Geologic units in Esmeralda county, Nevada

Additional scientific data in this geographic area

Alluvium, undifferentiated (Holocene and Pleistocene) at surface, covers 45 % 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.

Younger silicic ash flow tuffs (Miocene) at surface, covers 9 % 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.

Crossbedded quartzite, siltstone, and phyllite (Lower Cambrian and latest Proterozoic) at surface, covers 6 % of this area

These lowermost Cambrian to Precambrian strata are scattered over much of central and eastern Nevada and form the base of the Phanerozoic part of the continental margin stratigraphic section. They include the Campito, Deep Spring, Harkless, and Poleta Formations, and the Reed Dolomite in Esmeralda County; the Gold Hill Formation in northern Nye County; unnamed quartzite and shale in White Pine County; the Osgood Mountain quartzite in Humboldt County; the Prospect Mountain Quartzite in northern Nye, Lincoln, Eureka, and Elko Counties; unnamed quartzite and shale in Lander and Clark counties; and the Stirling Quartzite, Wood Canyon Formation, and Zabriskie Quartzite in southern Nye County. In a number of places, these rocks are depositional on Late Proterozoic unit Zqs. In southernmost Clark County, CZq is lying unconformably directly on Early Proterozoic gneiss (Xm). In the east-central part of Nevada, CZq is overlain depositionally by Cambrian carbonate (Cc) of the Carbonate shelf sequence. In the Nolan belt, these rocks are depositionally overlain by unit Ctd. In the Osgood Mountains in Humboldt County, Permian and Pennsylvanian rocks of the Siliciclastic overlap assemblage (PIPacl, Pacl) rest unconformably directly on the Osgood Mountain Quartzite.

Younger tuffaceous sedimentary rocks (Pliocene and Miocene) at surface, covers 5 % 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.

Older felsic phaneritic intrusive rocks (Jurassic) at surface, covers 5 % 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.

Playa, lake bed, and flood plain deposits (Holocene and Pleistocene) at surface, covers 4 % 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.

Younger andesite and intermediate flows and breccias (Miocene) at surface, covers 4 % 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.

Intermediate silicic ash flow tuff (lower Miocene and Oligocene) at surface, covers 3 % 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 gravels (Pleistocene and Pliocene) at surface, covers 3 % 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.

Younger rhyolitic flows and shallow intrusive rocks (Miocene) at surface, covers 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.

Nolan Belt - Shale, chert, phyllite, quartzite, and limestone (Ordovician to Cambrian) at surface, covers 2 % of this area

Rocks included in this unit have been mapped as the Broad Canyon Formation and Crane Canyon sequence in Lander County (Means, 1962), the Palmetto Formation in Esmeralda and Nye Counties (Ferguson and Cathcart, 1954), the Van Duzer Limestone in northern Elko County (Coats, 1971; Coats, Howard, and Greene, 1984; Decker, 1962; Ehman, 1985), and many other unnamed and locally named rocks. These rocks are strongly deformed, although the nature of the deformation is variable across the belt (Oldow, 1984b) and not well understood regionally. This unit is usually shown both in fault contact with adjacent units Ctd and CZq and gradational with them. Unit Pacl of the Siliciclastic overlap assemblage is shown unconformably deposited on this unit in Wall Canyon of the Toiyabe Range in Nye County. In a few cases, this unit is a stratigraphic continuation from Ctd, but in most places it represents undifferentiated rocks of both Ordovician and Cambrian age that overlap with Ctd, or whose age is poorly constrained.

Felsic phaneritic intrusive rocks (Cretaceous) at surface, covers 2 % 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.

Nolan Belt - Phyllite, schist, shale, thin-bedded limestone, chert, and siltstone (Cambrian) at surface, covers 2 % of this area

