Geologic units in Churchill county, Nevada

Additional scientific data in this geographic area

Alluvium, undifferentiated (Holocene and Pleistocene) at surface, covers 26 % of this area

Unit is present in all counties. Some counties divided the alluvium into younger and older units, and some did not. For those that did not, or used other generalized terms for Quaternary rocks, the unit Qal has been used for the general undivided alluvium. Additionally, when polygons have been edited and changed to alluvium, Qal was used as the general value; hence it now is present in all counties. Qya-Younger alluvium: Map unit is used in Churchill, Elko, Esmeralda, Eureka, Humboldt, Lander, and Lincoln Counties where geologic information suggests better-defined younger versus older alluvium. It is mostly interchangeable with Qal, except that it implies some specifically younger Quaternary deposits.

Playa, lake bed, and flood plain deposits (Holocene and Pleistocene) at surface, covers 21 % of this area

Map unit used in all counties for recent lake beds, playas, and flood plains. Polygons from the 1978 State map unit Qp were added where no playa was shown on the county maps.

Intermediate silicic ash flow tuff (lower Miocene and Oligocene) at surface, covers 16 % of this area

Welded and nonwelded silicic ash flow tuffs. Aside from alluvium, this unit covers more of Nevada than any other rock, with over 4,000 polygons representing it on this map. It is principally exposed in the central regions of the State. It locally includes thin units of air fall tuff and sedimentary rocks. It includes rocks mapped on the Washoe South, Lyon, Douglas, and Carson Counties maps as the Hartford Hill Rhyolite Tuff (now abandoned); on the Nye South map as the tuff of White Blotch Spring, the tuffs of Antelope Springs, and the tuff of Monotony Valley; in Lander County it is mapped as the Bates Mountain Tuff, Caetano Tuff, Edwards Creek Tuff, New Pass Tuff, tuff of Hall Creek, and the tuff of McCoy Mine; in Lander and Pershing Counties it is the Fish Creek Mountains Tuff; on both of the Nye County maps it is the Fraction Tuff; it also includes the Pancake Summit Tuff, Northumberland Tuff, Shingle Pass Tuff, some outcrops of Darrough Felsite shown to be Tertiary (other outcrops have been shown to be Mesozoic or Paleozoic), tuffs of Moores station, tuffs of Peavine Canyon, tuffs of the Pancake caldera complex, the Stone Cabin Formation, tuff of Saulsbury Wash, tuff of Kiln Canyon, the Tonopah Formation, tuffs of Hannapah, tuff of Bald Mountain, the Needles Range Formation, and the Calloway Well Formation on the Nye North map; in Esmeralda County it is the Kendall Tuff and latite; and in northern Nye and Lander Counties it is the Toiyabe Quartz Latite (now abandoned), and other unnamed units. It corresponds to unit Tt2 on the 1978 State map. It crops out in every county except Clark.

Older alluvium and alluvial fan deposits (Pleistocene and Pliocene) at surface, covers 11 % of this area

Unit consists mostly of older alluvium and alluvial fans. It also includes various stream deposits, gravel, fanglomerates, and older gravels. It is not very consistent in description from county to county. This is used in all counties except Clark.

Andesite and basalt flows (Miocene and Oligocene) at surface, covers 10 % of this area

Generally poorly age constrained. This unit includes rocks originally mapped as the Pyramid sequence in Washoe County, the Mizpah Trachyte in Nye County, the Malpais Basalt, Rabbit Spring Formation, and Mira Basalt in Esmeralda County, and many other poorly dated unnamed basaltic and andesitic rocks around the State. It corresponds to unit Tba on the 1978 State map.

