ABSTRACT
The stratum of Mesozoic Upper Jurassic is the largest one in the area, whose lithology is cinereous tuff with angular gravel, and sandstone locally. The lithology of the Upper Cretaceous stratum is Amaranth, silicic tuff with sandstone, glutenite locally. The stratum of Upper Cretaceous is mainly exposed nearby the bank of Yongan River. The alluvium of the Holocene mainly consists of loose
1 INTRODUCTION
The large underground caves of Feifeng Mountain were formed by excavating the tuff stone in the ancient time of China, whose gross area is more than 30 000 m2. Now the mountain with caves is open up for tour, showing its excavating ways, structure of grottos and the scientific highlights within the project. At the northern toe of the mountain slope, there exists the Yongan River, which is now used for ecological drift. However, because of the steep terrain, joining in the rock mass and the long-term weathering, the rockfall and potential rockfall on northern slopes of the Feifeng Mountain is serious.
