The fission-track ages were obtained on zircons from tuffs of the Neogene Tertiary in Oga Peninsula, Akita Prefecture, Japan, as follows:
Shibikawa Group: Pink Tuff 2.8 m. y.
Wakimoto Group: Middle Tuff 6.8
Kitaura Group: Kitaura Tuff 7.5
Funakawa Group: Anzenji Tuff 12
Minami-Hirasawa Tuff 13
Nishikurosawa Group: Nishikurosawa Tuff 16
Daijima Group: Sugoroku Pumice-Flow 25
Hokakejima Welded Tuff 20
Monzen Group: Shinzan Rhyolite 26
Hornblende Biotite Adamellite 62