The net patterned mud was formed about 3 million years ago. During ice age, lot of Fe and Fe+2 appeared on the surface of the red mud and penetrate through the crack in the mud. Due to the oxidation reduction, the red mud turned into light yellow color. Therefore the red mud turned into net patterned red mud. For a very long period of time the boulder was buried in the red net patterned mud and was dyed with the same net pattern. Normally people call this kind of boulder, net patterned stone.