As part of the massive ongoing effort to map Sonoma County with high-res imagery and lidar, historic imagery of the county was collected and georeferenced. The Sonoma County Agricultural Preservation and Open Space District funded SFEI to mosaic 72 historic aerials taken over Sonoma County by the Department of Defense in 1942. Mark Tukman put together this web service with a image swiping tool showing the combination of the 2011 imagery service and the mosaiced historic imagery.
 
Sonomaopenspace.maps.arcgis.com

About the historic imagery: In 1942, the Department of War collected air photos in anticipation of a possible strike.  These photos are the earliest complete image set for Sonoma County and give us an unprecedented look at Sonoma County's agriculture and open space prior to the post World War II baby boom.

These images are snaps from the service, both from an area outside Rohnert Park in Sonoma County: on the bottom is the image from 1942, on the top is the area in 2011 showing considerable development.