This map from the Geological Survey of Alabama shows the location of rocks from various geologic time periods that are found in the state. The oldest rocks (with "Ma" standing for "million years ago") are found in the northeastern portion of the state where the ancient Appalachian Mountains intrude into the landscape. The Mesozoic and Cenozoic rocks clearly show the shape of the Gulf's retreating shoreline as the sea shrank in size over time. The rock deposits in green trace the Black Belt through the middle of the state.
Courtesy of Geological Survey of Alabama