Serpentine communities occur in scattered areas across Sonoma County. These communities support a number of rare and endangered plant species. From a vegetation mapping perspective, these are important areas. Because thesy are small, geographically isolated, and occur uncommonly across the County's landscape, it will be important to clearly identify these areas and compile existing field data for them before our mapping work begins. Serpentine areas on the North Coast have been studied significantly in the past 75 years, and much is known about their composition. In the April, 2009 issue of the Journal Fremontia (California Native Plant Society), Roger Raiche provides a great botanical profile of the Cedars, the county's largest serpentine area.
The serpentine areas of Sonoma County are associated with several soil types. Among these are soils from the Henneke Series, soils from the Montara series, and soils from the Huse series.
The interactive map below shows the 1997 Soil Survey Geographic (SSURGO) soils data overlaid on Bing aerial imagery. Pan and zoom to move around on the map. Access the "Bookmarks" to navigate to the major serpentine areas in the county. If you click "View Larger Map," a larger map will open in ArcGIS.com with more functionality. This map's default extent is an area of serpentine soils (mainly the Henneke series) and vegetation north of Occidental near the Bohemian Highway.
Joe Kinyon (Sonoma Land Trust) just sent me a link to link to a new geologic map service from USGS. Joe says the service "provides an authoritative and fairly comprehensive reference for geologic spatial data in Sonoma County and elsewhere." It beats Googling and dowloading data in various formats from multiple sources. Here's the link: http://ngmdb.usgs.gov/maps/MapView/. Thanks Joe!