The Yasumiba ruins is located at an altitude of 280 meters on a 60 meter wide ridge on the slopes of Mount Ashitaka, protected by steep cliffs on all sides. Excavated in 1964 by Meiji University, the site was found to contain a large number of microliths buried below a pyroclastic layer of ash from an eruption of Mount Fuji 2.5 meters below the present ground level. Two traces of semi-circular hearths made from rounded riverstones were also found, containing fragments of charcoal. One hearth was 180 cm x 100 cm, and the smaller was approximately 50 cm in diameter. Carbon dating of the charcoal indicated that these hearths were used 14,300 years ago. The number of stone tools and core fragments recovered was 4412 items.