Samgak Mountain forms the core of the three Mountain peaks: Baekundae (836.5m), Insubong (810.5m), and Man-gyeong-dae (787.0m).
Mountain is composed of the end of the Jurassic Great Barrier Reef Granite (biotite granite or granite diorite) and different shape of granite dome showing beautiful natural landscapes.
Due to its beautiful shape, many people come to visit the mountain for many years. The old name of Man-gyeong-dae was called Guk-mang-bong and its peak is irregular.
There is a folktale that two princes of King Dongmyeong named Onjo and Biryu of Goguryeo Dynasty have settled in Bu-ah-ak mountain, and this was the Mt. Triangle.
Mt. Triangle has a value as a spiritual mountain with a mysterious figure, and it also has national symbolic values as a place where Korean ancestors have offered memorial services, practiced virtues, built castles, and fought battles.

* Source : Website from the Bureau of Cultural Properties of Seoul