Younger tuffaceous sedimentary rocks (Pliocene and Miocene) at surface, covers 3 % of this area

Tuffaceous and other young Tertiary sedimentary rocks. Most of these rocks are sedimentary with a strong volcanic component - a few are tuffaceous with a strong sedimentary component. This unit includes rocks originally mapped as the High Rock sequence in Washoe County; the Horse Camp Formation in northern Nye County; the Esmeralda Formation in Mineral and Esmeralda Counties; older lake beds in Lincoln County; the Belted Range Tuff; the Indian Trail Formation (now abandoned); Timber Mountain, Paintbrush, and Crater Flat Tuffs; Wahmonie and Salyer Formations in southern Nye County; the Siebert Tuff in Esmeralda County; the Muddy Creek Formation in Clark County; and the Thousand Creek and Virgin Valley “beds” in Humboldt County; and other unnamed units. It corresponds to units Ts3 and Tts from the 1978 State map. It is present in all counties.

Jungo Terrane - Turbiditic, fine-grained, terrigenous clastic rocks (Middle Jurassic to Upper Triassic) at surface, covers 2 % of this area

The Jungo terrane, also called the Lovelock assemblage or Fencemaker allochthon (Oldow, Satterfield, and Silberling, 1993), consists of complexly deformed, thick basinal, turbiditic, fine-grained, terrigenous clastic rocks, mainly Norian, but also as young as Pliensbachian (Late Triassic and Early Jurassic) age. It crops out in southern Washoe, Churchill, Humboldt, and Pershing Counties. These rocks represent the basinal facies component of the Auld Lang Syne Group (Burke and Silberling, 1973; Lupe and Silberling, 1985). The Jungo terrane has no known basement and is structurally detached from coeval shelf facies (Silberling, Jones, and others, 1992). It is locally overlain unconformably by Middle or Upper Jurassic peritidal sedimentary rocks (Jcg) intruded by a gabbroic igneous assemblage (Silberling, 1991). Rocks included with the Jungo terrane were originally mapped as the Grass Valley Formation of the Auld Lang Syne Group in Humboldt and Pershing Counties; some rocks were mapped as the Happy Creek Volcanic “series” (now the Happy Creek Volcanic Complex) in Humboldt County, the Nightingale sequence in southern Washoe County, the Osobb Formation of the Auld Lang Syne Group in Churchill County, and the Winnemucca and Raspberry Formations of the Auld Lang Syne Group (Compton, 1960) in the Santa Rosa Range in Humboldt County.

Sand dunes (Holocene and Pleistocene) at surface, covers 1 % of this area

Unit is present in Clark, Humboldt, Lincoln, Churchill, Washoe, and Pershing Counties. There may be sand dunes in other counties that are not distinguished.

Older gravels (Pleistocene and Pliocene) at surface, covers 1 % of this area

Unit is used for pre-Lake Lahontan deposits, weakly consolidated gravel and sand, older gravels, pediment gravels, and gravel deposits. It includes all units designated as QToa on the 1978 State map. This unit is used in all counties.

Intermediate andesite and intermediate flows and breccias (lower Miocene and Oligocene) at surface, covers 1 % of this area

Andesite flows and breccias and other related rocks of intermediate composition such as dacite, rhyodacite, quartz latite, and biotite-hornblende porphyries. This unit includes units mapped as the South Willow Formation on the Washoe North map, the Milltown Andesite on the Nye South and Esmeralda County maps, the Mizpah Trachyte on the Nye North map, and other units. It corresponds to unit Ta2 on the 1978 State map. It crops out in all counties except Clark, Eureka, Lyon, Douglas, and Carson.

Younger andesite and intermediate flows and breccias (Miocene) at surface, covers 0.9 % of this area

Includes some rocks mapped as the Kate Peak and Alta Formations on the Washoe South map; Wahmonie and Salyer Formations on the Nye South map; Gilbert Andesite on the Esmeralda map; pyroxene, hornblende phenoandesite, and phenodacite on the Elko map; and other unnamed units. It corresponds to the unit Ta3 on the 1978 State map. It is present everywhere except Eureka and White Pine Counties.

