U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY

Geologic map of the Antelope Knoll quadrangle 

northern Mohave County, Arizona

by 

George H. Billingsley

Open-File Report 94-449

1994

This report is preliminary and has not been reviewed for conformity with U.S. 

Geological Survey editorial standards or with the North American Stratigraphic 

Code. Any use of trade, product, or firm names is for descriptive purposes 

only and does not imply endorsement by the U.S. Government.
INTRODUCTION

The Antelope Knoll 7.5' quadrangle is located in northern Mohave County, 

northwestern Arizona. The quadrangle is about 26 km south of the Arizona/Utah 

State line and about 30 km southwest of Colorado City, Arizona, the nearest 

settlement (fig. 1). Elevations range from about 1,814 m (5,951 ft) at 

Antelope Knoll (central part of quadrangle) to 1,408 m (4,620 ft) on the 

southwestern edge of quadrangle. Access to the area is by improved dirt road 

locally referred to as the Temple Trail, a branch road from the Navajo Trail 

to Colorado City, Arizona (fig. 1). Several unimproved dirt roads lead from 

the Temple Trail to various locations within the quadrangle area. Travel on 

the Temple Trail can be done with 2 wheel drive vehicles; all other roads need 

high clearance vehicles or 4 wheel drive in muddy conditions.

The area is managed by the U.S. Bureau of Land Management, including 

about 5 sections belonging to the state of Arizona. The area supports a 

sparse growth of sagebrush, cactus, cliffrose bush, grass, and various high 

desert shrubs. A light cover of pinyon pine and juniper trees are east of the 

Hurricane Cliffs, southwest corner of the quadrangle.

PREVIOUS WORK

The area is included on two Arizona state geologic maps, one by Wilson 

and others (1969), and the other by Reynolds (1988). A geologic map is 

available for the upper Hurricane Wash and vicinity (Billingsley, in press, 

b), and The Grandstand 7.5' quadrangle (Billingsley, 1993b), all bordering 

this quadrangle on the west. A geologic map of the lower Hurricane Wash and 

vicinity lies adjacent to the northwest corner of this quadrangle 

(Billingsley, in press, a). The White Pockets quadrangle (Billingsley, 1994), 

borders this area on the north. Preliminary geologic maps are also available 

for the Grand Canyon area about 45 km south of this quadrangle (Huntoon and 

others, 1981; Billingsley and others, 1983; Wenrich and others, 1986).

MAPPING METHODS

A preliminary geologic map was made from 1:24,000 scale aerial 

photographs. In particular, many of the Quaternary alluvial units having 

similar lithologies were mapped using photogeologic methods. Detailed field 

investigations were then conducted to check photo interpretations and to 

obtain descriptions for all map units.

GEOLOGIC SETTING

The map area lies within the Shivwits and Uinkaret Plateaus, subplateaus 

of the southwestern part of the Colorado Plateau physiographic province. The 

physiographic boundary between the higher elevations of the Uinkaret Plateau 

and the lower elevations of the Shivwits Plateau is demarcated along 

the upper part of the Hurricane Cliffs escarpment, a youthful fault scarp 

(fig. 2). The Shivwits and Uinkaret Plateaus are characterized by relatively 

flat-lying Paleozoic and Mesozoic strata that have an average regional dip of 

less than 2° east, except along the Hurricane Cliffs where dips of the 

Hurricane Monocline reach as much as 24° east.

The Hurricane Fault and Monocline is the major structural feature of the 

quadrangle. The resulting fault scarp, the Hurricane Cliffs, exposes more 

than 305 m of Permian strata. East of the Hurricane Cliffs, on the Uinkaret 

Plateau, about 67 m of Triassic strata are exposed under Quaternary basalt 

flows (southeast corner of map). Vertical displacement among various segments 

of the Hurricane Fault is estimated to be over 500 m.
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Figure 1. Index map of northern Mohave County, northwestern Arizona, showing 

the Antelope Knoll 7.5' quadrangle.
Cenozoic deposits consists of igneous, surficial alluvium, and landslide 

deposits of Quaternary age. The igneous rocks are mapped as vent areas, 

pyroclastic deposits and basalt flows. The surficial deposits include 

artificial-fill and quarries, stream-terraces, alluvial-fans, talus, and 

landslide debris. These deposits form geomorphic features and erosional 

surface deposits having intertonguing or gradational contacts. The 

distribution of these Quaternary deposits are an important factor to consider 

in future environmental, land, and range management planning in this area by 

federal, state, and private organizations.

STRATIGRAPHY

The Paleozoic and Mesozoic stratigraphic units within the map area 

include, in order of decreasing age, the Toroweap, and Kaibab Formations 

(Lower Permian), and the Moenkopi Formation (Middle? and Lower 

Triassic). The base of the Seligman Member of the Toroweap Formation is not 

exposed along the bottom of the Hurricane Cliffs owing to a cover of alluvial 

fan deposits. The upper part of the underlying Hermit Formation (Lower 

Permian) would likely be exposed along the base of the Hurricane Fault scarp 

were it not for the alluvial cover. The Coconino Sandstone (Lower Permian), 

found in the Grand Canyon area south of this quadrangle, pinches out northward 

from the Grand Canyon and does not reach this area. Most of the Toroweap 

Formation is well exposed in the lower steep slopes and ledges of the 

Hurricane Cliffs as gray siltstone, sandstone, gypsum, and limestone. The 

Kaibab Formation forms the upper part of the Hurricane Cliffs and much of the 

bedrock surface of the Shivwits and Uinkaret Plateaus where not covered by 

Quaternary volcanic rocks or alluvial deposits. The Kaibab bedrock is 

composed of gray cherty limestone and gray to white siltstone and gypsum. 

