Welcome to California!I line in So Cal but will try to help.
I went to Google Earth and asked for shooting ranges Marin County.
I got several down in the Bay area and I got one in Petaluma:
Circle S Ranch & Shooting RangeGo to the Circle S web page. They have links to other ranges in the area. This is a small sample of their links. I know nothing about any of them as I live in So Cal.
Marin, Sonoma, Napa, Lake, Solano, Mendocino Counties & North:Wing & Barrel Ranch, Sonoma (Private Hunting Club)
Circle S Ranch and Outdoor Shooting Range
West of Petaluma in Two Rock
Konocti Rod and Gun Club
Lake County Rod & Gun Club
Napa Rifle & Pistol Club
The Redwood Gun Club (Arcata)
Russian River Sportsmens Club (Duncans Mills)
Sebastopol Rifle & Pistol Club
Sonoma County Shooting Association
Sonoma Valley Muzzleloaders
Monthly shoots are held at Marie Hill Ranch, West of Cloverdale
Ukiah Rifle & Pistol Club (Ukiah Gun Club)
Valley of the Moon Trap Club (Sonoma)