This portion of the data release presents sediment grain-size data from samples collected on the Elwha River delta, Washington, in July 2018 (USGS Field Activity 2018-648-FA). Surface sediment was collected from 39 locations using a small ponar, or 'grab', sampler from the R/V Frontier in water depths between about 1 and 17 m around the delta. An additional 35 samples were collected by hand at low tide. A hand-held global satellite navigation system (GNSS) receiver was used to determine the locations of sediment samples. The grain size distributions of suitable samples were determined using standard techniques developed by the USGS Pacific Coastal and Marine Science Center sediment lab. Grab samples that yielded less than 50 g of sediment were omitted from analysis. The grain-size data are provided in a comma-delimited spreadsheet (.csv).