U.S. DEPARTMENT OF THE INTERIOR TO ACCOMPANY MF-2368

U.S. GEOLOGICAL SURVEY

GEOLOGIC MAP OF PART OF THE UINKARET VOLCANIC FIELD,

MOHAVE COUNTY, NORTHWESTERN ARIZONA

By George H. Billingsley and W. Kenneth Hamblin

# INTRODUCTION

The geologic map of part of the Uinkaret Volcanic Field is one product
of a cooperative project between the U.S. Geological Survey, the
National Park Service, and the Bureau of Land Management to provide
geologic information about this part of the Grand Canyon-Parashant
Canyon National Monument of Arizona. The Uinkaret Volcanic Field is a
unique part of western Grand Canyon where volcanic rocks have preserved
the geomorphic development of the landscape. Most of the Grand Canyon,
and parts of adjacent plateaus have already been mapped. This map
completes one of the remaining areas where uniform quality geologic
mapping was needed. A few dozen volcanoes and lava flows within the
Grand Canyon are not included in the map area, but their geologic
significance to Grand Canyon development is documented by Hamblin (1994)
and mapped by Billingsley and Huntoon (1983) and Wenrich and others
(1997). The geologic information in this report may be useful to
resource managers of the Bureau of Land Management for range management,
biological, archaeological, and flood control programs.

The map area lies within the Shivwits, Uinkaret, and Kanab Plateaus,
which are subplateaus of the Colorado Plateaus physiographic province
(Billingsley and others, 1997), and is part of the Arizona Strip north
of the Colorado River. The nearest settlement is Colorado City, Arizona,
about 58 km (36 mi) north of the map area (fig. 1). Elevations range
from about 2,447 m (8,029 ft) at Mount Trumbull, in the northwest
quarter of the map area, to about 732 m (2,400 ft) in Cove Canyon, in
the southeast quarter of the map area. Vehicle access is via the
Toroweap and Mount Trumbull dirt roads (fig. 1). Unimproved dirt roads
traverse other parts of the area except in designated wilderness. Extra
fuel, two spare tires, and extra food and water are highly recommended
for travelers in this remote area.

The U.S. Bureau of Land Management, Arizona Strip Field Office, St.
George, Utah manages most of the area. In addition, there are 12
sections belonging to the State of Arizona, about 12 sections are
private land, and several sections are within the Grand Canyon National
Park and Lake Mead National Recreational Area (U.S. Department of the
Interior, 1993). The private land is in Potato Valley and Lake Valley,
southwest and west of Mount Trumbull, and in Whitmore Canyon and
Toroweap (Tuweap) Valley. Portions of the Sawmill Mountains, Mount
Logan, and Mount Trumbull areas were originally established as part of
the Dixie National Forest in 1904. In 1924, Dixie National Forest land
became part of the Kaibab National Forest. Then on February 13, 1974,
management of this part of the Kaibab National Forest was transferred to
the Bureau of Land Management, Arizona Strip Field Office (personal
commun. Becky Hammond, Bureau of Land Management, 1997). Mount Logan and
part of the Sawmill Mountains are now designated as the Mount Logan
Wilderness Area, and Mount Trumbull is designated as the Mount Trumbull
Wilderness Area. Most of the map area is now part of the new Grand
Canyon-Parashant Canyon National Monument established January 11, 2000.

Lower elevations within Hells Hollow, Whitmore Canyon, Toroweap Valley,
and Cove Canyon support a sparse growth of sagebrush, cactus, grass, and
a variety of desert shrubs. Sagebrush, grass, cactus, cliffrose bush,
pinion pine, and juniper trees thrive at elevations above 1,830 m (6,000
ft). Ponderosa pine and oak forests thrive at higher elevations in the
Mount Trumbull and Mount Logan areas.

Surface runoff within the map area drains south towards the Colorado
River through Hells Hole, Hollow, Whitmore Canyon, Toroweap Valley, and
Cove Canyon. Upper Toroweap Valley, upper Hells Hollow, and Whitmore
Canyon are part of the physiographic area of Grand Canyon, but are not
within Grand Canyon National Park (Billingsley and others*,* 1997). As
of January 11, 2000, these areas are now part of the new Grand
Canyon-Parashant Canyon National Monument.

![](media/image1.png){width="6.606944444444444in"
height="5.575694444444444in"}

**Figure 1**. Map showing the Mount Trumbull NW (A), Mount Trumbull NE
(B), Mount Logan (C), and Mount Trumbull SE (D), U.S. Geological Survey
7.5-minute quadrangles and adjacent mapped areas, northern Mohave
County, northwestern Arizona.

# PREVIOUS WORK

Dutton (1882) made the earliest geologic map of the Uinkaret Plateau. A
reconnaissance photogeologic map was produced by Koons (1945), and later
compiled onto a state geologic map of Arizona by Wilson and others
(1969), and then recompiled to a different scale by Reynolds (1988). The
first recorded survey of the Uinkaret Volcanic Field was by Powell
(1875) in 1869-72. Powell named the Uinkaret Plateau and applied the
names of Mount Trumbull, Mount Logan, and Mt. Emma to prominent peaks.
He discovered the Toroweap Fault and estimated its displacement to be
about 244 m (800 ft) (Powell, 1875). Geologic maps of the Mount Logan
and Mount Trumbull NW quadrangles (Billingsley, 1997a, b) are compiled
into the western half of the map area. Geologic mapping of adjacent
areas (fig. 1) include upper Hurricane Wash and vicinity, which adjoins
the northwest corner of this map (Billingsley, unpub. data a); upper
Parashant Canyon and vicinity bordering the western edge of this map
(Billingsley and others, 2000); and Clayhole Valley and vicinity, which
borders the northern edge of this map (Billingsley, unpub. data b). A
geologic map by Wenrich and others (1997) borders the southern edge of
the map area.

# MAPPING METHODS

This map was produced using 1:24,000-scale 1976 aerial photographs
followed by extensive field checking. Volcanic rocks were mapped as
separate units when identified on aerial photographs as mappable and
distinctly separate units associated with one or more cinder cones and
flows. Several basalt flows and associated cinder cones at similar
stratigraphic levels could not be distinguished as separate units with
certainty and were mapped as general Quaternary basalt units (Qp and Qb
south of Mount Trumbull, Qp1 and Qb1 north of Mount Trumbull) based on
stratigraphic relations and coalescing basalt flows. Textural and
mineral characteristics are not distinctive enough to separate
individual basalt units.

Many of the Quaternary alluvial deposits that have similar lithology but
different geomorphic characteristics were mapped almost entirely by
photogeologic methods. Stratigraphic position and amount of erosional
degradation were used to determine relative ages of alluvial deposits
having similar lithologies. Each map unit and structure was investigated
in detail in the field to insure accuracy of description.

# GEOLOGIC SETTING

The boundary between the lower Shivwits and higher Uinkaret Plateaus is
the Hurricane Fault. The Shivwits Plateau is west of the Hurricane Fault
on the downthrown side, and the Uinkaret Plateau is east of the fault on
the upthrown side. The boundary between the Uinkaret and Kanab Plateaus
is the Toroweap Fault; the Uinkaret Plateau is west of the Toroweap
Fault on the downthrown side, and the Kanab Plateau is east of the fault
on the upthrown side.

Nearly flat-lying Paleozoic and Mesozoic sedimentary strata that have an
average regional dip of about 1º ENE characterize the Shivwits,
Uinkaret, and Kanab Plateaus, except near the Hurricane and Toroweap
Faults. Strata along the downthrown side of these faults are largely
covered by alluvium, basalt flows, or landslide debris, but exposures in
the Grand Canyon 5 km (3 mi) south of this map area show Paleozoic
strata dipping east toward the fault planes about 14º along the
Hurricane Fault and about 4º along the Toroweap Fault. These dips may
reflect a weak monoclinal structure associated with both faults as
suggested by Huntoon (1990) and indicated by Billingsley and Huntoon
(1983) and Wenrich and others (1997), but the monoclinal axis is not
shown on the map because the monoclines are weakly present along these
segments of the Toroweap and Hurricane Faults. Tilted strata west of the
faults illustrate a reverse fault drag as suggested by Hamblin (1965).
Maximum vertical separation of strata across the Hurricane and Toroweap
Faults is estimated at about 610 m (2,000 ft) and 198 m (650 ft),
respectively.

Tertiary and Quaternary volcanic rocks and surficial deposits are widely
distributed in the map area. The volcanic rocks are mostly
alkali-olivine basalt flows and pyroclastic deposits of the Uinkaret
Volcanic Field. These rocks cover about two-thirds of the map area. At
least 154 pyroclastic cones are present in the map area. An additional
35 pyroclastic cones are just south of the map area (Billingsley and
Huntoon, 1983; Wenrich and others, 1997) and 24 more are just north of
the map area (Billingsley and Workman, 1999) bringing the total number
of volcanic cones in the Uinkaret Volcanic Field to about 213. Tertiary
age volcanoes began erupting about 3.6 Ma at four separate areas within
the Uinkaret Volcanic Field and later became surrounded or covered by
numerous Pliocene and Pleistocene volcanic deposits.

Mapped surficial deposits include stream channel, floodplain, terrace
gravels, alluvial fans, talus debris, valley-fill, colluvial, and
landslide deposits. Artificial fill and quarry deposits are also mapped.
Map contacts between Quaternary deposits are arbitrary because of
intertonguing and (or) gradational lateral and vertical changes. The
subdivision of Quaternary surficial units on the map is intentionally
detailed because these units strongly influence the management of
rangeland, flood control, biological studies, soil erosion, and the
planning of road construction. All surficial deposits in the map area
are Pleistocene or younger, because they contain materials derived from
Quaternary volcanic deposits (Billingsley, 1997a, b; unpub. data a, b;
Billingsley and others, 2000).

# PALEOZOIC AND MESOZOIC SEDIMENTARY ROCKS

There are about 1,220 m (4,000 ft) of Cambrian, Devonian, Mississippian,
Pennsylvanian, and Permian strata exposed in the map area and about 600
m (1,970 ft) of Triassic strata. The Paleozoic and Mesozoic rocks are
sedimentary and are, in order of decreasing age, the Muav Limestone
(Cambrian), the Temple Butte Formation (Devonian), the Redwall Limestone
(Mississippian), the lower Supai Group undivided (Pennsylvanian and
Mississippian), the Esplanade Sandstone of the Supai Group (Permian),
the Hermit Formation, Coconino Sandstone, Toroweap Formation, and Kaibab
Formation (Permian), the Moenkopi Formation (Triassic), and the Chinle
Formation (Triassic). The Coconino Sandstone is mapped as a separate
unit as with current Grand Canyon nomenclature because it forms a
mappable unit, but the Coconino Sandstone intertongues within the lower
part of the Seligman Member of the Toroweap Formation as suggested by
Fisher (1961), Schleh (1966), Rawson and Turner (1974), Billingsley
(1997a), and Billingsley and others (2000).

All Paleozoic rocks are well exposed in Cove Canyon, in the southeast
quarter of the map area, and Permian strata form the walls of Toroweap
Valley and Whitmore Canyon. Whitmore Canyon was originally called
Queantoweap Valley (Koons, 1945), and it is not known when the name was
changed. Gray to red or reddish gray interbedded siltstone, sandstone,
limestone, and gypsum of the Harrisburg Member of the Kaibab Formation
form the bedrock surface of all the plateaus where not covered by
Mesozoic strata, volcanic rocks, or alluvial deposits.

The Mesozoic rocks consist mainly of red siltstone and sandstone of the
Moenkopi Formation and mudstone of the lower part of the Chinle
Formation. A complete section of these rocks is well exposed in Hells
Hole, a steep-walled amphitheater that drains into Whitmore Canyon. The
Chinle Formation is exposed west of Mount Logan (Hells Hole) and west of
the Hurricane Fault. Most of the Triassic Moenkopi strata are covered by
Quaternary basalt flows and landslide debris in the Sawmill Mountains,
Mount Logan, and Mount Trumbull areas. Early Tertiary and Quaternary
erosion removed an unknown thickness of the upper part of the Chinle
Formation and all subsequent younger strata before deposition of the
Tertiary basalts. An unknown thickness of Chinle Formation is present
under the Tertiary basalt flows that cap Mount Trumbull because Chinle
float material occurs in landslide debris on the western and northern
flanks of Mount Trumbull.

A regional unconformity separates the Permian and Triassic strata. After
deposition of the Harrisburg Member of the Kaibab Formation, streams
eroded valleys as deep as 50 m (160 ft). These paleovalleys are now
filled with sediments of the Timpoweap Member of the Moenkopi Formation
(Triassic). The chert, limestone, sandstone, and gypsum clasts within
the Timpoweap Member are derived from the Kaibab Formation. Pebble
imbrications in the Timpoweap Member indicate that east- and
northeast-flowing streams deposited these clasts.

# VOLCANIC ROCKS

## Quaternary volcanic rocks

Quaternary basalt flows are more widespread than Tertiary basalt flows
and generally surround the Tertiary flows at lower elevations. The
Quaternary basalt flows are generally associated with a late-stage
eruptive phase that resulted in the formation of numerous pyroclastic
cinder cones. There are about 154 Quaternary cinder cones within the map
area. Fissure eruptions along north-south fractures and joints in the
bedrock have allowed for extensive simultaneous eruptions of basalt
flows and pyroclastic cones that form several aligned cones such as Mt.
Emma, Petty Knoll, and Slide Mountain. In most cases, the dying stages
of gaseous vents appear to have formed large pyroclastic cones on top of
associated basalt flows as lava spread out and coalesced with flows from
other nearby eruptive centers. However, in some cases the basalt flow
appears to have been the last stage when basalt flows rafted away parts
of the cone. In either case, basalt flows and associated pyroclastic
cones in this map and report are treated as a same-time, single,
eruptive phase, even when map contacts show pyroclastic cones are
younger than the basalt flows. Many of the basalts carry mantle derived
peridotite inclusions indicating that the magma originated from the
upper mantle (Best and others, 1970). Dutton (1882) and Koons (1945)
observed the tendency for cones on the Uinkaret Plateau to align
parallel to faults but to occur in the areas between them. Area mapping
and adjacent mapping (Billingsley and others, 2000) show that volcanic
cones and dikes align to local bedrock joint and fracture systems that
predate faulting.

K-Ar ages have been determined for some of the basalt flows. Jackson
(1990) reported a 0.635±0.24 Ma age from a basalt flow in the upper
reaches of Toroweap Valley. The location of his sample was not reported,
but Jackson mentioned an offset of the flow of about 36 m (118 ft) along
the Toroweap Fault. The road into Toroweap Valley (this map area)
parallels the Toroweap Fault and is built on the basalt of Graham Ranch
flow that entered Toroweap Valley from the east. The basalt of Graham
Ranch is offset by the Toroweap Fault about 34 to 36 m (110 to 118 ft)
and is likely the same basalt from which Jackson (1990) obtained the
0.63 Ma date.

Billingsley (1994a) reported a K-Ar age of 0.83±0.28 Ma for the Antelope
Knoll Basalt about 29 km (18 mi) north of the map area at the north
margin of the Uinkaret Volcanic Field. There are several K-Ar ages
between 1.2 Ma and 0.44 Ma reported by Hamblin (1994) from basalt flows
along the south edge of the Uinkaret Volcanic Field within the Grand
Canyon (about 9.6 km \[6 mi\] south of the map area). Wenrich and others
(1995) reported a K-Ar age of 0.76±0.08 Ma for a basalt flow in Tuckup
Canyon about 9.6 km (6 mi) east of the map area and a 0.407±0.07 Ma age
for a dike about 17.6 km (11 mi) east of the map area. Anderson and
Christensen (1989) reported a K-Ar age of 0.203 Ma for basalt in the
lower reaches of Toroweap Valley (southeast edge of the map area), but
did not specify a site or range of age error. The youngest basalt flow
in the Uinkaret Volcanic Field is about 1,000 years old as determined by
cosmogenic ^3^He dating methods (Fenton, 1998). This young volcano is
about 3 km (2 mi) south of Mount Trumbull and east of Little Spring and
is informally named the basalt of Little Spring (this report). This
basalt is comparable in surface characteristics and texture to the
1,000-year-old Sunset Crater Volcano near Flagstaff, Arizona.

