The granite cliffs at Cape Foulwind form a resistant barrier to the powerful waves from the Tasman Sea and have protected the sedimentary formations behind. Ranging in elevation from 20 metres to 60 metres above sea level, Cape Foulwind forms a prominent headland, nearly 20 km from the Paparoa Range.
The granite at Cape Foulwind was formed during the Devonian Period, some 360 -370 million years ago. This was a time when New Zealand was connected to Australia as a part of the huge Gondwana Continent and the granite is evidence of that connection. Foulwind granite is mostly composed of quartz, large white feldspar crystals and black mica.
From the northern end of the granite outcrop, a sequence of sedimentary rocks is exposed for over 2.5 km along the cliffs above Gibson’s Beach. This sedimentary sequence provides an excellent, almost unbroken geological record of 40 million years from Eocene times and is a great “window into the past”. The oldest rocks are sandstones and carbonaceous mudstones of the Brunner Coal Measures, which are progressively succeeded by siltstone and mudstone, quartz sand, limestone, calcareous mudstone, and blue grey fine sandstone (“papa”). Reef extending out from the cliffs are well worth exploring.
Granite was extensively quarried for the Westport Harbour breakwaters and high quality limestone was quarried between 1958 and 2016 for local cement production.

The beach sands along the seashore are notable for the economic minerals they contain. As seen in the beaches, there is often clear separation into light grey and dark grey coloured bands. The lighter grey minerals (quartz, feldspar, and mica) are quite separate from the heavy minerals in the dark bands , known as blacksand. The heavy mineral suite is dominated by ilmenite, garnet, and zircon. Small amounts of monazite and gold are also present.
The process that forms the black sand layers can be observed today on many West Coast beaches e.g., Nine Mile beach. During storms, waves carry sand towards the high water mark with the backwash sufficient to lift and remove lighter minerals (quartz, feldspar, and mica) while leaving behind the heavy fraction – the gold-bearing black sand.

Charleston is a wonderful place for geology and rocks and minerals. From the ancient basement rocks of gneiss and granite that form the coastal cliffs and Paparoa Range, the gold bearing black sand deposits, limestone karst country with extensive caves and towering white cliffs, beds of white quartz sand, thick coal seams and fossil bearing mudstones there is great diversity.

The prominent terraces from Charleston south to the Four Mile River provide an important record of sediment deposition during interglacial periods and contain fine sand deposits which have been transported northwards along the coast from the central part of the West Coast. These marine sands have significant areas of gold bearing black sand which were extensively worked during the 1860’s gold rush.

In a few locations there are pegmatite veins which were emplaced into the existing granite /gneiss rock about 100 million years ago. The best example is near the Deep Creek dam where a pegmatite vein is 15 metres thick and this comprises very large (up to 1.5 metres) crystals of quartz and feldspar, 25 cm mica plates and rare crystals of beryl.