Five geologic formations form the surface of the southern portion of Florida: the Tamiami Formation, Caloosahatchee Formation, Anastasia Formation, Miami Limestone, and the Fort Thompson Formation. The Tamiami Formation is a compression of highly permeable light colored fossiliferous sands and pockets of quartz, thick. It is named for the Tamiami Trail that follows the upper bedrock of the Big Cypress Swamp, and underlies the southern portion of the Everglades. Between the Tamiami Formation and Lake Okeechobee is the Caloosahatchee Formation, named for the river over it. Much less permeable, this formation is highly calcitic and is composed of sandy shell marl, clay, and sand. Water underneath the Caloosahatchee Formation is typically very mineralized. Both the Tamiami and Caloosahatchee Formations developed during the Pliocene Epoch.