Alone setting in the center of Taiwan Strait, PengHu Island is the home of winds and seas, as well as basalt.  In Year 81^st of ROC(1992), GouDing Yu, JiShan Yu, and Siao  BaiSha Yu were noted as ‘PengHu Basalt Protection Zone’, and according to Cultural Asset Protection Law, change or destroy natural status in the natural protection zone shall be prohibited.  PengHu Islands gradually formed with erupted basalt lava from the early Miocene around 18-17 million years ago to the late Miocene around 8 million years ago or even to early Pliocene.  The volcano activities lasted for several million to 10 million years.  Main in YuWong Island beds (70% of total land beds), land beds of PengHu Islands include lower and upper parts, the former from sea surface down to 320 meters below, major with soil and tuff mixes and basalt and Gabbro (70 meters in thickness) (17 million years ago) on the top, and the latter forms by layers of basalts, sea or marine mudstones, and sandstones (20 to 75 meters in thick), and even agglomerate and tuff on the bottom in somewhere.  The upper zone is dense columnar basalt to make special landscape in PengHu, and the lower part is the cellular basalt mixed with veined stone and calcite.  Between both is an illusive aggregation surface with clay and peat land on it.  Basalts of igneous rocks are major structures in PengHu, sedimentary rocks are very few among basalts, and metamorphic rocks have the smallest amounts, only scattered in Hua Yu.  In cooling balsa magma shrank to create some same-distance shrinking centers and present hexangular columnar fractures, so called as columnar joints, the most unique landscape in PengHu.