Introduction to the Stone Mortar Group: The natural stone mortar group is located in the river under Sanjiu Highway in Jiulong River. It is named because its shape is very similar to the stone mortar used to pound rice in ancient China. The bottom of the river in this part of the park is entirely composed of gravel rock formations. The largest natural stone mortar can reach 2 meters in diameter and is deep enough for a person to squat down; the smallest is 0.2 meters.