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Lithologic classifications of river gravels in the Sauk River watershed

January 3, 2022

The rock type, or lithology, of river gravels provides information about the bedrock source area of that material, and can act as a tracer to help assess relative gravel contributions from tributaries or distinct valley deposits. Between July 2020 and August 2021, gravels at 29 sites in the Sauk, Suiattle and White Chuck rivers were collected and sorted into simple lithologic categories. The data release here provides a summary of those raw data. These data support analyses presented in Anderson et al. (2022). Each row of the attached comma-separated value (CSV) file reports masses, in kilograms, of gravel in various lithologic categories for a given sample. Each sample consisted of 25-30 kg of gravel with intermediate-axis diameters between 32 and 64 mm. Three to four samples were generally collected at a given site. The majority of gravels were collected from active low-relief gravel bars. Additional samples were collected from river gravels contained in a low terrace flanking the contemporary active channel of the Sauk River. Gravel was sorted into a maximum of six possible lithologic classes. These include a vesicular dacite associated with Glacier Peak, other extrusive volcanics, intrusive igneous material, foliated metamorphics, greenschist, and 'other.' At a number of sites, only the dacite and other extrusive material was were sorted out, with the remaining clasts lumped into the 'other' category. At a few sites, this was further reduced to just the dacite, with all other material lumped in 'other.' The PDF in this data release contains more details on these lithologic categories.