Shale, thin-bedded limestone, phyllite, hornfels, quartzite, chert, and siltstone are typical of this Cambrian unit which exhibits regional metamorphism suggesting significant burial depths have heated and recrystallized many of these rocks. This unit includes rocks mapped informally as the Bull Run Dolomite and Edgemont Formation in northern Elko County by Ehman (1985); the Crane Canyon sequence in the Toiyabe Range; some regions mapped as Dunderberg Shale; and the Swarbrick Formation in northern Nye County, the Emigrant Formation in southern Nye and Esmeralda Counties, the Mule Spring Limestone in Esmeralda County, the Preble Formation in Humboldt and Pershing Counties (Madden-McGuire, 1991), the Paradise Valley Chert in Humboldt County, and the Schwin Formation (Gilluly and Gates, 1965) in the Shoshone Range in Lander County. In most exposures this unit lies transitionally above the Cambrian-Precambrian quartzite unit CZq. In places this unit is transitional into OCtd. This unit is also in structural contact with DCs, DOts, OCc, OCtd, CZq, the Golconda terrane (GC), and the Dutch Flat terrane (DF). In the Osgood Mountains (Boskie and Schweickert, 2001; Crafford and Grauch, 2002; Madden-McGuire and Marsh, 1991), the Bull Run Mountains (Ehman, 1985), the Toiyabe Range (Means, 1962), and the Miller Mountain area (Oldow, 1984b) these rocks exhibit complex polyphase deformation with a strong west-vergent component. At Edna Mountain near Golconda in Humboldt County, these rocks are unconformably overlain by both Pacl and PIPacl of the Siliciclastic overlap assemblage.

Quartzite, siltstone, conglomerate, limestone, and dolomite (Late Proterozoic) at surface, covers 1 % of this area

Limestone, quartzite, dolomite, siltstone, conglomerate, and metamorphic rocks crop out in the southeastern, east-central, and northeastern regions of the State as part of Zqs. It forms the Proterozoic base of the continental margin stratigraphic section. This unit includes the Johnnie Formation in southern Nye and Lincoln Counties, schist in Elko County, the McCoy Creek Group metamorphic rocks in Elko and White Pine Counties, and the Wyman Formation in Esmeralda and southern Nye Counties. This rock is overlain by CZq. Its base is not exposed.

Intermediate rhyolitic flows and shallow intrusive rocks (lower Miocene and Oligocene) at surface, covers 1 % 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.

Basalt flows (Holocene to Pliocene) at surface, covers 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.

Andesite and basalt flows (Miocene and Oligocene) at surface, covers 0.8 % 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.

Basin Assemblage - Shale, chert, quartzite, greenstone, and limestone (Devonian to Upper Cambrian) at surface, covers 0.6 % of this area

Includes the Valmy Formation in Eureka, Humboldt, Lander, and Pershing Counties; Devonian to Upper Cambrian mudstone, shale, chert, siltstone, and gray quartzite in Elko County (Leslie, Isaacson, and others, 1991); Devonian to Ordovician slate, chert, limestone, and sandstone in Mineral County; Devonian to Upper Cambrian rocks in Eureka County (Finney, Perry, and others, 1993); some rocks originally mapped as the Palmetto Formation in Esmeralda County (Albers and Stewart, 1972; Ferguson and Cathcart, 1954); and the Sonoma Range Formation (Ferguson, Muller, and Roberts, 1951) in the Sonoma Range in Humboldt County (later included with the Valmy Formation). The distinctions between these rocks and rocks of the Slope assemblage (DOts) are (1) a more complex and varied history of deformation; (2) less well-defined internal stratigraphic characteristics, which may be a function of structural complexity; (3) fewer shale, siltstone, and sandstone interbeds; (4) less carbonate; and (5) in the Roberts Mountains at least, the Ordovician rocks of this unit are older than the Slope assemblage Ordovician rocks. Like unit DOts, no basement is preserved with these rocks, making it difficult to determine where they were originally laid down, and how far they have been transported. This unit includes Devonian, Silurian, Ordovician, and uppermost Cambrian rocks imbricately faulted and folded together. In a few places, Silurian rocks are defined regionally and broken out separately (Ss), but for the most part they are included in this unit. Likewise, significant exposures of Devonian rocks have been included in unit MDst, but many more are not differentiated from this unit. A great variety of depositional settings are present in ocean basins, and this diversity is represented in these rocks (Watkins and Browne, 1989). While these rocks share a common deformation history indicative of east-directed transport from folding and thrusting along regional structures in different areas of Nevada, these rocks have been subject to additional distinct tectonic events during the Mesozoic and the Paleozoic resulting in significant spatial variability in the structure of these rocks (Evans and Theodore, 1978; Oldow, 1984b).

