Named for Sedgwick Peak, highest point in Portneuf Range, ID. Type area lies along crest of Portneuf Range from Sedgwick Peak north-northwest for about 5 mi. Exposures on southwest side of the northern of Twin Knobs in SW1/4 NE1/4 sec 12, T10S, R38E, Bannock Co, ID, Snake River basin, designated the type section. Consists of medium-bedded, fine to very fine grained quartzites that are tan to green on fresh surfaces and dark brown, dark green to black on weathered surfaces. Some quartzite beds contain scattered coarse grains and are pink, tan, brown, and pale gray. Thin, thinly laminated green, tan and brown argillite and tan quartzitic siltstone are interbedded with the quartzite. Is 300 ft thick at type section. Forms a moderately continuous belt along and near crest of Portneuf Range. Overlies Windy Pass Argillite Member (new); underlies the Twin Knobs Formation (new). Is of Early Cambrian age. Has Scolithus tubes, trilobites (130 ft above base). Geologic map.

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

Raised to formation rank and assigned to Brigham Group [elevated to group rank] as the uppermost of 7 formations in the southern Portneuf Range, Bannock Co, ID in the Snake River basin, and in Bear River Range, Bear Lake Co, ID on the Wasatch uplift. Thicknesses of 299 to 738 ft reported. Overlies Windy Pass Argillite of Brigham Group. Underlies Twin Knobs Formation. May correlate with member B of Gibson Jack Formation. Cross section. Is a marine unit assigned to depositional sequence 4. Cambrian age.

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