The lower part of the Moenkopi Formation is composed of gray conglomerate and 

sandstone, light-brown to red siltstone and sandstone, gray gypsum, and gray 

limestone. Most of the Moenkopi Formation crops out along the base of 

Quaternary basalt flows, east edge of the quadrangle.

A large Triassic paleovalley is eroded into the Harrisburg Member of the 

Kaibab Formation and is filled with conglomerate, limestone, and sandstone 

strata of the Timpoweap Member of the Moenkopi Formation, northwest corner of 

the quadrangle area (fig. 2). This paleovalley is called Mustang valley and 

is mapped for more than 19 km west of this quadrangle (Billingsley, in press, 

a). Mustang valley is covered by igneous rocks for a few kilometers in the 

vicinity of Antelope Knoll, and crops out in the southeast part of the 

quadrangle where the paleovalley is mostly removed by erosion (fig. 2). Two 

smaller unnamed Triassic paleovallies in the western part of the quadrangle 

probably join Mustang valley in the vicinity of Antelope Knoll. Both small 

paleovallies are mapped for about 10 km west of this quadrangle (Billingsley, 

1993c).

The outcrops of igneous rocks are basalt flows and pyroclastic deposits 

that overlie strata of the Kaibab and Moenkopi Formations. The basalt flows 

originate from vent areas associated with thick pyroclastic cinder and scoria 

deposits that form prominent cinder cones on the basalt flows. The igneous 

rocks represent the northern extent of the Uinkaret Volcanic Field (Hamblin 

and Best, 1970; Hamblin, 1970). Two whole-rock K-Ar ages have been obtained 

for the basalts in this part of the volcanic field and several more are 

pending.
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Antelope Knoll is the largest of four cinder cones in the Quadrangle 

(fig. 2). The cinder and scoria deposits at Antelope Knoll are as much as 180 

m thick and form a prominent cinder cone on the Uinkaret Plateau. The basalt 

flow from Antelope Knoll flowed in a northerly and easterly direction onto a 

gently east-dipping bedrock surface of the Harrisburg Member of the Kaibab 

Formation and the Timpoweap and lower red members of the Moenkopi Formation. 

The flow, or flows, are mapped as one map unit. The basalt flow, and 

associated cinder and scoria deposits, are named Antelope Knoll Basalt, for 

Antelope Knoll volcano, the type area, northern Mohave County, Arizona (Sees. 

13, 18, 19, and 24, T. 38 N., Rs. 8 and 9 W.; fig. 2; Billingsley, 1994). The 

Antelope Knoll Basalt is comprised of reddish-black cinder and scoria deposits 

at Antelope Knoll and a dark gray, finely-crystalline groundmass of basalt 

having few or no phenocrysts. A sample of the Antelope Knoll Basalt obtained 

near the Navajo Trail north of this quadrangle (T. 39 N., R. 8 W., sw} of sec. 

6, White Pockets quadrangle, Arizona; Billingsley, 1994) yielded a whole-rock 

K-Ar age of 0.83±0.28 Ma (Harold Mehnert, U.S. Geological Survey Isotope 

Laboratories, Denver, Colorado, written commun., 1993).

The Antelope Knoll Basalt flowed eastward over bedrock and alluvium for 

about 5 km, descending about 122 m for a gradient of about 40 m per kilometer. 

Thus, the landscape at the time of the flow, was much the same as it appears 

today. The eastern reaches of the Antelope Knoll Basalt flowed east and north 

within a shallow valley of mostly alluvium and bedrock eroded into the 

Moenkopi Formation. The bulk of the basalt flowed northward down a drainage 

that may have been a tributary to Clayhole Wash for nearly 19 km, descending 

about 122 m, for a gradient of about 33 m per kilometer

A small segment of the Antelope Knoll Basalt, east-central edge of the 

quadrangle (Sec. 16, T. 38 N., R. 8 W.), flowed down a narrow drainage and 

onto what may have been the drainage level of Clayhole Wash. This segment of 

basalt is about 45 m higher and 2 km west of the present Clayhole Wash 

drainage. Thus, Clayhole Wash has eroded its valley deeper at an average rate 

of about 0.6 m per 10,000 years, or 0.06 m per 1,000 years in the last 830,000 

years. This figure is similar to the 0.075 m per 1,000 years at the northern 

end of the Antelope Knoll Basalt flow (Billingsley, 1994).

Other basalt flows and associated igneous deposits that are mapped 

separately from the Antelope Knoll Basalt, are basalt flows and pyroclastic 

deposits associated with Maryland Knoll volcano, here named the Maryland Knoll 

Basalt. The Maryland Knoll Basalt appears to merge with, or share a common 

boundary with part of the Antelope Knoll Basalt. This common boundary 

suggests a similar Pleistocene age for both basalts. The Maryland Knoll 

Basalt was not sampled for age dating.

