GEOLOGIC SUMMARY adjoins the eastern border (Billingsley and Hampton, 2000). by George H. Billingsley The Mount Trumbull 30´ x 60´ quadrangle encom- The geologic map of the Mount Trumbull 30´ x 60´ passes approximately 5,018 km2 (1,960 mi2) of land quadrangle is a cooperative product of the U.S. Geologi- within Mohave and Coconino Counties of northwestern cal Survey, the National Park Service, and the Bureau of Arizona. The quadrangle is bounded by longitude 113° to Land Management that provides geologic map coverage 114° and latitude 36°00´ to 36°30´. Elevations within the and regional geologic information for visitor services map area range from 2,447 m (8,028 ft) at Mount Trum- and resource management of Grand Canyon National bull on the Uinkaret Plateau, northeast quarter of the map Park, Lake Mead Recreational Area, and Grand Canyon area, to 353 m (1,156 ft) at Lake Mead, southwest quarter Parashant National Monument, Arizona. This map is a of the map area. compilation of previous and new geologic mapping that The map area lies mostly within the southwest- encompasses the Mount Trumbull 30´ x 60´ quadrangle ern part of the Colorado Plateau and partly within the of Arizona. southeastern edge of the Basin and Range geologic prov- Dutton (1882) made the first early reconnaissance inces. The Colorado Plateau is locally subdivided into geologic map of the Uinkaret Plateau, which is part of seven physiographic areas as shown by Billingsley and this map area. More recently, Huntoon and others (1981, others (1997): the Grand Canyon, the Kanab, Uinkaret, 1982) and Billingsley and Huntoon (1983) produced geo- Shivwits, and Sanup Plateaus north of Grand Canyon, logic maps of the south half of this area that were later and the Coconino and Hualapai Plateaus south of Grand revised by Wenrich and others (1996, 1997). Geologic Canyon (fig. 1). The approximate position of the Grand maps within the north half of the map area were produced Wash Fault separates the Basin and Range province from by Lucchitta and Beard (1981a, b), Billingsley (1997a, the Colorado Plateau province. The northwest part of the b, c), Billingsley and others (2000), and Billingsley and map area is referred to as the Grand Wash Trough within others (2001, 2002, unpub. data). A geologic map of the the Basin and Range (fig. 1). Littlefield 30´ x 60´ quadrangle borders the northern The boundary between the Kanab and Uinkaret edge of this map (Billingsley and Workman, 2000) and a Plateaus is marked along the Toroweap Fault, which is a geologic map of the Grand Canyon 30´ x 60´ quadrangle geologic and topographic feature. The boundary between

114°00' 113°00' 36°30' U UINKARET PLATEAU

U TEA Mount Trumbull

U

TROUGH T TEA L PLA U

TEA A PLA U Bundyville F TEA (Mount Trumbull)

WASH H Tuweap S SHIVWITS PLA

A

W

KANAB PLA

D

GRAND

N

A

R AND RANGE

G

r ive R o rad COLORADO olo SANUP U C

BASIN Mount Dellenbaugh TEA

PLA

C olo rado R i v SANUP COCONINO HUALAPAI e

r PLATEAU PLATEAU 36°00' Figure 1. Index map of the Mount Trumbull 30' x 60' quadrangle, Arizona showing the physiographic provinces and subprovinces.

1 the Uinkaret and Shivwits Plateaus is marked along the are exposed at the bottom of Grand Canyon along a one- Hurricane Fault that forms the Hurricane Cliffs, a promi- mile reach of the Colorado River between Miles 189.6 nent west-facing fault scarp. The boundary between the and 190.6 as measured from Lees Ferry, Arizona. The Shivwits Plateau and Sanup Plateau is marked along the majority of the map area is characterized by gently east north rim of the Grand Canyon and northward along the and northeast dipping Paleozoic and Mesozoic strata that upper Grand Wash Cliffs to Hidden Canyon. The Sanup overlie Early Proterozoic crystalline metamorphic rocks. Plateau is a narrow flat platform or topographic bench Paleozoic rocks comprise most of the cliffs and between the north rim and the inner gorge of the Grand slopes in the walls of Grand Canyon and display remark- Canyon and between the upper and lower Grand Wash able east-west facies and thickness changes. The Perm- Cliffs. The Sanup Plateau extends to the Hurricane Fault ian Kaibab Formation (Pk) generally forms the rim of at Whitmore Canyon. Grand Canyon north and east of the Colorado River and The nearest settlements to the map area are Colorado the plateau surface of the Shivwits, Uinkaret, Kanab, and City, Arizona about 58 km (36 mi) north of the northeast Coconino Plateaus because of its resistance to erosion. corner of the map area, and St. George, Utah about 90 However, the Kaibab Formation has been removed along km (56 mi) north of Mount Trumbull. There are two the southern part of the Shivwits Plateau due to Laramide abandoned settlements within the map area, Tuweap and uplift and subsequent erosion allowing the Toroweap Mount Trumbull (fig. 1). The town of Mount Trumbull, Formation (Pt) to form the canyon rim in some areas. A locally known as Bundyville, is near the base of the Hur- significant unconformity separates the Kaibab Formation ricane Cliffs on the Shivwits Plateau about 16 km (10 mi) from the underlying Permian Toroweap Formation. Chan- west of Mount Trumbull mountain. Today, Bundyville is nels as much as 43 m (140 ft) deep have eroded into the little more than a small cluster of local ranches and one soft strata of the Woods Ranch Member of the Toroweap abandoned historic schoolhouse. Tuweap is in the upper Formation in Toroweap, Whitmore, and Mohawk Canyon reaches of Toroweap Valley, a northern tributary to Grand areas. Otherwise, the Toroweap Formation maintains a Canyon consisting of a few abandoned ranch buildings. general overall thickness throughout the map area. The Toroweap Campground is in Grand Canyon National limestone of the Brady Canyon Member of the Toroweap Park in the lower reaches of Toroweap Valley on the rim Formation thickens from east to west while sandstone of the inner gorge of Grand Canyon and provides a spec- and gypsum of the Seligman Member thins from east to tacular overlook of the Colorado River (Colorado River west. The Permian Coconino Sandstone (Pc) intertongues Mile 174 to 183). within the lower part of the Seligman Member of the Access to the plateau regions north of Grand Canyon Toroweap Formation (Pt) in the vicinity of Parashant and is by dirt roads that are maintained by the Bureau of Whitmore Canyons (Fisher, 1961; Schleh, 1966; Rawson Land Management of the Arizona Strip Field Office in and Turner, 1974; Billingsley and others, 2000). Because St. George, Utah. Access to the Coconino and Hualapai the name Coconino Sandstone is well established in the Plateaus in the southwestern and southeastern part of the Grand Canyon nomenclature and it forms a significant map area is by jeep trails and dirt roads maintained by mappable cliff unit within the walls of Grand Canyon, the Hualapai Tribe and requires permits from the Tribe the Coconino Sandstone is herein maintained as a sepa- for access and travel. Access into the depths of Grand rate map unit. The Coconino Sandstone unconformably Canyon in this map area is rather limited to a few non- overlies the Hermit Formation and pinches out in the maintained trails and a go-at-your-own-risk type of west third of the map area, which allows the Toroweap hiking. Visitors north of the Colorado River must obtain Formation to overlie the Hermit Formation. The Permian hiking permits and information from the backcountry Hermit Formation (Ph) undergoes a facies change from a office at Grand Canyon National Park, Grand Canyon deltaic siltstone and sandstone sequence in the east quar- Village, Arizona, or from the Toroweap Ranger Station ter of the map area to a thicker marine-shoreline sand- in Toroweap Valley. Visitors south of the Colorado River stone and siltstone sequence in the west quarter of the must obtain permits from the Hualapai Tribe at Peach map area. A regional unconformity separates the Hermit Springs, Arizona. Formation from the underlying Esplanade Sandstone, but the unconformity is difficult to locate in the map area because the erosional relief is little more than 3 m (10 ft) GEOLOGIC SETTING at the top of a sandstone ledge about 60 m (200 ft) above Erosion by earlier Laramide and Tertiary streams the sandstone bench of the Sanup Plateau in the Grand and the Colorado River and its tributaries have exposed Wash Cliffs area and in Parashant Canyon. about 365 m (1,200 ft) of Mesozoic strata, over 1,220 m The Supai Group (McKee, 1982) includes, in (4,000 ft) of Paleozoic strata, and about 30 m (100 ft) of descending order, the Esplanade Sandstone, Wescogame Early Proterozoic crystalline metamorphic rock complex Formation, Manakacha Formation, and Watahomigi For- within the map area. The Early Proterozoic rocks (Xgr) mation. The Permian Esplanade Sandstone of the Supai

2 3 Group (Pe) is composed of an upper siltstone slope unit, The Mississippian Redwall Limestone (Mr) gener- a middle sandstone cliff unit, and a lower siltstone and ally maintains a constant thickness throughout the map sandstone slope unit near and east of the Hurricane Fault. area except where removed by erosion in Late Missis- However, west of the Hurricane Fault, the middle sand- sippian time. The Redwall Limestone consists of marine stone cliff unit intertongues with marine limestone beds limestone and dolomite beds that form a major gray cliff of the Pakoon Limestone between the Grand Wash Cliffs throughout the Grand Canyon area. The Devonian Temple and the Hurricane Fault. The Permian Pakoon Limestone Butte Formation (Dtb) forms a distinctive dark-gray band of McNair (1951) contains Early Permian marine fossils of limestone and dolomite ledges beneath the light-gray that establish a Permian age for the Esplanade Sandstone Redwall Limestone cliff and generally maintains a uni- throughout Grand Canyon. The Permian Esplanade form thickness of about 138 m (450 ft) from east to west Sandstone and Pakoon Limestone cliff is mapped as across the map area. The Temple Butte Formation is one unit (Pep) west of the Hurricane Fault and as part of readily identified in the field by a strong fetid smell when the upper Supai Group. West of the Grand Wash Cliffs, rocks of this unit are freshly broken. The Cambrian Tonto the Esplanade Sandstone thins and pinches out and the Group (_m, _ba, and _t) gradually thickens from east to Pakoon Limestone becomes the upper part of the Call- west across the map area and is composed of the upper ville Formation. The Upper Mississippian and Pennsyl- Muav Limestone, the middle Bright Angel Shale, and the vanian part of the lower Supai Group, undivided (M*s), lower Tapeats Sandstone. These Cambrian units are rec- maintains a regional thickness but includes a significant ognized on the basis of their distinctive rock types: lime- east-west facies change from a deltaic continental deposit stone and dolomite lithology form the Muav Limestone; along the east edge of the map area to a marine limestone shale and siltstone lithology form the Bright Angel Shale; and calcareous sandstone along the Grand Wash Cliffs and sandstone and conglomerate lithology form the of the west edge of the map area. The Pennsylvanian Tapeats Sandstone. The map contact between these three Wescogame and Manakacha, and the Mississippian and units is gradational and lithologically defined in both the Pennsylvanian Watahomigi Formations that comprise vertical and lateral sense. The Muav Limestone forms the lower Supai Group are not subdivided on the map gray cliffs of limestone and dolomite that are separated because the individual unconformities that separate these by slope-forming tongues of green shale and siltstone of formations are difficult to establish in the field because of the Bright Angel Shale. But the map contact between the their subtle expression. The entire Supai Group becomes Muav Limestone and Bright Angel Shale is arbitrarily the Callville Formation west of the Grand Wash Cliffs. marked at the base of the lowest prominent cliff-form- However, the Esplanade Sandstone and Pakoon Lime- ing limestone, the Rampart Cave Member of the Muav stone are exposed and mapped as such at The Cocks- Limestone (McKee and Resser, 1945). The Bright Angel comb, east of the Wheeler Fault southwest edge of the Shale slope is composed of green to reddish-green shale map at Lake Mead, and are not mapped as the Callville and siltstone with minor ledges of limestone typical of Formation for map consistency. Muav Limestone lithology in the upper part and tongues A regional unconformity separates the lower Supai of brown sandstone typical of the Tapeats Sandstone Group (Watahomigi Formation) from either the underly- lithology in the lower part. The map contact between the ing Surprise Canyon Formation or the Redwall Lime- Bright Angel Shale and the Tapeats Sandstone is arbi- stone. The unconformity between the lower Supai Group trarily marked in a transition zone of about 30 m (100 ft) and the Surprise Canyon Formation and between the Sur- near the bottom of the slope-forming Bright Angel Shale prise Canyon Formation and the Redwall Limestone often near the top of the cliff-forming Tapeats Sandstone. The merge at the same horizon to form a more significant ero- Tapeats Sandstone forms a thin-bedded, brownish-red sional unconformity that separates the Supai Group from conglomeratic sandstone cliff that unconformably over- the underlying Redwall Limestone. The unconformity lies Proterozoic crystalline rocks. between the Surprise Canyon Formation and the Redwall Sedimentary rocks of Mesozoic age once covered Limestone is significantly expressed where river - chan the entire map area before Laramide and Tertiary erosion nels as much as 122 m (400 ft) deep have eroded into removed most of these rocks. The Mesozoic rocks are the Redwall Limestone. These erosion channels are filled generally composed of nonresistant red and white mud- with lower conglomerate and sandstone deposits that rep- stone, siltstone, and sandstone. Most of the Mesozoic resent a continental environment that was subsequently rocks are preserved under Tertiary and Quaternary basalt buried by upper limestone and sandstone deposits that flows on the Shivwits, Uinkaret, and Kanab Plateaus or represent an estuarine marine environment of the Sur- concealed beneath Quaternary alluvium and landslide prise Canyon Formation. The type section and thickest deposits. The 365 m (1,200 ft) of the Moenkopi Forma- sequence of the Mississippian Surprise Canyon Forma- tion (^m) at Hells Hole in upper Whitmore Canyon, cen- tion (Ms) is on the Hualapai Plateau in the southwest tral part of the map area, is the most complete, thickest, corner of the map area near Colorado River Mile 264. and closest outcrop of the Moenkopi Formation to Grand

2 3 Canyon other than at Lees Ferry, Arizona (Colorado contact produced east-dipping monoclines in the overly- River Mile 0). The Mesozoic rocks exposed at Hells ing Paleozoic strata (Huntoon, 1993). Examples, from Hole include about 122 m (400 ft) of the Chinle Forma- west to east, were monoclinal segments along the Main tion (^c) representing the closest outcrop of this forma- Street, Hurricane, and Toroweap Fault zones, the largest tion to Grand Canyon other than at Lees Ferry, Arizona. being the Hurricane Monocline in the southeastern part Hells Hole also contains the most complete section of the of the map. Permian Harrisburg Member of the Kaibab Formation. According to Huntoon (1990), late Cenozoic exten- Cenozoic deposits include Tertiary and Quaternary sion supplanted Laramide compression and caused basalts, alluvium, and landslides. The youngest volcanic reactivation of the same ancient basement faults that rock is the Little Spring Basalt (this map), dated at about had already been reactivated by Laramide compression. 1,000 years old (Fenton, 1998), consisting of two basalt However, the motions along the basement faults were flows and a pyroclastic cone on the Uinkaret Plateau. opposite to those in Laramide time. Late Tertiary move- Other Quaternary volcanic rocks generally range from ments were mostly down-to-the west in normal faulting about 75 to 400 ka, and Tertiary volcanic rocks range in contrast to Laramide up-to-the-west reverse fault- in age from about 3.6 to 17 Ma. The alluvial deposits ing. The first sense of displacement on the monoclines are composed of fluvial terrace-gravel and alluvial fan began to reverse as normal faulting propagated upward deposits. Landslide deposits are most common around into Paleozoic and younger rocks. As normal faulting and below Tertiary or Quaternary volcanic outcrops. progressed, faults propagated along the strikes of the Only the thickest and most extensive Quaternary depos- basement faults beyond the limits of the Laramide mono- its are shown. Thin veneers over distinct outcrops of clines producing the generally north-trending, now-con- bedrock are omitted. tinuous, down-to-the-west fault escarpments such as the Hurricane Cliffs. By late Pliocene and Quaternary time, extension progressed to such a degree that new normal STRUCTURAL GEOLOGY faulting began to fragment the basement blocks lying Minor east-dipping Laramide monoclines and late between the reactivated basement faults giving rise to Tertiary and Quaternary normal faults are the charac- the multiple parallel, en echelon, and intersecting normal teristic structures found in the Paleozoic and Mesozoic fault patterns and grabens shown on the map. The density rocks. East northeast-west southwest Laramide compres- of the normal faults increases with depth as revealed by sional folding caused gentle regional warping of the crust the greater numbers of faults on the Esplanade surface and significant regional uplift. This activity began in compared to the Kaibab surface throughout the map area. Late Cretaceous time and continued into early Tertiary This reveals that the faults are propagating upward from time. The uplift caused erosion of most of the Mesozoic the basement. In the extreme, the most densely faulted strata from the region, as well as deep dissection of the areas have undergone regional extensional sagging such Paleozoic rocks in the vicinity of what is now the Grand as the area centered on the mouth of Parashant Canyon. Canyon. This erosion produced a step-bench topography Reverse drag along the principal normal faults is that persists to the present. The south-facing, 610-m- common throughout the map area. Reverse drag along high (2,000-ft-high) erosional escarpment comprised of normal faults is defined by Hamblin (1965) as a sag- Pennsylvanian and Permian rocks north of the Colorado induced infolding of the rocks toward the fault plane River and the beveled surface across older rocks on the within the hanging wall. The infolding fills space cre- Hualapai Plateau were essentially eroded to their pres- ated at depth as displacement occurs along normal fault ent position by the close of Laramide time. Early Ter- surfaces that dip less steeply with increasing depth. The tiary, north-flowing, pre-Colorado River streams eroded result is that reverse drag exacerbates the displacement canyons as deeply as the Precambrian basement on the along those faults. It also accentuates pre-existing mono- east side of the Hualapai Plateau immediately south clinal dips on the downdropped western blocks within of this map. Their presence reveals that deep canyons the fault zones. Reverse drag is prevalent in the Paleozoic containing northerly and easterly flowing streams were and Mesozoic strata along the Dellenbaugh, Main Street, present before the west-flowing Colorado River became Hurricane, and Toroweap Faults (Billingsley and others, integrated from east to west across the region in Pliocene 2000, 2001). time (Young, 1999). Cenozoic faulting on this part of the Colorado Pla- As Laramide compression took place, buried, gen- teau began to manifest itself as offsets at the surface in erally north-trending, pre-existing Precambrian faults late Pliocene time, about 3.6 to 2.5 Ma (Billingsley and were reactivated, giving rise to reverse faulting in the Workman, 2000). Faulting has been an ongoing process metamorphic basement complex along structural trends shown by the fact that vertical offsets between succes- that now define the physiographic subdivisions within sively younger late Tertiary and Quaternary units dimin- the map area. The offsets at the Precambrian-Paleozoic ish across several faults in the map area. This relation is

