U.S. Bureau of Land Management (BLM) has a goal to develop fine-scale vegetation maps for all the public lands it manages in California. To help meet this goal BLM contracted Aerial Information Systems, Inc. (AIS) to conduct vegetation classification development, fine-scale vegetation mapping, and accuracy assessment (AA) of approximately 22,061 acres within Colusa and Lake counties of California, under Contract GS00F170GA-Order No.140L1221F0044. AIS subcontracted the California Native Plant Society (CNPS) to conduct classification development work needed for this project, as well as AA field data collection. The California Department of Fish and Wildlife’s (CDFW) Vegetation Classification and Mapping Program (VegCAMP) provided in-kind service to allocate AA sample sites and score the vegetation map using the AA data.The study area, referred to as Walker Ridge or Molok Luyuk, which means Condor Ridge in the Native American Patwin language of the Yocha Dehe Wintun Nation, is located in the inner North Coast Ranges, east of Clear Lake and west of the town of Williams in the Sacramento Valley. This area has a large serpentinite outcrop that contains a high diversity of plants and plant communities, and is home to dozens of threatened and endangered (T&E) plants and animals. The vegetation classification developed for the project follows Federal Geographic Data Committee (FGDC) and National Vegetation Classification Standards (NVCS). The classification is based on new and previous survey information and classification work. The map was produced applying heads-up digitizing techniques using a base of 2020 60-centimeter National Agricultural Imagery Program (NAIP) imagery (true-color and color infrared), in conjunction with ancillary data and imagery sources. Map polygons are assessed for Vegetation Type, Percent Cover, Exotics, Development Disturbance, and other attributes. The minimum mapping unit (MMU) is 1 acre. Exceptions were created for vegetation stands of special significance. In this mapping effort, riparian vegetation and wetland types were mapped to a 1/4-acre MMU. Polygons representing land use were mapped with a 1-acre MMU. There were a total of 42 mapping classes composed of 30 alliances and alliance-level types such as Provisional Alliances, Semi-natural Alliances, and Mapping Units; and 5 Miscellaneous Classes relating to features such as agriculture, water, and urban disturbance; and 7 upper-level hierarchical types, such as Macrogroup and Group. Field reconnaissance and accuracy assessment enhanced map quality. The overall accuracy assessment ratings for the final vegetation map was 89.7 percent overall fuzzy accuracy.More information can be found in the project report, which is bundled with the vegetation map published for BIOS here: https://filelib.wildlife.ca.gov/Public/BDB/GIS/BIOS/Public_Datasets/3100_3199/ds3159.zip