Apatite fission track analysis of gneiss samples across the Knersvlakte plain in the coastal area of western South Africa reveals the existence of a relatively deeply incised paleovalley flanked by high ridges formed during the Mid Cretaceous. This paleovalley coincides with the present course of the Krom River through the Great Escarpment.
Modelling of the fission-track data suggests that the main stage of intense channel erosion, triggered by uplift of the catchment area, occurred between ~120 and ~110 Ma and was followed by a period of progressive hillslope erosion and interfluve degradation. It is suggested that the paleo-Karoo River and its tributaries were responsible for the formation of this relief. The present-day lower relief formed by continuing erosion starting at ~90 Ma, time when all the analysed samples had already been exhumed to a depth corresponding to temperatures below 60°C (~2 to 3 km).