The rocks at Mathesons Bay comprise Waipapa Terrane greywacke overlain by sediments of the early Miocene Waitemata Group, the latter of which is divided between the basal, shallow marine Cape Rodney Formation, and the turbidite deposits of the Pakiri Formation. These sediments form part of sequence that is inferred to reflect the subsidence of the area from a shallow rocky shore to a deep marine basin beginning approximately 21.7 million years ago.
The rocks at Mathesons Bay are composed of Waipapa Terrane greywacke overlain by sediments from the early Miocene Waitemata Group, which is divided into the Cape Rodney Formation (shallow marine) and the Pakiri Formation (turbidite deposits). These sediments form part of a sequence suggesting that the area's shoreline gradually transitioned to a deep marine basin around 21.7 million years ago.