The upper approximately 600 m portion of the 1 km high table-topped mountain, or mesa, consists of 450-510 million years old (Ordovician) rocks belonging to the two lowermost layers of the Cape Fold Mountains.
The uppermost, and younger of the two layers, consists of extremely hard quartzitic sandstone, commonly referred to as “Table Mountain Sandstone”, or “Peninsula Formation Sandstone” (as it is known as at present), which is highly resistant to erosion and forms characteristic steep grey crags.
The 70 m thick lower layer, known as the “Graafwater Formation”, consists of distinctively maroon colored mudstones, which were laid down in much thinner horizontal strata than the Table Mountain Sandstone strata above it. The Graafwater rocks can best be seen just above the contour path on the front of Table Mountain, and around Devils Peak. They can also been seen in the cutting along Chapman’s Peak Drive. These rocks are believed to have originated in shallow tidal flats, in which a few Ordovician fossils, and fossil tracks have been preserved.
The overlying Table Mountain Sandstone probably arose in deeper water, either as a result of subsidence, or a rise in the sea level.
The Graafwater rocks rest on the basement consisting of Cape Granite. Devil’s Peak, Signal Hill, the City Bowl and much of the “Cape Flats”, however, rest on heavily folded and altered phyllitesand hornfelses known informally as the Malmesbury shales.
The Cape Granite and Malmesbury shales form the lower, gentler slopes of the Table Mountain range on the Cape Peninsula. They are of late Precambrianage, pre-dating the “Graafwater rocks” by at least 40 million years.
The basement rocks are not nearly as resistant to weathering as the Table Mountain Sandstone, but significant outcrops of the Cape Granite are visible on the western side of Lion’s Head, and elsewhere on the Peninsula (especially below Chapman’s Peak Drive, and The Boulders near Simon’s Town).
The weathered granite soil of the lower slopes of the Peninsula Mountain range are more fertile than the nutrient-poor soils derived from Table Mountain Sandstone. Most of the vineyards found on the Cape Peninsula are therefore found on these granitic slopes of the Table Mountain range.
The mountain owes it table-top flatness to the fact that it is a syncline mountain, meaning that it once was the bottom of a valley.
The anticline, or highest point of the series of folds that Table Mountain was once part of, lay to the east, but that has been weathered away, together with the underlying softer Malmesbury shale and granite basement, to form the “Cape Flats”. The “Cape Flats” form the isthmus that connects the Cape Peninsula to the Mainland. The Fold Mountains reappear as the Hottentots-Holland Mountain range on the mainland side of the “Cape Flats”.
Table Mountain is the northernmost end of a 50 km long, and roughly 6–10 km wide, Cape Fold Mountain range that forms the back bone of the Cape Peninsula, stretching from the Cape of Good Hope in the south to Table Mountain and its flanking Devil’s Peak (to the east) and Lion’s Head-Signal Hill (to the west) in the north. Table Mountain forms the highest point of this range. The range runs parallel to the other Cape Fold Mountain ranges on the mainland to the east.