The Fairfield Osborn Preserve is a 411 acre (1.6 km²) nature reserve situated on the northwest flank of Sonoma Mountain in Sonoma County, California. There are eight plant communities within the property, oak woodland being the dominant type. Other communities include chaparral, Douglas fir woodland, native Bunch grass, freshwater marsh, vernal pool, pond and riparian woodland. The flora is extremely diverse including many native trees, shrubs, wildflowers, grasses, lichens and mosses.