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Grain-size data for sediment samples collected in Whiskeytown Lake, northern California, in 2018 and 2019

July 12, 2021

The Carr Fire ignited in northern California in July 2018, and ultimately burned almost 300,000 acres (approximately half on federal lands), resulting in a federal major-disaster declaration (DR-4382). Approximately 93% of the area within Whiskeytown National Recreation Area was burned extensively during the Carr Fire, including all of the landscape surrounding and draining into Whiskeytown Lake. Whiskeytown Lake, a federally managed reservoir, subsequently acted as a sediment trap for material eroded from hillslopes and streambeds in the aftermath of the Carr Fire. The U.S. Geological Survey measured topographic change associated with sediment deposition and erosion in and around Whiskeytown Lake after the Carr Fire, in order to support calculations of post-fire sediment yield from the surrounding landscape. This data release includes grain-size data from sediment samples collected in submerged and subaerial regions in Whiskeytown Lake and around the reservoir margin. Data collection and analysis have been supported by funds through H.R. 2157, the Additional Supplemental Appropriations for Disaster Relief Act of 2019. Samples were collected using a Van Veen grab sampler deployed from a boat (the R/V San Lorenzo), or by hand from subaerial regions. Sediment grain size was analyzed at the USGS laboratory in Santa Cruz, Calif. Particles coarser than 2 mm were sieved using a RO-TAP sieve shaker, and particles finer than 2 mm were analyzed with a Coulter laser particle-size analyzer (LPSA), after organic matter had been removed using a hydrogen peroxide solution. Several months after the samples were analyzed, a problem was discovered with the LPSA that had caused inaccurate measurement of the coarse silt content (sizes approximately from 0.040 to 0.063 mm). Grain-size distribution of particles coarser than 0.063 mm is thought to have been unaffected, and the proportions of silt (0.040 to 0.063 mm) and clay (finer than 0.004 mm) also were thought to have been measured accurately. The full data set is reported here, but users should be aware that due to this instrument error the data between approximately grain sizes from 0.040 to 0.063 mm may be over-estimated and have unknown degrees of uncertainty. Proportions of gravel, sand, silt, and ratios among these size fractions, are considered accurate.