The Eureka Quartzite was named in the Eureka area by Hague (1883). The type section was designated by Kirk (1933) for exposures on the southwest side of Lone Mountain, 18 miles northwest of Eureka.

A very sparse fauna, and its occurrence between highly fossiliferous and well dated Ordovician units, suggest that the Eureka Quartzite is Middle Ordovician (middle Trenton) in age. The lower contact of the Eureka is a regional unconformity (Nolan and others, 1956; Merriam, 1963; Langenheim and Larson, 1973), and the upper contact is locally an unconformity and locally conformable with overlying units (Nolan and others, 1956; Merriam, 1963). Kleinhampl and Ziony (1985) found that the upper unconformity mapped by Quinlivan and Rogers (1974) in the Hot Creek Range to be the result of faulting which removed the Ely Springs Dolomite. This may well be the case in several other Eureka sections where an upper unconformity is postulated.

The contact between the Eureka and underlying Pogonip Group is commonly covered, but where exposed may be either sharp, or gradational, over a thin zone (Hyde and Huttrer, 1970; Hose and Blake, 1976). An unconformity of regional significance exists at the base of the Eureka Quartzite (Nolan and others, 1956; Gilluly and Gates, 1965; Gilluly and Masursky, 1965; Stewart and McKee, 1977). Near Eureka, the Eureka Quartzite lies unconformably upon the Ordovician Antelope Valley Limestone. Some 35 miles northward in the Roberts Mountains, both the Antelope Valley and Ninemile Formations have been removed along the unconformity placing the Eureka on the Goodwin Limestone, the basal portion of the Ordovician Pogonip Group. At Cortez, 20 miles farther to the north, the Eureka lies on Cambrian Hamburg Dolomite suggesting2,600 feet of section below the Eureka Quartzite was eroded before deposition of the Eureka at Cortez (Stewart and McKee, 1977).

In general, Eureka quartzites are dense, white to dark gray, pure quartzite, and brown or pink, milky to vitreous purple, red, or brown orthoquartzite. The cliff-forming quartzites are often fine to medium-grained with well sorted and well rounded quartz grains. Thicker sections show an upper white vitreous massive quartzite, with a lower darker brown, cross-laminated quartzite below (Kirk, 1933). Commonly the lower third of the formation shows cross-lamination (Roberts and others, 1967). Where several colors of quartzite are present, the white units are commonly confined to the upper part of the formation (Kirk, 1933; Merriam, 1963). Dolomitic cement is common in most sections in the basal and uppermost several feet of the Eureka (Kleinhampl and Ziony, 1985). Where the lower unit is missing and upper member is thinned, as in the Monitor and Antelope Ranges, the Copenhagen Formation takes the place of the Eureka Quartzite (Nolan and others, 1956).

In the Wheeler Mountain area of the Independence Mountains, the Eureka is composed of 420 feet of medium to light gray, grayish-orange weathering quartzite. The lower 170 feet are cross-bedded. This is overlain by limey fossiliferous quartzite with orthid brachiopods, and gray massive quartzite (Kerr, 1962). Near Burns Creek, the Eureka is about 557 feet thick and has a basal light gray quartz sandstone at the basal contact with the Pogonip Group. The lower portion of the formation also contains dolomite, and the upper portion of the Eureka is a brown-yellow, vitreous, fine to medium-grained, subrounded quartzite (Kerr, 1962; Coats, 1985).

In the Pinon Range, the Eureka is a white, thick-bedded, fine to medium-grained, well sorted quartzite which locally grades into the overlying dolomites of the Hanson Creek Formation (Smith and Ketner, 1975). In the Ruby Mountains, the Eureka is about 200 feet of massive, white, vitreous quartzite with minor tremolite and very rare graphite, feldspar and muscovite (Howard, 1966). In the Buck Mountain - Bald Mountain area to the south, the Eureka is composed of vitreous, light gray to white orthoquartzite with friable, porous and less resistant quartz sandstone in the upper portion of the formation (Rigby, 1960).

In the northern Shoshone Range, a single small sheared outcrop of Eureka is present in Sec. 20, T. 29 N., R. 45 E. (Gilluly and Gates, 1965). The lower third of the formation appears to be removed along a fault at the base of the unit. The Eureka here is a white, vitreous, well-sorted and rounded, medium-grained quartzite with 4 to 8 foot thick bedding. Quartz composes about 99 percent of the rock with accessory metamorphic minerals including kyanite, staurolite, and hornblende (Gilluly and Gates, 1965). In the Cortez Mountains, the Eureka is mostly very pure white quartzite; however layers of dolomitic sandstone, siltstone and argillite are present in the basal 55 feet of the section (Gilluly and Masursky, 1965).

In the northern Reveille Range, the Eureka is composed of white, fine-grained, laminated and cross-bedded, equigranular quartzite which weathers a reddish-brown (Ekren, Rogers, and Dixon, 1973). The upper portion of the unit includes a small amount of dolomitic quartzite as does the lower third of the formation.

