These ridges, usually about 3 or 4 feet above sea level, are formed from old beaches left stranded in ancient times, when the marsh moved southward toward the Gulf. They are one of the rare relief features in a terrain measured in inches above sea level, extending along a regular, sandy Gulf shoreline stretching some 114 miles from the Sabine River on the west to Vermilion Bay on the east. The earliest inhabitants of the area are thought to have been members of the Attakapas tribe around 500 B.C., and remnants of their burial mounds and middens (dumping grounds) can still be traced here and there on the ridges. Early explorers found one shaped like a pyramid, another, near Grand Lake, was in the form of an alligator.

The satellite image below, of a portion of the Louisiana coastline, highlights a chenier plain in the southern half of the image, which is composed of multiple sets of the nearly parallel beach ridges. These cheniers are high topographic landforms comprised of coarse-grain sands and shell fragments separated by lower areas of brackish marsh. The higher, better drained cheniers often support oak trees and other types of upland vegetation types, that show up as green-yellow in this image.

The formation of these beach ridges is complex and still not completely understood; however, in general the process includes: (1) periodic deposition of sediments by ancestral Mississippi River systems; (2) westward longshore drift (coastal currents) transporting sediments deposited in the Gulf of Mexico; (3) deposition of transported sediments and seaward growth of mud flats and coastal marshes; and (4) reworking of sediments by hurricanes and major storms, ultimately forming the coarse-grained ridges closely aligned to the configuration of the coastline at the time of the chenier's formation.