Alabama Landscapes

The Valley and Ridge

Geology

The Valley and Ridge developed on folded and thrust-faulted sedimentary rocks, ranging age from Cambrian to Pennsylvanian (570 to 290 millions of years).   Table 1 shows the geologic column of these rocks.

Figure VRG1.  Geologic Map of the Valley and Ridge.  (From Geologic Map of Alabama 1988 Alabama Geological Survey.)

The complexity of the geologic map (Figure VRG1) is a result of closely-spaced  thrust faults and folds.   The sense of movement on all the major thrusts (red in Figure VR2) is to the northwest (i.e., the hangingwall blocks are to the southeast).  Figure VRG2 also shows the traces of the axes of two large folds: Birmingham anticline and Cahaba syncline.  There are many folds east of the Cahaba syncline but their number precludes including them on the map at this scale.  In particular, the area marked CDB on Figure VRG2 between the Yellowleaf-Eden and the Pell City fault consists of multiple small thrust faults and folds.  Unlike the folds of the Cumberland Plateau, many of these folds are plunging, i.e. their fold axes are inclined to the surface.  Thus, there is a complex relationship between landforms, rock type and structure.

Figure VRG2. Structural Map of the Valley and Ridge showing major thrust faults (red), Birmingham anticline (green dotted) and Cahaba syncline (green solid). H: Helena thrust fault, Y: Yellowleaf-Eden thrust fault, J: Jones Valley thrust fault, O: Oppossum Valley trust fault, P: Pell City thrust fault, T: Talladega thrust fault, CDB: Coosa Deformed Belt. (After Thomas and Osborne 1994, Geological Society of Alabama.) Broken numbered lines are lines of profiles discussed elsewhere. 

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