Start by pulling in to Maxwell Farms Park. There is an entrance fee of $7 per car, but entrance is free to members. Follow the signs for the Sonoma Bike Path and you'll be on your way. The start of this hike is gorgeous. You're lead past rolling lawns, pretty woods, and frisbee golf courses. Half a mile in, you're going to cross into Sonoma Historical State Park.
This crossing is pretty seamless until you reach the mansion of General Vallejo. This historic general commanded Mexico's troops in California when Mexico won Independence from Spain. His house and some of the lands around it have been preserved. You can step off the path and enjoy the outside of the building, but it's unfortunately not dog friendly. When you and your pup are ready to press on, get back on the trail for the last leg of your hike!
The last half mile of the hike brings you out of the parks and into working wine country. You'll pass vineyards and traces of the old rail lines. This path used to be a rail line, but it's been converted for pedestrian, equestrian, and cycling use! From the farmland you'll pass more and more buildings until you wind up at the end of your hike--downtown Sonoma! You can explore the surrounding blocks from your Fourth Street and Lovall Valley Drive exit point. Or turn right around and let your nose lead you back to the car!
The Sonoma Bike Path is a woofderful way to spend some time, and it won't even eat your whole day!