一条区域性正断层切穿三叠纪薄板状灰岩变形地层。经长期岩溶水蚀，沿断裂带生成崎岖曲折的嶂谷。该嶂谷高逾十丈，底宽顶窄，谷底深幽，怪石嶙峋，似刀劈斧砍。谷顶狭窄，只见一线天空；两厢谷壁悬空卡住三、五崩塌巨石，摇摇欲坠之势，令人毛骨悚然。面对如此险要关隘，飞鸟怯步，神鬼无计，奈何不得。作为要塞，“一夫当关，万夫莫开”，绝不言过。三叠纪是地质年代中的一个时期，属于中生代的第一个纪，开始于约2.52亿年前，结束于约2亿年前。

A regional normal fault cut through Triassic laminated limestone deformation stratum. After long-term karst water erosion, a bumpy narrow gorge is generated along fault zone. The height of this narrow gorge is beyondhundred feet with wide bottom and narrow top. The valley is very deep, covering with grotesque shapes of rocks looking like cutting knives and chopping axes. Up its narrow ravine you can only see a glimmer of sky; small groups of collapse stones are hanging from both sides of valley wall, as if they can fell down at anytime making you terrified. Facing with such a dangerous fort, evenflying birds and deities can do nothing. As a key fortress, it is never an overstatement to say “if one rock is in the way, nobody could pass”.Triassic is a period of geological age, belonging to the first period of Mesozoic era, which began about 252million years ago and ended about 200million years ago.