The Nevada Formation was restricted by Merriam (1940) to a type section a few miles south of Devils Gate at Modoc Peak. Nolan and others (1956) revised the Nevada Formation based on work in the Diamond Mountains. Five units were named in ascending order: the Beacon Peak Dolomite, Oxyoke Canyon Sandstone, Sentinel Mountain Dolomite, Woodpecker Limestone, and Bay State Dolomite. The Modoc Peak section has since been broken out as Beacon Peak Dolomite overlain by Bartine Limestone and Coils Creek Limestone of Murphy and Gronberg (1970), which is in turn overlain by the Sadler Ranch Formation of Kendall and others (1983).

As if this were not enough stratigraphic confusion, Carlisle and others (1957) devised an entirely new set of names for units within the Nevada Formation based upon relationships in the Sulphur Spring and Pinon Ranges. In ascending order they are the McColley Canyon Member, Union Mountain Member, and Telegraph Canyon Member. The McColley Canyon was later raised to formational rank by Johnson (1962) and has been assigned to the transitional facies, although it is in essence gradational between the eastern and transitional facies. The Oxyoke Canyon was also later designated as a formation (Kendall, 1975).

The McColley Canyon is equivalent to the Beacon Peak Dolomite, while the Union Mountain Member is correlative with the Oxyoke Canyon sandstone of Nolan and others (1956). The Telegraph Canyon Member is equivalent to the Bay State, Woodpecker, and Sentinel Mountain Dolomite Members of Nolan and others (1956) as well as the Simonson Dolomite.

Recently, the Nevada has been abandoned as a formation and each of its members has been raised to formational rank within the northern Antelope Range by Hose and others (1982). The formational designations used are, once again in ascending order, Beacon Peak Dolomite, McColley Canyon Formation, Denay Limestone, and Fenstermaker Wash Formation (a new name). Under this re-classification the Beacon Peak is equivalent to the Sevy Dolomite of eastern Nevada and western Utah. Portions of the Denay correlate with the Woodpecker Limestone of the Newark Mountain-Alhambra Hills and Diamond Mountains (Hose and others, 1982). The Fenstermaker Wash Formation is temporally equivalent with the Bay State Dolomite in the southern Fish Creek Range. Obviously this nomenclature is grossly overcomplicated and very nearly useless in any regional sense.

The reader will unfortunately see all of the above as well as other designations on various maps, and within various publications and theses throughout the area. It has been included by necessity on our map since most sections of the Nevada remain undivided using the newer nomenclature. Often the term Nevada Group is applied as a catchall for these formations and members (Johnson, 1966).

The various members described by Nolan and other (1956), followed by those of Carlisle and others (1957) are discussed below. The formations broken out of the "Nevada Group" by several workers are outlined separately in following sections.

The Nevada as defined in the Diamond Mountains by Nolan and others (1956) is equivalent to the Sevy Dolomite and Simonson Dolomite plus part of the lower Guilmette of areas to the east, while the Devils Gate Limestone of the Diamond Mountains is equivalent to the remainder of the Guilmette Formation. The top of the Oxyoke Canyon Sandstone Member is the approximate top of the Sevy Dolomite (Hose and Blake, 1976).

The Nevada Formation contains abundant faunal evidence indicating a late Early and Middle Devonian (Coblenzian through Givetian) age.

The basal of five members in the Nevada Formation was designated the Beacon Peak Dolomite by Nolan and others (1956) for exposures which disconformably overly the Lone Mountain Dolomite on the lower west slope of Beacon Peak in the Diamond Mountains. It is composed of light grey to brown, porcellaneous dolomite which weathers a pale grey to blue, and commonly breaks with concoidal fracture (Nolan and others, 1956). Thin, brown-weathering, well-rounded, quartz-rich sandstones 1/4 inch to 6 inches in thickness are interbedded in the upper half of the formation. The thicker sandstone beds are prominently cross-bedded. These sands pass upward with a sharply gradational contact into the overlying Oxyoke Canyon Sandstone Member. Thickness of the Beacon Peak varies from 470 to 940 feet in the Lone Mountain-Diamond-Roberts Mountains area (Roberts and others, 1967). The Beacon Peak is discussed in a following section as an individual formation.

The Oxyoke Canyon Sandstone has a type locality along the southwest slope of Beacon Peak, 7 miles southeast of Eureka. The member is predominantly light grey to brown weathering, fine to medium-grained, quartz sandstone with a dolomitic matrix. Beds are often several feet in thickness with prominent cross-bedding, and occasional worm casts (Nolan and others, 1956). Along faults, the sandstones are often vitreous and quartzitic, and are quite difficult to distinguish from the Eureka Quartzite. A few beds of Beacon Peak-type dolomite are present in the lower portion of the formation, and 2 to 5 foot thick beds of quartzitic light grey to white granular and vuggy dolomite are common in the upper portion of the member (Nolan and others, 1956). The thickness of the member varies considerably from 400 feet to less than 20 feet in the Diamond Range-Sulphur Spring Range area. The Oxyoke is discussed in a following section as a separate formation.

