U.S. DEPARTMENT OF THE INTERIOR TO ACCOMPANY MAP I-2628 U.S. GEOLOGICAL SURVEY Version 1.0

GEOLOGIC MAP OF THE LITTLEFIELD 30' x 60' QUADRANGLE, MOHAVE COUNTY, NORTHWESTERN ARIZONA By George H. Billingsley and Jeremiah B. Workman

INTRODUCTION 10 km north of the north-central part of the map and are the largest settlements near the map area. This map is one result of the U.S. Geological Survey's Interstate Highway 15 and U.S. Highway 91 provide intent to provide geologic map coverage and a better under­ access to the northwest corner of the map area, and Arizona standing of the transition in regional geology between the State Highway 389 provides access to the northeast corner. Basin and Range and Colorado Plateaus in southeastern Ne­ Access to the rest of the map area is by dirt roads maintained vada, southwestern Utah, and northwestern Arizona. Infor­ by the U.S. Bureau of Land Management, Arizona Strip Dis­ mation gained from this regional study provides a better trict, St. George, Utah. The area is largely managed by the understanding of the tectonic and magmatic evolution of an U.S. Bureau of Land Management, the Arizona Strip Dis­ area of extreme contrasts in late Mesozoic-early Tertiary trict, which includes sections of land controlled by the State compression, Cenozoic magmatism, and Cenozoic extension. of Arizona. There are several isolated sections of privately This map is a synthesis of 32 new geologic maps encom­ owned lands, mainly near the communities of Littlefield, passing the Littlefield 30' x 60' quadrangle, Arizona. Geo­ Beaver Dam, and Colorado City. If traveling in this area, logic information presented in this map and report may aid always take plenty of extra water and food; and two spare future land management decisions about land use, flood con­ tires are recommended. trol, and environmental and range management programs for Elevations range from 2,442 m (8,012 ft) at Hancock federal, state, and private agencies. Peak of Mount Bangs, Virgin Mountains, in the northwest The Littlefield 30' x 60' quadrangle encompasses ap­ corner of the map, to 506 m (1,660 ft) at the Virgin River, at proximately 3,100 km2 (1,937 mF) of northwestern Arizona. the northwest edge of the map. The Colorado Plateau region The map area is bordered on the north by the Utah-Arizona averages about 1,525 m (5,000 ft) in elevation. state line and is approximately 5 km east of the Nevada­ Most of the drainages on the Colorado Plateau and those Arizona state line (see map). The quadrangle is bounded by on the west and north slopes of the Virgin Mountains flow long 113° to 114° and lat 36°30' to 37°. The east three-quar­ northward into the Virgin River. Drainages on the east and ters of the map area is within the southwestern part of the south slopes of the Virgin Mountains, the Grand Wash Trough Colorado Plateaus province (herein referred to as the Colo­ area, and the west edge of the Colorado Plateau drain south­ rado Plateau), and the west quarter is within the Basin and ward to the Colorado River. Range province. The Basin and Range is locally subdivided Compilation of this map is from new geologic mapping into three physiographic areas; the Mesquite Basin, the Vir­ by Bohannon (1991, 1992), Bohannon and others (1991), gin Mountains, and the Grand Wash Trough (fig. 1, on map Bohannon and Lucchitta (1991 ), Lucchitta and others (1995a, sheet). The Colorado Plateau is subdivided into three physi­ b), Billingsley ( 1990a, b, c, d; 1991 a, b, c, d; 1992a, b, c, d; ographic areas; the St. George Basin, the Shivwits Plateau, 1993a, b, c, d, e, f; 1994a, b, c, d, e, f, g; 1995), and Billingsley and the Uinkaret Plateau (fig. 1, on map sheet). The St. and Bohannon (1995). Geologic maps of the Grand Canyon, George Basin is part of the transition zone between the Colo­ about 30 km south of this quadrangle, are available (Huntoon rado Plateau and the Basin and Range that extends north­ and others, 1981; Billingsley and Huntoon, 1983; Wenrich ward into Utah. The arbitrary boundary between the Basin and others, 1997; and Billingsley 1997a, b, c). and Range, the transition zone, and the Colorado Plateau is based on physiographic, geologic, and topographic relations GEOLOGIC SETTING (Stokes, 1977; Billingsley, 1993g). Settlements within the map area include small commu­ The map area is characterized by gently dipping Paleo­ nities of less than 250 people at Littlefield and Beaver Dam, zoic and Mesozoic strata for much of the Colorado Plateau, Arizona, in the northwest corner of the map; Mt. Trumbull and structurally deformed Paleozoic, Mesozoic, and Ceno­ (locally known as Bundyville ), in the south-central part of zoic strata in the Basin and Range. Proterozoic crystalline map; and Colorado City, Arizona, a community of over 5,000 and metamorphic rocks overlain by Paleozoic, Mesozoic, and people, in the northeast corner of the map. Hilldale, Utah, Cenozoic strata are exposed only in the Virgin Mountain area. lies adjacent to Colorado City on the north side of the Utah­ The map area is in a transitional setting between the Arizona state line. St. George and Hurricane, Utah, are about miogeosynclinal section of rocks to the west, in the south- eastern Great Basin, and the platform sequence of rocks in (Billingsley, 1993g, unpub. data a). Compressional folding the Colorado Plateau to the east; overall, the area displays and regional uplift began in Late Cretaceous and early Ter­ an east-to-west facies change and westward thickening of tiary time (Huntoon, 1990), causing erosion from the Pale­ strata. The stratigraphic nomenclature established for rocks ocene(?) through early Pliocene time. Basaltic deposition of the Colorado Plateau, chiefly in southern Utah and the began during the late Pliocene(?) and continued through Pleis­ Grand Canyon region of Arizona, differs from that used in tocene time. During the late Pliocene(?) and Pleistocene, east­ the southern Great Basin. For this quadrangle, nomenclature west extension produced several normal faults that form from both provinces is used, but most nomenclature reflects west-facing fault scarps, such as the Hurricane Cliffs. In that of the Grand Canyon region because of stratigraphic simi­ addition, several horst-and-graben structures have offset Paleo­ larities and closer proximity to Grand Canyon type localities. zoic and Mesozoic strata, forming north-south structurally The Virgin River and its tributaries have dissected the controlled valleys (Billingsley, unpub. data a, b, c, d, e). northern part of the map area exposing about 2,555 m of Small monoclines and relatively short, doubly-plunging Paleozoic strata, about 2,300 m of Mesozoic strata, and about anticlines and synclines on the Colorado Plateau have gen­ 300 m of Cenozoic strata. The Triassic, Jurassic, and parts erally northerly strikes. of the Cretaceous sections once covered the entire map area, The Hurricane Fault, whose fault scarp forms the Hur­ but have been largely eroded, except where preserved under ricane Cliffs, separates the lower Shivwits Plateau from the late Tertiary and Quaternary basalt flows. The highland higher Uinkaret Plateau. The maximum displacement along areas of the Colorado Plateau are capped by Tertiary the Hurricane Fault is about 850 m at the north edge of the basalts that form tabletop mountains such as Black Rock, map, decreasing southward to about 510 m near the middle Wolf Hole, and Seegmiller Mountains. Tertiary basalt flows of the map, then increasing to more than 670 m at the south that flowed southward make up widespread deposits in the edge of the map (Billingsley, unpub. data a, b). Strata on the Grand Wash Trough area. Quaternary basalt flows on the down thrown side of the Hurricane Fault dip toward the fault Uinkaret Plateau in the southeast quarter of the map area, plane as much as 20 degrees at some locations. The increase are a remnant of the Pleistocene landform in this area. in dip toward the Hurricane Fault is considered by Hamblin The oldest basalts are in the Grand Wash Trough and ( 1965) to be reverse drag flexures associated with movement generally range from 6 to 4 million years in age. The young­ along the fault. Huntoon ( 1990) believes the Hurricane est basalts are in the Uinkaret Volcanic Field on the Fault overlies deep-seated reverse faults that folded the Uinkaret Plateau and are generally less then 850,000 years strata up-to-the-west during Late Cretaceous and Early Ter­ in age (fig. 1, on map sheet). In general, the basalts young tiary time producing a monoclinal flexure along the fault. from west to east across the map area. None of the basalt The reverse drag scenario is adopted for this map. flows are tilted, but many have been faulted. Most of the Equal offset of the 3.6±0.18 Ma Bundyville basalt Tertiary and Quaternary basalt deposits overlie slightly tilted (Billingsley, 1997a) and underlying Mesozoic strata along strata, forming an angular unconformity. the Hurricane Fault, 13 km south of this map area, indicate Quaternary stream deposits, wind deposits, and collu­ that extension along the Hurricane Fault began after deposi­ vial surficial deposits cover much of the landscape. Thick tion of the basalt. Approximately 380 m of the offset oc­ deposits of gypsum and gypsiferous siltstone and mudstone curred before the basalt flow from Moriah Knoll cascaded within the landslide deposits are easily removed by solution. over the Hurricane Cliffs. The basalt flow has since been The landslide masses containing these rocks on steep slopes offset 130m during the last 850,000 years (Billingsley, 1994f, beneath the basalt-capped mountains are unstable in wet con­ unpub. data d). ditions. Fractures and small land-failure faults, too small to On the Colorado Plateau area of this map, several ma­ show at this map scale, have developed in the basalt rims jor and minor faults offset Tertiary and Quaternary basalt above landslides, especially on the east slopes where slip­ flows, as young as 1.6 Ma (Dutchman Draw Fault, northeast page is facilitated along east-dipping strata. Landslides date part of map), equally as much as underlying strata. Several from drainage incision, probably from the early Pleistocene, younger Quaternary basalts are cut by faults, but are not off­ and continue intermittently to the present. Gypsum, a com­ set as much as the underlying strata, which suggests that most, mon mineral in the bedrock of the Colorado Plateau area, is of not all of the faults on the Shivwits and Uinkaret Plateaus largely responsible for the failure of several earthen dams on probably became active about 3.5 to 2 million years ago. All the plateau through dissolution. major and several minor faults on the Colorado Plateau show minor displacement of Quaternary alluvial deposits STRUCTURAL GEOLOGY (Billingsley, 1993g, 1994g, unpub. data a, b, c, d, e). A recent magnitude 5.6 earthquake southeast of St. George, Utah, High-angle to nearly-vertical normal faults in gently September 1993 (Billingsley, unpub. data a; Pearthree, P.A., tilted strata are the characteristic structures found on the and Wallace, T.C., 1992), indicates that tectonic activity con­ Shivwits and Uinkaret Plateaus (Billingsley, 1994g, unpub. tinues today. data a, b, c, d, e). Folds are common in the St. George Basin

2 In the Basin and Range, Late Cretaceous and early for economic deposits of copper and uranium oxide miner­ Tertiary compression resulted in major_ folding, reverse fault­ als; whereas, the shallow structures are unlikely to be miner­ ing, and thrust faulting that produced the Virgin Mountains. alized (Wenrich, 1985). This tectonism initiated a period of erosion and deposition The Hidden Mines are located on a breccia pipe in the in Paleocene(?), Oligocene, and early Miocene time. East­ Hermit Formation in Hidden Canyon (sec. 16, T. 36 N., R.13 west extension during the late Miocene began to form the W). The mine tailings contain copper minerals, but no pro­ Mesquite Basin, the Grand Wash Trough, and the Grand Wash duction records are available. Minor amounts of uranium Cliffs (Hintze, 1986; Bohannon and others, 1993). were reported in samples from cores drilled in 1982 by Path­ The Grand Wash Fault, whose fault scarp forms the finder Mines (oral commun., 1991 ). There are two small cop­ Grand Wash Cliffs, separates the Basin and Range province per prospects on the Colorado Plateau within the map area. from the Colorado Plateau province. Movement along the The prospect on the Shivwits Plateau (sec. 13, T. 38 N., Rs. Grand Wash Fault began in the early or middle Miocene 8 and 9 W.; Billingsley, 1994b) is associated with a breccia (Bohannon and others, 1993). Hobble Graben, a 240-m-deep pipe. The prospect on the Uinkaret Plateau (sec. 31, T. 38 structure near the Grand Wash Cliffs, formed as part of the N., R.10W.; Billingsley, 1993c) is not associated with a brec­ associated extension of the Grand Wash Trough. Hobble cia pipe. Copper may have been hauled from the prospects, Graben deepens and widens near its junction with the Grand but no production records are available. Wash Fault, and its northwest strike aligns with the West Thick-bedded gypsum occurs in the Toroweap and Branch segment of the Grand Wash Fault system. Kaibab Formations. Gypsum is being mined from the Har­ Offset along the Grand Wash Fault is very small in the risburg Member of the Kaibab Formation about 5 km south vicinity of Black Rock Mountain but increases both north­ of Interstate Highway 15, north-central edge of the map area ward and southward. Total offset is as much as 3,000 m near (sec. 25, T. 41 N., R. 13 W.). Also a thick pocket-of gypsum the Colorado River, south of this map area (Lucchitta, 1979), occurs within the upper Callville Formation and and about 1,100 m at the north edge of the map area. At Queantoweap Sandstone north of the Virgin River (north­ Black Rock Mountain, the displacement along the structure west corner of the map). A few quarries for sandstone are has been transferred to the West Branch Fault that splays operated intermittently on Lost Spring Mountain (northeast westward from the Grand Wash Fault and the Sullivans quarter of the map). Canyon Fault. Strata between the West Branch and Gypsum dissolution in the Harrisburg Member of the Sullivans Canyon Faults and the Grand Wash Fault are Kaibab Formation has resulted in small sinkholes and caves nearly flat-lying. where the unit is exposed on the Colorado Plateau. The sink­ The Piedmont Fault (Moore, 1972) separates the Virgin holes are most common in the northern part of the Shivwits Mountains from the Mesquite Basin and is mostly buried by Plateau. The karst is Holocene and perhaps Pleistocene in alluvial deposits. The fault trace can be observed as small age, because young alluvium partly fills many of the depres­ fault scarps in the alluvial fans along the lower slopes of the sions and several depressions occur within alluviated val­ Virgin Mountains. The total offset along the Piedmont Fault leys (Billingsley, 1993g, 1994g, unpub. data a, b, c, d, e). is as much as 6 km (Bohannon and others, 1993). Circular collapse structures, minor folds, and other sur­ ACKNOWLEDGMENTS face irregularities on the Colorado Plateau are due to disso­ lution of gypsum and gypsiferous siltstone not only in the This map is a product of several geologists that have Kaibab, but also in the Toroweap and the lower part of the worked in the area and contributed their expertise and hard Moenkopi Formations. Some bowl-shaped depressions in the work as indicated on the map as sources of geologic data. Kaibab Formation, characterized by inward-dipping strata, We are especially grateful to the following individuals for may be the surface expressions of collapse-formed breccia their advice, revisions, and information: Brian Atwater, L. pipes originating from dissolution of the deeply buried Mis­ Sue Beard, Bruce H. Bryant, Clay M. Conway, Gary L. sissippian Redwall Limestone (Wenrich and Huntoon, 1989). Dixon, Wendell Duffield, Donald P. Elston, DaveS. Harwood, Such features were not observed in the Basin and Range part James G. Honey, King N. Huber, Angela Jayko, Jonathan C. of the map. Matti, David M. Miller, Paul Stone, Victoria Todd, Wesley Suspected breccia pipes have inward dipping strata and A. Ward, Gordon Weir, Van S. Williams, Peter W. Huntoon, are marked on the map by a dot and the letter C. Some deep­ and Charles W. Barnes. Special thanks for technical support seated breccia pipes are known to be overlain by gypsum go to Tony Bryant, Kelly Burke, Thomas W. Judkins, Marjorie collapse features related to thinning by dissolution of gyp­ Maclachlan, Carol Ostergren, Susan Priest, Dale Russell, sum within the Woods Ranch Member of the Toroweap For­ Kathryn Thompson, Charles L. Powell, II, Kathy Nimz, and mation (Wenrich and others, 1997). However, breccia pipes Jan L. Zigler. cannot be distinguished with certainty from shallow collapse structures on the plateaus caused by the dissolution of gyp­ sum. The deep-seated collapse structures are potential hosts