4 5 well expressed along the Hurricane and Toroweap Faults, indicated on the map by red dots. Collapse features that which displace multiple basal flows and alluvium of dif- are probably breccia pipes are indicated by black dots. fering ages (Jackson, 1990). The faults in the map area Sinkholes, minor folds, and other surface irregulari- are currently active as revealed by offsets of alluvium ties on the Uinkaret and Shivwits Plateaus are caused by deposited across them (Huntoon, 1977) and are indicated dissolution of gypsum and gypsiferous siltstones within as solid fault traces across alluvial deposits. the Harrisburg Member of the Kaibab Formation and the Basalts erupted through joints and fractures onto the Woods Ranch Member of the Toroweap Formation. The plateaus and within Grand Canyon in the map area. Best youth of many sinkholes is revealed by their sheer walls, and Brimhall (1970) note the following relation between freshness of collapse debris within them, and disrupted volcanism and structure on the Uinkaret Plateau. (1) local drainage. Normal faulting and volcanism have operated simultane- ously throughout most of late Cenozoic time although ACKNOWLEDGMENTS the inception of faulting predates basaltic volcanism. The cooperation and support of Lake Mead National (2) A shift in fault activity from the Grand Wash to the Recreation Area of the National Park Service and the Ari- Hurricane-Toroweap zones has been paralleled in time zona Strip Field Office of the Bureau of Land Manage- by an eastward shift in volcanism. (3) Vents throughout ment are gratefully appreciated. We also appreciate the the region lie between fault lines and are independent of advice, revisions, and information of Peter W. Huntoon them with few exceptions. (4) Many of the basalts carry of Boulder City, Nevada, Jeremiah B. Workman, Charles mantle-derived olivine inclusions, indicating that the Powell, Theresa Iki, and Jan Zigler of the U.S. Geologi- magma originated from the upper mantle. Dutton (1882) cal Survey for their technical advice and assistance in and Koons (1945) observed the tendency for cones on the the preparation of this map and report. Becky Hammond Uinkaret Plateau to align parallel to faults but to occur in of the Bureau of Land Management provided the aerial the areas between them. photographs. Deeply eroded outcrops of dike swarms on or below the Esplanade Sandstone surface indicate that the dikes are localized along fractures, joints, and minor faults DESCRIPTION OF MAP UNITS that parallel nearby normal faults. Examples include the SURFICIAL DEPOSITS Whitmore dike swarm (Twi) about 1.6 km (1 mi) west of Qs the Hurricane Fault and south of Whitmore Canyon; the Stream-channel alluvium (Holocene)—Light- dikes of Parashant Canyon and Hundred and Ninetysix gray to light-brown and reddish-brown, Mile Creek (Tp6i) in Parashant Canyon, Colorado River unconsolidated mud, sand, gravel, pebbles Mile 196 and in Hundred and Ninetysix Mile Canyon; the and boulders. Subject to flash flood debris dikes of Colorado River Mile 202 (T2i) about 1.5 km (1 flows. Thickness, 0.5 to 2 m (2 to 6 ft) mi) west of Colorado River Mile 202; and several dikes Qf Floodplain deposits (Holocene)—Light-gray (Tsgi) in the walls of Tincanebitts and Dry Canyons in to light-brown mud and fine- to coarse- the southwest quarter of the map area. The fact that vents grained, unconsolidated silt and sand and do not preferentially occur along the principal late Ceno- lenses of pebble to cobble gravel; uncon- zoic faults indicates that, in general, upward movement solidated. Locally includes cinder and of magma was independent of the faults at great depths. basalt fragments. Intertongue or overlap The dikes and vents tended to localize on extended frac- valley-fill alluvium (Qv) or young alluvial tures in the Paleozoic section in close proximity to the fan (Qay) deposits. Form relatively flat sur- surface. The parallelism between the intruded fractures faces having little or no vegetation. Subject and nearby faults implies that late Cenozoic extension to frequent flooding or ponding. Thickness, either created or opened the fractures. 1 to 3 m (3 to 10 ft) Many bowl-shaped depressions in the Harrisburg Qd Sand sheet and sand dune deposits (Holo- Member of the Kaibab Formation and Woods Ranch cene)—Grand Wash Trough area: Light- Member of the Toroweap Formation characterized by red and tan, fine- to medium-grained, inward dipping strata are the surface expressions of well-sorted wind-blown quartz sand. Sand breccia pipes that have propagated upward from the material derived from erosion of local red Mississippian Redwall Limestone (Wenrich and Hunt- siltstone and sandstone outcrops of Rocks oon, 1989). Breccia pipes within the Grand Canyon are of the Grand Wash Trough (Tgr) and rede- easily identified in the Permian and Pennsylvanian strata posited as stream-channel alluvium (Qs), as columns of downward displaced, brecciated rock sur- then redeposited as wind-blown sand sheet rounded by a yellowish-white bleached zone containing and small sand dune deposits along wide ring fractures. Breccia pipes with exposed breccia are drainages in Grand Wash Trough area.

4 5 Commonly form local climbing or fall- Qay Young alluvial fan deposits (Holocene and ing dunes over young and older alluvial Pleistocene)—Brown, red, and gray slope- terrace (Qgy and Qgo) embankments and forming, unsorted mix of mud, silt, sand, steep nearby talus slopes. Support moder- pebbles, cobbles, and boulders. Clasts ate grass vegetation. Only thick or large are mostly angular but some are rounded; sand sheet or dunes shown. Several smaller locally consolidated by calcite and gypsum drainages have sand sheet or dune deposits cement. Sandstone, limestone, chert, and that are too small to show at map scale. gravel are derived locally from Paleozoic Thickness, 0.5 to 5 m (2 to 15 ft) and Mesozoic outcrops in Grand Canyon Qr Colorado River terrace and gravel deposits and Grand Wash Trough areas. Include (Holocene and Pleistocene)—Mud, silt, alluvial fan debris flows, sheet wash allu- and fine- to coarse-grained sand and gravel vium, minor aeolian sand deposits, and interbedded with poorly sorted, angular- to alluvial valley-fill Qv ( ) deposits. Subject well-rounded pebbles, cobbles, and boul- to extensive sheet wash erosion, flash flood ders adjacent to Colorado River. Overlap debris flows, and arroyo erosion. Only larg- and intertongue with local alluvial debris est or thickest deposits shown. Most talus fans and flows. Young Qgy( ) and old (Qgo) deposits on canyon slopes are not shown to alluvial terrace-gravel deposits are mapped emphasize bedrock geology. Thickness, 1 as one unit (Qr) along Colorado River to 30 m (3 to 100 ft) because map scale is too small to sepa- Qv Valley-fill alluvium, undivided (Holocene rate them. Include local wind-blown sand and Pleistocene)—Gray and light-brown sheet and small sand dune deposits. Clasts silt, sand, and lenses of pebble to small- are primarily comprised of sandstone, boulder gravel; partly consolidated by limestone, chert, basalt and well-rounded gypsum cement. Includes well-rounded quartzite and volcanic rocks that have clasts of limestone, sandstone, subrounded originated upstream from distant upper to angular chert fragments, and subrounded basin uplifts. Terrace gravels underlie and to subangular basalt clasts near volcanic overlie local basalt flows 3 to 122 m (10 outcrops. Arbitrary map contact with young to 400 ft) above Colorado River, southeast alluvial fan (Qay), young alluvial terrace quarter of map area. Higher terrace-gravel (Qgy), stream-channel alluvium (Qs), and deposits are partly consolidated by calcium floodplain Qf ( ) deposits. Represents less and gypsum. Age of terrace deposits com- active, low-gradient, alluvial stream-chan- monly between 0.100 to 0.150 Ma (Fenton, nel or shallow-valley deposits. Alluvial 1998). Deposits are interbedded with local valleys subject to sheetwash flooding or landslide and talus debris. Thickest depos- temporary ponding; often cut by arroyos as its, downstream from the Toroweap and much as 3 m (10 ft) deep. Supports moder- Hurricane Faults, as much as 60 m (200 ft) ate growth of sagebrush, grass, and cactus Qgy Young alluvial terrace deposits (Holocene on Colorado Plateau and mostly cactus and and Pleistocene)—In Grand Wash Trough, grass in Grand Wash Trough. Thickness, 1 include lower three terraces along streams to 6 m (3 to 20 ft) as mapped by Billingsley and others Qt Travertine deposits (Holocene and Pleisto- (unpub. data). Unit consists of light-brown, cene)—Gray, white, tan, massive, porous, pale-red and gray silt, sand, pebbles, cliff-forming carbonate deposits. Formed cobbles, and boulders, partly consolidated by chemical precipitation of calcium by calcium and gypsum. Composed mostly carbonate from springs. Form massive, of well-rounded to sub-angular limestone, rounded mounds or thick-layered encrusta- sandstone, chert, and basalt clasts as large tions on steep slopes or cliffs downslope of as 1 m (3 ft) in diameter. Unit is locally spring outlets. Several deposits represent inset and overlaps old terrace-gravel (Qgo) spring discharges that were probably active deposits and interbedded with young allu- during Pleistocene time but are currently vial fan (Qay) deposits. Terraces are 2 to dry. Travertine incorporates angular clasts 30 m (6 to 100 ft) above local streambeds. and boulders of talus and rounded Colorado Only thick or large deposits shown. Thick- River gravel. Only thickest deposits shown ness, 3 to 30 m (6 to 100 ft) along Colorado River, southeast and south-

6 7 west corner of map area. Several minor Grand Wash Trough, composed mainly of deposits in Grand Wash Trough area are gray, coarse-grained sand and gravel matrix too small to show at map scale. Thickness, containing subangular to rounded pebbles about 1 to 25 m (3 to 80 ft) and boulders of limestone, sandstone, and Ql Landslide deposits (Holocene and Pleis- chert derived from Grand Wash Cliffs east tocene)—In Grand Canyon, form large of Grand Wash. West of Grand Wash, com- unconsolidated to partly consolidated posed of coarse-grained sand and gravel masses of Paleozoic rock debris. Include mixed with subangular to rounded pebbles detached blocks of strata that have rotated and boulders of Proterozoic schist, gneiss, backward and slid downslope against and granite mixed with Paleozoic limestone parent wall as loose incoherent masses of and sandstone clasts. Surfaces are hard and broken rock and deformed strata, partly rocky and eroded by arroyos as much as 10 surrounded by local talus, rock glaciers, m (30 ft) deep in some areas of the Grand and rock-fall debris. Some large landslides Wash Trough and Colorado Plateau. Sup- in Grand Canyon were likely triggered port moderate growth of sagebrush, cactus, by earthquakes along the major faults in grass, pinyon pine and juniper trees on the area. Landslide masses are common Colorado Plateau and sparse growth of around Tertiary volcanic mountains on the cactus, grass, and desert shrubs in Grand Colorado Plateau and around basalt flows Wash Trough. Thickness, 3 to 30 m (9 to in the Grand Wash Trough area. Landslide 100 ft) or more masses in Grand Wash Trough are unstable QTa Old alluvium (Pleistocene and Pliocene)—On where overlying red siltstone and sandstone Shivwits Plateau, composed of white, gray, of the Grand Wash Trough (Tgr), especially and reddish-brown slope-forming siltstone, during wet conditions. Only large or signif- coarse-gravel, and conglomerate, partly icant landslide deposits are shown. Thick- unconsolidated, capped by calcrete soil. ness, 10 to 60 m (30 to 200 ft) Overlies basalt of the Shivwits Plateau Qgo Older alluvial terrace deposits (Holocene(?) (Tsb). White and gray angular chert pebbles and Pleistocene)—Similar to young allu- are dominant clasts averaging about 5 cm vial terrace (Qgy) deposits and partly con- in diameter derived from the Kaibab For- solidated by calcite and gypsum cement. mation (Pk). Includes lag gravel of yellow, Surface has developed a thin soil that brown, white, and red, well-rounded, multi- forms a smooth surface texture compared colored quartzite pebbles 2.5 to 19 cm (1 to to younger terrace surfaces. Commonly 8 in) in diameter, and small petrified wood overlapped by or interbedded with talus fragments derived from the Shinarump and landslide (Ql) debris deposits and older Member of the Chinle Formation. Locally alluvial fan (Qao) deposits. Include abun- includes small basalt fragments derived dant basaltic clasts that form thin desert from underlying basalt of the Shivwits pavement near landslide deposits. In Grand Plateau. Discontinuous calcrete beds Wash Trough, support moderate growth of form thin, lumpy surface producing white grass, cactus, and desert shrubs. On Colo- patches of calcrete gravel and alluvium on rado Plateau, support moderate growth of weathered surface of basalt flows that are grass, cactus, and sagebrush, juniper trees easily recognized on aerial photographs. and pinyon pine trees. Thickness, 2 to 5 m Unconformable contact with underlying (6 to 15 ft) basalt of the Shivwits Plateau (Tsb). Unit Qao Older alluvial fan deposits (Holocene(?) and may have formed an extensive deposit over Pleistocene)—Similar to young alluvial northern extent of the basalt of the Shivwits fan (Qay) deposits, partly consolidated and Plateau now heavily eroded commonly capped by calcrete soil 1 to 2 Tay Alluvium and calcrete soil deposits (Pliocene m (3 to 6 ft) thick. On plateaus, composed and Miocene)—Gray and light-brown, mainly of gray to brown, fine-grained sand slope-forming, silt, sand, coarse gravel in and silt matrix mixed with subangular to coarse-grained gravely matrix alluvium; rounded pebbles and boulders of basalt, includes subangular to well-rounded lime- limestone, sandstone, and chert. Some stone and dolomite pebbles, cobbles, and basalt boulders are 1 m (3 ft) in diameter. In boulders up to 1 m (3 ft) in diameter. Include

6 7 basalt clasts derived from basalt flows Tb( ) desert vegetation, mainly cactus of various of the Grand Wash Trough; partly consoli- types and creosote bush. Thickness, 60 m dated by calcium and gypsum cement. Form (200 ft) or more cliffs or weathers to rounded resistant hills. Tg Undifferentiated gravel deposits of the Unit overlain by thin to thick calcrete soil Hualapai Plateau (Pliocene to lower deposits, 1 to 8 m (3 to 25 ft) thick. Unit is Paleocene(?))—Gray and light-brown silt, poorly sorted to moderately sorted. Calcrete sand, pebbles, cobbles, and small boulders soil deposits that cover basalt flows form consisting mostly of Paleozoic clasts mixed thin, rough, and discontinuous beds aver- with Proterozoic clasts in some locations. aging about 1.2 m (5 ft) thick and contain Clasts are angular to well rounded in sandy scattered cobbles of basalt up to 30 cm (12 matrix; partly consolidated by calcite. in) in diameter. Pebble imbrications show Deposits commonly covered by thick allu- southward flow of depositing streams in vium, lag gravel, calcrete soil, or volcanic Grand Wash Trough area. Unit is strongly rocks (Tv). Include the Buck and Doe Con- dissected by modern erosion. East of Grand glomerate and Coyote Spring Formation of Wash drainage, unit is composed of gray and Young (1999), undivided. Lag gravel makes light-brown, poorly sorted, consolidated, it difficult to distinguish the stratigraphic silt, sand, gravel, cobbles, and boulders sequence in areas of low relief. Fill older derived from Paleozoic rocks in the Grand drainages and paleovalleys on the Hualapai Wash Cliffs; clasts are composed of about Plateau, southwest quarter of map area. 80 percent limestone and dolomite, and 10 Thickness, 1 to 30 m (3 to 100 ft) percent chert in gray gypsiferous siltstone and sandstone matrix, all capped by calcrete VOLCANIC ROCKS soil 3 to 4 m (10 to 12 ft) thick; weathers light brown. Rounded and subrounded Quaternary volcanic deposits (Holocene, limestone and chert clasts are strongly pitted Pleistocene, and Pliocene(?))—Includes and etched on weathered surfaces and often basalt flows, dikes, and pyroclastic deposits coated by calcrete rind on underside. Uncon- in the Uinkaret Volcanic Field and Shivwits formably overlie red siltstone and sandstone Plateau areas (Billingsley and others, 2000, (Tgr) and unmapped conglomerate deposits 2001, 2002, unpub. data). Pyroclastic cones west of Wheeler Fault. Unconformably typically overlie basalt flow, but are closely overlies older gypsum and limestone sedi- associated in time. Although the cones are ment facies (Tgg and Tgl) between Grand generally younger than the basalt flows, Wash drainage and Grand Wash Cliffs. some basalt flows may have flowed out Support sparse growths of desert vegetation, from under pyroclastic cones while others mainly cactus of various types and creosote may have built up on top of the flows. bush. Thickness, 15 to 60 m (50 to 200 ft) Described from youngest to oldest: Tao Alluvial deposits (Pliocene and Miocene)— Little Spring Basalt (Holocene)—Infor- Gray to dark-gray, slope-forming schist, mally named by Billingsley (1997a) and granite, gneiss, and amphibole clasts Billingsley and others (2001). Herein for- derived from Proterozoic outcrops of the mally named for Little Spring (SE1/4 sec. Virgin Mountains about 9 to 11 km (6 to 16, T. 34 N., R. 8 W.) just west of Arkansas 7 mi) northwest of map area. Include clasts Ranch, Uinkaret Plateau, Mohave County, composed of white and gray angular chert, Arizona. The olivine basalt and associated subrounded to rounded gray and dark-gray cinder cone represent the youngest volcanic limestone and dolomite clasts averag- rocks in the Uinkaret Volcanic Field and the ing about 5 cm (3 in) in diameter derived map area. Based on cosmogenic 3He dating from Paleozoic rock outcrops of the Virgin (Fenton, 1998), the Little Spring Basalt is Mountains (Bohannon and Lucchitta, 1991; about 1,000 years old, similar in age to Beard, 1996). Poorly sorted to moderately basalt flows at Sunset Crater near Flagstaff, sorted. Unconformably overlie red siltstone, Arizona. Divided into: sandstone, and conglomerate facies (Tgr) Qlsp Pyroclastic deposits—Red-brown, gray, and strata of the Kaibab and Moenkopi and reddish-black basaltic scoria, bombs, Formations. Unit is strongly dissected by cinder, and other scoriaceous ejecta depos- modern erosion. Support sparse growth of its. Consist of two deposits that are part of

