As helpful for natives as it is for visitors, Explorer's Guide Napa & Sonoma: A Great Destination reveals the richness and color of this remarkable place. There are well-known as well as undiscovered wineries, a wealth of eateries, the best accommodations, and important travel information. Also included is an events calendar, “If Time Is Short” options, local history, color photos and maps, and essential information to help you find the best ways to spend your vacation time. Explorer's Guide Napa & Sonoma: A Great Destination, now in its ninth edition, has been acclaimed repeatedly by The Wine Advocate and Wine & Spirits.
We have an older version of this book, but I assume the formats are similar. Ours is getting tattered and torn - we pull it out to plan wine country getaways, when we're on our wine country adventures, and when we want to look up wineries we visited (or think we visited!).
The chapters of the book are divided by county (Napa/Sonoma) and then into wineries, restaurants, accommodations, and other miscellaneous stuff. This format makes it extremely easy to find what you're looking for and to plan your day by the area you'll be visiting. All of the basic information is included, and the reviews are honest.
I do wish they'd included some of the more obscure wineries, but I guess those are left for only the most dedicated of winos to find :)