Tuffaceous limestone, siltstone, sandstone, and conglomerate (Holocene to Pliocene) at surface, covers 0.5 % of this area

Present in Esmeralda, Elko, Mineral, Lyon, Douglas, Carson, and Eureka Counties and corresponds to unit QTs on the 1978 State map.

Intermediate andesite and intermediate flows and breccias (lower Miocene and Oligocene) at surface, covers 0.4 % 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.

Landslide deposits, colluvium, and talus (Holocene to Pliocene) at surface, covers 0.4 % 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.

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

Poorly dated mafic intrusions are concentrated in two regions of Nevada, northwestern and west-central to southwestern parts of the State. They crop out in northern Nye, Mineral, Esmeralda, Eureka, Humboldt, and Lander Counties, and include rocks described on the county maps as dioritic to andesitic rocks, diorite and related rocks, and granodiorite.

Mafic phaneritic intrusive rocks (Miocene to middle Eocene) at surface, covers 0.3 % 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.

Andesite flows and breccias (Holocene to Pliocene) at surface, covers 0.2 % of this area

Present in southern Washoe, Esmeralda, Lyon, Douglas, Carson, Mineral, and Lander Counties. It corresponds to unit QTa on the 1978 State map.

Golconda Terrane - Basinal, volcanogenic, terrigenous clastic, and minor carbonate rocks (Permian to Upper Devonian) at surface, covers 0.2 % 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).

Felsic phaneritic intrusive rocks (Miocene (?) to Jurassic (?)) at surface, covers 0.2 % 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.

Siliciclastic Overlap Assemblage - Shale, sandstone, and limestone (Lower Triassic) at surface, covers 0.2 % of this area

Shale with interbedded sandstone and minor limestone characterize the Lower Triassic Candelaria Formation (Ferguson, Muller, and Cathcart, 1954). This vertically coarsening sequence grades up into a distal volcanogenic turbidite in the middle and a proximal turbidite and breccia near the top (Stewart, 1980). The basal strata of the Candelaria are earliest Triassic (Griesbachian) and the highest are late Early Triassic (early Spathian) (Speed, Silberling, and others, 1989). It is equivalent in age to the marine Dinwoody Formation of northwestern Utah and southeastern Idaho, and possibly, to the lower part of the predominantly volcanic Koipato Group in northwestern Nevada (Poole and Wardlaw, 1978). The Candelaria Formation is mainly exposed near the old mining camp of Candelaria, located a little more than 20 mi south of Mina, in Mineral County. Another exposure also has been described from the southern Toquima Range in Nye County, and a collection of Early Triassic fauna was recovered from flaggy brown siltstone from the west side of the Toiyabe Range east of Ione (Poole and Wardlaw, 1978). Early Triassic conodonts in clastic rocks in the northern Hot Creek Range near Morey Peak suggest that some of these rocks may also be correlative with the Candelaria. These additional Early Triassic locals suggest that the Candelaria may have been more extensive, or is still unrecognized elsewhere in the central part of the State. The nature of the basal contact is critical to determining the appropriate paleogeographic setting and regional grouping for this unit. If the basal contact is a major structure, then the Candelaria likely represents a section of one of the many Mesozoic terranes that have been emplaced from the west. If the contact is fundamentally sedimentary, albeit disconformable or unconformable, then it constrains an important piece of the paleogeographic tectonic puzzle of Nevada geology. The Candelaria Formation lies on the subjacent Permian Diablo Formation where it is described as unconformable by Ferguson and others (1954), conformable by Speed and others (1977, p. 303), and nearly conformable by Page (1959). The Candelaria near Willow Spring in the Toquima Range is described as a “probable unconformity” by Poole and Wardlaw (1978). The regional map relations for this unit suggest that the base is a disconformity or slight unconformity with the underlying Diablo Formation (Ferguson, Muller, and Cathcart, 1954; Page, 1959), but not a major structure. The Diablo Formation, included here with the Permian siliciclastic overlap assemblage, lies with marked unconformity on lower Paleozoic basinal rocks of chert, argillite, and shale, as discussed below. The Candelaria Formation is unusual in that it is the oldest Mesozoic sedimentary sequence known in Nevada, and is present in a restricted area only over the Permian rocks of the Siliciclastic overlap assemblage, which also suggests that it was originally deposited directly on those rocks. The presence of volcaniclastic rocks in the upper part of the section is an important tectonostratigraphic link to the rocks of adjacent terranes. Rocks near Quinn River, Nevada that are almost as old and contain volcaniclastic rocks in the upper part of the section, belong to the Black Rock-Jackson terrane (Blome and Reed, 1995; Jones, 1990). Triassic rocks of similar age exposed south of Jarbidge in northeastern Elko County are juxtaposed with Permian rocks of the Siliciclastic overlap assemblage and may correlate with the Candelaria, but the base of the section is unknown and no volcanic facies are reported from those rocks, so they are currently included with the Cratonal sequence, TRmt.

