If California is the rock star of the American wine industry, the Sonoma and Napa valley regions are the A-list celebrities.
Home to more than 4600 wineries, the West Coast state makes 85 per cent of the wine produced in the US, but it's at the two parallel valleys just north of San Francisco where you'll find the top-quality plonk.
First up, you have to be careful not to get your counties and your valleys confused — Sonoma County is a huge area encompassing Sonoma Valley and multiple other AVAs (American Viticultural Areas), while Napa Valley is just one of the AVAs in Napa County. Both make up part of San Fran's "Wine Country" region, and one AVA, Los Carneros, straddles the two.
In terms of looks, as a newcomer you'd be hard-pressed to tell the difference between each region's picturesque rolling hills, but there are differences in attitude.
Attention-seeking Napa is flashier and more touristy, while Sonoma is more relaxed and less commercial.
The best times to visit are spring and autumn — in particular, the "fall" combines fine weather with the grape harvest and the start of the wine-making season.
The good news is that both are an easy day trip from San Francisco, but if you're short on time, which one do you point the car towards? Here's a quick run-down. (Note that many of the wineries have tasting fees and some are by appointment only.)
How to get there: Travel northeast either via I-80 or US-101. It will take you around 90 minutes.
If you're staying: Skip Napa, the main town in the valley, and head north to the charming settlements of St Helena or Calistoga, which offer more attractive accommodation options and a wider variety of eateries. Calistoga is also known for its hot springs, mineral water and mud baths.
Best known for: Cabernet sauvignon and chardonnay.
What else is there to do? There are other ways to relax than quaffing wine you know.
Feel better about indulging with a spot of wellness therapy, whether it's a yoga workout or a massage or spa treatment at one of the luxurious facilities dotted around the region.
More info: napavalley.com
Napa Valley is the most famous wine region in the US, shooting to glory when one of its wines beat a French vintage at a blind-tasting competition in Paris in 1976. The history goes way back beyond that, however, to 1838 when George Calvert Yount, founder of the town of Yountville, planted the first commercial vineyards in the valley.
The 8km-wide region is further inland than Sonoma and slightly longer, at 48km. It became California's first AVA in 1981 and these days, despite its massive reputation and 400-plus wineries, is responsible for less than 5 per cent of the state's wine output.
Napa's dry, Mediterranean-style climate produces great pinot noir, merlot, sauvignon blanc and zinfandel over its 17,500ha of grapes, but its standout drops are its cabernet sauvignon and chardonnay.
Your best bet is to head for Highway 29, the main road through the valley, and see which of the many wineries take your fancy.
Travel northwest either via I-80 or US-101. It will take you around an hour.
If you're staying: You'll probably want to stick around Sonoma township, somewhere close to its historic plaza, which is a National Historic Landmark.
One of the most historic settlements in California, Sonoma was the site of the 21st and final Spanish mission, Mission San Francisco Solano, settled in 1823. It was also the site of the short-lived 1846 Bear Flag Revolt, when a small group of US settlers rebelled against the Mexican government and proclaimed California an independent republic. Many of the buildings of the time — look for examples of the adobe style — still stand on the plaza and surrounding streets.
You'll also find great restaurants, artisan boutiques, galleries, farmers' markets and plenty of charming accommodation.
Known for: Cabernet sauvignon, zinfandel, merlot and chardonnay.
What else is there to do? Head up the road to the Jack London State Historic Park at Glen Ellen, formerly a ranch owned by the famous author and adventurer in the early 1900s.
Sonoma Valley is more low-key than Napa and half its length, with fewer wineries (about 100) and tourists. It dates back even further than its co-valley, with the first vineyards planted by Franciscan mission fathers in 1824. The closest wine region to San Francisco, Sonoma Valley is very dry, has cool nights and is isolated either side by the Mayacamas and Sonoma mountain ranges.
Reds rule here, especially zinfandels and big cabernet sauvignons, but its chardonnay and pinot noir are also well-regarded.
Buena Vista Winery, founded in 1857 by Agoston Haraszthy, is the state's oldest commercial winery, and still operates from its original site east of Sonoma. Now a California Historic Landmark, the winery's history — surviving bankruptcy, Prohibition, the Depression and a phylloxera infestation — is as interesting as the wines that it produces.
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