The Kettle River Range in Ferry County, Washington, is underlain by sillimanite-grade rocks of the Tenas Mary Creek sequence. Two >800-m-thick sheets of augen gneiss occur above and below feldspathic quartzite, biotitic gneiss, and minor marble. Polyphase deformation (including mylonites and east-trending lineations) and slightly uraniferous aplitic to pegmatitic bodies are common. Cataclasis is common, and rocks of the Tenas Mary Creek sequence appear to be in tectonic contact with overlying upper Paleozoic phyllitic rocks. Fine-grained biotitic metasedimentary rocks occurring locally between the phyllitic rocks and rocks of the Tenas Mary Creek probably are older than the late Paleozoic phyllitic...