Gabbro complex, anorthosite, and albitite (Early Cretaceous to Middle Jurassic) at surface, covers 0.8 % of this area

A large complex of gabbroic rocks forms a series of related intrusions in the northern parts of the Stillwater Range and Clan Alpine Mountains of Churchill County and in the West Humboldt Range of Pershing County (Willden and Speed, 1974). It also may extend into the Trinity Range and Shawave Mountains in western Churchill County (Greene, Stewart, and others, 1991). The complex contains highly differentiated facies near the periphery of the body and more homogeneous gabbro in the interior. Layered rocks near the margins include picrite, olivine gabbro, hornblende gabbro, and anorthosite. The homogeneous rocks consist largely of feldspathic hornblende gabbro and analcite gabbro. The complex is interpreted to be part of a continental Jurassic volcanic arc that is the northern continuation of a Jurassic continental margin arc that extended from the Sonora Desert region in the south to northern California in the north (Dilek and Moores, 1995; Zientek, Sidder, and Zierenberg, 2004). Biotites from several places in the gabbro have been dated by K/Ar and range from 140 to 170 Ma.

Felsic phaneritic intrusive rocks (Cretaceous) at surface, covers 0.8 % of this area

Granodiorite, granite, and related rocks make up the largest group of granitic intrusions exposed in Nevada. They are present in every county, and are especially abundant in west-central Nevada in an arcuate belt along the border with California extending north and eastward towards Idaho.

Older andesite and intermediate flows and breccias (lower Oligocene to middle Eocene) at surface, covers 0.8 % of this area

Unit includes andesite or dacite flows, flow breccias, and hypabyssal rocks in Lander County, andesitic to latitic flows, pyroclastic rocks, and phenoandesitic and phenolatitic flows in Elko County, and other undifferentiated volcanic rocks in other counties. Present in Humboldt, northern Nye, Churchill, Elko, Eureka, Lander, and White Pine Counties. It corresponds to the 1978 State map unit Ta1.

Humboldt Assemblage - Limestone, dolomite, shale, sandstone, and conglomerate (middle Upper to upper Lower Triassic (Carnian to Spathian)) at surface, covers 0.7 % of this area

Unit consists of the Star Peak Group which lies depositionally on the volcanic and volcaniclastic rocks of the Koipato Group (TRkv). Map unit includes rocks mapped as Cane Spring, Natchez Pass, Prida, Augusta Mountain, Congress Canyon, Fossil Hill, Favret, Dixie Valley, and Tobin Formations, including Smelser Pass, Panther Canyon, and Home Station Members of the Augusta Mountain Formation. Basaltic flows and volcanic breccias (TRvm) are present in the Humboldt and northern Stillwater Ranges within the Smelser Pass Member of the Augusta Mountain Formation. The Star Peak Group includes carbonate platform deposits and grades westward into slope and basin paleogeographic environments. Complex stratigraphic patterns of carbonate and terrigenous rocks in the lower part of the group result from localized relative uplift. Widespread diagenetic secondary dolomitization of calcareous rocks complicates the stratigraphic patterns (Nichols and Silberling, 1977b). There is a major unconformity within the Star Peak Group underneath the Panther Canyon Member, which is late Ladinian (late Middle Triassic) in age. The Panther Canyon Member rests in places directly on the noncarbonate rocks of either the Koipato Group (TRkv) or the Golconda terrane (GC), and elsewhere on varying thicknesses of secondary dolomite that replaces Star Peak Group carbonate rocks. The Star Peak Group crops out in Churchill, Humboldt, Lander, and mostly Pershing Counties. Abundant fossil data from the Star Peak Group indicates this unit is latest Early (Spathian) to middle Late (Carnian) Triassic in age (Nichols and Silberling, 1977b).

Flows, basaltic tuffs, and lapilli tuffs (Middle (?) Jurassic) at surface, covers 0.6 % of this area

Layered tuff, lapilli tuff, bedded agglomerate, tuff breccia, autobreccia, and lava, chiefly basaltic. Jurassic mafic volcanic rocks are present in the Stillwater Range in Churchill County, with smaller exposures in the West Humboldt Range. In the Stillwater Range they are intimately associated with gabbroic intrusive rocks (Jgb). They conformably overlie and locally are interbedded with quartz arenite (Jcg). The lavas are homogeneous basalts that contain microphenocrysts of labradorite, diopsidic augite, and talc-hematite after olivine. The groundmass is plagioclase-clinopyroxene-iron oxide (Willden and Speed, 1974). They are believed to be Middle Jurassic because they are thought to be comagmatic with the gabbro (Jgb). This unit is included within the 1978 State map unit Jgb.

