The main feature is soft sandstone of the Upper Cretaceous Nanaimo Group, frequently exposed, otherwise with a thin overburden of podzolic soil. The sandstone is distinguished by its flowing, rounded forms; these appear to be volcanic bubbles but are actually the result of erosion by weathering. There are also areas of shale. The topography is steep, with occasional small plateaux; the park is basically the sheer southern slope of Mount Galiano.
