CHAPTER III: MISSISSIPPI’S ECOLOGICAL FRAMEWORK-ECOREGIONS OF MISSISSIPPI 71
Part 4: Upper East Gulf Plain Ecoregion
The Upper East Gulf Coastal Plain (UEGCP) ecoregion encompasses 33,861,051 acres. This large
ecoregion ranges from southern Illinois, western Kentucky and Tennessee, throughout much of
Mississippi, east to Alabama and a limited area of Georgia and southeastern Louisiana. The region is
bounded on the west by the MSRAP and on the north by the Ohio River, and Tennessee River. The
eastern margin occurs at the contact point with older rocks of the Piedmont and Southern Ridge and
Valley. This region has rugged terrain and hilly topography In addition, the southern boundary
approximates the range limits of major potential natural vegetation types oak-hickory-pine to the north,
and southern mixed hardwood forests to the south.
Coastal and fluvial processes have considerably reworked the land surface of the region. Approximately
70 million years ago, the area would have been around 4,000 foot elevation. However, the earth's crust
sagged forming the Mississippi Embayment. During the Tertiary and Cretaceous periods the Embayment
trough was repeatedly invaded by shallow seas leaving behind hundreds of meters of sediments that
occupy broad bands approximately paralleling the Gulf of Mexico. The result is a region of belted
character, in the form of inner lowlands and cuestas and other low-ridge landforms.
The upper Mississippi Embayment is underlain by an ancient, buried rift zone. This buried rift has acted
as a "zone of weakness" in the continental crust and serves to localize earthquake activity in the central
United States. There have been many large magnitude earthquakes and abundant seismic activity in the
region. The New Madrid earthquake (1811-1812) was among the strongest earthquakes in recorded
United States history, resulting in up to nine feet of land subsidence in the upper part of the region.
Further south, the geologic structure of the region has been affected by the presence of underground salt
Upper East Gulf Coastal Plain
Count ies