An escarpment formed by the carbonate Keg River and evaporitic Chinchaga formations of Middle Devonian age extends southwards from the Slave River 30 km west of Fort Smith, Northwest Territories. Newly described folds in the bedrock are due to hydration of the anhydrite to gypsum in the Chinchaga Formation underlying the escarpment. Local groundwater flow has also dissolved subsurface cavities in the Chinchaga Formation. As these openings grew, the carbonates of the Keg River Formation subsided along stepped normal faults. Depressions within the fault blocks occurred where subsidence was concentrated along joints.