The Sentinel Mountain Dolomite gradationally overlies the Oxyoke Canyon Member. It is named for exposures at the head of Oxyoke Canyon in the Diamond Range (Nolan and others, 1956). The Sentinel Mountain is composed of alternating, thick-bedded, coarse-grained, light-gray dolomite, and mottled, finely laminated, chocolate brown dolomites with a strong petroliferous odor when broken. The brachiopod Stringocephalus is common. A thickness of 410 to 600 feet is suggested from sections in the Diamond Range, Alhambra Hills and Lone Mountain (Nolan and others, 1956). The upper contact with the overlying Woodpecker Limestone Member is gradational over several hundred feet.

The Woodpecker Limestone has a type area in the "gulch draining the south slope of Woodpeckers Peak, which is situated on the north boundary of Oxyoke Canyon" (Nolan and others, 1956). The Woodpecker is characterized by thin to medium-bedded, argillaceous to sandy limestone, with considerable lithologic variability. Fine-grained to porcellaneous, light to dark grey, tan, or blue platy limestones are typical, with occasional clay or silty partings that weather to a pink color. Fine-grained calcareous shales are commonly intercalated with the limestones (Nolan and others, 1956). In some sections the limestones are locally dolomitic. The Woodpecker Member is 220 to 500 feet thick in the Eureka area and has a sharp upper contact with the uppermost Bay State Dolomite Member which is marked by light-gray dolomitic sand with varying thickness (Roberts and others, 1967).

The Bay State Dolomite is typed for massive dark colored dolomites exposed in a section above the Bay State Mine on Newark Mountain. It is exposed throughout the Diamond Mountains-Alahambra Hills area (Nolan and others, 1956). The basal portion of the member is an irregularly bedded, light-grey, dolomitic sandstone form 50 to 80 feet in thickness. Above these sands are massive to faintly laminated, dark-grey to black or purplish dolomites with abundant cylindrical corals of Clodopora forming "Spaghetti beds". The upper portion of the member shows alternating lighter and darker grey petroliferous dolomites similar to the Sentinel Mountain dolomites. Heads of Stromatopora and small cups of Syringopora and brachiopods are common locally. The Bay State is 600 to 850 feet thick showing a gradational contact about 50 feet in thickness with the overlying thick bedded limestones of the Devils Gate Formation (Nolan and others, 1956).

In the Sulphur Spring and Pinon Ranges, Carlisle and others (1957) distinguished three members within the Nevada Formation. The lowermost member, the McColley Canyon, is named for exposures which conformably overly the Lone Mountain Dolomite along McColley Canyon in the northern Mineral Hill Quadrangle. The basal four-fifths of the unit are medium to thick-bedded, gray limestone, and interbedded dolomitic limestone and calcareous dolomite, locally with dolomitic, well-rounded quartz sand up to 70 feet in thickness near its base (Carlisle and others, 1957). The upper beds are thin-bedded and platy, yellow-weathering, argillaceous and fossiliferous limestone, and calcareous dolomite. The entire formation is dolomitic in some localities and ranges in thickness from 200 to 625 feet. The McColley Canyon has been raised to formational status and is discussed in the Lower Paleozoic Transitional Assemblage section.

The middle Union Mountain Member is named for carbonates exposed along the crest of Union Mountain in the northeastern portion of the Mineral Hill Quadrangle (Carlisle and others, 1957). Three units are commonly present. A basal, cross-stratified, light grey to brown, sandy dolomite and dolomitic sand is overlain by a middle, brown, sandy dolomite and grey clastic crinoidal dolomite, with an upper unit of grey, sandy and coarsely crystalline dolomite with vugs from a pin-point to 1 cm across (Carlisle and others, 1957). The entire member varies from 700 to 1,200 feet in thickness.

The uppermost member was named the Telegraph Canyon after exposures along Telegraph Canyon in the central Mineral Hill Quadrangle (Carlisle and others, 1957). The base of the Telegraph Canyon is composed of alternating light and dark gray, mottled, finely laminated dolomite from 6 inches to 2 feet in thickness (Carlisle and others, 1957). Elongate fossiliferous chert nodules are both parallel and transverse to bedding in these lower dolomites. A "limestone tongue" of thin and poorly-bedded, blue-grey, fossiliferous limestone and minor thin-bedded, grey dolomite with nodular chert is present between the lower and upper portions of the member. The upper beds are also alternating light and dark mottled dolomites with a Cladopora "spaghetti" texture (Carlisle and others, 1957). The Telegraph Canyon Member varies in thickness from 800 to 1,950 feet and is conformably overlain by the Devils Gate Limestone (Roberts and others, 1967).

In the Reveille Range, Ekren, Rogers, and Dixon (1973) divided the Nevada into two units. The upper unit is about 510 feet thick and is composed of medium to dark-gray, fine-grained, laminated to thin-bedded, limestone and silty limestone. The upper portion of the unit contains several lenticular layers of thick-bedded limestone with abundant subangular limestone clasts as much as 8 inches in diameter. The lower unit is a dark-gray, fine to medium-grained laminated to thick-bedded dolomite about 140 feet thick with some beds containing scattered angular dolomite clasts. The upper unit contains a faunal zone intermediate between the Stringocephalus and Warrenella Kirki zones, while the lower unit contains conodonts suggesting an Emsian age.

