Major Land Resource Area 131A

Southern Mississippi River Alluvium

Accessed: 10/09/2025

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Description

MLRA 131A, Southern Mississippi River Alluvium, is in Louisiana (32 percent), Arkansas (26 percent), Mississippi (26 percent), Missouri (12 percent), Tennessee (3 percent), and Kentucky (1 percent). A small part of Illinois also is in the area. This MLRA makes up about 29,555 square miles (76,585 square kilometers). It includes the towns or cities of Lake Providence, Morgan City, and Houma, Louisiana; Greenville, Yazoo City, and Clarksville, Mississippi; Eudora, Helena, and West Memphis, Arkansas; Caruthersville, Kennett, and Sikeston, Missouri; and the west edge of Memphis, Tennessee. The cities of Baton Rouge and New Orleans, Louisiana, are just outside this area. This area makes up most of the Mississippi Alluvial Plain Section of the Coastal Plain Province of the Atlantic Plain. It is on the alluvial plain along the lower Mississippi River, south of its confluence with the Ohio River. The landforms in the area are level or depressional to very gently undulating alluvial plains, backswamps, oxbows, natural levees, and terraces. The parts of the MLRA south of Baton Rouge, Louisiana, are on a deltaic plain. The Mississippi River has the third largest drainage basin in the world, exceeded in size only by the watersheds of the Amazon and Congo Rivers. It drains 41 percent of the 48 contiguous states of the United States. The basin covers more than 1,245,000 square miles, includes all or parts of 31 states and two Canadian provinces, and roughly resembles a funnel which has its spout at the Gulf of Mexico. Waters from as far east as New York and as far west as Montana contribute to flows in the lower river. For the purpose of ecological site concepts, the MLRA was separated by the Technical team into six sub-regions based on various assemblages of data reviewed.

Key publications

Land Resource Regions and Major Land Resource Areas of the United States, the Caribbean, and the Pacific Basin

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Ecological site keys

MLRA 131A Site Key

I. St Francis Basin

A. Backswamp

1 Ponded Depressions ... F131AY105AR – Western Lowlands - Frequently Flooded and Ponded Oxbow and Swale Forest

2 Very Deep, Poorly Drained Clayey Alluvium

i. Level Surfaces (Talfs) ... F131AY201AR – St. Francis - Wet Clayey Backswamp Flat

ii. Low Ridges (Rises) ... F131AY202AR – St. Francis - Low Clayey Backswamp Ridge Forest

3 Poorly to Somewhat Poorly Drained Clayey Over Loamy ... F131AY203AR – St. Francis - Wet Transitional Backswamp Forest

B. Pleistocene Valley Train

1 Somewhat Excessively to Excessively Drained Ridges and Braid Bars ... F131AY204AR – St. Francis - Braid Bar Woodland

2 Moderately Well to Well Drained Interfluves ... F131AY205AR – St. Francis - Loamy Braided Interfluve Forest

3 Poorly to Somewhat Poorly Drained Interfluves ... F131AY206AR – St. Francis - Wet Braided Interfluve Forest

4 Poorly Drained Remnant Channels ... F131AY207AR – St. Francis - Braided Channel Forest

C. Holocene Meander Belts and Floodplains

1 Somewhat Excessively to Excessively Drained ... F131AY208AR – St. Francis - Sandy Natural Levee and Meander Scroll Forest

2 Old Natural Levee

i. Moderately Well to Well Drained ... F131AY209AR – St. Francis - Old Loamy Natural Levee and Meander Scroll Forest

ii. Somewhat Poorly Drained ... F131AY210AR – St. Francis - Old Moderately Wet Natural Levee and Meander Scroll Forest

iii. Poorly Drained ... F131AY211AR – St. Francis - Old Wet Natural Levee and Meander Scroll Forest

3 Recent Natural Levee

i. Well Drained ... F131AY212AR – St. Francis - Recent Loamy Natural Levee and Meander Scroll Forest

ii. Somewhat Poorly to Moderately Well Drained ... F131AY213AR – St. Francis - Recent Moderately Wet Natural Levee and Meander Scroll Forest

iii. Poorly to Somewhat Poorly Drained ... F131AY214AR – St. Francis - Recent Wet Natural Levee and Meander Scroll Forest

