Nezha legend: Why did Nezha become the Rocky Mountain?

Stonehenge destroyed Nezha's soul and controlled Nezha's body and magic.

According to the plot of The Legend of Nezha, Shijie became a magic stone, which made Nezha miserable and destroyed Nezha's spirit. He controlled Nezha's body and mana, and made Nezha become his own incarnation, owning and controlling Nezha's spirit.