Two units of the Late Permian Gerringong volcanic facies are exposed on Bombo Headland. The Kiama Sandstone member forms a narrow wave-cut platform and adjacent vertical cliff face around the south-eastern extremity of the quarry. To the north, the sandstone dips below sea level and is overlain by about 20m of porphyritic basalt, termed Bombo Latite member. The contact between the two units is well-exposed in the cliff section at the eastern end of the two points comprising the headland section. The red-brown colour (due to oxidization of haematite) of the sandstone contrasts markedly with the grey-black latite, which displays spectacular columnar jointing elsewhere in the quarry. Isolated columns 5–5 meters in height stand adjacent to the coast between the north and south parts of the quarry; just to the north the sea wall exposes cross-sections of the columns 1-2.5 metres in diameter, resulting in a "Giants Causeway" appearance.