Sand Springs Terrane - Basinal volcanogenic rocks and carbonate turbidites (Lower Jurassic and Upper Triassic) at surface, covers 0.5 % of this area

The Sand Springs terrane is a highly deformed, thick, mainly basinal volcanogenic assemblage of rocks at least partly of early Mesozoic age and possibly having affinities with rocks of the Black Rock-Jackson terrane (Silberling, 1991). The presumably oldest Mesozoic rocks are volcanogenic and carbonate turbidites interbedded with mudstone which grade upward into interbedded basinal carbonates and volcanogenic rocks containing Late Triassic faunas (Oldow, 1984a). Elsewhere, interbedded carbonate, volcanic, and volcanogenic rocks are assigned an Early to Middle Jurassic age and represent relatively shallow-marine to subaerial deposition (Oldow, 1984a). Although structural relations in the Sand Springs terrane are locally complicated by later Cenozoic deformation, the rocks appear to have been involved in major northwest-southeast shortening between the Early Jurassic and Late Cretaceous (80 Ma) (Oldow, 1984a). The rocks of the Sand Springs terrane crop out in southern Washoe, Pershing, Churchill, Mineral, and northern Nye Counties.

Intermediate rhyolitic flows and shallow intrusive rocks (lower Miocene and Oligocene) at surface, covers 0.4 % of this area

Includes rocks mapped as the rhyolite of Big Sand Springs Valley on the Nye North map, the Sandstorm Formation in Esmeralda County, rhyolite flow domes in the Sheep Creek Range in Lander County, and other units. It corresponds to unit Tr2 on the 1978 State map. It is present in Nye, Lincoln, Churchill, Esmeralda, Eureka, Mineral, Elko, Humboldt, and Lander Counties.

Felsic phaneritic intrusive rocks (Miocene to Eocene) at surface, covers 0.3 % of this area

Tertiary felsic intrusive rocks are widely scattered in every county across the State. They are generally described as granitic rocks, granodiorite, monzonite, quartz monzonite, alaskitic granite, quartz diorite, dacite, and rhyodacite in the places where they are shown separately on county maps.

Felsic phaneritic intrusive rocks (Miocene (?) to Jurassic (?)) at surface, covers 0.3 % of this area

Poorly dated felsic intrusions described as granitic rocks, granite porphyry, granodiorite, quartz monzonite, and many undivided plutonic rocks are included here. They crop out in every county except Elko and northern Washoe.

Younger silicic ash flow tuffs (Miocene) at surface, covers 0.3 % of this area

Includes units mapped as the High Rock sequence on the Washoe North map; the Timber Mountain, Paintbrush, Crater Flat, and Belted Range Tuffs, and Indian Trail Formation (now abandoned) on the Nye South map; the Thirsty Canyon Tuff on the Nye South and Esmeralda maps; and other unnamed units. Locally it includes tuffaceous sedimentary rocks interstratified with tuffs. It is present in the northernmost part and southernmost parts of the State, and is not exposed in the central region. It corresponds to unit Tt3 on the 1978 State map, although a few rocks also mapped as Trt on the 1978 State map also are included. It is present in Clark, Churchill, Washoe, Nye, Lincoln, Lyon, Douglas, Carson, Esmeralda, Elko, Humboldt, Pershing, and Mineral Counties.

Rhyolitic intrusive rocks with aphanitic groundmass (Miocene to middle Eocene) at surface, covers 0.2 % of this area

Tertiary rhyolitic intrusive rocks also are present in every county of Nevada. They include many rocks mapped as rhyolite or rhyolite porphyry, rhyolite intrusive rocks, rhyolite plugs or flows, microgranite dikes, and many other undifferentiated intrusive rocks.

