The age of Dashan is hidden in the rocks. According to relevant data, people can know the age of trees by their annual rings, and determine the age of animals by observing the degree of tooth wear. Mountains also have rings, but they are different and much more complicated. We know that a mountain is composed of pieces of rocks, and we usually know the age of the mountain by knowing the age of the rocks, so the age of the mountain is hidden in the rocks.