The hike through Jack London State Historic Park to the top of Sonoma Mountain runs through redwood groves, meadows, and vineyards. Vigorous blackberry bushes provide some sustenance -- but bring water, because it gets hot up there in the summer.
The mountain trail is mostly a fire road, and is mostly brutally uphill for about 3.5 miles on the way up. Once on top, the views are pretty dramatic, though -- and the descent is refreshingly easy.
The park also has Jack London's cottage, which you can tour, as well as his grave and the remains of Wolf House, which burned down before he was finished building it.
The park has been spared closure, unlike many of California's state parks, thanks to some Valley of the Moon organizations.