Metavolcanic rocks (Jurassic (?) and Triassic (?)) at surface, covers 0.2 % of this area

Metamorphosed (generally greenschist-facies) andesite and dacite flows and breccias, flow-banded rhyolite and rhyodacite, welded tuff, local hypabyssal intrusive rocks, and minor amounts of volcaniclastic sandstone and conglomerate (Greene, Stewart, and others, 1991). This unit includes the Peavine sequence in Washoe County, and other unnamed metasedimentary and metavolcanic rocks in Lyon, Douglas, Carson, and Churchill Counties. These rocks are considered distinct from the other metavolcanic and metasedimentary rocks in adjacent Mesozoic terranes. They are included in unit JTRsv on the 1978 State map.

Younger rhyolitic flows and shallow intrusive rocks (Miocene) at surface, covers 0.2 % of this area

Rhyolitic flows, domes, plugs, breccias, quartz latite, rhyodacite, quartz porphyry dikes, and other shallow intrusive rocks. This unit includes rocks mapped as the Cañon Rhyolite on the Washoe North map, the Jarbidge Rhyolite and phenorhyolitic and phenodacitic flows and domes on the Elko County map, and other unnamed units. It has a distribution similar to Tt3, with exposures in the northern and southern parts of the State, but only crops out in a few places in the central region. It corresponds to unit Tr3 on the 1978 State map, and also includes a few rocks mapped as Trt on the 1978 State map. This unit is exposed in every county except White Pine.

Humboldt Assemblage - Shale, siltstone, sandstone, and minor carbonate (Lower Jurassic to Upper Triassic) at surface, covers 0.1 % of this area

Rocks of the Grass Valley, Osobb, and Dun Glen Formations, and their unnamed overlying rocks elsewhere known as the Winnemucca Formation, exposed in Pershing, Churchill, Lander, and Humboldt Counties, characterize this unit. These rocks are depositional on top of the Star Peak Group carbonate and detrital rocks (TRc). Crossbedding, lode casts, and other depositional features indicate uniform northwest-trending current directions. The lithology and depositional characteristics of these rocks suggest shallow marine conditions on and around a westerly prograding delta (Silberling and Wallace, 1969). Fossils from these rocks range in age from Late Triassic (Norian) to Early Jurassic (Toarcian) (Silberling and Wallace, 1969).

Quartz Mountain Terrane - Orthoquartzite, feldspathic sandstone, and volcanic rocks (Mesozoic or Paleozoic, possibly Jurassic) at surface, covers 0.1 % of this area

The Quartz Mountain terrane, of unknown Mesozoic or Paleozoic age, is distinguished lithologically by the association of orthoquartzite with feldspathic sandstone and (or) volcanic rocks (Silberling, oral commun., 2006). Other rock types include metapelite, dolomite, and locally derived coarse clastic rocks (Silberling and John, 1989). This structurally disrupted mass is intricately intruded by and structurally brecciated with igneous rocks in the Lodi Hills. The structures that bound the intrusive rocks are thought to postdate the fault or faults on which the sedimentary rocks of the Quartz Mountain terrane were originally emplaced (Silberling and John, 1989). Exposures in the La Plata quadrangle mapped as the Mountain Well sequence, have here been assigned to the Quartz Mountain terrane (John and Silberling, 1994). These rocks are exposed in Churchill and northern Nye Counties.

Basalt flows (Holocene and Pleistocene) at surface, covers 0.1 % of this area

Basalt flows, plugs, cinder cones, basaltic ash, scoria, and basaltic sediments. They are present in Nye, Esmeralda, and Churchill Counties.

