CENTRAL WASHINGTON UNIVERSITY FIELD SCHOOL: WENAS CREEK MAMMOTH SITE - INITIAL DISCOVERY AND INVESTIGATION

Finds of isolated, single mammoth elements are common in Central and Eastern Washington, but in most cases, these bones have been recovered without due documentation of their stratigraphic and spatial contexts. Another isolated find was made in February 2005 when contractors working on a private road on lands belonging to Mayo Ranches, northwest of Selah, Washington, discovered fragments of the left humerus of a mammoth (Mammuthus sp.). The site is positioned on a bench approximately 21 m above the Wenas Creek floodplain on a northeast facing slope, about 415 m above sea level; some 95 m in elevation above and roughly 12 km northwest of the furthermost reaches of the Missoula flood deposits. Given this location and the landowner's supportive interest, Central Washington University initiated a field school in June. The field school provided students with hands-on experience in designing and implementing scientific research using both archaeological and palaeontological techniques. The primary objective of our field school was to document the geographic and geologic context of this mammoth site. A total of 37 m of trench was excavated into the bench by backhoe, both parallel and perpendicular to the find location, to document the depositional history of the slope. Stratigraphy at the site includes alluvium, colluvium, and reworked loess deposits. Additional research was carried out to recover further palaeontological data from this location. As part of this secondary objective, a ground-penetrating radar (GPR) survey was completed in two grids located up- and down-slope from the find. Tentative GPR results indicated a few anomalies in both sections, and these were subsequently investigated using 2m by 2m test excavation units. Each unit was excavated in 10 cm levels, with the sediment from each level screened through 3.175 mm (1/8 inch) mesh. Additionally, a five percent sub-sample of each unit was wet sieved through 1 mm sieves. As reconstructed, the humerus was roughly 100 cm in length, with both epiphyses fully fused. A sample of the mammoth humerus was submitted for AMS radiocarbon dating. The Wenas Creek mammoth represents the northernmost documented record of indigenous mammoth in the greater Yakima River drainage, and the first evidence of this genus in the Wenas Valley.