Jangsan Mountain shows an unusually high percentage of rock fields a.k.a. block stream since the mountain is made up of volcanic ash, lava, and pyroclastic flow erupted from a stratovolcano formed during a violent rhyolitic volcanic activity 70-60 million years ago. The block stream is a field of rock fragments broken off rock cliffs and piled on a slope. This forms when rocks split along the joints by weathering process and fall down along the slopes to the base of the mountain over the years. Jangsan geosite contains volcanic rocks such as spherulitic rhyolites, rhyolitic tuff, and porphyritic rhyolite; and magnificent landforms like Jangsan Falls, block stream, and inselberg (a hill or mountain rising from a plain). Since the site is in a round shape, even a little walk into it makes a nice getaway from the city. Also enjoyable is a scenic view of an urban area along the coast from the mountain top e.g. Haeundae and Gwangan Bridge.