Geologic units in Saint Mary Parish, Louisiana

Alluvium (Holocene) at surface, covers 39 % of this area

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

Delta Plain, Fresh Marsh (Holocene) at surface, covers 35 % of this area

Gray to black clay of very high organic content, some peat.

Natural Levees (Holocene) at surface, covers 23 % 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.

Delta Plain, Saline Marsh (Holocene) at surface, covers 0.6 % of this area

Gray to black clay of very high organic content, some peat.

Chenier Plain, Fresh Marsh (Holocene) at surface, covers 0.1 % of this area

Gray to brown to black clay and silt of high organic content.