Actually from what little I know, Sonoma County isn't really part of the main weed growing region:
"The Emerald Triangle refers to a region in Northern California so named because it is the largest cannabis producing region in the United States. Mendocino County, Humboldt County, and Trinity County are the three counties in Northern California that make up this region."
"The Emerald Triangle refers to a region in Northern California so named because it is the largest cannabis producing region in the United States. Mendocino County, Humboldt County, and Trinity County are the three counties in Northern California that make up this region."
http://en.wikipedia.org/wiki/Emerald_Triangle