8 9 a single pyroclastic cone formed from two County, Arizona (Billingsley and others, closely spaced vent areas. Cone is about 2001). Incorrectly named the Sage Basalt 41 m (135 ft) high on basalt flow surface by Billingsley and Workman (2000) and (elev. 2,138 m [7,015 ft]). Only east half Billingsley and Hampton (2000) before it and southwest part of cone is preserved; was know that the name Sage Basalt was rest of cone has been rafted away on lava already in use. Includes three unnamed flows toward the northwest and southeast, pyroclastic cones and associated basalt suggesting that the cone is older than the flows in the upper reaches of Toroweap flow. Support growths of a few ponderosa Valley. Divided into: pine trees and oak trees. Thickness, 41 m Qgrp Pyroclastic deposits—Red-brown and (135 ft) reddish-black scoriaceous basalt frag- Qlsb Basalt flows—Dark-gray, finely crystalline ments, ash, and cinder deposits; partly con- to glassy, alkali-olivine basalt. Ground- solidated. Include three pyroclastic cones mass composed of glass, plagioclase, and aligned along north-south, near vertical olivine. Forms clinkery aa surface. Basalt bedrock fracture system. Deposits overlie flowed northwest about 1.8 km (1 mi) and associated basalt flows. Only western part southeast about 2.4 km (1.5 mi). Support lies within map area. Toroweap Fault off- sparse ponderosa and oak trees. Overlie sets north cone 26 m (85 ft). North cone older Quaternary basalt flows (Qb), pyro- is about 134 m (440 ft) high, central cone clastic deposits (Qp), and young alluvial about 70 m (230 ft) high, and south cone fan (Qay) deposits. Thickness, 3 to 7 m (10 about 60 m (200 ft) high to 21 ft) Qgrb Basalt flows—Dark-gray, finely crystalline Basalt of Larimore Tank (Pleistocene)— to glassy, alkali-olivine basalt. Groundmass Informally named for Larimore Tank, a contains plagioclase, olivine, and augite stock tank on U.S. Geological Survey Hat laths. Includes abundant olivine pheno- Knoll 7.5´ quadrangle (sec. 16, T. 37 N., crysts 0.25 to 5 mm in diameter composing R. 7 W.), Uinkaret Volcanic Field, Mohave about 30 percent of basalt in some outcrops. County, Arizona (Billingsley and others, Overlie Harrisburg Member of the Kaibab 2001). Incorrectly named Cave Basalt by Formation (Pk). Northern part of basalt of Billingsley (1994) and Billingsley and Graham Ranch flow and pyroclastic cone Workman (2000) before it was known the is offset about 26 m (85 ft) down-to-the- name Cave Basalt was already in use west by the Toroweap Fault; southern part Qltb Basalt flows—Dark-gray to black, finely is offset about 34 m (110 ft) down-to-the- crystalline, alkali-olivine basalt. Basalt west, about half of total offset of Toroweap has coalesced from five pyroclastic vent Fault, 67 m (220 ft) in underlying Paleozoic areas just north of map area aligned along strata. Thickness, 3 to 18 m (10 to 60 ft) northwest-southeast-trending fractures in Basalt of the Uinkaret Plateau (Pleisto- underlying Permian strata. Contains abun- cene)—Informally named and include dant olivine phenocrysts 0.25 to 1 mm in several pyroclastic cones and associated diameter. Overlain by young alluvial fan basalt flows of similar age north and south (Qay) deposits. Dissolution sinkholes asso- of Mount Trumbull. Basalts are assumed ciated with karstification of the Harrisburg to have erupted during a similar eruptive Member of the Kaibab Formation have phase throughout the map area north and formed under basalt flows allowing basalt south of Mount Trumbull. Several flows to collapse as much as 18 m (60 ft). Sink- have coalesced from numerous vent areas holes are partly filled with ponded alluvium. to form a single massive basalt flow that Basalt flowed into upper part of Toroweap cascaded into Toroweap Valley and Whit- Valley but mostly north towards Clayhole more Canyon. Basaltic units north of Mount Valley north of map area (Billingsley, Trumbull are designated with a number 1994). Thickness, 1 to 12 m (3 to 40 ft) (Qi1, Qb1, Qp1) because stratigraphic rela- Basalt of Graham Ranch (Pleisto- tions in upper Toroweap Valley suggest that cene)—Informally named for Graham these basalt flows may be slightly older than Ranch in upper Toroweap Valley, the type basalt deposits (Qi, Qp, and Qb) south of area (sec. 3, T. 35 N., R. 7 W.), Uinkaret Mount Trumbull. Other Quaternary basalt Volcanic Field, Uinkaret Plateau, Mohave flows and associated pyroclastic deposits

8 9 that have mappable boundaries are infor- Toroweap Valley from higher terrain of mally designated on the map with an eleva- the Uinkaret Mountains. Basalt cascades tion number (Qp6375) representing the are steep where they flowed over the Hur- highest associated pyroclastic cone or infor- ricane Fault scarp at Hells Hollow drainage mally named for a nearby ranch shown on in upper Whitmore Canyon and over cliffs U.S. Geological Survey 7.5´ quadrangles of the Kaibab and Toroweap Formations in Qi/Qi1 Intrusive rocks—Dark-gray to black Whitmore Canyon and Toroweap Valley. alkali-olivine basalt dikes and necks. Form Basalt flowed over the Moenkopi, Kaibab, nearly vertical dikes or necks that com- and Toroweap Formations south of Mount monly protrude above surrounding volcanic Trumbull. Cosmogenic 3He dating of basalt or bedrock deposits. Variable widths range surfaces in upper Whitmore Canyon indi- from 0.5 to 6 m (1 to 18 ft). Neck or plug cate an average age of about 0.100 Ma, and in Kaibab Formation southeast of Mount flow surfaces in lower Whitmore Canyon Trumbull is partly covered. Best examples and Toroweap Valley have an average age are near Paws Pocket, east side of Whit- of about 0.150 to 0.200 Ma (Fenton, 1998). more Canyon, east-central part of map Thickness, 6 to 91 m (18 to 300 ft) Qp/Qp1 Pyroclastic deposits—Reddish-gray, black, Basalt of Kenworthy Ranch (Pleisto- and red to gray tuff, ash, scoriaceous ejecta, cene)—Informally named for the Kenwor- bombs, and cinder deposits; partly consoli- thy Ranch in Sink Valley, Uinkaret Plateau, dated. Include about 17 pyroclastic depos- Mohave County, Arizona (sec. 1, T. 35 N., its north of Mount Trumbull (Qp1) such R. 9 W.; Billingsley, 1997b; Billingsley and as Craigs Knoll and about 36 pyroclastic others, 2001). Divided into: vents south of Mount Trumbull (Qp) such Qkrp Pyroclastic deposits—Reddish-black and as Mount Emma, Slide Mountain, and Petty red tuff, ash, scoriaceous ejecta, and cinders Knoll in the Uinkaret Mountains between overlie associated basalt flows. Map con- Whitmore Canyon and Toroweap Valley. tact is approximate. Include three unnamed Deposits are associated with coalesc- cinder cones that align north-south. North ing basalt flows that issued from several pyroclastic cone just west of Kenworthy vents. Locally form fine- to coarse-grained Ranch is about 49 m (160 ft) high, middle cinder sheet deposits on basalt flows near cone is about 24 m (80 ft) high, and south cones. Map contacts are approximate and cone about 24 m (80 ft) high show only the thickest deposits, not entire Qkrb Basalt flows—Light- to dark-gray, finely pyroclastic blanket deposit. No K-Ar ages crystalline, alkali-olivine basalt. Include are available, but cosmogenic 3He ages at small phenocrysts of augite and olivine in scattered locations indicate an age of 0.100 glassy groundmass. Flows radiate from all to 0.200 Ma (Fenton, 1998). Thickness, 6 to three pyroclastic cones coalescing to form 180 m (18 to 600 ft) large elongated north-south oval flow mass. Qb/Qb1 Basalt flows—Dark-gray to black, finely Overlie Harrisburg Member of the Kaibab crystalline, alkali-olivine basalt. Olivine Formation (Pk). Thickness, 15 m (50 ft) and plagioclase phenocrysts common. Basalt of Marshall Ranch (Pleisto- Include scoriaceous material from pyro- cene)—Informally named for Marshall clastic deposits. Basalt flows north of Ranch about 2.5 km south of Kenworthy Mount Trumbull originated from several Ranch, Uinkaret Plateau, Mohave County, pyroclastic vents and generally flowed east Arizona (sec. 13, T. 35 N., R. 9 W.; Billing- into upper Toroweap Valley. Basalt flows sley, 1997b; Billingsley and others, 2001). overlie the Moenkopi Formation near pyro- Divided into: clastic cones and the Kaibab Formation Qmrp Pyroclastic deposits—Reddish-black and farther away from the cones. Flows went red tuff, ash, scoriaceous ejecta, and cin- down alluviated valleys before reaching ders overlie associated basalt flows. Include Toroweap Valley. Basalt flows in upper two unnamed pyroclastic cones and three Toroweap Valley (Qb1) are mostly covered smaller secondary spatter cones. Secondary with young alluvial fan (Qay) deposits and cones appear to have erupted from basalt basalt flows Qb ( ) that originated south of flows that came from south pyroclastic Mount Trumbull. South of Mount Trumbull, cone. North pyroclastic cone is about 73 m basalt cascaded into Whitmore Canyon and (240 ft) high and south cone is about 85 m

10 11 (280 ft) high (sec. 16, T. 35 N., R. 8 W.; Billingsley and Qmrb Basalt flows—Gray-black, finely crys- others, 2001). Divided into: talline, alkali-olivine basalt. Majority of Qp6457 Pyroclastic deposits—Reddish-black cinder basalt flowed in radial pattern from south and scoriaceous deposits. Include two pyroclastic cone. Basalt also flowed west smaller cones that partly overlie associated about 3 km (2 mi). Partly overlie the basalt basalt flow from cone 6457. North cone of Potato Valley (Qpvb) at south margin may have erupted from the basalt flow. and overlie Harrisburg Member of the Pyroclastic cone (hill 6457) is 36 m (120 Kaibab Formation elsewhere. Thickness, ft) thick, and north cone about 24 m (80 ft) 12 to 36 m (40 to 120 ft) thick Basalt of hill 6375 (Pleistocene)—Infor- Qb6457 Basalt flows—Dark-gray alkali-olivine mally named for unnamed pyroclastic basalt. Basalt flowed north from hill 6457 cone (hill 6375) at the north end of Sink about 0.8 km (0.5 mi) onto young alluvial Valley, Uinkaret Plateau, Mohave County, fan (Qay) and floodplain (Qf) deposits. Arizona (sec. 31, T. 35 N., R. 8 W.; Billing- Thickness, 36 m (120 ft) sley, 1997b; Billingsley and others, 2001). Basalt of Potato Valley (Pleistocene)— Divided into: Informally named from Potato Valley, Qp6375 Pyroclastic deposits—Reddish-black cinder Uinkaret Plateau, Mohave County, Arizona and scoriaceous ejecta overlie associated (sec. 25, T. 35 N., R. 9 W.; Billingsley, basalt flow. Include small cone at the north 1997b; Billingsley and others, 2001). end of associated basalt flow that may be Includes several pyroclastic cones and local splatter cone deposit derived from associated basalt flows along north and basalt flow. Main cone deposit, hill 6375, is west edge of Potato Valley. Divided into: about 64 m (290 ft) thick Qpvp Pyroclastic deposits—Red and black Qb6375 Basalt flows—Dark-gray alkali-olivine cinder, tuff, ash, and scoriaceous ejecta. basalt. Basalt flowed west 0.8 km (0.5 mi) Include two main pyroclastic cones on and north about 1.5 km (1 mi). Overlies north and west sides of Potato Valley and Harrisburg Member of the Kaibab Forma- five small pyroclastic vents. The two main tion (Pk). Thickness, 1 to 12 m (3 to 40 ft) cones appear to be the main sources for Basalt of hill 6646 (Pleistocene)—Infor- associated basalt flows that ring the north mally named for unnamed pyroclastic and west side of Potato Valley. Several cone (hill 6646) at northwest end of Sink small cones on basalt flows appear to Valley, Uinkaret Plateau, Mohave County, have erupted from the flow as secondary Arizona (sec. 35, T. 36 N., R. 9 W.; Billing- eruptions. Dikes in Hells Hole (QTi) south sley, 1997b; Billingsley and others, 2001). of Potato Valley may be associated with Divided into: Potato Valley cones. Thickness, 106 m (350 Qp6646 Pyroclastic deposits—Red and black ft) on west side of Potato Valley and 85 m cinder and scoriaceous deposits overlie (280 ft) on north side associated basalt flow. Include one large Qpvb Basalt flows—Dark-gray alkali-olivine pyroclastic cone and two adjacent small basalt. Flows on north side of Potato cones. There are three eruptive vent areas Valley erupted from unnamed cinder cone that formed the main cone aligned along a and flowed northwest about 3 km. Flow north-south strike, similar to north-south appears to have merged or coalesced with strike of basaltic cones in Kenworthy flows from two cones on west side of Potato Ranch area. Main pyroclastic cone is about Valley forming a basalt dam responsible for 76 m (250 ft) thick the accumulation of alluvial sediments in Qb6646 Basalt flows—Dark-gray alkali-olivine Potato Valley. Basalt flows on west side of basalt. Basalt flowed north about 3 km (2 Potato Valley flowed mostly north about 5 mi). Overlies Harrisburg Member of the km (3 mi). Thickness, 2 to 25 m (6 to 85 ft) Kaibab Formation (Pk). Thickness, 10 to Basalt of hill 6588 (Pleistocene)—Infor- 30 m (30 to 100 ft) mally named for highest of four pyroclastic Basalt of hill 6457 (Pleistocene)—Infor- cones on east flank of Mount Trumbull, the mally named for unnamed cinder cone (hill type area, Uinkaret Volcanic Field, Mohave 6457) north of and below Mount Trumbull, County, Arizona (sec. 36, T. 35 N., R. 8 Uinkaret Plateau, Mohave County, Arizona W.; Billingsley and others, 2001). Includes

10 11 pyroclastic deposits and associated basalt Thickness, 183 m (600 ft) flows. Divided into: Qcbb Basalt flows—Light-gray and dark-gray Qp6588 Pyroclastic deposits—Reddish-black to alkali-olivine basalt. Include lower and mostly black and gray ash, cinder, sco- upper basalt flows separated by pyroclastic riaceous fragments, and basaltic boulders; deposits (Qcbp). No K-Ar age available. partly consolidated. Include four pyro- Lower basalt accumulated on Harrisburg clastic cones aligned in 2-km-long (1-mi- Member of the Kaibab Formation (Pk) and long) northwest-southeast trend. Deposits lower strata of the Moenkopi Formation mostly overlie associated basalt flows and (^m). Estimated thickness of lower flow, landslide deposits (Ql); often incorporated about 40 m (130 ft). Upper basalt erupted into basalt flows on steep east slopes of hill near top of Craigs Knoll and flowed west, 6588. Variable thickness because of steep north, and east about 8 km (5 mi). Esti- terrain, 2 to 55 m (6 to 180 ft) mated thickness of upper flow, 3 to 20 m Qb6588 Basalt flows—Dark-gray and light-gray, (10 to 65 ft) finely crystalline, alkali-olivine basalt. Little Tanks Basalt (Pleistocene)—For- Include interbedded scoriaceous pyroclas- mally named for a local stock tank labeled tic deposits. Basalt cascaded down steep “Little Tanks reservoir” in the type area just slope into Toroweap Valley over land- north of map area, Mohave County, Ari- slide deposits (Ql) and lower strata of the zona (sec. 5, T. 36 N., R. 10 W.). Basalt and Moenkopi Formation (^m) and Harrisburg associated pyroclastic deposits form Cinder Member of the Kaibab Formation (Pk). Knoll (sec. 29, T. 36 N., R. 10 W.), north- Flows partly buried by undivided basalt central edge of map. K-Ar age, 1.0±0.4 Ma flows (Qb) and young alluvial fan (Qay) (Billingsley, 1993; Billingsley and Work- deposits in Toroweap Valley. Thickness, 2 man, 2000). Divided into: to 10 m (6 to 30 ft) Qlp Pyroclastic deposits—Red-brown and Basalt of Craigs Knoll and Berry Knoll reddish-black basaltic scoria and cinder (Pleistocene)—Informally named for deposits; partly consolidated. Unit forms Craigs Knoll (sec. 4, T. 35 N., R. 8 W.), and Cinder Knoll, a 15-m-high (50-ft-high) Berry Knoll (sec. 24, T. 36 N., R. 9 W.), pyroclastic cone capped by basalt flow Uinkaret Plateau, Mohave County, Arizona Qlb Basalt flows—Dark-gray, finely crystalline (Billingsley, 1997b; Billingsley and others, to glassy, alkali-olivine basalt. Ground- 2001; Billingsley and Workman, 2000). mass composed of plagioclase, olivine, Includes dikes, pyroclastic deposits, and and augite. Unit contains abundant olivine basalt flows that appear to have erupted phenocrysts 0.25 to 1 mm in diameter. simultaneously at Craigs Knoll and Berry Unit unconformably overlies Harrisburg Knoll and at unnamed pyroclastic cone Member of the Kaibab Formation (Pk) between Craigs Knoll and Berry Knoll. and Timpoweap Member and lower red Divided into: member of the Moenkopi Formation (^m). Qcbi Intrusive dikes or necks—Greenish-black Thickness, 1 to 3 m (3 to 10 ft) olivine basalt. Widths of dikes shown on QTi Hells Hole dikes (Pleistocene or Plio- map are approximate cene(?))—Dark-gray alkali-olivine basalt. Qcbp Pyroclastic deposits—Gray and red- Include three dikes in the Kaibab and dish-gray to black cinder, tuff, ash, and Moenkopi Formations in Hells Hole. Form scoriaceous ejecta; mostly consolidated nearly vertical walls that stand out in relief into welded tuff. Form cliff on east side in some places as much as 3 to 4 m (10 to of Craigs Knoll and steep slope on south 12 ft) high and about 0.5 to 2 m (2 to 6 ft) and west side. Deposits mostly covered by wide. Dikes are aligned in general north- dark-gray basalt on north flank of Craigs south trend and appear to connect to pyro- Knoll. Include small secondary pyroclas- clastic vents on west side of Potato Valley tic deposit on south flank of Craigs Knoll. (Qpvp); also may be source for basalt of Deposits overlie associated basal basalt Mount Logan (Tmlb) due to close proxim- flow exposed on south flank of Craigs ity to Mount Logan. Vertical exposure is Knoll, and an upper associated basalt nearly 610 m (2,000 ft) flow overlies pyroclastic deposits, mostly Tertiary volcanic deposits (Pliocene and on north and west flanks of Craigs Knoll. Miocene)—Include basalt flows, dikes,

