Gently undulating, almost featureless plain near sea level. This would form, theoretically, by various erosional processes that reduce areas of initially high relief produced by active uplift to areas of virtually no relief. The lack of present-day peneplains tends to discredit the theory, but some geomorphologists propose that large areas of low relief at high altitude in some mountains are evidence of uplifted peneplains. Others question whether the dynamic relationship between erosion and rock type would ever allow the development of a peneplain, even over very long timespans.
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After the streams in an area have reached base level, lateral erosion is dominant - as the streams erode the highland areas between them. Finally, the upland is almost gone: the stream floodplains merge in an area of very low to no topographic relief. The resulting flat plain is the ultimate stage in the cycle of erosion or geographical cycle.
The streams within a peneplained region show extensive meandering and braiding. If the area is subsequently uplifted due to adjacent orogenic processes, without internal deformation within the peneplain, the streams will again begin downward erosion - creating incised meanders, water gaps, and other unique geomorphic features.
A peneplain can be mistaken for a depositional plain. However, the rocks beneath a peneplain have been folded and tilted by tectonic forces, while the rocks beneath a depositional plain lie in horizontal layers.