MSMississippi Geography

The border stayed where the river used to be

Mississippi's western boundary is the Mississippi River as it ran in 1817. The river did not agree to stay. Meanders that swing three miles wide eventually cut through their own necks, the channel jumps, and the state line does not follow. The result is a frayed edge with pockets of Mississippi stranded on the Arkansas and Louisiana bank, matching pockets of those states left on the Mississippi side, and a chain of oxbow lakes marking abandoned bends: Moon Lake, Lake Washington, Eagle Lake, Lake Beulah.

Vicksburg lost the river altogether. In April 1876 a flood cut straight across DeSoto Point opposite the city and the main channel walked away, leaving the port that had withstood a 47-day siege in 1863 sitting on a dead loop with no navigable water. The Army Corps of Engineers fixed it in 1903 by diverting the Yazoo River into the old bend. The Vicksburg waterfront today is the Yazoo Diversion Canal, and the Mississippi runs a mile off to the west.

The Delta is not a delta

What Mississippi calls the Delta has nothing to do with the river's mouth, which lies 300 miles south in Louisiana. It is the Yazoo Basin, an alluvial floodplain roughly 200 miles long and up to 70 miles wide, boxed in by the Mississippi River on the west and the Yazoo River on the east, running from around Memphis down to Vicksburg. Thousands of years of overbank flooding laid silt tens of feet deep across it. The gradient is measured in inches per mile and the whole basin is close to featureless, which is why field patterns there are drawn by drainage ditches rather than by contour.

Its eastern boundary is anything but gradual. A band of loess, glacial dust blown east off the Mississippi's outwash plains during the ice ages, lies up to 90 feet thick and stands as a line of bluffs from Memphis through Vicksburg to Natchez. Loess holds a vertical face when it is cut, so old wagon routes that wore down into it became sunken roads walled by earth twenty feet high, most visibly along the Natchez Trace. That 444-mile parkway from Natchez to Nashville largely follows a ridge that separates the Pearl and Tombigbee drainages, which is why the original trail stayed dry.

The whole state fits in 807 feet

Woodall Mountain in Tishomingo County reaches 807 feet, four miles from the Alabama line. Only Florida, Delaware and Louisiana have lower high points, and since the low point is sea level on the Gulf, every foot of Mississippi's vertical range fits inside 807 feet. A gravel road goes to the summit.

That northeastern corner is the only part of the state with exposed rock worth the description, sandstone outcrops and small gorges at Tishomingo State Park on the outer fringe of the Appalachian foothills. Everything else belongs to the Gulf Coastal Plain, but the plain is not uniform. Running east from the Loess Hills there is the Yazoo Basin, then the North Central Hills, then the Flatwoods, then the Black Prairie, a crescent of Cretaceous chalk whose dark alkaline soil gave the Black Belt its name and its cotton economy, then the Tombigbee Hills, and southward the Pine Hills and the Coastal Meadows.

Barrier islands and the highest surge on record

Mississippi has 44 miles of general coastline, but it is coast in name only: the shore faces Mississippi Sound, a shallow lagoon seven to fifteen miles wide, and the open Gulf lies beyond a chain of barrier islands. Cat, West Ship, East Ship, Horn, Petit Bois and Round islands migrate steadily westward as longshore drift shifts sand along them. Hurricane Camille split Ship Island in two on 17 August 1969, opening a channel that became known as Camille Cut. The Corps of Engineers closed it in 2019 with about 1.6 million cubic yards of dredged sand, making the island whole for the first time in half a century.

The barrier chain did not save Pass Christian on 29 August 2005. Hurricane Katrina drove a storm surge measured at approximately 27.8 feet ashore there, the highest ever recorded in the United States. Camille had put 24 feet across the same beach 36 years earlier. Horn and Petit Bois islands are federally designated wilderness inside Gulf Islands National Seashore, which means no structures and no vehicles.

Hot, wet and a second tornado season

Holly Springs reached 115 F on 29 July 1930. Corinth fell to minus 19 F on 30 January 1966. Between those extremes the state averages 50 to 65 inches of rain a year, rising toward the coast, which makes Mississippi one of the wettest states in the country and explains the loblolly pine that grows back over any field left alone.

Mississippi sits in the part of the South sometimes called Dixie Alley, and its tornado climatology differs from the Plains in three ways that matter. Storms often arrive wrapped in heavy rain and cannot be seen coming. A large share of them strike after dark. And there is a distinct second season in late autumn on top of the spring peak. The EF4 that destroyed most of Rolling Fork on the night of 24 March 2023 travelled across open Delta farmland with nothing to slow it.

Common questions about Mississippi geography

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