3 DESCRIPTION OF MAP UNITS light-red, very fine grained to fine-grained, well-sorted sand sheets and small dunes SURFICIAL DEPOSITS on bedrock surfaces in upper Grand Wash Trough area; sand locally derived from Qs Stream-channel alluvium (Holocene )-Uncon­ outcrops of the rocks of the Grand Wash solidated, unsorted, interlensing clay, silt, Trough (Tgw) and the Navajo Sandstone sand, and pebble to boulder gravel. (JRn). On Colorado Plateau, consists of Intertongues or overlaps flood-plain (Qt), white and light-red, fine-grained, well­ upper part of valley-fill (Qv), young allu­ sorted quartz sand derived locally from vial fan (Qay), and talus (Qt) deposits. Inset stream-channel (Qs) deposits that form to young. and old terrace-gravel (Qgy and small climbing dunes, sand sheets, or levee Qgo) deposits and old alluvial fan (Qao) dunes along banks of Short Creek, northeast deposits. Stream channels subject to high­ corner of map area; commonly stabilized energy debris flows and flash floods. Little by grass. Only active sand sheets and dunes or no vegetation in stream channels, except shown; thin sand deposits stabilized by veg­ a few salt cedar (tamarisk) trees. Estimated etation not mapped. Sand sheets and dunes thickness 3 to 6 m formed by regional southwesterly winds. Qf Floodplain deposits (Holocene)-ln Basin and Thickness ranges from 1 to 5 m Range area, gray to brown, interbedded, Ott Travertine deposits (Holocene and Pleis­ silt, sand, and pebble to boulder gravel tocene?)-Gray, porous, thin-bedded, along Beaver Dam Wash and Virgin River; freshwater, calcium carbonate deposit. unconsolidated, subject to frequent channel Weathers to rough pitted surface. Derived erosion; deposits shown are from 1976 from warm spring outlets along east bank aerial photo interpretation along Beaver of Virgin River at and near Interstate Dam Wash and Virgin River. On Colorado Highway 15 bridge, northwest corner of Plateau, mostly gray, interbedded silt and map area. Locally includes silt, sand, sand; locally contains cinder and basalt pebbles, and cobbles derived from fragments near basaltic areas, partly con­ sheetwash erosion of pediment calcrete solidated or cemented by gypsum and (Qpc) and young alluvial fan (Qay) sedi­ calcite. Intertongues or overlapped by ments. Includes encrustation of local roots stream-channel (Qs), dune sand (Qd), young and leaves preserved as modern fossils. alluvial fan (Qay), and talus (Qt) depos­ Forms cliff or resistant bench. Thickness its. Forms flat surface, as opposed to gently is 1 to 4 m sloping valley-fill areas, because subject Qc Colluvial deposits (Holocene and Pleis­ to frequent low-energy flooding or ponding. tocene?)-Colorado Plateau area, north­ No vegetation in local dry lake basins; east quarter of map, consists of two types: sparsely vegetated by growths of sagebrush, ( 1) ponded deposits associated with en­ cactus, and rabbitbrush. Thickest depos­ closed depressions on basalt flow surfaces, its are on Colorado Plateau, central area sinkhole depressions on the Harrisburg of map along Sullivan and Main Street Member (Pkh) of the Kaibab Formation, Grabens and base of Hurricane Cliffs. or enclosed depressions caused by land­ Thickness ranges from 1 to 10 m slide blocks and (2) deposits associated Qd Dune sand and sand sheet deposits (Holocene)­ with extensive sheetwash alluvium over In Basin and Range, light-reddish-orange, bedrock. In basalt flow, sinkhole, and very fine grained to fine-grained, well-sorted landslide areas, contain white to gray silt, sand sheets and small complex dunes on fine-grained sand, and black to reddish, pediment calcrete (Qpc) surfaces west of fine-grained cinder, scoria, and basalt clasts; Virgin River; forms falling dunes along locally consolidated by gypsum and cal­ west bank of Beaver Dam Wash and Virgin cite cement. Similar to floodplain (Qf) de­ River; sand locally derived from outcrops posits but generally not associated with of the Muddy Creek Formation (Tmc). drainages. Subject to frequent ponding. Sup­ Forms white, very fine grained to fine­ ports sparse growths of grass. Sheetwash grained, well-sorted sand sheets and small deposits near Colorado City, Arizona (at dunes in Virgin River floodplain areas in northeast corner of map area) consist of dry season (not shown on map). Includes pale-red, tan, and brown, fine-grained sand,

4 silt, and gravel; partly cemented by gyp­ regions, intertongues with stream-channel sum and clay; locally contains boulders (Qs), young alluvial terrace (Qgy), flood­ of the Shinarump Member (ics) of the plain (Qf), talus (Qt), upper part of val­ Chinle Formation as much as 2m india­ ley-fill (Qv), and older alluvial fan (Qao) meter. Clay content greatest near outcrops deposits near their downslope ends. Subject of the Petrified Forest Member (icp) of to erosion by flash floods, debris flows, the Chinle Formation near Colorado City and sheetwash. Sparsely vegetated by area. Lag gravel forms thin desert pave­ creosote bush, cactus, grass, and sagebrush ment on colluvial surface south and west below the 5,000-ft elevation; moderately of the Shinarump Member outcrop. Lag vegetated by sagebrush, pinion pine, and gravel consists of numerous black, brown, juniper trees above 5,000 ft. Estimated yellow, red, and gray, very well rounded range of thickness about 3 to 24 m quartzite and chert pebbles, 1 to 5 em in Qv Valley-fill alluvial deposits (Holocene and diameter, and occasional rounded, gray­ Pleistocene)-Gray and light-brown clay, white petrified wood fragments, all derived silt, sand, and lenses of pebble to small from the Shinarump Member (ics) of the boulder gravel; partly consolidated. Chinle Formation. Locally includes inte­ Intertongues or overlapped by young allu­ grated, poorly defined, windblown, sand­ vial fan (Qay), talus (Qt), and stream-channel sheet deposits (not mapped). Overlapped (Qs) deposits. Subject to low-energy by young alluvial fan (Qay) and upper part sheetwash flooding; larger valleys on of valley-fill (Qv) deposits. Approximately Colorado Plateau often cut by arroyos, some 1 to 12 m thick as deep as 11 m. Where major valley-fill Qgy Young alluvial terrace deposits (Holocene and deposits are cut by deep arroyos, alluvium Pleistocene?)-On Colorado Plateau, un­ no longer accumulates and valley-fill consolidated to partly consolidated, light­ alluvium is classified as young alluvial brown, pale-red, and gray silt, sand, and terrace (Qgy) deposit. On Colorado Pla­ pebble to boulder gravel composed equally teau, thickly vegetated by sagebrush, cactus, of well-rounded, limestone, sandstone, and and grass; no trees. In Basin and Range, basalt clasts. Similar lithology in Basin and sparsely vegetated by cactus, creosote bush, Range except clasts dominated by meta­ grass, and some mesquite and catclaw trees. morphic and igneous rock types west of Thickest deposits are on Colorado Plateau; Virgin Mountains. Commonly intertongues estimated overall thickness, 3 to 18 m or overlapped by stream-channel (Qs), Qt Talus deposits (Holocene and Pleistocene)­ floodplain (Qf), valley-fill (Qv), young U nsorted breccia debris composed of sand, alluvial fan (Qay), and talus (Qt) depos­ gravel, and small to large angular blocks its. Subject to high-energy flooding or ero­ of local bedrock on steep to moderately sion. Forms bench about 1 to 3 m above steep slopes. Locally includes boulders as modern stream beds in Basin and Range large as 3 m in diameter. Includes silt, sand, area and about 1 to 9 ·m above modern and gravel partly cemented with gypsum stream beds on Colorado Plateau area. and calcite. Intertongues with younger Moderately vegetated by grass, cactus, and (Qay) and older alluvial fan (Qao), valley­ creosote bush below 5,000 ft elevation and fill (Qv), young (Qgy) and old alluvial terrace by sagebrush, cactus, grass, and pinion pine (Qgo), and landslide (QI) deposits. Supports or juniper trees at higher elevations. sparse growtli of sagebrush, cactus, grass, Thickness, 1 to 10 m and creosote bush below 5,000 ft; includes Qay Young alluvial fan deposits (Holocene and some juniper and pinion trees at higher Pleistocene?)-On Colorado Plateau, un­ elevations. Only extensive deposits shown. consolidated and unsorted clay, silt, and As much as 9 m thick sand; contains gravel lenses of subangular Ql Landslide deposits (Holocene and Pleistocene)­ to rounded pebbles and boulders of basalt, Unconsolidated masses of unsorted rock chert, limestone, and sandstone. In Basin debris. On Colorado Plateau, includes de­ and Range, similar lithologies to Colorado tached blocks of strata that have rotated Plateau but include abundant clasts of meta­ backward and slid downslope as loose in­ morphic and igneous rocks that are partly coherent masses of broken rock and de­ cemented by gypsum and calcite. In both formed strata, often partly surrounded by

5 talus. Found principally below basalt flows yellowish-brown to light-gray, moderately of several basalt-capped mountains and sorted, massive to thin-bedded, cliff­ buttes and often includes strata of the forming siltstone and sandstone. Includes Moenkopi Formation. In Basin and Range thick beds or nodules of white caliche and area, locally found along Beaver Dam Wash caliche-cemented siltstone that produces and Virgin River and isolated areas of lighter-tone surface on aerial photographs. Virgin Mountains. Supports growth of Unit locally covered by dune sand (Qd). sagebrush, cactus, grass, and creosote bush Exposed caliche nodules at surface are below 5,000 ft; some pinion and juniper deeply pitted or etched by solution weath­ trees at higher elevations. Unstable when ering. Generally forms flat to gently sloping wet, especially below basalt-capped moun­ surfaces, locally tilted as much as 4 o east; tains on Colorado Plateau. Minor rockfalls dissection is variable; surfaces are locally or landslides not shown; mapped areas are faulted. Surfaces are subject to modern potential rockfall or landslide hazard areas. sheetwash flow and local flooding. Base Thickness ranges from 3 to 22 m of unit generally forms low, angular, un­ Qao Older alluvial fan deposits (Holocene(?) and conformable contact with the underlying Pleistocene )-On Colorado Plateau, similar Muddy Creek Formation (Tmc). Generally to younger alluvial fan deposits (Qay), but less than 5 m thick basalt clasts are dominant lithology and Qgo Older alluvial terrace deposits (Holocene(?) often coated with desert varnish. Forms and Pleistocene)-Similar to younger conspicuous bench or tableland about 20 alluvial terrace deposits (Qgy), but forms to 50 m above younger alluvial fan deposits terraces 6 to 12 m above stream-channel and forms protective caprock over nonre­ (Qs) or valley-fill (Qv) deposits along sistant beds of the Kaibab and Moenkopi tributary drainages on Colorado Plateau, Formations. Partly cemented with gypsum and about 25 to 90 m above stream-channel and calcite. Merges with talus (Qt), younger (Qs) deposits along Virgin River and alluvial fan (Qay), or landslide (QI) de­ Beaver Dam Wash in Basin and Range area. posits. Deposits at base of Hurricane Cliffs Composed of well-rounded clasts of chert, are locally faulted as much as 12 m along limestone, sandstone, quartzite, basalt, and Hurricane Fault. In Basin and Range, simi­ metamorphic clasts; quartzite and basalt lar lithologies as young alluvial fan (Qay) clasts are common in uppermost terraces deposits; has yellowish, smooth, lighter­ of Colorado Plateau and igneous and tone surface texture on aerial photos metamorphic clasts common in Basin and because of thick soil development; partly Range area; unit commonly cemented by consolidated by calcite cement. Clasts are calcite and gypsum. Merges with and often dominated by metamorphic and granitic covered by local talus (Qt) or young al­ rocks west of Virgin Mountains; basalt luvial fan (Qay) deposits. Alluvial terraces clasts common east of Virgin Mountains. 67 to 73 m above alluvial fan deposits, Locally, deposits are faulted as much as south of Interstate Highway15 Black Rock 18 m along Piedmont Fault, west side of Interchange, contain quartzite clasts from Virgin Mountains. Regionally, surface Utah that show that an ancestral Virgin clasts have well developed desert varnish; River flowed west along a course marked clasts within deposit have coating of approximately by Interstate Highway 15. caliche. Partly overlapped by younger Thickest deposits are along Virgin River alluvial fan (Qay) and active stream (Qs) and Beaver Dam Wash area, northwest deposits on upper slopes. Strongly incised quarter of map. Thickness, 2 to 14 m and eroded by arroyos that contribute Ta Old alluvium (Pleistocene and Pliocene)-In material to younger alluvial fans at Basin and Range, Grand Wash Trough area, downslope ends. Sparsely vegetated by southwest corner of map area; consists of creosote bush, sagebrush, cactus, and grass silt, sand, pebbles, cobbles, and boulders in all regions. Thickness ranges from 9 to in widespread, sheetlike deposits that 50 m formed on pediment surfaces; strongly Ope Pediment calcrete (Holocene(?) and Pleis­ dissected by modern erosion. Poorly sorted tocene)-Mesquite Basin area of Basin and to moderately sorted, angular to subrounded Range, northwest corner of map area. Pale- constituents as large as several meters in