A basalt flow and associated pyroclastic deposit of Deadman Knoll 

volcano, and a nearby unnamed cinder cone (southeast edge of quadrangle), are 

mapped as part of extensive basalt flow and associated cinder cones that are 

aligned in a northwest strike. Southeast of this quadrangle (Moriah Knoll and 

Hat Knoll 7.5' quadrangles), are several cinder cones, called Seven Knolls, 

that align in a northwest strike. Deadman Knoll appears to be the northern 

extent of the Seven Knolls volcano alignment, all occupying about the same 

elevation, and all overlie similar bedrock strata of the Kaibab and Moenkopi 

Formations. The northwest alignment of the Seven Knolls volcanoes matches the 

northwest strike of near vertical joints in the underlying bedrock strata.

Antelope Knoll, Maryland Knoll, and Deadman Knoll cinder cones and 

basalt flows, all occupy similar elevations on the Uinkaret Plateau and have
similar compositional characteristics. The basalts in this quadrangle appear 

to merge or share common boundaries and are thus considered to be a similar 

Pleistocene age as the Antelope Knoll Basalt. Olivine is a common phenocrysts 

in all of the basalts. Future K-Ar ages will probably show that most, if not 

all of the basalts in an around this quadrangle, are Pleistocene in age.

A basalt flow in the southwest corner of the quadrangle came from a 

cinder cone about 1 km south of this quadrangle called Moriah Knoll (Moriah 

Knoll quadrangle, Arizona, 1971) and is called the Moriah Knoll Basalt 

(Billingsley, 1993c; in press, b). A whole-rock K-Ar age of the Moriah Knoll 

Basalt is 2.3±1.5 Ma (Harold Mehnert, U.S. Geological Survey, Denver, Colo. 

written commun., 1993). According to Harold Mehnert, the sample was not the 

best for K-Ar dating purposes because of alteration, as a result, the date has 

an error range of 1.5 m.y. Thus, the 2.3 Ma age is not considered a reliable 

age for the Moriah Knoll Basalt. The Moriah Knoll Basalt is likely to be a 

Pleistocene age because it occupy's the same erosional surface as the Antelope 

Knoll Basalt, and are only 8 km apart.

A unique feature of the Moriah Knoll Basalt is that it flowed north for 

about 6.4 km down a small drainage cut into soft gypsum and siltstone of the 

Harrisburg Member of the Kaibab Formation. The basalt continued down the 

drainage and over the Hurricane Cliffs onto outcrops of the Harrisburg Member 

of the Kaibab Formation and alluvial slopes of the Shivwits Plateau below. 

Prior to the flow, the drainage had deepened by headward erosion into the 

Hurricane Cliffs fault scarp for a distance of only a few hundred meters. The 

Moriah Knoll Basalt still clings to steep canyon walls of the Fossil Mountain 

Member of the Kaibab where the flow had descended to the down-dropped, eastdipping block of Kaibab strata on the west side of the first segment of the 

Hurricane Fault (southwest corner of quadrangle). Displacement along this 

first segment of the Hurricane Fault was about 110 m before the basalt flow. 

Offset of the Moriah Knoll Basalt along this first segment is about 73 m for a 

total offset of about 183 m along this segment of the Hurricane Fault. Strata 

of the Kaibab on the west side of the Hurricane Fault dip as much as 24° east 

towards the fault scarp.

After crossing the first segment of the Hurricane Fault, the Moriah 

Basalt divided into two flows: one flow traveled a short distance south along 

the base of the first segment of the Hurricane Fault scarp, and a second, 

larger flow continued northwest and steeply down and across the second and 

third segments of the Hurricane Fault. The basalt flow overlies thin alluvial 

deposits and beveled east-dipping strata of the Harrisburg and Fossil Mountain 

Members of the Kaibab Formation in a steep drainage onto the Shivwits Plateau.

The Moriah Knoll Basalt was offset down to the west about 26 m along a 

second segment of the Hurricane Fault, and about 30 m along a third (westernmost) segment of the fault. Offset of underlying strata in the second and 

third segments of the Hurricane Fault are unknown, but add up to several 

hundred meters. Total estimated offset of the Moriah Knoll Basalt on all 

segments of the Hurricane Fault is about 130 m in the last 2.3 m.y. Minimum 

vertical offset along the various segments of the Hurricane Fault, before the 

Moriah Knoll Basalt, is estimated to be as much as 380 m. Thus, total offset 

along all segments of the Hurricane Fault is estimated to be as much as 510 m 

in this area.

If the Moriah Knoll Basalt is close in age to the Antelope Knoll Basalt 

as suspected, then most of the offset along the Hurricane Fault occurred 

before 830,000 years ago, and about 130 m of offset has occurred within the
last 830,000 years. Just north of the Arizona-Utah State line near the town 

of Hurricane, Utah, a basalt flow 0.293±0.087 Ma is vertically displaced about 

87 m by the Hurricane Fault (Hamblin and others, 1981), indicating continued 

Pleistocene activity along the Hurricane Fault.

The earliest offset along the Hurricane Fault is less than 3.6±0.18 Ma 

because the Bundyville basalt (dated at 3.6±0.18 Ma), about 36 km south of 

this quadrangle (Koons, 1945; Hamblin and Best, 1970; Hamblin, 1970; Reynolds 

and others, 1986), is offset as much as the underlying strata, indicating that 

most, if not all displacement along that section of the Hurricane Fault, 

occurred within the last 3.6 Ma (Billingsley, in press, b).

The Quaternary age assigned to the alluvial deposits in this quadrangle 

is based mainly on field relationships of these deposits to Pleistocene 

basalts in this quadrangle and nearby areas (Billingsley, 1993a, 1994, in 

press, a and b). Many of the alluvial deposits contain basalt clasts that are 

downslope from basaltic outcrops of Pleistocene age. Therefore, all alluvial 

and surficial deposits of this quadrangle are Pleistocene age and younger. 

