Alabama rises from the coastline, its gently dipping rock layers exposing deeper and older formations in majestic order as one moves north. (more below)
Created by Andrew Alden from the U.S. Geological Survey's Geologic Map of the United States, 1974, by Philip King and Helen Beikman (fair use policy)
Click the map for a larger version
The yellow and gold stripes nearest the Gulf of Mexico coast represent rocks of Cenozoic age, younger than 65 million years. The southernmost green stripe labeled uK4 marks the Selma Group. The rocks between it and the dark green stripe of the Tuscaloosa Group, labeled uK1, all date from Late Cretaceous time, starting at about 95 million years ago.
The more resistant layers in this sequence crop out as long low ridges, steep on the north and gentle on the south, called cuestas. This part of Alabama formed in the shallow waters that have covered most of the central continent throughout geologic history.
The Tuscaloosa Group gives way to the compressed, folded rocks of the southernmost Appalachian Mountains to the northeast and the flat-lying limestones of the interior basins to the north. These different geologic elements give rise to a great variety of landscapes and plant communities, in what outsiders might consider a flat and uninteresting region.
The Geological Survey of Alabama has much more information on the state's rocks, mineral resources and geologic hazards.
More about Alabama Geology
Other Alabama resources from About.com:
Alabama Geography, State Symbols and Facts
Alabama Weather & Climate
Alabama National Parks