Geoarchaeology of Holocene Terrace Deposits Near Glenns Ferry, Idaho

Sediments associated with archaeological sites provide information that can be used to infer local formational processes and broader-scale environmental conditions. Laboratory studies were conducted of sediment samples collected as part of the 2009 Boise State University Archaeological Field School excavations near Glenns Ferry, in southwestern Idaho. The site, 10-EL-216, is on a Holocene-aged terrace running along the west bank of the Snake River. The terrace landform can be interpreted as the product of alluvial and aeolian erosion and deposition. For instance, large boulders near the excavation site were deposited about 14,500 radiocarbon years ago by the Bonneville flood. Since that event, wind has transported loess across the landscape and alluvial processes have been active within the floodplain of the Snake River. Stratigraphic samples were collected from river bank profiles and a series of excavation units that were dug at intervals spreading approximately 120 m north to south across the terrace. Sediment samples were collected from various strata within these units. The sediment samples from the site were analyzed to contribute to the understanding of the depositional formation processes related to the site. The data obtained from sediment analysis – including particle size distribution, percent carbonate, and mineral composition – were used to construct a stratigraphic cross-section which shows the vertical and horizontal features of the terrace and to evaluate late Quaternary environments