Introduction to the First Line of Sky: Walking westward along the Dadu River, you can see the cliffs on both sides getting closer and closer, and the scenery becomes more and more quiet. Before you know it, you are in the canyon at the boundary between Leshan City and Ya'an City. ditch. Baixiong Valley is more than 2,000 meters deep and more than 4,000 meters long. It is most famous for its "line of sky" landscape: there are only more than 20 meters between the two mountains in the valley. Looking upward, the sky seems to have turned into a small bamboo leaf.