6 diameter; unconsolidated (Bohannon, VOLCANIC ROCKS 1991). Includes-isolated deposits on gently sloping surfaces of basalt flows (Tb) as Young basalts, undivided (Pieistocene)-On much as 140m above modern stream beds. Colorado Plateau, includes basalt flows and Supports moderate growth of desert veg­ dikes at Black Knolls (Uinkaret Plateau), etation, mainly grass. Includes light-brown flows and numerous dikes just north· of East to medium-orange-brown, medium- to Mesa (St. George Basin), and flows in the fine-grained, poorly sorted sandstone and Little Black Mountain area (St. George siltstone intrabasaltic sediments that may Basin). Whole rock K-Ar age ranges from be, in part, equivalent to but indistinguish­ 0.58±0.30 Ma at Black Knolls to 1. 7±0.4 able from upper part of the Muddy Creek Ma at Little Black Mountain (Billingsley, Formation (Tmc); contains scattered pebbles unpub. data a) of basalt, as much as 30 em in diameter, Qj Intrusive dikes (Pieistocene)-Dark-gray, and pebbles of black and white chert, finely crystalline, olivine alkali basaltic metavolcanic rocks, and sandstone. Thick­ dikes in most areas; black andesitic ba­ ness of intrabasaltic sediments as much as salt with augite, olivine, and plagioclase 90 m (Lucchitta and others, 1995a, b), but phenocrysts in others. X-ray fluorescence averages about 50 m. On Colorado Pla­ spectrography shows phenocrysts of augite teau, includes two separate deposits: (1) and olivine; groundmass composed mainly Shivwits Plateau between Hobble Graben of plagioclase, augite, glass, and olivine and Sullivan Draw, central part of map area (Wenrich and others, 1995). Dikes are not (Billingsley, 1994g) and (2) Uinkaret Pla­ found at Little Black Mountain. Dikes teau between Cottonwood Canyon and commonly vertical; widths range from 0.3 Clayhole Wash, northeast-central part of to 1 m and protrude 0.2 to 2m above local map area (Billingsley, unpub. data c). surfaces. All dikes are generally aligned Shivwits Plateau deposits are light-brown, parallel to vertical and subvertical bedrock unconsolidated silt, sand, and gravel. joints. This unit includes dikes at Black Contains white chert and limestone locally Knolls and 6.5 km southeast of Black derived from the Kaibab Formation and Knolls, a dike southwest of Moriah Knoll, sparse, well-rounded basalt and quartzite dikes associated with the Sage Basalt (Qsp pebbles as much as 4.8 em in diameter and and Qsb), the basalt of Hat Knoll (Qhp rare petrified wood clasts from the and Qhb ), and the basalt of Seven Knolls Shinarump Member of the Chinle Forma­ (Qskp and Qskb) of the Uinkaret Plateau, tion. Basalt source may be Diamond Butte east and southeast quarter of the map area. (K-Ar age 4.3±0.6 Ma; Billingsley, unpub. Includes numerous dikes and necks near data b) or Poverty Mountain just south of unnamed buttes north of and at East Mesa this map area (K-Ar age 4.7±0.26 Ma; Best in St. George Basin, north-central part of and others, 1980). Thickness ranges from map, that are generally not physically con­ 1.5 to 15 m. Uinkaret Plateau deposits are nected to, but locally associated with, light-gray, unconsolidated silt, sand, gravel, nearby basalt flows and pyroclastic depos­ and numerous pebbles. Contains black, its. Includes dikes on and near West Mesa brown, and yellow, well-rounded chert and (north-central part of map) and dikes quartzite pebbles and rare petrified wood associated with the Little Tanks Basalt (Qip pebbles, all averaging less than 2.4 em in and Qlb ), Shivwits Plateau, south-central diameter; derived from the Shinarump edge of map area Member ("Res) of the Chinle Formation. Qb Basalt flows (Pieistocene)-Dark-gray, finely Deposits occupy ancestral Clayhole Wash crystalline to glassy groundmass of alkali drainage that is now abandoned due to olivine basalt. Contains olivine, augite, and headward erosion from Rock Canyon area plagioclase phenocrysts. Typically consists and stream capture of Clayhole Wash from of one flow on top of two unnamed buttes Cottonwood Canyon (Billingsley, 1992d). north of East Mesa and west of the Hurri­ Thickness about 1 to 3 m cane Cliffs, St. George Basin, north-central part of map; one flow at and south of Little Black Mountain west of Washington Fault, St. George Basin, north-central edge of

7 map; and one flow at Black Knolls, Qsp Pyroclastic deposits-Reddish-black and red Uinkaret Plateau, northeast quarter of map glassy fragments and scoriaceous ejecta, area. Flows vary from 1 m thick at Black cinders, and bombs; partly consolidated. Knolls to about 10m thick at Little Black Includes two 24-m-high pyroclastic cones, Mountain and less than 15 m thick at at the southeast corner of this map, and unnamed buttes north of East Mesa two cones 134 and 97 m high, 0.3 and 3 Cave Basalt (Pieistocene)-lnformally intro­ km respectively, south of the southeast duced by Billingsley ( 1994e, unpub. data corner of this map; the highest cone has d), and formally named here for numer­ the Sage triangulation station on top. The ous sinkhole depressions in the basalt flow four cones of the Sage Basalt are aligned north of .Toroweap Valley, the type area, in a north-south trend and are offset by Uinkaret Plateau, northern Mohave County, the Toroweap Fault as much at 26m down Arizona. One of the sinkholes is labeled to the west (southeast corner of this map). "cave" on the USGS Hat Knoll quadrangle, Offset of the underlying Kaibab Forma­ southeast corner of this map (sec. 33, T. tion by the Toroweap Fault is about 67 m 37 N., R. 7 W.). Unit consists of five un­ down to the west named pyroclastic cones and thin lava flows Qsb Basalt flows-Dark-gray to black alkali oli­ that coalesced and flowed north towards vine basalt, vuggy with calcite fillings; Clayhole Wash and partly south to altered olivine in glassy groundmass. The Toroweap Valley just south of the southeast lava flowed out in a radial pattern from corner of this map area. Sinkholes in the each cone, but most of the basalts flowed Cave Basalt are as much as 20 m deep. north and west about 0.5 to 2.4 km into A whole-rock K-Ar age of 0.63±0.24 Ma the upper reaches of Toroweap Valley. was obtained by Jackson (1990a, b) from Overlies the Harrisburg Member (Pkh) of the Sage Basalt (Qsb) about 3 km south the Kaibab Formation of the southeast corner of the map. Divided Undivided basalt (Pieistocene)-Dark-gray oli­ into: vine basalt, southeast edge of map. Includes Qcp Pyroclastic deposits-Red and reddish-black basalt flows and associated pyroclastic basaltic scoria and cinder deposits; partly cones of Pugh Knoll and Spencer Knoll, consolidated. Forms five pyroclastic cones southeast corner of map area (Billingsley, 30 to 135 m tall that align in a north-south 1994e). Deposits are assumed to be Pleis­ trend tocene age because of similar composition Qcb Basalt flows-Dark-gray, finely crystalline and stratigraphic position to other volca­ to glassy alkali olivine basalt. Contains nic rocks in the Uinkaret Volcanic Field. abundant olivine phenocrysts 0.25 to 1 mm Lava flowed in northerly directions similar in diameter. Most of the flows advanced to other nearby basalt flows in this part northward down unnamed drainages and of map area. Divided into: wrapped around the south and east sides Qup Pyroclastic deposits-Reddish-black to black of the basalt pad of Hat Knoll, extending and brown, basaltic, scoriaceous cinder about 15 km into Cabin Valley and deposits. Forms Spencer Knoll, a 113-m­ Clayhole Valley. Numerous sinkhole high pyroclastic cone, and Pugh Knoll, a depressions in the Cave Basalt are the result 60-m-high cone at the southeast edge of of solution of gypsum in the underlying map area Harrisburg Member (Pkh) of the Kaibab Qub Basalt flows-Dark-gray, finely crystalline, Formation. Ranges from 1 to 25 m thick alkali olivine basalt; fine-grained ground­ Sage Basalt (Pieistocene)-Named for a trian­ mass of plagioclase, olivine, augite, and gulation point labeled "Sage" on top of glass. Olivine is the most common con­ a 134-m-high pyroclastic cone 1 km south stituent in flows. Basalt overlies strata of of the southeast corner of this map near the Harrisburg Member (Pkh) of the Kaibab the upper reaches of Toroweap Valley (just Formation and the lower red member (Rml) south of the map), the type area, Kanab of the Moenkopi Formation. Numerous lava Plateau, northern Mohave County, Arizona flows, which flowed mostly in a northerly (USGS Mount Trumbull NE 7 .5' quad­ direction, originate from Pugh Knoll and rangle, sec. 26, T. 36 N., R. 7 W). Divided other unnamed volcanoes south of this map into: area. At Spencer Knoll, lava flowed in a

8 radial pattern about 1.5 km from Spencer from different pyroclastic cones that have Knoll. ·About 1 to 50 m thick coalesced into one thick flow that spread Antelope Knoll Basalt (Pleistocene)-Named out in a radial pattern from Seven Knolls for Antelope Knoll, a pyroclastic cone 140 cones; most of the basalt flowed east and m high that forms a prominent landmark north into an ancestral Clayhole Valley east of the Hurricane Cliffs on the Uinkaret drainage area. Flow surfaces partly cov­ Plateau; type area for the Antelope Knoll ered by pyroclastic deposits (Qskp) within Basalt, sees. 13, 18, 19, and 24, T. 38 N., 2 km of cones. Forms protective caprock Rs. 8 and 9 W., northern Mohave county, called Seven Knolls Bench that overlies Arizona. K-Ar age is 0.83±0.28 Ma gently east-dipping strata of middle and (Billingsley, 1994c, unpub. data c, d). lower part of the Harrisburg Member (Pkh) Divided into: of the Kaibab Formation, and the lower Qap Pyroclastic deposits-Reddish-black and red member ("Rml) and Virgin Limestone brown cinder and scoria deposits similar Member ("Rmv) of the Moenkopi Forma­ in composition to Antelope Knoll Basalt. tion. Flows range from 2 to 40 m thick Includes glass fragments, augite, and olivine Basalt of Hat Knoll (Pieistocene)-lnformally phenocrysts. Partly consolidated as welded named for Hat Knoll, a 132-m-high pyro­ tuff and scoria. Forms rounded cinder cone cl~stic cone near Clayhole Valley (sec. 20, of Antelope Knoll about 140 m thick T. 37 N., R. 7 W.), Uinkaret Volcanic Field, Qab Basalt flows-Dark-gray, finely crystalline, northern Mohave County, Arizona (Billingsley, alkali basalt; glassy groundmass. X-ray 1994e, unpub. data d). Divided into: fluorescence spectrography shows sparse Qhp Pyroclastic deposits-Red to reddish-brown, phenocrysts of olivine in groundmass domi­ basaltic scoria and cinder deposits; partly nated by plagioclase, augite, and glass consolidated. Overlies basalt flows of Hat (Wenrich and others, 1995). Flow surfaces Knoll, the middle red member ("Rmm) and are p_artly covered by pyroclastic depos­ the Virgin Limestone Member ("Rmv) of its (Qap) within 1 to 2 km of Antelope the Moenkopi Formation. Forms the promi­ Knoll. Overlies thin alluvium of tributaries nent 132m high cinder cone of Hat Knoll to Clayhole Wash (outcrops too small to Qhb Basalt flows-Dark-gray, finely crystalline, show at this map scale), the Harrisburg alkali olivine basalt. Contains abundant Member (Pkh) of the Kaibab Formation, olivine and plagioclase phenocrysts 1 to and the Timpoweap Member ("Rmt) and 5 mm in diameter. Includes a small ba­ lower red member ("Rml) of the Moenkopi salt flow on the north and west sides of Formation. Basalts flowed east, then north Hat Knoll. Majority of the basalt flowed as far as 17 km down ancestral tributary east about 2.4 km. Basalt surface partly to Clayhole Wash drainage. Ranges from covered by pyroclastic deposits (Qhp) near 2 to 15 m thick Hat Knoll. Basalt overlies gently east­ Basalt of Seven Knolls (Pieistocene)-lnfor­ dipping strata of the middle red member mally named for Seven Knolls, an align­ ("Rmm), the Virgin Limestone Member ment of seven pyroclastic cones, including ("Rmv), and the lower red member ("Rml) three more unnamed cones and Deadman of the Moenkopi Formation. Thickness, 4 Knoll (sees. 10, 15, 23, and 26, T. 37 N., to 60 m R. 8 W.; Billingsley, 1994c, unpub. data d). Basalt of Maryland Knoll (Pieistocene)-ln­ Divided into: formally named for Maryland Knoll, a 92- Qskp Pyroclastic deposits-Reddish-brown and m-high pyroclastic cone about 4 km south black, basaltic scoria and cinder depos­ of Antelope Knoll, the type area in the its. Includes about 14 cinder cones or vent Uinkaret Volcanic Field, northern Mohave areas that form a small range of pyroclastic County, Arizona (sec. 31, T. 38 N., R. 8 cones aligned parallel to subvertical bed­ W.). Includes two vent areas and associ­ rock joint system oriented N. 10° W. ated basalt flows (Billingsley, 1994f, unpub. Ranges from 30 to 76 m thick data d). Divided into: Qskb Basalt flows-Dark-gray, finely crystalline Qmkp Pyroclastic deposits-Red-brown and black basalt. Groundmass composed of plagioclase, basaltic scoria, glass, and cinders; uncon­ olivine, and augite; contains small phe­ solidated. Forms pyroclastic cone of Mary­ nocrysts of olivine. Includes several flows land Knoll and small unnamed cone 0.3

