The archaeological record varies with the fluvial style and sedimentation of a river, thus controlling the location, preservation, and recognition of archaeological sites. This project identifies archaeological site patterning and preservation along a fluvial system in Iowa that has been relatively stable since the last glaciation. The Upper Des Moines River in Iowa formed approximately 12,500 yr. cal BP as an englacial channel routing glacial meltwater south along the Des Moines Lobe. During the last glacial retreat, the channel incised forming what is now called the High Terrace (TH). Early post-glacial occupations in Iowa would have had access to this the high terrace and uplands. Thus, the Paleoindian and early to middle Archaic site distributions along the Upper Des Moines River are found in upland and upper terrace locations. The intermediate terrace (TI) formed between 4000 and 1000 yr. cal BP and represents the elevation of the river flood plain during this period. Late Archaic people had access to this surface as well as the TH and uplands. By 1000 yr. cal BP, the Upper Des Moines River had eroded down to bedrock and established a floodplain at the level of the lower terrace. Subsequent erosion produced the modern channel configuration with an established series of dated terraces (High Terrace (TH), Intermediate Terrace (TI), and Low Terrace (TL)). The Woodland period peoples would have had access to the current/modern fluvial landscape.
To assess site locations strategies of populations that inhabited the Upper Des Moines River valley in the Holocene, 721 archaeological sites were examined and classified using site reports and artifacts as Paleoindian, Archaic, Woodland, Historic and Unknown. The sites were then mapped and associated with geomorphic features in the valley. As expected, Paleoindian sites and Early to Middle Archaic sites were all located on the upper terrace and uplands because the intermediate and lower terraces had not yet formed. Late Archaic people had access to the floodplain that formed intermediate terrace as well as the uplands and upper terrace. Woodland period sites occurred on high (upland and TH), intermediate (TI), and low (TL and floodplain) elevation landforms along the river. The study demonstrated there was a preference for burials/ceremonial sites being placed at higher elevations (TI and higher) and habitation sites being placed at lower elevations (TL and current floodplain) near the main river channel.