Kairimu cave was formed in a 30 ft band of Lower Oligocene limestone, the drainage system being determined mainly by a shallow syncline in the limestone. Development of the two largest and oldest passages was initiated under phreatic conditions after uplift in Late Miocene time, but the main episode of cave formation was controlled by vadose conditions. During Late Pliocene and Early Pleistocene high-sea-level regimes the cave was flooded and filled in with silt and clay. This history is suggested by the height of the cave entrance above sea level (350 ft) and was confirmed by microfloral age determinations of the clay fill. Several smaller passages were formed later.