12 13 and pyroclastic deposits in the Uinkaret tions are needed to determine the sequence Volcanic Field on the Shivwits Plateau, and of events between the basalt of Mount the Grand Wash Trough of the Basin and Logan and the basalt of Bundyville, which Range area appear to be the same age (3.6 Ma) based Basalt north of Mount Emma (Pliocene)— on close proximity to each other (about Gray-black alkali-olivine basalt; includes 3.5 km [2 mi] apart), stratigraphic position several basalt flows, pyroclastic deposits, where both units overlie the same 122-m- and intrusive rocks. Unit largely covered thick (400-ft-thick) section of the Chinle by Quaternary pyroclastic (Qp) deposits Formation (^c), and similar thickness at Mount Emma and other north-south- Tmlb Basalt flows—Light-gray, finely crystal- aligned pyroclastic cones and associated line, alkali-olivine basalt; contains red and basalt flows (Qb). Unit is offset down-to- green olivine phenocrysts 1 mm in diameter the-west about 250 m (820 ft) by southern in glassy groundmass; includes plagioclase splay of the Hurricane Fault. There are no laths in glassy groundmass. Plagioclase K-Ar ages available, but age estimated to be masses form white spotted blotches in about 2.6 to 3.6 Ma based on stratigraphic some areas. Basalt flow(s) overlie Petrified position, elevation, and flow direction of Forest Member of the Chinle Formation basalt of Mount Logan (Tmlb) and basalt of (^c) east side of Hells Hole (sec. 12, T. 34 Mount Trumbull (Tmb). Divided into: N., R. 9 W.). Eastern extent of basalt may Tei Intrusive rocks—Gray-black alkali-olivine overlie upper red member and Shnabkaib basaltic plug or dike. Unit partly exposed Member of the Moenkopi Formation (^m). and offset by the Hurricane Fault. Most Basalt dikes (QTi) may be source for basalt of unit covered by landslide deposits (Ql). of Mount Logan below the summit of Width of plug is probably in excess of 90 Mount Logan in Hells Hole. Basalt flowed m (300 ft) and appears to be source of Ter- east about 5.3 km (3 mi) from near the tiary basalt flows north of and under Mount summit of Mount Logan, descending about Emma pyroclastic deposits. Plug does not 335 m (1,100 ft). Average thickness, about protrude above ground surface; highly 67 m (220 ft) altered and weathered Basalt of Bundyville (Pliocene)—Informally Tep Pyroclastic deposits—Reddish-black cinder, named the Bundyville basalt for the aban- scoria, ash, and other scoriaceous ejecta; doned settlement of Mt. Trumbull (Bun- deeply eroded. Associated with intrusive dyville; Hamblin and Best, 1970; Hamblin, plug (Tei) on downthrown side of Hurricane 1970), Shivwits Plateau, Mohave County, Fault north of Mount Emma. Thickness, 12 Arizona, (secs. 23, 24, 25, and 26, T. 35 N., m (40 ft) R. 10 W.). Exposed on downthrown side Teb Basalt flows—Near Mount Emma, gray- of Hurricane Fault in northwest quarter of black alkali-olivine basalt; plagioclase laths map area (Billingsley and others, 2000). K- common in glassy groundmass. Consist of Ar age, 3.6±0.18 Ma (Reynolds and others, several basalts that flowed east and south 1986). Divided into: from plug (Tei) area. Underlying strata con- Tbi Intrusive dikes—Dark-gray alkali-olivine cealed, but because of similar elevation as basalt. Dikes are nearly vertical and oriented basalt of Mount Logan, it is assumed basalt N. 40° W. and nearly parallel to the Hurri- overlies the Chinle Formation (^c) or upper cane Fault. Widths, 1 to 3 m (2 to 10 ft) Moenkopi Formation (^m). Thickness, 122 Tbb Basalt flows—Dark-gray, finely crystal- m (400 ft) line, olivine basalt. Groundmass contains Basalt of Mount Logan (Pliocene)—Infor- olivine. Include one to three basalt flows mally named Mount Logan basalt for that form a caprock overlying purple and Mount Logan (Reynolds and others, 1986). white mudstone and sandstone beds of Forms prominent Mount Logan (elev. 2,398 the Petrified Forest Member of the Chinle m [7,866 ft]) on Uinkaret Plateau, Mohave Formation (^c). Flow surfaces locally County, Arizona (sec. 12, T. 34 N., R. 9 W.; distorted by landslide and soft sediment Billingsley and others, 2000, 2001). K-Ar deformation of underlying soft mudstone age, 2.63±0.34 Ma obtained from a basalt that has been caused by earthquakes related flow on Mount Logan, but a specific loca- to the Hurricane Fault. Basalt predates tion was not disclosed. New age determina- any offset of strata along Hurricane Fault

12 13 implying that the fault is younger than 3.6 flows derived north of the map areaQb ( ) Ma. Flows assumed to have originated from in Cottonwood and Grand Wash drainages. local dikes (Tbi) that are largely covered by Include dikes or necks of dark-gray alkali- basalt, landslide, or talus debris. Thickness, olivine basalt on east side of Cottonwood 30 to 55 m (100 to180 ft) Wash, south of Pakoon Springs that intrude Basalt of Mount Trumbull (Pliocene)—First gray gypsum, gypsiferous siltstone, and red described by Koons (1945), informally siltstone and sandstone (Tgr). Pyroclastic named Mount Trumbull basalt for Mount deposits not present. Widths, as much as 30 Trumbull by Hamblin and Best (1970) and m (100 ft) Hamblin (1970), Uinkaret Plateau, Mohave Tb Basalt flows—Consist of two or more basalt County, Arizona, (sec. 27, T. 35 N., R. 8 flows (Damon and others, 1996). Light-gray W.; southeast quarter of map area; Billing- to medium-gray alkali-olivine basalt. Age of sley and others, 2001). Forms prominent upper flow at Pakoon Springs, 3.99±0.06 to landmark on Uinkaret Plateau. K-Ar age, 4.70±0.07 Ma. Age of lower basalt at Grand 3.6±0.18 and 3.67±0.09 Ma (Reynolds and Wash Bay, Lake Mead, that may have origi- others, 1986). Divided into: nated from dikes or necks (Ti) along east Tmi Intrusive rocks—Gray-black, finely crys- side of Cottonwood Wash (southwest edge talline, alkali-olivine basalt. Forms highest of map area), 3.24±0.05 Ma (Damon and point on north side of Mount Trumbull others, 1996). Include interbedded alluvial (elev. 2,447 m [8,029 ft]). Source for sediments between basalt flows along Cot- Tertiary basalt flows on Mount Trumbull. tonwood, Grand, and Pakoon Wash drain- Width, 120 m (400 ft) or more ages in upper part. Source of upper basalt Tmb Basalt flows—Gray-black, finely crystal- flows appears to have originated from pyro- line, alkali-olivine basalt. Groundmass clastic vents and dikes in northern part of contains olivine phenocrysts and plagio- Grand Wash Trough (north of map area) that clase laths. Consist of one or more thin occupy Grand, Cottonwood, and Pakoon basalt flows that form caprock overlying Wash paleodrainages. Interbedded allu- concealed purple and white mudstone vial sediments are composed of gray and and sandstone beds of the Petrified Forest light-brown, poorly sorted, slope-forming, Member of the Chinle Formation (^c) on consolidated conglomerate, gravel, sand, west side of mountain (exposed in land- and silt. Contain Proterozoic and Paleozoic slide float material) that overlie upper red clasts derived from the Virgin Mountains member and possible Shnabkaib Member northwest of map area. Thickness of intra- of the Moenkopi Formation (^m) on east basaltic sediments are as much as 90 m (300 side of mountain (exposed as landslide ft; Lucchitta and others, 1995a, b), but aver- blocks). Partly covered by Quaternary age about 24 m (80 ft) thick in map area and pyroclastic (Qp) deposits. Thickness, 30 to thin southward. Lower basalt flow contains 60 m (100 to 200 ft) calcite-filled veins and vugs. Basalt at Olaf Basalt of the Grand Wash Trough (Plio- Knolls (sec. 1, T. 35 N., R. 15 W.) is light- to cene)—Include intrusive dikes and necks medium-gray alkali-olivine basalt. Majority (Ti), basalt flows derived from north of of basalt flowed in radial pattern from high- map area and from Olaf Knolls (Tb), and est point of Olaf Knolls approximately 2.5 interbedded fluvial sediments (not shown km (1.5 mi) to southwest, 1.5 km (1 mi) on map) between basalt flows (Billingsley to northeast, and 1.5 km (1 mi) to west. and others, unpub. data) Flows occupy Grand Wash paleodrainage Ti Dikes and necks—At Olaf Knolls, consists and unconformably overlie red siltstone and of light-gray alkali-olivine basalt dike that sandstone (Tgr) deposits. All basalt flows intrudes red sandstone and siltstone (Tgr) overlain by conglomerate and calcrete (Tay) rocks of the Grand Wash Trough. Form deposits and partly overlain by young and highest part of Olaf Knolls volcanic area old alluvial fan (Qay and Qao) deposits. (elev. 985 m [3,232 ft]). Hachured symbol Basalt flows exposed 1.5 km (1 mi) south- on map marks possible small mar or caldera east of Olaf Knolls near Grand Wash Cliffs depression on north flank of Olaf Knolls. may have originated from another source Age of Olaf Knolls assumed to be about 4 north of map area or possibly Olaf Knolls. to 4.5 Ma based on relation to nearby basalt Combined thickness of upper basalt and

14 15 interbedded sediments, 2 to 140 m (6 to 460 Poverty Mountain Basalt (Pliocene)— ft). Thickness of lower basalt, 2 to 10 m (6 Informally named Shivwits basalt by Best to 30 ft) and others (1980) and Reynolds and others Whitmore dike swarm (Pliocene) (1986) in conjunction with the basalt of Twi Intrusive dikes—Dark-gray to black the Shivwits Plateau flows south of map alkali-olivine basalt. K-Ar age, 4.56±0.12 area. Formally named Poverty Mountain Ma (Wenrich and others, 1995). Form Basalt for Poverty Mountain, the type area, nearly vertical dikes eroded down to bed- Shivwits Plateau, west-central edge of map rock surface of Esplanade Sandstone and area (secs. 29 and 32, T. 35 N., R.11 W.; Pakoon Limestone (Pep) about 2 km (1.3 Billingsley and others, 2000). K-Ar age, mi) southwest of Whitmore Canyon and 3 4.75±0.26 Ma (Reynolds and others, 1986). km (1.5 mi) west of Colorado River Mile Divided into: 188. Dikes parallel joints and nearly verti- Tpi Intrusive neck—Medium-gray, finely cal fractures in bedrock for about 3.3 km (2 crystalline, alkali-olivine basalt. Forms mi) along north-south trend. Dikes exposed small dike associated with basalt flows and in the Esplanade Sandstone and Pakoon pyroclastic deposits near eastern part of Limestone (Pep) and lower part of the mountain. Dike and nearby small pyroclas- Hermit Formation (Ph) 1.6 km (1 mi) west tic vents are aligned northwest-southeast of Colorado River Mile 188 only produced and are main sources for basalt flows (Tpb) one basalt flow (Twb). Dike widths, 0.5 to on Poverty Mountain 1.2 m (2 to 3.5 ft) Tpp Pyroclastic deposits—Reddish-black and Twb Basalt flow—Dark-gray to black alkali- red fragments of scoria, cinders, and small olivine basalt. Includes small olivine phe- ribbons overlie basalt flows at and near nocrysts and plagioclase laths in glassy vent areas. Interbedded with basalt flows groundmass. Basalt emerged from dike near dike (Tpi) and pyroclastic cone areas. (Twi) in lower part of Hermit Formation Largest cone is about 25 m (80 ft) thick (Ph) and flowed down steep debris slope Tpb Basalt flows—Medium-gray to light-gray, descending about 60 m (200 ft) onto upper finely crystalline, alkali-olivine basalt. part of Esplanade Sandstone and Pakoon Include augite and olivine phenocrysts less Limestone (Pep). Basalt preserves soft than 1 mm in diameter in glassy ground- strata of the Hermit Formation as a basalt- mass. Basalt overlies gently east-northeast- capped hill informally called “Whitmore dipping (2° average) upper red member Hill” (sec. 26, T. 32 N., R. 9 W.; elev. 1,161 and Shnabkaib Member of the Moenkopi m [3,808 ft]). Basalt flow implies that ero- Formation and the Harrisburg Member of sion exposed at least the Esplanade Sand- the Kaibab Formation. Basalt flowed in stone at this location by 4.5 Ma. Thickness, radial pattern from three vent areas over 18 m (60 ft) upper strata of the Moenkopi Formation. Basalt of Poverty Knoll (Pliocene)—Infor- Basalt flows coalesced and flowed west mally named for Poverty Knoll, a 245-m- and down across east-dipping Triassic high (800-ft-high) mesa or flat-topped knoll strata into upper reaches of Hidden Canyon on Shivwits Plateau, north-central part of paleodrainage. Thickness, 30 to 92 m (100 map area (sec. 2, T. 35 N., R. 11 W.; Bill- to 300 ft) ingsley and others, 2000). Divided into: Grassy Mountain Basalt (Pliocene)—For- Tpki Intrusive dike—Light-gray, finely crys- mally named Grassy Mountain Basalt for talline, alkali-olivine basalt. Forms small Grassy Mountain, the type area, Shivwits knoll, center-top of Poverty Knoll Plateau (secs. 3, 4, 9, 10, T. 33 N., R. 11 Tpkb Basalt flow—Light-gray, finely crystalline, W.; Billingsley and others, 2000). Divided alkali-olivine basalt containing plagioclase into: laths and olivine phenocrysts 1 mm in Tgi Intrusive dikes—Dark-gray, finely crys- diameter in glassy groundmass; contains talline, alkali-olivine basalt. Source areas about 35 percent olivine phenocrysts. Flow for associated basalt flows and pyroclas- emerged from central dike and flowed in tic deposits on Grassy Mountain. Dikes radial pattern over Shnabkaib Member of are aligned with nearly vertical east-west the Moenkopi Formation. Thickness aver- bedrock joints and fractures of this area. ages about 37 m (120 ft) Widths, 0.5 to 2 m (1 to 6 ft)

14 15 Tgp Pyroclastic deposits—Red to reddish- There appear to be no flows associated black, angular, scoriaceous cinder frag- with dikes of Colorado River Mile 202, but ments and ash deposits; unconsolidated. some basalt flows on the Shivwits Plateau Spatially associated with intrusive dikes; east of Mollies Nipple may be associated interbedded with local basalt flows Tgb( ). with dikes of Colorado River Mile 202. Thickness, 1 to 6 m (3 to 20 ft) Dikes extend from the Muav Limestone Tgb Basalt flows—Dark-gray, finely crystal- (_m) up almost into the lower Toroweap line, alkali-olivine basalt; olivine pheno- Formation (Pt) near Mollies Nipple, east crysts averaging 1 mm in diameter form edge of Shivwits Plateau. Dikes are aligned about 25 percent of rock sample from to similar northwest-trending dikes at interior of basalt flow. One or more flows Yellow John Mountain on nearby Shivwits interbedded with pyroclastic deposits near Plateau. Widths, 0.1 to 3 m (1 to 10 ft) dikes. Basalts flowed generally west and Basalt of the Shivwits Plateau (Miocene)— northwest and overlie upper red member Informally named for Shivwits Plateau, and Shnabkaib Member of the Moenkopi Mohave County, Arizona. Mount Dellen- Formation (^m). Thickness, 12 to 60 m (40 baugh is highest point (elev. 2,155 m [7,072 to 200 ft) ft]) that forms a regional landmark on the Tp6i Dikes of Parashant Canyon and Hundred southern Shivwits Plateau; type section for and Ninetysix Mile Creek (Miocene)— basalt of the Shivwits Plateau (sec. 2, T. 31 Dark-gray, fine-grained to coarsely crystal- N., R.12 W.). Includes the 6.2±0.30 Ma and line, olivine-augite basalt. Dikes commonly 7.64±0.30 Ma Shivwits basalt of Lucchitta form recessive cracks in limestone rocks of and McKee (1974), 6.78±0.15 Ma Dellen- canyon walls that appear as open eroded baugh basalt (Reynolds and others, 1986), joints. Commonly eroded and chemically 7.06±0.49 Ma Mt. Dellenbaugh basalt of altered or decomposed, especially near Col- Best and others (1980), 8.2±0.1 Ma Price orado River Mile 197 and in Hundred and Point basalt of Wenrich and others (1995). Ninetysix Mile Creek. Several dikes paral- Includes numerous dikes, necks, pyroclas- lel or occupy faults, but most parallel or tic deposits, and extensive basalt flows. occupy northwest-southeast-trending joints Divided into: and fractures in bedrock for 25 km (15 mi) Tsi Intrusive rocks—Gray-black, finely crys- distance. No associated basalt flows are talline, alkali-olivine basalt. Approximate present. Dikes intrude Cambrian through map contacts. Source for extensive basalt Permian rocks from Colorado River Mile flows and minor pyroclastic deposits on 197 to north rim of Parashant Canyon on the Shivwits Plateau (average elev. 1,829 m Shivwits Plateau and southeast of Colorado [6,000 ft]). Dikes trend about N. 30° W., River into upper reaches of Hundred and similar to dikes of Colorado River Mile 202 Ninetysix Mile Creek. K-Ar age, 6.34±0.1 (T2i) east of Shivwits Plateau. Dike widths, Ma from dike on Sanup Plateau, north side 0.1 to 2 m (1 to 6 ft) of Parashant Canyon (Wenrich and others, Tsp Pyroclastic deposits—Reddish-black scoria 1995). Other dikes near Colorado River and cinder fragments, partly consolidated. are too chemically altered or decomposed Form small pyroclastic cones, heavily for K-Ar age dating techniques. Dikes at eroded and partly covered by basalt flows. Colorado River Mile 197 extend upward Often interbedded with basalt flows near over 1,050 m (3,450 ft) into Esplanade vent areas. Thickness, 12 m (40 ft) Sandstone and Pakoon Limestone (Pep) Tsb Basalt flows—Gray-black, finely crystal- where inner gorge is 3 km (2 mi) wide. Dike line, alkali-olivine basalt. Includes one or widths, 0.3 to 3 m (1 to 10 ft) more thin basalt flows that overlie red and T2i Dikes of Colorado River Mile 202 (Mio- white mudstone, siltstone, and gypsum of the cene)—Light-gray, coarsely to finely lower Moenkopi Formation (^m) and gray crystalline, olivine-augite basalt. Include siltstone, gypsum, and cherty limestone of three to four dikes that parallel and occupy the Kaibab Formation (Pk). Groundmasses northwest-trending joints, fractures, and commonly contain olivine phenocrysts and minor faults in Paleozoic bedrock. Com- plagioclase laths. Form composite volca- position is basalt and andesite. K-Ar age noes of Blue Mountain, south of map area, is 5.76±0.26 (Wenrich and others, 1995). Yellow John Mountain and Mount Dellen-