The cosmogenic ^3^He dating technique identifies other very young basalt
flow surfaces in the map area. According to Fenton (1998), basalt flow
surfaces south of Mt. Emma that cascaded into Toroweap Valley and
Whitmore Canyon are about 0.100 Ma. Some of these basalt flows and
associated pyroclastic deposits form mappable units in the northwest
quarter of the map area. The basalt flows and pyroclastic deposits of
Slide Mountain, Petty Knoll, and Mt. Emma are among the most prominent
and impressive Quaternary volcanoes and appear to have erupted at about
the same time. Lava from many of the volcanoes in the Mt. Emma chain
form flows that coalesced and cascaded down drainages and over the
general landscape westward into Whitmore Canyon and eastward into
Toroweap Valley (Canyon) to the Colorado River south of the map area
(Hamblin, 1994; Billingsley and Huntoon, 1983; Wenrich and others, 1997;
Fenton, 1998).

Toroweap Valley is about 5 km (3 mi) wide and contains as much as 100 m
(300 ft) of basalt and alluvium in the upper reaches and as much as 670
m (2,200 ft) in the down-stream part of the valley. Toroweap Valley was
at grade with the Colorado River before basalt flows began filling the
canyon approximately 0.150 to 0.200 Ma (Fenton, 1998) as evidenced by
the nearly 860 m (2,820 ft) of basalt fill overlain by only a few meters
of alluvium at the confluence of Toroweap Valley and the Colorado River,
5 km (3 mi) south of the map area. There may have been a few Tertiary
flows that partially filled Toroweap Valley before Quaternary flows
filled the canyon. Further studies of the volcanic rocks are needed to
determine the sequence of basaltic events that filled Toroweap Valley.
The Toroweap Valley is now filled with basalt, and only recently has
alluvium begun to accumulate in low areas. A younger basalt flow and
pyroclastic cone, Vulcan\'s Throne 3 km (2 mi) south of the southeast
corner of the map (average cosmogenic age of 0.074±.04 Ma), is deposited
on top of the 0.200 Ma Quaternary flows at the mouth of Toroweap Valley
(Fenton, 1998). The alluvium and basalt near Vulcan's Throne are offset
as much as 5 m (15 ft) by Holocene movement along the Toroweap Fault;
this offset clearly defines the Toroweap Fault in Toroweap Valley.
Faulting along the Toroweap Fault in Prospect Valley south of the
Colorado River occurred as recently as 0.038 Ma or earlier based on
cosmogenic ^3^He dating of the volcanic flows in Prospect Valley south
of Vulcan's Throne (Fenton, 1998).

Most of the Quaternary basalts are combined into general
undifferentiated map units based on the coalescing of basalt flows from
several vent areas that erupted at about the same time north and south
of Mount Trumbull. Some of the Quaternary basalt units are formally or
informally named for nearby geographic locations or the elevation of the
highest cinder cone associated with a mappable flow. Based on
stratigraphic position, the basalt flows that spread into Toroweap
Valley from the west in the north half of the map appear to be older
than those that flowed from the west in the south half. However, the
timing of these westerly flows reaching Toroweap Valley may be a factor
of distance from the source, rather than a difference in age. The basalt
of Graham Ranch entered upper Toroweap Valley from the east and appears
to be slightly older than the flows that came from the west, because it
is overlain by flows from the west. But the flow from the east traveled
a much shorter distance than those from the west traveled, which
suggests a possible similar age for basalts east and west of the
Toroweap Fault. The basalt of Larimore Tank in the upper reaches of
Toroweap Valley originated north of the map area and is probably the
second youngest basalt in the map area based on stratigraphic position
and freshness of flow surfaces (the Cave Basalt of Billingsley, 1994b;
Billingsley and Workman, 1999). The youngest basalt in the map area is
the basalt of Little Spring south of Mount Trumbull.

Quaternary basalt flows preserved the geomorphic history of landscape
development in Toroweap Valley, but further study and accurate age
determinations of the basalts are needed. The chronologic age of
volcanic events in the map area is based on stratigraphic position of
flows, freshness and weathering of flow surfaces, and geomorphic
relation to alluvial deposits. Quaternary basalts are briefly described
from youngest to oldest.

## Basalt of Little Spring

The youngest volcanic rocks in the Uinkaret Volcanic Field consist of a
partially formed double cinder cone and lava flow about 3 km (2 mi)
south of Mount Trumbull. The basalt flow and cinder cone are informally
named the basalt of Little Spring for Little Spring, Uinkaret Plateau,
northern Mohave County, Arizona (SE1/4 sec. 16, T. 34 N., R. 8 W.).
Little Spring is about a kilometer southwest of the vent area for the
basalt of Little Spring in landslide debris near the base of the basalt
of Mount Logan on the east side of Mount Logan. Little Spring is one of
three permanent springs in the south half of the Uinkaret Plateau.
Cosmogenic dating methods of the flow surface of the basalt of Little
Spring indicate that the flows are about 1,000 years old (Fenton, 1998).
Other criteria supporting this age are the freshness of the basalt flow
surface, roughness, character, degree of weathering, and characteristics
similar to the 1,000-year-old basalt flows at Sunset Crater National
Monument near Flagstaff, Arizona.

The basalt of Little Spring originated from two closely associated vents
and coalesced into one large pool of lava that spread in a northerly and
southerly direction. A red pyroclastic cone was formed on top of the
lava, but the lava continued to flow north and south rafting away the
southern and northern part of the pyroclastic cone material. When the
eruption finally ended, only the east half and part of the southwest
edge of the pyroclastic cone remained. Rafted remnants of the
pyroclastic cone are scattered at various locations on the basalt flow.
There is no soil cover and very little vegetation on the flow surface.
Vegetation grows only on scattered remnants of the pyroclastic material
rafted farther south and north from the vent area.

## Basalt of Larimore Tank

This unit was originally named Cave Basalt by Billingsley (1994b) and
Billingsley and Workman (1999) for numerous sinkholes in the basalt
flow. The name was incorrectly used on those two maps because the
authors were unaware that the name Cave Basalt was already in use.
Therefore, the name is herein informally changed to basalt of Larimore
Tank, a stock tank labeled "Larimore Tank" on the U.S. Geological Survey
Hat Knoll 7.5-minute quadrangle just north of the map area, Uinkaret
Plateau, northern Mohave County, Arizona (sec. 16, T. 37 N., R. 7 W.).
The basalt of Larimore Tank consists of five unnamed pyroclastic cones
that are aligned in a northwest-southeast orientation just north of the
northeastern corner of the map area. Lava flows from each vent coalesced
into one thin flow indicating that the five vents were erupting
simultaneously. Most of the basalt flowed north towards Clayhole Valley
(Billingsley, 1994b), but some basalt spread south into the uppermost
reaches of Toroweap Valley (this map).

Numerous sinkholes pit the basalt of Larimore Tank, some as much as 18 m
(60 ft) deep. The sinkholes are the result of solution weathering of
gypsum in the underlying Harrisburg Member of the Kaibab Formation. The
jointed and fractured nature of the basalt flow probably allowed water
to gradually seep down into the underlying gypsum allowing for a more
consistent dissolution of the gypsum. Where gypsum is exposed at the
surface near the basalt of Larimore Tank, water was not able to
penetrate and quickly ran off. The basalt of Larimore Tank flowed south
into upper Toroweap Valley and around an older flow mapped as the basalt
of Graham Ranch.

## Basalt of Graham Ranch

The basalt of Graham Ranch is found near the Graham Ranch in upper
Toroweap Valley, Kanab Plateau, in the northeast corner of the map area
(the type area, Uinkaret Volcanic Field, northern Mohave County,
Arizona, sec. 3, T. 35 N., R. 7 W.). Billingsley and Workman (1999)
inadvertently named this basalt the Sage Basalt before it was known that
the name Sage was already in use. The name Sage Basalt is also
incorrectly used by Billingsley and Hampton (2000).

The basalt of Graham Ranch is an alkali-olivine basalt with three
associated pyroclastic cones. All three cones are aligned north-south
just east of the Toroweap Fault. Basalt from the cones coalesced into
one flow that traveled in several directions. The radial pattern and
coalescing of flows indicate that the three vent areas erupted at about
the same time. Most of the basalt flowed 2.5 km (1.5 mi) west into the
upper reaches of Toroweap Valley near Graham Ranch.

The largest, northernmost cone of the basalt of Graham Ranch is offset
down-to-the-west by the Toroweap Fault. The offset is estimated to be as
much as 26 m (85 ft), based on topographic expression. Offset is visible
on aerial photos, but the fault line is difficult to locate in the field
due to erosion of the pyroclastic deposits. Displacement of the
underlying Kaibab Formation is estimated to be about 67 m (220 ft)
down-to-the-west based on exposures of marker beds on both sides of the
fault in the Harrisburg Member of the Kaibab Formation. The middle
pyroclastic cone is about 70 m (230 ft) high. Some of the basalt from
this cone may have flowed over the Toroweap Fault into Toroweap Valley,
but the flow is not exposed on the downthrown side because it is covered
by alluvium. The southern pyroclastic cone is comprised of two vents
that coalesced into one, forming a 67 m (220 ft) cone. The basalt flow
from this cone is alkali-olivine basalt like the others; olivine
phenocrysts make up about 30 percent of the rock. Most of the basalt
from this southern cone flowed west and descended into Toroweap Valley
over the Toroweap Fault scarp. The basalt was later offset 36 m (120 ft)
by movement on the Toroweap Fault. Thus, about half of the 67 m (220 ft)
of separation along this part of the Toroweap Fault occurred since the
eruption of the basalt of Graham Ranch, about 0.635±0.34 Ma. The basalt
of Graham Ranch flowed at least another 2.5 km (1.5 mi) down Toroweap
Valley after cascading over the Toroweap Fault.

## Undifferentiated basalts

Volcanic rocks north and south of Mount Trumbull are informally referred
to as undifferentiated alkali-olivine basalt flows and pyroclastic
deposits that erupted from several vent areas at about the same time.
Most of the vents have formed large pyroclastic cones aligned in a
general north-south orientation that reflect local bedrock fracture and
joint systems. These deposits are collectively assumed to be Quaternary
age (Billingsley, 1994b, 1997a, b). Basalt flows north of Mount Trumbull
are labeled Qb1, and basalts south of Mount Trumbull are labeled Qb
because the flows south of the mountain may be slightly different in age
based on geomorphic relationships in Toroweap Valley. Fenton (1998)
suggests that the flows south of Mount Trumbull are in the 0.150 to
0.100 Ma age range. Additional work is needed to determine the
chronological order of deposition for Quaternary volcanic rocks in this
part of the Uinkaret Volcanic Field.

A large pyroclastic cone in upper Toroweap Valley (hill 5579) is one of
three vents in Toroweap Valley that formed near the Toroweap Fault. Two
vents are in the southern reaches of Toroweap Valley. There are no
basalt flows visibly associated with hill 5579; if basalt flows are
present, they are totally covered by alluvium or younger basalt flows
from south of Mount Trumbull.

Just southwest of hill 5579 is a large intrusive dike within the
Harrisburg Member of the Kaibab Formation that includes pyroclastic
deposits around its perimeter. No trace of the cone is present.

## Other Quaternary basalts

Some of the Quaternary volcanic rocks in the northwest quarter of the
map area have formed isolated mappable units that abut or overlap basalt
flows of similar age. For descriptive purposes, the mappable volcanic
units of this area are informally named for nearby ranches or the
highest elevation of an associated pyroclastic cone, such as basalt of
Kendrick Ranch or basalt of hill 6375. These alkali-olivine basaltic
rocks are so similar in texture and characteristics that they may have
erupted at or about the same time. Hand samples have very similar
compositional and textural characteristics and cannot be distinguished
from one another with certainty. Future studies of these rocks may
suggest a chronologic order of the eruptions that shaped this remarkable
landscape. These mappable volcanic units are not listed in chronologic
order.

## Basalt of Craigs Knoll and Berry Knoll

The basalt of Craigs Knoll and Berry Knoll is informally named for the
flows and pyroclastic deposits associated with Craigs Knoll (sec. 4, T.
35 N., R. 8 W.), Berry Knoll (sec. 24, T. 36 N., R. 9 W.), and the
unnamed pyroclastic cone between them (sec. 30, T. 36 N., R. 8 W.),
Uinkaret Plateau, northern Mohave County, Arizona, in the northwest
quarter of the map area. Craigs Knoll is a 300-m-high (1,000 ft) cinder
cone about 5 km (3 mi) northeast of Mount Trumbull. Berry Knoll is a
110-m-high (360 ft) pyroclastic cone in the northwest corner of the map
area. These three volcanoes may have erupted simultaneously and the
resultant basalt flows now form a combination of one or more flows
informally mapped as the basalt of Craigs Knoll and Berry Knoll
(Billingsley, 1994b).

Craigs Knoll has been extensively eroded on its east side revealing at
least two eruptive phases. The first phase is the eruption of a basalt
flow onto a nearly flat bedrock surface of low, hilly terrain of the
Harrisburg Member of the Kaibab Formation. The extents of the
first-phase flows are not known because they were subsequently covered
by younger basalt flows during a second eruptive phase. A gray and tan
pyroclastic cone, Craigs Knoll, formed on top of the first basalt flow
before the second eruptive phase began.

The second eruptive phase, a fissure-type eruption on the north flank of
Craigs Knoll, began shortly after Craigs Knoll pyroclastic cone was
formed. The time interval of this hiatus is unknown but was likely only
a few months or years. The second eruptive phase produced a thick series
of basalt lavas that flowed in a radial pattern on the north flank of
Craigs Knoll and covered the north half of the cone and surrounding
landscape west, north, and east of Craigs Knoll. This eruptive phase
formed a small cone on the north flank of Craigs Knoll that became
partly buried by subsequent basalt flows. The second phase of basalt
flows at Craigs Knoll flowed north about 8 km (5 mi), (Billingsley,
1994b and unpub. data b).

After the second eruptive phase ended, the basalts were offset about 60
m (200 ft) along a north-south fault on the west flank of Craigs Knoll.
Displacement of the basalt and underlying Kaibab Formation strata are
the same, indicating that the fault is younger than the basalt flows
(Billingsley 1994b). There are no age determinations for either the
first or second eruptive phases of Craigs Knoll.

## Tertiary Volcanic rocks

There are four outcrops of Tertiary basalt flows in the map area. These
Tertiary flows form a protective caprock over soft strata of the Chinle
and Moenkopi Formations at Mount Trumbull and Mount Logan, along the
downthrown block of the Hurricane Fault (west-central edge of the map
area), and just north of Mt. Emma. The Tertiary basalts flowed over a
relatively flat erosional surface of tilted strata of the Chinle and
Moenkopi Formations. The Mesozoic and Paleozoic strata have a regional
dip of about 1º to 2º east, and the basalts erupted before faulting
began. There are very few pyroclastic deposits associated with the
Tertiary basalts except near Mt. Emma.

A period of erosion occurred between the Tertiary and Quaternary
eruptions that may have lasted about 2.6 Ma. During this interval, the
Moenkopi and Chinle strata were eroded from any area not capped by
Tertiary basalt flows. Capped area quickly became buttes or mesas
because underlying Triassic strata easily eroded along flow margins.
Today, the Tertiary flows form basalt capped mountains.

Resultant erosion around the Tertiary basalts allowed steep unstable
hillside failures to develop. Mass movement of these landslide blocks is
a major erosional component, making the Tertiary basalt capped areas
smaller to become isolated mountains today.

About 6.5 km (4 mi) south of Mt. Logan and just north of Mt. Emma
(southwest quarter of map area) is an outcrop of Tertiary basalt that
Hamblin (1970) called a Stage I basalt (the oldest basalt of the area).
This basalt remains unnamed and unsampled for age determination and
other analyses. Hamblin (1970) suggests that the Stage I basalt flows of
Mount Trumbull, Mount Logan, Bundyville basalt, and the basalt north of
Mt. Emma were all once part of a continuous lava field. The Stage I
flows appear to be separate flows as mapped, but they may have similar
eruptive times.

