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.
Other Alabama resources from About.com:
About Huntsville
Alabama Campgrounds
Alabama Geography, State Symbols and Facts
Alabama Weather & Climate
Alabama Maps
Alabama National Parks
Alabama Archaeology