9 km southeast of Maryland Knoll. About Craigs Knolls. Divided into: 92 m thick Qcbp Pyroclastic deposits-Gray and reddish-gray Qmkb Basalt flows-Dark-gray, finely crystalline to black cinder, tuff, ash, and scoriaceous basalt composed of plagioclase, olivine, ejecta; partly consolidated. Overlies as­ and augite groundmass with olivine phe­ sociated basalt flow. Thickness is about nocrysts. Includes two pyroclastic vents 115m at Berry Knoll and 183m at Craigs that are 0.3 km apart and two basalt flows Knoll that flowed eastward to coalesce into one Qcbb Basalt flows-Light-gray and dark-gray, al- flow. Flow shares common boundary with kali-olivine basalt and andesite(?). Basalt or abuts against Antelope Knoll Basalt flows that radiate out from Berry Knoll (Qab); appears to be partly overlain by the and Craigs Knoll appear to have erupted basalt of Seven Knolls (Qskb). Surface is simultaneously because the flows coalesced partly covered by pyroclastic deposits into one general flow mass between both (Qmkp) near Maryland Knoll. Overlies the vent areas. Basalt from Berry Knoll flowed Harrisburg Member (Pkh) of the Kaibab north about 2 km joining with basalt flows Formation. Flows extend about 3 km east from Craigs Knoll. South of this map area, of Maryland Knoll. Thickness, 2 to 20m lavas from Craigs Knoll flowed about 8 Basalt of Moriah Knoll (Pieistocene)-Infor­ km north and northeast down drainages mally named for Moriah Knoll, a 122-m­ eroded into the Harrisburg Member (Pkh) high pyroclastic and basaltic cone in of the Kaibab Formation; may overlie the Uinkaret Volcanic Field (sees. 7, 12, 18, lower red member (liml) of the Moenkopi and 13, T. 37 N., Rs. 8 and 9 W.), north­ Formation in some areas south of this map. ern Mohave county, Arizona, about 3.5 km Variable thickness, 3 to 20 m east of Hurricane Cliffs (Billingsley, 1994f, Little Tanks Basalt (Pieistocene)-Named for unpub. data d). Divided into: Little Tanks Reservoir, sec. 5, T. 36 N., Omp Pyroclastic deposits-Red-brown and reddish- R. 10 W ., the type area, northern Mohave black scoria, glass, and cinder deposits; County, Arizona, south-central part of map unconsolidated. Includes thin, vesicular area (Billingsley, 1993e). K-Ar whole-rock basalt flows in lower part (thickness age is 1.0±0.4 Ma (Billingsley, unpub. data unknown); forms Moriah Knoll pyrocla~tic b). Divided into: cone. As much as 92 m thick Qlp Pyroclastic deposits-Red-brown and black Qmb Basalt flow-Dark-gray to black, fine-grained, fragments of angular basaltic scoria de­ vesicular alkali basalt. Includes sparse, posits. Includes augite and olivine phenoc­ small phenocrysts of olivine and augite in rysts; unconsolidated. Forms unnamed groundmass dominated by plagioclase, pyroclastic cone. As much as 40 m thick augite, and glass. Vesicles commonly filled Qlb Basalt flow-Dark-gray, finely crystalline, with calcite. Basalt is only flow in northern olivine basalt. Groundmass composed of Uinkaret Volcanic Field that flowed over plagioclase, olivine, and augite. Includes the Hurricane Cliffs and Hurricane Fault. two areas of basalt flows that radiate out Offset of basalt by the Hurricane Fault is from dikes or vent areas. Flow surfaces 130 m; offset of underlying Paleozoic strata partly covered by pyroclastic (Qip) deposits. prior to the flow is 380 m. Ranges from Overlies the Harrisburg Member (Pkh) of about 3 to 30 m thick the Kaibab Formation, the lower red Craigs Knoll/Berry Knoll basalt (Pieis­ member (Rml) and the Virgin Limestone tocene)-Informally named from Craigs Member (limv) of the Moenkopi Forma­ Knoll just south of this map about 5 km tion, and older alluvial fan (Qao) depos­ (sec. 4, T. 35 N., R. 8 W.), and Berry Knoll, its. Averages about 6 m thick southeast edge of this map (sec. 24, T. 36 East Mesa Basalt (Pieistocene)-Named for N., R. 9 W.), the type area, Uinkaret East Mesa, a narrow north-south-trending Plateau, northern Mohave County, Arizona mesa on Shivwits Plateau near St. George (Billingsley, 1994f, 1997b). Includes dikes, Basin, north-central part of map area, sec. pyroclastic deposits, and basalt flows that 31, T. 41 N., R. 10 W., the type area, appear to have erupted simultaneously at northern Mohave County, Arizona. K-Ar Craigs Knoll, Berry Knoll, and another age is 1.4±0.25 Ma (Billingsley, 1992c, unnamed cinder cone between Berry and unpub. data a). Divided into:

10 Qep Pyroclastic deposits-Red-brown cinder and Mountain (Billingsley, 1994g). In Basin scoria and dark-gray- to black, angular, and Range, includes basalt flows defined glassy basalt fragments; unconsolidated. by Bohannon and others (1991), Bohannon Forms pyroclastic cones as much as 50 m and Lucchitta (1991), Bohannon (1992), thick and Lucchitta and others (1995a, b), mainly Qeb Basalt flows-Dark-gray, finely crystalline in Grand Wash Trough area. K-Ar whole­ to glassy basalt; massive. Surface of basalt rock ages of basalt flows in Grand Wash partly covered with fine-grained calcar­ Trough area are 4.7±0.18 Ma, 5.45±1.11 eous silt deposits and red-brown pyroclastic Ma, and 6.87±0.20 Ma (Reynolds and (Qep) deposits near vent areas. Overlies others, 1986). K-Ar ages of 6.85 Ma on thin alluvium (not shown on map), and the flows 10 km south of map area in Grand Shnabkaib Member C~ms), middle red Wash Trough and 3.8 to 3.79 Ma on flows member ("Rmm), and Virgin Limestone 50 km south of map area at Sandy Point, Member ("Rmv) of the Moenkopi Forma­ Lake Mead, and Grand Wash Bay area tion. Basalt flowed mostly in northwest- reported by Damon and others ( 1978) erly direction. Basalt and underlying strata Ti Intrusive dikes-Dark-gray, finely crystalline, offset 97 m by the Dutchman Draw Fault olivine or andesitic basalt; plagioclase laths at north end of flow. Variable thickness, and glassy groundmass; vesicular. Weathers 9 to 55 m blue-gray, crumbly. Often eroded to present West Mesa Basalt (Pieistocene)-Named for erosion surface. On Colorado Plateau, dikes West Mesa, a narrow north-trending mesa are on Black Rock Mountain,- south of on the Shivwits Plateau south of St. George Black Rock Mountain, and southwest of Basin, north-central part of map area, sec. Mustang Knoll (central part of map area). 19, T. 40 N., R. 10 W., the type area, In Basin and Range, includes numerous northern Mohave County, Arizona. K-Ar dikes between Black Rock and Mud Moun­ age is 1.6±0.3 Ma (Billingsley, 1992c, tain in the upper Grand Wash Trough area unpub. data a). Divided into: Tb Basalt flows-On Colorado Plateau, dark-gray, Qwp Pyroclastic deposits-Red-brown to black, finely crystalline olivine basalt or andesitic angular, glassy fragments of basalt and basalt; plagioclase laths in glassy ground­ scoria. Includes two small basaltic deposits mass; columnar joints at base. Approximately about 1. 7 km south of the main basalt flows 48 m thick at Mustang Knoll and 36 m thick and pyroclastic deposits on West Mesa. Forms at nearby unnamed knoll. Source of flows pyroclastic cones as much as 60 m thick may be from Black Rock Mountain, but Qwb Basalt flows-Dark-gray basalt; finely crys- intrusive dikes located 1 to 2 km southwest talline groundmass. Consists of one or two of Mustang Knoll and unnamed knoll may flows with large columnar joints at base be source area. In Basin and Range, medium­ in some areas. Overlies the Virgin Lime­ to dark-gray, finely crystalline olivine ba­ stone Member ("Rmv), the lower red member salt; plagioclase laths in glassy groundmass; ("Rml), and the Timpoweap Member ("Rmt) olivine crystals as much as 4 mm in diam­ of the Moenkopi Formation, the Harris­ eter; vesicular. Includes upper and lower burg Member (Pkh) of the Kaibab Forma­ basalt flows of Mud Mountain (Lucchitta tion, and young alluvial fan (Qay) deposits. and others, 1995a, b). Forms single flow or, Main flows radiate out from two large and in places, as many as 10 flows locally as one small pyroclastic vent areas; most of thick as 10 m each. Thickness ranges from the basalt flowed northwest. Includes two 1.5 m to as much as 150 m small isolated basalt flows, dikes, and Tbp Pyroclastic deposits-Red-brown, angular, pyroclastic deposits 1. 7 km south of south olivine basalt fragments; unconsolidated. end of West Mesa. Base of flow is about Associated with volcanic vent areas, over­ 36 m lower than base of the East Mesa lies basalt flows south of Mud Mountain Basalt, which is about 1 km north. Thick- in Grand Wash Trough area. Thickness ness ranges from 1 to 35 m ranges from 15 to 24 m Older basalts, undivided (Piiocene)-On Colo­ Seegmiller Mountain Basalt (Piiocene)­ rado Plateau, includes basalt capping Mus­ Named for Seegmiller Mountain, northern tang Knoll and nearby unnamed knoll, Mohave County, Arizona, sec. 31, T. 40 Shivwits Plateau, south of Black Rock N., R. 11 W., the type area, northern

11 Mohave County, Arizona (Billingsley, 1990c; flows form resistant caprock over less re­ unpub. data a). K-Ar age is 2.35±0.31 and sistant beds of the Chinle, Moenkopi, and 2.44±0.51 Ma (Reynolds and others, 1986). Kaibab Formations. Basalt flows in northern Divided into: part of Wolf Hole Mountain flowed in Tsp Pyroclastic deposits-Red and black, sco­ northerly direction. Ranges from 15 to 114 riaceous cinder and ash deposits. Forms m thick one pyroclastic cone capped by basalt in Black Rock Canyon Basalt (Pliocene)-For­ central part of Seegmiller Mountain, a small mally named for Black Rock Canyon of pyroclastic cone on east edge of mountain Hurricane Wash, Shivwits Plateau, northern along Main Street Fault, and a small area Mohave County, Arizona (sec. 33, T. 41 near ven! along Washington Fault north N., R. 10 W.). K-Ar age is 3.5±0.6 Ma of Seegmiller Mountain. Includes interbedded (Billingsley, 1994b, unpub. data a) pyroclastic deposits between basalt flows Tbrb Basalt flow(s)-Dark-gray, finely crystalline, near vent areas. Variable thickness as much alkali olivine basalt; glassy groundmass. as 30m Contains sparse olivine phenocrysts. Source Tsb Basalt flow-Dark-gray, finely crystalline of flow(s) not certain, but probably near olivine and augite basalt. Surfaces are summit of bench mark labeled "Butte" on blocky and partly covered with caliche, USGS Lizard Point 7 .5' quadrangle, valley-fill (Qv), alluvial fan (Qay), and Mohave County, Arizona (elevation 5,104 pyroclastic (Tsp) deposits. Overlies lower ft), west of Black Rock Canyon (north­ part of the Shnabkaib Member ("Rms) of east quarter of map area). Basalt overlies the Moenkopi Formation at south end of east-dipping strata of the Shinarump ("Res) Seegmiller Mountain, upper part of the and Petrified Forest Members ("Rep) of the Shnabkaib at north end. Basalt offset same Chinle Formation along the Hurricane amount as underlying strata as much as Monocline. Basalt flowed east and appears 50 to 70 m by the Main Street Fault and to have stopped against Hurricane Cliffs as much as 60 to 70 m by the Washing­ fault scarp, then flowed north down ton Fault. Consists of several flows from Hurricane Wash. Most of basalt flow is 30 m to as much as 60 m thick severely distorted by landslides. Average Wolf Hole Mountain Basalt (Piiocene)-Named thickness, about 8 m for Wolf Hole Mountain, the type area, Hobble basalt (Pliocene)-lnformally named northern Mohave County, Arizona, sec. 8, from Hobble Canyon, the type area, Shivwits T. 39 N., R. 12 W. K-Ar age is 3.1±0.4 Plateau, northern Mohave County, Arizona, Ma (Billingsley, 1993g). Divided into: sec. 8, T. 37 N., R. 13 W. K-Ar age is Twp Pyroclastic deposits-Red-brown, glassy, cin­ 3.6±0.54 Ma (Billingsley, 1991d, 1994g) ders, scoria, and basaltic ribbon fragments; Thb Basalt flow-Dark-Gray, finely crystalline, oli- unconsolidated. Forms 60-m-high cone vine basalt. Source of flow is large dike Twb Basalt flows-Dark-gray, finely crystalline just west of Hobble Canyon drainage in olivine basalt. Surfaces are blocky. Includes Hobble Graben, sec. 4, T. 37 N., R. 13 W. basalt flows of Mokaac Mountain, a north­ (southwest quarter of map area). Flow erly extension of Wolf Hole Mountain. erupted through the Shnabkaib Member Basalt sources probably erupted simulta­ ("Rms), and probably part of the upper red neously from 12 vent areas that encom­ member ("Rmu) of the Moenkopi Forma­ pass Wolf Hole and Mokaac Mountains. tion in Hobble Graben, then flowed south­ Basalt flows overlain by thin alluvial west from and out of Hobble Graben onto valley-fill (Qv) deposits that accumulated the lower red member ("Rml) of the in relatively flat drainage areas; valley­ Moenkopi Formation and the Harrisburg fill alluvium, containing calcrete-cemented Member (Pkh) of the Kaibab Formation. silt, sand, and angular fragments of ba­ Basalt flowed down ancestral Jump Can­ salt, as much as 3 m thick at some loca­ yon drainage towards Grand Wash Cliffs tions; also overlain by pyroclastic deposits (Billingsley, 1994g). About 9 m thick on Wolf Hole Mountain. Alluvial mate­ Black Rock Mountain Basalt (Piiocene)­ rial may have a wind-transported origin, Named for Black Rock Mountain, the type while stream erosion accumulated mate­ area, Shivwits Plateau, northern Mohave rials into shallow drainage valleys. Basalt County, Arizona, sec. 12, T. 39 N., R. 14

