First appears [on east side of the Black Hills] northeast of Hermosa, Custer Co, SD, on Chadron arch, lying between Unkpapa sandstone (new) and Lakota formation (new). Thickens rapidly northward and passes around the northern and western sides of the Black Hills [SD and WY, in Williston and Powder River basins]. Beyond the edge of Unkpapa sandstone, lies conformably on Sundance formation. Is Jurassic in age.
Source: GNU records (USGS DDS-6; Denver GNULEX).
Pg. 593, fig. 122, map. Beulah clays. Upper Jurassic fresh or brackish water deposits. In Hay Creek coal field, Crook County, northeastern Wyoming, consist of: (1) ATLANTOSAURUS beds, 25 to 35 feet of whitish and light-gray clays with some sandy shales and concretions of white calcareous clay, the upper layers in many localities carrying fossil wood and the bones of saurians; (2) light-gray, thin-bedded sandstone, 5 to 10 feet. Underlie Hay Creek coal formation with greatest unconformity in section, and unconformably overlie Lower Jurassic marine beds. Long outcrops of these clays occur 3 or 4 miles north of Beulah, in Red Water Valley [Crook County, northeastern Wyoming].
[Recognized in Black Hills area, northeastern WY and western SD.]
Source: US geologic names lexicon (USGS Bull. 896, p. 177).
Substitutes Morrison formation for rocks formerly known as the "Atlantosaurus beds" and Beulah shale [clays] in the Black Hills region, WY and SD.
Source: GNU records (USGS DDS-6; Denver GNULEX).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
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