## Tertiary basalts north of Mt. Emma

The Tertiary basalts north of Mt. Emma are largely buried by Quaternary
basaltic eruptions of Mt. Emma and associated volcanoes. The basalt
erupted from a single large vent area and accumulated to about 183 m
(600 ft) thick. The bulk of the lava seems to have accumulated in a
local basin or valley and flowed east and northeast about 2 km (1.3 mi).
A small portion of the lava flowed west but thinned rapidly as if it
were flowing uphill. A southern extension of the Hurricane Fault system
cuts the Tertiary basalt north of Mt. Emma offsetting these rocks about
250 m (820 ft) down-to-the-west.

## Basalt of Mount Logan

East of the Hurricane Fault at Hells Hole is a Tertiary basalt that
forms Mount Logan. The basalt overlies about 122 m (400 ft) of the
Chinle Formation. Reynolds and others (1986) informally introduced the
name Mount Logan basalt. Paul Damon sampled basalt on Mount Logan in
1968 but did not specify a location other then Mount Logan. The sample
yielded a K-Ar age of 2.63±0.34 Ma. This age is about 1 million years
younger than the nearby basalt of Bundyville (3.60±0.018 Ma) to the
west, but the basalt of Mount Logan and the basalt of Bundyville overlie
the same 122 m (400 ft) of the Chinle Formation, separated by Hells Hole
and the Hurricane Fault. The age of the basalt of Bundyville has a
smaller margin of error than the Mount Logan age and is assumed to be
the age for the basalt of Mount Logan. Based on stratigraphic position,
thickness, and close proximity, about 2 km (1 mi) apart, the basalt of
Bundyville and the basalt of Mount Logan are likely one and the same
(fig. 2). Hand specimens from either basalt have the same general
characteristics and textural composition, but chemical analyses have not
been done. Further analysis is needed to verify whether both basalts are
really the same.

![](media/image2.png){width="6.5625in" height="3.0625in"}**Figure 2**.
Schematic west-east cross section from Cold Spring Wash (tributary of
upper Whitmore Canyon) through Hells Hole to Mount Logan, northern
Mohave County, Arizona. Thickness of units and vertical scale are
approximate. Surficial and volcanic units: Qal, alluvium; Ql, landslide;
Tbb, basalt of Bundyville; Tlb, basalt of Mount Logan; QTi, intrusive
dikes. Chinle Formation; \^cp, Petrified Forest Member. Moenkopi
Formation; \^mu, upper red member; \^ms, Shnabkaib Member; \^mm, middle
red member; \^mv, Virgin Limestone Member; \^ml, lower red member.
Kaibab Formation: Pkh, Harrisburg Member; Pkf, Fossil Mountain Member.
Toroweap Formation: Ptw, Woods Ranch Member; Ptb, Brady Canyon Member;
Pts, Seligman Member. Ph, Hermit Formation.

The source of the basalt of Mount Logan is uncertain, but may have
originated from dikes exposed in Hells Hollow about several hundred
meters west of the western edge of the basalt flows at the highest point
of Mount Logan. These dikes are oriented in a north-south trend similar
to the Quaternary basalt vent areas of this region, and may be
associated with those basalts instead of Mount Logan. The basalt of
Mount Logan flowed east about 5.5 km (3.5 mi) descending about 305 m
(1,000 ft) towards Toroweap Valley over an eroded surface of the Chinle
and Moenkopi Formations. The rate of descent was about 87 m/km (285
ft/mi). The flow would have, and perhaps did, reach the Toroweap Valley
or Fault.

## Basalt of Bundyville

Hamblin (1970) was the first to report on the basaltic rocks 6.4 km (4
mi) east of the town of Mt. Trumbull (Bundyville) along the east-central
edge of the map area and informally referred to them as the Bundyville
basalt. The name Bundyville basalt was again used informally by Reynolds
and others (1986) and Billingsley and others (2000) and is informally
used as the basalt of Bundyville in this report because of its uncertain
relationship to the basalt of Mount Logan. The basalt of Bundyville is
present along the west side of the Hurricane Fault on the downthrown
side and overlies the Petrified Forest Member of the Chinle Formation
about 4 km (2.5 mi) west of the map area.

The basalt of Bundyville was sampled for a K-Ar age determination in
1968 by Paul Damon, University of Arizona, and yielded a 3.60±0.018 Ma
age (Reynolds and others, 1986). The basalt of Bundyville overlies about
122 m (400 ft) of soft strata of the Petrified Forest Member of the
Chinle Formation (Billingsley and others, 2000). The Chinle was eroded
to a nearly flat surface and may have been the northerly extent of the
Whitmore Canyon drainage when the basalt of Bundyville erupted. Sometime
after deposition of the basalt of Bundyville, the Hurricane Fault became
active, offsetting both the basalt and underlying strata about 610 m
(2,000 ft).

The basalt of Bundyville probably came from fissures that parallel the
Hurricane Fault and are now buried by subsequent flows or landslide and
talus debris (fig. 2). Several basalt dikes exposed in Hells Hole may
represent some of the source dikes for the basalt of Bundyville;
however, the dikes are aligned in a north-south direction not parallel
to the Hurricane Fault but parallel to the general north-south
Quaternary volcanoes in this part of the map area. There are no K-Ar
ages for these dikes and, because of their relations to both Tertiary
and Quaternary basalts; they are labeled as Quaternary (QTi). Landslide
and talus debris cover most of the Moenkopi and Chinle strata around and
below outcrops of the basalt of Bundyville. Periodic movement along the
Hurricane Fault may have distorted the flow surface of the basalt of
Bundyville into a lumpy, hummocky expression, because it overlies soft
mudstone and shale of the Chinle Formation (fig. 2). More recently,
perhaps in the last several tens of thousands of years, earthquakes and
wet conditions have probably caused landslide masses to creep downslope
around the flow edges. The landslide masses disintegrate into blocky
talus deposits at their distal ends.

On aerial photos, Death Valley Lake (west-central edge of the map area)
resembles a volcanic crater because of a circular ring of small rocky
peaks that surround the lake. The Hurricane Fault goes through Death
Valley Lake. The ridges on the east side of the lake and fault are rocks
of the Shnabkaib Member of the Moenkopi Formation, and rocks on the west
side of the lake and fault are those of the basalt of Bundyville.
West-dipping basalt ridges on the west side of Death Valley Lake may
either be dikes that parallel the Hurricane Fault or basalt flows that
have been bent upward by fault drag.

## Basalt of Mount Trumbull

Koons (1945) first mentioned the basaltic rocks on top of Mount Trumbull
and informally referred to them as the Mount Trumbull basalt as did
Hamblin (1970) and Billingsley (1997b). The basalt of Mount Trumbull
caps Mount Trumbull, the highest mountain in the Uinkaret Volcanic
Field, Uinkaret Plateau, northern Mohave County, Arizona (sec. 27, T. 35
N., R. 8 W., elev 8,029 ft; north-central part of map area). The K-Ar
age of the basalt of Mount Trumbull is 3.67±0.09 Ma and 3.47±0.63 Ma
(Hamblin and Best, 1970; Best and others, 1980; Reynolds and others,
1986).

The basalt came from a large dike or neck on the north side of the
mountain, which forms the highest point on the mountain. Some basalt
flowed west about 1.5 km (1 mi) onto an eroded surface of the Shinarump
or Petrified Forest Member of the Chinle Formation. Most of the basalt
flowed east and southeast and descended over 300 m (1,000 ft) in about
2.5 km (1.5 mi), a scenario similar to the basalt of Mount Logan. The
basalt of Mount Trumbull preserves the Triassic strata of this area. The
steep soft slopes around Mount Trumbull have subsequently been covered
by landslide and talus debris similar to those of other nearby Tertiary
basalt outcrops.

Near the top of Mount Trumbull on the south edge of the mountain is a
60-m-high (200 ft) pyroclastic cone (elev 7,847 ft) that is probably
Quaternary age. This volcano (7847) erupted onto the basalt of Mount
Trumbull surface and flowed down the south flank of Mount Trumbull over
landslide debris. This flow was later subjected to further landslide
disruption. Cone 7847 is aligned with other north-south oriented
Quaternary pyroclastic cones both north and south of Mount Trumbull and
for this reason is considered Quaternary in age.

# STRUCTURAL GEOLOGY

Gently tilted Paleozoic and Mesozoic strata offset by near-vertical
normal faults constitute the major structural elements of this part of
the Uinkaret Volcanic Field. The regional dip of the Paleozoic and
Mesozoic strata increases from about 4º east on the west side of the
Toroweap Fault in Toroweap Valley to about 14º east on the west side of
the Hurricane Fault in Whitmore Canyon (Hamblin, 1965; Billingsley and
Huntoon, 1983; Wenrich and others, 1997). Huntoon (1990) documented that
the Toroweap and Hurricane Faults overlie deep-seated reverse faults
that produced east-dipping monoclines with strata up-to-the-west during
Late Cretaceous and early Tertiary time. Pliocene and Pleistocene
extension has reactivated these deep-seated faults producing normal
down-to-the-west fault separations along the Toroweap and Hurricane
Monoclines, reversing the Cretaceous and Tertiary offset. However, the
monoclinal flexure, although present as a minor fold in the map area, is
not present everywhere along the Toroweap and Hurricane Faults in the
map area. Most of the monoclinal development is in the Grand Canyon and
within the lower part of Whitmore Canyon of this map area.

Reverse drag along the Hurricane and Toroweap normal faults is common in
the map area. Reverse drag along normal faults is defined by Hamblin
(1965) as a sag-induced infolding of the rocks toward the fault plane
within the hanging wall. The infolding fills space created at depth as
displacement occurs along normal fault surfaces that dip less steeply
with increasing depth. The result is that reverse drag exacerbates the
displacement along those faults. It also accentuates preexisting
monoclinal dips on the downdropped western blocks within the fault
zones. Reverse drag is prevalent in the Paleozoic and Mesozoic strata
along the Hurricane and Toroweap Faults (Billingsley and others, 2000).

Toroweap Valley and Whitmore Canyon appear to have been partially
established before volcanism and faulting began along weak trends of the
Hurricane and Toroweap Monoclines. Tertiary basalt flows may have
reached parts of Toroweap Valley before faulting began. Activation of
the faults likely accentuated the headward erosion from the Colorado
River along these faults into Toroweap Valley and Whitmore Canyon.

The Toroweap Fault separates the Uinkaret Plateau (west side) from the
Kanab Plateau (east side). The maximum separation of Paleozoic and
Mesozoic strata along the Toroweap Fault is about 198 m (650 ft) at the
south edge of the map area, decreasing to about 67 m (220 ft) in the
upper reaches of Toroweap Valley. About half of the offset along the
northern part of the Toroweap Fault took place after deposition of the
basalt of Graham Ranch during the Pleistocene, approximately 630,000
years ago. Based on data from this and other mapping west and north of
the area (Billingsley, 1997a, b; unpub. data a, b; Billingsley and
others, 2000), the Toroweap Fault probably became active sometime during
the past 2 to 2.5 m.y. The Toroweap Fault trace can be determined
accurately on aerial photos because of relatively recent offset of
basalt flows and alluvial deposits in Toroweap Valley.

The Hurricane Fault separates the Uinkaret Plateau (east side) from the
Shivwits Plateau (west side). The maximum separation of Paleozoic and
Mesozoic strata along the Hurricane Fault in the map area is about 610 m
(2,000 ft) in the northwest corner of the map (Billingsley and others,
2000). Fault separation decreases to about 550 m (1,800 ft) in upper
Hells Hole. The fault trace shows visible displacement of relatively
recent basalt flows and alluvial fan deposits in Whitmore Canyon.
Estimated offset of strata along the Hurricane Fault is based on the
Chinle/Moenkopi contact and the basalt/Chinle contact on both sides of
the fault. Separation of the basalt of Bundyville and underlying strata
are equally offset along this segment of the Hurricane Fault, making the
fault younger than the 3.6 Ma basalt of Bundyville or the 2.6 Ma basalt
of Mount Logan. Separation of Quaternary basalts along the Hurricane
Fault is as much as 34 m (112 ft) just south of the southwest corner of
the map and displacement of alluvium is as much as 3 m (10 ft).

A southern extension the Hurricane Fault near Mt. Emma rapidly dies out
southward and may reach the Grand Canyon about 5 km (3 mi) south of the
map area. Other faults south of the map area, all down-to-the-west, may
be southern extensions or splays of the Hurricane Fault system
(Billingsley and Huntoon, 1983). These faults are largely covered by
Quaternary basalt flows, but where they are exposed, they bend
southwestward and rejoin the Hurricane Fault near the Colorado River.

Locally warped and bent strata, too localized to show at map scale, are
the result of Pleistocene and Holocene dissolution of gypsum in the
Harrisburg Member of the Kaibab Formation. Distorted strata in the
Harrisburg Member are common along drainages or joints on the plateaus,
especially in upper Toroweap Valley. Gypsum dissolution in the
Harrisburg Member has also resulted in several small and large sinkholes
and caves on the Kanab and Uinkaret Plateaus. The karst is Holocene and
Pleistocene in age based on several sinkholes that have developed in the
basalt of Larimore Tank in upper Toroweap Valley. Locations of sinkholes
forming enclosed basins or depressions are indicated on the map by a
triangle symbol.

## Breccia pipe structures

Circular collapse structures, minor folds, and other surface
irregularities are due to dissolution of gypsum and gypsiferous
siltstone in the Kaibab or Toroweap Formations. Some bowl-shaped
depressions in the Kaibab Formation, characterized by inward-dipping
strata, may be the surface expression of a breccia pipe originating from
dissolution of the deeply buried Mississippian Redwall Limestone
(Wenrich and others, 1997; Wenrich and Sutphin, 1989). Collapse features
are marked on the map by a dot and the letter C.

# ACKNOWLEDGMENTS

We appreciate the advice, revisions, and information of Wendell
Duffield, Susan Priest, Paul Stone, Charles Powell II, Jan Zigler, and
Theresa Iki of the U.S. Geological Survey for their scientific
assistance in the preparation of this report. Aerial photos provided by
Becky Hammond, geologist with the Bureau of Land Management, Arizona
Strip Field Office, St. George, Utah are greatly appreciated.