12 W. (northwest quarter of map area). K-Ar upper Moenkopi rocks preserved east of age is 3.7±0.6 Ma (Billingsley, 1990a, Hurricane Cliffs. Source of flow unknown, 1993g) assumed to have originated from local Tbb Basalt flows-Dark-gray, finely crystalline, feeder dikes at Diamond Butte now cov­ olivine basalt flows. Matrix is andesine­ ered by landslide and talus debris. About labradorite laths, clinopyroxene, oxides, 30 m thick and olivine. Includes associated thinly scat­ tered red pyroclastic deposits near vent SEDIMENTARY ROCKS areas (not mapped) and intrusive dikes near top of Black Rock Mountain. On Colorado Sedimentary rocks of the Grand Wash Trough plateau, east half of Black Rock Moun­ and Mesquite Basin (Pleistocene and tain, basalt flowed northward towards Low Miocene)-Commonly referred to as the Mountain and the Virgin River canyon Muddy Creek Formation (Tmc) in the descending 550 m in 13 km, a gradient of Mesquite Basin part of map area. Com­ 42 m/km; at south end of Black Rock monly referred to as rocks of the Grand Mountain, flows descended eastward 457 Wash Trough in the grand Wash Trough m in 7 km, a gradient of 65 m/km. Ba­ area (Tgw). In the Mesquite Basin, north­ salt forms north sloping unconformable west corner of map, Muddy Creek Forma­ caprock over the Shinarump Member ("Res) tion (Tmc) includes all sedimentary rocks of the Chinle Formation at southern part below pediment calcrete {Qpc) deposits of Black Rock Mountain, transcending all (Billingsley, 1995; Billingsley and members of the Moenkopi Formation to Bohannon, 1995). In Grand Wash Trough, the Fossil Mountain Member (Pkf) of the rocks of the Grand Wash Trough (Tgw) Kaibab Formation. In Basin and Range, include sediments deposited in closed west half of Black Rock Mountain, basalt basins not connected to the Muddy Creek flowed southwestward down a valley along Formation type section and all sedimen­ east side of Virgin Mountains over vari­ tary rocks beneath lowest basalt flows (Tb ous rock strata from the Miocene rocks of and Tbb) and above the Rainbow Gardens the Grand Wash Trough to the Permian Member (Thrl, Thrt, and Thrc) of the Horse Kaibab Formation. Basalt descended 915 Spring Formation (Bohannon, 1991; Beard, m in 32 km, a gradient of 46 m/km. Ba­ 1996) salt flows are offset by faulting on Colo­ Tmc Muddy Creek Formation-In Mesquite rado Plateau, but not in Basin and Range. Basin, Muddy Creek consists of pinkish­ Numerous basalt flows range from 3 to 100 red, gray, and white, fine-grained, thinly m thick laminated, thick- to thin-bedded, calcar­ Basalt of Diamond Butte (Piiocene)-lnfor­ eous, gypsifereous, slope-forming sand­ mally named for Diamond Butte, the type stone and siltstone interbedded with area, Shivwits Plateau, northern Mohave localized calcrete soil zones and locally County, Arizona, south-central part of map includes channel lenses of thin-bedded, area (sec. 33, T. 37 N., R. 10 W.). Includes medium- to coarse-grained, low-angle basalt flow on Twin Butte about 4 km east cross-stratified sandstone. Calcrete beds, of Diamond Butte. K-Ar whole-rock age 1 to 2 m thick contain carbonate nodules is 4.3±0.6 Ma (Billingsley, 1993f, unpub. as large as 20 em in diameter. Locally data b). Divided into: includes unsorted, thick beds of cross-strati­ Tdb Basalt flow-Dark-gray, massive, finely crys­ fied quartzite conglomerate and coarse­ talline, olivine basalt. Groundmass con­ gained sandstone of multicolored, very well tains sparse olivine phenocrysts. Consists rounded chert, quartzite, limestone, and of one, possibly two flows, that forms dolomite cobbles and pebbles. Along Virgin caprock for Diamond and Twin Buttes; flow River and Beaver Dam Wash, includes at Diamond Butte overlies beveled beds dark-gray to brown, cliff-forming conglom­ of the lower part of the upper red mem­ erate, gravel, and sandstone; poorly sorted, ber ("Rmu) of the Moenkopi Formation and moderately well bedded. Clasts composed beveled beds of upper part of the upper of reddish-brown, brown, red, grayish­ red member at Twin Butte. Basalt flowed green, and light-green, well-rounded rhyo­ east over east-dipping strata; no basalt or lite, black schist, gneiss, gabbro, diorite,

13 red pegmatite, granite, white quartz, gray Thrt Tuffaceous limestone and sandstone unit- limestone and dolomite, red sandstone, and Green to white tuffaceous, cliff-forming dark-gray basalt. Boulders as large as 43 limestone and crystalline limestone em in diameter; contains calcite cement. interbedded with green to light-brown, Unconformably overlies or intertongues ledge-forming calcareous sandstone and with fine-grained sediments of the Muddy tuffaceous sandstone and slope-forming Creek white claystone. Unit is nonmarine and Tgw Rocks of the Grand Wash Trough (informal airfall-tuff beds are rare. Tuffaceous lime­ name)-Composed of a lower conglom­ stone beds are 2- to 50-cm thick; calcar­ erate facies and an upper sandstone and eous sandstone and tuffaceous sandstone siltstone facies, undivided. Lower conglom­ beds are 0.5 to 1 m thick; laminated erate facies consists of a light-gray and claystone beds are 1 to 5 m thick; claystone brown, ledge and slope-forming conglom­ beds more common in upper part. Sand­ erate; poorly sorted, poorly bedded. Clasts stone is conglomeratic in places with small, locally derived from Virgin Mountain area rounded clasts of chert, quartzite, and of Proterozoic gneiss and Paleozoic car­ carbonate fragments (probably Paleozoic) bonate rocks. Intercalated with sandstone in carbonate matrix. Unconformable contact and siltstone facies. Variable thickness, with underlying conglomerate unit. 50 to conglomerate may be locally as thick as 100 m thick 600 min subsurface. Upper sandstone and Thrc Conglomerate unit-Brown and red-brown, siltstone facies consists of pinkish-red to nonmarine, cliff-forming, well-sorted con­ orange-red, slope-forming sandstone, silt­ glomerate. Bedding is poorly defined and stone, and minor amounts of conglomer­ discontinuous. Clasts are subrounded to ate. Sandstone is medium- to fine-grained, subangular cobbles and pebbles from 1 to gypsifereous, silty and clayey carbonate 70 em in diameter. Conglomerate is clast matrix. Conglomerate beds contain small supported in sandy, calcareous matrix. subrounded to angular clasts of Protero­ Unconformable contact with the Willow zoic crystalline rocks; clasts are well sorted, Tank Formation (Kwt). 3 to 50 m thick matrix supported, and commonly found on Kwt Willow Tank Formation (Lower Cretaceous)- crossbed surfaces. Upper sandstone and Outcrops in Grand Wash Trough, east flank siltstone facies thickness ranges from 0 to of Virgin Mountains, Basin and Range. 450 m, thickening southeastward. Rocks Red, gray, brown, and tan, nonmarine of the Grand Wash Trough unconformably claystone, siltstone, sandstone, and con­ overlie members of the Horse Spring glomerate. Conglomerate occurs mostly at Formation as an angular unconformity base as discontinuous unit, but also oc­ (Beard, 1996). About 62 m exposed along curs throughout formation in small amounts. Virgin River Named the Jacobs Ranch Formation by Rainbow Gardens Member of the Horse Moore ( 1972), but called the Willow Tank Spring Formation (Miocene)-Named the Formation by Bohannon (1991) because Cottonwood Wash Formation by Moore of its close lithologic similarity to the (1972), but because these rocks have close Willow Tank Formation in North Muddy lithologic and stratigraphic similarity to Mountains, 60 km west of this map. area the Rainbow Gardens Member of the in southern Nevada (Longwell, 1949). Horse Spring Formation, this usage is fol­ Unconformable contact with the underlying lowed herein as used by Bohannon ( 1984 ). Navajo Sandstone. About 60 m thick Divided into: J'Rn Navajo Sandstone (Jurassic and Triassic?)- Thrl Limestone unit-Pale-brown, pinkish-white, Outcrops in Grand Wash Trough, east flank and light-gray, medium- to coarse-grained, of Virgin Mountains, Basin and Range. Red thin- to medium-bedded, crystalline, cliff­ and less commonly pale-yellow to white, forming limestone and intraformational cliff-forming, fine-grained, well-sorted, limestone breccia; nonmarine, lacustrine. quartz arenite sandstone; eolian. Discon­ Wavy, parallel, and continuous beds about tinuous, nonparallel beds with large-scale 0.1 to I m thick. Gradational contact with (as much as 10 m thick) planar cross­ underlying Tuffaceous limestone unit. stratification. Sand grains are frosted, very About 75 to 100 m thick well rounded quartz. Correlative with, and

14 lithologically identical to, the Aztec Sand­ or channel-fill troughs of pebbles and cobbles stone of southeastern Nevada. Gradational composed of well-rounded quartzite, black and intertonguing contact with the under­ metamorphic clasts, and chert in coarse­ lying Kayenta and Moenave Formations, grained sandstone matrix. About 30 percent arbitrary map boundary. About 850 to 1,100 of clasts are black, well-rounded quartzite m thick or chert. Includes flat-bedded and medium­ "R Km Kayenta and Moenave Formations, undivided trough cross-bedding sets of medium-grained (Upper Triassic?)-Outcrops in upper sandstone and conglomerate. Includes Grand Wash Trough of Basin and Range, petrified wood fragments and logs. Uncon­ and north of this map in St. George Basin formable contact with the underlying upper area. Upper part is the Kayenta Formation; red member ("Rmu) of the Moenkopi For­ red, fine-grained, thick-bedded, very well mation, fills erosional channels as much sorted, ledge- and slope-forming sandstone as 5 m deep. Unit mined for natural stone and siltstone. Includes large-scale cross­ in quarries, for "picture stone" in upper stratification sets similar to that of the Na­ part. Picture stone is light-red to brown, vajo Sandstone; interbedded with thin-bedded, coarse-grained, cross-bedded, sandstone fine-grained sandstone and red siltstone. that contains prominent red and black iron­ Gradational and arbitrary contact between stained Liese gang banding. Variable thick­ the Kayenta and Moenave Formations. ness as channel fill, thickest at Lost Spring Lower part is the Moenave Formation; brick Mountain, where it forms resistant caprock red and dark-red, fine-grained, well-sorted, of Lost Spring Mountain (northeast corner slope-forming sandstone and siltstone. Low­ of map). Thickness ranges from 0 to 55 m angle cross-stratification common in sand­ Moenkopi Formation (Middle? and Lower Tri­ stone beds. Gradational contact with the assic)-Divided into, in descending order, underlying Chinle Formation, arbitrary map the upper red, Shnabkaib, middle red, Vir­ boundary placed at top of first white car­ gin Limestone, lower red, and Timpoweap bonate beds or purple siltstone beds of the Members as used by Stewart and others Chinle. Combined thickness about 170m ( 1972). Boundary between Middle? and Chinle Formation (Upper Triassic)-Includes, Lower Triassic lies within the upper red in descending order, the Petrified Forest member (Morales, 1987). Formation as a and Shinarump Members as used by Stewart whole gradually thickens northwesterly and others ( 1972). Outcrops mapped in across map area. Divided into: Black Rock and Virgin Mountain area of "Rmu Upper red member (Middle? and Lower Basin and Range and north edge of map Triassic)-Heterogeneous sequence of in St. George Basin and Uinkaret Plateau cliff- and slope-forming red conglomer­ of Colorado Plateau. Divided into: ate, sandstone, siltstone, mudstone, and "Rep Petrified Forest Member-White, blue-gray, minor gray gypsum. Erosional unconformity green-gray, pale-red, and purple-red, slope­ at bottom of lowest red sandstone cliff forming mudstone, siltstone, and coarse­ (middle part of unit) at Lost Spring grained sandstone. Contains bentonitic clays Mountain has relief as much as 2 m and derived from decomposition of volcanic may represent boundary between Middle ash. Only lower part of unit is exposed in and Lower Triassic (not shown on map). map area (northeast corner). Mostly covered Most complete and thickest exposure is by stream-channel alluvium (Qs ), dune sand at Lost Spring Mountain (northeast cor­ (Qd), floodplain (Qf), young alluvial ter­ ner of map), limited exposure elsewhere race (Qgy), and colluvial (Qc) deposits. due to erosion and landslide-debris cover Unconformable contact with the underlying such as at Black Rock, Wolf Hole, cliff-forming Shinarump Member; locally Seegmiller, and Little Black Mountains fills channels eroded into the Shinarump (north-central part of map). Arbitrary Member. About 60 m thick contact with the underlying Shnabkaib "Res Shinarump Member-Orange-brown, Member placed in slope at top of high­ black, tan, cliff-forming, cross-stratified est thick white siltstone and dolomite bed to massive-bedded, coarse-grained, pebble of the Shnabkaib. Top of unit beveled by conglomerate and conglomeratic sandstone. erosion. Unit thickens from about 30 m, Weathers brown or black. Includes lenses southwestern part of map, to about 73 m

