This digital dataset contains historical geochemical and other information for 45 samples of produced water from 38 sites in the Placerita and Newhall Oil Fields in Los Angeles County, southern California. Produced water is a term used in the oil industry to describe water that is produced from oil wells as a byproduct along with the oil and gas. The locations from which these historical samples have been collected include 17 wells, 6 storage tanks, and 15 unidentifiable sample sources. Well depth, perforation depths, and (or) depths referred to on geochemistry reports as interval of zone produced, are available for all 17 wells. Designated well use and sample descriptions provide further insight about what the samples represent. The well use designation for 13 of the wells is OG (oil/gas). The samples (16) associated with these wells likely represent produced water based on well designation and history, although samples from two wells (Dataset ID 23 and 32) are described as formation water. Four wells have a site type designation of "injectate" based on the current designated well use (INJ, injection; or WD, water disposal), but samples from two of the four wells (Dataset ID 31 and 35) likely represent produced or formation water as well history records indicate that sample collection predated conversion to (Dataset ID 31) or the commencement of (Dataset ID 35) use for water disposal. Limited information is available about historical samples from storage tanks and unidentifiable sample sources. These samples may represent pre- or post-treated composite samples of produced water from single or multiple wells. The numerical water chemistry data were compiled by the U.S. Geological Survey (USGS) from the following sources: scanned laboratory analysis reports available from the California Geologic Energy Management Division (CalGEM) Underground Injection Control (UIC) program, analytical reports located within well history files in CalGEM's online Well Finder (WF) database, analytical reports available as PDFs (Portable Document Format) documents located on the State Water Resources Control Board GeoTracker (SWRCB-GT) website, and data compiled by the USGS for the National Produced Water Geochemical Database (USGS PWDB). Sample site characteristics, such as well construction details, were attributed using a combination of information provided with the scanned laboratory analysis reports and well history files from CalGEM Well Finder. The compiled data are divided into two separate data files described as follows: 1) a summary data file identifying each site by name, the site location, basic construction information, and American Petroleum Institute (API) number (for wells), the number of chemistry samples, period of record, sample description, and the geologic formation associated with the origin of the sampled water, or intended destination of the sample (formation into which water was to intended to be injected for samples labeled as injectate), specific sample dates for each site, and an inventory of which constituent groups were sampled on each date; and 2) a data file of geochemistry analyses for selected water-quality indicators, major and minor ions, nutrients, trace elements, dissolved organic carbon (DOC), naturally occurring radioactive material (NORM), tracers, semi-volatile organic compounds (SVOCs), volatile organic compounds (VOCs), hydrocarbons, and organic acids. Ion (charge) balance calculations and percent error of these calculations were included for samples having a complete suite of major ion analyses. Analytical method, reporting level, reporting level type, and supplemental notes were included where available or pertinent. A data dictionary was created to describe the geochemistry data file and is provided with this data release.