Iouzan is also known as the "Tsume-no-maru" of Katsuyama-kan, the residence of Nobuhiro Takeda, founder of the Matsumae clan, and the Kakisaki clan. The summit of the mountain is also home to the Iiozan Touda-ji Temple.
Climbing to the top of the mountain, one can see the mouth of the Amanogawa River, which was once busy with shipping on the Japan Sea, and the Japan Sea with Okushiri Island and Oshima Island floating on it. At the foot of the mountain, white grave markers standing in the sea breeze mark more than 600 tombs, estimated to be those of people who lived in Katsuyama-kan, and the sheer number of them is astonishing.
In recent years, graves following Ainu funerary practices have been unearthed among the Buddhist-style graves, and are considered an important discovery that shows the relationship between the Japanese and the Ainu.
In addition, some of the artifacts excavated from the Katsuyama-kan site and replicas of the tombs are on display at the Katsuyama-kan Site Guidance Facility, which opened in 2005.