Geologic units in Shelby county, Tennessee

Alluvial deposits (Quaternary) at surface, covers 20 % of this area: Alluvial Deposits - Sand, silt, clay, and gravel. In flood plain of Mississippi River more than 100 feet thick; in smaller streams generally less than 20 feet thick.
Lithology: sand; silt; clay or mud; gravel
Jackson (?) Formation (Tertiary) at surface, covers 0.7 % of this area: Jackson (?) Formation - Sand, with layers of gray clay, silt, and lignite. Exposed only in bluffs along Mississippi River; thickness at least 60 feet.
Lithology: sand; clay or mud; silt; lignite
Loess (Quaternary) at surface, covers 75 % of this area: Loess - Clayey and sandy silt, gray to brown, massive. Maximum thickness about 100 feet along bluffs of Mississippi River; thins eastward. (Minimum mapped thickness 4 feet.)
Lithology: silt
Alluvium - Alluvial deposits in major stream channels or in mappable meanders of major streams (Phanerozoic | Cenozoic | Quaternary | Holocene) at surface, covers 0.3 % of this area: Alluvial deposits in major stream channels or in mappable meanders of major streams - Includes alluvial deposits in natural levees in some areas.
Lithology: alluvium