Penghu Islands is composed by almost a hundred of large and small islands and islets, apart from Huayu, they are all composed of several layers of basalt coulee and partly sedimentary rock mezzanine; even though the islands are only 127km2 in area, it houses such unique natural basalt landscape that the Taiwan mainland cannot compete against! According to geologists, the basalt in Penghu is formed by countless inconsecutive volcano activities, during which the lava rose up from beneath the shallow sea or from fissures underground and cooled once reached surface. So far, the oldest basalt known is the Wangan basalt, its lava effused 17 million years ago, and since then, there had been volcano activities every one or two million years up until 8.2 million years ago, when the basalt on Dongyuping were formed, and volcano activities ceased.

The Penghu basalt coulee tends to form a perpendicular column once cooled, and after years of weathering and erosion, such basalt columns form a spectacular geological view with columnar joints placed side by side, some erecting into the sky, some crooked or bent, presenting various forms. Professor Wang Shin of Department of Geography, National Taiwan University once said, "Compared to the World-class North Ireland Basalt landform, the landscape in Penghu Basalt Reservation Area is just as spectacular, if not better! "

Basalt lava from the oceanic crust is a type of volcanic rock, and such lava will cool rapidly when reaching the surface, thus contracting and chap into pentangle or hexagon columns, this is called  "jointing ". The structure of a joint is multi-variant, and thus the most unique natural landscape of Penghu Basalt.

Basalt with a dense texture is often grayish-black in color, and according to the different mineral elements inside the rock, there can be different shade variances. If the air inside the lava did not escape in time when the lava cooled, it will become air holes, thus forming the