The geological units encountered in the Clark Creek are assigned to three named stratigraphic intervals; the Peoria loess, the Upland Complex (also known as the Citronelle formation), and the Fleming Formation . They can be seen in order of increasing age as one descends from the parking area to the creek bottom. Radiocarbon dates from the Peoria loess establish that these materials were deposited in the Pleistocene Epoch, about 22,000 to 20,000 years before the present. The sediments of the Upland Complex are probably older than 100,000 years, but the scarcity of fossils makes their age difficult to assess reliably. They are generally considered to be Pleistocene or Late Pliocene in age and thus may be as much as 2,000,000 years old. The Fleming Formation is assigned to the Pliocene and Miocene Epochs of the Tertiary Period, and the sediments were deposited about 5 to 10 million years ago.

NOW ADD SOME PHOTOS AND DESCRIBE THE SEDIMENT TYPES AND CONDITIONS OF DEPOSITION.

The Citronelle formation is the most important formation. It was deposited 2.8 million to 6.6 million years ago during the Pleistocene Era. It consists basically of sands and small gravel placed by means of streams crossing a gently sloping coastal plain (similar to that of present day southern Louisiana). Iron oxide nodules are known to exist throughout the formation. These iron oxide nodules were formed during the time in which the sands were being transformed into soil, they account for the deep red spots found in the formation. The Citronelle formation extends from Amite and Wilkinson counties of Mississippi through East and West Feliciana Parishes down to East Baton Rouge Parish in Louisiana. The formation ranges in thickness from 30 to 290 feet. Upon exposure to the environment the formation dries out and becomes hard and ledgy. This along with a cementing action forms a siltstone ledge that forms the waterfalls in the area.

Pascagoula clay of the Miocene Era underlies the Citronelle. Deposits of the Miocene Era were deposited 6.6 to 22.5 million years ago. They consist basically of silts and clays with some sand. This clay has been exposed in a few places along the creeks bottom.

The formation covering the Citronelle formation consists of the loess layer. This formation was deposited during the last 2.8 million years. The lack of fossils and no stratification of layers suggests that the deposit was placed by wind instead of water. A high amount of carbonate exists in this formation. When water leeches through this formation some of the carbonate is dissolved into the water. As the water travels down to the Citonelle formation, this carbonate reacts with the sands in the formation and upon drying out a cementing action takes place forming the hard siltstone ledges associated with the unique waterfalls of the area.
 

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