The Tokibariyama Formation of Oligocene is divided into the Uzuki Rhyolitic and Oku Andesitic Members in ascending order．These members consit mainly of rhyolitic pyroclastic rocks and andesite lavas，respectively．Some thin beds of sandstone or conglomerate are intercalated．This formation generally strikes NE～NNE and dips eastward．The Kori Formation of Miocene unconformably covering the Tokibariyama Formation consists of acidic tuff，sandstone，conglomerate and basalt lava．
These formations are cut by NNE-SSW～NE−SW and NW-SE faults and are bended due to the NESW monocline．This monocline continues to the NW-SE fault southward．Some dikes intrude concordantly with these faults．