The oldest alluvial unit of this map area, terrace-gravel (Qg3 ), contains 

basalt clasts derived from the Antelope Knoll and Seven Knolls Basalts. 

Details of the stratigraphic sequence of alluvial deposits are given in the 

description of map units.

STRUCTURAL GEOLOGY

The Hurricane Fault and Monocline have a northerly strike in the 

southwest corner of this quadrangle. Both structures turn to a southwesterly 

direction southwest of this quadrangle (Billingsley, 1993c; in press, b) and a 

northwesterly direction northwest of the this quadrangle (Billingsley, 1993b, 

in press, a). The axis of the Hurricane Monocline is located approximately 

just west of and parallel to the Hurricane Fault because the greatest bend of 

strata is found on the downthrown block. Strata of the Kaibab Formation dip 

as much as 24° west of the main segment of the fault, and generally less than 

5° east on the east side of the fault. The greater dip of strata on the 

downthrown block is accentuated by reverse fault drag (Hamblin, 1970).

The axis of the Hurricane Monocline is approximately located on the 

quadrangle based on deep exposures in the Grand Canyon about 86 km south of 

this quadrangle (fig. 3; Huntoon, 1989; Huntoon and others, 1981; Wenrich and 

others, 1986). Changes in strike of exposed monoclines of the eastern Grand 

Canyon area are.linked to intersecting basement faults that have been 

reactivated during the Late Cenozoic (Huntoon, 1989).

The graben structures shown on the downthrown side of the Hurricane 

Monocline in figure 3 are likely buried under thick alluvial deposits just 

west of the quadrangle area. Tertiary congressional stresses resulted in the 

development of the Hurricane Monocline along favorably oriented, pre-existing 

faults in the Precambrian basement in Laramide time (Huntoon, 1989; Elston and 

Young, 1991).

The Hurricane Fault scarp forms the Hurricane Cliffs, a prominent 

landmark in northwestern Arizona. The Hurricane Fault line is mostly covered 

by talus and alluvial deposits, but appears to be a normal vertical fault with 

a fault plane dipping west as suggested by Hamblin and Best (1970). The 

Hurricane Fault cuts alluvial deposits vertically as much as 25 m or more 

along the main segment. Even though the fault line is visible in alluvial
WEST

LOWER PALEOZOIC ROCKS 

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LATE CENOZOIC NORMAL FAULTING

HANGING WALL DIPS ACCENTUATED 

DURING EXTENSION

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LATE CENOZOIC CONFIGURATION AFTER CONTINUED EXTENSION

Figure 3. Stages w the development of a typical north-trending monocline 

fault zone, Grand Canyon region, Arizona (Huntoon, 1989, p. 80).
deposits, the fault is dotted on the map because of extensive talus and 

younger alluvial cover, except along one small segment where the alluvium 

appears recently faulted.

Small folds present in the quadrangle are probably related, in part, to 

early Laramide compressional stresses (Huntoon, 1989), and to later 

extensional stresses allowing strata to bend or fold into graben structures. 

Locally, warped and bent strata too small to show at map scale are the result 

of solution of gypsum in the Harrisburg Member of the Kaibab Formation. These 

deformed strata are commonly associated with solution of gypsum along 

drainages.

Circular collapse structures with a surface expression as a bowl-shaped 

area having inward-dipping strata, may be collapse-formed breccia pipes that 

originated in the deeply buried Mississippian Redwall Limestone (Wenrich and 

Huntoon, 1989; Wenrich and Sutphin, 1989). Such features are marked by a dot 

and the letter C on the map. However, they cannot be distinguished with 

certainty from shallow collapse structures caused by the removal of gypsum by 

solution. Moreover, some deep-seated breccia pipes are known to be overlain 

by gypsum collapse features (Wenrich and others, 1986). The deep-seated 

breccia pipes potentially contain economic deposits of copper and uranium 

minerals (Wenrich, 1985).

Shallow sinkholes and karst caves are associated with the solution of 

gypsum in the Harrisburg Member of the Kaibab Formation. The sinkholes are 

Holocene and probable Pleistocene age because of their young appearance. 

Hundreds of sinkhole depressions that are breached by drainages on the 

Uinkaret Plateau surface are not marked on this map. Only sinkholes that form 

an enclosed basin or depression are shown by a triangle symbol. Several minor 

drainages originate at sinkhole depressions in the quadrangle.

DESCRIPTION OF MAP UNITS

Surficial deposits

Qaf Artificial fill and quarries (Hoiocene)--Alluvial and bedrock material 

removed from pits and trenches to build stock tanks and drainage 

diversion dams

Qs Stream-channel alluvium (Holocene)--Unconsolidated and poorly sorted, 

interlensing silt, sand, and pebble to boulder gravel. Active wash 

or large arroyo. Intertongues, inset to, or locally overlies valleyfill (Qv), alluvial-fan (Qa L and Qa2 ), and terrace-gravel (Qg^ Qg 2 , 

and Qg,) deposits. .Stream channels subject to high-energy flows and 

flash floods and support little or no vegetation. Contacts 

approximate. Estimated thickness 1 to 3 m

Qg 1 Young terrace-gravel deposit (Holocene)--Unconsolidated, light-brown to 

pale-red siltstone, sandstone, and lenses of gravel containing 

pebbles and boulders of well-rounded limestone and sandstone and 

angular and subrounded chert derived from the Kaibab and Toroweap 

Formations. Includes lenses of gray silt and sand and locally wellrounded to subangular basalt clasts. Includes reworked materials 

