Seorak Mountain is formed out of granite rock created during the Cretaceous era of the Mesozoic period. Around the same time, there were tectonic shifts in the region that expanded the East Sea, raising the body of bedrock around Seoraksan. The shift stressed the rock, creating cracks and fractures in the granite. The rock around the fractures were penetrated more easily by water, and they were eroded over time, helping form the Gongnyong Ridge. In the Gongnyong Ridge, most of the rock has been eroded or cracked away, with only the solid core remaining to form the spiked rock formations. Those spiked rock formations make the hiking trail through the ridge very steep, without flat areas.