Middle aged or mature landscapes were characterized by William Morris Davis (1889) in the River Lifecycle Maturity Scheme. These three images show a cross-section illustration of Erosion, and then two oblique views of different mature systems. Dakota bad lands and Appalachian mountains are examples of this middle aged terrain.
Classification continues with a youthful Stream eroding the landform, until eventually the stage of mature Erosion is revealed. Detecting the transition from young to mature is partly subjective. The cycle progresses based on changes in the structure and composition of the landscape.Image from: Stages in the fluvial cycle of Erosion Davis, W.M., 1909: Geographical essays. Boston