Geologic units in Washoe county, Nevada

Additional scientific data in this geographic area

Basalt (Miocene) at surface, covers 23 % of this area

Basalt flows, plugs and dikes, some olivine basalt, and andesite and latitic rocks. This unit corresponds with unit Tb on the 1978 State map. It is present on the Washoe North, Washoe South, Lincoln, Clark, Elko, Eureka, Humboldt, Nye South, and Lander County maps.

Alluvium, undifferentiated (Holocene and Pleistocene) at surface, covers 18 % 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.

Andesite and basalt flows (Miocene and Oligocene) at surface, covers 11 % 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 rhyolitic flows and shallow intrusive rocks (Miocene) at surface, covers 10 % 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.

Younger tuffaceous sedimentary rocks (Pliocene and Miocene) at surface, covers 8 % 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.

Playa, lake bed, and flood plain deposits (Holocene and Pleistocene) at surface, covers 7 % 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.

Older alluvium and alluvial fan deposits (Pleistocene and Pliocene) at surface, covers 6 % 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.

Felsic phaneritic intrusive rocks (Miocene (?) to Jurassic (?)) at surface, covers 4 % 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 andesite and intermediate flows and breccias (Miocene) at surface, covers 3 % 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 andesite and intermediate flows and breccias (lower Miocene and Oligocene) at surface, covers 2 % 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.

Intermediate silicic ash flow tuff (lower Miocene and Oligocene) at surface, covers 2 % 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 2 % 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 silicic ash flow tuffs (Miocene) at surface, covers 1 % 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.

Felsic phaneritic intrusive rocks (Cretaceous) at surface, covers 0.9 % 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.

Sand Springs Terrane - Basinal volcanogenic rocks and carbonate turbidites (Lower Jurassic and Upper Triassic) at surface, covers 0.8 % 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.

Landslide deposits, colluvium, and talus (Holocene to Pliocene) at surface, covers 0.6 % 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.

Metavolcanic rocks (Jurassic (?) and Triassic (?)) at surface, covers 0.5 % 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.

Basalt flows (Holocene to Pliocene) at surface, covers 0.3 % 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.

Glacial moraines (Holocene and Pleistocene) at surface, covers 0.2 % of this area

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

Black Rock-Jackson Terrane - Basinal, island arc, carbonate, and volcanogenic rocks (Middle Jurassic to Mississippian) at surface, covers 0.2 % of this area

This composite terrane includes Mississippian to Middle Triassic oceanic-basin and island-arc rocks in isolated exposures in northwesternmost Nevada originally assigned to the Black Rock terrane, and Upper Triassic to Middle Jurassic volcanogenic and volcanic rocks of the Jackson terrane in the same region. These rocks crop out in southern Washoe, Humboldt, and Pershing Counties. Parts of the Black Rock terrane can be interpreted as the base of the Jackson terrane, but they are generally structurally juxtaposed throughout the region (Jones, 1990; Russell, 1984; Silberling, Jones, and others, 1987; Wyld, 1990). Rocks of this terrane have affinities with correlative rocks in the Eastern Klamath and Northern Sierra terranes in California (Silberling, Jones, and others, 1992).

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 - Pine Nut assemblage - Volcanogenic, carbonate, and clastic rocks (Middle (?) Jurassic to Middle Triassic) at surface, covers < 0.1 % of this area

This assemblage is composed of Upper Triassic basinal-marine volcanic and carbonate rocks overlain by Lower Jurassic fine-grained, marine siliciclastic and tuffaceous sedimentary rocks, and by partly nonmarine sandstone, coarse clastic rocks, and volcanic rocks of late Early Jurassic and possibly younger age. This assemblage has stratigraphic similarities to the Luning-Berlin and Pamlico-Lodi assemblages, but shares only part of their late Mesozoic structural history, and is separated from them by the linear trace of the northwesterly trending Pine Nut fault (Oldow, 1984a; Silberling, Jones, and others, 1992). Structurally, the rocks are involved in only a single phase of tight to isoclinal folds with north-northwest striking axial planes, and no major internal thrust faults are known (Oldow, 1984a). The Pine Nut assemblage crops out in southern Washoe, Lyon, Douglas, Carson, and Mineral Counties, and includes rocks originally mapped as the Excelsior Formation, the Peavine sequence, and other metasedimentary and metavolcanic rocks.

Felsic phaneritic intrusive rocks (Miocene to Eocene) at surface, covers < 0.1 % 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.

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.

Sand dunes (Holocene and Pleistocene) at surface, covers < 0.1 % 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.

Andesite flows and breccias (Holocene to Pliocene) at surface, covers < 0.1 % 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.

Jungo Terrane - Turbiditic, fine-grained, terrigenous clastic rocks (Middle Jurassic to Upper Triassic) at surface, covers < 0.1 % 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.

Tertiary volcanic flow rocks, unit 17 (Cascade Range) (Tertiary (2-24 Ma)) at surface, covers < 0.1 % of this area

Tertiary volcanic flow rocks; minor pyroclastic deposits.

Plio-Pleistocene and Pliocene loosely consolidated deposits (Miocene to Pleistocene) at surface, covers < 0.1 % of this area

Pliocene and/or Pleistocene sandstone, shale, and gravel deposits; in part Miocene.

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

Rhyolite dome (Holocene to Pliocene) at surface, covers < 0.1 % of this area

Unit is only present in southern Washoe and Mineral Counties. It corresponds to unit QTr on the 1978 State map.

Undivided pre-Cenozoic metavolcanic rocks, unit 2 (undivided) (Paleozoic(?) to Mesozoic(?)) at surface, covers < 0.1 % of this area

Undivided pre-Cenozoic metavolcanic rocks. Includes latite, dacite, tuff, and greenstone; commonly schistose.

Hot spring travertine, sinter, and tufa (Holocene to Pliocene) at surface, covers < 0.1 % of this area

Calcareous and siliceous sinter and tufa deposits that are present in Washoe, Nye, Elko, Eureka, and Lander Counties.

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.

Mesozoic volcanic rocks, unit 5 (Northern Sierra Nevada and Eastern Klamath Mountains) (Late Permian(?) to Jurassic) at surface, covers < 0.1 % of this area

Undivided Mesozoic volcanic and metavolcanic rocks. Andesite and rhyolite flow rocks, greenstone, volcanic breccia and other pyroclastic rocks; in part strongly metamorphosed. Includes volcanic rocks of Franciscan Complex: basaltic pillow lava, diabase, greenstone, and minor pyroclastic rocks.

Quaternary volcanic flow rocks, unit 1 (Cascade Volcanic Field) (Quaternary) at surface, covers < 0.1 % of this area

Quaternary volcanic flow rocks; minor pyroclastic deposits; in part Pliocene and Miocene.

Silicic vent rocks (Eocene to Pliocene) at surface, covers < 0.1 % of this area

Plugs and domal complexes of rhyolitic, rhyodacitic, and dacitic composition; includes related near-vent flows, flow breccia, and deposits of obsidian, perlite, and pumice. Locally includes resurgent domes related to caldera complexes. In southeast Oregon many domal complexes younger than 11 Ma exhibit a well-defined southeast to northwest age progression (Walker, 1974; MacLeod and others, 1976) from about 11 Ma to less than 1 Ma