早期，地壳抬升，岩体裂隙发育，地下河水溶蚀山体，将山体内部掏空，形成地下溶洞。后因地壳继续抬升，地下水位不断下降而逐渐出露于地表，其两端成开口状，并透光。该穿洞高约30m，宽约80m,平治河从其下穿过。内壁裂隙发育，钟乳石多沿着裂隙生长。气势恢宏奇秀，岩壁光滑如磨，巧夺天工，故称光岩。

In the early stage, the crust was uplifted, and the fissures in rocks were developed. Groundwater along fissures eroded mountain body, a cave was formed. Then the earth's crust continued to uplift, the groundwater level continuously fell and the cave was exposed to the surface. The front and back parts of the cave were connected, so light can pass the cave. The karst cave is about 30m high and 80m wide, and Pingzhi river passed under it. The fissures in the inner wall were developed, and the stalactites grew along the fissures. It is fairly magnificent and the rock wall is smooth and polished, hence the name Guangyan.