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Geologic units in Johnson county, Georgia

Neogene undifferentiated (Neogene) at surface, covers 95 % of this area

Includes Altamaha Grit (Dall, 1892); Citronelle Formation (Matson & Berry, 1916); and "Hawthorn Formation" (Cooke, 1939). (*) - outcrops of indurated sandstone and claystone

Irwinton Sand (Eocene) at surface, covers 3 % of this area

Up-dip equivalent of Twiggs Clay, Sandersville Limestone, and Cooper Marl. As mapped, also includes younger clastics of indefinite Late Tertiary age.

Twiggs Clay (Eocene) at surface, covers 2 % of this area

Twiggs Clay

Stream alluvium (Quaternary) at surface, covers 0.3 % of this area

Stream alluvium and undifferentiated terrace deposits

Aeolian sand deposits - parabolic dunes (Quaternary) at surface, covers < 0.1 % of this area

Aeolian sand deposits - parabolic dunes