GEOLOGIC MAPPING AT OREGON CAVES NATIONAL MONUMENT, CAVE JUNCTION, OREGON

Geologic mapping of Oregon Caves National Monument was completed during the summer of 2007 as a GeoCorps America Program project. The monument is located in T40S, R6W, Josephine County, Oregon and includes a variety of metamorphic and igneous rocks in its 488 acres. The majority of the assemblage belongs to the lower Rattlesnake Creek terrane, which consists of marble, argillite, metasediment, and metachert. The Josephine Ophiolite complex outcrops as an area uplifted by thrust faults. The complex consists of peridotite, serpentinite, skarn, and metamorphosed basalt and gabbro. Diorite dikes originating from the Greyback Pluton intrude the surrounding terrane and ophiolite units. A digitized map was made using ESRI ArcGIS Desktop for public display and ranger interpretation at the monument. The complex geologic history and dense old growth forest had limited the precision of previous geologic maps that are necessary for other geologic projects to be carried out. Rock samples were collected in order to do detailed rock descriptions and some oriented samples were prepared for thin sections. Further studies include detailed structural analysis of the marble unit and petrographic analysis of the oriented thin sections from several units within the monument.