16 17 baugh on Shivwits Plateau. Partly covered escarpment of upper Grand Wash Cliffs into by Quaternary and Tertiary alluvium (QTa) Snap Canyon drainage and into Grand Wash east of Wildcat Ranch at northern reaches of Trough below lower Grand Wash Cliffs. basalt flow. Basalt generally flowed in radial Snap Canyon was filled to a depth of several patterns from prominent mountain volcanic hundred meters by alluvial deposits (Tgc) centers onto relatively flat eroded surface of at time of Snap Point flow. Alluvial deposit east- and northeast-dipping Moenkopi and forms large alluvial debris fan at the mouth Kaibab Formations. Longest basalt flows of Snap Canyon (Billingsley and others, generally flowed northwest. Thickness, 3 to unpub. data). Snap Point Basalt flowed into 122 m (10 to 400 ft) Grand Wash Trough and was subsequently Snap Point Basalt and Garrett dikes (Mio- buried by younger alluvial fan deposits. cene)—Includes basalt flow on Snap Point, Modern erosion has removed most of the upper Grand Wash Cliffs, and at Never- alluvial deposits (Tgc) from around the Snap shine Mesa, Grand Wash Trough (Bill- Point Basalt to form an inverted topographic ingsley and others, unpub. data). Includes feature called Nevershine Mesa. Thickness, associated dikes (Garrett dikes) in Sanup 3 to 10 m (10 to 30 ft) Plateau and at Colorado River Mile 264 Volcanic rocks of the Hualapai Plateau, in Grand Canyon. Informally named Snap undivided (Early to middle Miocene)— Point basalt in Reynolds and others (1986) Deposits include scattered remnants of and Wenrich and others (1995). Because of basalt flows in southwest corner of map the isolation and mappable occurrence of area that appear to have originated from the basalt flows and associated dikes, the Snap 17.4±0.9 Ma Iron Mountain basalt south- Point Basalt is herein formally named Snap west of the map area and the 15.3±0.3 Ma Point Basalt for Snap Point, the type area, Grapevine Canyon volcanic rocks south of Shivwits Plateau, Mohave County, Arizona the map area (Wenrich and others, 1995). (sec. 16, T. 32 N., R. 14 W.). K-Ar age is Includes the 17.4±0.3 Ma plug of The 9.07±0.80 Ma at Snap Point (Reynolds and Grand Pipe, a breccia pipe named by Wen- others, 1986) and 9.2±0.13 Ma for Gar- rich and others (1996), Sanup Plateau, 3 km rett dikes on Sanup Plateau (Wenrich and (2 mi) north of Colorado River Mile 275 others, 1995). Divided into: Tvi Plug of The Grand Pipe—Alkali-olivine Tsgi Intrusive dikes—Dark-gray, greenish, basalt plug or dike in ring fracture of The finely crystalline, alkali-olivine basalt. Grand Pipe of Wenrich and others (1996) Contain phenocrysts of augite and olivine on the Sanup Plateau. K-Ar age, 17.4±0.3 less than 1 mm in diameter. Form near-ver- Ma (Wenrich and others, 1996). Plug is tical dikes orientated in north-south align- about 10 m (30 ft) in diameter and is the ment parallel to local joints and fractures source for remnants of eroded basalt flow in Paleozoic bedrock units. Include dikes on small hill on south side of The Grand in Pigeon Canyon north of Snap Point that Pipe lie on similar north-south trend of Garrett Tv Basalt flows—Alkali-olivine basalt flows. dikes south of Fort Garrett Point. Intrude all Scattered remnants of basalt are part of Paleozoic rocks in walls of Grand Canyon extensive flows that flowed north down on both sides of Colorado River Mile 264 drainages from Iron Mountain about 11 and in tributaries of Tincanebitts and Dry km (7 mi) southwest of map area and flows Canyons. Exposed dikes in canyon walls from the Grapevine Canyon volcanic area reveal that Grand Canyon was not as deep south of the map. Basalt overlies Tertiary or wide 9 m.y. ago as it is today. Dike gravel deposits that may be part of the Buck widths, 0.5 m (1 to 2 ft) and Doe Conglomerate of Young (1999). Tsgb Basalt flows—Dark-gray alkali-olivine No age or chemical studies have been done basalt. Basalt originates from dike source on these basalts. Thickness, 2 to 4 m (6 to near highest part of Snap Point. Consists of 12 ft) two separate basalt flows, one flowed east about 2.4 km (1.5 mi) down drainage eroded SEDIMENTARY ROCKS into Fossil Mountain Member of the Kaibab Formation (Pk) on the Shivwits Plateau and Rocks of the Grand Wash Trough (Pliocene another flowed west down steep erosional and Miocene)—The Tertiary and Qua-

16 17 ternary alluvial rocks in the Grand Wash vial debris fans at the mouths of Pigeon, Trough were collectively called the Muddy Pearce, and Snap Canyons and several Creek Formation by Lucchitta (1979), but small unnamed drainages from the Grand recent studies by Bohannon (1984, 1991, Wash Cliffs. Lower part of unit includes 1992), Bohannon and others (1993), and lenses of reddish and red-brown sandstone Beard (1996) have determined that these gravel and conglomerate, poorly sorted and sedimentary rocks are not connected to consolidated by calcite and gypsum cement. the Muddy Creek Formation of the Muddy Gradational and intertonguing vertical River area farther west but are rocks that and horizontal contact arbitrarily marked have formed in separate basins at about between lithologic change at bottom of con- the same time as the Muddy Creek. The glomeratic facies (Tgc) and top of underly- Hualapai Limestone of Lucchitta (1979) ing limestone and siltstone facies (Tgl), and is equivalent to sediments of gypsum and gypsum and gypsiferous siltstone facies gypsiferous siltstone facies (Tgg) and (Tgg). Unit gently folded and highly frac- limestone and siltstone facies (Tgl) north tured near base of Grand Wash Cliffs. Unit of Lake Mead. Tertiary sediments, alluvial thins rapidly west from Grand Wash Cliffs, rocks (Tgx, Tgg, Tgl, Tgc, Tgr, Tao, Tay), thickest near mouths of Snap, Pigeon, and and volcanic rocks (Tb) of the Grand Wash Pearce Canyon drainages. Thickest section, Trough unconformably overlie the Horse about 760 m (2,500 ft) Spring Formation (Ths; Billingsley and Tgl Limestone and siltstone facies (Mio- others, unpub. data). Divided into: cene)—Gray, silty, crystalline limestone, Tgr Red siltstone, sandstone, and conglomerate light-red, gray, and greenish-gray gypsifer- facies (Pliocene and Miocene)—Dark-red ous siltstone, gray to reddish-gray calcare- to orange-red, slope-forming, medium- to ous sandstone, and gray to white gypsum. fine-grained, gypsiferous siltstone and Limestone beds are vuggy, irregularly sandstone overlain by cliff-forming, gray bedded, 1 to 10 m (3 to 30 ft) thick. Contain to light-orange-brown, coarse- to fine- abundant plant and algae fossils indicative grained, poorly sorted, consolidated silt, of freshwater inland basin deposits. Include sand, gravel, and conglomerate. Clasts interbedded gray, greenish-gray, and red- in upper conglomerate consist of about dish-gray gypsiferous mudstone and silt- 90 percent limestone and dolomite, 5 stone that grade into underlying gypsum percent sandstone, and 5 percent chert in and gypsiferous siltstone facies (Tgg). Silt- gray gypsiferous siltstone and sandstone stone and sandstone beds thin or thicken gravel matrix. Base of unit not exposed but laterally at expense of equivalent limestone assumed to unconformably overlie rocks of beds. Sandstone beds are conglomeratic in the Grand Wash Trough (Tgl, Tgg, and Tgx) places with small, rounded clasts of chert, and Mesozoic and Paleozoic rocks along quartzite, and carbonate fragments. Grada- basin margins. Conglomerate beds con- tional and arbitrary vertical and horizontal tain small subrounded to angular clasts of contact with underlying gypsum and gyp- Proterozoic crystalline rocks along Pakoon siferous siltstone facies (Tgg). Intertongues Wash, northwest edge of map area. About laterally into Proterozoic-clast conglomer- 130 m (425 ft) of unit exposed along Grand ate facies (Tgx) in lower part of unit and Wash and Pakoon Wash drainages, increas- unconformably overlies Proterozoic-clast ing to about 450 to 470 m (1,475 to 1,550 conglomerate facies (Tgx) in upper part ft) or more north of map area (Lucchitta of unit east of Wheeler Fault. Limestone and others, 1995a, b; Billingsley and Work- beds are moderately folded as much as man, 2000) 13° in upper part of basin near Grand Tgc Paleozoic-clast conglomerate facies (Mio- Wash. Includes one white and one light- cene)—Gray, cliff-forming, rounded to brown (0.5 to 1 m [1 to 3 ft]) thick tuff bed subrounded clasts of Paleozoic limestone between limestone beds. Limestone beds and sandstone from 1 to 70 cm (1 to 28 in) are likely the equivalent of the Hualapai in diameter mixed with coarse gravel and Limestone of Lucchitta (1979) south of conglomerate derived from Paleozoic rocks Lake Mead. Thickens south to as much as of the Colorado Plateau. Consolidated by 305 m (1,000 ft) at Lake Mead. Thickness calcium and gypsum cement. Forms allu- in map area, 60 to 70 m (200 to 230 ft)

18 19 Tgg Gypsum and gypsiferous siltstone facies face where it is covered by younger rocks (Miocene)—Gray and gray-white gypsum, of the Grand Wash Trough. The Thumb greenish-gray, light-red, and reddish-gray Member of the Horse Spring Formation gypsiferous siltstone and mudstone. Upper may be present in subsurface. Age of Rain- 15 to 20 m (50 to 65 ft) consists mostly of bow Gardens Member of the Horse Spring multicolored, banded, thin-bedded mud- Formation is bracketed between 26 Ma and stone and gypsiferous siltstone interbedded 18.8 Ma (Beard, 1996). Only one outcrop with thin-bedded (0.5 to 1 m [1 to 3 ft]), is exposed in map area just east of Tassi dark-gray limestone beds. Includes beds Spring on upthrown side of Wheeler Fault of pinkish-white to light-gray, cliff-form- (southwest corner of map area). Uncon- ing tuffaceous limestone and white tuff formable contact with underlying Kaibab beds, 0.5 to 1 m (1 to 3 ft) thick in upper Formation and both units dip 24° to 34° part. Forms Gyp Hills badlands area east east-southeast. Unconformably overlain by of Wheeler Fault. Upper siltstone and Proterozoic-clast conglomerate facies (Tgx) mudstone beds grade downward into gray of rocks of the Grand Wash Trough. Incom- silty gypsiferous siltstone and massive gray plete section, 132 m (435 ft) exposed gypsum. Unit gently folded except along ^c Chinle Formation, undivided (Upper Trias- trace of Wheeler Fault where beds dip west sic)—Includes the Shinarump and Petri- as much as 65°. Base of unit not exposed. fied Forest Members. Shinarump Member Intertongues with Proterozoic-clast con- locally missing or has undergone local facies Tgx glomerate facies ( ). Thickness, 120 m change to sandstone lithology similar to (400 ft) or more sandstones in Petrified Forest Member. The Tgx Proterozoic-clast conglomerate facies Chinle Formation at Hells Hole is 21 km (13 (Miocene)—Dark-gray to reddish-brown, mi) north of Colorado River Mile 188 and is cliff- to resistant slope-forming conglom- the thickest Chinle Formation deposit near- erate. Includes interbedded lenses of est to the Colorado River of Grand Canyon gravel and sandstone, poorly sorted and other than at Lees Ferry, Arizona. Petrified moderately well bedded; consolidated. Forest Member is white, blue-gray, pale- Clasts are composed of reddish-brown, red and purple, slope-forming mudstone, brown, red, grayish-green, and light-green, siltstone, and coarse-grained sandstone; well-rounded rhyolite, black biotite schist, contains small, very well rounded pebbles gneiss, gabbro, diorite, red pegmatite, gran- of black, yellow, brown, and red quartzite. ite, white quartz, gray limestone and dolo- Includes white, coarse-grained, ledge-form- mite, and red sandstone derived from the Jumbo Peak about 19 km (12 mi) west of ing sandstone at base that may be equivalent map area. Include large boulders as much to the Shinarump Member of the Chinle For- as 1.5 m (5 ft) in diameter that were prob- mation; contains brown, yellow, white, and ably carried in by large debris flows. Base red petrified wood fragments. Unit contains of unit not exposed. About 675 m (2,275 ft) bentonitic clays derived from decomposi- exposed near east side of Wheeler Fault tion of volcanic ash. Unconformable contact with overlying basalt of Bundyville (Tbb) Horse Spring Formation (Miocene and Oli- west of Hurricane Fault and basalt of Mount gocene)—Named the Cottonwood Wash Logan (Tmlb) east of Hurricane Fault. Ero- Formation by Moore (1972), but these sion has removed an unknown thickness of rocks have close lithologic and stratigraphic similarity to the Rainbow Gardens Member upper part of the Chinle Formation. Unit Ql of the Horse Spring Formation as proposed is mostly covered by landslide debris ( ). by Bohannon (1984) and formally defined Unconformable contact with underlying by Beard (1996) slope-forming upper red member of the Ths Rainbow Gardens Member—Includes basal Moenkopi Formation; erosional relief less conglomerate and middle limestone and than 2 m (6 ft) at Hells Hole marked by color sandstone unit. Consists of complex inter- contrast between red Moenkopi Formation tonguing sequence of clastic and carbon- and purple-white Chinle Formation in slope. ate lithofacies. Upper unit of the Rainbow Thickness, 122 m (400 ft) Gardens Member is not exposed within map ^m Moenkopi Formation, undivided (Middle(?) area but is assumed to be present in subsur- and Lower Triassic)—Includes, in descend-

18 19 ing order, the upper red member, Shnabkaib ft) just north of map area (Billingsley and Member, middle red member, Virgin Lime- Workman, 2000). Thickness, 20 m (65 ft). stone Member, lower red member, and the Lower red member consists of red, fine- Timpoweap Member as defined by Stewart grained, thin-bedded, sandy siltstone; and and others (1972). In general, Moenkopi gray, white, and pale-yellow laminated Formation is mostly eroded from map gypsum and minor sandstone. Lower area except for isolated outcrops beneath part contains redeposited gypsum and Tertiary volcanic rocks at Mount Trum- siltstone of Harrisburg Member of the bull, Mount Logan, Poverty Knoll, Poverty Kaibab Formation. Gradational contact Mountain, Grassy Mountain, and Yellow with underlying conglomerates of the Tim- John Mountain. A complete section of the poweap Member; locally, unconformably Moenkopi Formation crops out at Hells overlies Harrisburg Member of the Kaibab Hole 21 km (13 mi) north of Colorado Formation where Timpoweap is absent. River Mile 188, upper Whitmore Canyon. Thickens in paleovalleys and pinches out Total thickness of the Moenkopi Formation onto eroded paleohills of underlying Har- at Hells Hole, 365 m (1,200 ft). risburg Member. Unit distinguished from Upper red member consists of red, thin- red siltstone of Harrisburg Member of the bedded, cliff- and slope-forming siltstone Kaibab Formation by dark-red color and and sandstone. Gradational lower contact thin-bedded, platy beds of the lower red placed at uppermost thick white or light- member as opposed to massive-bedded, gray calcareous siltstone and dolomite of pale-red, undulating siltstone and gray Shnabkaib Member. Unit thins south and limestone beds of Harrisburg Member. east, thickens north. Thickness, 122 m (400 Thickness, 0 to 20 m (0 to 65 ft). ft). Timpoweap Member consists of light- Shnabkaib Member is white, laminated gray, slope- and cliff-forming conglomer- to thin-bedded, slope- and ledge-forming, ate in lower part and light-gray to light-red, aphanitic dolomite interbedded with light- slope-forming calcareous sandstone in gray, calcareous, silty gypsum. Gradational upper part. Conglomerate composed of lower contact at lowest thick white or light- subangular to rounded pebbles and cobbles gray, calcareous, silty dolomite of middle of gray and dark-gray limestone, white and red member. Unit thins south and west, brown chert, and gray sandstone in matrix thickens north. Thickness, 135 m (440 ft). of gray to brown, coarse-grained sandstone. Middle red member consists of red-brown, Consolidated by calcite and gypsum. All thin-bedded to laminated, slope-forming detritus in Timpoweap Member derived siltstone and sandstone. Includes white and from Kaibab Formation. Fills paleovalleys gray gypsum beds, minor white platy dolo- about 1,500 m (5,000 ft) wide and as much mite, green siltstone, and gray-green to red as 70 m (230 ft) deep eroded into Har- gypsiferous mudstone. Gradational lower risburg Member of the Kaibab Formation. contact about 10 m (30 ft) above gray lime- Imbrication of pebbles in conglomerate stone bed of Virgin Limestone Member. show general northeastward flow of depos- Unit thins west, south, and east, thickens iting streams. Thickness, 0 to 70 m (230 ft) north. Thickness, 122 m (400 ft). Pk Kaibab Formation, undivided (Lower Perm- Virgin Limestone Member consists of one ian)—Includes, in descending order, the light-gray, thin-bedded to thinly laminated, Harrisburg and Fossil Mountain Mem- ledge-forming limestone bed, 0.5 to 2 m (1 bers as defined by Sorauf and Billingsley to 6 ft) thick, and overlying pale-yellow, (1991). Entire unit is removed by modern red, and bluish-gray, thin-bedded, slope- erosion from some areas of the north rim forming gypsiferous siltstone. Pinches of Grand Canyon. Thickness of Kaibab out south and west in map area, thickens Formation, 0 to 160 m (0 to 530 ft), but as north and includes two limestone beds much as 198 m (650 ft) in channel areas. at north edge of map area and as many Harrisburg Member consists of reddish- as four limestone beds near St. George, gray and brownish-gray, slope-forming Utah. Unconformable contact at base of gypsum, siltstone, sandstone, and limestone. limestone bed with underlying lower red Includes, in descending order, an upper member; erosional relief as much as 2 m (6 slope, middle cliff, and lower slope unit.

