USGS Visual Identifier
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Geologic Unit: Pearlette

Pearlette family of ash beds (informal)*
Pearlette ash (informal)*
[†?] Pearlette Ash Bed of Sappa Member of Sheridan Formation (NE)
[†?] Pearlette Ash Member of Crooked Creek Formation (KS,OK)
[†?] Pearlette Ash Member of Sappa Formation (KS,NE,SD)
[†?] Pearlette Ash Member of Tule Formation (CO,KS,NE,TX)
Considered informal by the USGS. For informal usage, the rank or lithologic term should not be capitalized.
[Discrepancy concerning usage. See remarks under "Publication History".]


Geologic Province:
Anadarko basin*
Central Kansas uplift*
Cherokee basin*
Denver basin*
Forest City basin*
Great Basin province*
Gulf Coast basin*
Iowa shelf*
Las Vegas-Raton basin*
Nemaha anticline*
Palo Duro basin*
Paradox basin*
Salina basin*
Sedgwick basin*
Sioux uplift*
Wasatch uplift*
Areal Extent:

Type Locality:
Not designated. Named from old Pearlette Post Office, Meade Co., KS (Cragin, 1896).
Separated into 3 ash types: Pearlette type O named from occurrence along Onion Creek, in SE/4 NE/4 sec. 26, T. 24 S., R. 24 E., Grand Co., UT, and occurrence at three localities in Meade Co., KS; Pearlette type B named from occurrence in Borchers local fauna at Cudahy mine, Meade Co., KS (Naeser and others, 1973).

Type B: Huckleberry Ridge ash (informal). Type S: Mesa Falls ash (informal). Type O: Lava Creek B ash (informal).

Unit Name History:
[Please note: Izett and others (1972), Boellstorff (1973), and Keller and others (1974) have yet to be added from the GNC index card files. Until then, feel free to contact us if you would like complete bibliographic citations.]
Named as a formation of Tule division of Cummins (Cragin, 1896).
Revised, assigned to Crooked Creek Formation (Hibbard, 1949).
Revised, assigned to Atwater Member of Crooked Creek Formation of Meade Group (Hibbard, 1958).
Revised (Semken, 1966).
Extended into UT (Izett and others, 1972).
Revised, informal designation applied to ash beds called type B (about 2 m.y.), type S (about 1.2 m.y.), and type O (about 0.6 m.y.) (Naeser and others, 1973).
Extended into IA (Boellstorff, 1973).
Extended into MO (Keller and others, 1974).
Formal usage of Pearlette Ash Member of Sappa Formation abandoned; replaced with 3 informal ash types (type B called Huckleberry Ridge ash, type S called Mesa Falls ash, and type O called Lava Creek ash); Areal limits (Izett and Wilcox, 1982).
[Discrepancy in GNU records (USGS DDS-6) concerning usage. Denver GNULEX lists only "Pearlette family of ash beds". The comprehensive GNU file GEONAMES indicates the Pearlette is considered a formal bed by the Nebraska Geol. Survey; and a formal member by the Colorado, Kansas, Nebraska, Oklahoma, South Dakota, and Texas Geol. Surveys. Uncertain if these designations are currently accepted by the State Geol. Surveys. --unresolved.]

Note: If you need more information, please contact Nancy Stamm (
Asterisks (*) indicate usage by the U.S. Geological Survey. Other usages by state geological surveys.

"No current usage" implies that a name has been abandoned or that it has fallen into disuse. Former usage and, if known, replacement name given in parentheses ().

Slashes (/) indicate unit name usage violates the 1983 North American Stratigraphic Code. This violation may be explained within brackets ([ ]).

U.S. Department of the Interior, U.S. Geological Survey, Reston, VA, USA
Database project personnel
Last modified: 15-Jan-2013