A wide distribution of alkali basalt of the Tertiary Period can be found in Goseong area in Gangwon Province as well as Baekryeongdo; Shinun-ri, Ahsan; Gwongwan-ri, Pyeongtaek; Jogok-ri, Boeun; Pohang Basin; and Yangnam Basin. The Tertiary basalt in Goseong has been developed in a small scale along Mt. Goseongsan (298.5m above sea level), Mt. Oeumsan (290m), Mt. Duitbaejae (225m) and Mt. Unbongsan (285m), forming a plug dome at a half to two-thirds of the peak heights. (Plug dome or lava dome is formed when highly viscous lava got upheaved through conduits and extruded in the crater after solidification) Columnar joints are characteristic of the Tertiary basalt. Compared with the Quaternary basalt in Cherowon and Jeju Island, it was eroded so severely that not only the original form of the columnar joints but also their debris like taluses and block streams can be observed. The Goseong basalt is made of the Tertiary basaltic magma which intruded into the Mesozoic biotite granite long before the occurrence of the Quaternary basalts in Cheorwon area. The volcanic eruption was caused by hotspots in the east of Eurasian Plate, not the subduction of the Pacific Plate. It is estimated that the basalt here was formed by partial dissolution of garnet peridotite in the upper mantle and the magma was created 160km deep in the earth. Heading up toward the ground surface, the magma had captured peridotites 57-67km below the surface and reached the ground quickly before the melting of the rocks occurred. As a result, the Goseong basalt includes many different kinds of xenoliths. Mountaintops like Galmibong in Jukwang-myeon and 166 Peak exhibit pentagonal or hexagonal joints that have been severely fragmented while Mt. Unbongsan shows at the foot of the mountain rock blocks and taluses from column debris; the debris was from 30-40cm radius hexagonal columns but later got broken into 1cm radius and streamed downslope. The columnar or polygonal joints on the peaks of the Mt. Duitbaejae, Mt. Oeumsan, 240 Peak and Mt. Goseongsan have been poorly developed thus their facies looks like a bundle of pencils. By the way, a traditional folk village named Wanggok village in Obong-ri is located approximately 5km away from the Mt. Unbongsan to the north. It is surrounded by five basaltic mountaintops, i.e., Mt. Oeumsan (290m above sea level), Mt. Duitbaejae (225m), Galmibong (105m), 240 Peak, and 166 Peak, Therefore, the village is in the form of an ark isolated from the outside. The outset of the village’s formation was the reclusion of Ham Buyeol who opposed a new dynasty, Joseon, in the 14th century. Since then, the Ham Family of Gangneung, the Choi Family of Gangneung, and the Kim Family of Yonggung have settled together and built a village of kin groups. The village has maintained its traditional environments such as natural landscapes, traditional houses and agriculture-based living over 150 years since the reconstruction due to devastation by the Japanese Invasion of Korea in 1592. Especially, it features a classic housing style of the northeastern Korea and a cluster of thatched houses. Those styles assume the structure of traditional houses in the northern part of Gangwon Province, i.e., a house with several wings, where a barn is attached to a kitchen in an L-shape to survive a long, cold winter. The village was designated as No. 235 Important Folk Relic in January, 2000 in recognition of its historical and academic value.