The California State Water Resources Control Board (State Water Board) initiated the Oil and Gas Regional Monitoring Program (RMP) to assess effects of oil and gas development on groundwater designated for any beneficial use. The U.S. Geological Survey (USGS) is the technical lead in conducting the RMP through the California Oil, Gas, and Groundwater (COGG) Program, working in cooperation with the State Water Board, and in partnership with other State and local agencies. The USGS collected and analyzed groundwater, surface water, and associated quality control (QC) samples in the Poso Creek Oil Field study area during February 2020-December 2021. Groundwater samples were collected from eleven irrigation, two domestic, two public supply, four monitoring wells, two institutional wells, and two surface water sites located within a five km buffer zone surrounding the Poso Creek Oil Field in Kern County, California. Samples were collected using established groundwater data-collection protocols and procedures. Samples were analyzed for water-quality indicators, major and minor ions, nutrients, trace elements, volatile organic compounds (VOCs), naturally occurring radioactive material, geochemical and age-dating tracers, dissolved organic carbon (DOC), dissolved standard and hydrocarbon gases (methane through hexane), and dissolved noble gasses, atmospheric gases, and surrogates. Approximately two hundred and eight constituents and water-quality indicators were measured. QC samples analyzed as part of the Poso Creek Oil Field study included replicates, source-solution blanks, field and equipment blanks, and laboratory spikes and surrogates.