Obsidian forms when felsic lava cools rapidly, producing a natural glass so sharp that a freshly fractured edge can be thinner than a surgical scalpel blade. The volcanic formations around the Kirigamine Highlands in central Nagano created rich deposits of this material, and the Jomon people -- Japan's prehistoric hunter-gatherer-potters -- recognized its value early. Through a technique called lithic reduction, they fractured obsidian nodules into razor-sharp blades, arrowheads, scrapers, and knives. The Hoshigato site sits within the Higashimata National Forest on the eastern flank of Mount Hoshigato, where miners dug shallow pits and connected them into a sprawling network that followed the obsidian-bearing rock formations across the mountainside.

What makes Hoshigato extraordinary is not just its scale but its reach. Physicochemical analysis -- essentially fingerprinting the obsidian's chemical composition -- has confirmed that material from these mines ended up in settlements distributed across an enormous swath of Japan, from the Tohoku region in the northeast to the Tokai region along the Pacific coast, distances of up to 300 kilometers. This was not casual scavenging. The consistency of extraction over thousands of years, spanning from the Early Jomon period (approximately 5,000 to 3,500 BCE) through the Final Jomon period (1,700 to 400 BCE), points to organized production and sustained trade networks linking highland mining communities with lowland settlements. The Jomon people, often characterized simply as hunter-gatherers, were running a supply chain that would be impressive in any era.

The site was first identified in 1920, but serious archaeological investigation did not begin until excavations between 1959 and 1961 revealed the full extent of the mining operation. A subsequent dig in 1997 added further detail to the picture. In 2015, the Japanese government designated Hoshigato a National Historic Site, recognizing its importance as evidence of Jomon-period resource extraction and trade. Today, no public facilities exist at the site. Access is controlled by the Shimosuwa Town Board of Education, preserving the 193 pits in the quiet of the Higashimata forest exactly as centuries of mountain weather have shaped them. The Hoshigato Museum Yanoneya in nearby Shimosuwa displays artifacts recovered from the site, offering visitors a tangible connection to the miners who once worked these slopes.

Hoshigato does not stand alone. The Kirigamine Highlands and the broader Yatsugatake region form one of Japan's most important obsidian source areas, with multiple extraction sites scattered across the volcanic landscape. The area has been designated part of a Japan Heritage story celebrating the Jomon culture of the Central Highlands, linking obsidian mines, pottery workshops, and settlement sites across Nagano and Yamanashi prefectures. From the air, the forested ridgelines reveal nothing of the industry that once thrived beneath the canopy. But underfoot, the 35,000 square meters of interconnected mining pits remain -- shallow depressions in the earth that once fed a continent-spanning appetite for the sharpest material the natural world could provide.