The polygon shapefile contains the boundaries of 515 groundwater basins and subbasins as defined by the California Department of Water Resources (Bulletin 118, 2003). 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. Bulletin 118 defines the recognized groundwater basins and subbasins throughout the State of California. The Bulletin 118 document provides information on these basins/subbasins and the nature and extent of groundwater occurrence and management within the State. The Bulletin 118 dataset makes the geographic locations and extent of the 515 basins/subbasins publically available, for use in external mapping/GIS applications. Horizontal positional accuracy was established by professional judgement. According to Bill Brewster, 100% of the linework is better than 10 mile accuracy. Some places are better than 10 mile accuracy. This layer is presented in the WGS84 coordinate system for web display purposes. Downloadable data are provided in native coordinate system or projection.