Dogs are allowed at some local California State beaches. (This means on the beach not on the bluffs above the beach.) For a list click Dog Beaches.
Too many to describe:
Click here for a list of city and county parks, including the above and a few others, like ones in Rohnert Park.
Click here for a brochure of parks in Petaluma, including Rocky Memorial mentioned above.
Badger Dog Park, 750 Heron Dr. Healdsburg. Best for small dogs.
Sonoma Dog Park, 175 First St. W., Sonoma.
Walking in Sonoma County...mostly 
Lynn, I recently discovered your delightful blog, “Walking in Sonoma County…mostly,” as well as your informative website, backtowalking, and entertaining articles in the Sonoma County Gazette. I’m really enjoying your stories. You write about the very issues I’m wanting to know about: what you see and experience on your walks, which walks are dog friendly, how to prepare for your walks to make them most enjoyable and comfortable, and when are the best times for enjoying nature in Sonoma County (and elsewhere!). Thank you so much!
Thank you. I’m glad I can be of help. — Lynn