The Koster site is an ancient, deeply buried archaeological site located on Koster Creek, a narrow tributary stream incised into the alluvial deposits of the lower Illinois River Valley. The Illinois River is itself a major tributary of the Mississippi River in central Illinois and the site lies only about 48 kilometers (30 miles) north of where Illinois meets the Mississippi today at the town of Grafton. The site is stunningly important in North American prehistory, for its well-preserved human occupations dating back nearly 9,000 years, and the impact of its discovery so deep within the alluvial fan.

Chronology

The following chronology is derived from Struever and Holton; the horizons were what was visible in the field, although later analysis proved there were 25 distinct occupations in Koster's stratigraphy.

Horizon 1, Mississippian, AD 1000-1200

Horizon 1b, Middle-Late Woodland (Black Sand phase), AD 400-1000

Horizon 2, Early Woodland (Riverton), 200-100 BC

Horizon 3, Late Archaic, 1500-1200 BC

Horizon 4, Late Archaic, 2000 BC

Horizon 5, Middle-Late Archaic

Horizon 6, Middle Archaic (Helton phase), 3900-2800 BC, 25 human burials

Horizon 7, Middle Archaic

Horizon 8, Middle Archaic, 5000 BC

Horizon 9, Middle Archaic, 5800 BC

Horizon 10 Early-Middle Archaic, 6000-5800 BC

Horizon 11, Early Archaic, 6400 BC, 9 human burials, 5 dog burials

Horizon 12, Early Archaic

Horizon 13, Early Archaic (Kirk notched point), 7500-6700 BC

Horizon 14, sterile

At the surface, Koster covers an area of approximately 12,000 square meters (about 3 acres), and its deposits extend more than 9 meters (30 feet) into the river's alluvial terraces. The site is at the contact between the limestone bluffs and upland loess plains to the east and the Illinois River floodplain to the west. Occupations present within the date of the deposit from Early Archaic through the Mississippian period, radiocarbon-dated to between about 9000 to 500 years ago. During most of the prehistoric occupation of the site, the Illinois River was located 5 km (3 mi) to the west with a seasonally fluctuating backwater Lake within one km (half-mile). Chert sources for making stone tools are in the nearby limestone bluffs lining the valley and included Burlington and Keokuk, sources which vary in quality from fine-grained to coarse-grained.

Site Discovery

In 1968, Stuart Struever was a faculty member in the anthropology department at Northwestern University in Evanston, Illinois. He was a "down-stater," however, having grown up far from Chicago in the small town of Peru, Illinois, and he never lost the ability to speak the language of the down-stater. And so it was that he made true friendships among the landowners of the Lowilva, the local name for the Lower Illinois Valley, where the Mississippi River meets Illinois. Among the life-long friends he made were Theodore "Teed" Koster and his wife Mary, retired farmers who just happened to have an archaeological site on their property, who just happened to be interested in the past.

Struever's investigations (1969-1978) at Koster farm revealed not only the middle and early late Woodland materials reported by the Kosters but a stratified multi-component archaic period site of astonishing depth and integrity.

Archaic Occupations at Koster

Beneath the Koster farm lies evidence of 25 different human occupations, beginning with the early Archaic period, around 7500 BC, and ending with the Koster farm. Village after village, some with cemeteries, some with houses, beginning some 34 feet below the modern Koster farmstead. Each occupation was buried by the deposits of the river, each occupation leaving its mark on the landscape nonetheless.

Probably the best-studied occupation to date (Koster is still the focus of many graduate theses) is the set of Early Archaic occupations known as Horizon 11, dated 8700 years ago. Archaeological excavations of Horizon 11 have revealed a thick midden of human occupation residues, basin-shaped storage pits and hearths, human graves, diverse stone, and bone tool assemblages, and floral and faunal remains resulting from human subsistence activities. Dates on Horizon 11 range from 8132-8480 uncalibrated radiocarbon years before the present (RCYBP).

Also in Horizon 11 were the bones of five domesticated dogs, representing some of the earliest evidence for the domestic dog in the Americas. The dogs were purposefully buried in shallow pits and they are the earliest known dog burials in North America. The burials are essentially complete: all of them are adults, none exhibit evidence of burning or butchery marks.

Impacts

In addition to the vast amount of information garnered about the American Archaic period, the Koster site is also important for its long-term interdisciplinary research efforts. The site is located near the town of Kampsville, and Struever set up his lab there, now the Center for American Archaeology and a major center of archaeological research in the American Midwest. And, perhaps most importantly, the Northwestern University excavations at Koster proved that ancient sites could be preserved hidden deep beneath the valley floors of major rivers.

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