Geologic map showing part of the May Creek schist and related rocks, Jackson County, Oregon

The metamorphic rocks shown on the accompanying geologic map occupy the northeasternmost part of the Klamath Mountains Province and are in fault contact to the east with Tertiary rocks of the Western Cascades Province.Two of the four lithotectonic belts of the Klamath Mountains Province as defined by Irwin (1966) are represented in the mapped area: the western Paleozoic and Triassic belt and the western Jurassic belt (fig.1).Although Irwin's (1966) nomenclature is still in use, readers should note that these names do not accurately reflect the currently regarded ages of these units.The tectonostratigraphic terrane terminology used in this report has been widely adopted.Rocks in this part of the western Paleozoic and Triassic belt consist of rocks commonly referred to as the May Creek terrane and the Applegate terrane (Silberling and others, 1987; Irwin, in press).The westernmost part of the mapped area, part of Irwin's (1966) western Jurassic belt, includes rocks belonging to Silberling and others' (1987) Rogue Valley subterrane of the western Klamath terrane.The western Paleozoic and Triassic belt is a complex collage of metamorphosed accreted oceanic and island arc material that spans the entire length of the Klamath Mountains in southwestern Oregon and northern California.In southwestern Oregon, the rocks of the western Paleozoic and Triassic belt are known as the Applegate Group, an extensive unit that includes a wide variety of volcanic, sedimentary, and crystalline rocks.These rocks were originally described, but not named, by Diller (1914), who believed that they were Devonian and Carboniferous in age on the basis of poorly preserved fossils in limestone.The rocks were later named the Applegate Group by Wells and others (1949), who assigned them a Triassic(?)age.Later reconsideration of fossil collections caused the age of the Applegate to be revised to Late(?) Triassic (Wells and Peck, 1961).Still