15 at Lost Spring Mountain area stone, gray limestone, green mudstone, and "Rms Shnabkaib Member (Lower Triassic)­ brown platy calcarenite. Basal limestone Interbedded and intertonguing, white, light­ bed contains abundant small echinoderm gray, laminated, slope-forming, aphanitic columnals with star shaped interiors and dolomite, silty gypsum, and red siltstone. small, poorly preserved brachiopods in top Includes red, thin-bedded mudstone, silt­ part of bed, and fossil algae in next two stone, and sandstone beds in lower and upper limestone beds. Limestone beds upper part. Exposed locally below late thickest at north edge of map, thinning to Pliocene basalt-capped mountains in north­ two limestone beds at south edge of map. central part of map and at Lost Spring Lowest limestone bed is thickestand most MountaiQ.. Gradational contact with the extensive in map area. Unconformable middle red member placed at base of lowest contact with the lower red member. Lowest bed of white or light-gray dolomitic lime­ limestone bed thickens and thins as part stone or gypsiferous siltstone of the of channel fill cut into the lower red Shnabkaib Member. Thickness variable member as much as 3 m deep in north­ because of arbitrary contacts; regionally east quarter of map area. Unit as a whole thickens northwesterly across map area thickens northward across map area from from 115 to 210 m about 25 to 60 m "Rmm Middle red member (Lower Triassic)-Red­ "Rml Lower red member (Lower Triassic )-Red, brown, thin-bedded, slope-forming, lami­ thin-bedded, slope-forming, sandy siltstone, nated siltstone and sandstone, white and interbedded with gray, white, and pale­ gray gypsum, minor white platy dolomite, yellow laminated gypsum and sandstone. green siltstone, and gray-green to red Lower beds contain reworked gypsum and gypsiferous mudstone. Includes abundant siltstone of the Harrisburg Member (Pkh) veinlets of gypsum in siltstone. Gradational of the Kaibab Formation. Lower part contact with the Virgin Limestone Mem­ includes a marker bed of reddish-gray, ber placed at top of highest gray limestone coarse-grained to conglomeratic, thin­ bed of the Virgin Limestone Member. Unit bedded, calcareous, low-angle cross-strati­ gradually thickens northeasterly across map fied, ledge-forming sandstone 2 to 4 m thick area from 45 to 55 m from Hurricane Cliffs eastward. Marker "Rsu Upper red member, Shnabkaib Member, bed includes raindrop impressions and rare and middle red member, undivided carbonaceous plant fossils stained green (Middle? and Lower Triassic)-In Grand by malachite copper minerals near Short Wash Trough area, used where the upper Creek (northeast quarter of map). red, Shnabkaib, and middle red cannot be Interbedded or gradational contact with easily differentiated from one another, or underlying limestone, sandstone, or con­ where one or more of those members are glomerate of the Timpoweap Member absent or covered. Lithologic descriptions ("Rmt); otherwise unconformable contact are same as above. Units are generally with the Harrisburg Member (Pkh) of the slope-forming; have conformable contact Kaibab Formation. Locally fills with the underlying Virgin Limestone paleovalleys eroded into the underlying Member ("Rmv) or undifferentiated lower Kaibab Formation or pinches out onto part of the Moenkopi Formation ("Rmb ). paleohills of the Kaibab. Thickness ranges Units dip southeast along east flank of from 0 to 85 m with thickest deposits in Virgin Mountains and are mostly covered northeast quarter of map area by alluvial deposits. Unit as a whole thick­ "Rmt Timpoweap Member (Lower Triassic)-On ens northward to about 235 m Colorado Plateau area, includes an upper "Rmv Virgin Limestone Member (Lower Trias­ and lower part. Upper part consists of gray, sic)-Consists of three and sometimes four, cliff-forming, light-gray, fine-grained, light-gray, thin-bedded to thinly-laminated, thick-bedded sandy limestone as much as ledge-forming limestone beds, 1 to 22 m ·3 m thick overlying conglomerate in thick, separated by slopes of white to pale­ eastern-most outcrops; includes gray, yellow, red, and blue-gray, thin-bedded, interbedded, coarse-grained, low-angle gypsum and gypsiferous siltstone. Includes cross-bedded sandstone locally containing thin beds of brown, red, and green silt- small chert pebbles. Lower part consists

16 mainly of cliff- and slope-forming, gray, marine fossils of crinoids, pelecypods, dark-gray, white and red-brown. conglom­ gastropods, cephalopods, worm trails, and erate consisting of subangular to rounded crustaceans (Poborski, 1954). Lower red pebbles and cobbles of limestone, chert, member; grayish-red and light-brown, and quartzite derived from the Kaibab gypsiferous, ripple-laminated, slope­ Formation. Includes yellow, red-brown, forming siltstone and cross-stratified sand­ interbedded, calcareous, thin-bedded, cross­ stone. In places, includes conglomerate at stratified, sandstone, siltstone, gray gypsif­ base that may be the Timpoweap Mem­ erous siltstone, and yellow to gray, ber of the Moenkopi Formation, but not thin-bedded sandy limestone. Conglomerate differentiated. Unconformable contact with is pebble-supported in most areas with the Kaibab Formation difficult to locate pebbles compressed into one another; where because of similar lithologies between the matrix-supported, matrix is gray limestone Harrisburg Member (Pkh) of the Kaibab and coarse-grained sandstone. Conglom­ and the lower red member ("Rml) of the erate clasts are as much as 30 em in dia­ Moenkopi Formation. Average thickness, meter throughout map area. Unconformable about 70 m contact with the underlying Harrisburg "Rmlt Lower red member and Timpoweap Member (Pkh) and Fossil Mountain (Pkf) Members undivided (Lower Triassic)-On Colorado of the Kaibab Formation as Triassic Plateau, same lithologies as the lower red paleovalleys (fig. 1, on map sheet). Imbri­ member ("Rml) and the Timpoweap Mem­ cation of pebbles in conglomerate indicates ber ("Rmt) of the Moenkopi Formation as easterly flow of depositing streams. Aver­ interbedded mixed lithologies. Fills shallow age paleovalley width is about 305 m at paleovalleys eroded into the Harrisburg bottom with sloping paleovalley walls that Member (Pkh) of the Kaibab Formation widen upward to about 490 m or more. that form tributary paleovalleys to major Paleovalley depths range from about 45 paleovalleys. Unconformable contact with to 110 m. Paleovalley names (fig. 1, on the Harrisburg Member (Pkh) of the Kaibab map sheet) are from Billingsley (1990a, Formation; unit locally eroded away or b, c, d; 1991a, b). Rock Canyon Conglom­ obscured where overlain by alluvial de­ erate was proposed and abandoned by posits. Variable thickness 5 to 20 m Gregory ( 1948, 1952), used by Nielsen Kaibab Formation (Lower Permian)-Divided and Johnson (1979), and Nielsen (1986, into, in descending order, the Harrisburg 1991). Timpoweap Member of the Moenkopi and Fossil Mountain Members as defined Formation is used in this report as used by by Sorauf and Billingsley (1991). Formation Stewart and others (1972). Unit as a whole as a whole thickens northwestward across thickens from west to east across map area map area. Divided into: and is largely confined to narrow deeper Pkh Harrisburg Member-Includes an upper, paleovalleys in western part of map, more middle, and lower part. Upper part con­ widespread and confined to shallower sists mainly of slope-forming, red and gray, paleovalleys in eastern part of map. Thick­ gypsiferous siltstone, sandstone, gray ness ranges from 0 to as much as 110 m gypsum, and thin-bedded gray limestone. "Rmb Basal members, Virgin Limestone Mem­ Includes caprock of resistant, pale-yellow ber and lower red member, undivided or light-gray, fossiliferous (mollusks and (Lower Triassic)-In Grand Wash Trough algae) sandy limestone averaging about 1 area, used where the Virgin Limestone m thick that weathers black or brown Member and lower red member cannot be (Billingsley, 1970). Upper part is mostly easily differentiated from one another or eroded from west two-thirds of map area where one or more of those members are and locally covered by basalt. Thickest absent. Virgin Limestone Member; light deposits are as much as 50 min St. George olive-gray to light-gray, ledge- and slope­ Basin area; unit gradually thins southward forming, aphanitic to very finely crystalline, across map area. Gradational contact with thinly laminated limestone beds that range middle part. Middle part consists of two from about 10 em to 1 m thick, separated cliff-forming limestone beds that together by brownish-gray, greenish-gray, and light gradually thicken from 6 m to as much as olive-gray siltstone. Limestone beds contain 14m southeastward across map area. Top

17 bed is gray, thin-bedded, cherty limestone Unconformity has local relief of as much that weathers dark brown or black, often as 4.6 m; contact mostly covered by ta­ forming bedrock surface of the exposed lus and landslide debris. Unit as a whole Harrisburg Member (Pkh) on Colorado maintains uniform thickness throughout Plateau. Bottom bed is light-gray to white, map area averaging about 92 m, gradually thick-bedded, sandy limestone separated thinning east and south of map area and from top bed by thin-bedded gypsiferous thickening southwestward (86 m thick in sandstone. Both beds thicken and thin at central Grand Canyon [Billingsley, 1970]) expense of each other; bottom bed fills Toroweap Formation (Lower Permian)-On erosional channels as much as 4 m deep. Colorado Plateau, divided into, in descend­ Erosional unconformity separates middle ing order, the Woods Ranch, Brady Can­ part from lower part. Lower part consists yon, and Seligman Members as defined by of slope-forming, light-red, fine- to medium­ Sorauf and Billingsley (1991 ). In Basin grained gypsiferous siltstone and sandstone; and Range, divided into, in descending interbedded with gray, medium-grained, order, the Woods Ranch Member and lower thin-bedded limestone and gray to white, part which includes the Brady Canyon and massive-bedded gypsum. Lower part main­ Seligman Members undivided (Bohannon tains uniform thickness across map area and others, 1991): of about 40 m, gradually thinning south­ Ptw Woods Ranch Me~ber-Gray gypsiferous eastward. Solution of gypsum in lower part siltstone and pale-red silty sandstone has locally distorted limestone beds of interbedded with white to gray, laminated middle part causing them to slump or bend to massive-bedded gypsum. Commonly into local drainages. Gypsum is mined from covered by talus and landslide debris. lower·part about 5 km south of Interstate Gradational contact with the underlying Highway 15, northwestern part of map area. Brady Canyon Member is placed at litho­ Gradational contact between the slope­ logic break between limestone cliff of the forming Harrisburg Member and the cliff­ Brady Canyon Member (Ptb) and siltstone­ forming Fossil Mountain Member. gypsum slope of the Woods Ranch Member Harrisburg Member locally removed by (Ptw). Much local subsidence and distortion erosion of paleovalleys and subsequently of beds from solution of gypsum within filled by the Timpoweap and the lower red unit. Thickest deposits ( 110 m) are along members (limt and liml) of the Moenkopi Hurricane Cliffs, east-central part of map Formation (fig. 1, on map sheet). Harris­ area, gradually thinning east, west, and burg deposits occupy wide northwest-trend­ south from this area. Locally thins and ing trough-like embayment across map area; thickens from 30 to 110 m owing to thickest deposits as much as 107 m in solution of gypsum northwest quarter of map; as much as 80 Ptb Brady Canyon Member-Gray, fossilifer­ m thick in central Grand Canyon area ous, medium-bedded, medium- to coarse­ (Billingsley, 1970) grained, cliff-forming limestone, weathers Pkf Fossil Mountain Member-Yellow-gray to dark-gray. Includes thin beds of dolomite light-gray, fine- to medium-grained, thin­ in upper and lower parts. Gradational bedded, cliff-forming, fossiliferous, sandy, contact with the underlying Seligman cherty limestone. Unit characterized by Member; contact placed at lithologic and black-weathering chert bands in cliff out­ topographic break between cliff-forming crops. Intergrades with the overlying limestone and slope-forming sandstone. Harrisburg Member; arbitrary contact Thickest deposits are along the Grand Wash placed at uppermost cherty limestone cliff, Cliffs, southwest quarter of. map area (about which is difficult to locate in flatland 90 m), gradually thinning eastward to about exposures. Locally cut into by paleovalley 65 m, central Grand Canyon area erosion and subsequently filled with de­ (Billingsley, 1970) posits of the Timpoweap Member (limt) Pts Seligman Member-Gray, thin-bedded, and the lower red member (liml) of the ledge-forming sandy limestone in upper Moenkopi Formation. Unconformable part; gray to red, slope-forming, thin­ contact with the underlying Woods Ranch bedded, interbedded calcareous and gypsif­ Member (Ptw) of the Toroweap Formation. erous sandstone, siltstone, silty limestone,

