The San have a legend that the wildly twisting Fish River Canyon was gouged out by a frantically scrambling snake, Koutein Kooru, as he was pursued into the desert by hunters. However, the geological story is a bit different…
Fish River, which joins the Orange River 110km south of the canyon, has been gouging out this gorge for aeons. Surprisingly, Fish River Canyon is actually two canyons, one inside the other, which were formed in entirely different ways. It’s thought that the original sedimentary layers of shale, sandstone and loose igneous material around Fish River Canyon were laid down nearly two billion years ago, and were later metamorphosed by heat and pressure into more solid materials, such as gneiss. Just under a billion years ago, cracks in the formation admitted intrusions of igneous material, which cooled to form the dolerite dykes (which are now exposed in the inner canyon).
The surface was then eroded into a basin and covered by a shallow sea, which eventually filled with sediment – sandstone, conglomerate, quartzite, limestone and shale – washed down from the surrounding exposed lands. Around 500 million years ago, a period of tectonic activity along crustal faults caused these layers to rift and to tilt at a 45-degree angle. These forces opened a wide gap in the earth’s crust and formed a large canyon.
This was what we now regard as the outer canyon, the bottom of which was the first level of terraces that are visible approximately 170m below the eastern rim and 380m below the western rim. This newly created valley naturally became a watercourse (the Fish River, oddly enough), which began eroding a meandering path along the valley floor and eventually gouged out what is now the 270m-deep inner canyon.