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Mineral Resources > Online Spatial Data > Geology > by state > Montana Geology

Geologic units in Wibaux county, Montana

Fort Union formation (Phanerozoic | Cenozoic | Tertiary Cretaceous-Late | Paleocene) at surface, covers 83 % of this area

Fort Union formation: Clay shale, siltstone, and sandstone; local lenses of impure limestone, and numerous lignitic beds; contains Tertiary plant and animal fossils but no dinosaurs; base generally placed at the lowest of the succession of lignite beds within it; includes the Tongue River member, Lebo shale member, and Tullock member.

Lithology: shale; siltstone; sandstone; coal; limestone

Alluvium (Phanerozoic | Cenozoic | Quaternary) at surface, covers 0.3 % of this area

Alluvium: mainly valley fill consisting of silt, sand, and gravel; includes some terrace deposits and glacial drift of Pleistocene age in some areas; locally includes hot spring tufa. The older part of the alluvium, where present, is probably of Pliocene age.

Lithology: alluvium; glacial drift; carbonate

Fox Hill sandstone (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 3 % of this area

Fox Hills sandstone: Typically shaly sandstone grading upward into massive brownish sandstone with white sandstone of the Colgate member locally at top.

Lithology: sandstone; mudstone

Bullion Creek Formation (Phanerozoic | Cenozoic | Tertiary | Paleocene) at surface, covers 0.1 % of this area

Yellow-brown silt, sand, clay, sandstone, and lignite; river, lake, and swamp sediment; as thick as 200 meters (600 feet).

Lithology: silt; sand; clay or mud; sandstone; coal

Pierre shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 5 % of this area

Pierre shale: dark-gray clay shale with calcareous and ferruginous concretions and sandy members.

Lithology: shale; sandstone; bentonite

Hell Creek formation (Phanerozoic | Mesozoic Cenozoic | Cretaceous-Late Tertiary | Paleocene) at surface, covers 10 % of this area

Hell Creek formation: somber-gray sandstone and greenish shaly clay and mudstone containing dinosaur bones; a few thin lignite and subbituminous coal beds.

Lithology: sandstone; mudstone; coal

Slope Formation (Phanerozoic | Cenozoic | Tertiary | Paleocene) at surface, covers < 0.1 % of this area

Gray-brown and yellow-brown silt, sand, clay, sandstone, and lignite; river, lake, and swamp sediment; as thick as 100 meters (300 feet).

Lithology: silt; sand; clay or mud; sandstone; coal