The Devonian Frog Mountain Formation thickens abruptly eastward across the Eastern Coosa thrust fault from \u3c12 m on the west to\u3e70 m on the east. The thin Frog Mountain on the west unconformably overlies the Cambrian-Ordovician Knox Group. The thin Frog Mountain (mostly shale) is overlain by the Mississippian Maury Shale (~1 m thick) and Fort Payne Chert (~50 m thick). The thick Frog Mountain on the east rests on the Middle Ordovician Athens Shale, a black shale \u3e150 m thick. The Athens overlies the Knox Group. The thick Frog Mountain is nearly all sandstone and is overlain by Fort Payne Chert which is only ~1 m thick
In the Eastern Coosa hanging wall, an upper-level out-of-the-syncline thrust fault with thick Frog Mountain in the hanging wall cuts more than 290 m stratigraphically down section from Athens to lower Knox in the footwall. The upper-level Frog Mountain thrust sheet crosses over the Eastern Coosa fault, and truncates folds in the Eastern Coosa footwall, moving ~2 km.
The thick Frog Mountain Formation associated with the Eastern Coosa thrust sheet has been transported ~100 km cratonward. The Frog Mountain Formation was deposited over a low topographic high, which was in the location of the Blountian peripheral foreland bulge
