The Tokoro River is the largest river flowing into the Sea of Okhotsk in Hokkaido. In its lower basin in the coastal area of Tokoro Town, Kitami City, some of the largest-scale prehistoric sites in Japan are gathered including the national historic site, the "Tokoro Site." The most remarkable aspects of these archaeological sites are the conditions of pit houses preserved on the coastal dunes as depressions with small long-term post disturbances until the present day. The more than 3,000 pit houses include residences from the Jomon, Epi-Jomon, and Satsumon ages, as well as those of the Okhotsk culture—a maritime ethnicity from the north. In addition to pit houses, various archaeological sediments have been found including late Upper Paleolithic sites, shell mounds of Jomon, sending-back sites, and chashi ruins of Ainu culture. Signs of human activities almost uninterrupted for more than 20,000 years can be detected, which is also an important characteristic of the sites.

In 1957, archaeological excavations in Tokoro Town, Kitami City were initiated by the Department of Archaeology, Faculty of Letters at the University of Tokyo. Since then, investigations have been carried out annually. Through the formation of bases for area studies such as establishment of the Tokoro Field Laboratory (1967) and the Tokoro Research Laboratory of the University of Tokyo’s Faculty of Letters (1973), academic excavations in the form educational training in field archaeology for students have continued until today. Artifacts unearthed at excavations for more over 60 years are currently stored in the Tokoro Research Laboratory, and are exhibited to the public at the Tokoro Gallery of Archaeological Finds of the University of Tokyo.

In addition, a preliminary survey of buried cultural property associated with development activities of the Tokoro area was started by Kitami City (former Tokoro Town) in 1975, and since then preliminary surveys have been executed several times. In particular, excavations at the Tokoro River Estuary Site in the mouth of the Tokoro River from 1988 to 2002 yielded a large number of artifacts that exceeded the total materials of the University. These artifacts found during the preliminary survey have been stored at Kitami City's Tokoro Buried Cultural Property Center, and exhibited to the public at “Tokoro Archaeological Museum (Tokoro Iseki no Yakata)”.