Conglomerate, limestone, and quartz sandstone (Middle and Lower Jurassic) at surface, covers 0.1 % of this area

The Boyer Ranch Formation in the Clan Alpine and Stillwater Ranges in Pershing and Churchill Counties consists of a basal conglomerate overlain by partly silicified limestone that is overlain by quartz sandstone. In places it rests unconformably over Upper Triassic or younger rocks (Speed and Jones, 1969) of the Jungo terrane (JO), constraining its maximum age, and elsewhere it is faulted over Late Triassic and Early Jurassic rocks (Speed and Jones, 1969). The occurrence of conglomerate-bearing clasts of underlying units at the base of the formation supports the interpretation of unconformable basal contacts even though the unit is strongly folded (Speed and Jones, 1969). It is overlain by volcanic rocks that are comagmatic with the adjacent Middle Jurassic gabbro. In the Pamlico-Lodi (WPL) and Luning-Berlin (WLB) assemblages of the Walker Lake terrane and the Gold Range assemblage (JTRgor), a coarse clastic and shallow marine unit of Jurassic age has been mapped as the Dunlap Formation (Stewart and Carlson, 1978). It lies unconformably over both Permian and Triassic rocks (Oldow, 1981), and disconformably over other Triassic and Lower Jurassic rocks (Oldow and Bartel, 1987). Some of the rocks mapped as Dunlap likely belong in unit Jcg, however, it is not consistently defined on the Nye, Mineral, and Esmeralda County maps, and in many places rocks originally mapped as Dunlap have turned out to be a variety of other units. The Dunlap Formation therefore has not been separated from the other Mesozoic rocks on this map at this time, but it may belong with a more regional Jcg unit that defines an important mid-Mesozoic tectonic constraint.

Andesite, rhyolite, tuff, and volcaniclastic rocks (Middle and Lower Triassic) at surface, covers < 0.1 % of this area

Andesite, rhyolite, tuff, and generally siliceous volcaniclastic rocks make up the Koipato Group, which lies unconformably below the Humboldt assemblage. The Koipato Group consists of altered porphyritic andesite flows and flow breccia of the Limerick Greenstone, altered felsite and coarse-grained tuffaceous sedimentary rocks of the Rochester Rhyolite, and quartz-rich ash-flow tuff and tuffaceous sedimentary rocks of the Weaver Rhyolite. It is present in Churchill, Humboldt, Lander, and mostly Pershing Counties where it unconformably overlies deformed rocks of the Golconda terrane (GC). The upper part of the Koipato contains late Early Triassic (Spathian) fossils (Silberling, 1973; Wallace, Tatlock, and others, 1969). It is depositionally overlain by the Star Peak Group (TRc), a sequence of carbonate platform deposits at the base of the Humboldt assemblage. Radiometric dates from the 1970s (McKee and Burke, 1972) suggest a Middle to Early Triassic age.

Older tuffaceous sedimentary rocks (lower Miocene and Oligocene) at surface, covers < 0.1 % of this area

Locally includes minor amounts of tuff. It includes rocks mapped as the Titus Canyon Formation on the Nye South map, the Gilmore Gulch Formation on the Nye North map, lacustrine limestone in Lincoln County, and other unnamed units. This unit corresponds to unit Ts2 on the 1978 State map. It is present in Nye, Lincoln, Elko, and Lander Counties.

Golconda Terrane - Basinal, volcanogenic, terrigenous clastic, and minor carbonate rocks (Permian to Upper Devonian) at surface, covers < 0.1 % of this area