from alluvial-fans (Qa. and Qa2 ), terrace-gravel (Qg 2 and Qg 3 ), talus 

(Qt), and landslide (Ql) deposits. Locally cut by arroyos. Forms 

alluvial benches about 1 to 3 m above local stream beds. Averages 

about 1 to 3 m thick

10
Qa L Young alluvial fan deposit (Holocene)--Unconsolidated gray silt and 

sand. Contains lenses of coarse gravel composed of subangular to 

rounded pebbles and cobbles of limestone, chert, and sandstone 

locally derived from the Hermit, Toroweap, Kaibab, and Moenkopi 

Formations. Locally includes well-rounded to sub-angular basalt 

clasts. Partly cemented by gypsum and calcite. Overlaps, 

intertongues, or partly includes reworked materials from streamchannel (Qs), valley-fill (Qv), terrace-gravel (Qg 1? Qg2 , and Qg 3 ), 

and older alluvial-fan (QaJ deposits. Alluvial fans subject to 

erosion by sheet wash and flash floods. Supports sparse growths of 

sagebrush, cactus, and grass. As much as 4 m or more thick

Qv Valley-fill deposit (Holocene and Pleistocene)--Partly consolidated gray 

and light-brown silt, sand, and lenses of pebble to small-boulder 

gravel. Intertongues or overlaps talus (Qt), terrace-gravel (Qg p 

Qg 2 and Qg 3 ) deposits, and alluvial fan (Qa x and Qa2 ) deposits. 

Subject to sheetwash flooding and temporary ponding; cut by arroyos 

as much as 2 m deep in larger valleys. Supports sparse growths of 

sagebrush, grass, and cactus. As much as 5 m thick

Qt Talus deposit (Holocene and Pleistocene)--Unsorted debris consisting of 

breccia composed of small and large angular blocks of local basalt 

bedrock as much as 2 m in diameter. Includes silt, sand, and gravel; 

partly cemented by calcite and gypsum. Intertongues with alluvialfan (Qa 1 and Qa2 ), valley-fill (Qv), and terrace-gravel (Qg x and Qg 2 ) 

deposits. Supports sparse growths of sagebrush, cactus, and grass. 

Only relatively extensive deposits shown. As much as 3 m thick

Ql Landslide deposit (Holocene and PIeistocene)--Unconsolidated and

unsorted masses of rock debris, including detached blocks of bedrock 

strata that have rotated backward and slid downslope as loose, 

incoherent masses of broken rock and deformed strata, often 

surrounded by talus. Includes blocks of strata of the Fossil 

Mountain Member of Kaibab Formation along the upper ledges of the 

Hurricane Cliffs. Supports sparse growth of sagebrush, cactus, 

grass, juniper and pinyon pine trees. Unstable when wet. Only large 

masses are shown. As much as 35 to 45 m thick

Qg 2 Intermediate terrace-gravel deposit (Holocene and Pleistocene)--Similar 

to young terrace-gravel deposits (Qg^ but partly consolidated. 

Contains well-rounded basalt clasts as much as 12 cm or more in 

diameter. Forms benches as abandoned stream channels about 2 to 4 m 

above local stream beds and about 1 to 3 m above young-terrace gravel 

(Qgj) deposits. Intertongues with and locally overlain by talus (Qt) 

and young alluvial-fan (Qa^) deposits. Locally inset against higher 

terrace-gravel (Qg 3 ) deposits. Approximately 2 to 4 m thick

Qa2 Intermediate alluvial fan deposit (Holocene and Pleistocene)--Similar to 

young alluvial-fan (Qa L ) deposits and partly cemented by calcite and 

gypsum. Locally overlapped by young alluvial-fan (QaJ, young 

terrace-gravel (Qg,), valley-fill (Qv), and talus (QtJ deposits. 

Locally includes abundant subrounded to subangular basalt clasts. 

Supports sparse growths of sagebrush, cactus, and grass. Ranges from 

2 to 4 m thick

11
Qg 3 Older terrace-gravel deposit (Pleistocene)--Similar to young and

intermediate terrace-gravel (Qg, and Qg2 ) deposits, but 2 to 6 m 

higher than intermediate (QgJ deposits and about 4 to 8 m above 

local drainages. Composed of well-rounded limestone, sandstone, 

chert, and basalt clasts in sandy gravely matrix. Basalt clasts 

mainly derived from local basalt flows, but contain clasts from areas 

father south and southeast of this quadrangle. Partly consolidated 

by calcite, clay, and gypsum cement. As much as 6 m thick

IGNEOUS ROCKS

Antelope Knoll Basalt (Pleistocene)--Named for Antelope Knoll volcano, 

type area for Antelope Knoll Basalt. Antelope Knoll is located in 

central part of quadrangle, Sees. 13, 18, 19, and 24, T. 38 N., Rs. 8 

and 9 W., northern Mohave County, Arizona. Includes basalt flows and 

associated pyroclastic deposits. Divided into:

Qai Antelope Knoll intrusive vent area (Pleistocene)--Includes two vent 

areas for basaltic flows north and east from Antelope Knoll. Vent 

areas are approximately marked on map owing to thick cover of 

reddish-black cinder and scoria (Qac) deposits

Qac Antelope Knoll cinder and pyroclastic deposit (Pleistocene)--Reddishblack and brown fragments of angular basaltic cinder and scoria 

deposits. Includes dark-gray augite(?) and olivine(?) glass 

fragments; partly consolidated as welded scoria. Forms cinder 

cone as much as 150 m thick 

Qab Antelope Knoll Basalt flow(s) (Pleistocene)--Dark-gray, finely

crystalline, aphanitic groundmass. Surfaces of flows are partly 

covered by cinder and pyroclastic (Qac) deposits within 1 to 2 km 

of Antelope Knoll. K-Ar whole rock age is 0.83±0.3 Ma (Harold 

Mehnert, U.S. Geological Survey Isotope Laboratories, Denver, 

Colorado, written commun., 1993). Overlies alluvium, Harrisburg 

Member of Kaibab Formation, and lower red member and Timpoweap 

Member of Moenkopi Formation. Ranges from 2 to 15 m thick 

Seven Knolls Basalt (Pleistocene)--Named for Seven Knolls volcanoes, 

type area for Seven Knolls Basalt. Seven Knolls volcanoes are in 

Sees. 10, 15, 23 and 26, T. 37 N., R. 8 W., northern Mohave County, 

Arizona (U.S. Geological Survey Moriah Knoll and Hat Knoll 7.5' 

quadrangles, 1971). Includes basalt flows and associated pyroclastic 

deposits of Deadman Knoll and unnamed knoll, southeast corner of 

quadrangle. Divided into: 

Qsi Seven Knolls vent area (Pleistocene)--Vent areas are covered by

reddish-brown to black cinder and scoria deposits that form cinder 

cones; source vent areas for local basalt flows of Seven Knolls 

Basalt. Basalt flowed in a northerly direction from vent areas 

Qsc Seven Knolls cinder and pyroclastic deposit (Pleistocene)--Reddishbrown and black fragments of angular basaltic scoria and cinder 

deposits. Includes Deadman Knoll and unnamed cinder cone in 

southeast corner of quadrangle; unconsolidated. Associated with 

Seven Knolls Basalt flows. Forms cinder cones 30 to 60 m thick

12
Qsb Seven Knolls Basalt flow(s) (Pleistocene)--Dark-gray, finely

crystalline groundmass composed of plagioclase, olivine, and 

augite; contains small phenocrysts of green olivine. Includes one 

or more flows that merge into one thick flow from Deadman Knoll 

and unnamed knoll which merges with basalt flows from Seven Knolls 

volcanoes 1 to 6 km southeast of this quadrangle. Flow surfaces 

partly covered by cinder and pyroclastic (Qsc) deposits. Overlies 

middle and lower part of Harrisburg Member of Kaibab Formation, 

and lower red member and Virgin Limestone Member of Moenkopi 

Formation. Ranges from 2 to 15 m thick

Maryland Knoll Basalt (Pleistocene)--Named for Maryland Knoll volcano, 

type area for Maryland Knoll Basalt. Maryland Knoll is in the south 

central part of quadrangle, Sec. 31, T. 38 N., R. 8 W., northern 

Mohave County, Arizona. Includes basalt flows and pyroclastic 

deposits. Divided into:

Qmi Maryland Knoll intrusive vent area (Pleistocene)--Includes two vent 

areas approximately marked on map for source of Maryland Knoll 

Basalt and pyroclastic (Qmc) deposits

Qmc Maryland Knoll cinder and pyroclastic deposit (Pleistocene)--Redbrown and black fragments of angular basaltic scoria, glass, and 

cinder deposit; unconsolidated. Forms two cinder cones as much as 

90 m thick 

Qmb Maryland Knoll Basalt (Pleistocene)--Dark-gray, finely crystalline,

aphanitic groundmass composed of plagioclase, olivine, and augite. 

Includes two flows that merge into one flow. Basalt flow shares 

common boundary or abuts against Antelope Knoll Basalt; partly 

overlain by Seven Knolls Basalt. Surface is partly covered by 

cinder and pyroclastic (Qmc) deposits. Overlies Harrisburg Member 

of the Kaibab Formation. Flow extends for about 3 km east from 

Maryland Knoll. Ranges from 2 to 20 m thick 

QTm Moriah Knoll Basalt (Pleistocene-Pliocene?)--Named for Moriah Knoll

volcano in Sees. 7, 12, 18, and 13, T. 37 N., Rs. 8 and 9 W., (Moriah 

Knoll 7.5' quadrangle, 1971), about 1 km south of quadrangle edge, 

northern Mohave County, Arizona (Billingsley, 1993c; in press, b). 

Moriah Knoll is type area for Moriah Knoll Basalt. Black, aphanitic, 

vesicular basalt. Includes minor olivine phenocrysts and vesicles 

commonly filled with calcite. K-Ar whole rock age is 2.3+1.5 Ma 

(Harold Mehnert, U.S. Geological Survey Isotope Laboratories, Denver, 

Colorado, written commun., 1993). One flow, about 3 m thick

SEDIMENTARY ROCKS

Moenkopi Formation (Lower Triassic)--Includes, in descending order, the 

Virgin Limestone Member, lower red member, and Timpoweap Member as 

used by Stewart and others (1972). Divided into:

"Emv Virgin Limestone Member Consists of one light-gray, ledge-forming 

limestone bed containing star-shaped crinoid plates and poorly 

preserved Composita brachiopods in top part. Upper part of Virgin 

Limestone has been eroded away. Overlain by Seven Knolls Basalt. 