**DESCRIPTION OF MAP UNITS**

SURFICIAL DEPOSITS

> **Surficial deposits (Holocene and Pleistocene)---**Surficial deposits
> are differentiated from one another chiefly on the basis of difference
> in morphologic character and physiographic position observed on aerial
> photographs. Older alluvial fans and terrace-gravel deposits generally
> exhibit extensive erosion whereas younger deposits are actively
> accumulating material or are lightly eroded as observed on 1976 aerial
> photographs

Qaf **Artificial fill deposits and quarries (Holocene)---**Alluvial and
bedrock material removed from pits and trenches to build stock tanks and
drainage diversion dams

Qs **Stream-channel alluvium (Holocene)---**Interlensing silt, sand,
pebbles, and boulder gravel; unconsolidated and poorly sorted. Locally
overlaps alluvial fan (Qa1 and Qa2), terrace-gravel (Qg1), upper part of
valley-fill (Qv), and floodplain (Qf) deposits. Inset against some
young-intermediate alluvial fan (Qa1) and old terrace-gravel (Qg2)
deposits. Stream channels subject to intermittent high-energy flows and
flash floods. Little or no vegetation in stream channels except some
sagebrush. Contact with other alluvial deposits is approximate.
Thickness 1 to 3 m (3 to 10 ft)

Qf **Floodplain deposits (Holocene)---**Light-gray or tan silt, sand,
and interlensing pebbles, cobbles, and gravels; unconsolidated. Locally
contain cinder and basalt fragments. Intertongue with or overlap
valley-fill (Qv) and young alluvial fan (Qa1) deposits. Form relatively
flat surfaces that have little or no vegetation and have some drainage
outlet. Subject to frequent flooding or ponding. Thickness 1 to 3 m (3
to 10 ft)

Qg1 **Young terrace-gravel deposits (Holocene)---**Light-brown,
pale-red, and gray silt, sand, and pebble to boulder gravel composed of
well-rounded limestone and sandstone and angular to subrounded chert
clasts locally derived from the Toroweap and Kaibab Formations; include
rounded to subrounded basalt clasts derived from locally exposed basalt
flows or other alluvial deposits and landslide debris. Form terraces
about 1 to 3 m (3 to 10 ft) above modern streambeds in Hells Hollow,
Whitmore Canyon, and Langs Run drainages and lower Toroweap Valley.
Locally inset into old terrace-gravel (Qg2) deposits in Hells Hollow and
Whitmore Canyon area. Thickness 1 to 4 m (3 to 12 ft)

Qa1 **Young alluvial fan deposits (Holocene)---**Gray-brown silt, sand,
gravel, and boulders. Include interlensing coarse gravel composed of
subangular to rounded pebbles and cobbles of limestone, chert, and
sandstone clasts locally derived from the Kaibab and Toroweap
Formations. Locally includes well-rounded to sub-angular basalt clasts
and pyroclastic debris on and near Quaternary volcanoes north and south
of Mount Trumbull, often mixed with clasts from the Toroweap and Kaibab
Formations on west side of Toroweap Valley and upper Whitmore Wash.
Partly cemented by gypsum and calcite. Overlapped by or intertongue with
upper part of valley-fill (Qv) and floodplain (Qf) deposits. Intertongue
with or overlap young-intermediate alluvial fan (Qa2) deposits. Subject
to extensive erosion by sheet wash, flash flood debris flows, and minor
arroyo erosion. Support moderate growth of sagebrush, cactus, and grass.
Thickness 1 to 10 m (3 to 30 ft) or more

Qc **Colluvial deposits (Holocene and Pleistocene)---**White to gray
silt and fine-grained sand, black and red, fine-grained cinder, scoria,
and basalt clasts. Locally confined to basins, playas, or depressions in
landslides around Mount Trumbull and Mount Logan areas. Similar to
floodplain (Qf) deposits, but limited to local internal accumulations
generally not associated with stream drainages. Subject to temporary
ponding. Support sparse growth of grass. Thickness 1 to 3 m (3 to 20 ft)

Qv **Valley-fill deposits (Holocene and Pleistocene)---**Gray and
light-brown silt, sand, and lenses of pebble to small-boulder gravel;
partly consolidated by gypsiferous siltstone and calcite. Contain
well-rounded clasts of limestone, subrounded to angular chert fragments,
and subrounded to angular basalt pebbles and pyroclastic gravel mixture.
Intertongue with or overlap alluvial fan (Qa1 and Qa2) deposits.
Represent relatively less active, low-gradient alluvial stream-channel
or shallow valley drainage deposits, mainly on plateau surfaces and in
Toroweap Valley. Subject to sheetwash flooding and temporary ponding;
cut by arroyos as much as 2 m (6 ft) deep. Support moderate growth of
sagebrush, grass, and cactus. Thickness 1 to 4 m (3 to 12 ft)

Qt **Talus deposits (Holocene and Pleistocene)---**Unsorted breccia
debris composed of small and large angular blocks of local bedrock on
steep to moderately steep slopes below bedrock outcrops. Include silt,
sand, and gravel partly cemented by calcite and gypsum. Intertongue with
alluvial fan (Qa1, Qa2, and Qa3) deposits and commonly associated with
landslide (Ql) deposits. Support sparse growth of sagebrush, cactus,
grass, pinion, juniper, and oak. Only thick or extensive deposits shown.
Thickness 2 to 6 m (6 to 20 ft)

Ql **Landslide deposits (Holocene and Pleistocene)---**Unconsolidated
masses of unsorted rock debris. Include detached bedrock blocks that
have rotated backward and slid downslope as loose incoherent masses of
broken rock and deformed strata. Found principally below Esplanade
Sandstone in Cove Canyon area, below the canyon rim of Cove Canyon and
Toroweap Valley, and below Tertiary basalt flows. Support sparse to
moderate growth of cactus and grass at elevations below 5,000 ft and
moderate forest of oak, juniper, ponderosa pine, and pinion trees at
higher elevations. May become unstable in wet conditions. Thickness 3 to
18 m (10 to 60 ft)

Qg2 **Old terrace-gravel deposits (Holocene and Pleistocene)---**Similar
to young terrace-gravel deposits (Qg1) but partly consolidated by
gypsiferous siltstone and calcite. Composed mainly of gray to brown,
fine-grained sand and silt matrix mixed with subangular to rounded
pebbles and boulders of basalt and limestone as much as 1 m in diameter
in Hells Hollow and Whitmore Canyon areas. Form terraces about 2 to 4 m
(6 to 12 ft) above modern streambeds and about 1 to 2 m (3 to 6 ft)
above young terrace gravel (Qg1) deposits. Locally inset into
young-intermediate alluvial fan (Qa2) deposits in Hells Hollow and
Whitmore Canyon drainages. Intertongue or locally overlain by talus (Qt)
and young alluvial fan (Qa1) deposits. Thickness 2 to 25 m (6 to 80 ft)

Qa2 **Young-intermediate alluvial fan deposits (Holocene and
Pleistocene)---**Similar to young alluvial fan (Qa1) deposits, but
partly cemented by calcite and gypsum. Surfaces are rocky and eroded by
arroyos as much as 10 m (30 ft) deep. Commonly overlapped by young
alluvial fan (Qa1) deposits. Intertongue with or overlap valley-fill
(Qv) and talus (Qt) deposits. Contain abundant subrounded to subangular
Quaternary basalt clasts and cinders on west side of Toroweap Valley and
east side of Hells Hollow and Whitmore Canyon drainages. Support
moderate growth of sagebrush, cactus, grass, and some juniper trees.
Thickness 2 to 30 m (6 to 100 ft)

Qa3 **Old alluvial fan deposits (Pleistocene)---**Similar to young and
young-intermediate alluvial fan (Qa1 and Qa2) deposits, partly cemented
by calcite and gypsum. Surface has thin soil development forming a
smooth texture on aerial photos; often exhibits arroyo erosion averaging
about 1 to 2 m (3 to 6 ft) deep on east side of Mount Trumbull. Commonly
overlapped by or intertongue with talus (Qt) and landslide (Ql)
deposits. Contain abundant Quaternary and Tertiary basaltic clasts that
form thin desert pavement near landslide (Ql) masses. Support moderate
growth of grass, cactus, sagebrush, juniper, and pinion pine trees.
Thickness 2 to 10 m (6 to 30 ft)

VOLCANIC ROCKS

Quaternary deposits

> **Basalt of Little Spring (Holocene)---**Informally named herein for
> Little Spring (SE 1/4, sec. 16, T. 34 N., R. 8 W.), just southwest of
> Mount Trumbull, Uinkaret Plateau, northern Mohave County, Arizona
> (northeast quarter of map area). The olivine basalt flows and
> associated double cinder cone represent the youngest volcanic rocks in
> the Uinkaret Volcanic Field based on 3-He cosmogenic dating methods
> (Fenton, 1998), the freshness of flow surfaces, and similarities to
> basalt flow surfaces at Sunset Crater National Monument near
> Flagstaff, Arizona; the basalt of Little Spring is about 1,000 years
> old. Divided into:

Qlsp **Pyroclastic deposits**---Red-brown, gray, and reddish-black
basaltic scoria, bombs, cinder, and scoriaceous ejecta deposits.
Consists of two deposits that may have been part of a double pyroclastic
cone formed from two closely associated vent areas. Eastern part of
pyroclastic cone is about 41 m (135 ft) high and deposited on associated
basalt flow surface (elev 7,015 ft). Only east half and southwest part
of cone is present; the rest of cone has been rafted away on lava flows
from the vent area toward the northwest and southeast. Support a few
ponderosa pine and oak trees. Thickness 41 m (135 ft)

Qlsb **Basalt flows**---Dark-gray, finely crystalline to glassy, alkali
olivine basalt. Groundmass composed of plagioclase and olivine. Forms
clinkery broken aa surface. Splatter debris common near both vent areas.
Basalt flowed northwest about 1.8 km (1.1 mi) and spread out into local
valley and southeast about 2.4 km (1.5 mi) down a steep gradient into
another local valley. Overlies older Quaternary basalt flows (Qb),
pyroclastic (Qp) deposits, and young alluvial fan (Qa1) deposits.
Thickness 3 to 7 m (10 to 23 ft)

> **Basalt of Larimore Tank (Pleistocene)---**Informally named for
> Larimore Tank, a stock tank just west of the basalt flow on U.S.
> Geological Survey Hat Knoll 7.5\' quadrangle, Uinkaret Volcanic Field,
> northern Mohave County, Arizona (sec. 16, T. 37 N., R. 7 W.).
> Incorrectly named the Cave Basalt in Billingsley (1994b) and
> Billingsley and Workman (1999) before it was known that this name was
> already in use

Qltb **Basalt flows**---Dark-gray to black, finely crystalline
alkali-olivine basalt. Basalt has coalesced from five pyroclastic vents
aligned along northwest-southeast fracture or joint system of underlying
Permian strata. Contain abundant olivine phenocrysts 0.25 to 1 mm in
diameter. Overlain by valley fill (Qv), and young to young-intermediate
alluvial fan (Qa1 and Qa2) deposits. Sinkholes have developed under
basalt flow in gypsum or gypsiferous siltstone units of the Harrisburg
Member (Pkh) of the Kaibab Formation causing basalt to collapse into
sinkholes as deep as 18 m (60 ft). Sinkholes are partly filled with
ponded alluvium similar to localized floodplain (Qf) and colluvial (Qc)
deposits. Basalt flowed south into upper part of Toroweap Valley when
eruptions ceased. Most of the basalt flowed north (Billingsley, unpub.
data a). Thickness 1 to 12 m (3 to 40 ft)

> **Basalt of Graham Ranch (Pleistocene)---**Informally named for Graham
> Ranch in upper Toroweap Valley, (sec. 3, T. 35 N., R. 7 W.); the type
> area, Uinkaret Volcanic field, Uinkaret Plateau, northern Mohave
> County, Arizona. Incorrectly named the Sage Basalt by Billingsley and
> Workman (1999) and Billingsley and Hampton (2000) before the name Sage
> Basalt was already in use. Divided into:

Qgrp **Pyroclastic deposits**---Red-brown and reddish-black scoriaceous
basalt, ash, and cinder deposits; partly consolidated. Consist of three
pyroclastic cones that include six vent areas aligned along north-south
oriented, near-vertical bedrock-fracture or joint systems in underlying
Paleozoic rocks. Three vent areas form northern cone, one vent forms a
central cone, and two vents form southern cone. Deposits overlie
associated basalt flows. Toroweap Fault offsets the northern pyroclastic
cone and basalt flow about 26 m (85 ft). The northern cone is about 134
m (440 ft) high, central cone about 70 m (230 ft) high, and southern
cone about 60 m (200 ft) high, representing relative thickness

Qgrb **Basalt flows**---Dark-gray, finely crystalline to glassy alkali
olivine basalt. Groundmass composed of plagioclase, olivine, and augite
laths. Include abundant olivine phenocrysts 0.25 to 5 mm in diameter,
which form about 30% of flow in southern part. Unit overlies Harrisburg
Member of the Kaibab Formation on Kanab Plateau and alluvium in upper
Toroweap Valley of the Uinkaret Plateau. Basalt flow is offset about 26
m (85 ft) down-to-the-west by the Toroweap Fault north of Graham Ranch;
offset about 34 m (110 ft) down-to-the-west south of Graham Ranch which
is about half of total offset of Toroweap Fault, 76 m (220 ft).
Thickness 3 to 18 m (10 to 60 ft)

> **Quaternary basalts, undivided (Pleistocene)---**Informally named to
> include several pyroclastic cones and associated basalt flows of
> similar age north and south of Mount Trumbull. Basalts are assumed to
> have erupted penecontemporaneously because several flows have
> coalesced from several adjacent pyroclastic cones. Basaltic units
> north of Mount Trumbull are designated with Qb1 because the
> stratigraphic relationships in upper Toroweap Valley suggest that
> these flows may be older than flows (Qb) south of Mount Trumbull.
> Other Quaternary basalt flows and associated pyroclastic deposits that
> have mappable boundaries are informally designated with the elevation
> of the highest associated pyroclastic cone (hill) or informally named
> for a local nearby ranch designated on U.S. Geological Survey
> 7.5-minute quadrangles. These basalt units are randomly listed and are
> not assigned in order of increasing or decreasing age because all
> units may be similar in age. Divided into:

Qp1 **Pyroclastic deposits**---Reddish-gray, black, and red to gray tuff
and welded tuff, ash, scoriaceous ejecta, cinder, and bomb deposits;
partly consolidated in most cones. Include about 17 pyroclastic cones
with one or more vents per cone that overlie coalescing basalt flows.
Locally form thick, fine- to coarse-grained cinder deposits near cones.
Map contacts are approximate and show thickest deposits. No K-Ar ages
are available. Thickness 6 to 124 m (20 to 400 ft)

Qb1 **Basalt flows**---Dark-gray to black, finely crystalline,
alkali-olivine basalt. Olivine and plagioclase phenocrysts common.
Basalt flows originate from several pyroclastic vents or fissures north
of Mount Trumbull and generally coalesce to flow eastward into upper
Toroweap Valley. Basalt flows probably overlie Triassic strata of the
Moenkopi Formation near pyroclastic cones and flowed over the Kaibab
Formation and alluvial valleys before reaching Toroweap Valley. Basalt
flows in Toroweap Valley south of Mount Trumbull are mostly covered with
valley-fill and young alluvial deposits (Qv and Qa1) and basalt (Qb)
flows. Thickness 6 to 15 m (20 to 50 ft)

Qp **Pyroclastic deposits**---Reddish-gray, black, red, and gray tuff,
ash, scoriaceous ejecta, bombs, and cinder deposits; partly
consolidated. Form Slide Mountain, about 183 m (600 ft) high, Petty
Knoll, about 110 m (360 ft) high, and Mt. Emma about 150 m (500 ft)
high, and several unnamed pyroclastic cones that average about 60 m (200
ft) high in the Uinkaret Mountains between Whitmore Canyon and Toroweap
Valley. Include about 36 pyroclastic cones formed by one or more vent
areas that overlie associated coalesced basalt flows. Consolidated as
gray welded tuff and ash at Slide Mountain, Petty Knoll, and Mt. Emma.
Include fine- to coarse-grained cinder sheet or ash deposits about 6 m
(20 ft) thick near cones. K-Ar age determinations are not available. Map
contacts are approximate and show thickest deposits

Qb **Basalt flows**---Dark-gray and light gray, finely crystalline,
alkali-olivine basalt. Include scoriaceous material from pyroclastic
deposits. Basalt cascaded from higher terrain of Uinkaret Mountains into
Whitmore Canyon and Toroweap Valley. Lava cascades are steep where they
flow over the Hurricane Fault scarp south of Hells Hollow and over upper
cliffs of Toroweap Valley and Whitmore Canyon areas. Flows overlie the
Moenkopi, Kaibab, and Toroweap Formations. Flows are partly buried by
young-intermediate alluvial fan (Qa2) deposits in Hells Hollow drainage
south of Hells Hole and various alluvial deposits in Whitmore Canyon and
Toroweap Valley. Flows are partly eroded but surfaces are well
preserved. There are no K-Ar ages available for (Qb) basalt flows south
of Mount Trumbull, but some flows dated by cosmogenic methods indicate
most of these flows are about 0.100 Ma (Fenton, 1998). The K-Ar age from
middle part of Mount Logan may not represent age of the basalt of Mount
Logan because Quaternary age basalts overlie Tertiary basalts in this
area. Thickness 6 to 183 m (20 to 600 ft)

Qi **Basalt necks (Pleistocene)---**Greenish-black, finely crystalline,
alkali olivine basalt necks. One neck is exposed in Harrisburg Member of
Kaibab Formation 3 km (2 mi) southeast of Mount Trumbull and another is
associated with a pyroclastic cone about 5 km (3 mi) north of Mount
Trumbull. Necks are several meters in diameter and have been eroded to
near bedrock surface. Approximate diameters shown on map

> **Basalt of Kenworthy Ranch (Pleistocene)---**Informally named for the
> Kenworthy Ranch in Sink Valley, Uinkaret Plateau, northern Mohave
> County, Arizona (sec. 1, T. 35 N., R. 9 W.). Divided into:

Qkrp **Pyroclastic deposits**---Reddish-black and red tuff, ash,
scoriaceous ejecta, and cinders; unconsolidated. Overlie associated
basalt flows. Map contact is approximate. Include three unnamed cinder
cones aligned in north-south orientation. The northern pyroclastic cone
(hill 6430) is about 49 m (160 ft) high; just west of Kenworthy Ranch,
the middle cone (hill 6348) is about 24 m (80 ft) high; and the southern
cone (hill 6355) is about 24 m (80 ft) high, reflecting approximate
thickness

Qkrb **Basalt flows**---Light- to dark-gray, finely crystalline
alkali-olivine basalt. Include small phenocrysts of augite and olivine
in glassy groundmass. Flows radiate out from all three pyroclastic cones
and coalesce to form a large, elongated, north-south, oval-shaped
basalt-flow mass. Overlie Harrisburg Member of the Kaibab Formation.
Thickness 15 m (50 ft)

> **Basalt of Marshall Ranch (Pleistocene)**---Informally named for
> Marshall Ranch about 2.5 km (1.5 mi) south of Kenworthy Ranch and west
> of Mount Trumbull, Uinkaret Plateau, northern Mohave County, Arizona
> (sec. 13, T. 35 N., R. 9 W.). Divided into:

Qmrp **Pyroclastic deposits**---Reddish-black and red tuff, ash,
scoriaceous ejecta, welded tuff, and cinders; mostly unconsolidated.
Overlie associated basalt flows. Include two unnamed pyroclastic cones
and three smaller secondary spatter cones. Secondary cones appear to
have originated from southern-most pyroclastic cone (hill 6633).
Northern pyroclastic cone (hill 6538) is about 73 m (240 ft) high and
southern cone (hill 6633) is about 85 m (280 ft) high, reflecting
relative thickness

Qmrb **Basalt flows**---Gray-black, finely crystalline, alkali-olivine
basalt. Majority of basalt came from southern pyroclastic cone (hill
6633) and flowed out in a radial pattern, mostly in a westerly direction
about 3 km (2 mi). Partly overlie basalt of Potato Valley and Harrisburg
Member of the Kaibab Formation. Thickness 12 to 36 m (40 ft to 120 ft)

> **Basalt of hill 6375 (Pleistocene)**---Informally named for unnamed
> pyroclastic cone (hill 6375) at north end of Sink Valley, northwest of
> Mount Trumbull, Uinkaret Plateau, northern Mohave County, Arizona
> (sec. 31, T. 35 N., R. 8 W.). Divided into:

Qp6375 **Pyroclastic deposits**---Reddish-black cinder and scoriaceous
ejecta overlying associated basalt flow. Include small deposit at north
end of basalt flow that appears to be local splatter cone originating
from the flow. Hill 6375 is about 64 m (210 ft) thick

Qb6375 **Basalt flow**---Dark-gray alkali-olivine basalt. Consists of
one basalt flow that flowed west about 0.5 km (0.25 mi) and north about
1.5 km (1 mi). Overlies Harrisburg Member of the Kaibab Formation.
Thickness 1 to 12 m (3 to 40 ft)

> **Basalt of hill 6646 (Pleistocene)**---Informally named for unnamed
> pyroclastic cone (hill 6646), northwest end of Sink Valley, northwest
> of Mount Trumbull, Uinkaret Plateau, northern Mohave County, Arizona
> (sec. 35, T. 36 N., R. 9 W.). Divided into:

Qp6646 **Pyroclastic deposits**---Red and black cinder and scoriaceous
deposits overly associated basalt flow. Include one large pyroclastic
cone and two smaller adjacent cones. Three vents formed large cone (hill
6646). Cone has elongated north-south orientation that aligns with
basaltic cones of Kenworthy Ranch. Main pyroclastic cone is about 76 m
(250 ft) thick

Qb6646 **Basalt flow**---Dark-gray alkali-olivine basalt. Basalt flowed
north about 3 km (2 mi). Overlies Harrisburg Member of the Kaibab
Formation. Thickness 10 to 30 m (30 to 100 ft)

> **Basalt of hill 6457 (Pleistocene)**---Informally named for unnamed
> cinder cone (hill 6457) just north of Mount Trumbull, Uinkaret
> Plateau, northern Mohave County, Arizona (sec. 16, T. 35 N., R. 8 W.).
> Divided into:

Qp6457 **Pyroclastic deposits**---Reddish-black cinder and scoriaceous
deposits. Include two smaller cones that partly overlie basalt flow from
cone 6457 and appear to have erupted from the flow. Pyroclastic cone
(hill 6457) is 36 m (120 ft) high, northern cone (no number) is about 24
m (80 ft) high reflecting relative thickness

Qb6457 **Basalt flow**---Dark-gray alkali-olivine basalt. Consists of
one flow from hill 6457 that flowed north about 0.8 km (0.50 mi) onto
flat alluvial-filled valley. Thickness about 36 m (120 ft)

> **Basalt of Potato Valley (Pleistocene)**---Informally named from
> Potato Valley west of Mount Trumbull, Uinkaret Plateau, northern
> Mohave County, Arizona (sec. 25, T. 35 N., R. 9 W.). Includes several
> pyroclastic cones and associated basalt flows along north and west
> edge of Potato Valley. Divided into:

Qpvp **Pyroclastic deposits**---Red and black cinder, tuff, ash, and
scoriaceous ejecta. Include two main pyroclastic cones and five
associated vent areas. Main pyroclastic cone on north side of Potato
Valley is not named or numbered, but elevation is about 6680. A large
pyroclastic cone on west side of Potato Valley is hill 6744. Both cones
overlie associated flows and appear to be main source of basalt. Several
smaller pyroclastic cones on associated flows appear to have erupted
from the flows, such as hill 6370, 6484, 6482, and two other unlabeled
hills. Western cone is about 106 m (350 ft) thick, northern cone is
about 85 m (280 ft) thick

Qpvb **Basalt flows**---Dark-gray alkali-olivine basalt. Flows on north
side of Potato Valley erupted mostly from unnamed cinder cone (elev
about 6680) and flowed northwest about 3 km (2 mi). These flows appear
to have merged with flows from pyroclastic cone (hill 6744) on western
side of Potato Valley and together have formed a basaltic dam or valley
blockage responsible for the accumulation of alluvium now filling Potato
Valley. Basalt on west side of Potato Valley flowed mostly north about 5
km (3 mi). Thickness 2 to 25 m (6 to 50 ft)

> **Basalt of hill 6588 (Pleistocene)---**Informally named for highest
> of 4 pyroclastic cones on east flank of Mount Trumbull, Uinkaret
> Volcanic Field, northern Mohave County, Arizona (sec. 36, T. 35 N., R.
> 8 W.). Includes pyroclastic deposits and associated basalt flows.
> Divided into:

Qp6588 **Pyroclastic deposits**---Reddish-black to mostly black and gray
ash, cinder, scoriaceous fragments, and basaltic boulders; partly
consolidated with interbedded basalt flows. Include four pyroclastic
cones aligned in northwest-southeast orientation for about 2 km (1.25
mi). Deposits mostly overlie associated basalt flows and landslide
debris but are often interbedded with basalt flows on steep eastern
slopes of hill 6588. Variable thickness because of steep terrain, about
2 to 55 m (6 to 180 ft)

Qb6588 **Basalt flows**---Dark-gray and light-gray, finely crystalline,
alkali-olivine basalt. Include interbedded scoriaceous pyroclastic
deposits. Basalt cascades steeply over landslide debris and strata of
the Moenkopi and Kaibab Formations into Toroweap Valley. Flows partly
buried by undivided basalt flows (Qb) and alluvial fan (Qa1 and Qa2)
deposits in Toroweap Valley. Thickness 2 to 10 m (6 to 30 ft)

> **Basalt of Craigs Knoll and Berry Knoll (Pleistocene)---**Informally
> named for Craigs Knoll (sec. 4, T. 35 N., R. 8 W.), and Berry Knoll
> (sec. 24, T. 36 N., R. 9 W.), northwest of Mount Trumbull, Uinkaret
> Plateau, northern Mohave County, Arizona. Includes dikes, pyroclastic
> deposits and basalt flows that may have erupted simultaneously at
> Craigs Knoll, Berry Knoll, and unnamed pyroclastic cone (hill 6342)
> between Craigs and Berry Knoll. Divided into:

Qcbi **Intrusive dikes or necks**---Greenish-black olivine basalt.
Widths of dikes shown are approximate

Qcbp **Pyroclastic deposits**---Gray and reddish-gray to black cinder,
tuff, ash, and scoriaceous ejecta; mostly consolidated into welded tuff.
Form cliff on east side of Craigs Knoll and steep slope on south and
west side. Deposits mostly covered by dark-gray basalt on west and north
flank of Craigs Knoll. Include smaller pyroclastic cone deposit on
southern flank of Craigs Knoll. Overlie associated basalt flow on south
flank of Craigs Knoll. Thickness 183 m (600 ft)

Qcbb **Basalt flows**---Light-gray and dark-gray alkali-olivine basalt.
Unit includes lower and upper basalt. Lower basalt accumulated on
Harrisburg Member of the Kaibab Formation and perhaps on lower members
of the Moenkopi Formation. Estimated thickness of lower flow about 40 m
(130 ft). Upper basalt erupted near top of Craigs Knoll, north flank,
and flowed west, north, and east about 8 km (5 mi). Thickness 3 to 20 m
(10 to 65 ft)

QTi **Basaltic dikes in Hells Hole (Pleistocene(?) or
Pliocene(?))---**Gray-black alkali-olivine basalt. Near vertical dikes 1
to 2 m (3 to 6 ft) wide. Dikes are aligned N. 10° W. with local joint
and fractures in Paleozoic and Mesozoic bedrock parallel to Quaternary
pyroclastic cones north, east, and southeast of Hells Hole. Dikes near
Hurricane Fault are aligned closer to northwesterly trend of the fault
and may be associated with the basalt of Bundyville. Widths of dikes
shown are approximate

Tertiary volcanic deposits

> **Basaltic rocks north of Mt. Emma (Pliocene)---**Gray-black
> alkali-olivine basalt; includes several basalt flows, pyroclastic
> deposits, and intrusive necks and dikes. Pliocene rocks largely
> covered by Quaternary pyroclastic deposits of Mt. Emma and nearby
> north-south oriented pyroclastic cones and associated basalt flows.
> Unit offset about 200 m (650 ft) down-to-the-west by Hurricane Fault.
> No age determinations for these deposits, but are assumed to be
> Pliocene, based on similar flow direction, stratigraphic position, and
> elevation of other Pliocene basalts at Mount Logan and Mount Trumbull.
> Divided into:

Ti **Intrusive rocks**---Gray-black alkali-olivine basaltic neck. Only
part of intrusive neck exposed and offset by fault. Most of unit covered
by landslide debris. Diameter of neck unknown. Source for associated
Tertiary basalt flows north and east of neck area is mostly covered by
Quaternary volcanic rocks of Mt. Emma

Tp **Pyroclastic deposits**---Reddish-black cinder, scoria, ash, and
scoriaceous ejecta; heavily eroded. Associated with intrusive neck (Ti)
on downthrown side of local fault connected to the Hurricane Fault.
Thickness 12 m (40 ft)

Tb **Basalt flows**---Gray-black alkali-olivine basalt; plagioclase
laths common in glassy groundmass. Consist of several basalts that
flowed east and south from intrusive neck area. The underlying strata
are concealed, but because of similar stratigraphic position to basalt
of Mount Logan and basalt of Mount Trumbull, it is assumed that this
basalt overlies strata of either the Chinle Formation or upper Moenkopi
Formation. Thickness 122 m (400 ft)

> **Basalt of Mount Logan (Pliocene)---**Informally named for Mount
> Logan (Reynolds and others, 1986), elev 2,400 m (7,866 ft); Uinkaret
> Plateau, northern Mohave County, Arizona (sec. 12, T. 34 N., R. 9 W.).
> K-Ar age is 2.63±0.34 Ma obtained from an unspecified location on
> Mount Logan. This 2.63 age may reflect a younger flow rather than the
> oldest Mount Logan flow. New K-Ar age determinations are recommended
> to determine sequence of basaltic events at Mount Logan

Tmlb **Basalt flows**---Light-gray, finely crystalline, alkali-olivine
basalt; contain red and green olivine phenocrysts 1 mm in diameter in
glassy groundmass; include plagioclase laths in glassy groundmass.
Plagioclase masses form white spotted blotches in some basalt flows.
Basalt flows overlie Petrified Forest Member of the Chinle Formation at
Hells Hole. Eastern extent of basalt may overlie upper red member and
Shnabkaib Member of the Moenkopi Formation. Basalt dikes below summit of
Mount Logan in Hells Hole may be source for the basalt of Mount Logan,
but these dikes are aligned with Quaternary basalt cones and flow in the
Sawmill Mountains just north of Hells Hole and may be the source for
those deposits. The basalt of Mount Logan flowed east about 5.3 km (3.3
mi) from the summit of Mount Logan descending about 335 m (1,100 ft).
Basalt of Mount Logan is recharge area for local springs such as Big
Spring and Little Spring, which emerge in landslide debris below
basalt-flow margins. Thickness 67 m (220 ft)

> **Basalt of Bundyville (Pliocene)---**Informally named for abandoned
> settlement of Bundyville (town of Mt. Trumbull; Hamblin and Best,
> 1970; Hamblin, 1970), Shivwits Plateau, northern Mohave County,
> Arizona, (secs. 23, 24, 25, and 26, T. 35 N., R. 10 W.). Unit is
> present in northwest quarter of map area on downthrown side of
> Hurricane Fault. K-Ar age is 3.6±0.18 Ma (Reynolds and others, 1986).
> Divided into:

Tbi **Intrusive dikes**---Dark-gray alkali-olivine basalt. Dikes are
near vertical and oriented N. 40° W. and nearly parallel the Hurricane
Fault. Widths approximate on map and vary from 1 to 3 m (3 to 11 ft)

Tbb **Basalt flows**---Dark-gray, finely crystalline, olivine basalt.
Groundmass contains olivine crystals. Consist of several flows that form
a caprock overlying purple and white mudstone and sandstone beds of
Petrified Forest Member of the Chinle Formation. Flow surfaces are
locally distorted by soft-sediment deformation of underlying mudstone.
Flows are assumed to have originated from local dikes (Tbi) that
parallel the Hurricane Fault and are largely covered by basalt or
landslide and talus debris. Thickness 30 to 55 m (100 to 180 ft)

> **Basalt of Mount Trumbull (Pliocene)---**Informally named for Mount
> Trumbull by Hamblin and Best (1970) and Hamblin (1970); Uinkaret
> Plateau, northern Mohave County, Arizona, (sec. 27, T. 35 N., R. 8 W.,
> central part of map area). K-Ar age is 3.6±0.18 Ma and 3.47±0.63 Ma
> (Reynolds and others, 1986). Divided into:

Tmi **Intrusive rocks---**Gray-black, finely crystalline, alkali-olivine
basalt. Map contact approximate. Form highest point on Mount Trumbull
(elev 8,029 ft), north side of Mountain. Source of Tertiary basalt flows
on Mount Trumbull. Width of dike about 120 m (400 ft) or more

Tmb **Basalt flows---**gray-black, finely crystalline, alkali-olivine
basalt. Groundmass contains olivine phenocrysts and plagioclase laths.
Consist of one or more thin basalt flows that form caprock over purple
and white mudstone and sandstone beds of Petrified Forest Member of the
Chinle Formation, west side of mountain (exposed in landslide float
material) and over red sandstone and siltstone of upper red member and
possibly Shnabkaib Member of the Moenkopi Formation on east side of
mountain. Partly covered by Quaternary pyroclastic cone southeast of
Nixon Spring, south side of mountain. Western half of outcrop is
recharge area for Nixon Spring, which emerges in landslide debris near
base of basalt flow. Thickness 30 to 60 m (100 to 200 ft)

SEDIMENTARY ROCKS

> **Chinle Formation (Upper Triassic)---**Includes the Shinarump and
> Petrified Forest Members, undivided. Both Members are mapped as the
> Petrified Forest Member for this report

