Rock: mixed granite. Some of it crumbles easy while other is strong and tight like .. ah nevermind
One theme of this rock is there are many small holes in areas so it is great for feet holds.
Other areas aren't likethat at all and resemble typical granite style
Songnisan is one beautiful and mystic place. As soon as you step off the bus you are refreshed with pine scented air.
If you hike the trails you will frequently come across restaurants. And at the top the view is fantastic.
Enjoy searching for boulders even outside the park ground and in fact you may have better luck.
As far as finding boulders along the paths you may be out of luck. At least from my experience and I have traveled about half a third of the trails.
Buses from Seoul and Cheongju.
From Cheongju it is about 6,000won.
Find boulders? just walk in any direction. I recommend not actually going hiking up too much. I climb all around the main temple grounds and even not in the park. You can find boulders just walking on the outside of the town.
Take a pad and a smile.
Rock may crumble on you a little.
Take a brush for the moss.
Some of the best spring water I have had in Korea is across the way from the main gate into songnisan just past pay entrance. Fill-up because after that I have not seen free springs. You'll have to pay for water.
I also recommend bring toilet paper if you are going to be hiking up.
Plus a great restaurant. OH MY GOD IT IS GOOD. Is the second restaurant up. It is at the fork of the trail. The kimchi tofu is out of this world and the pay-jong is also the best. Worth the price. 10,000 won for each item. Super nice people .