In the Copenhagen Canyon area of the Monitor Range, the Eureka is divided into three members by Bortz (1959). The basal 3 feet are porous, poorly cemented, pinkish-gray quartz arenite. This is overlain by a middle member of about 182 feet of light gray, vitreous orthoquartzite with strong iron-staining in the lower 90 feet of the unit. The upper member is about 15 feet of light-gray, slightly porous orthoquartzite which is conformably overlain by the Hanson Creek Formation (Bortz, 1959).

In the Hot Creek Range, Quinlivan and Rogers (1974) described three members within the Eureka Quartzite. The upper unit is probably the Ely Springs Dolomite, which is gradationally overlying the Eureka Quartzite. It contains dolomitic sandstone and interbedded lenticular Girvanella-bearing dolomite commonly in beds 1 or 2 feet thick. The lower two units are about 140 feet in thickness and consist of light gray, massive, well-sorted quartzite with thin layers and partings of dark-gray argillite in the lower 80 feet of the unit. In the Hot Creek Range, the quartzite is fine to medium-grained, laminated and cross-laminated. The upper portion is white-weathering and the lower portion is dark-brown weathering.

In the White Pine, Grant, Cherry Creek, and Egan Ranges, the Eureka is a yellowish to white, fine to medium-grained quartzite which varies in induration from friable sandstone to tight quartzite (Moores and others, 1968; Fritz, 1968; Playford, 1961). Most of the quartzite is massive and even-bedded, but is strongly cross-bedded in some thin beds. The upper portion of the formation is often porous and friable over a few feet to 100 feet (Kellogg, 1960). Lumsden (1964) reported that 70 percent of the unit in the White Pine Range is quartz sandstone with thin beds of yellowish and brown, argillitic shale.

In the northern Schell Creek Range, the Eureka is locally present as a cliff-forming vitreous white to reddish-brown, recrystallized and intensely brecciated quartzite (Young, 1960). The Eureka has been intimately involved in low-angle faulting and varies from slivers a few feet thick to as much as 200 feet in thickness (Young, 1960). In the Snake Range the Eureka consists of light gray to brownish gray, vitreous, well sorted quartzite, and pinkish to reddish weathering, calcareous sandstone and silty sandstone. Bedding in the Eureka is commonly 6 to 36 inches in thickness (Whitebread, 1969).

In the western portion of the Red Hills, west of the Kern Mountains, the Eureka is a white and pink, vitreous quartzite with a few feet of medium-gray, thin-bedded limestone beneath it which Bartel (1968) felt may represent the Pogonip. The section is tectonically thinned as it is in several sections in the surrounding Egan, Snake, Cherry Creek and Schell Creek Ranges. In the southern Deep Creek Range the Eureka is a faulted, white, vitreous, fine to coarse-grained quartzite. The upper portion of the formation is arenaceous dolomite and porous and friable sandstone which is often tectonically eliminated (Nelson, 1959).

In the northern Wilson Creek, Bristol, and Fairview Ranges the Eureka is a white to light gray, vitreous, sugary, massive or cross-bedded quartzite which contains beds of sandstone and dolomitic sandstone (Tschanz and Pampeyan, 1970). The lower 50 to 150 feet of the formation is commonly brownish or yellowish quartzite which overlies the Ordovician Pogonip Group. In the Wood Hills, the Eureka Quartzite has been metamorphosed to a weakly to moderately schistose metaquartzite with minor amounts of diopside, tremolite, and muscovite (Thorman, 1970).

In the Kingsley Range, the Eureka is a vitreous, white, massive, well rounded and sorted quartzite (Buckley, 1967). In the Toana-Goshute Ranges, the formation is a massive medium to coarse-grained quartz arenite which is white at the base and blue-gray near the top. It rests on the Pogonip Group and is overlain by the Fish Haven Dolomite (Pilger, 1972; Coats, 1985). In the Pilot Range, it is a light gray, fine to medium-grained quartzite (O'Neill, 1968).

In the southern Snake Mountains, Peterson (1968) described the Eureka as pink, white and black, dolomitic, medium-grained orthoquartzite that weathers pink, orange and reddish-brown. The lower 150 feet of the formation are cross-bedded. In the northern Snake Range, Gardner (1968) described 1212 feet of section he attributed to the Eureka Quartzite. The upper 170 feet of white to light gray orthoquartzite is probably Eureka Quartzite with the underlying limestone, dolomitic limestone and orthoquartzite representing the Swan Peak portion of the Pogonip Group (Coats, 1985). The Eureka overlies the Pogonip and underlies the Hanson Creek Formation.

In the Elk Mountains, the Eureka consists of a basal 100 feet of cross-laminated, yellowish-white and mottled, red-brown to red quartzite and an upper 150 feet of pure white, fine-grained quartzite (Mathias, 1959).

The Eureka varies in thickness from 100 feet in the Sulphur Spring Range (Roberts and others, 1967), 200 feet in the Copenhagen Canyon area and 220 feet at Martins Ridge in the Monitor Range (Bortz, 1959; Webb, 1958), 150 to 200 feet in a faulted sections in the northern Shoshone Range (Gilluly and Gates, 1965), 310 feet in the northern Reveille Range (Ekren, Rogers, and Dixon, 1973), 400 feet in the Cortez Mountains (Gilluly and Gates, 1965), 350 feet at Lone Mountain (Merriam, 1940), and 500 feet in the Roberts Mountains (Roberts and others, 1967).

