Located in the northernmost region of South Korea -Yanggu-gun in Haean-myeon, Haean Basin is one of the most remarkable landforms in the nation created by differential erosion. The basin is surrounded by Gachilbong (1,242m above sea level), Mt. Daewusan (1,178.5m) and Mt. Dosolsan (1,147.9m), the high peaks over 1,000m made of metamorphic rocks. However, the altitude of its granitic floor is only about 400m; such a great difference in altitude accentuates its bowl-like shape. In the past, a lot of snakes lived in the area but, they were completely driven away at the end of the Joseon Period after people began to raise pigs following the advice from a Buddhist monk. The name Hae-an means 'Pigs brought peace to the village'. Meanwhile, the basin was called a punch bowl by the UN forces during the Korean War because of its morphological characteristics. Geologically, it is composed of the Precambrian metamorphic sedimentary rocks and the Jurassic Daebo intrusive granites. (Daebo granite: intrusive granite of Daebo orogeny, the most prominent orogeny) The rims of the basin are composed of the Precambrian metamorphic sedimentary rocks highly resistant to weathering and erosion whereas the slopes and floor of the basin are of the Jurassic biotite granites less resistant to weathering. Granite biotite schist is most widely distributed in this area. After having been metamorphosed at high temperature generated upon granitic intrusion, rocks surrounding the granites became resistant to weathering and remained as the outer rims. However, granites, as plutonic rocks, were quickly eroded since they were less resistant to weathering and formed the basin The granite that currently comprises a floor of the Haean Basin was formed about 200 million years ago when magma intrusion occurred about 20km deep in the earth. At that time, large radial crushing took place at the point where the top of the magma and the bottom of the base rock came into contact; such a structure is subject to erosion and deep-seated weathering as it gives way to water that infiltrates deep into the ground.