In the Carlin-Pinon Range, the Nevada Formation is exposed in fragmented partial sections which have been divided into three members (Smith and Ketner, 1975). The basal member is the Beacon Peak Dolomite Member which is up to 675 feet thick. The Beacon Peak is thin to thick-bedded, gray to brown, grainy dolomite which contains crossbedded, well rounded, quartz sandstone up to 25 feet thick at the base. Locally at Pine Mountain, the unit has been recrystallized near an intrusive, and also contains two bands of blue-gray, dense, laminated limestone in beds 1 to 4 feet thick with poorly preserved brachiopods and corals. These limestones are 30 to 50 feet thick and are unique within the dolomite sequence (Smith and Ketner, 1975). A 25 foot thick unit of yellow and tan argillaceous thin-bedded dolomite is equivalent to the Bartine Member of the McColley Canyon Formation (Murphy and Gronberg, 1970) exposed at Lone Mountain.

In the Pinon Range, the Beacon Peak is gradationally as well as abruptly overlain by the Oxyoke Canyon Sandstone Member which is zero to 415 feet thick. The Oxyoke Canyon Member is white, pink, gray, and light brown, thin to thick-bedded, cross-bedded, slightly dolomitic sandstone and vitreous quartzite. The sandstones and quartzites are generally well sorted and rounded and are locally interbedded with gray, fine to medium-grained, dolomite lenses. The sandstone is gradationally overlain by the Upper Dolomite member that varies from 845 feet to 2,065 feet in thickness (Smith and Ketner, 1975). The upper Dolomite is alternating brown and gray, mottled dolomite with fine, locally contorted laminations. The bedding within the dolomite is thick to massive and is locally cross-bedded, with the brown layers strongly fetid (Smith and Ketner, 1975). The Upper Dolomite Member is gradationally overlain by the Devils Gate Limestone.

In the Ruby Mountains, Willden and Kistler (1969) described the Nevada Formation in the Cedar Mountain klippe in the Jiggs Quadrangle as dark-gray to gray, laminated and mottled dolomite. In the central Ruby Mountains the thin-bedded, laminated dolomites of the Nevada Formation gradationally overly the Lone Mountain Dolomite and are conformably overlain by the Devils Gate Limestone. The formation is composed of alternating light, medium, and dark gray, fine to medium-grained dolomite with coral-stromatoporoid reefs in the upper portion of the unit (Willden and Kistler, 1969).

The Nevada Formation has also been mapped in the Lone Mountain area of the Independence Mountains where it is fine to coarse-grained, thick-bedded calcarenite with a few sandy or quartzose beds near the middle of the unit (Lovejoy, 1959; Ketner, 1974). In the Swales Mountain, area the Nevada is composed of an upper portion of thick-bedded, dark gray calcarenite, with some beds of black chert (Ketner, 1975). The lower portion is dominantly thin-bedded to massive, fine-grained to locally coarse-grained, dark gray-brown, yellow weathering silty argillaceous limestone. The Nevada Formation at Swales Mountain rests on a thrust.

The Nevada Formation in the Sulphur Spring and Antelope Ranges, and Diamond Mountains is commonly about 2,000 to 3,000 feet in thickness (Larson and Riva; 1963, Nolan and others, 1974). It is 1,600 to 3,200 feet thick in the Carlin-Pinon Range (Smith and Ketner, 1975), 1,200 feet in the central Ruby Range (Willden and Kistler, 1979), 1,800 feet in the Swales Mountain area (Evans and Ketner, 1971), about 1,450 feet thick in the Pancake Range near Portuguese Mountain (Quinlivan and others, 1974), 650 feet thick in an incomplete section exposed in the Hot Creek Range (Quinlivan and Rogers, 1974), and about 650 feet thick in the northern Reveille Range (Ekren, Rogers and Dixon, 1973).

The Nevada Formation or Group is exposed within the Diamond, Roberts, Simpson Park, Ruby and Independence Mountains, Mahogany Hills, Lone Mountain, Monitor, Hot Creek, Sulphur Spring, Fish Creek, Antelope, Hot Creek, Reveille, Pancake, and Carlin-Pinon, Ranges.

Kendall and other (1983) have summarized lithofacies within the Nevada Group into three distinct platform to basinal depositional belts: 1) a western belt composed of slope and basinal limestones (Simpson Park Mountains); 2) an eastern belt of shallow-water dolomites (Diamond Mountains) and 3) a transitional belt where major lithofacies intertongue (Modoc Peak area).

The Nevada Group in the southern Diamond Mountains indicates generally shallow deposition of the Sentinel Mountain Dolomite, deeper deposition during deposition of the Woodpecker Limestone, and a return to shallow marine deposition during deposition of the Bay State Dolomite (Hose and others, 1982).