Rhyolitic intrusive rocks with aphanitic groundmass (Miocene to middle Eocene) at surface, covers 0.1 % 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.

Gold Range Assemblage - Terrigenous clastic and volcanogenic rocks (Lower Jurassic and Upper Triassic) at surface, covers < 0.1 % of this area

The Gold Range assemblage consists of mainly nonmarine, terrigenous clastic, and volcanogenic rocks of probable Late Triassic to Middle Jurassic ages, and local volcanic rocks having younger Mesozoic radiometric ages (Silberling, 1991). It is lying with angular unconformity over Permian rocks included in the Golconda terrane (GC). The oldest rocks are interbedded, subaerial and shallow-marine terrigenous clastic, volcaniclastic, and minor carbonate rocks overlain by shelf carbonates containing Early Jurassic pelecypods. Unfossiliferous quartz arenite and coarse clastic rocks disconformably overlie the shelf carbonate and grade upward into poorly sorted volcanogenic sandstone and coarse clastic rocks (Oldow, 1984a; Oldow and Bartel, 1987). The assemblage is deformed by northeast-trending folds associated with the overlying Luning thrust as well as younger northwest-trending folds (Oldow, 1984a). Archbold and Paul (1970) named these rocks the Gold Range Formation. They were originally mapped as the Luning Formation and in a few cases, the Excelsior Formation by early workers (Archbold and Paul, 1970, p. 6). Speed (1977a) later modified the definition of the Gold Range Formation. Oldow (1981) included some of these rocks in the Water Canyon assemblage. These rocks were included with the Paradise terrane (Silberling, Jones, and others, 1987; Silberling, Jones, and others, 1992), but have been separated here in agreement with Silberling (1991). Silberling (1991) used “Gold Range terrane” to include the unconformably underlying Permian rocks of the Mina Formation. Since the basement rocks are here included with the Golconda terrane, the term “Gold Range assemblage” is used only for the Mesozoic rocks unconformably overlying the Permian basement. The Gold Range assemblage is in the same tectonostratigraphic position as the Humboldt assemblage - both are overlying rocks of the Golconda terrane with a strong angular unconformity. While these assemblages are similar in overall age, they have different stratigraphic sequences and thus paleogeographic settings. The exact stratigraphy of the Gold Range assemblage and whether or not it includes younger Cretaceous volcanic rocks (Silberling, Jones, and others, 1987; Stewart, 1980) is not clear. This assemblage crops out in Esmeralda, Mineral, and northern Nye Counties.

Older alluvium and alluvial fan deposits (Pleistocene and Pliocene) at surface, covers < 0.1 % 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.

Siliciclastic Overlap Assemblage - Sandstone, siltstone, limestone, conglomerate, and carbonaceous limestone (Permian) at surface, covers < 0.1 % of this area

Unit is mapped in Elko, Mineral, Humboldt, Lander, Eureka, White Pine, northern Nye, and Esmeralda Counties. Included in this unit are the Carbon Ridge Formation in Eureka and White Pine Counties, parts of the Carlin sequence of Coats (1987), the sandstone and siltstone of Horse Mountain in Elko County, the Edna Mountain Formation in Humboldt and Elko Counties, the Garden Valley Formation in Eureka County, and the Diablo Formation in northern Nye, Mineral, and Esmeralda Counties. In the Candelaria area south of Mina, unit Pacl rests unconformably on deformed Upper Cambrian through Devonian Basin assemblage (DCs) and is overlain by the Lower Triassic Candelaria Formation (TRcl). In the Toiyabe Range, it lies unconformably on deformed Cambrian through Ordovician rocks of the Nolan belt (OCtd). In the Simpson Park Mountains and the Sulphur Spring Range, it rests unconformably on Ordovician and Devonian Slope assemblage rocks (DOts). In the Diamond Mountains it rests unconformably on the Ely Limestone (IPMbc). In the Eureka area, Pacl unconformably overlies the Ely Limestone (IPMbc) and the Diamond Peak Formation (IPMcl) and is unconformably overlain by Cretaceous conglomerate (Kcg). Near Golconda it unconformably overlies PIPacl. In the Adobe Range in Elko County it overlies Foreland basin assemblage rocks (IPMcl, MDcl) and PIPacl, and in the Snake Mountains and HD Range of northeast Nevada it lies unconformably on lower Paleozoic Slope and Basin assemblage rocks (DCs, Ss, DOts) and on older Siliciclastic overlap assemblage rocks (PIPacl).

