ALLUVIAL STYLES AFFECT THE ARCHEOLOGICAL SETTLEMENT RECORD, WITH EXAMPLES FROM THE MISSOURI, RED, MISSISSIPPI RIVER VALLEYS

The record of human occupation in alluvial settings varies with the alluvial style of the river, resulting in archeological records controlled by three factors; location of occupation, preservation, and recognition of the sites. The variable alluvial styles of the lower Missouri River, lower Red River, and the lower Mississippi River valleys present opportunities and constraints to occupation and sustained settlement, and resulted in widely varying archaeological patterns that are partly dependent upon the geomorphology. Prehistoric human occupation of the narrow Missouri valley floor is limited, with only 0.061 recorded sites/km2. Additional sites are likely buried by thick vertical accretion sediment on the limited prehistoric portions of the floodplain and within valley-margin alluvial/colluvial fans. The absence of sites from the youngest cultural period, are attributed to shifts in settlement patterns. Prehistoric occupation of the lower Red and Mississippi rivers was much more extensive than that of the Missouri River and the density of occupation is 0.274 sites/km2 and 0.277 sites/km2 respectively. Many sites along the active meander belt of the Red River were lost due to high rates of channel migration but many significant sites have been preserved. The wide valley and high rates of sedimentation suggest that many sites are likely buried, particularly along natural levees. Recorded sites are also present along streams that incise the terrace, along the terrace margin, and along small channels that cross the backswamp. Spatial and temporal site distribution along the lower Mississippi valley is distinct because the Mississippi valley is wide, terraces are young and not highly dissected, and the floodplain has relief so that it is not broadly inundated by floodwater with relatively low sediment concentrations; thus sites are not likely to be buried or eroded. Most of the significant Archaic through Mississippian period floodplain sites are located along the surfaces of abandoned Mississippi and distributary meander belts which aggraded above the backswamp. Abundant Paleo-Indian through Mississippian period sites are also distributed across undissected terraces. Only a few significant Mississippian sites are present along the active meander belt and in the backswamp where flooding was common