During the
Upper Paleolithic period, roughly until 13,000 years ago, the shapes and types of stone tools, such as
stone axes, spears, and
microlith blades evolved due to rapid changes in the environment, which resulted in changes in the fauna available for hunting. Microliths, thin and razor-shape blades of stone which were used by embedding into shafts of wood or bone, appears towards the end of the Upper Paleolithic. The Yasumiba ruins is one of several sites from this period which have been identified in the gently rolling foothills of
Mount Ashitaka. This site is located at an elevation of 280 meters on a 60 meter wide ridge, protected by steep cliffs and swamps on all sides.
Excavated in 1964 by
Meiji University, the site was found to contain a large number of
microlith blades,
lithic cores and
flakes buried below a
pyroclastic layer of ash from an eruption of
Mount Fuji 2.5 meters below the present ground level. The microlithic blade culture in Japan is roughly divided into two cultures, one is of conical microlithic cores and the other is of boat-bottomed microlithic cores. This site is typical of the former, and the material used was primarily
obsidian which originated in what is now
Nagano Prefecture or from
Kōzushima, one of the
Izu islands, indicating some form of long distance trade and a maritime capability for the inhabitants of the Japanese archipelago even at that early time in prehistory. The number of stone tools and core fragments recovered was 4412 items. Two traces of semi-circular hearths made from rounded riverstones were also found, containing fragments of charcoal, and it is presumed that these hearths were located within a
pit dwelling. These were the first Japanese Paleolithic period hearths to be discovered. 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 site is approximately five minutes by car from
Tōmei Expressway Numazu IC, and having been backfilled after excavation, is currently a grassy mound with a small signpost. ==See also==