Located on Buksan, Sinseondae features colonnades on a smaller scale. The colonnades are found approximately 2.4 km northeast of the summit of Medeungsan at approximately 750 m above sea level, which is about 200 m lower than the Gwangseokdae colonnades. The rocks are composed of Mudeungsan tuff. Well-developed pentagonal or hexagonal columns are well observed. The height ranges 5-6 m and the face widths range from 1 m to 1.5 m. Some colonnades have several joints developed in the inner-sides, caused by weathering process. Persistent weathering has resulted in various vertical and horizontal fractures as secondary structures. A closer examination on the planar surface where the silver grass hill (also known as Eoksaepyungjeon) is located has revealed that steep cliffs intersect with gentle slopes. These are estimated to be cryoplanation surfaces which have undergone the flattening process through repeated freezing and thawing under periglacial conditions. Sinseondae and the Eoksaepyungjeon are the only geosites of Mudeungsan that are located in Damyang-gun. The vertical and horizontal joints developed in the colonnades are the results of weathering processes, which makes the fractures unique geological heritage. Furthermore, like the colonnades formed in Mudengsan tuff, the secondary fractures provide information on the eruptions and evolution of Mudeungsan. Studies on Eoksaepyungjeon allow geologists to grasp deeper understanding on the Earth’s environmental changes, resulted by the flattening of landscapes and slopes under periglacial conditions.