The Kawado Formation of the Paleogene Sakurae Group in central Shimane Prefecture consists of acidic crystal tuff，lower andesite，mudstone，upper andesite and acidic welded tuff members，in ascending order．The Kawado Formation is probably intra-caldera fill of the Sakurae cauldron，and is in fault contact with Sangun
metamorphic rocks which form the basement of the cauldron．The cauldron rim consists of several cross faults，forming an irregular boundary．A number of dikes and plutons of andesite，rhyolite and quartz-porphyry are emplaced in and around the cauldron．The Kawado Formation gently dips west in the eastern part of the area，but is folded with E-W axes in the central part．The presence of several hidden faults between the eastern and western parts can be infenled from this structural discontinuity．Lava domes lie along the axes of two anticlines in the central part of the cauldron．