In conjunction with the release of California’s Groundwater Update 2020, DWR has compiled a comprehensive list of the official basin boundary descriptions for all of California’s 515 groundwater basins. These descriptions were originally developed by DWR as part of California’s Groundwater (B-118) Update 2003 and have since been updated for some groundwater basins as a result of the 2016 and 2018 Basin Boundary Modifications. To make locating descriptions easier, they have been organized by region which is determined by the first number of the basin number (i.e. 1-XXX).

The original basin descriptions developed for California’s Groundwater (B-118) Update 2003 also included summaries of the hydrologic and hydrogeologic setting, groundwater storage capacity and water budget, groundwater level and quality trends, well yields, basin management, and references. This additional information contained in the basin descriptions will now be referred to as “basin reports” and are still available online as part of the Bulletin 118 - Update 2003 report.

The following data and resources were used for the SGMA Basin Prioritization of California’s 515 groundwater basins and subbasins. The Department of Water Resources is mandated by California Water Code Section 10933(b) to prioritize each basin based on eight components.

For more information about how the data was analyzed for Basin Prioritization please see Sustainable Groundwater Management Act Basin Prioritization - Process and Results Document.

Additional questions or requests for information related any of the Basin Prioritization datasets should be directed to the Sustainable Groundwater Management Office at sgmps@water.ca.gov.

For more information on SGMA Basin Prioritization please visit the SGMA Basin Prioritization Homepage.

In conjunction with the release of California’s Groundwater Update 2020, DWR has compiled a comprehensive list of the official basin boundary descriptions for all of California’s 515 groundwater basins. These descriptions were originally developed by DWR as part of California’s Groundwater (B-118) Update 2003 and have since been updated for some groundwater basins as a result of the 2016 and 2018 Basin Boundary Modifications. To make locating descriptions easier, they have been organized by region which is determined by the first number of the basin number (i.e. 1-XXX). The original basin descriptions developed for California’s Groundwater (B-118) Update 2003 also included summaries of the hydrologic and hydrogeologic setting, groundwater storage capacity and water budget, groundwater level and quality trends, well yields, basin management, and references. This additional information contained in the basin descriptions will now be referred to as “basin reports” and are still available online as part of the Bulletin 118 - Update 2003 report.

Ten hydrogeologic provinces of California are represented by a region- class feature called "provinces" within this digital data set. These provinces were identified and defined in the USGS Water Resource Investigation Report (WRIR) 03-4166 (Belitz and others, 2003) titled, "Framework for a Ground-water Quality Monitoring and Assessment Plan for California". Hydrogeologic provinces are generalized areas where hydrology and/or geology have similar characteristics. The Southern Cal Islands group was not previously defined as a province in WRIR 03-4166, and is therefore identified as a group in this dataset. These provinces were created by grouping polygons from two formally created digital data sets into respective provinces. New polygons were created where necessary. The two digital data set sources consisted of watershed polygons (calwater) and groundwater basin polygons (gw_basins) compiled to create an original publication of hydrogeologic province boundaries in the form of a region-class within the data set. By symbolizing on the region- class, the user can view the ten hydrogeologic provinces and one grouped province in their simplest representation, without watershed and ground- water basin boundaries obscuring the province areas. Original polygons for both the watershed data set and the ground-water basin data set were retained as much as possible.

The dataset is a feature class showing the boundaries of 515 groundwater basins and subbasins as defined by the California Department of Water Resources as last modified by the Basin Boundary Emergency Regulation adopted on October 21, 2015 and subsequent modifications requested through the Basin Boundary Modification Request Process. This data is current as of December 9, 2022. The file is in ESRI geodatabase format and is intended for use with compatible GIS software. Groundwater basins are represented as polygon features and designated on the basis of geological and hydrological conditions - usually the occurrence of alluvial or unconsolidated deposits. When practical, large basins are also subdivided by political boundaries, as in the Central Valley. Basins are named and numbered per the convention of the Department of Water Resources.

