RECENT ADVANCES IN THE GEOLOGICAL MAPPING AND CENOZOIC LITHOSTRATIGRAPHY OF THE PINE RIDGE RESERVATION (OGLALA SIOUX TRIBE), SOUTHWESTERN SOUTH DAKOTA

In the years from 1996 to 2006 the University of Nebraska STATEMAP program mapped and revised the lithostratigraphy of northwestern and north-central Nebraska adjacent to the southern borders of South Dakota and the Pine Ridge Reservation. Since 2008 the faculty and students from the Department of Math, Science, and Technology at Oglala Lakota College, in collaboration with staff from the Oglala Sioux Tribe's Natural Resource Regulatory Agency and Land Office, and faculty and students from the South Dakota School of Mines and Technology, South Dakota State University, the University of Illinois at Urbana-Champaign, and Chadron State College, has continued this work and extended Nebraska's mapped units into Fall River County, South Dakota and the Pine Ridge Reservation (Shannon, Bennett, and Jackson counties). Our recent 1:24,000 geologic mapping has focused on the mapping of the stratigraphy adjacent to the Whiteclay Fault in southern Shannon County. As a result of this mapping we have correlated the Cretaceous Niobrara Formation, the Eocene Yellow Mounds Paleosol (Niobrara Formation), the Late Eocene Peanut Peak and Big Cottonwood Creek members of the Chadron Formation, and the Oligocene Whitney Member and Sharps beds of the Brule Formation into and across Shannon County. In addition, the Oligocene West Ash Creek beds, Monroe Canyon Formation, and Coffee Mill Butte beds, the Oligo-Miocene Harrison Formation, and the Early Miocene Anderson Ranch Formation and Wounded Knee beds have been correlated through Shannon and Jackson counties. No new strata have been recognized since Gaddie and LaGarry (2010) reported the Wanblee and Ghost Canyon beds in Jackson County. This work is ongoing, and our goal is a detailed geologic map of the Pine Ridge Reservation that will enable Tribal agencies to map radionuclide contaminant pathways, manage the surface waters of the White River watershed, and monitor the reservation's groundwater supplies. This work was funded by the NSF TCUP Phase III (Tinant and LaGarry), NSF PEEC (Tinant and LaGarry), and NSF EPSCoR R2 T1 (LaGarry) programs.