Geologic units in Washington county, Missouri

Additional scientific data in this geographic area

Eminence Dolomite, Potosi Dolomite (Late Cambrian-Croixian Series) at surface, covers 51 % of this area

Eminence Dolomite - dolomite with some druse - coated chert. Potosi Dolomite - dolomite with abundance of druse - coated chert.

Gasconade Dolomite (Early Ordovician-Ibexian Series) at surface, covers 29 % of this area

Coarse - crystalline cherty dolomite with a basal Gunter Sandstone Member.

Elvins Group - (including Derby-Doerun Dolomite, Davis Formation), Bonneterre Dolomite (Late Cambrian-Croixian Series) at surface, covers 10 % of this area

Derby-Doerun Dolomite - alternating thin dolomite, siltstone, and shale; Davis Formation - glauconitic shale with fine - grained sandstone, limestone, and dolomite); Bonneterre Dolomite - dolomite, dolomitic limestone, and limestone; glauconitic in lower part.

Roubidoux Formation (Early Ordovician-Ibexian Series) at surface, covers 8 % of this area

Sandstone, chert and interbedded dolomite

Lamotte Sandstone (Late Cambrian-Croixian Series) at surface, covers 1 % of this area

Sandstone with some dolomitic and shaly lenses; coarse - graines to conglomeratic and arkosic at base.

St. Francois mountains volcanic supergroup (Precambrian Y) at surface, covers 1.0 % of this area

Chiefly alkali rhyolitic ash - flow tuffs, lava flows, and bedded tuffs, with minor trachytes.

St. Francois Mountains intrusive suite (subvolcanic, alkali granitic ring complexes) (Precambrian Y) at surface, covers 0.4 % of this area

St. Francois Mountains intrusive suite (subvolcanic, alkali granitic ring complexes).

Diabase dikes and sills (Precambrian Y) at surface, covers < 0.1 % of this area

Diabase dikes and sills.