DWR has a long history of studying and characterizing California’s groundwater aquifers as a part of California’s Groundwater (Bulletin 118). California's Groundwater Basin Characterization Program provides the latest data and information about California’s groundwater basins to help local communities better understand their aquifer systems and support local and statewide groundwater management.

Under the Basin Characterization Program, new and existing data (AEM, lithology logs, geophysical logs, etc.) are integrated to create continuous maps and three-dimensional models. To support this effort, new data analysis tools have been developed to create texture models, hydrostratigraphic models, and aquifer flow parameters. Data collection efforts have been expanded to include advanced geologic, hydrogeologic, and geophysical data collection and data digitization and quality control efforts will continue. To continue to support data access and data equity, the Basin Characterization Program has developed new online, GIS-based, visualization tools to serve as a central hub for accessing and exploring groundwater related data in California.

Additional information can be found on the Basin Characterization Program webpage.

DWR's Evaluation of Groundwater Resources

Maps and Models

DWR is undertaking local, regional, and statewide investigations to evaluate California's groundwater resources and develop state-stewarded maps and models. New and existing data have been combined and integrated using the analysis tools described below to develop maps and models that describe grain size, the hydrostratigraphic properties, and hydrogeologic conceptual properties of California’s aquifers. These maps and models help groundwater managers understand how groundwater is stored and moves within the aquifer. The models will be state-stewarded, meaning that they will be regularly updated, as new data becomes available, to ensure that up-to-date information is used for groundwater management activities. The first iterations of the following maps and models will be published as they are developed:

• Texture Models
• Hydrostratigraphic Models
• Aquifer Recharge Potential Maps
• Extent of Important Aquifer Units
• Depth to Basement
• Depth to Freshwater

Click on the link below for each local, regional, or statewide investigation to find the following datasets.

Local Investigations

• Madera & North Kings: AEM data collection, lithology log digitization, texture model development, aquifer recharge potential mapping analysis.
• Pajaro: AEM and tTEM data collection
• Western San Joaquin Valley: AEM data collection, lithology and geophysical log data digitization, texture model development.
• Prospect Island: AEM data collection, FloaTEM data collection test.

Regional Investigations

• Sacramento Valley: AEM data collection, texture model development, aquifer recharge potential mapping analysis.
• Four County Area of San Joaquin Valley (Madera, Fresno, Kings, and Tulare)
• San Joaquin Valley

Statewide Investigations

• Statewide AEM Surveys: AEM data collection, geophysical and lithology log data digitization.

Data Collection & Compilation

As a part of the Basin Characterization Program, advanced geologic, hydrogeologic, and geophysical data will be collected to improve our understanding of groundwater basins. Data collected under Basin Characterization are collected at a local, regional, or statewide scale depending on the scope of the study. Advanced data collection methods include:

• Airborne electromagnetics (AEM)
• All-terrain vehicle towed electromagnetics (tTEM)
• Watercraft towed electromagnetics (FloaTEM)
• Geophysical borehole logging

Digitized Existing Lithology and Geophysical Logs

Lithology and geophysical logging data have been digitized to support the Statewide AEM Survey Project and will continue to be digitized to support Basin Characterization efforts. All digitized lithology logs with Well Completion Report IDs will be imported back into the OSWCR database. Digitized lithology and geophysical logging can be found under the following resource:

• Digitized Lithology and Geophysical Logs.

Analysis Tools and Process Documents

To develop the state-stewarded maps and models outlined above, new tools and process documents have been created to integrate and analyze a wide range of data, including geologic, geophysical, and hydrogeologic information. By combining and assessing various datasets, these tools help create a more complete picture of California's groundwater basins. All tools, along with guidance documents, are made publicly available for local groundwater managers to use to support development of maps and models at a local scale. All tools and guidance will be updated as revisions to tools and process documents are made.