18 dolomite, and gypsum in middle part; and stone and siltstone, and changes northwest­ brown, purple, ·and yellow, slope-forming, ward to an all white sandstone in the Virgin fine- to medium-grained, thin-bedded, low­ River canyon area (Billingsley, 1997b). In­ to high-angle crossbedded and planar­ formally includes an upper sandstone unit, bedded sandstone in lower part. Includes a middle sandstone and siltstone unit, and gray-brown, cliff-forming, high-angle a lower sandstone unit. Upper unit is about crossbedded sandstone bed in lower part 60 m thick in the Virgin River canyon, that thickens and thins along Grand Wash thickens northwestward and thins south and Cliffs northward to Virgin River Canyon, southeastward; middle unit is a sandstone and thickens westward to form large cliff and siltstone sequence, about 213 m in as much as 50 m high in Virgin Moun­ Virgin River canyon area, thickens north­ tains area; often called the Coconino westward and thins southeastward. Lower Sandstone (Bohannon, 1991; Bohannon and unit is 60 m thick and equivalent to upper others, 1991; Billingsley, 1997b). Recent slope units of the Esplanade Sandstone of mapping by Billingsley (unpub. data d) McKee (1982) in western and central Grand suggests that the Coconino Sandstone may Canyon, but is included as part of the intertongue with the Seligman Member Hermit Formation in this map area; lower (Pts) of the Toroweap Formation. Over­ 60 m thins southeastward and thickens all, unit forms steep slope. Erosional contact northwestward. Arbitrary contact between with the underlying Hermit Formation the Hermit Formation and the Queantoweap placed between gray-brown, high-angle, Sandstone placed at lowest red siltstone cross-bedded sandstone, or slope-forming, bed in cliff of white sandstone in Virgin gypsiferous, flat-bedded sandstone of the River canyon area, erosional contact at base Seligman Member (Pts) and red or pale­ of red slope-forming sandstone-siltstone yellow, thick-bedded, ledge-forming sand­ sequence and top of white sandstone cliff stone of the Hermit Formation (Ph). of the Esplanade Sandstone along the Grand Thickness ranges from 8 to 50 m Wash and Hurricane Cliffs. Unit as a whole Ptl Toroweap Formation, lower part undivided­ thickens west and northwestward (thick­ Includes the Brady Canyon and Seligman ness unknown), thins southeastward to Members (Ptb and Pts) as defined above, about 200 m in central Grand Canyon but combined in Basin and Range area of (Billingsley, 1970), and thins northeast­ map because the Seligman Member is too ward to about 137 m along upper Hurri­ thin to show at this map scale (Bohannon cane Cliffs area (Billingsley, 1997b). and others, 1991). Combined thickness Maximum thickness, Virgin River canyon, about 70 m about 333 m Ph Hermit Formation (Lower Permian)-Con­ Pep Esplanade Sandstone and Pakoon Limestone sists of an upper steep-slope-forming, pale­ (Lower Permian)-On Colorado Plateau, yellow to light-red, massive, calcareous, light-brown to light-red, white, fine- to fine-grained sandstone, grading downward medium-grained, thick cross-bedded (sets into a middle sequence of ledge-forming, 3 to 12m thick), cliff-forming sandstone. interbedded white and light-red, medium­ The name Esplanade Sandstone is restricted bedded, fine-grained sandstone and thin­ to the Grand Wash Cliffs, Grand Canyon, bedded red siltstone, grading downward and the Hurricane Cliffs of the Colorado into lower cliff-forming, white, cross­ Plateau; includes the Pakoon Limestone bedded, medium- to fine-grained sandstone; of MeN air ( 19 51) that intertongues into the lower part includes interbedded dark-red, basal part of the Esplanade Sandstone of thin-bedded, lenticular siltstone beds McKee (1982). Pakoon Limestone is gray, between cross-bedded sets. Most, if not medium- to coarse-grained, thin-bedded, all sandstone was originally a light-red cliff-forming limestone and sandy dolo­ color, later bleached to white or pale-yellow. mite; weathers brown-gray with sugary Unit as whole is slope forming, coarse texture. Limestone and dolomite beds sepa­ grained, and stratigraphically equivalent to rated by gray-purple, thin-bedded siltstone Hermit Formation (Shale) in Grand Can­ and sandstone beds; limestone is fossil­ yon. Unit changes south and west into a iferous in upper part; includes lenses and mostly red, medium- to fine-grained sand- pods of brown chert. Locally trough cross-

19 stratified. The Pakoon Limestone is in­ (Billingsley, 1997b). Unit thickens north­ cluded in the upper part of the Callville westward from the Virgin River becoming Limestone (or the Bird Spring Formation) indistinguishable from, and including, in the Virgin River canyon area and Virgin overlying sandstone beds of the Hermit Mountain area (Bohannon and others, Formation. The Queantoweap Sandstone 1991). The Pakoon Limestone intertongues may need to be renamed in future studies with lower part of the Esplanade Sandstone north of Virgin River canyon because the along Hurricane Cliffs and in western Grand term "Queantoweap" is an obsolete Grand Canyon areas. Forms a disconformable con­ Canyon term (replaced by the term Espla­ tact with the underlying Callville Lime­ nade Sandstone). About 124m thick at Virgin stone that is difficult to locate; contact can River canyon be narrowed down by fossil faunas between Callville Limestone (Lower Permian; Upper, Lower Permian and Upper Pennsylvanian Middle, and Lower Pennsylvanian)-In types. Thickness about 13 7 m along Grand Basin and Range, Virgin Mountains, and Wash Cliffs. Equivalent to the Queantoweap Virgin River canyon areas, upper part in­ Sandstone at Virgin River canyon and Vir­ cludes rocks mapped as the Pakoon Lime­ gin Mountain area (Billingsley, 1997b). Unit stone, and lower part includes rocks mapped is 175 m thick along Hurricane Cliffs, north­ as the Callville Limestone by Hintze eastern part of map area, thinning southward (1986); also includes rocks mapped as the to about 115m thick in central Grand Can­ Bird Spring Formation by Bohannon and yon (Billingsley, 1970); about 160m thick others (1991). Divided into: along Grand Wash Cliffs PIPe Limestone, cherty limestone, arenaceous Pq Queantoweap Sandstone (Lower Permian)­ limestone, and calcareous sandstone­ In Virgin Mountains and Virgin River can­ Gray, light-gray, and white, thin- to yon (northwest quarter of map area): tan medium-bedded (0.5 to 1 m thick), ledge­ and white, fine-grained to very fine grained, forming arenaceous ·limestone; weathers medium- to thick-bedded (2 to 3m), cross­ brown and yellow-brown; chert pods and stratified cliff- or ledge-forming sandstone. lenses are brown. Cross-bedding common Includes pale-red, thin-bedded silty sand­ in sandstone and sandy limestone beds. stone beds between cross-bedded sets in Cherty limestone is about 10 to 30 per­ upper part. Cross-stratification includes cent of formation; arenaceous limestone mixed high-angle and low-angle cross­ and calcareous sandstone interbedded with stratified sets representing both eolian limestone form about 10 to 20 percent of coastal or marine offshore dune environ­ formation. Basal 10 m of formation is ment. Locally includes gypsiferous facies slope-forming silty limestone and reddish­ of Bohannon and others ( 1991 ). Locally weathered siltstone. Unit highly fossiliferous confined to small area north of Virgin River in west half of map and gradually thickens canyon, northwest corner of map area: red­ westward across map area. Average thick­ brown, red, gray-brown, and yellow-brown, ness about 360 m silty, sandy, slope-forming gypsum. Gyp­ PIPeg Gypsiferous facies-Gray, thin-bedded (1 m sum comprises about 20 to 30 percent of to 20 em thick), slope-forming, gypsiferous unit. Bedding irregular and poorly defined. dolomite alternating with white gypsum This is only place where gypsum is present beds. Unit is present in upper part of the in the Queantoweap Sandstone, Pakoon Callville Limestone (Pakoon Limestone Limestone, and Callville Limestone region­ equivalent) and restricted geographically ally. May have once been more widespread, to same area as gypsiferous facies of lower but, if so, has been removed from most areas part of the Queantoweap Sandstone. Fa­ by dissolution (Bohannon and others, 1991). cies is an uncommon local occurrence Gradational contact with underlying gypsif­ of evaporite deposition of the Callville erous unit (PIPeg) and the upper Callville Limestone. Grades laterally into gray Limestone (PIPe), 0 to 100 m thick. The limestone of the Callville Limestone. name Queantoweap Sandstone applies to Lower part of the Callville may, in part, the Virgin River canyon, Virgin Mountains, be Early Mississippian age based on Mis­ and Beaver Dam Mountains of southeast­ sissippian conodonts in the Watahomigi ern Nevada and southwestern Utah Formation of the Supai Group in Grand

20 Canyon (Martin and Barrick, 1999). Ero­ Dtb Temple Butte Formation (Upper and Middle sional and topographical contact between Devonian)-As defined by Be us ( 1980). slope-forming siltstone-limestone beds Mapped as unnamed limestone and dolo­ of the Callville Limestone and the cliff­ mite (Bohannon, 1991; Bohannon and forming Redwall Limestone. 0 to 100m others, 1991 ). Exposed in Virgin and thick Beaver Dam Mountains, northwest quar­ Mr Redwall Limestone (Upper and Lower Mis­ ter of map area. Dark-gray and medium­ sissippian)-Equivalent to the Monte gray, medium- to fine-grained, sugary Cristo Limestone of Basin and Range textured, medium-bedded (0.4 to 2 m thick), (Hewett, 1931). Consists of four members ledge-forming dolomite. Includes thin in Grand Canyon as described by McKee purple-gray siltstone and calcareous sand­ (1963). Undivided members include, in de­ stone beds between larger dolomite beds. scending order, the Horseshoe Mesa Mem­ Probably equivalent to the Valentine ber (lithologic equivalent to the Yellowpine Member and part of the Crystal Pass Member of the Monte Cristo Limestone; Member of the Sultan Limestone of Hewett basal part lithologic equivalent to the Ar­ (1931). The unconformity at the base of rowhead Member of the Monte Cristo the Temple Butte represents a major break Limestone); the Mooney Falls Member in the Paleozoic rock sequence during the (lithologic equivalent to the Bullion Late Cambrian, most or all of the Ordovi­ Member of the Monte Cristo Limestone); cian, all of the Silurian, and most of the the Thunder Springs Member (lithologic Early and Middle Devonian time. Thick­ equivalent to the Anchor Member of the ness ranges from about 60 to 120 m thick Monte Cristo Limestone); and the £n Nopah Formation (Upper Cambrian)-As Whitmore Wash Member (lithologic mapped by Bohannon ( 1991 ), and equivalent to the Dawn Member of the Bohannon and others (1991). Light-gray, Monte Cristo Limestone). Horseshoe Mesa medium-grained, thin-bedded, ledge­ Member: brownish-gray, medium-grained, forming dolomite. Base of unit contains thin-bedded (0.5 to 1 m thick), ledge and yellowish to brownish-gray, thin-bedded, cliff-forming limestone; includes minor discontinuous, slope-forming sandy dolo­ amounts of brownish chert nodules and mite that weathers dark or medium brown. lenses. Basal part is dark-gray, very thin This basal unit may be the Dunderberg bedded ( 10 to 20 em thick), aphanitic, Shale Member, but is not differentiated on recessive, 10-m-thick limestone; weathers map. Distinguished from underlying do­ yellowish-brown. Mooney Falls Member: lomite by yellow color and slope-forming medium-gray, medium- to coarse-grained, beds at base. About 115 m thick massive to thick-bedded, cliff-forming, Tonto Group (Upper, Middle, and Lower bioclastic limestone. Thunder Springs Cambrian)-Includes in descending or­ Member: medium-gray, medium- to coarse­ der, the Muav Limestone, Bright Angel grained, thin-bedded, cliff-forming, Shale, and Tapeats Sandstone as defined bioclastic limestone interbedded with white by Noble (1922) and modified by McKee to gray chert lenses and beds that weather and Resser ( 1945); units recognized on the brown or black. Chert lenses and beds 5 basis of their distinct lithologies. All the to 20 em thick; amount of chert varies from limestone and dolomite lithology in the 20 to 50 percent of member. Whitmore Cambrian sequence belongs to the Muav Wash Member: medium to dark-gray, very Limestone, the shale and siltstone belong coarse grained to coarse-grained, massive, to the Bright Angel Shale, and the sand­ cliff-forming, crystalline and bioclastic stone and conglomerates belong to the limestone and dolomite; weathers light­ Tapeats Sandstone gray. The Red wall Limestone forms single £m Muav Limestone (Upper and Middle Cam­ uniform cliff that generally appears brian)-lncludes in descending order, un­ unbedded from distance except where chert named light-gray dolomite, 130 m thick; bands of the Thunder Springs Member are informal striped unit, about 75 m thick present. Unconformable contact with the (Bohannon and others, 1991), including underlying Temple Butte Formation. subdivisions described by McKee and Averages about 213 m thick Resser ( 1945) and mapped by Bohannon

21 (1991) and Bohannon and others (1991); of the Bright Angel Shale and cliffs of the the Havasu Member, about 20m thick; the Tapeats Sandstone. Unit overall thickens Gateway Canyon Member, about 50 m northwestward and thins southeastward, thick; the Kanab Canyon and the Peach depending on arbitrary boundaries between Springs Members, about 75 m thick; the the Muav Limestone and the Tapeats Spencer Canyon, Sanup Plateau, and Sandstone. Thickness about 60 to 100 m Rampart Cave Members, about 60 m thick. £t Tapeats Sandstone (Lower Cambrian)- Unit mostly comprised of cliff-forming, Pale-red and light-brown, fine- to medium­ d~k-gray and brown-gray, medium-grained grained, thin-bedded (5 to 50 em thick), to crystalline, thin- to medium-bedded (20 well-sorted, cliff-forming sandstone and em to 1 m thick), silty limestone, sandy quartzite; weathers dark red and yellow limestone, and dolomite and calcareous brown. Upper part is yellow brown and mudstone; weathers yellow brown, rust lower part is reddish. Most beds have brown, or brown gray often with sugary low- to moderate-angle cross-stratification. or pitted surface texture. Includes- green­ Upper part includes thin beds of greeP.­ ish micaceous shale bed partings between ish shale between sandstone beds that are limestone beds in upper and lower part. equivalent to the Bright Angel Shale li­ Contact with the underlying Bright An­ thology. Variable unconformable contact gel Shale is arbitrarily placed at the bot­ with underlying crystalline rocks. Thickness tom of the Rampart Cave Member, which ranges from about 65 to 80 m in Grand Canyon generally represents a Xc Crystalline rocks, undivided (Early Protero- topographic and lithologic break between zoic)-Gneiss, schist, and granitic rocks. limestone cliffs of the Muav Limestone Not studied in detail; description follows and shale slopes of the Bright Angel Shale. Moore (1972). Garnet-biotite gneiss, The lower half of the Muav contains garnet-sillimanite-biotite schist, gneissic unnamed interbedded shale beds that are hornblendite, granitic gneiss, amphibolite, lithologically equivalent to the Bright Angel and granitic and gabbroic intrusives. Lo­ Shale. Unit as a whole is about 410 m thick cally dikes and sills of coarsely crystalline in northwest quarter of map area, thick­ pink granite are abundant in gneiss and ens northwestward into Nevada and thins these masses closely follow grain of southeastward to about 200 m in central gneissic foliation and compositional lay­ Grand Canyon area ering. More or less concordant dike swarms £ba Bright Angel Shale (Middle Cambrian)­ of light-colored pegmatite containing Described by McKee and Resser ( 1945), quartz, feldspar, and muscovite are locally mapped by Bohannon ( 1991) and Bohannon abundant. Exposed in Virgin Mountains and others (1991). Upper third of unit of Basin and Range, northwest quarter of consists of black to dark-gray shale that map area probably correlates to the Chisholm Shale of the Basin and Range; overlies dark-gray to reddish-gray, thin-bedded, iron-stained, REFERENCES CITED ledge-forming limestone that is discontinu­ ous on regional basis; weathers rusty brown; Beard, L. Sue, 1996, Paleogeography of the Horse Spring Forma­ is about 10 m thick; may correlate to the tion in relation to the Lake Mead Fault system, Virgin Moun­ Lyndon Limestone of the Basin and Range. tains, Nevada and Arizona: Geological Society of America Lower two-thirds of unit consists of black Special Paper 303, p. 27-60. to dark-gray, slope-forming shale; weathers Best, M.G., McKee, E.H., and Damon, P.E., 1980, Space-time com­ gray and light brown; contains interbedded position patterns oflate Cenozoic mafic volcanism, southwest­ yellow-brown, thin-bedded sandstone litho­ em Utah and adjoining areas: American Journal of Science, v. logically equivalent to the Tapeats Sand­ 280, p. 1035-1050. Beus, S.S., 1980, Late Devonian (Fresnian) paleogeography and stone. Beds range from less than 1 em to paleoenvironments in northern Arizona, in Fouch, T.D., ed., about 5 em thick. Lower unit commonly Paleozoic paleogeography of the west-central United States; covered by talus or alluvium. Lower unit Rocky Mountain Paleogeography Symposium 1: Society of may correlate in part to the Pioche Shale Economic Paleontologists and Mineralogists, Rocky of Basin and Range. Arbitrary lithologic Mountain Section, Denver, Colorado, p. 59-69. and topographic contact between slopes Billingsley, G.H., 1970, General geology ofTuckup Canyon, cen-

