Terranes of the Klamath Mountains, California-Oregon, are primarily the products of transpressive-transtensional margin processes that span the mid-Devonian to Middle Jurassic time interval. One of the more enigmatic units of this orogen is the early Mesozoic, north-south–trending, medially situated North Fork terrane. Based on the integration of new and previously published data, ophiolitic rocks in the North Fork terrane are interpreted as the basement to superjacent mafic metavolcanic units and associated metasedimentary strata. We propose that these volcanic and sedimentary rocks accumulated in a forearc position relative to the eastern Klamath fringing arc. New mapping in the southern Klamath Mountains...