Glacial moraines (Holocene and Pleistocene) at surface, covers < 0.1 % of this area

Sediments are present in southern Washoe, northern Nye, Esmeralda, Elko, Humboldt, White Pine, and Lander Counties in high mountain ranges.

Metaquartzite (Lower Cambrian and latest Proterozoic) at surface, covers < 0.1 % of this area

This highly metamorphosed equivalent of CZq crops out in the Ruby Mountains and East Humboldt Range in Elko County, in the Toquima and Monitor Ranges in northern Nye County, and at the northern tip of the White Mountains in Mineral and Esmeralda Counties. In the Ruby Mountains it is transitional into OCcm, and in the White Mountains it is transitional into OCtd.

Carbonate Shelf Sequence - Limestone, dolomite, and quartzite (Middle Ordovician to Upper Cambrian) at surface, covers < 0.1 % of this area

Carbonate platform rocks are present in Nye, Lincoln, Elko, Eureka, Lander, White Pine, Esmeralda, and Clark Counties. This unit is primarily Ordovician in age but does include Upper Cambrian rocks at the base (Page, Lundstrom, and others, 2005). The Pogonip Group, including the Antelope Valley Limestone is the most common name used. In Clark County it also includes the Ely Springs Dolomite, and includes the Eureka Quartzite in White Pine and Clark Counties. Unit OCc corresponds to depositional sequence 2 of Cook and Corboy (2004). Where Ocq is mapped separately, it overlies OCc. Otherwise OCc is depositional under SOc, or in southern Nye and Clark Counties, it is overlain directly by DSc where SOc is not differentiated. Unit OCc depositionally overlies unit Cc.

Quaternary alluvium and marine deposits (Pleistocene to Holocene) at surface, covers < 0.1 % of this area

Alluvium, lake, playa, and terrace deposits; unconsolidated and semi-consolidated. Mostly nonmarine, but includes marine deposits near the coast.

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.

Felsic phaneritic intrusive rocks (Triassic) at surface, covers < 0.1 % of this area

Intrusive rocks crop out in the East Range and Humboldt Range in Pershing County associated with the Koipato Group volcanic rocks (TRkv). They intrude upper Paleozoic rocks of the Golconda terrane (GC) and rocks of the Koipato Group. Limited older evidence suggests that these rocks may be Triassic (Silberling and Wallace, 1967; Wallace, Silberling, and others, 1969; Wallace, Tatlock, and Silberling, 1960; Wallace, Tatlock, and others, 1969), but new data (du Bray and Crafford, 2007) suggests that most of the intrusive rocks mapped as Triassic in the East and Humboldt Ranges are Cretaceous or younger. In northern Esmeralda County between the Royston Hills and the Monte Cristo Range small exposures of Upper Triassic plutons are inferred to relate to the Lee Vining intrusive epoch in eastern California (Stewart, 1980). These rocks also intrude into the Golconda terrane (GC).

