The Watershed Boundary Dataset (WBD) is a seamless, national hydrologic unit dataset. Hydrologic units represent the area of the landscape that drains to a portion of the stream network. (https://www.usgs.gov/national-hydrography/watershed-boundary-dataset) It is maintained by the U.S. Geological Survey (USGS) in partnership with the states. The Department of Water Resources is the steward for the California portion of this dataset. The hydrologic units (HU) in the WBD form a standardized system for organizing, collecting, managing, and reporting hydrologic information for the nation. The HUs in the WBD are arranged in a nested, hierarchical system with each HU in the system identified using a unique code. Hydrologic unit codes (HUC) are developed using a progressive two-digit system where each successively smaller areal unit is identified by adding two digits to the identifying code the smaller unit is nested within. WBD contains eight levels of progressive hydrologic units identified by unique 2- to 16-digit codes. The dataset is complete for the United States to the 12-digit hydrologic unit. The 8-digit level unit is often referred to as HUC8 and is a commonly used reference framework for planning and environmental assessment. This particular version of the dataset was created by downloading the CA State extract of the National Hydrography Dataset from the USGS website https://www.usgs.gov/national-hydrography/access-national-hydrography-products and then performing a geoprocessing operation in ArcGIS Pro software to clip the HUC8s at the state of California political boundary. (https://data.cnra.ca.gov/dataset/california-county-boundaries2). A web map service was created with this dataset, but at it's original digitized resolution it can take a long time to render in a web map application. This dataset is a simplified version, created by use of the ArcGIS Simplify Polygon tool with the Douglas-Peucker Line simplification algorithm, reducing the vertex count from 1,095,449 to 9108. This dataset was reprojected from the original NAD 83 Geographic Coordinate System to WGS 1984 Web Mercator auxiliary sphere for use in web map applications. Any questions about this dataset may be sent to jane.schafer-kramer@water.ca.gov