In the hills around Matsue city, the alkali basalts are widely distributed. These basalts, lava flows and tuff beds, are embedded in sandstone beds. They are called the Matsue formation and comporse the upper part of the Izumo group.
Six lava flows and two tuff beds are good key beds in the Matsue formation. The sedimentary imbricate structure of that formation are shown by these key beds.
The upper Cenozoic geologic units, in descending order, are as follows :
- Terrace gravel III
- Kisuki pumice bed
Pleistocene - Kurayoshi pumice bed
- Terrace gravel II ( = Nogi bed)
- Terrace gravel I
Pliocene -Misasa group -Wakurayama andesite
- Rakuzan basalt (BL6) and conglomerate (BG3) member
(sandstone)
- Moriwaki tuff member (AT)
(sandstone)
- Tokodai basalt member (BL 5)
(sandstone)
- Kawazu tuff member (BT)
-Matsue (sandstone)
Miocene formation - Tsuda basalt (BL 4) and conglomerate (BG 2) member
(sandstone)
Agenogi basalt member (BL 3)
(sandstone)
- Hanamagari basalt (BL 2)
(sandstone)
- Chausuyama basalt (BL 1) and breccia (BG 1) member
-Fujina and Furue formations (mudstone)