The Thaynes Formation or Limestone was named for about 1,190 feet of limestone, calcareous and quartz sandstone, and reddish shale along Thaynes Canyon in the Park City mining district area of Utah (Boutwell, 1907)

The Thaynes Formation is considered Early Triassic (Scythian) in age.

In the O'Neill Pass area of the Snake Mountains, the Thaynes Formation is composed of thick, alternating beds, of black to blue-gray and light brown weathering limestone, interbedded with thin beds of crossbedded siltstone (Bezzerides, 1967). Gardner (1967) described the Thaynes in the Snake Mountains as thin to thick-bedded, gray to olive, locally carbonaceous limestone with 10 to 20 percent interbeds of thin calcareous siltstone and silty shale.

In the Windermere Hills, the Thaynes Formation conformably overlies the Triassic Dinwoody Formation and is composed of dark gray limestone (calcisiltite and calcilutite) with a collapse breccia near the base which may have originally represented evaporite beds (Oversby, 1972).

In the southern Pequop Mountains, the Thaynes is divided into two informal members by Snelson (1955). The basal member is about 2,450 feet of gray limestone with overlying fissile olive-green shale, siltstone, and limestone. The upper member is about 450 feet of orange and gray weathering, finely crystalline, argillaceous, current-bedded limestone with pelecypods. Overlying the limestone are interbedded siltstones, shales, argillaceous limestone and minor chert. The Thaynes conformably overlies the Dinwoody in the Pequop Mountains.

In the Currie Area, the Thaynes Formation was divided into three informal members by Nelson (1956). The basal member is about 1,560 feet of massive, medium-gray, medium-grained limestone. It is overlain by light-gray to olive, fossiliferous, arenaceous limestone and poorly exposed, yellow-brown and green-gray, calcareous shale and siltstone interbedded with thin gray limestone. The middle member is about 376 feet of medium-bedded, medium-grained gray limestone. The upper member of the Thaynes is about 263 feet of interbedded greenish-brown, yellow and gray siltstone, limestone, dolomite and shale with pelecypods (Nelson, 1956).

In the Dolly Varden Mountains, several hundred feet of Triassic sediments can be correlated with the Thaynes Formation (Snow, 1964). The unit is composed of thin-bedded gray, brown weathering limestone interbedded with chocolate-brown shale and olive-green calcareous shale. The formation is locally contact metamorphosed in the Dolly Varden Mountains (Snow, 1964).

In the central Butte Mountains, the Thaynes Formation is composed of a basal, brown-red, silicified limestone overlain by about 135 feet of poorly exposed, dolomitic and locally cherty, yellow to pink limestone. This silty and locally rippled limestone contains abundant chert and quartzite pebbles in lenticular beds up to 10 feet thick in the lower portion of the limestone. The overlying 140 feet are greenish-gray to brown, thin to medium-bedded, silty, fossiliferous, locally oolitic, coarsely bioclastic limestone with cephalopods and pelecypods. The upper 23 feet of the unit is composed of light green to greenish-brown weathering, silty, fissile shale (Sides, 1966).

In the Ferguson Mountain area near the southern tip of the Goshute Mountains, the Thaynes is dark-brown crystalline limestone overlain by yellowish, variegated shaly limestone and rests disconformably on the Ferguson Mountain Formation or Kaibab Limestone (Berge, 1960).

In the Medicine Range, the Thaynes Formation was divided into two informal members by Collinson (1966, 1968). The lower member is interbedded calcareous sandstone, sandy limestone and lenticular chert-pebble conglomerate which grades laterally into coarse-grained sandstone. The conglomerates and sandstones are locally graded and cross-stratified. The upper member is poorly exposed interbedded limestone and calcareous siltstone.

The Thaynes Formation is about 620 feet thick in the O'Neill Pass area of the Snake Mountains (Bezzerides, 1967; Gardner, 1967), 425 feet in the central Butte Mountains (Sides, 1967), 520 feet in the Medicine Range (Collinson, 1968), 350 feet in the Windermere Hills (Oversby, 1972), 240 feet in the Ferguson Mountain area (Berge, 1960), 2,190 feet in the Currie Area (Nelson, 1956), about 400 feet in the Dolly Varden Mountains (Snow, 1964), and 2,900 feet in the southern Pequop Mountains (Snelson, 1955).

The Thaynes occurs in the Twin Springs and Currie Hills, Medicine Range, Ferguson Mountain area near the southern Goshute Mountains, Dolly Varden, Butte and Pequop Mountains, northern Windermere Hills, northern Snake Mountains, near Mount Ichabod in T. 43 N., R. 56 E., and in the northeastern corner of the study area in T. 47 N., R. 69 E.

The limestones and mudstones of the Thaynes Formation represent shallow open marine shelf and carbonate shoal sediments (Collinson and Hasenmueller, 1977). The sandstones and conglomerates represent small strandline-type channel deposits.