Named as one of four newly named formations and the structurally highest formation of the newly named Riggins Group. Named for Squaw Creek, a tributary to the Little Salmon River. Type section designated along Little Salmon River from Riggins to Captain John Creek, Idaho Co, ID in Idaho Mountains province. Present thickness in Riggins syncline is about 6,000 ft. Overlies Lightning Creek Schist (new) of Riggins north and south of Riggins. Overlies Berg Creek Amphibolite (new) of Riggins Group east of Riggins. Consists of light- to dark-gray phyllite and fine-grained schist. Compositional layering and lamination are conspicuous. Varies in grain size form aphanitic phyllite to medium-grained gneiss. Plagioclase is the dominant mineral and quartz is the next most dominant. Rock types vary widely and intergrade complexly. Were sedimentary rocks derived from source region of volcanic rocks. Schists have been isoclinally folded and extremely sheared. Shown as Paleozoic and Mesozoic age on geologic map. Known to be older than Idaho batholith.
[NOTE: The Department of the Interior's Secretarial Order 3404, issued on November 19, 2021, formally identifies the term “squaw” as derogatory. That Order will create a federal Derogatory Geographic Names Task Force, to find replacement names for geographic features in use by federal agencies. We’re awaiting guidance from the Task Force, and will then take the appropriate actions.]

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

Some medium- and high-grade metamorphosed volcanic rocks mapped east of the Salmon River area are mapped as metamorphic units whose relative age and correlation are unknown; these rocks are tentatively correlated with the Seven Devils Group; they are shown as Permian and Triassic age; they are also mapped as present in two plates--the Rapid River and North Fork plates--of the Wallowa terrane. These metamorphosed rocks were assigned to the Riggins Group and mapped as one of its formations--Squaw Creek Schist [See Below], Lightning Creek Schist, Berg Creek Amphibolite, or Fiddle Creek Schist, depending on locality. There is no evidence found during this study to indicate that rocks of the Riggins and the Wallowa are different island arcs. Also, all identifiable map characteristics useful for distinguishing the formations have been obliterated by multiple episodes of metamorphism and deformation. The mapped units cannot be correlated with or assigned to individual formations with confidence. Therefore, the name Riggins and its component formations are not recognized in this study.
[NOTE: The Squaw Creek Schist is in the process of being renamed, in accordance with the Department of the Interior's Secretarial Order 3404, issued on November 19, 2021, formally identifying the term “squaw” as derogatory.]

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