The subsurface geology of the Yumigahama sandbar has been reconstructed mainly on the basis of drilling data from 15 drillcores put down by the Ministry of Construction in 1995~1996.The sandbar is underlain by layers of Holocene sand,Holocene mud and Pleistocene sand,in descending order. Two volcanic ash layers,the SKP(Sanbe-Kisuki Pumice)and the DMP(Daisen-Matsue Pumice)are intercalated in upper part of the Pleistocene deposits,and the K-Ah volcanic ash layer(6,300 yr B.P.)is intercalated in the muddy Holocene deposits.