There is a progressive northward thickening from the Monitor Range with about 183 feet, to 350 feet in the Roberts Mountains (Nolan and others, 1956). The Eureka lies disconformably on Middle Ordovician (Pogonip Group) in the Roberts Mountains to Upper Cambrian (Hamburg Dolomite) in the Cortez and Tuscarora Mountains. There is no evidence of significant angularity along this unconformity, however formations above the Eureka are thin toward the southwest (Merriam, 1960).

In White Pine County the Eureka thickens southward and eastward (Hose and Blake, 1976). It is cut out along an unconformity(?) in the southern Ruby Mountains with local exposure of 100 to 234 feet in the Buck Mountain - Bald Mountain area (Rigby, 1960), 10 to 175 feet thick in the Cherry Creek Range (Fritz, 1968; Hose and Blake, 1976), 140 feet in the Hot Creek Range (Quinlivan and Rogers, 1974), 235 feet in the Pancake Range (Quinlivan and others, 1974), 310 feet in the northern Egan Range (Woodward, 1964) to 465 to 621 feet in the Whipple Ranch area of the Egan Range (Kellogg, 1963), 300 to 400 feet thick in the central Schell Creek Range (Drewes, 1967), 250 to 400 feet in the White Pine Mining District (Humphrey, 1960), 450 feet in the White Pine Range (Lumsden, 1964), 440 feet in the southern Snake Range (Whitebread, 1969), 200 to 300 feet in the southern Deep Creek Range (Nelson, 1959), 490 feet in the southern Egan Range (Playford, 1961), 15 to 25 feet in the western Red Hills (Bartel, 1968), 450 feet thick in the White Pine Mountains (Lumsden, 1964), and 390 feet in the Horse Range (Ptacek, 1962).

In Elko County it is 200 feet thick in the Ruby Mountains (Howard, 1966), 1,500 feet at the Carlin Mine, 200 feet in the Kingsley Range (Buckley, 1967), 420-950 feet in the Toana-Goshute Ranges (Pilger, 1972; Coats, 1985), 150 to 260 feet in the Pilot Range (Blue, 1960: O'Neill, 1968), 8 feet at Spruce Mountain (Hope, 1972), 725 feet in the Windermere Hills (Coats, 1985), 900 to 1,250 feet in probable fault repeated sections in the Snake Mountains (Peterson, 1968; Gardner, 1968) and 170 feet in the northern Snake Mountains (Coats, 1985), up to 200 feet in the northern Schell Creek Range (Young, 1960), 150 to 325 feet in the Wood Hills-Pequop Range (Thorman, 1970), 70 feet in the Pinon Range (Smith and Ketner, 1975), 557 to 1027 feet in faulted sections in the Independence Range (Kerr, 1962), and 250 feet in the Elk Mountains (Mathias, 1959).

The Eureka is exposed within the Fish Creek Range, Mahogany Hills, Monitor, Pancake, Reveille, Hot Creek, Shoshone, Sulphur Spring Ranges, Roberts, Tuscarora, Cortez, Independence, and central Ruby Mountains, Cherry Creek, Schell Creek, Egan, Grant, White Pine, Horse, Quinn Canyon, Snake, southern Deep Creek, Wilson Creek, Bristol, and Fairview Ranges, Kingsley, Toana-Goshute, Pilot, Pequop and Pinon Ranges, Spruce Mountain, Red Hills, Wood Hills, Snake, Bull Run, and Elk Mountains. It is absent in the Toquima, and Toiyabe Ranges, where rocks such as the Hanson Creek and Copenhagen Formations represent Eureka time.

Fossils are extremely rare within the Eureka Quartzite with the notable exception of corals at Cortez, Nevada which would suggest a shallow marine origin for the Eureka (Duncan, 1956).

The extremely pure, well sorted, well rounded, uniform, and crossbedded nature of the quartz sand suggests the Eureka formed as a beach-dune, or eolian continental-type sand. The Eureka was most probably deposited in near-shore intertidal and beach ridge regions. The lower Eureka appears eolian or marginal marine while the upper Eureka is probably more of an open marine facies (Nolan and others, 1956). The Eureka Quartzite is found on the Ordovician shelf and shelf margin and is not present in more basinal sections as in the Toquima and Toiyabe Ranges, where limestones such as the Ceasers Canyon or Copenhagen Canyon are present (Ross, 1977). Ketner (1966) has suggested a northeastern source terrain for the Eureka.

The Eureka is commonly exceedingly well cemented and strongly fractured and brecciated. The top of the formation, and substantial portions of the unit, are porous in some localities such as Lone Mountain. Both indigenous and fracture-enhanced porosity and permeability may be present in the Eureka Quartzite, making it an attractive potential reservoir in very local and specific areas.