[1] The site is located about 4.4 km west-southwest of JR East Kiryū Station at an elevation of 196.2 meters above sea level, and is a cutting through the central saddle of two hills extending from northeast to southwest.

The site was discovered in 1947 by a seller of nattō and amateur archaeologist Aizawa Tadahiro, who passed through this cutting every day on his way to work.

Site A was located on the north side of the hill and contained many stone tools buried between two distinct layers of red soil.

[4] Due to the acidic nature of the volcanic ash from which the red soil strata is made, little other than stone implements has been discovered in the Iwajuku excavations.

Large game animals such as the now extinct Naumann elephant, along with brown bears, giant deer, tigers, wolves and monkeys inhabited the area.

Over 180 stone tools were found in this layer, with materials including chert, obsidian, andesite, shale, hornfels, and agate.