The type section of the Newark Canyon Formation was assigned by Nolan and others (1956) to exposures in Newark Canyon about 6 miles east of Eureka from "Hunter's Ranch to Newark Summit on the west side of the Diamond Mountains".

The Newark Canyon Formation is Lower Cretaceous in age. It commonly overlies the Permian Carbon Ridge Formation with angular unconformity, and locally overlies the Ely Limestone and rocks as old as the Pogonip Group in the Eureka area (Nolan and others, 1956). It is unconformably overlain by Tertiary and Quaternary sediments and volcanics.

Nonmarine sandstone and conglomerates on the east side of the Cortez Mountains, originally assigned to the Rand Ranch Formation (Regnier, 1960), are now assigned to the Newark Canyon Formation (Roberts and others, 1967) based upon the presence of Cretaceous plant and pollen remains. Permian Unit G of Larson and Riva (1963) is also considered equivalent to the Newark Canyon Formation (Hose and Blake, 1976).

The Newark Canyon Formation is a sequence of poorly exposed and lithologically heterogeneous with freshwater limestones, siliceous and limestone conglomerates, siltstones, and sandstones (Nolan and others, 1956). The surrounding soil is a characteristic deep red color, and the resistant conglomerates are the most commonly exposed lithology.

Laminated gray or tan siltstones, moderately to well-sorted subangular to subrounded sandstones, and shales, are carbonaceous and dark brown to reddish-brown in color. Although poorly exposed, these units make up most of the Newark Canyon in the Diamond Range (Nolan and others, 1956; Roberts and others, 1967). The upper portion of the formation is typically composed of reddish weathering conglomerates as much as 50 feet thick, containing angular to subrounded fragments of white, red and green quartzite and cherts, and limestones up to several inches in diameter (Haworth, 1979).

In the Northern Simpson Park Mountains, thin shale, light to medium-grey fine-grained locally porous limestone containing Sequoia plant fragments, and fine-grained sandstones compose the Newark Canyon (Roberts and others, 1967). The eastern Cortez Mountains also contains freshwater limestones and conglomerates that are assigned to the Newark Canyon but were originally mapped by Regnier (1960) as the Rand Ranch Formation.

In the eastern Cortez Range, the Newark Canyon is composed of tan siltstone; poorly consolidated, evenly bedded and crossbedded, poorly sorted, fine to coarse-grained sandstone; and crossbedded, scoured, brown and red conglomerate with gray silty limestone in the upper few hundred feet. The basal member is several hundred feet of poorly consolidated, dark gray to black, massive mudstone (Regnier, 1960; Smith and Ketner, 1976).

In the Pancake Range, west of Duckwater, the Newark Canyon Formation consists of reddish-brown to gray conglomerate, shale, sandstone, and minor amounts of mudstone. The unit forms subdued hills and local ledges and cliffs (Kleinhampl and Ziony, 1985).

In the central Pinon Range, the Newark Canyon Formation is represented by small exposures of thin-bedded to papery, dark gray shale and mudstone, light to dark gray ostracodal and carbonaceous limestone, and gray, fine to medium-grained, angular to rounded sandstone (Smith and Ketner, 1976). Small exposures of conglomeratic sandstone and limestone in T. 27-28 N., R 53 E. are also included with the Newark Canyon Formation. Thicknesses were not measured or estimated.

The Newark Canyon Formation varies from about 1,400 to 1,800 feet in the Diamond Mountains, to 2,170 feet in the eastern Cortez Mountains (Smith and Ketner, 1976), and 4,000 feet thick north of Eureka (Nolan and others, 1956).

The Newark Canyon is exposed in the Eureka area and in isolated exposures within the Diamond, Simpson Park, and Cortez Mountains, Pancake and Pinon Ranges.

Gastropod, fish and plant fragments indicate a fresh water origin for the Newark Canyon. Rapid lateral facies variations with both coarse and fine-grained lithologies suggest the Newark Canyon may have been deposited on a modern Basin and Range topography. The Newark Canyon may reflect the earliest stages of Basin and Range structure (Nolan, 1962; Roberts and others, 1967).