The Riepetown Formation was designated by Steele (1960) for rocks originally named the Rib Hill Formation by Pennebaker (1932). The Rib Hill Formation was named for Rib Hill in Sec. 21, T. 16 N., R. 62 E., where three members were broken out. Later workers (Easton and others, 1953; Langenheim and others, 1960) restricted the Rib Hill to the lower sandstone member. Because of the preoccupation of the name Rib Hill by a quartzite unit in Wisconsin, Steele (1960) renamed the unit as the Riepetown Formation which is followed in this report. The Riepetown Formation was named for the town of Riepetown, and the type section for the unit is designated in Sec. 21, T. 16 N., R. 62 E. in the central Egan Range (Steele, 1960).

The Riepetown Formation is Permian (Wolfcampian) in age and conformably overlies the Permian Riepe Spring Limestone and underlies either the Permian Kaibab Limestone or the Arcturus Formation in differing areas. In areas east of the Egan Range, conventional criteria for separating the Riepetown or Rib Hill Sandstone from the Arcturus do not apply and the two are mapped together as a unit (Hose and Blake, 1976).

In general, the Riepetown Formation consists of fine to medium-grained, yellowish-gray, calcareous sandstone that forms narrow slopes, and interbedded light to medium-gray dolomite and sandy to silty limestone that form narrow ledges (Hose and Blake, 1976). At its type locality, the Riepetown Formation is about 1,000 feet of pale yellowish-gray to brownish and reddish weathering, very fine to medium-grained, rounded to subrounded, platy to thick-bedded quartz sandstone. Thin light gray, silty limestone is interbedded throughout the unit and composes a total of about 8 percent of the formation. The lower portion of the formation contains abundant Wolfcampian age fusulinids, while the upper 700 feet is barren of fossils (Steele, 1960). The formation also contains a variety of gastropods, pelecypods and ostracods and corals within both the limestones and sandstones in various localities (Steele, 1960; Hose and Blake, 1976).

In the Pancake Range west of Duckwater, Kleinhampl and Ziony (1985) have reported several hundred feet of section above the Ely Limestone which include the Riepe Spring Limestone and Riepetown Formation. The Riepetown is a quartz-rich, silty and sandy, yellowish to brown weathering limestone with interbedded reddish-brown calcareous siltstone and sandstone.

In the Egan Range, the upper portion of the Riepetown is medium to fine-grained, thin to medium-bedded, yellow-gray sandstone and siltstone and interbedded yellowish-gray dolomite and limestone, which is interbedded with thin platy yellowish-gray limestone. The lower portion contains coarse-grained and medium-bedded, gray bioclastic crinoidal limestone with nodular and lenticular limey cherts, and brick red and gray siltstones (Barosh, 1964; Brokaw and Shawe, 1965; Brokaw, 1967; Brokaw and Heidrick, 1966).

In the Cherry Creek Range south of McDermitt Canyon, Bissell (1964) divided the Riepetown into three members. The lower 670 feet is dark gray, red-brown and orange-tan calcisiltite, micritic and sandy limestone, fine-grained orthoquartzite, and thin fusulinal limestones. The middle member is 55 feet of olive gray to red micritic and skeletal coquinal limestones with abundant fusulinids. The upper member is 330 feet of thin to medium-bedded, dark gray and maroon siltstones, silty to argillaceous limestones, and quartz sandy skeletal limestones (Bissell, 1964).

In the Butte Mountains, the Riepetown is interbedded light gray-brown to yellow-gray, cherty, thin to medium-bedded limestone which is locally crinoidal, light gray to orange, calcareous siltstone and minor dolomite (Barosh, 1964). Sides (1967) reports that 50 percent of the unit is siltstone and sandstone, and the remaining 50 percent is limestone. The sandstones are faintly cross-bedded and appear to contain tracks and trails along bedding planes (Sides, 1966).

In the southern Pequop Mountains, the Riepetown has been divided by Bissell (1964) into four members. The lower 411 feet is thin to medium-bedded, dark blue-gray and red-brown, silty argillaceous limestone, and sandy calcisiltite and calcareous sandstone. The overlying 161 feet is dark gray and orange-brown, very fine-grained, calcareous sandstone, and thin-bedded, argillaceous limestone with small pelecypods. Above this is 79 feet of cherty, siliceous, thin-bedded, micritic, blue-gray limestone. The uppermost 519 feet is interbedded argillaceous and silty micritic limestone, fine-grained sandstone, cherty and sandy calcisiltite, and thin fusulinal limestone (Bissell, 1964).

In the northern Pahroc and southern Schell Creek Ranges and on Grassy Mountain, the Riepetown is grayish-pink, yellowish-brown and grayish-orange, thin-bedded and platy, argillaceous to sandy limestone with some calcareous sandstone interbeds. In the northern Pahroc Range, the lower part of the unit is grayish-orange paper-thin silty limestone (Tschanz and Pampeyan, 1970).

In the southern Schell Creek Range, Bissell (1964) described 5 units within the Riepetown. The basal 70 feet are thin-bedded and platy calcisiltites and argillaceous limestone and are overlain by 173 feet of thin to medium-bedded, gray, argillaceous limestone and fine-grained, locally calcareous sandstone. The next unit is 66 feet of red-gray, fine-grained, tight, silica-cemented orthoquartzite above which are 117 feet of interbedded yellow, pink, and gray silty to sandy dolomite and fine-grained orthoquartzite (Bissell, 1964).

In the Spruce Mountain Quadrangle, several hundred feet of the Riepetown overlie the Riepe Spring Limestone (Hope, 1972). The Riepetown is composed of tan-weathering platy siltstone, and thin-bedded gray to orange limestone.

In the Pilot and Leppy Ranges, the Riepetown is combined with several undivided and poorly exposed units about 2550 feet in thickness. It is dominantly a dark-brown, thin-bedded, argillaceous limestone with interbedded siltstone (O'Neill, 1968; Schaeffer and Anderson, 1960).

Variations in thickness within sections of the Riepetown Formation are in part the result of interpretational placement of the upper contact with the overlying Arcturus Formation. The Riepetown Sandstone is 1,008 feet at the type locality in the central Egan Range (Steele, 1960). It ranges from 800 to 1,300 feet in the central Egan Range according to Barosh (1964) and Brokaw and Heidrick (1966), and is about 470 feet thick in the southern Egan Range according to Playford (1961). It is 1,055 in the Cherry Creek Range (Bissell, 1964), at Moorman Ranch it is about 1,200 feet thick (Steele, 1960), 660 feet in the central Butte Mountains (Barosh, 1964) or 719 feet in the central Butte Mountains according to Sides (1966), 1,260 feet in the Pequop Mountains (Bissell, 1964), 600 to 1,500 feet thick in the Spruce Mountain Quadrangle (Hope, 1972), and 786 feet in the southern Schell Creek Range (Bissell, 1964). Several hundred feet of Riepetown Formation are present in an undivided section of Permian rocks in the Pilot and Leppy Ranges (O'Neill, 1968; Schaeffer and Anderson, 1960).

The Riepetown Formation is exposed in the Buck Mountain-Bald Mountain area, Maverick Springs, northern Cherry Creek, northern Grant, central Egan, southern Schell Creek, northern Pahroc, Pilot and Leppy Ranges, southern Pequop and Butte Mountains, Grassy Mountain, and the Spruce Mountain Quadrangle.

The sandy and silty skeletal limestones and fine-grained sandstone and siltstones of the Riepetown contain abundant fusulinids, bryozoans, pelecypods, various invertebrate tracks and cross-beds. These lithologies were deposited as very shallow marine deltaic sand aprons along the outer shelf.