Description: The subbasin delineations were based off Napa County"s prior planning subbasins (https://www.napacounty.gov/DocumentCenter/View/2635/Napa-County-Watershed-Map-PDF?bidId=).This layer was made by Environmental Science Associates (ESA) as part of Napa County"s 2025 Baseline Data Report.High quality Digital Elevation Model's (DEM) were combined to fully delineate subbasins. The Napa County Streams layer was used to burn streams into the DEM to ensure that subbasin delineations were consistent with the County"s streams layer.Raw catchments generated with the ArcGIS Pro hydrology toolset were subsequently merged together as necessary to adhere to original planning drainages. In cases where planning drainages were subdivided in greater detail then was delineated in the raw catchment layer, ESA defined pour points to manually delineate planning drainages using the "Subwatershed Delineation" geoprocessing tool. ESA worked with the County to identify areas requiring additional refinement, and further refined delineation based on a review of the delineation against satellite imagery, Google Earth Street View, and the DEM"s contour/ hillshade.