How were these delicate artifacts preserved for so long? Were the baskets discarded along the riverbank? Was the site abandoned after flooding?
The Biderbost site is partially made up of what is known as a wet site. Archaeological wet sites exist when waterlogged perishable artifacts like wood and basketry are preserved in an oxygen-free environment. The lack of oxygen inhibits the decay of organic materials by slowing bacteria growth, allowing wood objects to survive for thousands of years. In most cases, organic materials decay quickly and are not preserved in archaeological sites, making collections like Biderbost exceptional. Its location at the confluence of a small tributary and the Snoqualmie River create wet conditions almost year-round. After centuries of flooding, the artifacts were protected under layers of water-saturated soil.
Archaeological Investigation at Biderbost
At the time of the first excavation in 1960 by the Washington Archaeological Society, standard methods for the excavation of water-saturated sites had not been widely developed. The dig crew had to excavate in soggy conditions for most of their field excursions. In fact, it was so wet and muddy that crewmembers entertained the idea of naming it the "Hog-wallow site" (Nordquist 1960).
Radiocarbon Date of the Biderbost Site
One charcoal sample from the dry, upper portion of the site yielded an uncalibrated radiocarbon date of 2,000 ± 80 BP (Before Present). So far, the basketry artifacts have not been directly dated using radiocarbon dating methods. This would require a sample of the basketry to be used for dating. However, the date of 2,000 years ago can be inferred from indirect dating methods. By comparing Biderbost basketry stylistic traits to baskets from other sites, like Water Hazard in British Columbia (1700 BP), we can surmise that these artifacts are of similar age. The similarity in basketry from these two sites has been interpreted as evidence of a wide geographical range of interaction between cultural groups during this time period, nearly 2,000 years ago (Bernick 1998).
Video by Allison Deep
Photograph by Burke Museum