GEOMORPHIC STUDY OF THE OHANAPECOSH RIVER: ESTIMATING ANADROMOUS FISH DISTRIBUTION UP TO 8,000 YA TO AID ARCHAEOLOGICAL INVESTIGATIONS, MOUNT RAINIER NATIONAL PARK

The Ohanapecosh River is a 16-mile river located in the southeast portion of Mount Rainer National Park, Washington. In this study we develop a protocol for unraveling the Quaternary geomorphologic history of a ~5 mi stretch of Ohanapecosh River, from La Wis Wis Campground to Silver Falls, and its impacts on anadromous fish runs up to 8,000 ya. Pre-European contact humans relied on anadromous fish as a rich food source, and the furthest anadromous fish migration limits typically corresponded to the upstream limit of year-round human settlements. Archaeological sites indicating human presence have been identified at Ohanapecosh Campground; however, concurrent fish presence has not been established. Coho salmon and steelhead trout are among the current anadromous fish distribution, their runs halted by Silver Falls, located ~1.5 mi upstream from Ohanapecosh Campground. Other knickpoints and natural barriers such as log jams, debris flows and rock falls may have hindered past anadromous fish runs. These changes in river morphology were likely driven by climate-changing conditions and vegetative patterns that could be investigated using erosional history analysis and forest evolution data. Understanding the extent of anadromous fish habitats up to 8,000 ya along the Ohanapecosh River can be used as a surrogate for early human presence in the park. Developing a protocol for identifying changes in Quaternary river geomorphology can be a key insight to understanding landform morphology on a thousand-year time scale. Additionally, the results can help archaeologists reconcile current knowledge of pre-European contact human habitation with fish use, and potentially guide future investigations.