The Carbon Ridge has a type section on Carbon Ridge, just north of the mouth of Secret Canyon, 8 miles south of Eureka in Sec. 30, T. 18 N., R. 54 E. (Nolan and others, 1956).

The Carbon Ridge Formation is Permian (Wolfcampian to Leonardian) in age. Both the upper and lower contacts of the Carbon Ridge Formation are erosional unconformities. In the Diamond Mountains it rests with angular discordance on the Pennsylvanian Ely Limestone, and lies with near concordance on the Pennsylvanian and Mississippian Diamond Peak or Chainman Formations to the south of Eureka, providing evidence of a major unconformity. The Carbon Ridge is unconformably overlain by the Newark Canyon with local angularity (Nolan and others, 1957).

Steele (1960) suggested that the Carbon Ridge is in part equivalent to the Riepe Spring Limestone and overlying Riepetown Formation. He suggested that the Carbon Ridge Formation be raised to group status with these as regionally definable formations. Hose and Blake (1976) felt, that although approximately temporally equivalent, the Carbon Ridge Formation varied significantly in thickness and lithology from the Riepe Spring Limestone and Rib Hill Sandstone. In mapping the Carbon Ridge, Hose and Blake (1976) included the Permian Undifferentiated unit of Dott (1955) and Larson and Riva (1963) Permian units A through F. This designation is followed in this report.

The Carbon Ridge Formation is lithologically quite variable. In the Eureka area it is composed mainly of thin-bedded, dark gray to brownish, sandy and silty carbonaceous limestone which is locally cherty, and contains partings and interbeds of brownish, yellow, or purple sandstone, and dark-grey sandy and carbonaceous shales near the base. Significant amounts of fossiliferous limestone and chert-pebble conglomerates are present mainly in the upper portion of the unit (Nolan and others, 1956). Also interbedded are light-gray, coarse-grained, organic-detrital, fetid limestones which are locally highly fossiliferous primarily containing fusulinids (Hose and Blake, 1976). The limestones are also locally pebble-rich containing clasts of gray and green chert (Nolan and others, 1974).

In the Diamond Mountains, the Carbon Ridge is composed of thin-bedded to massive, quartz siltstone and cherty calcarenite, overlain by chert-bearing silty limestone which locally contain thin beds of chert-pebble conglomerate up to 1 foot thick (Larson and Riva, 1963; Barosh, 1964). Barosh (1964) assigned about 1,500 feet of thin-bedded shaly and sandy limestone, platy calcareous siltstone and argillaceous limestone, originally included with the Arcturus Formation, as the Carbon Ridge Formation.

In the Buck Mountain area, the Carbon Ridge overlies the Ely Limestone and is composed of three units (Barosh, 1964). The lower unit is about 385 feet of yellow-gray to olive, fine-grained limestone, and yellow-gray to olive silty limestone in beds 2 to 18 inches thick. The limestones contain nodules and lenses of chert, and cherty sandstone is present in the upper few feet of the unit (Barosh, 1964). The middle unit is about 100 feet of light-gray brown, bioclastic limestone with scattered chert granules. The upper unit is composed of 400 feet of alternating thin-bedded, cherty limestone, and calcareous siltstone (Barosh, 1964).

The Carbon Ridge is about 1500 to 1700 feet thick in the southern Diamond Mountains and Eureka area (Molan and others, 1956), 1,500 feet in the Pancake Range about 13 miles southeast of Carbon Ridge (Barosh, 1964), about 900 feet thick near Dry Mountain in the Buck Mountain area (Barosh, 1964), and varies from about 1,400 to 2,300 feet in the northern Diamond Mountains (Dott, 1955).

The Carbon Ridge, as designated, only crops out in the Eureka area, Diamond Mountains, Pancake Range, and Buck Mountain area.

Brachiopods, corals, crinoids, echinoid spines, pelecypods, cephalopods, fusulinids and trilobites have been recovered from the Carbon Ridge Formation suggesting shallow to moderate marine deposition. The Carbon Ridge was, as mentioned above, deposited in a north-south trending Permian depocenter centered in what is now the Diamond Mountains area.