This study focused to reveal mineralogical and petrochemical properties and the stratigraphy of the volcanic rocks along the downstream of the Hantan River in Choongaryong Rift Valley. The geological sequences of this area are as follows: The basement of this area consists of Precambrian metasedimentary rocks of the Yeoncheon System. The Biotite Granodiorite of Jurassic age intruded into the Yeoncheon System in the eastern side of the area. Several small exposures of the basalt of post-Jurassic age, which was maned as $quot;Tongjae Basalt$quot;occur dispersely along the west slope of the valley. A conglomerate formation overlay the eroded surface of Tongjae Basalt and contains rounded and angular pebbles and is unconformable overlain by Lapilli Lithic Tuff. A basalt outcrop exposed as small an exposure near Jangtanri creek and intruded the Lithic Tuff, maned as : Jangtanri Basalt.$quot; Granite porphyry dikes intruded into the Lithic Tuff in Tongjae area. An Alkali Loivine Basalt of the Cenozoic Era with 3∼11 different eruptions flowed on the surfaces of the abouve mentioned Precambian metasedimentary rocks, Biotite Granodiorite, Lithic Tuff and Unconsolidated in the valley and formed marrow plateaus. The Alkali Basalt consists mainly of olivine, diopside, hypersthene and labradorite, and is called in this study as $quot;Jeongog Basalt$quot;. the age of the last flow is estimated as late Pleistocene or early Holocene.

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