There are three distinct sections to this hike. You're going to start in Sonoma's vibrant, artistic downtown area. Park your car (for free!) at the Stebastiani Vineyards and you're mere blocks from Sonoma Plaza, the heart of downtown. Explore there, or hit the trail right away. The trail begins on 4th Street, across from the winery.
Dogs are allowed on this trail as long as they stay on leash, and you pick up after them. This is especially important during the second half of the hike, which takes you through Sonoma Historical State Park. Here you'll have an opportunity to step off the path and observe La Casa Grande. This is the old mansion of General Vallejo, who lead California for Mexico in the 19th century. Sadly, dogs are not permitted inside.
Continue out the other side of the park and you'll be in the last half mile of the hike. You'll walk through farmlands to a residential neighborhood, and the trail will end at Olson Park. Rest up with your pup, but don't paws for too long--you still have the way back to get to!
On this trail you're likely to meet fellow hikers. Cyclists also use the trail, so be sure your dog is comfortable around them. This trail is a staple of the area, so don't expect a totally secluded walk!
The Sonoma Bike Path -- Downtown Entrance is a great entryway into all this gorgeous area has to offer.