Goseok is a precipice of granite under Goseokjeong, standing 15m tall by the Hantangang River canyon. The granite was formed deep down below about 100 million years ago in the Cretaceous and later exhumed by crustal uplift and erosion over years. The Goseok exhibits landforms of fluvial erosion such as grooves and potholes while other granites around it show vertical and horizontal joints. It was completely buried by basaltic lava flow which erupted from 540,000 to 120,000 years ago but exposed at the earth’s surface again due to the erosion of the river. The riverbank made of the preexisting granite base is in a gentle slope while that of a basalt base forms a vertical cliff by the development of columnar joints. In particularly, the upper part of the basalt base is covered with a lava plateau, which results in an asymmetry between the banks on both sides of the river.