On July 24, 1989, rescue helicopters were searching for some missing hikers from Tokyo near the 7,514-foot Mount Asahi (Asahidake) on Japan’s northernmost island of Hokkaido, located in the northern part of the Daisetsuzan National Park.

The pilots noticed a giant SOS made from birch logs on the ground near the start of the Chubetsu River, Hokkaido. The tree trunks were arranged into letters, spelling out SOS in English. Each letter measured about 16 feet long and 10 feet wide. The SOS was about 2.5 miles (4km) from the summit of Asahidake.

The rescue team recovered the hikers about 2 miles (3.2 km) north of the sign. Once in the hospital, the hikers were asked about the SOS sign. They said they had nothing to do with its construction. If they never made that sign, the question was, who did?

Another search revealed a skeleton and a backpack with a mysterious tape recording. How did the man create the SOS sign without tools and broken bones? An enduring mystery from Japan’s Daisetsuzan National Park.

To read the full story, log in or become a member of StrangeOutdoors.com at: The mysterious Mount Asahidake SOS incident

See the latest list of Exclusive members-only articles on StrangeOutdoors.com