The Reservation Hill Formation is named for rocks exposed at Reservation Hill, Secs. 29 and 23, T. 46 N., R. 53 E., in the Mountain City and Owyhee Quadrangles (Coats, 1969).

The Reservation Hill Formation is thrust over the Mountain City Formation and is overridden by Tertiary sediments at the type locality. It is considered to resemble the Havallah Formation, and although no fossils have been recovered, it is assigned a Pennsylvanian and Permian age (Coats, 1969, 1985).

In the Mountain City and Owyhee Quadrangles, the Reservation Hill Formation is a lithologically diverse assemblage dominantly composed of fine-grained, pale-gray, dolomitic sandstone and siltstone that weather to a cream and pale reddish-brown (Coats, 1969, 1971, 1985). Also present are minor amounts of interbedded phyllite; metagraywacke which grades into micaceous and tremolitic quartzite and graphitic phyllite; meta-andesite up to 200 feet in thickness which is locally metamorphosed to schist; meta-rhyolite tuff beds up to 2 feet thick; and lenses of gray, siliceous dolomitic limestone up to 50 feet thick (Coats, 1969). Siltstone and phyllite are commonly rhythmically interbedded in thick sequences that show alternating beds 1 to 2 inches in thickness (Coats, 1969). A few thin beds of biotitic meta-chert and pure quartzite are also present in the Reservation Hill (Coats, 1971).

In the Elk Mountain Quadrangle area of the Jarbidge Wilderness, the Reservation Hill Formation is mainly composed of interbedded dolomitic siltstone and phyllite (Coats, 1985). It is metamorphosed near large granodiorite and quartz monzonite intrusive bodies that have introduced diopside, tremolite and wollastonite (Coats and others, 1977).

The Reservation Hill Formation is at least 500 feet thick at its type locality in the Mountain City Quadrangle (Coats, 1969), is several hundred feet in the Elk Mountains Quadrangle portion of the Jarbidge Wilderness (Coats, 1985), and several thousand feet thick in the Owyhee Quadrangle (Coats, 1971).

The Reservation Hill Formation is exposed in the Reservation Hill area in the eastern Owyhee and western Mountain City Quadrangles (Coats, 1969), and in the Elk Mountains Quadrangle portion of the Jarbidge Wilderness area (Coats and others, 1977).

Depositional setting for the Reservation Hill Formation is poorly understood. Most probably the formation represents dismembered portions of the Golconda allochthon deposited under generally deep marine conditions in a subduction zone setting.