The Woodruff Formation was named for exposures along and near Woodruff Creek in Sec. 25, T. 32 N., R. 52 E. in the northern Carlin-Pinon Range (Smith and Ketner, 1968).

The Woodruff Formation is middle to early Late Devonian in age. It is in part equivalent to the Slaven Chert, the Rabbit Hill Limestone, the upper part of the Roberts Mountains Formation, and the lower portion of the Pilot Formation (Gilluly and Gates, 1965; Merriam, 1963; Evans and Mullens, 1976; Coats, 1985). The Woodruff is unconformably overlain by both the Webb and Chainman Formations at the type section.

The Woodruff Formation is composed of siliceous mudstone, and chert, and lesser amounts of siliceous shale, thinly bedded siltstone, dolomitic siltstone, dolomite, limestone and sandy limestone to sandstone. These diverse lithologies are exposed in isolated blocks which are partially correlated on the basis of graptolite occurrences (Smith and Ketner, 1975).

The black to brown weathering cherts commonly have thin argillaceous partings and form beds from 1 to 4 inches thick that are interbedded with dolomitic siltstones, shales, and mudstones (Smith and Ketner, 1975). The shales in the Woodruff are dark gray to black and weather a light brown, gray or white color. The shales are carbonaceous and locally dolomitic and are often pencil weathering. Silicification within the shales is variable with abundant thin-bedded, brittle, conchoidally fracturing siliceous shale.

The siltstones are platy and shaley to punky, and weather to a gray or light brown color, as do the limestones and sandy limestones. These siltstones are both calcareous and carbonaceous and contain oval phosphate nodules up to 1.5 inches across (Smith and Ketner, 1975). In several localities the siltstones are so carbonaceous and sooty that they will blacken the hands. Thin-bedded gray weathering limestones are very minor in the Woodruff and occur as thin lenses from 2 to 30 feet thick with strike lengths up to 300 feet. Gray to brown clastic dolomite, in beds up to 6 inches thick, also composes a minor percentage of the unit (Smith and Ketner, 1975).

As designated, the Woodruff Formation also includes portions of about 1,200 feet of shaley siltstones, laminated brown to black chert, siliceous and black carbonaceous shales, arenaceous, fine-grained and thick-bedded limestones, and sandstone designated by Merriam (1967) as the Cockalorum Wash Formation. These uraniferous and vanadiferous units occur in isolated exposures within the southern Fish Creek Range (Hose, 1983) and also in the Hot Creek Range, where contacts with other units are generally faulted or covered with alluvium. The light-gray limestones in this unit contain eurypterid claws, Hexagonaria coral heads, algal debris and radiolaria; an assemblage very similar to that of the Woodruff in the Pinon Range (Smith and Ketner, 1968), as well as several sections of the Pilot Formation. Desborough and others (1979) included the Cockalorum Wash Formation in the Hot Creek Range with the Woodruff Formation and unnamed allochthonous Mississippian siliceous strata. Hose (1983) abandoned the Cockalorum Wash Formation designation in mapping the Cockalorum Wash Quadrangle. That group of rocks was reassigned to the Devils Gate Limestone, Pilot, Woodruff, Antelope Range and Webb Formations which are juxtaposed along high and low angle faults in the type area. Such a designation is followed in this report.

Hose (1983) described the Woodruff in the Fish Creek Range as dark brown to gray, pastel weathering, siliceous mudstone, cherty siltstone, and chert which is kerogenous and contains high concentrations of vanadium, molybdenum, selenium, and zinc, and several other metals.

In the northern Hot Creek Range, Potter (1976) correlated early Famennian mudstone, chert, porcelanite and minor quartz arenite with the Woodruff Formation. The dominant lithologies are tightly to gently folded, brecciated, thin-bedded, gray chert, and contorted, very thin-bedded, dolomitic and silty, brown, pink, and tan weathering mudstone with abundant eurypterid claws (Potter, 1976). Gray-green porcelanite and poorly sorted, medium to fine-grained, well-rounded quartz arenite are also interbedded within the unit.

In the Dobbin Summit area of the Monitor Range, Wise (1977) suggested a unit of bluish-gray dolomites, white porcelanite, brown fine-grained dolomitic quartz arenite, and brown-weathering light gray, thick-bedded cherts may possibly correlate with the Woodruff.

The Woodruff Formation is estimated to be 1,200 to 3000 feet thick in the Carlin-Pinon Range (Smith and Ketner, 1975), and is at least 350 feet thick in poorly exposed outcrops in the northern Hot Creek Range (Potter, 1976).

The Woodruff Formation is present in the Carlin-Pinon, Fish Creek and Hot Creek Ranges.

The depositional setting of the allochthonous Woodruff is poorly understood. Original water depth is somewhat ambiguous for the Woodruff Formation, like many of the allochthonous subduction-complex related sediments present within the Roberts Mountains allochthon. Arthropods and crinoids found in shales, siltstones and limestones, the presence of phosphate nodules, and dolomites of secondary, primary and detrital origin suggest a shallow marine shelf environment for the Woodruff. The radiolarian-rich Woodruff cherts may have been deposited under relatively deep marine conditions (Smith and Ketner, 1975).

Eight (8) surface geochemical samples of the Woodruff Formation were analyzed during this evaluation and indicate that the formation is organic-rich with an average TOC content of 2.55 percent. Maturity data show that the Woodruff is mature in surface exposures. The Woodruff has good source potential within a restricted area indicated on Overlays IX and X. The geochemical results for the Woodruff Formation are discussed within the Geochemical and Geothermal Data Volume of this evaluation.