The U.S. Geological Survey collected groundwater samples from 50 wells used for domestic and small system drinking water supplies in Shasta and Tehama Counties, California in 2018-2019. The wells were sampled for the Redding-Red Bluff Shallow Aquifer Study Unit of the California State Water Resources Control Board Groundwater Ambient Monitoring and Assessment (GAMA) Program Priority Basin Project’s assessment of the quality of groundwater resources used for domestic and small system drinking water supplies. Domestic and small-system wells are commonly screened at shallower depths than public-supply wells. Wells in the study unit generally tap unconsolidated to moderately consolidated coarse and fine-grained sediments derived from the northern Coast Ranges to the west and the Cascade Range to the east. The Redding-Red Bluff Shallow Aquifer study unit included 11 groundwater subbasins of the Sacramento Valley groundwater basin (California Department of Water Resources, 2003) and was divided into two study areas: Redding (Enterprise, Millville, South Battle Creek, Bowman, Rosewood, and Anderson) and Red Bluff (Bend, Antelope, Dye Creek, Los Molinos, and Red Bluff). In each study area, the collective area of all one-mile square sections estimated to contain domestic wells (Johnson and Belitz, 2015) was divided into equal-area grid cells, and a well was sampled in each cell: Redding, twenty-five 48-square kilometer cells, and Red Bluff, twenty-five 43 square kilometer grid cells. Groundwater samples from all 50 wells were analyzed for field water-quality parameters and microbial indicators, volatile organic compounds, pesticides and pesticide degradates, major ions and trace elements, chromium (VI), perchlorate, nutrients, gross alpha and gross beta particle activities, carbon-14 in dissolved inorganic carbon, stable isotopic ratios of water, tritium, sulfur hexafluoride, and noble gases. Groundwater levels were measured in 41 of the 50 wells. All results are presented in this data release, except results for sulfur hexafluoride and noble gases. This data release supports the following publication: Groundwater quality in the Redding-Red Bluff Shallow Aquifer Study Unit of the Northern Sacramento Valley, California: U.S. Geological Survey Fact Sheet 2020–3025, 4 p., https://doi.org/10.3133/fs20203025.