Mathesons Bay (Māori: Te Kohuroa; officially Te Kohuroa / Mathesons Bay)[1][2] is a small beach in the Rodney district of the Auckland Region of New Zealand.

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.

[4] 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.

Many fossil invertebrates can be found in the cliffs and rock platforms, notably brachiopods (Notosaria, Magasella), barnacles (Epopella, Tasmanobalanus, Bathylasma), bivalves (Eucrassatella, Crenostrea), gastropods (Sarmaturbo, Cellana), corals (Cyathoseris, Leptoseris, Keratoisis), an echinoid (Phyllacanthus) and bryozoans.

[5][6] The remnant of a fossilized methane seep was formerly exposed in the cliffs to the north of Mathesons Bay Reserve, but has subsequently been buried by rockfalls.