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Measure

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Ecoregions

Public Lands

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Madison Limestone, Darby or Three Forks, Jefferson, and Beartooth Butte Formations, and Bighorn Dolomite (WYMDO;0)

Geologic Formation in WY, MT

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Lithology

Siltstone

Sandstone

Shale

Other (102 mi²)

Geologic Age

Middle Ordovician – Mississippian (471.4 Ma – 323.6 Ma ago)

Geologic Unit Label

MDO

Madison Limestone or Group - Group includes Mission Canyon Limestone (blue-gray massive limestone and dolomite), underlain by Lodgepole Limestone (gray cherty limestone and dolomite). Darby Formation - Yellow and greenish-gray shale and dolomitic siltstone underlain by fetid brown dolomite and limestone. Three Forks Formation - Yellow and greenish-gray shale and dolomitic siltstone. Jefferson Formation - Fetid brown dolomite and limestone. Beartooth Butte Formation - Red sandstone, limy siltstone, and limestone. Occurs only in the Beartooth Mountains.

— USGS