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

Geologic units in Walworth county, South Dakota

Outwash, Collapsed (Phanerozoic | Cenozoic | Quaternary | Pleistocene [Upper Wisconsin]) at surface, covers 7 % of this area

Heterogeneous sand and gravel of glaciofluvial orgin. Deposited as outwash sediments that collapsed due to melting of buried ice. Thickness up to 90 ft (27m).

Lithology: sand; gravel

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

Eolian Deposits (Phanerozoic | Cenozoic | Quaternary) at surface, covers 20 % 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

Colluvium (Phanerozoic | Cenozoic | Quaternary) at surface, covers 0.1 % of this area

Clay to boulder-size clasts forming rubble residuum and talus. Thickness up to 30 ft (9m).

Lithology: clay or mud; silt; sand; gravel

Till, End Moraine (Phanerozoic | Cenozoic | Quaternary | Pleistocene [Upper Wisconsin]) at surface, covers 4 % of this area

Heterogeneous, clay with silt to boulder-size clasts of glacial orgin. A geomorphic feature that is characterized by elevated linear ridges with hummocky terrain locally at former ice sheet margins. Composite thicknessof all Upper Wisconsin till may be up to 300 ft (91 m).

Lithology: clay or mud; silt; sand; gravel

Till, Stagnation Moraine (Phanerozoic | Cenozoic | Quaternary | Pleistocene [Upper Wisconsin]) at surface, covers 48 % of this area

Heterogeneous, clay with silt to boulder-size clasts of glacial orgin. A geomorphic feature that is characterized by hummocky terrain with abundant sloughs resulting from stagnation of ice sheets. Composite thickness of all Upper Wisconsin till may be up to 300 ft (91 m).

Lithology: clay or mud; silt; sand; gravel

Java Formation (Phanerozoic | Cenozoic | Quaternary | Pleistocene-Early) at surface, covers 0.1 % of this area

Sand to gravel of fluvial orgin. Upper portion is tan to reddish-brown eolian silt with minor clay and fine-grained sand. Thickness up to 180 ft (55 m).

Lithology: sand; gravel; silt; clay or mud

Outwash, Terrace (Phanerozoic | Cenozoic | Quaternary | Pleistocene [Upper Wisconsin]) at surface, covers 2 % of this area

Heterogeneous clay to gravel of glaciofluvial orgin. Thickness up to 60 ft (18m)

Lithology: clay or mud; silt; sand; gravel

Pierre Shale (Phanerozoic | Mesozoic | Cretaceous-Late) at surface, covers 6 % 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

Pollock Formation (Phanerozoic | Cenozoic | Quaternary | Pleistocene [Upper Wisconsin]) at surface, covers 1 % of this area

Glaciolacustrine clay and silty clay with laminae of very fine-grained sand near the middle and base of the formation. Thickness up to 165 ft (50 m).

Lithology: clay or mud; sand

Outwash, Valley Train (Phanerozoic | Cenozoic | Quaternary | Pleistocene [Upper Wisconsin]) at surface, covers 0.6 % of this area

Heterogeneous silt to gravel. Confined to valleys of glaciofluvial orgin. Thickness up to 60 ft (18m).

Lithology: silt; sand; gravel