On the map, Sonoma County is separated from the Napa Valley by a narrow range of mountains called the Mayacamas. In the perception of the wine consuming public however, the low-slung Mayacamas might just as well be the Himalayas. Napa, just to the east, is the valley of glamorous wines, feuding Mondavis and "Falcon Crest." Sonoma is that other place nearby that also happens to make wine.

But if Sonoma County is less familiar than Napa, its claim to prominence is no less great. The historic center of wine-making north of the San Francisco Bay, Sonoma's viticulture began around 1820 in the vineyards surrounding the Sonoma Mission, which still stands in the quaint Sonoma town square. In the mid-1800s Sonoma became the first California region to gain a reputation outside the state, and it kept a short but significant lead over Napa for the rest of that century.

Early in this century, prohibition and the pesky phylloxera louse pretty much put an end to high quality wine making in both regions. Some wineries survived by making sacramental wines. Most perished. It wasn't until the mid-1960s that the modern wine boom began in earnest, and when it did, it started in Napa, where a combination of new technology and shrewd promotion put the once less renowned wine region more prominently in the public mind. Sonoma County had its own boomlet, but it has never quite regained the status it enjoyed in bygone times.

A major reason is that Sonoma County is harder to comprehend. Unlike the compact Napa Valley, Sonoma is the wine world's version of suburban sprawl. Distances between major wine growing areas are large. Regions and subregions abound, with differing styles and differing capabilities for making various wines successfully. What's more, consumers frequently confuse Sonoma Valley -- which is just one region of the county -- with the entirety of Sonoma County, which includes Alexander Valley, the Russian River, Dry Creek, and other areas of note. (Further complicating matters is the fact that Napa Valley and Napa County are synonymous.)

Some order has recently been imposed on the chaos through the U.S. Bureau of Alcohol, Tobacco and Firearm's approved viticultural area (AVA) appellation system, which divides regions into separate viticultural areas. Unlike some of the AVAs in Napa and elsewhere, the boundaries of which sometimes seem to reflect winemakers' egos and narrow commercial interests as much as substance, Sonoma's AVAs really mean something. They distinguish the regions by their terroirs (soil and climate), which have enormous effect on the character of the wines. Such AVAs give the consumer a fighting chance to know something about how a wine will taste before the cork is popped.

Listed below are the major AVAs of Sonoma County, with recommendations of top wineries for exploring the style of each region. My assessment of a winery's best offerings is listed in parentheses after the name.

Sonoma Valley/Carneros: Though the earliest wines made by the Franciscan monks from the Mission grape must have been truly dreadful, Sonoma Valley must have performed a collective penance, as it now produces some of the best wines in the county. Though many varieties are made successfully, the glory of the valley is its chardonnays, cabernets and merlots.

Carneros is a sub region of Sonoma Valley that also extends into Napa Valley. Carneros is rapidly emerging as the American Co~te d'Or -- owing to its formidable success with the Burgundian varieties of chardonnay and pinot noir. Or perhaps it might be called the American Champagne region -- owing to its success with sparkling wines. Cooling breezes from the San Francisco Bay that start in mid-afternoon appear to be the key to Carneros' uniqueness. The Gloria Ferrer Sparkling Wine facilities are located on the Sonoma side, and many other leading California sparkling wine houses also obtain their highest quality fruit from the region.

Recommended wineries: Kistler (chardonnay, cabernet/merlot), Matanzas Creek (chardonnay, merlot), Ravenswood (zinfandel, Pickberry vineyard cabernet), St. Francis (merlot, cabernet, chardonnay), Carmenet (cabernet/merlot), Gundlach Bundschu (merlot), Chateau St. Jean (sauvignon blanc, chardonnay), Buena Vista (pinot noir, chardonnay), B.R. Cohn (cabernet), Hacienda (pinot noir, cabernet, chardonnay), Kenwood (sauvignon blanc, cabernet), Arrowood (chardonnay), Sebastiani (good value in most varietals), Gloria Ferrer (sparkling wine).

Alexander Valley: Still looking much as it must have a century ago when grapes were first planted here, Alexander Valley seems to do well with almost every variety, ranging from gewurstraminer and rielsing to zinfandel. Until recently however, it excelled at nothing, but the showplace Simi and Jordan wineries have changed that, producing cabernet and chardonnay that rank with the very best for both name recognition and quality. Alexander Valley Vineyards also offers fine value in many of its wines.

Recommended wineries: Simi (cabernet, chardonnay, sauvignon blanc), Jordan (chardonnay, cabernet), Ferrari-Carano (chardonnay), Alexander Valley Vineyards (merlot, cabernet, chardonnay, gewurstraminer), Braren Pauli (merlot), Murphy-Goode (sauvignon blanc, chardonnay, merlot), Clos du Bois (cabernet, chardonnay), Sausal (zinfandel).

Dry Creek Valley: Known for its unsurpassed zinfandels and chenin blancs, Dry Creek is also showing strong potential for other varietals. The just-released 1986 Dry Creek "Reserve" cabernet is stunning, and after a shaky start, Domaine Michel is now emerging as a leading producer of highly sophisticated chardonnay and cabernet.

Recommend wineries: Dry Creek Vineyard (chenin blanc, sauvignon blanc, zinfandel, cabernet), Domaine Michel (cabernet, chardonnay), Quivira (zinfandel, sauvignon blanc), Lytton Springs (zinfandel), Bellerose (cabernet, merlot), Pedroncelli (cabernet, chardonnay, white zinfandel).

Russian River Valley/Green Valley/Chalk Hill: The expansive Russian River Valley appellation encompasses both the Green Valley and Chalk Hill sub-appellations. At least as cool as Carneros, the Russian River Valley and Green Valley challenge Carneros for quality in sparkling wines. Chardonnay and pinot noir are also strong.

Recommended wineries: Iron Horse (sparkling wines, pinot noir), Deloach (chardonnay, sauvignon blanc, pinot noir), Dehlinger (chardonnay, pinot noir, zinfandel).

Ben Giliberti is a freelance writer who writes regularly about wine.