Basal unconformity with as much as 1 m of relief truncates 

underlying red siltstone of lower red member. As much as 4 m 

thick

13
1ml Lower red member--Interbedded red, fine-grained, thin-bedded, 

gypsiferous sandy siltstone, gray, white, and pale-yellow 

laminated gypsum and minor sandstone. Lower beds contain reworked 

gypsum and siltstone of Harrisburg Member of Kaibab Formation. 

Interbedded or gradational contact with sandstone or conglomerate 

of Timpoweap Member arbitrarily placed at lowermost red siltstone 

bed. Unconformable contact with Kaibab Formation. Forms slope. 

Locally thickens and fills Triassic paleovalleys eroded into 

underlying Kaibab Formation. Forms slope. Ranges from 3 to 25 m 

thick

Imt Timpoweap Member Light gray conglomerate and sandstone.

Conglomerate composed of subangular to rounded pebbles and cobbles 

of gray and dark gray limestone, white and brown chert, and 

rounded quartzite in matrix of gray to brown, coarse-grained, lowangle.cross-bedded calcareous sandstone, gravel, and minor 

siltstone derived from Kaibab.Formation. Source for dark-gray 

limestone and quartzite may be Paleozoic rocks west of map area. 

Forms slope. Fills Triassic paleovalleys eroded into Kaibab 

Formation estimated as much as 70 m deep and about 800 m wide. 

Rocks of Timpoweap occupy one major paleovalley considered an 

eastern extension of Mustang valley (fig. 2; Billingsley, 1994; in 

press a) and two minor paleovalley's in southwest quarter of 

quadrangle. Imbrication of pebbles in conglomerate show a 

southeastward paleoflow of depositing streams. As much as 6 to 43 

m thick

Kaibab Formation (Lower Permian)--Includes, in descending order, 

Harrisburg and Fossil Mountain Members as defined by Sorauf and 

Billingsley (1991). Divided into:

Pkh Harrisburg Member--Includes an upper, middle and lower part. Upper 

part consists mainly of slope-forming, red and gray, interbedded 

gypsiferous siltstone, sandstone, gypsum, and thin-bedded gray 

limestone. Includes an upper resistant, pale-yellow or lightgray, fossiliferous (mollusks and algae), sandy limestone bed 

averaging about 1 m thick that weathers black or brown. Most of 

upper part is eroded from this quadrangle except in northeast 

quarter. Forms gradational contact with middle part. Middle part 

consists mainly of two cliff-forming marker limestone beds. Top 

marker bed consists of gray, thin-bedded, cherty limestone; 

weathers dark brown or black and often forms bedrock surface of 

exposed Harrisburg Member. Bottom marker bed consists of lightgray, thin-bedded, sandy limestone; both beds are only a few 

meters thick. Erosional unconformably separates middle part from 

lower part. Lower part consists of slope-forming, light-gray, 

fine- to medium-grained, gypsiferous siltstone, sandstone, mediumgrained, thin-bedded gray limestone, and gray massive bedded 

gypsum. Solution of gypsum in lower part has locally distorted 

limestone beds of middle part causing them to slump or bend into 

local drainages. Gradational and arbitrary contact between 

siltstone slope of Harrisburg Member and limestone cliff of Fossil 

Mountain Member. Harrisburg, in general, forms slope with 

limestone cliff in middle. As much as 92 m thick

14
Pkf Fossil Mountain Member--Light-gray, fine- to medium-grained, thinbedded, fossiliferous, sandy, cherty limestone. Chert weathers 

black. Contact with Woods Ranch Member of Toroweap Formation 

marked by solution and channel erosion with relief as much as 3 m; 

contact locally obscured by talus and minor landslides. Forms 

cliff. About 80 m thick

Toroweap Formation (Lower Permian)--Includes, in descending order, Woods 

Ranch, Brady Canyon, and Seligman Members as defined by Sorauf and 

Billingsley (1991). Divided into:

Ptw Woods Ranch Member Gray gypsiferous siltstone and pale-red silty 

sandstone interbedded with medium-bedded white laminated gypsum. 

Beds are locally distorted due to gypsum solution. Gradational 

and arbitrary contact between slope-forming Woods Ranch Member and 

cliff-forming Brady Canyon Member of Toroweap. Variable thickness 

from 55 to 80 m due to solution of gypsum

Ptb Brady Canyon Member--Gray, fetid, medium-bedded, fine- to coarsegrained, fossiliferous limestone; weathers dark dray. Includes 

thin-bedded dolomite in upper and lower part. Limestone beds 

average about 0.5 m thick. Includes chert lenses and nodules but 

these are 50% less than in Fossil Mountain Member of Kaibab. 