The Golconda terrane is composed of deformed and imbricated thrust slices of upper Paleozoic rocks including deep-marine, pelagic and turbiditic, carbonate, terrigenous clastic and volcaniclastic rocks, radiolarian chert and argillite, and pillow basalt (Silberling, Jones, and others, 1992). While the terrane is characterized by a great diversity of rock types, all rocks are strongly deformed with an east-vergent fabric, a distinguishing characteristic of this terrane (Brueckner and Snyder, 1985; Jones, 1991a; Miller, Kanter, and others, 1982; Murchey, 1990; Stewart, Murchey, and others, 1986). It crops out in a long sinuous belt, up to 100 mi wide in places. Southwest of Mina, the belt trends east from the California border to just north of Tonopah, and then bends north-south to the west of Longitude 117° to about 50 mi north of Winnemucca, where it bends again, sharply to the east-north of Tuscarora with significant exposures eastward and to the northern border of the State. Outcrops of the Golconda terrane are present in Mineral, Esmeralda, northern Nye, Churchill, Elko, Humboldt, Lander, and Pershing Counties. It includes some rocks originally mapped as Banner and Nelson Formations in Elko County; rocks originally mapped as the Excelsior Formation in Mineral and Esmeralda Counties, later assigned to the Black Dyke and Mina Formations by Speed (1977b); the original Havallah and Pumpernickel Formations (Muller, Ferguson, and Roberts, 1951; Roberts, 1964; Silberling and Roberts, 1962), later revised to structural sequences (Murchey, 1990; Stewart, MacMillan, and others, 1977; Stewart, Murchey, and others, 1986; Theodore, 1991; 1994) in Elko, Humboldt, Lander, and Pershing Counties; the Inskip Formation in Pershing County; the Mitchell Creek Formation in Elko County; the Pablo Formation in northern Nye County; and the Schoonover Formation (see unit GChr) in Elko County. In all of the places where rocks of the Golconda terrane were originally believed to form a stratigraphic sequence, detailed mapping and biostratigraphic analysis with radiolarians and conodonts has demonstrated that it is characterized by complex imbrications of rocks ranging from mid-Permian through latest Devonian age (Holdsworth, 1986; Jones, 1991b; Miller, Holdsworth, and others, 1984; Murchey, 1990; Stewart, MacMillan, and others, 1977). In Pershing County, the Golconda terrane is unconformably overlain by Triassic volcanic rocks of the Koipato Group (TRkv) which form the stratigraphic base to the Humboldt assemblage (TRc, JTRs). In Mineral and Esmeralda Counties, it is unconformably overlain by the Gold Range assemblage (JTRgor) of mainly nonmarine, terrigenous clastic, and volcanogenic Upper Triassic and younger rocks. Elsewhere in northern and southwestern Nevada, it is structurally overlain by Mesozoic accreted terranes. Across the length of its exposure from the Independence Mountains north of Elko to the Candelaria region south of Mina, the base of the Golconda terrane has a remarkably consistent structural emplacement relationship with adjacent rocks. It commonly lies on a low-angle structure above Permian and Pennsylvanian rocks of the Siliciclastic overlap assemblage. In places where these rocks are missing, it is faulted directly onto either the nearby lower Paleozoic Basin assemblage, the Nolan belt rocks, or the Harmony Formation of the Dutch Flat terrane. The type locality of this regional feature, the Golconda thrust is well exposed along Interstate Highway 80 at Edna Mountain near the town of Golconda (Ferguson, Roberts, and Muller, 1952), and in the open pits of mines near Battle Mountain (Theodore, T., oral commun., 2006). In southwestern Nevada, the lower Lower Triassic rocks of the Candelaria Formation overlie Permian and Pennsylvanian Siliciclastic overlap assemblage rocks, and the Golconda terrane is exposed nearby, but not observable directly on top of the Candelaria because of younger cover rocks. Elsewhere, there is no youngest age constraint for the age of emplacement. In several places, notably in the Osgood Mountains and the Toiyabe Range, it is also bounded by large, steeply dipping, mélange-like shear zones against older rocks of the Nolan belt. Stratigraphic and structural studies within the terrane have locally identified lithostratigraphic groupings (Erickson and Marsh, 1974a, b; Jones, 1991a; Murchey, 1990), but only the Home Ranch subterrane can presently be distinguished on a regional scale (GChr). Interpretations of the size and character of the late Paleozoic basin where these rocks formed and the nature of its Late Permian or Early Triassic accretion are as varied as the lithologic and structural characteristics of the terrane itself (see references above).

Mafic phaneritic intrusive rocks (Miocene to middle Eocene) at surface, covers < 0.1 % of this area

Tertiary mafic intrusive rocks are widely scattered across Nevada north of Clark County. They include rocks mapped as dacite and rhyodacite, diorite, quartz latite, and numerous undivided intrusive rocks on the county maps.