\^cp **Petrified Forest Member**---White, blue-gray, pale-red, and
purple, slope-forming interbedded fluvial mudstone, siltstone, and
coarse-grained sandstone. Contains small, well-rounded pebbles of
yellow, brown, and red quartzite, and brown, yellow, white, and red
petrified wood fragments in lower part within white, coarse-grained,
ledge-forming sandstone that is likely the equivalent of the Shinarump
Member of the Chinle Formation. Contains bentonitic clays derived from
decomposition of volcanic ash. Unconformable contact with the overlying
basalt of Bundyville just west of map area (Billingsley and others,
2000). Erosion removed an unknown thickness of upper part of Chinle
Formation and younger Mesozoic strata prior to deposition of the basalt
of Bundyville. Unit mostly covered by the basalt of Bundyville (Tbb) and
landslide deposits (Ql) west of Hurricane Fault; mostly covered by
basalt of Mount Logan east of Hurricane Fault and Hells Hole.
Unconformable contact with underlying slope-forming upper red member of
the Moenkopi Formation; erosional relief less than 2 m (6 ft) at Hells
Hole. Thickness 122 m (400 ft)

> **Moenkopi Formation (Middle? and Lower Triassic)---**Includes, in
> descending order, the upper red member, Shnabkaib Member, middle red
> member, Virgin Limestone Member, lower red member, and Timpoweap
> Member as used by Stewart and others (1972). Divided into:

\^mu **Upper red member (Middle? and Lower Triassic)---**Red,
thin-bedded, cliff- and slope-forming siltstone and sandstone.
Unconformably overlain by the Chinle Formation at Hells Hole and Sawmill
Mountain area; by the basalt of Mount Logan, east side of Mount Logan;
and by the basalt of Mount Trumbull at Mount Trumbull. Gradational
contact with underlying Shnabkaib Member of the Moenkopi Formation
arbitrarily placed at uppermost thick, white or light-gray calcareous
siltstone and dolomite beds. Regionally unit thins south and east,
thickens north. Thickness 120 m (400 ft)

\^ms **Shnabkaib Member (Lower Triassic)---**White, laminated,
slope-forming, aphanitic dolomite interbedded with light-gray,
calcareous, silty gypsum and gypsiferous siltstone. Gradational lower
contact with middle red member placed at lowest white or light-gray,
calcareous, silty dolomite of the Shnabkaib Member. Unit thins south and
west, thickens north. Thickness at Hells Hole about 135 m (445 ft)

\^mm **Middle red member (Lower Triassic)---**Red-brown, thin-bedded to
thinly laminated, slope-forming siltstone and sandstone. Includes
interbedded white and gray gypsum beds, minor white platy dolomite,
green siltstone, and gray-green to red gypsiferous mudstone. Gradational
and arbitrary lower contact with Virgin Limestone Member placed about 10
m (30 ft) above gray, ledge-forming limestone bed of Virgin Limestone.
Unit thins west, south, and east, thickens north. Thickness 120 m (400
ft)

\^mv **Virgin Limestone Member (Lower Triassic)---**Consists of one
light-gray, thin-bedded to thinly laminated, ledge-forming limestone 0.5
to 2 m thick. Includes overlying 10 m (30 ft) of pale-yellow, red, and
bluish-gray, thin-bedded, slope-forming gypsiferous siltstone. Unit
thins south and west, thickens north to include two limestone beds just
north of map area (Billingsley, unpub. data b) and as many as four
limestone beds near St. George, Utah (Billingsley and Workman, 1999).
Unconformable contact with underlying lower red member of the Moenkopi
Formation placed at base of limestone bed. Unit locally pinches out
against or unconformably overlies paleohills of Harrisburg Member of the
Kaibab Formation. Thickness 0 to 10 m (0 to 30 ft)

\^ml **Lower red member (Lower Triassic)---**Red, fine-grained,
thin-bedded, gypsiferous, slope-forming, sandy siltstone and gray,
white, and pale-yellow laminated gypsum and minor sandstone. Lower part
contains redeposited gypsum and siltstone of Harrisburg Member of the
Kaibab Formation. Gradational contact with underlying Timpoweap Member
of the Moenkopi Formation placed at lowermost red siltstone bed.
Locally, unconformably overlies Harrisburg Member of the Kaibab
Formation where Timpoweap Member is absent. Thickens in paleovalleys and
pinches out against eroded paleohills of underlying Harrisburg Member.
Thickness 0 to 20 m (0 to 65 ft)

\^mt **Timpoweap Member (Lower Triassic)---**Light-gray, slope- and
cliff-forming conglomerate in lower part and light-gray to light-red,
slope-forming calcareous sandstone with interbedded conglomerate lenses
in upper part. Conglomerate in lower part composed of subangular to
rounded pebbles and cobbles of gray and dark-gray limestone, white and
brown chert, and gray sandstone in matrix of gray to brown,
coarse-grained cherty sandstone. Upper part includes beds of low-angle
crossbedded, calcareous, yellow sandstone and conglomerate and minor red
siltstone. Cemented by calcite and gypsum. All detritus in Timpoweap
Member derived from erosion of the Kaibab Formation. Fills paleovalleys,
about 1,500 m (4,900 ft) wide and as much as 70 m (230 ft) deep, eroded
into Harrisburg Member of the Kaibab Formation. Imbrication of pebbles
in conglomerate shows general northeastward flow of depositing streams.
Thickness 0 to 70 m (0 to 230 ft)

> **Kaibab Formation (Lower Permian)---**Includes, in descending order,
> the Harrisburg and Fossil Mountain Members as defined by Sorauf and
> Billingsley (1991). Divided into:

Pkh **Harrisburg Member**---Includes upper, middle, and lower parts.
Upper part consists mainly of slope-forming, red and gray, interbedded
gypsiferous siltstone, sandstone, gypsum, and thin-bedded gray limestone
capped by a resistant, pale-yellow or light-gray, fossiliferous
(mollusks and algae) sandy limestone averaging about 1 m (3 ft) thick.
Gradational contact with middle part. Middle part consists of two
cliff-forming limestone beds as much as 2 m (6 ft) thick each. Upper bed
is gray, thin-bedded, cherty limestone that weathers dark brown or black
often forming bedrock surface east of Toroweap Fault on Kanab Plateau;
lower bed is light-gray, thin-bedded, sandy limestone. Both beds thicken
and thin locally and regionally thicken east and north, thin west. Minor
erosional unconformity separates upper and lower bed. Lower part
consists of slope-forming, light-gray and reddish-gray, gypsiferous
siltstone and fine- to medium-grained calcareous sandstone. Includes
interbedded gray, medium-grained, thin-bedded sandy limestone and gray,
massive bedded gypsum. Dissolution of gypsum in lower part locally
distorts limestone beds of middle part causing them to slump or bend
into local surface drainages on Uinkaret and Kanab Plateaus. Unit is
mostly covered by basalt flows west of Toroweap Valley on Uinkaret
Plateau. Gradational contact with underlying Fossil Mountain Member of
the Kaibab Formation arbitrarily placed at top of cherty limestone cliff
of the Fossil Mountain. Thickness about 75 m (250 ft)

Pkf **Fossil Mountain Member**---Light-gray, fine- to medium-grained,
thin-bedded, fossiliferous, cliff-forming, cherty limestone. Unit
characterized by cliffs of chert-banded limestone. Erodes into conical
pillars along cliffs on east side of Toroweap Valley and upper Cove
Canyon. Unconformable contact with underlying Woods Ranch Member of the
Toroweap Formation marked by channel erosion with relief as much as 2 m
(6 ft) locally, but as much as 30 m (100 ft) in lower Whitmore Canyon
and upper Toroweap Valley. Contact locally obscured by talus and minor
landslide debris. Unit thickens west, thins east. Thickness 60 to 65 m
(200 to 215 ft)

> **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, slope-forming gypsiferous siltstone
and pale-red silty sandstone interbedded with white laminated gypsum.
Beds locally distorted caused by gypsum dissolution. Gradational contact
with underlying Grady Canyon Member of the Toroweap Formation placed at
top of limestone cliff of Brady Canyon Member. Thickness 30 to 60 m (100
to 200 ft)

Ptb **Brady Canyon Member**---Gray, cliff-forming, medium-bedded, fine-
to coarse-grained, fetid, fossiliferous limestone; weathers dark gray.
Includes thin-bedded dolomite in upper and lower part. Limestone beds
average about 0.5 m (2 ft) thick and contain chert lenses and nodules.
Gradational contact with underlying Seligman Member of the Toroweap
Formation placed at base of limestone cliff. Contact commonly covered by
minor slump or talus debris. Unit thins east, thickens west. Thickness
60 m (200 ft)

Pts **Seligman Member**---Gray, thin-bedded, slope-forming dolomite and
gypsiferous sandstone. Includes gray to red, thinly interbedded
siltstone, sandstone, and gypsum. In lower part, includes brown, purple,
and yellow, fine- to medium-grained, thin-bedded, low- to high-angle
crossbedded and planar-bedded Coconino Sandstone that intertongues with
basal part of Seligman Member of the Toroweap Formation in Whitmore
Canyon and in Parashant Canyon about 13 km (8 mi) west of the map area
(Fisher, 1961; Schleh, 1966; Rawson and Turner, 1974; Billingsley 1997b;
Billingsley and others, 2000). Forms sharp, planar, unconformable
contact with underlying Hermit Formation where Coconino Sandstone is
absent. Unit often covered by talus (Qt) and alluvial fan (Qa1 and Qa2)
deposits. Thickness 12 m (40 ft)

Pc **Coconino Sandstone (Lower Permian)---**White, tan, yellowish-brown,
fine- to medium-grained, high-angle crossbedded, cliff-forming
sandstone. Sharp planar, intertonguing contact between flat-lying
sandstone beds of the Seligman Member of the Toroweap Formation. In some
areas, crossbedded sandstone of the Coconino Sandstone forms a sharp
planar contact with underlying Hermit Formation. Unit partly covered by
talus (Qt) and alluvial fan (Qa1 and Qa2) deposits in Toroweap Valley.
Thickness 35 to 45 m (115 to 150 ft)

Ph **Hermit Formation (Lower Permian)---**Light-red, yellowish-white,
fine-grained, thin- to medium-bedded, slope- and ledge-forming sandstone
and siltstone. Includes yellow silty sandstone beds 1 m (3 ft) thick
interbedded with thick beds of dark-red, slope-forming siltstone and
sandstone in upper part. Reddish sandstone beds commonly contain
yellowish-white bleached spots in upper part near contact with Toroweap
Formation or Coconino Sandstone. Sandstone beds are partly or completely
bleached yellow-white near contact with overlying Coconino Sandstone or
Seligman Member of the Toroweap Formation due to dissolution of ground
water in the Seligman Member of the Toroweap Formation (Pts) or the
Coconino Sandstone (Pc). Unit locally fills erosion channels cut into
underlying cliff-slope unit of upper Esplanade Sandstone as much as 6 m
(20 ft) deep; otherwise, contact is unconformable with erosional relief
averaging about 1 to 2 m (3 to 6 ft) in Cove Canyon area. Unit mostly
covered by alluvial fan (Qa1 and Qa2) and talus (Qt) deposits in
Toroweap Valley and Whitmore Canyon. Best exposures are in Cove Canyon.
Thickness 240 m (790 ft)

> **Supai Group---**Includes, in descending order, Esplanade Sandstone
> (Lower Permian), Wescogame Formation (Upper Pennsylvanian), Manakacha
> Formation (Middle Pennsylvanian), and Watahomigi Formation (Lower
> Pennsylvanian and Upper Mississippian) as defined by McKee (1975 and
> 1982). Age of the Watahomigi Formation is redefined by Martin and
> Barrick (1999). Divided into Esplanade Sandstone and lower Supai Group
> undivided:

Pe **Esplanade Sandstone (Lower Permian)---**Light-red and light-pinkish
gray, cliff-forming, fine- to medium-grained, medium-bedded (1 to 3 m
\[3 to 10 ft\]), well-sorted, calcareous sandstone interbedded with
dark-maroon-red, slope-forming siltstone. Forms an upper slope-cliff
unit, a middle cliff unit, and a lower slope unit. Upper slope-cliff
unit comprised of a red, thin-bedded siltstone and sandstone about 36 m
(120 ft) thick capped by a cliff of light-red, medium-grained,
thick-bedded, crossbedded sandstone about 25 to 30 m (80 to 100 ft)
thick. Red sandstone slope is similar in appearance to the Hermit
Formation and can be mistaken as part of the Hermit. Middle cliff unit
is light-red, fine- to medium-grained, crossbedded sandstone. Contains
small- to medium-scale, low-angle and high-angle planar crossbedded
sandstone and calcareous sandstone in upper half and flat, massive,
light-red to gray, low-angle crossbedded sandstone and calcareous
sandstone in lower half. Gray calcareous sandstone in lower part
undergoes facies change westward to become limestone cliff of Pakoon
Limestone west of Hurricane Fault. Thickness of middle cliff unit
averages about 60 m (200 ft). Lower slope unit consists of alternating
layers of sandstone, siltstone, mudstone, locally thin-bedded limestone
and basal limestone conglomerate. Thickness of lower slope unit averages
about 25 m (80 ft). Unconformable contact with underlying Wescogame
Formation in lower part of slope with local relief as much as 15 m (50
ft), but averaging about 11 m (35 ft). Thickness, about 153 m (500 ft)

M\*s **Lower** **Supai Group undivided (Pennsylvanian and
Mississippian)\--Wescogame Formation (Upper
Pennsylvanian)---**Light-red, pale-yellow, and light-gray, fine- to
coarse-grained sandstone, dolomitic sandstone, siltstone, mudstone, and
conglomerate. Forms an upper slope unit and lower cliff unit. Upper
slope unit is dark-red, fine-grained siltstone and mudstone and
light-red sandstone. Lower cliff unit is light-red to gray sandstone
with high-angle, large- and medium-scale, tabular crossbedded sets as
thick as 12 m (40 ft). Includes interbedded, dark-red, thin-bedded
siltstone in upper part. A limestone-chert conglomerate fills local
erosion channels as much as 24 m (80 ft) deep at base eroded into
underlying Manakacha Formation. Thickness 40 m (132 ft). **Manakacha
Formation (Middle Pennsylvanian)---**Light-red, white, and gray
sandstone, calcareous sandstone, dark-red siltstone, and gray limestone.
Forms an upper slope unit and lower cliff unit. Upper slope is a shaley
siltstone and mudstone interbedded with thin limestone and sandstone
beds. Lower cliff unit is crossbedded calcareous sandstone and sandy
limestone. Unconformable planer contact with underlying Watahomigi
Formation; erosional relief generally less than 1 m (3 ft). Thickness,
about 60 m (200 ft). **Watahomigi Formation (Upper Mississippian and
Lower Pennsylvanian)---**Gray and purple-red, slope-forming limestone,
siltstone, mudstone, and conglomerate. Includes cherty limestone
conglomerate of Lower Pennsylvanian age in upper two-thirds of slope
below sequence of alternating gray limestone and purplish-red shaley
siltstone and mudstone. Limestone beds in upper part contain red chert
nodules and chert veins. Lower third of slope unit is purplish-red
mudstone, siltstone, and thin-bedded, aphanitic to granular limestone in
upper part that contains fossil conodonts of Late Mississippian age
(Martin and Barrick, 1999). Unconformable contact with underlying
Redwall Limestone. The Surprise Canyon Formation (Upper Mississippian)
is not present in map area but is present just south of map as
valley-fill strata between the Watahomigi Formation and Redwall
Limestone (Billingsley and Beus, 1999). Thickness about 40 m (130 ft)

Mr **Redwall Limestone (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). **Horseshoe Mesa Member**---Light-olive-gray, thin-bedded,
cliff-forming, fine-grained, locally fossiliferous limestone.
Gradational contact with underlying massive-bedded limestone of the
Mooney Falls Member. Includes ripple-laminated and oolitic limestone
beds and some chert beds. Variable thickness 15 to 30 m (50 to 100 ft).
**Mooney Falls Member**---Light-gray, fine- to coarse-grained,
thick-bedded to very thick bedded (1 to 6 m \[4 to 20 ft\]),
cliff-forming, fossiliferous limestone. Includes dark-gray dolomite beds
in lower half; oolitic limestone and chert beds restricted to upper
part. Includes large-scale, tabular and planar cross-stratification in
upper third of unit. Disconformable contact with underlying Thunder
Springs Member distinguished by sudden appearance of interbedded chert,
a characteristic of Thunder Springs sediments. Thickness 122 m (400 ft).
**Thunder Springs Member**---About 50% white, thin-bedded bands and
lenses of fossiliferous chert and about 50% brownish-gray, finely
crystalline, thin-bedded, dolomite and fine- to coarse-grained
limestone. Weathers to distinctive prominent black and light-brown bands
on cliff faces. Disconformable contact with underlying Whitmore Wash
Member. Thickness 45 m (150 ft). **Whitmore Wash
Member**---Yellowish-gray and brownish-gray, thick-bedded, fine-grained,
fossiliferous, cliff-forming dolomite and limestone. Weathers dark gray.
Unconformable contact with underlying Temple Butte Formation. Limestone
beds fill low relief erosion channels as much as 2 to 3 m (5 to 10 ft)
deep. Contact generally recognized where major cliff of Redwall
Limestone overlies stair-step ledges of Temple Butte Formation.
Thickness 25 m (80 ft)

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 (1990).
Fine- to coarse-grained, thin- to medium-bedded, ripple-laminated ledges
of mudstone, sandstone, dolomite, and conglomerate. Unconformable
contact with underlying Cambrian undifferiented dolomite beds with
erosional relief as much as 12 m (40 ft). Unconformity represents a
major break in Paleozoic sequence involving the Late Cambrian, all of
the Ordovician and Silurian, and Early and Middle Devonian Periods.
Thickness 84 to 90 m (275 to 300 ft)

\_m **Muav Limestone (Upper and Middle Cambrian)---**Dark-gray,
light-gray, brown, and orange-red, limestone, dolomite, and calcareous
mudstone. The carbonate units consist of cliff-forming, fine- to
medium-grained, thin- to thick-bedded, mottled, fossiliferous, silty
limestone, limestone, and dolomite. About 63 m (210 ft) of upper part is
exposed in Cove Canyon

# REFERENCES CITED

Anderson, R.E., and Christensen, G.C., 1989, Quaternary faults, folds,
and related volcanic features of the Cedar City 1º x 2º quadrangle,
Utah: Utah Geological and Mineral Survey Miscellaneous Paper 89-6, 29 p.