Foreland Basin Assemblage - Shale, siltstone, sandstone, and conglomerate (Middle Pennsylvanian to Lower Mississippian) at surface, covers < 0.1 % of this area

Unit crops out across all of eastern Nevada, generally east of 116 west longitude, and somewhat farther west in the southern half of the State. It includes rocks mapped as the Chainman Shale in Elko, northern Nye, and Lincoln Counties; the Diamond Peak Formation in northern Nye, Elko, Eureka, and White Pine Counties; the Scotty Wash Quartzite in Lincoln County; the upper part of the Eleana Formation in Nye County; and undivided sedimentary rocks in Eureka and Lincoln Counties. Clastic and carbonate rocks mapped in Elko County, including undivided Moleen and Tomera Formations (the Tomera Formation includes Middle Pennsylvanian rocks) are also grouped here. Most of these rocks are Upper Mississippian and Lower Pennsylvanian in age, but unit IPMcl also includes Lower Mississippian rocks, overlapping with unit MDcl where they have not been clearly distinguished. In places the Chainman Shale is time transgressive into the Diamond Peak Formation, and in other places they represent different coeval facies, based on limited biostratigraphic data. Where possible, younger siliciclastic rocks have been separated from the older sequence that includes the Pilot Shale and Joana Limestone because of significant differences in the character of the rocks. Unit IPMcl is overlain conformably or disconformably in the eastern part of its exposure by carbonate rocks of units PIPc and (or) IPMbc. In the northern and western parts of its exposure it is overlain unconformably by Permian and Upper Pennsylvanian clastic rocks of the Siliciclastic overlap assemblage (Pacl or PIPacl). Assignment of siliciclastic Pennsylvanian units to either unit IPMcl or the unconformably overlying PIPacl is challenging unless biostratigraphic data are available and outcrop observations reveal the presence of the unconformity such as in Carlin Canyon (Dott, 1955). Unit IPMcl lies either conformably or disconformably above unit MDcl.

Carbonate Shelf Sequence - Dolomite, limestone, and shale (Cambrian) at surface, covers < 0.1 % of this area

Occurs in southern and eastern Nevada. The Bonanza King and Carrara Formations are the primary formations in southern Nye County; the Dunderberg Shale in northern Nye and Lincoln Counties; the Hamburg Dolomite in Eureka County; the Nopah Formation in southern Nye and Esmeralda Counties; the Patterson Pass and Pioche Shales, the Chisholm and Highland Peak Formations, and the Lyndon Limestone in Lincoln County; the Pole Canyon Limestone and the Lincoln Peak and Windfall Formations in northern Nye County; and undifferentiated limestone and dolomite in Lincoln, Clark, White Pine, Eureka, northern Nye, and Elko Counties. This unit is conformably overlain by the Ordovician shelf rocks (OCc), and is depositional on the underlying Proterozoic-Cambrian quartzite of CZq.

Ultramafic rocks and serpentine (Triassic or upper Paleozoic) at surface, covers < 0.1 % of this area

Ultramafic rocks are present in very small belts or lenses in a few places across the State. In the Candelaria Hills along the Mineral-Esmeralda County boundary, they crop out in a thrust complex that overlies the Candelaria Formation (TRcl). At Willow Spring, at the southern end of the Toquima Range south of Manhattan, serpentine is exposed again adjacent to the Candelaria Formation and deformed lower Paleozoic rocks (OCtd). A few small outcrops also are present on the east side of the Toquima Range near Belmont adjacent to lower Paleozoic rocks. In the Toiyabe Range in Nye County, scattered outcrops of serpentine form a narrow north-south trending belt adjacent to the Golconda terrane (GC), deformed lower Paleozoic rocks (OCtd, Ctd), and the Siliciclastic overlap assemblage. An early Triassic conodont was recovered near the serpentine near Marysville Canyon (Poole and Wardlaw, 1978), although the Candelaria Formation does not show on the map in this area. All of these exposures of ultramafic rocks are in a similar relative tectonic position above deformed lower Paleozoic rocks and the Siliciclastic overlap assemblage, and below the structurally overlying Golconda terrane. A narrow belt of serpentine and gabbro is exposed at the northern edge of the Golconda terrane in the Hot Springs Range in Humboldt County. In this case, the ultramafic rock is structurally above the Golconda terrane, and beneath the overlying Mesozoic Jungo terrane (JO).

Mesozoic granitic rocks, unit 3 (Sierra Nevada, Death Valley area, Northern Mojave Desert and Transverse Ranges) (Permian to Tertiary; most Mesozoic) at surface, covers < 0.1 % of this area

Mesozoic granite, quartz monzonite, granodiorite, and quartz diorite

Tertiary volcanic flow rocks, unit 18 (San Joaquin-Kings Canyon) (Tertiary (3-4 Ma)) at surface, covers < 0.1 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.