The Sonoma Mountains are a northwest–southeast trending mountain range of the Inner Coast Ranges in the California Coast Ranges System, located in Sonoma County, Northern California. The Sonoma Mountains range is approximately fourteen miles long. It separates the Sonoma Creek watershed from the Petaluma River and Tolay Creek watershe…The Sonoma Mountains are a northwest–southeast trending mountain range of the Inner Coast Ranges in the California Coast Ranges System, located in Sonoma County, Northern California. The Sonoma Mountains range is approximately fourteen miles long. It separates the Sonoma Creek watershed from the Petaluma River and Tolay Creek watersheds. The highest point of this range is Sonoma Mountain, elevation 2,287 ft.