• Location : 1101, Naengjeong-ri, Gwanin-myeon, Pocheon-si, Gyeonggi-do
• Information desk : 031-538-2106 The Culture & Tourism Department of Pocheon City Hall, Rep

This was designated as natural monument 436 in 2004 since it has graceful scenery and its academic value is recognized. Daegyo Stream is a tributary of Hantan River and it is called a ravine since it has a narrow and long valley; its total length is about 1.5 km. The ravine is a riverbed landform, which 25m~40m wide and about 30m high and has columnar joints. The absolute age of the Ridge Chuga basalt cliffs on both sides of the ravine is measured by employing the K-Ar method (a dating method using radioactive isotopes) and it is found that the basalt was formed when lava erupted 3 times or more about 270,000 years ago and that the basalt is very important for academically investigating into the 4th period of geological and topographical developments of the Korean peninsula. The basalt lava layers on both sides of the ravine are so thick as to comprise various joints like columnar joint, horizontal plate-form joint, and fan-form radial joint. Within the basalt ravine at Daegyo Stream, there is a shaman march which is said to be a place where shamans would offer sacrifices and the rare radiated joint is called Fan Rock since it is shaped after an unfolded fan.

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