Named the upper formation of Belt series for Swauger Ranch, Borah peak quad, Custer Co, ID, Northern Rocky Mountain region. Exposures of Swauger occur northeast of ranch in Ts12, 13, and 14N, Rs24 and 25E, and south of the ranch in Ts11 and 12N, Rs24 and 25E. Areal extent includes Custer and Lemhi Cos. No type locality designated. Extends into northern Lemhi Range but may not be as extensive as Lemhi quartzite, newly named basal formation of Belt series. Composed of pure quartzite that varies in color from purple to lavender to nearly white. Is distinctly bedded. Some beds are cross-bedded. Includes a few lenses of conglomerate and rusty impure dolomite. Maroon, green, brown, or dark-gray to black argillite present in Lemhi Range. Not as schistose as underlying Lemhi. Quartz grains are distinctly water worn and less well rounded than Lemhi. Top and bottom of formation not present in one exposure. May be at least 1 m thick. The geologically next-younger rocks in the quad informally designated the Ordovician or older rocks of Sawmill Gulch. Unfossiliferous. Assigned to the pre-Cambrian. Bears resemblance to Hoodoo quartzite. Geologic map and cross sections.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Underlies with angular unconformity Summerhouse Formation (new) at its type section in Summerhouse Canyon, Custer Co, ID in the Northern Rocky Mountain region. Underlies Wilbert Formation (new) at South Creek, Butte Co, ID in the Snake River basin. Of Precambrian Y age.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Removed from Belt Supergroup and name redescribed from Swauger Quartzite to Swauger Formation. Was deposited in the Belt miogeocline of east-central Idaho, rather than in Belt basin. Reference section designated in sec 34, T16N, R23E, Patterson quad, ID in Northern Rocky Mountain region. Some of the rocks (impure quartzite, lenses of white quartzite, conglomerate, rusty impure dolomite, and argillite) in central and southern Lemhi probably belong to younger Precambrian or Ordovician formations. Thickness uncertain due to faulting; 10,000 ft (3,100 m) at reference section but top cut by faulting. Lower contact with Gunsight Formation (new), upper formation of Lemhi Group (rank raised). Overlain with angular unconformity by Wilbert Formation in southern part of Lemhi Range and by Summerhouse Formation in west-central part of range (new names in Professional Paper 889-B), and by Kinnikinic Quartzite in east-central part of range.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Swauger Formation (revised). Underlies newly named Lawson Creek Formation at four localities in northernmost part of Lost River Range and adjacent Salmon River Mountains, Custer County, Idaho (Northern Rocky Mountain region); contact thought to be gradational. Overlies Lemhi Group. Correlates with part of Missoula Group. Age is middle Proterozoic (Proterozoic Y). Report includes correlation chart.

Source: Modified from GNU records (USGS DDS-6; Denver GNULEX).