The intensely folded rock strata of the crags to the east of this point are a striking example of why the parallel mountain ranges that run for more than 800km across the southern regions of South Africa are called the Cape Fold Mountains.
The strata were originally horizontal, formed from sediment that settled between 480 and 400 million years ago on the floor of what was then a vast alluvial plain.
Much later, between 280 and 230 million years ago, the region was subjected to intense compressional forces, which geologists believe were directed in several pulses from the south towards the north. This tremendous pressure, applied over some 50 million years, caused the strata to bow and bend into the contorted shapes and patterns visible today.
The sandstone is part of the Table Mountain Group (TMG) of rocks. High resistance to weathering means that TMG rocks tend to form the high ground across the region, although nature is constantly wearing it down through intense erosion involving rivers, rain, wind, rockfalls and earthquakes.
The most recent major moment in the geological history of Cogmans Kloof occurred between 150 and 90 million years ago, when a 5000‑metre downward displacement along the south of the Worcester Fault resulted in the juxtaposition of rocks of greatly differing ages.
The fault runs eastwards from a point just west of Wolseley, through Worcester and Robertson and beyond. Sudden movement along the Worcester Fault in 1969 caused South Africa’s largest earthquake in historical times, which registered 6.3 on the Richter Scale.
Cogmans River Floods
In January 1981, nature delivered a strong reminder of the powerful forces that shaped the Cogmans Kloof. Heavy rains across the southern Karoo caused the Keisie and Kingna rivers to flood. For more information about the floods, look out for similar signs at the Ashton Bridge as well as the Voortrekker Bridge at the entrance to Montagu.
Geomorphology ‑ the power of the Cogmans River
The striking appearance of the gorge, with its high peaks and steep rock faces on both sides, is testimony to the erosive power of the Cogmans River, which runs through it. This river starts just above the northern end of the gorge, at the confluence of the Keisie and Kingna rivers, and flows past Ashton to join the Breede River 18km further downstream. Geologists believe the river may well have existed prior to the uplift of the Langeberg range and was able to erode downwards at a pace equal to that of the rise of the land. When the downward erosion of the main river channel halted or slowed, the stream would tend to cut sideways, widening the gorge. When erosion of the main channel resumed, the terraces on the side remained. You are standing on such a terrace, reading this sign.