Data Analysis Tools

• Data2Texture: Data2Texture is an advanced spatial data interpolation tool for estimating the distribution of sediment textures from airborne electromagnetic data and lithology logs to create a 3D texture model

• Data2HSM - Smart Interpretation: Data2HSM via Smart Interpretation (SI) is a semi-automatic Python tool for delineating continuous hydrogeologic surfaces from airborne electromagnetic data products.

• Data2HSM - Gaussian Mixture Model: The Data2HSM via Gaussian Mixture Model tool ingests the AEM data and groups the data into a user-specified number of clusters that are interpreted as stratigraphic units in the hydrostratigraphic model (HSM)

• Data2HSM - Geological Pseudolabel Deep Neural Network: The GeoPDNN (Geological Pseudolabel Deep Neural Network) is a semi-supervised machine learning tool that integrates lithologic well logs and AEM data into plausible stratigraphic surfaces.

• Texture2Par V2: Texture2Par V2 is a groundwater model pre-processor and parameterization utility developed to work with the IWFM and MODFLOW families of hydrologic simulation code.

Process Documents

• Aquifer Recharge Potential Mapping: The Aquifer Recharge Potential (ARP) Mapping Process Document provides a framework for identifying locations that have relatively higher potential for managed aquifer recharge.

Data Visualization

Data access equity is a priority for the Basin Characterization Program. To ensure data access equity, the Basin Characterization Program has developed applications and tools to allow data to be visualized without needing access to expensive data visualization software. This list below provides links and descriptions for the Basin Characterization's suite of data viewers.

SGMA Data Viewer: Basin Characterization tab: Provides maps, depth slices, and profiles of Basin Characterization maps, models, and datasets, including the following:

• Aquifer Recharge Potential Maps
• Subsurface Texture Model Depth Slices
• Statewide AEM Survey Texture Depth Slices
• Lithology Log Location Maps
• Geophysical Logs Location Maps
• Statewide AEM Survey Profile Images

3D AEM Data Viewer: Displays the Statewide AEM Survey electrical resistivity and coarse fraction data, along with lithology logs, in a three-dimensional space.

California's Groundwater Subsurface Viewer: Provides a map view and profile view of the Statewide AEM Survey electrical resistivity and coarse fraction data, along with lithology logs. The map view dynamically shows the exact location of AEM data displayed.

Basin Characterization Exchange

The Basin Characterization

The dataset is a feature class showing the boundaries of 515 groundwater basins and subbasins as defined by the California Department of Water Resources as last modified by the Basin Boundary Emergency Regulation adopted on October 21, 2015 and subsequent modifications requested through the Basin Boundary Modification Request Process. Groundwater basins are represented as polygon features and designated on the basis of geological and hydrological conditions - usually the occurrence of alluvial or unconsolidated deposits. When practical, large basins are also subdivided by political boundaries, as in the Central Valley. Basins are named and numbered per the convention of the Department of Water Resources. The associated data are considered DWR enterprise GIS data, which meet all appropriate requirements of the DWR GIS Spatial Data Standards. DWR makes no warranties or guarantees, either expressed or implied, as to the completeness, accuracy or correctness of the data, nor accepts or assumes any liability arising from or for any incorrect, incomplete or misleading subject data. The official DWR GIS Data Steward for this dataset is Brett Wyckoff, who may be contacted at 916-651-9283, or at brett.wyckoff@water.ca.gov. Comments, problems, improvements, updates, or suggestions should be forwarded to the official GIS Data Steward as available and appropriate.

