During the early Cretaceous Period the ancient super continent of Gondwana split up and Africa was finally separated from South America, Australia, India and Antarctica. This split created stress fractures in southern Africa along pre-existing fault lines. As the stress fractures developed, so basins were formed.
One such basin is the Oudtshoorn Basin of the Eastern Little Karoo which extends as far west as Calitzdorp. This basin developed mainly along a deep fracture running from East to West along the base of the Swartberg called the "Cango Fault". The basin floor subsided mainly along its northern margin (a half-graben). Accompanying this, rejuvenated rivers on the new highlands of Gamkasberg and Rooiberg as well as from the uplifted area to the North, flowed into the Oudtshoorn basin. They carried with them vast amounts of scree and rock, fractured from the Table Mountain sandstone and quartzite's from the mountain chains surrounding the Little Karoo and deposited them on the emerging lake shores. This is why these basins are referred to as sedimentary basins.
The main type of sediment filling the basin is called Enon Conglomerate (named after the mission station at Enon, near Kirkwood, where a prime example thereof can be found) and consists of sandstone, mud and quartzite in a matrix - basically a mix of pebbles suspended in a sand "cement". The coarser material, up to 2 meters in diameter, is deposited at the base of the conglomerate. Coarser material was deposited first because of the initial large difference in elevation between the rim of the basin and its base - boulders were swept to the bottom of the basin before they could be eroded to finer material. In time, as the elevation between the top and the bottom decreased, the material swept down was subjected to more erosion, leading to decreased grain size and smoother pebbles.
Traditionally the Enon sediments in the Oudtshoorn basin are divided into four distinct layers: lower (base) Enon conglomerate, white small pebble conglomerate, buff Enon sandstone and upper (top) Enon mudstone and conglomerate. The upper (red) layer of mudstone and conglomerate almost encircles the basin.
Over the last 100 million years, erosion of the sediment within this basin has hollowed out the Riet Valley and has left these isolated koppies or mountains in a band stretching from De Rust almost to Calitzdorp. Initially eroding quite quickly, they subsequently formed an outer crust which was somewhat more resistant. Weathering has broken through some of this crust resulting in small caves and overhangs as is evident here in the Rooikoppe mountains.
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In order to qualify to log this cache, please email the answers to the following questions to the cache owner:
1. What do you think has led to the strange formations and hollows in the mountain surface?
2. What do you think has caused the red colouring in the mountains?
3. At which layer of Enon sedimentation do the Rooikoppe mountains occur?
4. If you turn to the south west you will see the side of a river bed. Along the river bank are lines formed by erosion. At what angle are these lines?
5. OPTIONALLY: Please upload a photo of yourself at the given coordinates with your GPSr.