Natives are generally defined as plants that occur naturally, or have been in an area for a very long time (endemic plants are ones that occur naturally AND uniquely in an area, and nowhere else).
California natives are well suited for Sonoma County because they:
- Are water thrifty and drought tolerant
- Are suited to the climate and soil types of the area
- Look right with the natural landscape
Sonoma County Master Gardener information on natives includes:
Other Native Plant Resources:
California Native Plant Link Exchanges
California Native Plant Society
CalFlora searchable wild California plant database
California Native Grasslands 
Ceanothus
Theodore Payne Foundation
Other reading on native plants:
Bornstein, Fross, O’Brien, California Native Plants for the Garden, 2005.
Lowry, Judith Larner, Gardening with a Wild Heart, 1999.
Smith, M. Nevin, Native Treasures, 2006.
Pacific Horticulture magazine (quarterly)
Fremontia, quarterly journal of the California Native Plant Society
©Sonoma County Master Gardeners