Geologic units in Saint Martin Parish, Louisiana

Alluvium (Holocene) at surface, covers 57 % of this area

Gray to brownish gray clay and silty clay, reddish brown in the Red River Valley, some sand and gravel locally.

Natural Levees (Holocene) at surface, covers 42 % of this area

Gray and brown silt, silty clay, some very fine sand, reddish brown along the Red River.

Prairie Terraces (Pleistocene) at surface, covers 2 % of this area

Light gray to light brown clay, sandy clay, silt, sand, and some gravels. Overlain by 1-9 meters of loess.