Louisiana Geologic Map

As the seas rose and fell over Louisiana, some version of the Mississippi River was carrying vast sediment loads here from the core of the North American continent and piling it on the rim of the Gulf of Mexico. Organic matter from highly productive marine waters has been deeply buried under the whole state and far offshore, turning into petroleum. During other dry periods, large beds of salt were laid down through evaporation. As a result of oil company exploration, Louisiana may be better known underground than on its surface, which is closely guarded by swamp vegetation, kudzu, and fire ants.

The oldest deposits in Louisiana date from the Eocene Epoch, marked by the darkest gold color. Narrow strips of younger rocks crop out along their southern edge, dating from Oligocene (light tan) and Miocene (dark tan) times. The speckled yellow pattern marks areas of Pliocene rocks of terrestrial origin, older versions of the wide Pleistocene terraces (lightest yellow) that cover southern Louisiana.

The older outcrops dip downward toward the sea owing to the steady subsidence of the land, and the coast is very young indeed. You can see how much the Holocene alluvium of the Mississippi River (gray) covers the state. The Holocene represents only the latest 10,000 years of Earth history, and in the 2 million years of Pleistocene time before that the river has wandered over the whole coastal region many times.

Human engineering has temporarily tamed the river, most of the time, and it's no longer dumping its sediment all over the place. As a result, coastal Louisiana is sinking out of sight, starved of fresh material. This is not permanent country.

More about Louisiana Geology

More Louisiana resources on About.com:
New Orleans Travel
Louisiana Maps
Louisiana Geography, State Symbols & Facts
Louisiana Scenic Roads
Louisiana Campgrounds
Louisiana National Parks
Louisiana State Parks
Louisiana Bed & Breakfasts
Louisiana Fishing
Louisiana French
Louisiana Hotels
Louisiana Archaeology