Fault-related folds develop above active faults, and as these faults propagate laterally so do the folds they produce. Geomorphic criteria useful in evaluating rates and direction of lateral propagation of active folds in the direction of propagation are: (1) decrease in drainage density and degree of dissection; (2) decrease in elevation of wind gaps; (3) decrease in relief of the topographic profile along the crest; (4) development of characteristic drainage patterns; (5) deformation of progressively younger deposits or landforms; and (6) decrease in rotation and inclination of forelimb. All these criteria are consistent with lateral propagation, but do not prove it. The presence of more than one wind or water gap formed by the same stream, however, is strong evidence of lateral propagation. Rates of lateral propagation of folding may be several times the rate of uplift and fault slip. Lateral propagation of anticlinal folds allows for a new explanation of how drainage may develop across active fold belts. Development of drainage across an active fold belt is probably a function of relatively long structurally controlled drainage diversion parallel to fold axes and development of relatively short antecedent stream reaches, around the nose (plunge panel) of a fold. Water and/or wind gaps form as uplift, drainage diversion, and stream capture associated with fold growth continue.

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