|Name||Ogallala Group or Formation|
Sedimentary > Clastic > Mixed-clastic > Siltstone-mudstone (Bed)
Sedimentary > Clastic > Mixed-clastic > Conglomerate-sandstone (Bed)
Igneous > Volcanic (Pyroclastic-air fall)
|Comments||Lenses and tabular zones of carbonate-cemented silt and sand are common. In a few southeast localities, fine to coarse sand and fine gravel are cemented by yellowish-green opal or chaledony. Deposits contain some local beds of volcanic ash. Lithology varies laterally and vertically within a short distance. Includes in decending order: Ash Hollow and Valentine FMs. Approx. max thickness 650 ft. May contain some deposits of pre-Miocene age.|
Burchett, R.R., 1986, Geologic Bedrock Map of Nebraska: Nebraska Geological Survey. Scale 1:1 million.
Diffendal, R.F. Jr, 1991, Geologic Map Showing Configuration of Bedrock Surface, North Platte 1x2 Quad. Nebraska: USGS Map I-2277. Scale 1:250K.
Swinehart, J.B., Souders, V.J., DeGraw, H.M., and Diffendal, R.F., 1985, Cenozoic paleography of the west-central United States, Society of Economic Paleontologist and Mineralogist, RMS, Rocky Mtn. Paleogeography Syp.3, p 209-229.
|Counties||Adams - Antelope - Arthur - Banner - Blaine - Boone - Box Butte - Boyd - Brown - Buffalo - Cedar - Chase - Cherry - Cheyenne - Clay - Custer - Dawes - Dawson - Deuel - Dixon - Dundy - Franklin - Frontier - Furnas - Garden - Garfield - Gosper - Grant - Greeley - Hall - Hamilton - Harlan - Hayes - Hitchcock - Holt - Hooker - Howard - Kearney - Keith - Keya Paha - Kimball - Knox - Lincoln - Logan - Loup - McPherson - Madison - Merrick - Morrill - Nance - Nuckolls - Perkins - Phelps - Pierce - Platte - Red Willow - Rock - Sheridan - Sherman - Sioux - Stanton - Thomas - Valley - Wayne - Webster - Wheeler|