GIS data available from David Magney:
Calleguas Creek Watershed ArcView shapefile datalayers (watershed boundary, city spheres of influence, natural vegetation, rare species tracked by the California Natural Diversity Data Base, land use, recommended wetland restoration sites, wetland reference sites [~50], isohyetal contours, sensitive habitats, streams, roads, geology {from USGS], soils [from STATSCO]).

Oak Woodland Vegetation for central/southern Ventura County as ArcView shapefile.

Vegetation/land cover for eastern Sulphur Mountain (central Ventura County) as ArcView shapefile.

PDF document of Ventura County Plant Species of Local Concern.