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Mineral Resources > Online Spatial Data > Geology > by state > South Dakota Geology

Geologic units in Ziebach county, South Dakota

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

White, tan, yellow, and gray, cross-bedded, fine- to medium-grained,silty sandstone interbedded with locally bentonitic, gray siltstone, claystone, and sandy to silty claystone. Characterized by uranium-bearing lignite beds and "clinker" beds fromed by burning coalseams. Thickness up to 420 ft (128 m).

Lithology: sandstone; siltstone; claystone

Alluvium (Phanerozoic | Cenozoic | Quaternary) at surface, covers 7 % of this area

Clay to boulder-size clasts with locally abundant organic material. Thickness up to 75 ft (23m).

Lithology: clay or mud; silt; sand; gravel

Hell Creek Formation (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 31 % of this area

Tan to brown, light- to dark-gray, "somber beds" of shale. Interbedded with brown to red carbonaceous shale, gray and brown bentonitic silty shale, and gray, brown and yellow siltstone, sandstone, and claystone-pebble conglomerate. Thickness 260-600 ft (79-183 m).

Lithology: shale; siltstone; sandstone; conglomerate

Pierre Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 23 % of this area

Blue-gray to dark-gray, fissile to blocky shale with persistent beds of bentonite, black organic shale, or light-brown chalky shale. Contains minor sandstone, conglomerate, and abundant carbonate and ferruginous concretions. Thickness 1,000-2,700 ft (305-823 m).

Lithology: shale; clay or mud; sandstone; conglomerate

Terrace Deposits (Phanerozoic | Cenozoic | Quaternary) at surface, covers 2 % of this area

Clay to boulder-size clasts deposited as pediments, paleochannels, and terrace fills of former flood plains. Thickness up to 75 ft (23m).

Lithology: clay or mud; silt; sand; gravel

Eolian Deposits (Phanerozoic | Cenozoic | Quaternary) at surface, covers 3 % of this area

(loess and sand dune) Silt to medium-grained sand. Deposited as sand sheets and barchan, linear, and dome-like dunes and as veneer on uplands. Thickness up to 300 ft (91m).

Lithology: silt; sand

Fox Hills Sandstone (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 34 % of this area

Bluish-green to green, white to dark-gray, yellow to tan, carbonaceous and iron-stained, cross-bedded, very fine- to coarse-grained, glaconitic sandstone and siltstone. Interbedded with gray and green to brown shale and silty shale. Thickness 25-400 ft (8-122 m).

Lithology: sandstone; siltstone; shale