20 21 Upper slope unit: red and gray, interbedded siltstone and silty sandstone interbedded gypsum, sandstone, siltstone, capped by with white laminated gypsum and gray yellowish-gray, fossiliferous sandy lime- thin-bedded limestone. Gypsum beds are as stone. Middle cliff unit: gray, thin-bedded, much as 3 to 5 m (10 to 15 ft) thick. Unit cherty limestone that weathers dark gray as a whole weathers as reddish-gray slope. and yellowish-gray sandy limestone. Lower Bedding locally deformed due to subsid- slope unit: yellowish-gray to pale-red, gyp- ence caused by dissolution of gypsum. siferous siltstone and calcareous sandstone; Contact with underlying Brady Canyon gray, thin-bedded sandy limestone; and gray Member is gradational and marked at top of to white, thick-bedded gypsum. Dissolution underlying limestone cliff of Brady Canyon within lower gypsum beds has resulted Member. Unit in general thins southward in local warping and bending of middle and thickens northward. Variable thickness limestone beds, especially at or near local owing to local channel erosion in upper drainages. Dissolution of gypsum in the part. Thickness, 18 to 60 m (60 to 200 ft). Harrisburg Member is responsible for many Brady Canyon Member is gray, cliff- collapse sinkholes on Shivwits, Uinkaret, forming, thin- to medium-bedded (0.05 to and Kanab Plateaus. Gradational contact 1.4 m [1 to 5 ft]) fine- to coarse-grained, marked at top of cherty limestone cliff of fetid, fossiliferous limestone. Weathers Fossil Mountain Member. Thickness, 0 to dark gray. Includes thin-bedded dolomite 80 m (0 to 265 ft) in north half of map, bev- in upper and lower part. Contains white and eled and removed by erosion along south gray chert nodules that make up less than edge of the Shivwits Plateau area. 8 percent of unit. Contact with underly- Fossil Mountain Member is light-gray, ing Seligman Member is gradational and cliff-forming, fine- to medium-grained, placed at lithologic break at base of lime- thin- to medium-bedded (0.3 to 2 m [2 to 6 stone cliff and top of sandstone-gypsum ft]), fossiliferous, sandy, cherty limestone. slope. Thickness, 40 m (130 ft) at east edge Unit characterized by gray and white chert of map area, increasing to as much as 137 nodules and chert lenses parallel to bed- m (450 ft) along upper Grand Wash Cliffs. ding; chert weathers dark gray to black. Seligman Member consists of light- Unit in general weathers medium gray. Sev- purple, yellowish-red, and gray, slope- eral chert nodules contain concentric black forming, thin-bedded dolomite interbedded and white bands and or fossil sponges. with calcareous sandstone and gypsum. Brecciated chert beds 1 to 3 m (0.5 to 10 In northeastern third of map area, unit is ft) thick common in upper part at contact gray to white, light-red gypsum and silty with overlying Harrisburg Member. Unit gypsum interbedded with yellowish-red, generally forms cliff rim of Grand Canyon. thin-bedded, calcareous sandstone and Weathers into pinnacles or detached pil- gray dolomite. Forms recess between the lars or spires. Unconformable contact cliff-forming Brady Canyon Member of the with underlying Woods Ranch Member of Toroweap Formation and the cliff-forming the Toroweap Formation characterized by Coconino Sandstone in southwestern two- channel erosion averaging about 3 m (10 thirds of map area. Forms a gypsiferous ft) in relief, but in some areas large erosion slope similar to the Woods Ranch Member channels or valleys are as much as 45 m of the Toroweap Formation in northwestern (145 ft) in depth and as much as 2 km (1.3 third of map area. The Coconino Sandstone mi) in width between lower Whitmore and intertongues with lower part of the Selig- Parashant Canyons and in upper Toroweap man Member of the Toroweap Formation Canyon. Thickness of Fossil Mountain as crossbedded sandstone set between Member, 70 to 120 m (240 to 385 ft) flat-bedded sandstone beds. The near- Pt Toroweap Formation, undivided (Lower shore crossbedded sandstone has an upper Permian)—Includes, in descending order, and lower gradational contact within the Woods Ranch, Brady Canyon, and Selig- flat-bedded marine sandstone of the lower man Members as defined by Sorauf and Seligman Member (Fisher, 1961; Schleh, Billingsley (1991). 1966; Rawson and Turner, 1974; Billing- Woods Ranch Member consists of gray sley and others, 2000). Where Coconino and light-red, slope-forming, gypsiferous Sandstone forms a cliff in central and

20 21 eastern Grand Canyon, flat-bedded sand- are most pronounced in northeastern part stone beds of the lower part of the Selig- of map area. Depth of channels decreases man Member of the Toroweap Formation westward to generally less than 3 m (10 ft) are present at the base of the cliff in most deep along the Grand Wash Cliffs, and the areas. Upper crossbedded sand dune sets of contact between the Hermit Formation and the Coconino Sandstone were beveled off Esplanade Sandstone/Pakoon Limestone and redistributed as flat-bedded sandstone is difficult to determine in the field. Along of the Seligman Member of the Toroweap the Grand Wash Cliffs, contact between Formation. Thickness, about 10 m (30 ft) in the Hermit Formation and Esplanade southern two-thirds of map area, increasing Sandstone/Pakoon Limestone is marked at to about 17 m (55 ft) in northern third the top of the first red or white cliff-form- Pc Coconino Sandstone (Lower Permian)—Tan ing, massive, sandstone bed. Dark-red, to white, cliff-forming, fine-grained, well- crumbly, thin-bedded siltstone that con- sorted, crossbedded quartz sandstone. tains poorly preserved plant fossils forms Contains large scale, high-angle, planar recesses between thicker sandstone beds crossbedded sandstone sets as large as 11 in lower 60 m (200 ft) of unit along the m (35 ft) thick, and low-angle crossbed- Grand Wash Cliffs. Similar plant fossils are ded sets less than 2 m (6 ft) thick in upper also present in dark-red siltstone deposits and lower part of cliff. Locally includes within deep erosion channels cut into the low-relief wind ripple marks on crossbed- Esplanade Sandstone (Pe) in eastern part of ded planar sandstone surfaces. Unit inter- map area. Thickens from 213 m (700 ft), tongues with marine sandstone and gypsum east edge of map area, to 244 to 260 m (800 beds in lower part of the Seligman Member to 860 ft) along the Grand Wash Cliffs of the Toroweap Formation in northeast- Supai Group (Lower Permian, Upper, Middle, ern two-thirds of map area (Fisher, 1961; and Lower Pennsylvanian, and Upper Schleh, 1966; Rawson and Turner, 1974; Mississippian)—Includes, in descending Billingsley and others, 2000). Crossbed- order, the Esplanade Sandstone east of Hur- ded sets thin and thicken laterally in upper ricane Fault (Pe), the Esplanade Sandstone Grand Wash Cliffs and Pakoon Ridge areas. and Pakoon Limestone west of Hurricane Sharp planar, unconformable contact with Fault (Pep), and the Wescogame, Manaka- underlying Hermit Formation; erosional cha, and Watahomigi Formations, undivided relief generally less than 1 m (3 ft) but (M*s) as defined by McKee (1975, 1982). locally as much as 2.5 m (8 ft). Thickness, Age of the Watahomigi Formation is Lower 47 m (155 ft), eastern third of map area, Pennsylvanian and Upper Mississippian by thins west and pinches out between Para- Martin and Barrick (1999). Divided into: shant Canyon and Snap Point along south Pe Esplanade Sandstone east of Hurricane edge of Shivwits Plateau. In northwest part Fault (Lower Permian)—Includes, in of map area, 3 to 9 m (10 to 30 ft) thick descending order, an upper cliff and slope, Ph Hermit Formation (Lower Permian)—Red, a middle cliff, and lower slope unit. Upper slope-forming, fine-grained, thin-bedded cliff and slope unit includes an upper, light- siltstone and sandstone. Includes red and red or white sandstone cliff and a lower, white, massive to low-angle crossbedded, dark-red siltstone, sandstone, and gypsum calcareous sandstone ledges in upper part, slope that visually resemble that of the northwest quarter of map area. Majority of Hermit Formation in eastern third of map unit is interbedded, slope-forming sand- area (Hurricane Fault and east of Hurricane stone and siltstone. Unit often bleached Fault). In western two thirds of map area, white or yellow near breccia pipes and at the upper cliff and slope undergoes a gradual upper contact with the Coconino Sandstone facies change west of the Hurricane Fault to due to reducing effect of ground water a light-red and white, low-angle crossbed- in the Coconino Sandstone. Base of unit ded and massive calcareous sandstone along unconformably overlies massive-bedded, Grand Wash Cliffs and at Pakoon Ridge, red and white sandstone of Esplanade which forms the upper part of the Esplanade Sandstone (Pe and Pep) throughout map Sandstone and Pakoon Limestone west of area. The deep erosion channels as much the Hurricane Fault (Pep) unit. Maximum as 16 m (50 ft) deep at the unconformity thickness of upper unit, about 67 m (220

22 23 ft) along east edge of map area, thinning facies change west of the Hurricane Fault westward to about 15 m (50 ft) in Grand to a light-red and white, low-angle cross- Wash Cliffs area. Middle cliff unit is com- bedded and massive calcareous sandstone posed of light-red, cliff-forming, fine- to along Grand Wash Cliffs and at The Cocks- medium-grained, medium-bedded 1 to 3 comb, southwest corner of map area, which m (3 to 10 ft) thick, well-sorted, calcareous forms the upper part of the Esplanade sandstone east of Hurricane Fault. Includes Sandstone and Pakoon Limestone west of gray, thin-bedded sandy limestone of the the Hurricane Fault (Pep) unit. Maximum Pakoon Limestone interbedded in lower half thickness of upper unit, about 67 m (220 ft) of Esplanade cliff west of Hurricane Fault. along east edge of map area at Lake Mead, Pakoon Limestone pinches out eastward thinning westward to about 15 m (50 ft) in about the Hurricane Fault area, but thick- Grand Wash Cliffs area. ens rapidly westward towards Grand Wash Middle cliff unit is composed of an upper, Cliffs and Pakoon Ridge where the Espla- light-red to white, fine- to medium-grained, nade Sandstone and Pakoon Limestone thick-bedded calcareous sandstone and of McNair (1951) are undivided (Pep). flat, massive, low-angle crossbedded sand- Middle cliff unit averages about 75 m (250 stone and calcareous sandstone in lower ft) thick at east edge of map area, thickening half that intertongue with gray limestone to about 91 m (300 ft) along Grand Wash beds of the Pakoon Limestone. Small- to Cliffs area. Lower slope unit is composed of medium-scale, planar low-angle, calcare- a basal limestone pebble conglomerate that ous sandstone crossbeds that include some grades upward into slope-forming, interbed- high-angle sets throughout compose nearly ded dark-red siltstone, light-red sandstone, half of the Esplanade Sandstone and Pakoon and gray, thin-bedded limestone that fills Limestone cliff along the Grand Wash channels eroded as much as 10 m (30 ft) Cliffs. Pakoon Limestone beds are gray to into underlying Wescogamie Formation of pinkish-gray, fine-to medium-grained, thin- the undivided Supai Group (M*s). Uncon- to medium-bedded limestone and oolitic formable contact between the Permian and limestone along Grand Wash Cliffs and Pennsylvanian strata in east two-thirds of The Cockscomb areas. Pakoon Limestone map area and a disconformity between the contains numerous Early Permian marine Permian and Pennsylvanian strata along fossils throughout unit in west half of map the Grand Wash Cliffs and in the Pakoon area, which establish Early Permian age Ridge area. Thickness of lower slope unit, (McNair, 1951) for Esplanade Sandstone about 25 m (80 ft) at east edge of map area, east of Hurricane Fault (Pe), and Esplanade thins westward and pinches out near Grand Sandstone and Pakoon Limestone west of Wash Cliffs. Overall, Esplanade Sandstone Hurricane Fault (Pep). Pakoon Limestone (Pe) and Esplanade Sandstone and Pakoon thins eastward and pinches out in the Limestone (Pep) are about 167 m (550 ft) vicinity of the Hurricane Fault in eastern thick in east half of map area, decreasing to part of map area. Pakoon Limestone beds about 107 m (350 ft) in west half form topographic bench of Sanup Plateau Pep Esplanade Sandstone and Pakoon Lime- along Grand Wash Cliffs area. Thickness of stone west of Hurricane Fault (Lower middle cliff unit averages about 91 m (300 Permian)—Esplanade Sandstone defined ft) in west half of map area and thins to by McKee (1975, 1982); Pakoon Lime- about 76 m (250 ft) in east half. stone defined by McNair (1951). Light-red Lower slope unit consists of alternating and pinkish-gray, cliff-forming, fine- to layers of light-red sandstone, dark-red medium-grained, medium-bedded (1 to 3 m siltstone and mudstone, and gray thin- [3 to 10 ft]), well-sorted, calcareous sand- bedded limestone of the Esplanade Sand- stone and interbedded, dark-red, slope- stone (Pe). Unconformable contact with forming siltstone. Includes an upper cliff underlying Wescogame Formation of the and slope unit, a middle cliff unit, and a Supai Group undivided (M*s) marked by lower slope unit as described for Esplanade erosion channels of as much as 10 m (30 Sandstone (Pe). ft) deep; channels contain limestone pebble In western two-thirds of map area, the conglomerate. Lower slope unit, about 25 upper cliff and slope undergoes a gradual m (80 ft) thick in eastern part of map area,

22 23 thins and pinches out near Grand Wash of Manakacha Formation. Erosional relief Cliffs area. Overall thickness of Esplanade is generally less than 1 m (3 ft). Thickness Sandstone and Pakoon Limestone west of of lower cliff, 30 m (100 ft). Average thick- Hurricane Fault, about 107 m (350 ft) along ness, 55 m (180 ft). Grand Wash Cliffs Watahomigi Formation consists of gray M*s Wescogame Formation (Upper Pennsyl- and purplish-red, slope-forming limestone, vanian), Manakacha Formation (Middle siltstone, mudstone, and conglomerate. Pennsylvanian), and Watahomigi Forma- Forms an upper ledge and slope unit and a tion (Lower Pennsylvanian and Upper lower cliff unit. Upper ledge and slope unit Mississippian), undivided—Supai Group is composed of a sequence of alternating as defined by McKee (1975, 1982). Age gray, thin-bedded cherty limestone ledges of the Watahomigi Formation is Lower and purplish-gray siltstone and mudstone Pennsylvanian and Upper Mississippian as slopes; limestone beds contain Early Penn- defined by Martin and Barrick (1999). All sylvanian conodont fossils (Martin and Bar- three formations are equivalent to the Call- rick, 1999); red chert lenses and nodules are ville Limestone (not exposed in map area) common. Includes limestone chert pebble of the Basin and Range west of the Grand conglomerate at base of upper ledge and Wash Cliffs. slope unit, which locally contains Pennsyl- Wescogame Formation forms an upper vanian fossils. Upper ledge and slope unit slope and lower cliff. Upper slope is com- averages 21 m (70 ft) thick throughout map posed of dark-red, fine-grained siltstone, area. Lower cliff unit consists of a basal, mudstone, and interbedded light-red sand- purplish-red mudstone and siltstone over- stone. Lower cliff is composed of light-red lain by thin-bedded aphanitic to granular to gray, high-angle, large- and medium- limestone with red chert nodules and chert scale, tabular-planar, crossbedded sand- veins. Conodonts in lower thin limestone stone sets as much as 10 m (30 ft) thick. beds are Late Mississippian age (Martin Includes interbedded dark-red, thin-bedded and Barrick, 1999). Includes purple silt- siltstone beds in upper part of cliff. Uncon- stone and gray limestone interbedded with formable contact with underlying Manaka- conglomerate that fill small channels eroded cha Formation marked by erosion channels into either the Surprise Canyon Formation as much as 24 m (80 ft) deep in western part (Ms) or Redwall Limestone (Mr) at the basal of map area, less than 10 m (30 ft) deep in erosional unconformity. In majority of map eastern part of map area. Channel deposits area, purple shale and mudstone of Wata- commonly composed of limestone chert homigi Formation unconformably overlie conglomerate. Thickness, 40 to 64 m (130 gray limestone of Redwall Limestone. Con- to 210 ft). tact with laterally discontinuous Surprise Manakacha Formation consists of light- Canyon Formation is often based on color red, white, and gray upper slope and lower change from purple mudstone of the Wata- cliff of sandstone, calcareous sandstone, homigi Formation to dark-red mudstone of dark-red siltstone, and gray limestone. the Surprise Canyon Formation. Unit aver- Upper slope unit consists of shaley silt- ages 30 m (100 ft) thick along east edge of stone and mudstone with minor amounts map area thickening to 60 m (200 ft) along of interbedded, thin-bedded limestone and Grand Wash Cliffs sandstone. Carbonate content increases Ms Surprise Canyon Formation (Upper Missis- westward to form numerous ledge-form- sippian)—Dark reddish-brown cliff- and ing, thin- and medium-bedded limestone slope-forming siltstone and sandstone; beds. Thickness of upper slope unit, about gray limestone and dolomite; and white 18 m (60 ft). Lower cliff unit is dominantly conglomerate in dark-red or black sand- a crossbedded, calcareous sandstone, stone matrix (Billingsley and Beus, 1999). dolomite, and sandy limestone. Carbonate Formation is present only as sedimentary content increases westward across map deposits in erosion channels and infillings area forming numerous gray limestone of karst features dissolved from the upper ledges. Unconformable contact between part of Redwall Limestone (Mr). Includes Manakacha and underlying Watahomigi an upper slope, middle cliff, and lower Formations at base of lower sandstone cliff slope unit.

