The area of Cheorwon was originally made up of wide valleys and low hills on a granite base with the Hantangang River running through them. During the Quaternary from 540,000 to 120,000 years ago, volcanic eruptions took place in Mt. Ori (452m above sea level) in Pyeonggang-gun and a high hill (680m) 4 km away from it and lava flowing along the river filled the valleys and lowlands to create a lava plateau. Such eruptions have occurred at least four times in a row. In the lava plateau, there are island-like areas of low hills called steptoes; they appear when the lava hasn’t completely filled the preexisting valleys and lowlands. Such examples are the Baengma Goji hills (395m above sea level) and Ice Cream Goji (219m), the major battlefields of the Korean War. Having been formed on a granite base covered by lava, the Cheorwon Plain is the only lava plateau found in the mainland of South Korea. Well-developed in such a basaltic layer are joints which allow water to drain quickly and thus hinder the storage of surface water and the retention of moisture. However, in case a sedimentary layer develops over the basaltic layer, it can make an arable land like the Cherwon Plain. The area is regarded as a top granary in Gangwon Province thanks to two things: building of irrigation system directing water from the Hantangang River and opening of Gyeongwon Line (railroad) in 1914.