A petrographic study of upper Devonian sandstones (Endicott and Hammond Terranes), Philip Smith Mountains and Arctic quadrangles, Brooks Range, Alaska, shows that the sand-sized detritus was derived from two petrographic provenances. Detrital modes, calculated from point counts of thin sections, show that the provenance for the Devonian clastic wedge (Endicott Terrane) was a recycled orogenic belt with major components of quartz, chert, and lithic fragments. Three petrofacies are distinguished. Their distribution indicates compositional changes vertically and laterally which reflect changing compositions in the source area. A petrographically different provenance supplied the sandstones that overlie the Skajit Limestone (Hammond Terrane). Characterized by high feldspar and abundant volcanic rock fragments, this petrofacies indicates first-cycle deposition close to the source area. A magmatica arc provenance is suggested.