This data release contains monthly 270-meter gridded Basin Characterization Model (BCMv8) climate inputs and hydrologic outputs for 17 California Coastal Basins (Eel River, Fort Bragg, Fort Ross, Klamath, Los Angeles, Mad River, Mattole, Napa Sonoma, Russian River, Salinas, San Diego, San Francisco Coastal South, Santa Clara River Valley, Santa Clara River Valley South Bay, Smith, South Bay, and South Delta) and the surrounding contributing watershed area containing 181 groundwater basins. Downscaled gridded climate inputs (Daly et al., 2008) include: precipitation (ppt), minimum temperature (tmn), maximum temperature (tmx), and potential evapotranspiration (pet). Gridded hydrologic variables include: actual evapotranspiration (aet), climatic water deficit (cwd), snowpack (pck), recharge (rch), runoff (run), and soil storage (str). The units for temperature variables are degrees Celsius, and all other variables are in millimeters. Monthly historical variables from water years 1896 to 2019 are summarized into water year files and long-term average summaries for water years 1981-2010. Four future climate scenarios were spatially downscaled from 6 kilometers to 270 meters, and run through the BCMv8 using the same model parameters. The future climate scenarios (Pierce et al., 2014) are all Representative Concentration Pathway (RCP) 8.5 and include: CanESM2, CNRM-CM5, HadGEM2-ES, and MIROC5 from California's Forth Climate Change Assessment. Future climate scenarios span from water year 2007 to 2099, and monthly variables were summarized by water year and the average 2070 to 2099 period. Streamflow for each calibration gage was calculated using a post processing Excel spreadsheet and BCMv8 recharge and runoff, and are provided in tabular comma separated .csv files. Raster grids are in the NAD83 California Teale Albers, (meters) projection in an open format ascii text file (.asc). References cited: Daly, C., Halbleib, M., Smith, J.I., Gibson, W.P., Doggett, M.K., Taylor, G.H., Curtis, J. and Pasteris, P.P., 2008. Physiographically sensitive mapping of climatological temperature and precipitation across the conterminous United States. International Journal of Climatology: a Journal of the Royal Meteorological Society, 28(15), pp.2031-2064. Flint, L.E., Flint, A.L., and Stern, M.A., 2021, The Basin Characterization Model - A monthly regional water balance software package (BCMv8) data release and model archive for hydrologic California (ver. 2.0, February 2023): U.S. Geological Survey data release, https://doi.org/10.5066/P9PT36UI. Pierce, D.W., Cayan, D.R. and Thrasher, B.L., 2014. Statistical downscaling using localized constructed analogs (LOCA). Journal of hydrometeorology, 15(6), pp.2558-2585.

California’s Groundwater (Bulletin 118) is the State’s official publication on the occurrence and nature of groundwater in California. The latest version of the report, California's Groundwater - Update 2020 was publicly released on November 16, 2021. The publication defines the boundaries and describes the hydrologic characteristics of California’s groundwater basins. California’s Groundwater also provides information on groundwater management and recommendations for the future.

With the passage of the Sustainable Groundwater Management Act in 2014, California’s Groundwater now serves an additional role by providing Groundwater Sustainability Agencies with three critical pieces of information regarding groundwater basins: Critical Conditions of Overdraft, Basin Boundaries, and Basin Priority. Updates to California’s Groundwater will be released every five years starting in 2020.

This dataset includes the latest update, historical publications and supporting documents for California's Groundwater

The California Groundwater Ambient Monitoring and Assessment Program (GAMA) is a statewide, comprehensive assessment of groundwater quality designed to help better understand and identify risks to groundwater resources. GAMA is being implemented by the California State Water Resources Control Board. The USGS is the technical lead for the Priority Basin Project (PBP), one of the components of the GAMA Program. The initial focus of the GAMA Priority Basin Project in 2004 to 2012 was on assessment of water-quality in groundwater resources used for public drinking water supply (Belitz and others, 2003; 2015). Groundwater basins and sub-basins (472 in total) were prioritized based upon a number of factors (Belitz and others 2003). Two hundred and twenty-seven of these basins and additional areas outside of basins were subsequently grouped into 35 study units comprising 87 Study Areas. The basin and sub-basin boundaries, local geology, local knowledge, and watershed data were used to define the Study Areas. The Study Areas each were divided into equal-area grid cells collectively referred as a "study area grid". The number and size of cells generated for each Study Area was based upon the size of the area being sampled, and the number of public-supply wells available to sample. Three Study Areas contained an insufficient number of public-supply wells for division into a study area grid and were instead directly sampled. The number of cells in a study area grid ranged from 7 to 122 (median 20), and the size of the cells ranged from 4 to 471 km2 (median 25 km2). Additional information about the design of individual study area grids can be found in the reports listed below. The 87 Study Areas are collected and assembled here into one GIS dataset.

