Geologic units in Yazoo county, Mississippi

Jackson group (Eocene) at surface, covers 46 % of this area

Yazoo clay, green and gray calcareous clay containing some sand and marl; Moodys Branch formation at base, shells embedded in glauconitic clayey quartz sand.

Alluvium (Holocene) at surface, covers 36 % of this area

Loam, sand, gravel, and clay; mapped only in Mississippi River Alluvial Plain.

Cockfield (Eocene) at surface, covers 11 % of this area

(Claiborne group), Irregularly bedded, more or less laminated liginitic clay, sand, and lignite; sparingly glauconitic.

Forest Hill formation and Red Bluff clay (Oligocene) at surface, covers 4 % of this area

Forest Hill sand, cross-bedded fine gray sand, laminated fine sand and clay, and a little lignite; in Wayne and Clarke Counties lower part merges eastward into Red Bluff clay, blue-green glauconitic, gypsiferous, fossiliferous clay and thin limestone beds.

Vicksburg group and Chickasawhay limestone (Oligocene) at surface, covers 3 % of this area

Chickasawhay limestone, sandy limestone, and sand, present only in eastern MS (mapped with it is the overlying Paynes Hammock sand of Miocene age); Vicksburg group, predominantly limestone and marl, but contains some bentonite and near the top, chocolate-colored clay and some sand.