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The Cougar Gulch area near Coeur d’Alene, Idaho, is a newly recognized Paleoproterozoic to Archean basement occurrence located in the southern Priest River complex. Here, a structural culmination exposes deeper levels of the core complex infrastructure, similar to where Archean basement is exposed in the northern portion of the complex near Priest River, Idaho. At Cougar Gulch, the basement rocks are composed of a variety of granitic orthogneisses and amphibolite, which are unconformably overlain by a graphite-bearing orthoquartzite. The orthoquartzite is in turn overlain by the Hauser Lake Gneiss. The similarity of structure, metamorphic fabrics, and kinematics here and in the northern portions of the complex is consistent with the Cougar Gulch area being the southern continuation of the Spokane dome mylonite zone.

Neoarchean amphibolites (2.65 Ga) have been identified as part of the basement sequence. These amphibolites had a basaltic protolith and can be distinguished geochemically from amphibolites found within the overlying Hauser Lake Gneiss (Mesoproterozoic, Lower Belt Group equivalent), which are metamorphosed Moyie sills. The Archean amphibolites have steeper REE (rare earth element) slopes and consistently higher REE values. Protoliths of the Paleoproterozoic orthogneisses (1.87–1.86 Ga) are calc-alkaline, “I-type” monzogranites and granodiorites, which exhibit subduction-related geochemical characteristics such as high LILE:HFSE (large ion lithophile element: high field strength element) concentrations, along with characteristic depletions in Nb, Ta, P, Ti, and Eu. A second distinctive geochemical unit of orthogneiss, the Kidd Creek tonalite, exhibits TTG (tonalite-trondhjemite-granodiorite) geochemical characteristics. The Kidd Creek tonalite has Sr/Y and La/Yb ratios, along with Y and HREE (heavy rare earth element) concentrations (no Eu anomalies) similar to Precambrian TTG compositions formed in subduction settings. Detrital zircon data from the orthoquartzite unit, along with characteristic graphite and its consistent stratigraphic level support correlation to the pre-Belt Gold Cup Quartzite in the northern part of the complex.

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