The California State Department of Conservation Farmland Mapping and Monitoring Program (FMMP) has started releasing its 2010 farm data that we have received permission to add. It is sorted by counties. Alameda County is the first county out. I have already converted it to OSM format and have reviewed it. But I would like to get one or two other people to review each county for quality control before they are uploaded. If you are interested let me know your email and I can send it to you for review. For more on this import see the page on the wiki at http://wiki.openstreetmap.org/wiki/California_Farms.