Splits of samples were prepared of heavy mineral separates and bulk separates less than 2mm for analysis using X-ray diffraction (XRD) and results were interpreted to identify mineral components as part of a study examining the occurrence of chromium and natural and anthropogenic hexavalent Chromium, Cr(VI), in groundwater. Data will be used to estimate naturally-occurring background Cr(VI) concentrations upgradient, near the plume margins, and downgradient from a mapped Cr(VI) contamination plume near Hinkley, CA (Izbicki and Groover, 2016). These XRD results are part of a data release including grain size distribution, photographic, and associated chemical and mineral analysis data for 36 sediment core and alluvium samples as well as select grains from magnetic and heavy mineral separates collected near Hinkley, CA. The cooperator for this study is the Lahontan Regional Water Quality Control Board. Results are provided in this data release organized by analysis type.