SPATIAL AND TEMPORAL PATTERNS OF HOLOCENE OCCUPATIONS IN ALUVIAL AND COLLUVIAL LANDSCAPES OF THE SALT RIVER VALLEY REGION, MISSOURI, USA: A GEOARCHAEOLOGICAL STUDY

Required archaeological study of the Rockies Express Pipeline-East (REX-East) project corridor demonstrated the need for all three levels of archaeological investigation from Phase I survey to Phase 3 mitigation. The 43.05 mile-long (69.2-km) project corridor ran through Audrain, Ralls, and Pike counties in northeastern Missouri before crossing the Mississippi River and entering Illinois. A broad geomorphological investigation was performed through the use of soil cores and deep trenches to help inform the archaeological survey and subsequent site investigations.

The University of Iowa Office of the State Archaeologist (OSA) and AMEC Earth and Environmental conducted Phase III investigations at six prehistoric archaeological sites: 23PI294, 23PI1337, 23PI1344, 23PI1365, 23PI1367, and 23PI1372. All six sites are located in Pike County, Missouri, on Holocene and late Wisconsinan terraces of the Salt River and its tributary, Grassy Creek. The Salt River is a major tributary to the Mississippi River in the upper Mississippi valley. The six sites are located on alluvial and colluvial features commonly seen in this region of the mid-continent. Site 23PI924 is located on late Holocene and Wisconinan fluvial terraces, 23PI1337 is located on an early-middle Holocene alluvial fan, 23PI144 is located on a late Wisconsin or early Holocene terrace remnant, while 23PI1365, 23PI1367, and 23PI1372 are located on coalesced bar and terrace landforms. Phase III geomorphological study of the six sites, again through the use of coring and trenching, led to better understanding the relationship of the sites to their individual landforms, and their terrace and floodplain environments.

Cultural deposits from the sites date the sediments to the early through late Holocene, locally veneered by Historic alluvium. Historical land-cover information and geologically-defined lithofacies help reconstruct the past environments the sites likely existed in. The resulting landscape reconstructions are used to compare these sites to each other and to other regional and local site location patterns. Preliminary results indicate that the spatial and temporal locations of sites depend primarily on the presence or absence of water and the stability of landforms, and secondarily on resource availability.