Gradational and arbitrary contact between cliff-forming limestone 

of Brady Canyon Member and slope-forming siltstone and gypsum of 

Seligman Member of Toroweap; commonly covered because of minor 

slump or talus debris. Forms cliff. Approximately 70 m thick

Pts Seligman Member Consists of an upper gray, interbedded, thin-bedded 

dolomite and gypsiferous sandstone; a middle gray to red, thinbedded, interbedded siltstone, sandstone, and gray gypsum; and a 

lower brown, purple, and yellow, fine- to medium-grained, thinbedded, low- to high-angle cross-bedded and planar-bedded 

sandstone, mostly covered. Contact with underlying Hermit 

Formation is covered by talus and alluvial deposits. Forms slope 

with ledges. About 45 m exposed

Contact--Dashed where approximately located

Fault Dashed where inferred or approximately located; dotted where 

concealed; bar. and ball on downthrown side. Number is estimated 

displacement in meters. Number with plus denotes minimum 

estimated displacement

Landslide detachment--Headward scarp of landslide, hachures point in 

direction of siide

Folds Showing trace of axial plane and direction of plunge; dashed 

where approximately located; dotted where concealed 

Anticline

Syncline

Monocline

Dome

15
Doubly plunging anticline

Strike and dip of beds Showing dip where known 

Inclined

Approximate Estimated from aerial photographs

Implied Interpreted from aerial photographs, dip amount not 

determined

Strike of vertical and near-vertical joints Interpreted from aerial

photographs 

Collapse structure--Circular collapses, strata dipping inward toward

central point. May reflect collapse of deep-seated breccia pipe

that originated in Redwall Limestone 

Sinkholes Steep-walled or enclosed depression or cave

Flow direction of basalt

REFERENCES CITED

Billingsley, G.H., 1993a, Geologic map of Wolf Hole Mountain and vicinity, 

Mohave County, northwestern Arizona: U.S. Geological Survey 

Miscellaneous Investigations Map Series 1-2296, scale 1:31,680.

___ 1993b, Geologic map of The Grandstand quadrangle, northern Mohave

County, Arizona: U.S. Geological Survey Open-File Report 93-588, scale 

1:24,000, includes pamphlet 15 p.

___ 1993c, Geologic map of the Russell Spring quadrangle, northern Mohave 

County, Arizona: U.S. Geological Survey Open-File Report 93-717, scale 

1:24,000, includes pamphlet 17 p.

___ 1994, Geologic map of the White Pocket quadrangle, northern Mohave

County, Arizona: U.S. Geological Survey Open-File Report 94-244, scale 

1:24,000, includes pamphlet, 11 p.

___ in press(a), Geologic map of the lower Hurricane Wash and vicinity, 

northwestern Arizona: U.S. Geological Survey Miscellaneous 

Investigations Map Series 1-2481, scale 1:31,680.

___ in press(b), Geologic map of the upper Hurricane Wash and vicinity, 

northwestern Arizona: U,S. Geological Survey Miscellaneous 

Investigations Map Series I- , scale 1:31,680.

Billingsley, G.H., Huntoon, P.W., 1983, Geologic map of the Vulcan's Throne 

and vicinity, western Grand Canyon, Arizona: Grand Canyon Natural 

History Association, Grand Canyon, Arizona, scale 1:48,000.

Elston, D.P., and Young, R.A., 1991, Cretaceous-Eocene (Laramide) landscape 

development and 01igocene-Pliocene drainage reorganization of Transition 

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96, no. B7, p. 12,389-12,406.

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Geological Society, Distributed by Utah Geological and Mineralogical 

Survey, University of Utah, Salt Lake City, Utah, p. 21-37.

16
Hamblin, W.K., and Best, M.G., 1970, The western Grand Canyon district:

Guidebook to the geology of Utah, no. 23, Brigham Young University, Utah 

Geological Society, Distributed by Utah Geological and Mineralogical 

Survey, University of Utah, Salt Lake City, Utah, 156 p.

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1:48,000.

Koons, E.D., 1945, Geology of the Uinkaret Plateau, northern Arizona: 

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the Triassic Moenkopi Formation and related strata in the Colorado 

Plateau region: U.S. Geological Survey Professional Paper 691, 195 p.

Wenrich, K.J., 1985, Mineralization of breccia pipes in northern Arizona: 

Economic Geology, v. 80, no. 6, p. 1722-1735.

Wenrich, K.J., Billingsley, G.H., and Huntoon, P.W., 1986, Breccia pipe and 

geologic map of the northeastern Hualapai Indian Reservation and 

vicinity, Arizona: U.S. Geological Survey Open-File Report 86-458-A, 

scale 1:48,000, includes pamphlet, 26 p.

Wenrich, K.J., and Huntoon, P.W., 1989, Breccia pipes and associated

mineralization in the Grand Canyon region, northern Arizona: in Elston, 

D.P., Billingsley, G.H., and Young, R.A., eds., Geology of Grand Canyon, 

Northern Arizona (with Colorado River Guides), 28th International 

Geological Congress Field Trip Guidebook T115/315, American Geophysical 

Union, Washington, D.C., p. 212-218.

Wenrich, K.J., and Sutphin, H.B., 1989, Lithotectonic setting necessary for 

formation of a uranium-rich, solution-collapse breccia-pipe province, 

Grand Canyon region, Arizona: U.S. Geological Survey Open-File Report 

89-0173, 33 p.

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of Arizona: Arizona Bureau of Mines, University of Arizona, scale 

1:500,000.

17
CORRELATION OF MAP UNITS

SURFICIAL DEPOSITS AND IGNEOUS ROCKS

Qaf Qs Qg,

Qg2

Qg 3

Qa,

Qa2

Qv

Qt Ql

Qai

QTm

Qac Qab Qmi Qmc Qmb Qsi Qsc Qsb

"

Ho

* PPH

Ple

k ce

^ Pleis

and 

CD

Unconformity

SEDIMENTARY ROCKS 

Unconformity

Low

Tri

Unconformity

Unconformity

Low

Per