This dataset includes the official groundwater basin boundary descriptions for California's 515 groundwater basins. To make locating descriptions easier, they have been organized by region. This resource contains descriptions for basins that start with the number nine (9-XXX) indicating they are located in the San Diego Region.

The California Groundwater Units dataset classifies and delineates the State into one of three groundwater based polygon units: (1) those areas defined as alluvial groundwater basins or sub-basins (DWR, 2002), (2) highland areas that are adjacent to and topographically upgradient of groundwater basins, and (3) highland areas not associated with any groundwater basin. In total, 938 Groundwater Units are represented. The Groundwater Unit dataset relates existing groundwater basins with their newly delineated highland areas which can be used in subsequent hydrologic studies. The method used to delineate highland areas is similar to methods used to delineate a contributing area, the difference being that highland areas are constrained to the immediately surrounding upslope (upsteam) area.

Highland areas were delineated based upon the surficial contributing area (watershed) immediately adjacent to each groundwater basin. The method of delineation is comparable to the method used for stream segments. However, highland areas are not intended to represent the entire surficial contributing area for a groundwater basin. Upslope (upstream) groundwater basins, which may be contiguous with a downstream basin, are not included in the delineation for the downstream basin because the upstream basins will have their own highland areas delineated. In addition, many groundwater basins in the Central Valley are divided along a river: one groundwater basin along the right bank, and another along the left bank. Therefore, each groundwater basin will have its own highland area delineated for each side of the river. Groundwater units can be combined if desired.

Some groundwater basins do not have an associated highland because the basin was completely bordered by other groundwater basins, or a combination of groundwater basins and the ocean.

This polygon shapefile represents groundwater basins located in Tehama County, California.

This polygon shapefile depicts areas identified basin prioritization areas within California. At the time of the study (June 2014), Final Basin Prioritization findings indicate that 127 of California's 515 groundwater basins and subbasins are High and Medium priority. These basins account for 96% of California's annual groundwater pumping and supply 88% of the population which resides over groundwater basins. The remaining 388 basins are Low and Very Low priority and comprise 75% of the groundwater basins in the State. There are 515 alluvial groundwater basins and subbasins in California as defined in DWR's Bulletin 118. These basins contribute close to 40 percent of the California's annual water supply in an average year and as much as 45 percent in dry years. During extensive dry or drought years, groundwater can provide close to 60 percent of the water supply. Statewide, approximately 30 million people, or 80 percent of Californians, live in areas overlying alluvial groundwater basins. Some communities are 100 percent reliant on groundwater. The California Department of Water Resources (DWR) implemented the California Statewide Groundwater Elevation Monitoring (CASGEM) Program in response to legislation enacted in California's 2009 Comprehensive Water package. As part of the CASGEM Program and pursuant to the California Water Code (CWC §10933), DWR is required to prioritize California groundwater basins, so as to help identify, evaluate, and determine the need for additional groundwater level monitoring.