Best, M.G., McKee, E.H., and Damon, P.E., 1980, Space-time composition
patterns of late Cenozoic mafic volcanism, southwestern Utah and
adjoining areas: American Journal of Science, v. 280, p. 1035-1050.

Beus, S.S., 1990, Temple Butte Formation, *in* Beus, S.S., and Morales,
Michael, eds., Grand Canyon geology: Oxford, N.Y., Oxford University
Press, and Flagstaff, Ariz., Museum of Northern Arizona Press, p.
107-118.

Billingsley, G.H., 1994a, Geologic map of the Antelope Knoll quadrangle,
northern Mohave County, Arizona: U.S. Geological Survey Open-File Report
94-449, scale 1:24,000,18 p.

\_\_\_, 1994b, Geologic map of the Hat Knoll quadrangle, northern Mohave
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1:24,000, 18 p.

\_\_\_, 1997a, Geologic map of the Mount Logan quadrangle, northern
Mohave County, Arizona: U.S. Geological Survey Open-File Report 97-426,
scale 1:24,000, 21 p.

\_\_\_, 1997b, Geologic map of the Mount Trumbull NW quadrangle,
northern Mohave County, Arizona: U.S. Geological Survey Open-File Report
97-488, scale 1:24,000, 19 p.

\_\_\_, unpub. data a, Geologic map of the upper Hurricane Wash and
vicinity, Mohave County, northwestern Arizona, scale 1:31,680.

\_\_\_, unpub. data b, Geologic map of Clayhole Wash and vicinity,
Mohave County, northwestern Arizona, scale 1:31,680.

Billingsley, G.H., and Beus, S.S., 1999, Geology of the Surprise Canyon
Formation of the Grand Canyon, Arizona: Rose, Eben, ed., Museum of
Northern Arizona Bulletin 61, Flagstaff, Arizona, Museum of Northern
Arizona Press, 254 p., 9 plates.

Billingsley, G.H., and Hampton, H.M., 2000, Geologic map of the Grand
Canyon 30\' x 60\' quadrangle, Coconino and Mohave County, northern
Arizona: U.S. Geological Survey Geologic Investigations Series Map
I-2688, scale 1:100,000.

Billingsley, G.H., Harr, Michelle, and Wellmeyer, J.L., 2000, Geologic
map of the upper Parashant Canyon and vicinity, Mohave County,
northwestern Arizona: U.S. Geological Survey Miscellaneous Field Studies
Map MF-2343, scale 1:31,680, 53 p.

Billingsley, G.H., Huntoon, P.W., 1983, Geologic map of the Vulcan\'s
Throne and vicinity, western Grand Canyon, Arizona: Grand Canyon,
Arizona, Grand Canyon Natural History Association, scale 1:48,000.

Billingsley, G.H., Spamer, E.E., and Menkes, Dove, 1997, Quest for the
pillar of gold, the mines and miners of the Grand Canyon: Grand Canyon,
Arizona, Grand Canyon Association Monograph No. 10, 112 p.

Billingsley, G.H., and Workman, J.B., 1999, Geologic map of the
Littlefield 30\' x 60\' quadrangle, Mohave County, northwestern Arizona:
U.S. Geological Survey Geologic Investigations Series Map I-2628, scale
1:100,000.

Dutton, C.E., 1882, Tertiary history of the Grand Canyon district: U.S.
Geological Survey Monograph 2, 264 p.

Fenton, C.R., 1998, Cosmogenic 3-Helium dating of lava dam outburst
floods in western Grand Canyon, Arizona: Salt Lake City, Utah,
University of Utah, Unpub. Masters Thesis, 76 p.

Fisher, W., 1961, Upper Paleozoic and lower Mesozoic stratigraphy of
Parashant and Andrus Canyons, Mohave County, northwestern Arizona:
Lawrence, Kansas, University of Kansas, Unpub. Ph.D. Thesis, 345 p.

Hamblin, W.K., 1965, Origin of \"Reverse Drag\" on the downthrown side
of normal faults: Geological Society of America Bulletin, v. 76, p.
1145-1164.

\_\_\_, 1970, Late Cenozoic basalt flows of the western Grand Canyon,
*in* Hamblin, W.K., and Best, M.G., eds., The western Grand Canyon
district: Guidebook to the geology of Utah No. 23, Provo, Utah, Brigham
Young University, Utah Geological Society, p. 21-38.

\_\_\_, 1994, Late Cenozoic lava dams of the western Grand Canyon:
Geological Society of America Memoir 183, 139 p.

Hamblin, W.K., and Best, M.G., eds., 1970, The western Grand Canyon
district: Guidebook to the geology of Utah No. 23, Provo, Utah, Brigham
Young University, Utah Geological Society, 156 p.

Huntoon, P.W., 1990, Phanerozoic structural geology of the Grand Canyon,
*in* Beus, S.S., and Morales, Michael, eds., Grand Canyon geology:
Oxford, N.Y., Oxford University Press, and Flagstaff, Ariz., Museum of
Northern Arizona Press, p. 261-310.

Jackson, G.W., 1990, The Toroweap Fault: one of the most active faults
in Arizona, *in* Arizona Geology: Arizona Geological Survey, v. 20, no.
3, p. 7-10.

Koons, E.D., 1945, Geology of the Uinkaret Plateau, northern Arizona:
Geological Society of America Bulletin, v. 56, p. 151-180.

Martin, Harriet, and Barrick, J.E., 1999, Conodont biostratigraphy,
chapter F, *in* Billingsley, G.H., and Beus, S.S., eds., Geology of the
Surprise Canyon Formation of the Grand Canyon, Arizona: Museum of
Northern Arizona Bulletin 61, p. 97-116.

McKee, E.D., 1963, Nomenclature for lithologic subdivisions of the
Redwall Limestone, Arizona: U.S. Geological Survey Professional Paper
475-C, p. 21-22.

\_\_\_, 1975, The Supai Group\--subdivision and nomenclature: U.S.
Geological Survey Bulletin 1395-J, p. 1-11.

\_\_\_, 1982, The Supai Group of Grand Canyon: U.S. Geological Survey
Professional Paper 1173, 504 p.

McKee, E.D., and Gutschick, R.C., 1969, History of the Redwall Limestone
of northern Arizona: Geological Society of America Memoir, v. 114, 726
p.

McKee, E.D., and Resser, C.E., 1945, Cambrian history of the Grand
Canyon region: Carnegie Institution of Washington Publication 563, 232
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McNair, A.H., 1951, Paleozoic stratigraphy of part of northwestern
Arizona: American Association of Petroleum Geologists Bulletin 35, p.
503-541.

Noble, L.F., 1922, A section of the Paleozoic formation of the Grand
Canyon at the Bass Trail: U.S. Geological Survey Professional Paper
131-B, p. 23-73.

Powell, J.W., 1875, Exploration of the Colorado River of the west and
its tributaries. Explored in 1869, 1870, 1871, and 1872, under the
direction of the Secretary of the Smithsonian Institution: 43rd
Congress, 1st Session, House Miscellaneous Documents, 300 p. (Reprinted
1961, Garden City, N.Y., Doubleday/Natural History Library.)

Rawson, R.R., and Turner, C.E., 1974, The Toroweap Formation; a new
look, *in* Karlstrom, T.N.V., Swann, G.A., and Eastwood, R.L., eds.,
Geology of northern Arizona with notes on archaeology and paleoclimate,
Part 1, Regional studies: Geological Society of America Rocky Mountain
Section Meeting, Flagstaff, Arizona, p. 155-190.

Reynolds, S.J., 1988, Geologic map of Arizona: Tucson , Arizona
Geological Survey Map 26, scale 1:1,000,000.

Reynolds, S.J., Florence, F.P., Welty, J.W., Roddy, M.S., Currier, D.A.,
Anderson, A.V., and Keith, S.B., 1986, Compilation of radiometric age
determinations in Arizona: Arizona Bureau of Mines and Geological
Mineral Technology Bulletin 197, 258 p., 2 maps.

Schleh, E.E, 1966, Stratigraphic section of Toroweap and Kaibab
Formations in Parashant Canyon, Arizona: Arizona Geological Society
Digest, v. 8, p. 57-64.

Sorauf, J.E., and Billingsley, G.H., 1991, Members of the Toroweap and
Kaibab Formations, Lower Permian, northern Arizona and southwestern
Utah: Rocky Mountain Geologist, v. 28, no. 1, p. 9-24.

Stewart, J.H., Poole, F.G., and Wilson, R.F., 1972, Stratigraphy and
origin of the Triassic Moenkopi Formation and related strata in the
Colorado Plateau region: U.S. Geological Survey Professional Paper 691,
195 p.

U.S. Department of the Interior, 1993, Arizona Strip District visitor
map, Arizona: Bureau of Land Management, scale 1:168,960.

Wenrich, K.J., Billingsley, G.H., and Blackerby, B.A., 1995, Spatial
migration and compositional changes of Miocene-Quaternary magmatism in
the western Grand Canyon: Journal of Geophysical Research, v. 100, no.
B7, p. 10,417-10,440.

Wenrich, K.J., Billingsley, G.H., and Huntoon, P.W., 1997, Breccia-pipe
and geologic map of the northeastern part of the Hualapai Indian
Reservation and vicinity, Arizona: U.S. Geological Survey Miscellaneous
Investigation Series Map I-2440, scale 1:48,000, 19 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): Washington, D.C.,
American Geophysical Union, 28th International Geological Congress Field
Trip Guidebook T115/315, 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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State of Arizona: Arizona Bureau of Mines, University of Arizona, scale
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U.S. DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP MF-2368

U.S. GEOLOGICAL SURVEY

DIGITAL DATABASE DESCRIPTION FOR THE GEOLOGIC MAP OF PART OF THE
UINKARET VOLCANIC FIELD, MOHAVE COUNTY, NORTHWESTERN ARIZONA

By Jessica L. Wellmeyer and Stephanie L. Dudash

### 

### INTRODUCTION

This is a digital geologic map database. This pamphlet describes what is
in this database and gives instructions for obtaining the data. There is
no paper map included in the Miscellaneous Field Studies report. The
report does include however, PostScript plot files containing images of
the geologic map sheet and an explanation sheet as well as the
accompanying text describing the geology of the area. For those
interested in a paper plot of information contained in the database or
in obtaining the PostScript plot files, please see the section entitled
"For Those Who Don't Use Digital Geologic Map Databases" below.

This digital map database, compiled from previously published and
unpublished data, and new mapping by the authors, represents the general
distribution of bedrock and surficial deposits in the Uinkaret volcanic
field. Together with the accompanying text file (uinkgeo.txt or
uinkgeo.doc), it provides current information on the geologic structure
and stratigraphy of the area covered. The database delineates map units
that are identified by general age and lithology following the spatial
resolution (scale) of the database to 1:31,680 or smaller. The content
and character of the database, as well as three methods of obtaining the
database, are described below.

### FOR THOSE WHO DON'T USE DIGITAL GEOLOGIC MAP DATABASES

Two sets of plotfiles containing images of much of the information in
the database are available to those who do not use an ARC/INFO
compatible GIS. Each set contains an image of a geologic map sheet and
the accompanying explanatory pamphlet. There is a set available in
PostScript format, and another in Acrobat PDF format. (See sections
below). Those who have computer capability can access the plotfile
packages in either of the two ways described below, however, these
packages do require ZIP utilities to access the plot files. Requests for
a tape copy of the digital database or plotfiles can be made by sending
a tape with request and return address to: Database Coordinator, U.S.
Geological Survey, 345 Middlefield Road, M/S 975, Menlo Park, CA 94025.
Plot files can also be acquired online at
http://geopubs.wr.usgs.gov/map-mf/mf2368

Those without computer capability can obtain plots of the map files
through USGS Plot-On-Demand service for digital geologic maps. To obtain
plots of the map sheet and accompanying pamphlet, contact the USGS
Information Services office at the following address: USGS Information
Services, Box 25286, Denver Federal Center, Denver, CO 80225-0046. Or by
phone (303) 202-4200, fax (303) 202-4695, or e-mail:
<infoservices@usgs.gov>. Be sure to include the map reference MF-2368.

### DATABASE CONTENTS

This digital database package consists of the geologic map database and
supporting data including base maps, map explanation, geologic
description, and references. A second package consists of PostScript
plot files of a geologic map, explanation sheet and geologic
description.

#### Digital Database Package

The first package is composed of geologic map database files for the
Uinkaret volcanic field. The coverages and their associated INFO
directory have been converted into ARC/INFO export files. These export
files are uncompressed, and are easily handled and compatible with some
Geographic Information Systems other than ARC/INFO. The export files
included are:

  ---------------- -------------- ---------------------------- -----------
  ARC/INFO export  Resultant      Description                  
  file             Coverage                                    

  uink_poly.e00    uink_poly/     Faults, contacts, and        
                                  geologic units               

  uink_point.e00   uink_point/    Strike and dip information   
                                  and annotation, point data   
                                  and annotation               

  uink_anno.e00    uink_anno/     Unit labels, fault and fold  
                                  names, and fault separations 

  uink_fold.e00    uink_fold/     Fold axes                    
  ---------------- -------------- ---------------------------- -----------

The database package also contains the following other export files with
extraneous data used in the construction of the database:

+---------------+-------------+----------------------------------------+
|               |             |                                        |
+---------------+-------------+----------------------------------------+
| [ARC/INFO     | #           | ######## Description                   |
| export        | ####### Res |                                        |
| file          | ultant File |                                        |
| ]{.underline} |             |                                        |
+---------------+-------------+----------------------------------------+
| para          | Pa          | Lineset                                |
| shant.lin.e00 | rashant.lin |                                        |
+---------------+-------------+----------------------------------------+
| gr            | grndcyn.mrk | Markerset                              |
| ndcyn.mrk.e00 |             |                                        |
+---------------+-------------+----------------------------------------+
| wp            | Wpgcmyk.shd | Shadeset                               |
| gcmyk.shd.e00 |             |                                        |
|               | geoline.lut | Lookup table for line symbols          |
| ge            |             |                                        |
| oline.lut.e00 | geomark.lut | Lookup table for marker symbols        |
|               |             |                                        |
| ge            | po          | Lookup table for polygon symbols       |
| omark.lut.e00 | lycolor.lut |                                        |
|               |             | Patternset                             |
| poly          | pattern.shd |                                        |
| color.lut.e00 |             |                                        |
|               |             |                                        |
| pa            |             |                                        |
| ttern.shd.e00 |             |                                        |
+---------------+-------------+----------------------------------------+

uink_hyp.tif.gz Zipped background hypsography image

uink_hyp.tfw World file accompanying uink_hyp.tif

#### PostScript Plotfile Package

The second digital data package available contains the PostScript images
described below:

  ------------------- ---------------------------------------------------
  uinkmap.eps         Encapsulated PostScript plottable file containing
                      complete map composition with geology, symbology,
                      annotation and base map of the Uinkaret volcanic
                      field

  uinkgeo.doc         A Word file of this report and the report
                      containing detailed unit descriptions and
                      geological information, plus sources of data and
                      references cited
  ------------------- ---------------------------------------------------

### PDF Plotfile Package

This package contains the Adobe Acrobat (.pdf) portable document format
files described below:

uinkmap.pdf A PDF file of the Uinkaret map sheet

uinkgeo.pdf A PDF file of this report, including the full geologic
report.

