Chiefly pelitic and quartzose metasedimentary rocks of greenschist facies exposed in west-central Alaska in the northeastern Medfra, southeastern Ruby and southwestern Kantishna River quadrangles. Micaceous quartzite and quartz-chlorite schist grade into quartz-muscovite-biotite-garnet schist; calc-schist and marble are subordinate. Unit locally includes small bodies of greenstone and greenschist-facies metabasite, granitic gneiss, and metamorphosed quartz porphyry. The porphyry is fine-grained, foliated, and banded felsic volcanic rock composed of large phenocrysts of embayed quartz and plagioclase in a very fine-grained quartzo-feldspathic groundmass that has a distinct micaceous overprint. Zircon fractions from two suites of samples of metamorphosed quartz porphyry yielded upper intercept ages of 850±30 Ma and 1,265±50 Ma, interpreted to be crystallization ages (Patton and others, 1980, 2009). Metamorphic minerals from the schist yield K/Ar isotopic cooling ages that range from 921 to 284.2 Ma (Patton and others, 2009), which indicate that this terrane of metamorphic rocks likely did not experience the mid-Cretaceous metamorphism commonly seen in other metamorphic rocks in Alaska