22 tral Grand Canyon, Mohave County, Arizona: Flagstaff, North­ ---I994a, Geologic map of the Formaster Well quadrangle, em Arizona University, unpublished MS thesis, 115 p. northern Mohave County, Arizona: U.S. Geological Survey ---I990a, Geologic map of the Purgatory quadrangle, north­ Open-File Report 94-243, scale 1:24,000, 10 p. em Mohave County, Arizona: U.S. Geological Survey Open­ ---1994b, Geologic map of the White Pockets quadrangle, File Report 90-540, scale 1:24,000. northern Mohave County, Arizona: U.S. Geological Survey ---I990b, Geologic map of the Wolf Hole Mountain West quad­ Open-File Report 94-244, scale 1:24,000, 1I p. rangle, northern Mohave County, Arizona: U.S. Geological ---1994c, Geologic map of the Antelope Knoll quadrangle, Survey Open-File Report 90-54I, scale I:24,000. northern Mohave County, Arizona: U.S. Geological Survey ---I990c, Geologic map of the Lizard Point quadrangle, north­ Open-File Report 94-449, scale 1:24,000, I8 p. em Mohave County, Arizona: U.S. Geological Survey Open­ ---1994d, Geologic map of the Little Clayhole Valley quad­ File Report 90-643, scale I :24,000. rangle, northern Mohave County, Arizona: U.S. Geological ---1990d, Geologic map of the Wolf Hole Mountain East quad­ Survey Open-File Report 94-290, scale I :24,000, I1 p. rangle, northern Mohave County, Arizona: U.S. Geological ---I994e, Geologic map of the Hat Knoll quadrangle, north- Survey Open-File Report 90-644, scale I :24,000. em Mohave County, Arizona: U.S. Geological Survey Open­ ---I99Ia, Geologic map of the Sullivan Draw North quad­ File Report 94-554, scale I :24,000, 14 p. rangle, northern Mohave County, Arizona: U.S. Geological ---I994f, Geologic map of the Moriah Knoll quadrangle, north­ Survey Open-File Report 9I-558, scale 1:24,000, 10 p. em Mohave County, Arizona: U.S. Geological Survey Open­ ---I991b, Geologic map of the Sullivan Draw South quad- File Report 94-634, scale 1:24,000, 14 p. rangle, northern Mohave County, Arizona: U.S. Geological ---1994g, Geologic map of Sullivan Draw and vicinity, Mohave Survey Open-File Report 91-559, scale I:24,000, 9 p. County, northwestern Arizona: U.S. Geological Survey Mis­ ---1991c, Geologic map of the Mustang Knoll quadrangle, celJaneous Investigations Series Map I-2396, scale I :3I ,680, northern Mohave County, Arizona: U.S. Geological Survey includes text and cross sections. Open-File Report 9I-560, scale I:24,000, 12 p. ---I995, Geologic map of the Littlefield quadrangle, northern ---I991d, Geologic map of the St. George quadrangle, north- Mohave County, Arizona: U.S. Geological Survey Open-File em Mohave County, Arizona: U.S. Geological Survey Open­ Report 95-559, scale I :24,000, I5 p. File Report 91-56I, scale 1:24,000, 11 p. ---I997a, Geologic map of the Mount Logan quadrangle, ---I992a, Geologic map of the Gyp Pocket quadrangle, north­ northern Mohave county, Arizona: U.S. Geological Survey em Mohave County, Arizona: U.S. Geological Survey Open­ Open-File Report 97-426, scale 1:24,000, 2I p. File Report 92-412, scale 1:24,000, 17 p. ---I997b, Permian clastic sedimentary rocks of northwestern ---1992b, Geologic map of the Hole-N-Wall Canyon quad­ Arizona, in Maldonado, Florian, and Nealey, L.D., eds., Geo­ rangle, northern Mohave County, Arizona: U.S. Geological logic studies in the Basin and Range-Colorado Plateau Tran­ Survey Open-File Report 92-432, scale 1:24,000, 15 p. sition in southeastern Nevada, southwestern Utah, and north­ ---1992c, Geologic map of the Yellowhorse Flat quadrangle, western Arizona, I995: U.S. Geological Survey Bulletin 2153- northern Mohave County, Arizona: U.S. Geological Survey F, p. I08-124. Open-File Report 92-442, scale I :24,000, 17 p. ---1997c, Geologic map of the Mount Trumbull NW quad­ ---1992d, Geologic map of the Rock Canyon quadrangle, rangle, northern Mohave County, Arizona: U.S. Geological northern Mohave County, Arizona: U.S. Geological Survey Survey Open-File report 97-488, scale 1:24,000, I9 p. Open-File Report 92-449, scale I :24,000, I7 p. Billingsley, G.H., and Huntoon, P.W., 1983, Geologic map of ---1993a, Geologic map of the Lost Spring Mountain East Vulcan's Throne and vicinity, western Grand Canyon, Ari­ quadrangle, northern Mohave County, Arizona: U.S. Geologi­ zona: Grand Canyon Natural History Association, Grand Can­ cal Survey Open-File Report 93-565, 9 p. yon, Arizona, scale I :48,000. ---I993b, Geologic map of the Lost Spring Mountain West Billingsley, G.H., and Bohannon, R.G., 1995, Geologic map of the quadrangle, northern Mohave County, Arizona: U.S. Geologi­ Elbow Canyon quadrangle, northern Mohave County, Arizona: cal Survey Open-File Report 93-566, scale I :24,000, 1I p. U.S. Geological Survey, Open-File Report 95-560, scale ---1993c, Geologic map of the Dutchman Draw quadrangle, 1:24,000, 16 p. northern Mohave County, Arizona: U.S. Geological Survey Bohannon, R.G., I984, Nonmarine sedimentary rocks of Tertiary Open-File Report 93-587, scale I :24,000, 12 p. age in the Lake Mead region, south-eastern Nevada and north­ ---1993d, Geologic map of The Grandstand quadrangle, north- western Arizona: U.S. Geological Survey Professional Paper em Mohave County, Arizona: U.S. Geological Survey Open­ I259, 72 p. File Report 93-588, scale 1:24,000, I5 p. ---I99I, Geologic map of the Jacobs Well and southern part ---1993e, Geologic map of the Little Tanks quadrangle, north­ of the Elbow Canyon quadrangles, Mohave County, Arizona: em Mohave County, Arizona: U.S. Geological Survey Open­ U.S. Geological Survey Miscellaneous Investigations Series File Report 93-682, scale 1:24,000, I3 p. Map I-2167, scale 1:24,000. ---I993f, Geologic map of the Russell Spring quadrangle, ---1992, Geologic map of the Red Pockets quadrangle, Mohave northern Mohave County, Arizona: U.S. Geological Survey County, Arizona: U.S. Geological Survey Miscellaneous In­ Open-File Report 93-717, scale I :24,000, I7 p. vestigations Series Map I-2288, scale I :24,000. ---1993g, Geologic map of the Wolf Hole Mountain and vicin­ Bohannon, R.G., Lucchitta, Ivo, and Anderson, R.E., I991, Geo­ ity, Mohave County, northwestern Arizona: U.S. Geological logic map of the Mountain Sheep Spring quadrangle, Mohave Survey Miscellaneous Investigations Series Map I-2296, scale County, Arizona: U.S. Geological Survey Miscellaneous In­ I :3I ,680, includes text and cross sections. vestigations Series Map 1-2265, scale I :24,000.

23 Bohannon, R.G., and Lucchitta, Ivo, 1991, Geologic map of the Survey Open-File Report 95-86, scale 1 :24,000. Mount Bangs quadrangle, Mohave County, Arizona: U.S. Martin, Harriet, and Barrick, J.E., 1999, Conodont Biostratigra­ Geological Survey Miscellaneous Investigations Series Map phy; Chapter F, in Billingsley, G.H., and Beus, S.S., eds., I-2166, scale 1:24,000. Geology of the Suprise Canyon Formation of the Grand Can­ Bohannon, R.G., Grow, J.A., Miller, J.J., and Blank, R.H., Jr., 1993, yon, Arizona: Museum of Northern Arizona Bulletin 61, p. Seismic stratigraphy and tectonic development of Virgin River 97-116. depression and associated basins, southeastern Nevada and McKee, E.D., 1963, Nomenclature for lithologic subdivisions of northwestern Arizona: Geological Society of America Bulle­ the Mississippian Redwall Limestone, Arizona: U.S. Geologi­ tin, v. 105, no. 4, p. 501-520. cal Survey Professional Paper 475-C, p. 21-22. Damon, P.E., Shafiqullah, Mehmet, and Scarborough, R.B., 1978, ---1982, The Supai Group of Grand Canyon: U.S. Geological Revised chronology for critical stages in the evolution of the Survey Professional Paper 1173, 504 p. lower Colorado River [abs.]: Geological Society of America McKee, E.D., and Resser, C.E., 1945, Cambrian history of the Abstracts with Programs, Cordilleran Section, v. 10, n. 3, p. Grand Canyon region: Carnegie Institution of Washington Pub­ 101-102. lication 563, 232 p. Gregory, H.E., 1948, Geology and geography of central Kane McNair, A.H., 1951, Paleozoic stratigraphy of part of northwest­ County, Utah: Geological Society of America Bulletin 59, p. em Arizona: American Association of Petroleum Geologists 211-248. Bulletin, v. 35, no. 3, p. 503-541. ---1952, Geology and geography of the Zion Park region, Utah Moore, R. T., 1972, Geologic map of the Virgin and Beaver Dam and Arizona: U.S. Geological Survey Professional Paper 220, Mountains, Arizona, in Moore, R.T., ed., Geology of the Vir­ 200p. gin and Beaver Dam Mountains, Arizona: The Arizona Bu­ Hamblin, K. W., 1965, Origin of "reverse drag" on the down thrown reau of Mines Bulletin 186, University of Arizona, Tucson, side of normal faults: Geological Society of America Bulletin, Arizona, 66 p., plates 1 and 2. v. 76, p. 1145-1164. Morales, Mike, 1987, Terrestrial fauna and flora from the Triassic Hewett, D.F., 1931, Geology and ore deposits of the Goodspring Moenkopi Formation of the southwest United States: Journal quadrangle, Nevada: U.S. Geological Survey Professional of the Arizona-Nevada Academy of Science, v. 22, p. 1-19. Paper 162, 172 p. 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24 Professional Paper 691, 195 p. Stokes, W.L., 1977, Physiographic subdivisions of Utah: Utah Geo­ logical and Mineral Survey Map 43, scale I :2,400,000. Wenrich, K.J., 1985, Mineralization of breccia pipes in northern Arizona: Economic Geology, v. 80, no. 6, p. 1722-1735. Wenrich, K.J., Billingsley, G.H., and Huntoon, P.W., 1997, Brec­ cia pipe and geologic map of the northeastern part of the Hualapai Indian Reservation and vicinity, Arizona: U.S. Geological Survey Miscellaneous Investigations Series Map 1-2440, scale 1:48,000, 19 p. Wenrich, K.J., and Huntoon, P.W., 1989, Breccia pipes and associ­ ated mineralization in the Grand Canyon region, northern Ari­ zona, in Elston, D.P., Billingsley, G.H., and Young, R.A., eds., Geology of Grand Canyon, northern Arizona (with Colorado River guides): 28th International Geological Congress Field Trip Guidebook T115/315, American Geophysical Union, Washington D.C., p. 212-218. Wenrich, K.J., Billingsley, G.H., Blackerby, B.A., 1995, Spatial migration and compositional changes of Miocene-Quaternary magmatism in the western Grand Canyon: Journal of Geo­ physical Research, v. 100, no. B 7, p. 10,417-10,440.

UNPUBLISHED DATA

Billingsley, unpub. data a, Lower Hurricane Wash and vicinity, Mohave County, northwestern Arizona ---unpub. data b, Upper Hurricane Wash and vicinity, Mohave County, northwestern Arizona ---unpub. data c, Clayhole Wash and vicinity, Mohave County, northwestern Arizona ---unpub data d, Clayhole Valley and vicinity, Mohave County, northwestern Arizona ---unpub data e, Upper Parashant Canyon and vicinity, Mohave County, northwestern Arizona

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1:r U.S. GOVERNMENT PRINTING OFFICE: 2000 - 573-047 / 20199 Region No. 8