24 25 Upper slope unit includes red-brown, beds that form recess about 1 to 3 m (3 to thin-bedded siltstone, calcareous sand- 10 ft) deep at base of unit near top of Red- stone, and reddish-gray, thin-bedded, sandy wall Limestone cliff. Fossils not common limestone. Contains numerous ripple marks except locally. Includes distinctive ripple- and marine fossils. Thickness, about 15 to laminated limestone beds, oolitic lime- 23 m (50 to 75 ft). stone, and some chert. Member thickens Middle cliff unit consists of reddish-gray, slightly from east to west across map area, thin-bedded, coarse-grained, silty sandy highly karstified with laterally extensive limestone. Contains numerous marine fos- karst breccia, locally absent where removed sils distinguishing it as the most fossilifer- by Late Mississippian paleovalley erosion. ous rock unit in Grand Canyon. Thickness, Thickness, 15 to 30 m (50 to 100 ft). 15 to 60 m (50 to 200 ft). Mooney Falls Member is light-gray, Lower slope unit consists of dark red- cliff-forming, fine- to coarse-grained, brown to black, iron-stained, thin-bedded, thick to very thick bedded (3 to 6 m [10 coarse- to medium-grained siltstone, to 20 ft]), fossiliferous limestone. Highly sandstone, limestone, and conglomerate; karstified with laterally extensive karst includes minor coal beds. Thin, low-angle breccias in upper part. Includes dark-gray crossbedded sandstone sets and siltstone dolomite beds in lower part, west quarter beds contain numerous plant and bone of map area; oolitic limestone and chert fossils, mudcracks, and ripple marks. Con- beds are restricted to upper part. Contains glomerate beds consist of white and gray large-scale, tabular and planar, low-angle chert clasts supported in coarse-grained cross-stratified limestone beds in upper chert sandstone or gravel matrix, all derived third of unit. Limestone weathers dark from Redwall Limestone (Mr). Conglomer- gray. Disconformable contact with underly- ate beds average about 8 m (25 ft) thick. ing Thunder Springs Member distinguished Includes local coal beds 1 m (3 ft) thick by weathered color change and lithology; in black shale slope in southwest corner of massive bedded, gray limestone of Mooney map area. The Redwall Limestone surface Falls Member overlies thin-bedded, dark- was a tropical sinkhole plain drained by gray to brown dolomite and chert beds of west-trending, low-gradient channels. The Thunder Springs Member. Thickness, 158 channels developed into major drainage m (520 ft). valleys with depths reaching up to 122 m Thunder Springs Member consists of (400 ft) cutting out 2/3 of the thickness of about 50 perecent white, cliff-forming, fos- the Redwall Limestone. The depth of karsti- siliferous, thin-bedded, alternating bands fication exceeded that of nearby channels. of white chert and about 50 percent brown- This environment was drowned by a marine ish-gray, thin-bedded (2 to 12 cm [1 to 7 transgression from the west that deposited in]) finely crystalline dolomite and fine- to carbonate sediments of the Surprise Canyon coarse-grained limestone. Limestone is Formation in the channels, valleys, and most common lithology in north half of karst, but did not cover the entire Redwall map area, dolomite more common in south Limestone surface. Maximum thickness, half. Weathers into distinctive prominent 122 m (400 ft), unit thins eastward black and light-brown bands on cliff face. Mr Redwall Limestone, undivided (Upper and Locally, includes large-scale crossbed- Lower Mississippian)—Includes, in ding and irregularly folded beds in north descending order, the Horseshoe Mesa, half of map area. Fossil content increases Mooney Falls, Thunder Springs, and Whit- from east to west across map area. Discon- more Wash Members as defined by McKee formable planar contact with underlying (1963), and McKee and Gutschick (1969). Whitmore Wash Member distinguished by Horseshoe Mesa Member is light olive- distinct lack of chert in Whitmore Wash gray, ledge- and cliff-forming, thin-bedded, Member. Thickness, 30 m (100 ft) in south fine-grained limestone. Weathers to form half of map area, increasing to 45 m (150 ft) receding ledges. Gradational and discon- in north half. formable contact with underlying massive- Whitmore Wash Member is yellowish- bedded limestone of Mooney Falls Member gray and brownish-gray, cliff-forming, thick- marked by thin-bedded, platy limestone bedded, fine-grained limestone. Weathers

24 25 dark gray. Fossiliferous in northwest quarter Sandstone in the lateral and vertical sense. of map area. Unit is mostly dolomite east However, the Muav Limestone map unit and northeast of map area. Unconform- includes tongues of Bright Angel Shale, able contact with underlying Temple Butte the Bright Angel Shale map unit contains Formation (Dtb) at erosion channels of low tongues of the Muav Limestone and Tapeats relief, about 2 to 3 m (6 to 10 ft) in depth. Sandstone, and the Tapeats Sandstone map Contact generally recognized where major unit contains tongues of Bright Angel Shale. cliff of gray Redwall Limestone overlies The Tonto Group overlies Early Proterozoic stair-step ledges of dark-gray Temple Butte (1.7 to 1.6 Ma) igneous and metamorphic Formation. Uniform thickness throughout rocks above what is regionally known as the map area, 25 m (80 ft). Overall, Redwall Great Unconformity Limestone increases in thickness east to _m Muav Limestone (Middle Cambrian)— west from about 183 m (600 ft) to 243 m Dark-gray, light-gray, brown, and orange- (800 ft) red, cliff-forming limestone, dolomite, Dtb Temple Butte Formation (Upper and Middle and interbedded thin calcareous mudstone. Devonian)—Purple, reddish-purple, dark- Includes, in descending order, the unclassi- gray, and light-gray, ledge-forming dolo- fied dolomite member, the Havasu Member, mite, sandy dolomite, sandstone, mudstone, Gateway Canyon Member, Kanab Canyon and limestone as defined by Beus (1990). Member, Peach Springs Member, Spen- Purple, reddish-purple, and light-gray, fine- cer Canyon Member, and Rampart Cave Member as defined by McKee and Resser to coarse-grained, thin- to medium-bedded, (1945) and three unnamed Bright Angel ripple-laminated ledges of mudstone, sand- Shale lithologic units between limestone stone, dolomite, and conglomerate fills members. Carbonate beds are composed channels eroded as much as 15 m (50 ft) into of fine- to medium-grained, thin- to thick- the underlying Cambrian strata in east half bedded, mottled, fossiliferous, silty lime- of map area. Channel deposits are overlain stone, limestone, and dolomite. Unnamed by dark to olive-gray, medium- and thick- Bright Angel Shale beds are composed of bedded dolomite, sandy dolomite, lime- green and purplish-red, micaceous, silt- stone, and sandstone that form a sequence of stone, mudstone, shale, and thin brown dark-gray ledges. Unconformity at base of sandstone beds. Contact between Muav Temple Butte represents major stratigraphic Limestone and underlying Bright Angel break in the Paleozoic record in Grand Shale is lithology dependent and placed at Canyon that represents erosion or non-depo- the base of lowest prominent cliff-forming sition during part of the Late Cambrian, all limestone of the Rampart Cave Member of of the Ordovician and Silurian, and most of the Muav Limestone. Intertonguing rela- the Early and Middle Devonian, represent- tions between Muav Limestone and Bright ing a hiatus of about 100 m.y. Dark-gray Angel Shale produce variable thicknesses of rocks of the Temple Butte Formation are limestone and shale units. Limestone units distinguished from underlying, light-gray thicken from east to west across the map rocks of Cambrian age by color contrast. area. Overall, the Muav Limestone thickens Unit thickens from 84 m (275 ft) in eastern from 185 m (600 ft) in eastern part of map part of map area to as much as 140 m (460 area to 425 m (1,400 ft) in western part ft) in western part _ba Bright Angel Shale (Middle Cambrian)— Tonto Group (Middle and Lower Cam- Green and purple-red, slope-forming silt- brian)—Includes in descending order, stone and shale and red-brown to brown Muav Limestone, Bright Angel Shale, and sandstone. Includes interbedded limestone Tapeats Sandstone as defined by Noble of the Flour Sack Member of McKee and (1922), modified by McKee and Resser Resser (1945) in upper part and ledge- (1945). For this map, all limestone and forming, red-brown sandstone member dolomite lithologies in the Cambrian in middle part. Includes interbedded, sequence are assigned to the Muav Lime- dark-green, medium- to coarse-grained, stone; all shale and siltstone lithologies to thin-bedded glauconitic sandstone; and the Bright Angel Shale; and all sandstone purplish-red and brown, thin-bedded, fine- and conglomerate lithologies to the Tapeats to coarse-grained, ripple-laminated sand-

26 27 stone in lower part. Intertonguing relations Best, M.G., McKee, E.H., and Damon, P.E., 1980, Space- produce variable thicknesses and litholo- time composition patterns of late Cenozoic mafic gies. Contact with Tapeats Sandstone is volcanism, southwestern Utah and adjoining areas: arbitrarily marked at lithologic change American Journal of Science, v. 280, p. 1035–1050. from dominantly green shale and siltstone Beus, S.S., 1990, Temple Butte Formation, in Beus, S.S., of the Bright Angel Shale to dominantly and Morales, Michael, eds., Grand Canyon geology: brown sandstone of the Tapeats Sandstone, Oxford, N.Y., Oxford University Press and Flag- generally about 10 m (30 ft) above Tapeats staff, Ariz., Museum of Northern Arizona Press, p. Sandstone cliff. Thickness, 150 m (500 ft) 107–118. _t Tapeats Sandstone (Middle and Lower(?) Billingsley, G.H., 1993, Geologic map of the Little Tanks Cambrian)—Brown and red-brown, quadrangle, northern Mohave County, Arizona: U.S. cliff-forming sandstone and conglomerate. Geological Survey Open-File Report 93–682, scale Includes an upper slope-forming transition 1:24,000, 13 p. zone of nearly equal distribution of brown ———1994, Geologic map of the Hat Knoll quadrangle, sandstone and green shale beds and lower northern Mohave County, Arizona: U.S. Geological cliff-forming sandstone and conglomeratic Survey Open-File Report 94–554, scale 1:24,000, sandstone. Lower cliff is composed mostly 14 p. of medium- to coarse-grained, thin-bedded, ———1997a, Geologic map of the Mount Logan quad- low-angle planar and trough crossbedded rangle, northern Mohave County, Arizona: U.S. sandstone and conglomeratic sandstone Geological Survey Open-File Report 97–426, scale beds 15 to 60 cm (6 to 24 in) thick. Silica 1:24,000, 21 p. cement gives appearance of quartzite. ———1997b, Geologic map of the Mount Trumbull NW Unconformable contact with underlying quadrangle, northern Mohave County, Arizona: U.S. Early Proterozoic surface forms the Great Geological Survey Open-File Report 97–488, scale Unconformity. Tapeats fills lowland areas 1:24,000, 19 p. and thins across or pinches out against Prot- ———1997c, Geologic map of the Poverty Spring erozoic highlands. Thickness, 0 to 122 m (0 quadrangle, northern Mohave county, Arizona: U.S. to 400 ft) Geological Survey Open-File Report 97-493, scale 1:24,000, 13 p. EARLY PROTEROZOIC CRYSTALLINE Billingsley, G.H., and Beus, S.S., 1999, Geology of the ROCKS Surprise Canyon Formation of the Grand Canyon, Arizona: Flagstaff, Ariz., Museum of Northern Ari- Intrusive and metamorphic rocks as defined by Ilg zona Press, Museum of Northern Arizona Bulletin and others, (1996), and Hawkins and others, (1996) 61, 254 p., 9 plates. Xgr Granite, granitic pegmatite, and aplites— Billingsley, G.H., Hamblin, K.W., Wellmeyer, J.L., and Granite plutons and stocks and pegmatite Dudash, S.L., 2001, Geologic map of part of the and aplite dikes emplaced synchronously Uinkaret Volcanic Field, Mohave County, north- with peak metamorphism. One small out- western Arizona: U.S. Geological Survey Miscel- crop in map area is at Colorado River Mile laneous Field Studies Map MF–2368, scale 1: 190 just south of Whitmore Canyon junc- 31,680; [available on the World Wide Web at http: tion with Colorado River. About 1.7–1.66 //geopubs.wr.usgs.gov/map-mf/mf2368/]. Ma (Ilg and others, 1996; Hawkins and Billingsley, G.H., and Hampton, H.M., 2000, Geo- others, 1996) logic map of the Grand Canyon 30´ x 60´ quad- rangle, Arizona: U.S. Geological Survey Geologic REFERENCES Investigations Series I–2688, scale 1:100,000, 15 p; [available on the World Wide Web at http: Beard, L.S., 1996, Paleogeography of the Horse Spring //greenwood.cr.usgs.gov/pub/i-maps/i-2688/]. Formation in relation to the Lake Mead Fault system, Billingsley, G.H., Harr, Michelle, and Wellmeyer, J.L., Virgin Mountains, Nevada and Arizona: Geological 2000, Geologic map of the upper Parashant Canyon Society of America Special Paper 303, p. 27–60. and vicinity, Mohave County, northwestern Arizona: Best, M.G., and Brimhall, W.H., 1970, Late Cenozoic U.S. Geological Survey Miscellaneous Field Studies basalt types in the western Grand Canyon region, in Map MF–2343, scale 1:31,680, 27 p. [available on Hamblin, W.K., and Best, M.G. eds., The Western the World Wide Web at http://geopubs.wr.usgs.gov/ Grand Canyon District, Guidebook to the Geology map-mf/mf2343/]. of Utah: Utah Geological Society, p. 57–74. Billingsley, G.H., and Huntoon, P.W., 1983, Geologic

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Formation; a new look, in Karlstrom, T.N.V., Swann, Lucchitta, Ivo, 1979, Late Cenozoic uplift of the south- G.A., and Eastwood, R.L., eds., Geology of northern western Colorado Plateau and adjacent lower Colo- Arizona with notes on archaeology and paleocli- rado River region: Tectonophysics, v. 61, nos. 1–3, mate: Part 1, Regional Studies: Geological Society p. 63–95. of America Rocky Mountain Section Meeting, Flag- Lucchitta, Ivo, Basdekas, P.G., Bohannon, R.G., Reick, staff, Arizona, p. 155–190. H.J., and Dehler, C.M., 1995a, Geologic map of the Reynolds, S.J., Florence, F.P., Welty, J.W., Roddy, M.S., Cane Springs quadrangle, northern Mohave County, Currier, D.A., Anderson, A.V., and Keith, S.B., 1986, Arizona: U.S. Geological Survey Open-File Report Compilation of radiometric age determinations in 95–86, scale 1:24,000. Arizona: Arizona Bureau of Mines and Geological Lucchitta, Ivo, and Beard, L.S., 1981a, Preliminary geo- Mineral Technologies, 197, 258 p. logic map of the Olaf Knolls quadrangle, Mohave Schleh, E.E., 1966, Stratigraphic section of Toroweap County, Arizona: U.S. Geological Survey Open-File and Kaibab Formations in Parashant Canyon, Ari- Report 81–1322, scale 1:24,000. zona: Arizona Geological Society Digest, v. 8, p. ———1981b, Preliminary geologic map of the Grand 57–64. Gulch Bench quadrangle, Mohave County, Arizona: Sorauf, J.E., and Billingsley, G.H., 1991, Members of the U.S. Geological Survey Open-File Report 81–1321, Toroweap and Kaibab Formations, Lower Permian, scale 1:24,000. northern Arizona and southwestern Utah: Rocky Lucchitta, Ivo, Dehler, C.M., and Basdekas, P.G., 1995b, Mountain Geologists, v. 28, no.1, p. 9–24. Geologic map of the Cane Springs Southeast quad- Stewart, J.H., Poole, F.G., and Wilson, R.F., 1972, rangle, northern Mohave County, Arizona: U.S. Stratigraphy and origin of the Triassic Moenkopi Geological Survey Open-File Report 95–48, scale Formation and related strata in the Colorado Plateau 1:24,000. region: U.S. Geological Survey Professional Paper Lucchitta, Ivo, and McKee, E.H., 1974, New geochrono- 691, 195 p. logic constraints on the history of the Colorado River Wenrich, K.J., Billingsley, G.H., and Blackerby, B.A., and its Grand Canyon [abs.]: Geological Society of 1995, Spatial migration and compositional changes America Abstracts with Programs, v. 7, p. 342. of Miocene-Quaternary magmatism in the western Martin, Harriet, and Barrick, J.E., 1999, Conodont bio- Grand Canyon: Journal of Geophysical Research, v. stratigraphy, Chapter F, in Billingsley, G.H., and 100, no. B7, p. 10417–10440. Beus, S.S., eds., Geology of the Surprise Canyon Wenrich, K.J., Billingsley, G.H., and Huntoon, P.W., Formation of the Grand Canyon, Arizona: Flagstaff, 1996, Breccia-pipe and geologic map of the north- Ariz., Museum of Northern Arizona Press, Bulletin western part of the Hualapai Indian Reservation and no. 61, p. 95–113. vicinity, Arizona: U.S. Geological Survey Geologic McKee, E.D., 1963, Nomenclature for lithologic subdivi- Investigations Series Map I–2522, 2 sheets, scale 1: sions of the Redwall Limestone, Arizona: U.S. Geo- 48,000, 16 p. logical Survey Professional Paper 475–C, p. 21–22. ———1997, Breccia-pipe and geologic map of the ———1975, The Supai Group, subdivision and nomen- northeastern part of the Hualapai Indian Reservation clature: U.S. Geological Survey Bulletin 1395–J, p. and vicinity, Arizona: U.S. Geological Survey Geo- 1–11. logic Investigations Series Map I–2440, 2 sheets, ———1982, The Supai Group of Grand Canyon: U.S. scale 1:48,000, 19 p. Geological Survey Professional Paper 1173, 504 p. Wenrich, K.J., and Huntoon, P.W., 1989, Breccia pipes McKee, E.D., and Gutschick, R.C., 1969, History of the and associated mineralization in the Grand Canyon Redwall Limestone of northern Arizona: Geological region, northern Arizona, in Elston, D.P., Billings- Society of America Memoir, v. 114, 726 p. ley, G.H., and Young, R.A., eds., Geology of Grand McKee, E.D., and Resser, C.E., 1945, Cambrian history Canyon, northern Arizona with Colorado River

28 29 guides, Lees Ferry to Pierce Ferry, Arizona: Ameri- can Geophysical Union, 28th International Geo- logical Congress Field Trips T115/T315 Guidebook, Washington D.C., p. 212–218. Young, R.A., 1999, Nomenclature and ages of Late Cre- taceous(?)—Tertiary strata in the Hualapai Plateau region, northwest Arizona, in Billingsley, G.H., Wenrich, K.J., Huntoon, P.W., and Young, R.A., Breccia pipe and geologic map of the southwestern part of the Hualapai Indian Reservation and vicin- ity, Arizona: U.S. Geological Survey Miscellaneous Investigations Series Map I–2554, 2 sheets, scale 1: 48,000, 50 p.

