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. The Redding-Red Bluff Shallow Aquifer study unit consisted of 2 study areas corresponding to 11 groundwater subbasins (subbasins listed clockwise beginning in the north): Enterprise, Millville, South Battle Creek, Bend, Antelope, Dye Creek, Los Molinos, Red Bluff, Bowman, Rosewood, and Anderson (California Department of Water Resources, 2003). Wells in the study unit were located in alluvial aquifers composed of sediments derived from the Coast Ranges to the west and the Cascades to the east of the study unit. Each of the two study areas were divided into equal area grid cells and the goal was to sample one well in each cell. This dataset identifies the boundaries and grid cells for the two study areas of the Redding-Red Bluff Shallow Aquifer Study Unit. 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