The 7 km terrain which stretches over Geomun Oreum (456 m above sea level), Buk Oreum, and Seonhul Gotjawal Forest is Jeju Island’s typical Gotjawal Forest (According to the local dialect, ‘got’ refers to forest, while ‘jawal’ refers to a thicket of trees and vines), known for its Dongbaekdongsan wetland. Dongbaekdongsan wetland has been designated as the Ramsar Wetland in 2011. Seonhul Gotjawal Forest mainly consists of hills, as high as few meters on a flat. Pits and valleys are also commonly found in the area. The slope of the hills ranges from 20 degrees to 50 degrees. All the hills have V-shaped depressions. The depressions range from a few meters to several tens of meters. The depressions are either empty or consist of rocks and soil. The depressions found in the area are considered to be tumuli, or pressure ridges. Tumuli form where fluid pressure within a lava tube or lava flow increases sufficiently to cause the surface to well and crack. Tumuli can also form when the lava flow encounters flat areas. Also, elevated landform in some areas are considered as tumuli as well. Trenches or circular volcanic pits formed after the lava caves underneath the tumuli collapsed.