A foredune section at Pig Bay, Motutapu, has been excavated to expose nonvolcanic beach sand below a single Rangitoto ash layer which, illi turn, is overlain by a series of wind-blown and water-laid sediments containing reworked ash. The date of the eruption was determined by carbon sample; as A.D. 1188 ± 50 years. The sediments above the Rangitoto ash include a number of well defined human occupation levels, some of which have yielded adzes of moa-hunter type.