ABSTRACTIt is readily apparent from both map and field observation that the patterns of channels and ridges in fluvially eroded terrain are closely intertwined. The purpose of this paper is the formulation of some of the principles governing their relationship. Specifically, the paper models the sequence and length distribution of ridge paths on the basis of the sequence and length distribution of channel paths within a given drainage basin.The modeling approach first codifies the channel and ridge networks within drainage basins in graph theoretical terms; it then takes advantage of the fact that ridge lines tend to run quasi-parallel to neighboring channels thus permitting the estimation of the former from the latter. Data were obtained from two drainage basins of the (environmentally homogeneous) Cumberland Plateau of Kentucky and the (environmentally complex) San Gabriel Mountains of southern California.Comparison of the observed length values of ridge paths with their values as derived from channel path data demonstrate the intimate relation between channels and ridges, thereby providing support for the model as a formal description of the ridge-channel interdependence.