The walls on both sides stand up against each other with a clearance of 1-2 meters wide. It is so named because looking up from the splitting rocks, one can only see a gleam of sky in between. It is the result of granite weathering and erosion along its vertical joints.

1.Running water eroded and weathered granite mass along its vertical joint (fracture).

2.The fracture was enlarged along with the processing of weathering and erosion.

3.Eventually, a nearly vertical ravine formed.