The California Air Basins layer is a polygon shapefile coverage representing the 15 California air basins, as defined in state statute and regulation. See the California Health and Safety Code, Section 39606 et seq. and California Code of Regulations, Title 17, Section 60100 et seq. Shapefile coverage. This data layer shows the air basin boundaries and their names, as of October 2014. The file has been updated using as main source the: California Environmental Protection Agency Air Resources Board maps (http://www.arb.ca.gov/knowzone/basin/basin.htm)

This dataset includes the official groundwater basin boundary descriptions for California's 515 groundwater basins. To make locating descriptions easier, they have been organized by region. This resource contains descriptions for basins that start with the number three (3-XXX) indicating they are located in the Central Coast Region

The California State Water Resources Control Board is currently in the process of improving the functionality and accessibility of information residing in their Water Quality Control Plans (aka Basin Plans). In order to achieve this, the data (i.e. statewide water quality objectives, beneficial uses, applicable TMDLs, etc.), are being transferred to a standardized digital format and linked to applicable surface water features. This dataset is limited to the beneficial uses data, while the water quality objectives, applicable TMDLs, etc. will be released at a later date. Data formats will include GIS data layers and numerous nonspatial data tables. The GIS layers contain hydrography features derived from a 2012 snapshot of the high-resolution (1:24000 scale) National Hydrography Dataset with added attribution. Nonspatial tables will contain various textual and numeric data from the Regional Basin and State Plans. The extent of the dataset covers the state of California and the non-spatial tables reflect the information and elements from the various plans used up to 2020. The GIS layers and associated attribution will enable the future integration of the various elements of the Basin Plans to ensure that all applicable Basin Plan requirements for a particular waterbody can be determined in a quick and precise manner across different modern mediums. The data are being managed and the project implemented by State and Regional Water Board staff using ESRI's ArcGIS Server and ArcSDE technology.The statewide layer is only provided as a map image layer service. The data is available as feature layer services by Regional Board extract. To view all regional board feature layer extracts go to the Basin Plan GIS Data Library Group here.

Water chemistry data from wells sampled by Standard Lithium Ltd. in Bristol and Cadiz Basins in San Bernardino County, California, USA

The purpose of this shapefile is to provide an accurate boundary reference for the purpose of mapping and data analysis. Boundary of the combined adjudicated Central and West Coast groundwater basins. Adjudication is a form of groundwater management in California through the courts. When groundwater resources do not meet water demands in an area, landowners may turn to the courts to determine how much groundwater can be rightfully extracted by each overlying landowner or appropriator. The court typically appoints a Watermaster to administer the judgment and to periodically report to the court. As of 2013, there were 24 adjudicated groundwater basins in California, with the majority of the adjudications located in Southern California in the South Coast hydrologic region. The majority of groundwater rights adjudications in California imposes extraction limits and/or initiates management actions in the event of declining groundwater levels or water quality degradation. It should be noted that the primary objective of adjudication is to provide a proportionate share of the available groundwater to the users within the basin so it can be extracted without having adverse effects to existing groundwater supplies. Environmental concerns were not considered when most of the judgments were written. These data were developed using the best available data for the California Water Plan Update 2013, however may contain errors.

The city of Santa Barbara, in cooperation with the U.S. Geological Survey (USGS) California Water Science Center, developed a three-dimensional density-dependent groundwater-flow and solute-transport model (the Santa Barbara Flow and Transport Model, or SBFTM), based on an existing groundwater-flow model, to simulate seawater intrusion into the Santa Barbara basin under various management strategies. In 2014, California adopted historic legislation to manage its groundwater: the Sustainable Groundwater Management Act (SGMA). Santa Barbara is interested in developing a better understanding of the sustainability of its groundwater supplies to avoid undesirable results: significant and unreasonable groundwater-level declines, reduction in groundwater storage, seawater intrusion, water-quality degradation, land subsidence, and surface-water depletion. The SBFTM uses the USGS code SEAWAT to simulate salinity transport and variable-density flow. The completed SBFTM was coupled with a management optimization tool, Borg, to develop five optimization scenarios that allow the decision makers to evaluate a range of optimal solutions given current water levels and chloride concentrations, and possible future climatic conditions. This USGS data release contains all of the input and output files for the simulations described in the associated model documentation report (https://doi.org/10.3133/sir20185059)