The U.S. Geological Survey collected water-quality samples from 3,359 sites between May 2004 and November 2024 for the California Groundwater Ambient Monitoring and Assessment Program Priority Basin Project (GAMA-PBP). The GAMA-PBP is a cooperative project with the California State Water Resources Control Board (SWRCB). The primary objectives of the GAMA-PBP are: (1) to assess the quality of groundwater resources used for public and domestic drinking water supplies, (2) to develop understanding of the natural and anthropogenic processes controlling groundwater quality and changes in groundwater quality, and (3) to improve the availability and usefulness of groundwater quality information to public. This data release publishes site type information and a generalized use category for the sites. The dataset comprises 3,213 wells, 81 springs, and 65 other types of sites. The generalized use category is partially derived from, but is not equivalent to, the use of site and use of water fields from the USGS National Water Information System (NWIS) data archive. Of the 3,063 wells and springs from which water is withdrawn for use, 1,696 are classified as production (includes sites used for public, commercial, industrial, institutional, and desalination water supplies), 1,123 as domestic, 263 as irrigation, and 16 as other water supply uses. Of the remaining sites, 229 are classified as observation wells, 6 are wells and springs from which water is withdrawn and not used, 63 are distribution system taps, and 4 are other types of sites. GAMA-PBP data are also served to the public through the SWRCB's GAMA Groundwater Information System (GAMAGIS), along with data from other federal, state, and local agency sources, and the generalized use categories in this data release are compatible with the use categories in SWRCB GAMAGIS. Prior to publication of this data release, SWRCB GAMAGIS classified all GAMA-PBP sites as "municipal", which resulted in erroneous characterization of approximately half of the sites. The generalized classification provided in this data release greatly improves the accuracy of site characterization, while still complying with Federal policies concerning release of location information for some types of sites. Version 1.0 posted September 29, 2021 Version 2.0 posted September 2, 2022 Version 3.0 posted October 25, 2023 Version 4.0 posted April, 2025