Walker Lake Terrane - Luning-Berlin assemblage - Carbonate and terrigenous clastic rocks (Middle (?) Jurassic to Middle Triassic) at surface, covers < 0.1 % of this area

Assemblage is underlain by the regionally extensive Luning thrust and lies structurally below the Pamlico-Lodi assemblage (WPL) (Oldow, 1984a). The Upper Triassic continental shelf sequence part of WLB consists of platform carbonate rocks and shallow-marine to deltaic-clastic rocks. Minor amounts of volcanogenic rocks are interbedded with terrigenous clastic rocks near the western margin of the assemblage (Oldow, 1984a). These are conformably overlain by Lower (Pliensbachian) to Middle Jurassic quartz arenite and coarse clastic rocks which grade upward into volcanogenic rocks (Oldow, 1984a; Oldow and Bartel, 1987). Rocks of the Luning-Berlin assemblage are involved in a complex deformational history involving first northwest-southeast thrusting, followed by second folds with north-northwest to west-northwest axial planes (Oldow, 1984a). The folding is constrained between Middle Jurassic and Late Cretaceous (90 Ma) (Oldow, 1984a). Rocks that have been assigned to the Dunlap, Gabbs, Sunrise, Luning, and Grantsville Formations are included in this assemblage (Silberling, 1984; Whitebread and John, 1992).

Landslide deposits, colluvium, and talus (Holocene to Pliocene) at surface, covers < 0.1 % of this area

Unit is mixed on the Washoe North map with basalt, tuff, diatomite, and tuffaceous sediments. It includes the units mapped as Qls from the 1978 State map. It is present in Churchill, Washoe, Nye, Esmeralda, Elko, Eureka, Humboldt, Lander, Lincoln, Mineral, and Pershing Counties.

Older felsic phaneritic intrusive rocks (Jurassic) at surface, covers < 0.1 % of this area

Concentrated in two areas of the State; common in the west-central part of the State along the California border in Mineral, Esmeralda, Lyon, Douglas, and Carson Counties. There is another more widely scattered group in eastern and central Nevada in Elko, Eureka, and White Pine Counties. Scattered occurrences also are present in Humboldt, Churchill, Lander, and Pershing Counties. Compositions are mainly granitic, granodiorite, and quartz monzonite.

Walker Lake Terrane - Pamlico-Lodi assemblage - Carbonate and volcanogenic rocks (Middle (?) Jurassic to Middle Triassic) at surface, covers < 0.1 % of this area

The Pamlico-Lodi assemblage differs stratigraphically from the Luning-Berlin assemblage in that the Triassic carbonate sequences are interstratified with volcanic and volcanogenic rocks, not continentally derived epiclastic chert, conglomerate, sandstone, and argillite (Oldow, Satterfield, and Silberling, 1993; Silberling and John, 1989). The uppermost part of the sequence is a regionally extensive carbonate shelf like the Luning-Berlin assemblage. This is conformably overlain by quartz arenite and poorly sorted coarse clastic rocks faunally dated as Early Jurassic that grade upward into volcanogenic sedimentary and volcanic rocks (Oldow, 1984a; Oldow and Bartel, 1987). The Pamlico-Lodi assemblage has a polyphase folding history similar to the Luning-Berlin assemblage that was caused by northwest-southeast directed thrusting that displaced the rocks tens of kilometers toward the southeast (Oldow, 1984a). Compared with the Luning-Berlin assemblage to the east, however, rocks of the Pamlico-Lodi assemblage manifest much more shortening from this first deformation of southeast-directed tectonic transport (Speed, Silberling, and others, 1989). This assemblage is exposed in Churchill, Mineral, and northern Nye Counties. It includes rocks mapped as Dunlap, Excelsior, Gabbs, Sunrise, and Luning Formations.

Older mafic phaneritic intrusive rocks (Jurassic) at surface, covers < 0.1 % of this area

Unit includes diorite in northern Elko County, diorite to granodiorite in the Toquima Range of northern Nye County, and dioritic rocks in western Churchill County.

Basalt flows (Holocene to Pliocene) at surface, covers < 0.1 % of this area

Olivine basalt and basaltic and andesitic rocks. This unit is present in Clark, Elko, Mineral, Esmeralda, Humboldt, Lincoln, Lyon, Douglas, Carson, Nye, Washoe, and Lander Counties. It corresponds to the 1978 State map unit QTb.