UNPUBLISHED DATA Billingsley, G.H., Beard, L.S., and Priest, S.S., unpub. data, Geologic map of the Grand Wash Cliffs and vicinity, Mohave County, northwestern Arizona, scale 1:31,680

30 31 APPENDIX

DIGITAL DATABASE DESCRIPTION

By

Jessica L. Wellmeyer

30 31 INTRODUCTION mtr_fold.e00 mtr_fold/ Fold axes and basal flow This map, compiled from previously published and direction arrows unpublished data and new mapping by the authors rep- pls_cov.e00 pls_cov/ Public Land Survey grid resents the general distribution of bedrock and surficial with section boundaries deposits in the Mount Trumbull quadrangle. The associ- hypso_cov.e00 hypso_cov/ Hypsography DLG ated database delineates map units that are identified by The database package also contains the following other general age and lithology following the spatial resolution export files with extraneous data used in the construction (scale) of the database to 1:100,000 or smaller. The con- of the database: tent and character of the database, as well as methods of obtaining the database, are described below. ARC/INFO Resultant Description export file File FOR THOSE WHO DONʼT USE DIGITAL GEO- geo1001.lin.e00 geo1001.lin Lineset LOGIC MAP DATABASES geo100.mrk.e00 geo100.mrk Markerset Two sets of plot files containing images of much of the wpgcmyk.shd.e00 wpgcmyk.shd Shadeset information in the database are available to those who do not use an ARC/INFO compatible Geographic Infor- geolin.lut.e00 geolin.lut Line lookup table mation System (GIS). Each set contains an image of a geomrk.lut.e00 geomrk.lut Marker lookup table geologic map sheet and the accompanying explanatory polycolor.lut.e00 polycolor.lut Color lookup table pamphlet. There is a set available in PostScript format and another in Acrobat PDF format (see sections below). PostScript Plot file Package Those who have computer capability can access the plot The second digital data package available contains the file packages online at http://geopubs.wr.usgs.gov/i-map/ PostScript images described below: i2766. Requests for a tape copy of the digital database or mtrmap.eps Encapsulated PostScript plottable plot files can be made by sending a tape with request and file containing complete map- com return address to: Database Coordinator, U.S. Geological position with geology, symbology, Survey, 345 Middlefield Road, M/S 975, Menlo Park, annotation, and base map of the CA 94025. Mount Trumbull quadrangle DATABASE CONTENTS mtrgeo.doc A Word document file of this report and the report containing detailed The digital database package consists of the geologic unit descriptions and geological in- map database and supporting data including base maps, formation, plus sources of data and map explanation, geologic description, and references. references cited A second package consists of PostScript plot files of a geologic map sheet and a pamphlet containing a geologic PDF Plot file Package description. The package contains the Adobe Acrobat (.pdf) portable Digital Database Package document format files described below: The first package is composed of geologic map database mtrmap.pdf A PDF file of the Mount Trumbull files for the Mount Trumbull quadrangle. The coverages quadrangle map sheet and their associated INFO directory have been converted mtrgeo.pdf A PDF file of this report, including into ARC/INFO export files. These export files are the full geologic report uncompressed and are easily handled and compatible with some Geographic Information Systems other than The Adobe Acrobat files were created from correspond- ARC/INFO. The export files included are: ing .eps files and are compatible with Adobe Acrobat version 3.0 and higher. ARC/INFO Resultant Description export file Coverage ACCESSING DATABASE CONTENTS mtr_anno.e00 mtr_anno/ Unit annotation, fault and ARC/INFO Export Files fold names, fault sepa- ARC export files are converted to their proper ARC/ ration values, point data INFO format using the ARC command ʻimportʼ with the and annotation option proper for the format desired. To ease conversion mtr_dip.e00 mtr_dip/ Strike and dip information and preserve naming convention, an AML is enclosed mtr_poly.e00 mtr_poly/ Faults, depositional con- that will convert all the export files in the database to tacts, and geological units coverages and graphic files and that will also create an

32 33 associated INFO directory. From the ARC command line 4 19262.079 13541.953 type: 320874.438 4041066.250 7.288 –6.551 Arc: &run import.aml 5 17083.956 2437.910 308460.563 3985836.250 4.829 11.450 ARC export files can be read by other Geographic Infor- mation Systems. Refer to your documentation for proper 6 14830.807 2423.889 procedure for retrieval of data. 297191.781 3986089.250 3.423 –3.987 7 12575.379 2417.995 PostScript and Portable Document Format Files 285922.688 3986356.750 –7.948 7.011 These files are packaged separately. PDF files come as 8 10323.882 2411.610 is and can be downloaded or copied directly to your 274653.313 3986638.750 0.547 0.516 hard drive with no conversion aside from opening the 9 8069.997 2412.013 file from Adobe Acrobat. The PostScript documents are 263383.563 3986935.250 –1.587 13.780 zipped and compressed to a smaller file size. They can be decompressed using WINZIP. 10 5817.939 2409.646 252113.484 3987246.250 5.357 –1.552 DATABASE SPECIFICS 11 3560.990 2415.001 240843.047 3987571.750 –10.735 7.888 Procedure Used 12 1320.077 5193.187 Stable-base maps were scanned at the Flagstaff U.S. 230000.109 4001781.500 6.251 –7.660 Geological Survey Field site using the Optronics 5040 raster scanner at a resolution of 50 microns (508 dpi). 13 1332.091 7967.923 The resulting raster file was in RLE format and converted 230429.297 4015651.750 17.797 –8.568 to the RLC format using the “rle2rlc” program written by 14 1339.500 10743.234 Marilyn Flynn. The RLC file was subsequently converted 230859.781 4029522.250 5.090 –6.231 to an ARC/INFO Grid in ARC/INFO. The linework was 15 3588.051 13512.951 vectorized in bulk using the ARC command gridline. A 242490.547 4043051.000 –0.453 3.888 tic file was created in lat/long and projected into the base 16 5825.796 13508.981 map projection (Transverse Mercator) using a central 253689.203 4042723.750 –8.428 5.742 meridian of –113.50W. Tics are defined in a 5-minute 17 8065.505 13507.507 grid of latitude and longitude in the geologic coverages 264887.500 4042411.250 –5.876 5.061 corresponding with quadrangle corners both in base maps and digital maps. The tic file was used to trans- 18 10305.215 13509.472 form the grid to Universal Transverse Mercator (UTM). 276085.500 4042113.000 –2.556 7.317 ARC/INFO generated a RMS report after transforming 19 12547.252 13515.253 the original grid to UTM. 287283.156 4041829.500 13.272 13.581 20 14782.670 13520.769 Scale (X,Y) = (5.003,5.001) 298480.531 4041560.500 –3.761 4.928 Skew (degrees) = (0.008) Rotation (degrees) = (–1.564) 21 17021.397 13530.592 Translation = (222692.085,3975993.211) 309677.625 4041306.250 –3.368 2.604 RMS Error (input,output) = (1.729,8.650) 22 19279.771 10768.284 320586.813 4027198.750 2.893 –7.113 Affine X = Ax + By + C 23 19298.435 7996.152 Y = Dx + Ey + F 320300.031 4013331.500 2.726 –0.373 A = 5.001 B = 0.137 C = 222692.085 D = -0.137 E = 4.999 F = 3975993.211 24 19318.081 5223.528 320014.125 3999464.500 6.529 3.529 tic id input x input y 25 17067.817 5208.030 output x output y x error y error 308763.469 3999703.500 1.223 –5.693 1 19334.976 2449.985 26 14817.261 5198.388 319729.063 3985597.750 –4.402 2.957 297512.531 3999956.750 –4.458 0.154 2 1309.199 2418.860 27 12568 .986 5189.377 229572.203 3987911.500 –0.834 –5.104 286261.281 4000224.500 1.673 –5.658 3 1349.961 13519.731 28 10318.483 5184.929 231291.531 4043393.000 6.547 1.375 275009.750 4000507.000 –2.440 —

32 33 tic id input x input y map. Descriptions of the database fields use the terms output x output y x error y error explained below: 29 8068.721 5181.342 Database Fields 263757.875 4000803.750 –2.379 — Parameter Description 30 5819.601 5185.985 252505.656 4001115.250 2.363 — Item name name of database field 31 3567.904 5187.798 Width maximum number of characters or 241253.063 4001441.250 –5.791 — digits stored 32 3574.673 7963.100 Output output width 241664.328 4015311.000 –2.483 — Type B — binary integer; F — binary 33 3580.674 10735.693 floating point number, I — ASCII 242076.828 4029180.750 –4.616 — integer, C — ASCII character string 34 5823.526 10732.584 N.dec. number of decimal places main- 253293.516 4028854.000 –4.968 — tained for floating point numbers 35 8066.975 10733.541 264509.844 4028541.750 –1.409 — LINES 36 10308.511 10733.492 The arcs are recorded as strings of vectors and described 275725.844 4028244.000 –7.235 — in the arc attribute table (AAT). They define the boundar- 37 12551.625 10736.793 ies of the map units, faults, and map boundaries in MTR_ 286941.531 4027961.000 –4.393 — POLY. These distinctions and the geologic identities of the boundaries are stored in the LTYPE field according 38 14794.358 10745.737 to their line type. 298156.906 4027692.250 –2.372 — 39 17035.413 10755.589 Arc Attribute Table Definition 309372.000 4027438.250 –8.332 — DATAFILE NAME: MTR_POLY.AAT 40 17053.446 7982.144 COLUMN ITEM NAME WIDTH OUTPUT TYPE N. DEC 309067.281 4013570.750 6.100 –3.110 1 FNODE# 4 5 B — 41 14807.019 7970.093 5 TNODE# 4 5 B — 297834.219 4013824.500 2.864 –10.371 9 LPOLY# 4 5 B — 42 12560.736 7963.444 13 RPOLY# 4 5 B — 286600.906 4014092.750 1.340 –5.149 17 LENGTH 4 12 F 3 43 10313.341 7960.335 21 MTR_POLY# 4 5 B — 275367.250 4014375.500 –4.916 3.426 25 MTR_POLY-ID 4 5 B — 44 8068.696 7956.796 39 LTYPE 35 35 C — 264133.281 4014672.750 2.836 –5.028 64 PTTYPE 35 35 C — 45 5822.617 7960.909 The AAT defined above represents the AAT in MTR_ 252898.984 4014984.500 4.792 10.468 POLY.

Lines, points, polygons, and annotation were edited DATAFILE NAME: MTR_FOLD.AAT using ARCEDIT. COLUMN ITEM NAME WIDTH OUTPUT TYPE N. DEC Following editing and annotation, the individual cover- 1 FNODE# 4 5 B — ages were projected into UTM projection. 5 TNODE# 4 5 B — 9 LPOLY# 4 5 B — Map Projection 13 RPOLY# 4 5 B — Parameter Description 17 LENGTH 4 12 F 3 Projection UTM 21 MTR_FOLD# 4 5 B — Units Meters on the ground 25 MTR_FOLD-ID 4 5 B — Zone 12 39 LTYPE 35 35 C — 64 PTTYPE 35 35 C — Datum NAD27 99 PLUNGE 3 3 I — The content of the geologic database can be described The AAT defined above represents the AAT in MTR_ in terms of the lines and the areas that compose the FOLD.

34 35 Description of AAT Item Names the PTYPE field by map label. Individual map units are Item Name Description described more fully in the accompanying text. FNODE# Starting node of the arc Polygon Attribute Table Definition TNODE# Ending node of the arc DATAFILE NAME: MTR_POLY.PAT LPOLY# Polygon to the left of the arc COLUMN ITEM NAME WIDTH OUTPUT TYPE N. DEC RPOLY# Polygon to the right of the arc LENGTH Length of the arc in meters 1 AREA 4 12 F 3 5 PERIMETER 4 12 F 3 MTR_POLY# Unique internal number 9 MTR_POLY# 4 5 B — MTR_POLY-ID Unique identification number 13 MTR_POLY-ID 4 5 B — LTYPE Line type 17 PTYPE 8 8 C — PTTYPE Point type PLUNGE Value of plunge of fold axis Description of Polygon Attribute Table Item Names The geologic line types relate to geologic line symbols in Item Name Description the line set GEO1001.LIN according to the lookup table AREA Area of polygon in square meters GEOLIN.LUT. PERIMETER Perimeter of polygon in meters Domain of Line Types recorded in LTYPE field MTR_POLY# Unique internal number MTR_POLY-ID Unique identification number MTR_POLY PTYPE Unit label contact_certain contact_river Domain of PTYPE (map units) fault_underwater Qb6588 high_angle_flt_approx Qb6646 high_angle_flt_certain _ba Pep Qb6375 Qi high_angle_flt_concealed _m Ph Qb6457 Qi1 low_angle_norm_flt_certain _t Pk Qltb Qkrb map_boundary Dtb Pt Qcbb Qkrp volcanic_mar H2O QTa Qcbi Ql MTR_FOLD M*s QTi Qcbp Qlb anticline_certain Mr Qao Qd Qlp basalt_flow_direction Ms Qay Qf Qlsb monocline_certain Pc Qb Qgo Qlsp monocline_concealed Pe Qb1 Qgy Qmrb plunging_anticline Qmrp Qv Tgg Tpi plunging_syncline Qp T2i Tgi Tpkb syncline_certain Qp1 ^c Tgl Tpki underwater_fold Qp6375 ^m Tgp Tpp Qp6457 Tao Tgr Tsb Domain of Markers recorded in PTTYPE field Qp6588 Tay Tsgb MTR_POLY Qp6646 Tb Tgx Tsgi fault_ball_fill Qpvb Tbb Ths Tsi xx Qpvp Tbi Ti Tsp Qr Teb Tmb Tv MTR_FOLD Qs Tei Tmi Tvi anticline Qgrb Tep Tmlb Twb syncline Qgrp Tg Tp6i Twi monocline Qt Tgb Tpb Xgr xx Tgc Arcs with a PTTYPE value of ʻxxʼ indicate that there is _ represents Cambrian strata, D represents Devonian no symbol attached to the arc. strata, * represents Pennsylvanian strata, P represents Permian strata, ^ represents Triassic strata, T repre- POLYGONS sents Tertiary strata, and Q represents Quaternary strata. Map units (polygons) are described in the polygon attri- Polygons were assigned colors based on their geo- bute table (PAT). This identifies the map units recorded in logic unit. The colors were assigned from the shadeset

34 35 WPGCMYK.SHD and are related to the lookup table coverage are merely leaders from a unit annotation to the POLYCOLOR.LUT related polygon. MTR_ANNO contains annotation with unit labels, fault separation, and monocline names. All POINTS annotation was in feature subclass anno.unit. Strike and dip information is recorded as coordinate data The textset used for all annotation was geofont.txt, with related information. This information is described specifically symbolset 30. Use of this textset allows for in the Point Attribute Table (PAT). ARC/INFO coverages proper symbol notation for unit symbols. The default cannot hold both point and polygon information, thus ARC/INFO textset does not allow for a proper geologic MTR_DIP has only a point attribute table, and MTR_ symbol indicating ʻTriassic.ʼ By using this alternate POLY has only a polygon attribute table. textset, the character pattern ʻ^mʼ prints instead as ^m. The only nonconventional text symbol used, was the ʻ^ʼ Point Attribute Table Definition (carat) indicating Triassic. DATAFILE NAME: HR_DIP.PAT COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC. BASE MAP PROCEDURE 1 AREA 4 12 F 3 The base map image was prepared from a Digital Line 5 PERIMETER 4 12 F 3 Graph (DLG) obtained online from the U.S. Geological 9 MTR_DIP# 4 5 B - Survey. While DLGs are available for many themes, I 13 MTR_DIP-ID 4 5 B - chose to only use hypsography and public land survey 17 PTTYPE 35 35 C - layers for the base of this map to decrease clutter and 52 DIP 3 3 I - preserve legibility of features. 55 STRIKE 3 3 I - Description of item names SPATIAL RESOLUTION Item Name Description Use of the digital geologic map database should not vio- AREA late the spatial resolution of the data. Although the digital PERIMETER form of the data removes the constraint imposed by the MTR_DIP# Unique internal number scale of a paper map, the detail and accuracy inherent in MTR_DIP-ID Unique identification number map scale are also present in the digital data. The data- PTTYPE Point type base was created and edited at a scale of 1:100,000 which DIP Dip angle in azimuth degrees means that higher resolution data is generally not pres- STRIKE Strike angle in degrees ent. Plotting at scales larger than 1:100,000 will not yield greater real detail, but may reveal fine-scale irregularities The coverage MTR_DIP contains strike and dip data below the intended resolution. and other pertinent structural data represented by point symbology, including collapses, sinkholes, and domes. OTHER FILES MTR_FOLD and MTR_POLY have point types defined in the AAT, which correspond with the defined linetype The lineset used to display the appropriate line weight for an arc. These point types are related to the lookup and symbology is GEO1001.LIN. It is related to the table GEOMRK.LUT and are from the symbolset database by a lookup table called GEOLIN.LUT. Simi- GEO.MRK. larly, the markerset for this database is GEO100.MRK, and its lookup table is GEOMRK.LUT. Colors in Domain of PTTYPE the polygon coverage (MTR_POLY) are assigned bedding based on the PTYPE and were chosen from a shade- exposed_breccia_pipe set called WPGCMYK.SHD and a lookup table dome POLYCOLOR.LUT. Annotation (unit labels, text labels, probable_breccia_pipe and printed numerical values) was displayed using a font sinkhole entitled GEOFONT.TXT which has capabilities for dis- vertical_joint playing proper notation of geologic text symbols. volcanic_vent Also enclosed in the database package is MTR.MET, the FGDC standard metadata for the database and ANNOTATION MTR.REV, a revision list with current information on the The coverage MTR_ANNO is strictly annotation to the status of all files in the database. polygon coverage. It is defined somewhat differently from the fold, polygon, and dip coverages. The arc attribute table is of negligible importance. Arcs in this

36