II. Western Lowlands

A. [Criteria]

III. Yazoo Basin

A. Backswamp

1 Ponded Depressions ... F131AY301MS – Yazoo - Frequently Flooded and Ponded Oxbow and Swale Forest

2 Very Deep, Poorly Drained Clayey Alluvium

i. Level Surfaces (Talfs) ... F131AY302MS – Yazoo - Wet Clayey Backswamp Flat Forest

ii. Low Ridges (Rises) ... F131AY303MS – Yazoo - Low Clayey Backswamp Ridge Forest

3 Somewhat Poorly to Poorly Drained Clayey Over Loamy ... F131AY304MS – Yazoo - Wet Transitional Backswamp Forest

B. Old Natural Levees

1 Somewhat Excessively to Excessively Drained ... F131AY305MS – Yazoo - Old Sandy Natural Levee and Meander Scroll Ridge Forest

2 Moderately Well to Well Drained ... F131AY306MS – Yazoo - Old Loamy Natural Levee and Meander Scroll Ridge Forest

3 Somewhat Poorly Drained (Fine-silty) ... F131AY307MS – Yazoo - Old Moderately Wet Natural Levee and Meander Scroll Ridge Forest

4 Somewhat Poorly to Poorly Drained (Fine particle size) ... F131AY308MS – Yazoo - Old Wet Natural Levee and Meander Scroll Forest

C. Recent Natural Levees

1 Excessively Drained ... F131AY309MS – Yazoo - Recent Sandy Natural Levee and Meander Scroll Ridge Forest

2 Well Drained ... F131AY310MS – Yazoo - Recent Loamy Natural Levee and Meander Scroll Ridge Forest

3 Moderately Well to Somewhat Poorly Drained ... F131AY311MS – Yazoo - Recent Moderately Wet Natural Levee and Meander Scroll Ridge Forest

4 Somewhat Poorly (Clayey over Loamy) to Poorly Drained ... F131AY312MS – Yazoo - Recent Wet Natural Levee and Meander Scroll Forest

D. Valley Train

1 Moderately Well to Well Drained Ridges and Braid Bars ... F131AY313MS – Yazoo – Pleistocene Valley Train Braid Bar Woodland

IV. Tensas Basin

A. Frequently Flooded

1 Very Poorly Drained ... F131AY401LA – Tensas Basin - Frequently Flooded Ponded Very Poorly Drained Oxbows and Swales

2 Excessively Drained ... F131AY407LA – Tensas Basin - Pointbars, Sandbars, and Splays

B. None to Frequently Flooded

1 Poorly Drained

i. Backswamp ... F131AY402LA – Tensas Basin - Poorly Drained Backswamp

ii. Ridge Swale ... F131AY403LA – Tensas Basin - Poorly Drained Ridge and Swale Complex

2 Somewhat Poorly Drained

ii. Wet Toe Slope ... F131AY406LA – Tensas Basin - Natural Levees and Ridge Hardwoods

i. Bottomland ... F131AY405LA – Tensas Basin - Somewhat Poorly Drained Bottomland Hardwoods

C. None to Occasionally Flooded

1 Well Drained ... F131AY406LA – Tensas Basin - Natural Levees and Ridge Hardwoods

V. Delta Basin

A. Frequently Flooded

1 Very Poorly Drained ... F131AY501LA – Delta Plain - Frequently Flooded Ponded Very Poorly Drained Oxbows and Swales

B. None to Frequently Flooded

1 Poorly Drained ... F131AY502LA – Delta Plain - Poorly Drained Backswamp

2 Somewhat Poorly Drained ... F131AY503LA – Delta Plain - Somewhat Poorly Drained Bottomland Hardwoods

C. None to Occasionally Flooded

1 Well Drained ... F131AY504LA – Delta Plain - Natural Levees and Ridge Hardwoods

VI. Batture Region

A. Rare to Frequently Flooded

1 Excessively to Very Poorly Drained ... F131AY601MS – Batture - Mississippi River Unprotected By Levee Sites

B. Frequently Flooded

1 Very Poorly Drained ... F131AY602MS – Batture - Frequently Flooded Very Poorly Drained Ponded Oxbow and Swale Forest

2 Poorly Drained ... F131AY603MS – Batture - Frequently Flooded Wet Backswamp Flat Forest

3 Excessively Drained ... F131AY606MS – Batture - Frequently Flooded Pointbars, Sandbars, and Splays

C. Occasional to Frequently Flooded

1 Somewhat Poorly to Moderately Well Drained ... F131AY604MS – Batture - Frequently Flooded Moderately Wet Low Ridge Forest

2 Excessively to Well Drained ... F131AY605MS – Batture - Frequently Flooded Natural Levee and Ridge Forest

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