawkins and others (1996), and Karlstrom and others (2003). There is at least a 50 to 75 percent chance that younger Proterozoic sedimentary 

rocks of the Grand Canyon Supergroup exposed in the eastern Grand Canyon area (Huntoon and others, 

1996) may be present in the southern and eastern subsurface of this map area.

Xu Crystalline rocks, undivided—Undivided intrusive and metamorphic rocks. Includes granite 

plutons, stocks, and pegmatite and aplite dikes, gabbro-diorite, and granodiorite rocks, 

garnet schist, hornblende-biotite schist, orthoamphibole-bearing schist and gneiss, and probable felsic metavolcanic rocks

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