The Acrobat files were created from corresponding .eps files and are
compatible with Adobe Acrobat version 3.0 and higher.

### ACCESSING DATABASE CONTENTS

**ARC/INFO Export Files**

ARC export files are converted to their proper ARC/INFO format using the
ARC command 'import' with the option proper for the format desired. To
ease conversion and preserve naming convention, and AML is enclosed that
will convert all the export files in the database to coverages and
graphic files, and will also create an associated INFO directory. From
the ARC command line type:

*Arc: &run import.aml*

ARC export files can be read by other Geographic Information Systems.
Refer to your documentation for proper procedure for retrieval of data.

**PostScript and Portable Document Format Files**

These files are packaged separately. PDF files come as is and can be
downloaded or copied directly to your hard drive with no conversion
aside from opening the file from Adobe Acrobat. The PostScript documents
are zipped and compressed to a smaller file size. They can be
decompressed using gzip.

### DATABASE SPECIFICS

#### Procedure Used

Stable-base maps were scanned at the Flagstaff USGS Field site using the
Optronics 5040 raster scanner at a resolution of 50 microns (508 dpi).
The resulting raster file was in RLE format and converted to the RLC
format using the "rle2rlc" program written by Marilyn Flynn. The RLC
file was subsequently converted to an ARC/INFO Grid in ARC/INFO. The
linework was vectorized using ArcScan. A tic file was created in
lat/long and projected into the base map projection (Polyconic) using a
central meridian of -113.125W. Tics are defined in a 2.5-minute grid of
latitude and longitude in the geologic coverages corresponding with
quadrangle corners both in base maps and digital maps. The tic file was
used to transform the grid into UTM. ARC/INFO generated a RMS report
after transforming the original grid into transverse UTM.

RMS Report for transforming uinkpoly2rot grid from

pixel space to UTM zone 12 shifted (uinkticutm).

Nearest resampling method.

Polynomial order = 2.

Forward Transformation Coefficients

coef \# coef x coef y

\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

0 -12698.740 26588.071

1 1.049 -0.130

2 0.060 1.034

3 0.000 0.000

4 0.000 0.000

5 0.000 0.000

\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

Forward Transformation Errors

gcp id input x input y

output x output y x error y error

\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

1 297536.803 41543.459

298480.527 41560.539 0.393 0.557

2 319332.885 42212.656

320874.430 41066.279 -0.347 -0.240

3 298335.156 14586.603

297834.227 13824.430 0.676 0.328

4 320195.170 15246.760

320300.031 13331.512 -0.719 -0.642

5 301701.590 23677.944

301789.623 22983.425 -1.474 -0.389

6 316257.107 24117.632

316750.877 22654.512 1.605 1.330

7 301430.525 32664.581

302001.061 32228.716 -0.127 -0.937

8 312199.474 37496.078

313309.939 36601.959 -0.006 -0.008

\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

Forward transformation RMS Error (X, Y) = (0.867, 0.679)

Forward transformation Chi-Square (X, Y) = (6.014, 3.686)

\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

Backward Transformation Coefficients

coef \# coef x coef y

\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

0 13536.002 -24399.542

1 0.947 0.119

2 -0.056 0.959

3 0.000 0.000

4 0.000 0.000

5 0.000 0.000

Backward Transformation Errors

gcp id input x input y

output x output y x error y error

\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

1 297536.803 41543.459

298480.527 41560.539 -0.356 -0.555

2 319332.885 42212.656

320874.430 41066.279 0.329 0.251

3 298335.156 14586.603

297834.227 13824.430 -0.643 -0.350

4 320195.170 15246.760

320300.031 13331.512 0.670 0.654

5 301701.590 23677.944

301789.623 22983.425 1.417 0.447

6 316257.107 24117.632

316750.877 22654.512 -1.498 -1.359

7 301430.525 32664.581

302001.061 32228.716 0.080 0.909

8 312199.474 37496.078

313309.939 36601.959 0.001 0.003

\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\-- \-\-\-\-\-\-\-\-\-\-\-\-\-\-\--
\-\-\-\-\-\-\-\-\-\-\-\-\-\-\--

Backward transformation RMS Error (X, Y) = (0.818, 0.689)

Backward transformation Chi-Square (X, Y) = (5.355, 3.794)

Lines, points, polygons and annotation were edited using the ARCEDIT and
ARCSCAN modules.

Following editing and annotation, the individual coverage's were
projected into UTM projection.

**Map Projection:**

Parameter Description

Projection UTM

Units Meters on the ground

Zone 12

Datum NAD 1927

The content of the geologic database can be described in terms of the
lines and the areas that compose the map. Descriptions of the database
fields use the terms explained below.

Database Fields:

+----------------------+-----------------------------------------------+
| [Pa                  | [Description]{.underline}                     |
| rameter]{.underline} |                                               |
+----------------------+-----------------------------------------------+
| Item name            | Name of database field                        |
+----------------------+-----------------------------------------------+
| Width                | Maximum number of characters or digits stored |
+----------------------+-----------------------------------------------+
| Output               | Output width                                  |
+----------------------+-----------------------------------------------+
| Type                 | B - binary integer; F- binary floating point  |
|                      | number, I -                                   |
|                      |                                               |
|                      | ASCII integer, C - ASCII character string     |
+----------------------+-----------------------------------------------+
| N.dec.               | Number of decimal places maintained for       |
|                      | floating                                      |
|                      |                                               |
|                      | point numbers                                 |
+----------------------+-----------------------------------------------+

### LINES

The arcs are recorded as strings of vectors and described in the arc
attribute table (AAT). They define the boundaries of the map units,
faults, and map boundaries in UINK_POLY. These distinctions and the
geologic identities of the boundaries are stored in the LINETYPE field
according to their line type.

Arc Attribute Table Definition:

  --------- -------------- ------- --------- ------- --------- ---------------
  COLUMN    ITEM NAME      WIDTH   OUTPUT    TYPE    N. DEC    ALTERNATE NAME

  1         FNODE#         4       5         B       \-        \-

  5         TNODE#         4       5         B       \-        \-

  9         LPOLY#         4       5         B       \-        \-

  13        RPOLY#         4       5         B       \-        \-

  17        LENGTH         8       18        F       5         \-

  25        UINK_POLY#     4       5         B       \-        \-

  29        UINK_POLY-ID   4       5         B       \-        \-

  33        LINETYPE       50      50        C       \-        \-

  83        NAME           50      50        C       \-        \-

  133       POINTTYPE      50      50        C       \-        \-

  183       UNIT           8       8         C                 
  --------- -------------- ------- --------- ------- --------- ---------------

The AAT defined above represents the AAT in UINK_POLY and UINK_FOLD is
virtually identical.

Description of AAT Items:

  ------------------------ ----------------------------------------------
  [Item]{.underline}       [Description]{.underline}

  FNODE#                   Starting node of the arc

  TNODE#                   Ending node of the arc

  LPOLY#                   Polygon to the left of the arc

  RPOLY#                   Polygon to the right of the arc

  LENGTH                   Length of the arc in meters

  UINK_POLY#               Unique internal number

  UINK_POLY-ID             Unique identification number

  LINETYPE                 Line type

  NAME                     Name of line feature

  POINTTYPE                Point type

                           
  ------------------------ ----------------------------------------------

The geologic line types relate to geologic line symbols in the line set
PARASHANT.LIN according to the lookup table GEOLINE.LUT.

**Domain of Line Types recorded in LINETYPE field:**

BASALT FLOW DIRECTION

BASALT FLOW DIRECTION TAIL

CONCEALED SYNCLINE

CONTACT

LANDSLIDE SCARP

NORMAL HIGH ANGLE CONCEALED FAULT

NORMAL HIGH ANGLE FAULT

SYNCLINE (uink_fold)

MONOCLINE (uink_fold)

CONCEALED MONOCLINE (uink_fold)

**Domain of Point Types recorded in POINTTYPE field**

bar and ball

syncline

monocline

none

### POLYGONS

Map units (polygons) are described in the polygon attribute table (PAT).
This identifies the map units recorded in the UNIT field by map label.
Individual map units are described more fully in the accompanying text.

Definition of Polygon Attribute Table:

  -------- -------------- ------- ----------- ------- ------- --------------
  COLUMN   ITEM NAME      WIDTH   OUTPUT      TYPE    N. DEC  ALTERNATE NAME

  1        AREA           8       18          F       5       \-

  9        PERIMETER      8       18          F       5       \-

  17       UINK_POLY#     4       5           B       \-      \-

  21       UINK_POLY-ID   4       5           B       \-      \-

  25       UNIT           8       8           C       \-      \-

  33       PATTERN        4       4           I       \-      \-
  -------- -------------- ------- ----------- ------- ------- --------------

Description of Item Names:

  ------------------------- ---------------------------------------------
  [Item Name]{.underline}   [Description]{.underline}

  AREA                      Area of polygon in square meters

  PERIMETER                 Perimeter of polygon in meters

  UINK_POLY#                Unique internal number

  UINK_POLY-ID              Unique identification number

  UNIT                      Unit label

  PATTERN                   Designated fill pattern for polygons
  ------------------------- ---------------------------------------------

Domain of UNIT (map units):

  ---------- -------------- ------------ ------------- ---------- ----------
  \_m        Qa3            Qg1          Qp6588        Ti         

  Dtb        Qaf            Qg2          Qp6646        Tmb        

  M\*s       Qb             Qi           Qpvb          Tmi        

  Mr         Qb1            Qkrb         Qpvp          Tmlb       

  Pc         Qb6375         Qkrp         Qs            Tp         

  Pe         Qb6457         Ql           Qgrb          \^cp       

  Ph         Qb6588         Qlsb         Qgrp          \^ml       

  Pkf        Qb6646         Qlsp         Qti           \^mm       

  Pkh        Qc             Qmrb         Qb1           \^ms       

  Ptb        Qltb           Qmrp         Qv            \^mt       

  Pts        Qcbb           Qp           Tb            \^mu       

  Ptw        Qcbi           Qp1          Tbb           \^mv       

  Qa1        Qcbp           Qp6375       Tbi                      

  Qa2        Qf             Qp6457                                
  ---------- -------------- ------------ ------------- ---------- ----------

\_ represents Cambrian strata, D represents Devonian, M represents
Mississippian, \* represents Pennsylvanian, P represents Permian strata,
T represents Tertiary strata, \^ represents Triassic strata, Q
represents Quaternary strata and 'xx' is a code for any undefined
strata. Polygons were assigned colors based on their geologic unit. The
colors were assigned from the shadeset WPGCMYK.SHD and are related to
the lookup table POLYCOLOR.LUT.

### POINTS

Strike and dip information is recorded as coordinate data with related
information. This information is described in the Point Attribute Table
(PAT). ARC/INFO coverages cannot hold both point and polygon
information, thus UINK_POINT has only a point attribute table, and
UINK_POLY has only a polygon attribute table.

Definition of Point Attribute Table:

  --------- --------------- ------- -------- ------- -------- ------------------
  COLUMN    ITEM NAME       WIDTH   OUTPUT   TYPE    N.DEC.   ALTERNATE NAME

  1         AREA            8       18       F       5        \-

  9         PERIMETER       8       18       F       5        \-

  17        UINK_POINT#     4       5        B       \-       \-

  21        UINK_POINT-ID   4       5        B       \-       \-

  25        NAME            30      30       C       \-       \-

  55        POINTTYPE       60      60       C       \-       \-

  115       DIP             3       3        I       \-       \-

  118       STRIKE          3       3        I       \-       \-
  --------- --------------- ------- -------- ------- -------- ------------------

Description of Item Names:

  ------------------------ ----------------------------------------------
  [Item Name]{.underline}  [Description]{.underline}

  AREA                     

  PERIMETER                

  UINK_POINT#              Unique internal number

  UINK_POINT-ID            Unique identification number

  NAME                     Feature name

  POINTTYPE                Point type

  DIP                      Dip angle in azimuth degrees

  STRIKE                   Strike angle in degrees
  ------------------------ ----------------------------------------------

The coverage UINK_POINT contains strike and dip data, and other
pertinent structural data represented by point symbology, including
collapses, sinkholes and domes. UINK_POLY has point types defined in the
AAT, which correspond to the defined linetype for an arc. These point
types are related to the lookup table GEOMARK.LUT and are from the
symbolset GRNDCYN.MRK.

**Domain of POINTTYPE:**

bedding

probable breccia pipe (c)

pyroclastic cone

sinkhole

vertical joint

### ANNOTATION

The coverage UINK_ANNO contains all annotation for the polygon coverage.
It is defined somewhat differently from the polygon and dip coverages.
The arc attribute table is of negligible importance. Arcs in this
coverage are merely leaders from a unit annotation to the related
polygon. UINK_ANNO contains annotation with unit labels, fault
separation, and monocline names. Annotation pertaining to unit name is
in subclass anno.unit, and all other annotation is contained in subclass
anno.fault.

The textset used for all annotation was geofont.txt, specifically
symbolset 38. Use of this textset allows for proper symbol notation for
unit symbols. The default ARC/INFO textset does not allow for a proper
geologic symbol indicating 'Triassic.' By using this alternate text set,
the character pattern '\^m' prints instead as \^m.

### BASE MAP PROCEDURE

The base map was prepared by piecing together 1:24,000-scale quadrangles
of the Mount Trumbull NE, Mount Trumbull SE, Mount Trumbull NW, and
Mount Logan and rescaling to 1:31,680. This new base was then scanned
using the Optronics 5040 raster scanner at a resolution of 50 microns.
This raster file was converted from RLE format to RLC format, and
subsequently converted to an ARC/INFO Grid file. The grid file was
converted into a registered TIFF in conjunction with a colormap file,
producing an image file with all linework in gray. No editing of the
actual linework or attribution was done.

### SPATIAL RESOLUTION

Use of this digital geologic map database should not violate the spatial
resolution of the data. Although the digital form of the data removes
the constraint imposed by the scale of a paper map, the detail and
accuracy inherent in map scale are also present in the digital data.
This database was created and edited at a scale of 1:31,680 and means
that higher resolution data is generally not present. Plotting at scales
of larger than 1:31,680 will not yield greater real detail, but may
reveal fine-scale irregularities below the intended resolution.

### OTHER FILES

The lineset used to display the appropriate line weight and symbology is
PARASHANT.LIN. It is related to the database by a lookup table called
GEOLINE.LUT. Similarly, the markerset for this database is GRNDMRK.MRK,
and its lookup table is GEOMARK.LUT. Colors in the polygon coverage
(UINK_POLY) are assigned based on the UNIT and were chosen from a
shadeset called WPGCMYK.SHD and a lookup table POLYCOLOR.LUT. Annotation
(unit labels, text labels and printed numerical values) were displayed
using a font entitled GEOFONT.TXT which has capabilities for displaying
proper notation of geologic text symbols.

Also enclosed in this database package is UINK.MET, the FGDC standard
metadata for the database and UINK.REV, a revision list with current
information on the status of all files described in this report and
found in the database.