REVISED LITHOSTRATIGRAPHY OF LATE PALEOGENE AND NEOGENE STRATA OF THE HIGH PLAINS AQUIFER IN WESTERN NEBRASKA, USA

Based on detailed (1:24,000) 1996-2006 geologic mapping and lithostratigraphic correlations, we revise, redescribe, and redefine strata of the High Plains Aquifer in western Nebraska, including volcaniclastic sandstones of the Arikaree Group (late Paleogene-early Neogene) and epiclastic sandstones of the Ogallala Group (Neogene). This sequence is underlain by impermeable siltstones of the White River Group and overlain by Quaternary deposits. The base of the Arikaree Group is narrowly incised into underlying strata and consists of fluvial sandstones and conglomerates of the West Ash Creek beds, Alliance beds, and the Gering Formation. This interval is the source of many spring-fed creeks and rivers in northwestern Nebraska. Overlying these are thick, widespread eolian sandstones of the Fort Robinson beds. These are overlain by eolian sandy siltstones of the Anderson Ranch Formation, compact eolian siltstones of the Antelope Creek beds, fluvial and eolian sandstones of the Metcalf beds, and eolian sandstones of the Mission Ranch beds. These strata are restricted to the Niobrara River canyon, high points of the eastern part of the Pine Ridge, and northeast of the Whiteclay Fault. The base of the Ogallala Group is the Runningwater Formation, which we divide into overbank sandstones of the Starvation Gulch beds and the fluvial sandstones and conglomerates of the Rushville beds. This unit is a source of municipal water. These strata are overlain by gravels filling the trace of the Whiteclay Fault called the Whiteclay gravel beds. This unit is a local water source. These strata are overlain by the Box Butte Formation, consisting of fluvial sandstones of the Red Valley Member and nodular claystone of the Dawes Clay Member. These strata are overlain by calcareous fluvial sandstones of the Sand Canyon Formation. These strata are overlain by discontinuous fluvial valley fills of the Sheep Creek and Olcott Formations. Overlying these strata are fluvial sandstones of the Wolf Creek beds. These beds are located along high points of the central Pine Ridge and along the South Dakota Border near Whiteclay. These strata are overlain by discontinuous fluvial valley fills of the Snake Creek Formation and the Patton Creek beds. This work was supported by 1996-2006 USGS STATEMAP programs, the University of Nebraska-Lincoln, the Nebraska National Forest, and Chadron State College.