Having celebrated 30 years as an official American Viticultural Area (AVA) last year, the Russian River Valley can say that many of its visionaries' dreams have come true. The region is now world-renowned for producing gorgeous pinot noir and chardonnay, among other wines.

With time and experience under their belts, today winemakers and growers are better able to determine the many nuances that differentiate the Russian River Valley's northern end from its south, its cool western edges from its warmer east, its benches and ridges from lower and higher elevations.

Those nuances are key to understanding how the region's starring grape, pinot noir, can take on perceptible differences in the glass. The aromas and flavors are both very much determined by the variations in climate — basically, how much fog creeps in — and soil.

At a new event in May called the Russian River Valley Pinot Classic, winemakers got together to talk about these differences, unofficially splitting the appellation into what they are calling "neighborhoods."

For discussion's sake, the neighborhoods were broken firmly into three, from warmer north to cooler south: the Middle Reach, Laguna Ridge and Green Valley. The Santa Rosa Plain and Sebastopol Hills as two more neighborhoods are under consideration.

The reason to subdivide is because the AVA itself is so big. When it was first approved in 1983, the Russian River Valley comprised 96,400 acres. An expansion in 2005 bumped it to 126,600 acres; another boundary re-draw in 2011 added new areas to the south and east, near Rohnert Park and Cotati, an increase of 9 percent.

The appellation now encompasses 169,029 total acres, 16,000 of them planted to wine grapes. (For the sake of comparison, the entire Napa Valley is about 225,000 acres).

So it's big and teeming in varied soils, from Franciscan to alluvial and the well-heeled Goldridge, a fine, sandy loam soil.

Mark McWilliams of Arista Winery on Westside Road in Healdsburg spoke to the Middle Reach's defining characteristics by first noting that the neighborhood boasts probably the greatest concentration of older plantings in the Russian River Valley. He pointed to such historic nearby properties as Bacigalupi Vineyards, Rochioli, Bucher, Allen Vineyard and the former Davis Bynum land, now farmed by Thomas George Estates.

"The pinots are darker, meatier, built to last," McWilliams said. "The aromatics are not as defined. The wines are about texture, length. They tend to be more broad on the palate. Acid is not a defining feature."

These wines are often expansive, lush, with firm tannic structure, yet soft.

Longtime Joseph Swan winemaker Rod Berglund is duly familiar with the Laguna Ridge, south of the Middle Reach near Forestville and cooler. It's a neighborhood known for wines of great minerality and complexity due to the mix of traditional Goldridge and Altamont soils, with layers of Franciscan soils at its northern end.

Joe Swan was the first to plant Pinot Noir in the Laguna Ridge after Prohibition, advised as he was by wine consultant Andre Tchelistcheff that pinot would do well there. Dehlinger and Lynmar established pinot vineyards early on there as well.

"The pinots have a wonderful mouthfeel and moderate acidity," noted Berglund. "They go from red to dark fruit, strawberry, mixed berry, pit fruit like plum and nectarine. They have a fascinating brambly, spicy character."

Laguna Ridge pinots are typically not as linear as those from cooler Green Valley nor as rich as those from the Middle Reach.

In Green Valley, Michael Browne of Kosta Browne Winery farms 20 acres of pinot noir from Keefer Ranch, a prime vineyard near Graton, a neighborhood steeped in Goldridge soils and the cooling coastal influence of the Pacific Ocean and San Pablo Bay.

Green Valley is also heavily forested with redwoods and fir, and its higher elevation sites are subject to consistent wind.

"The hallmarks of these pinots is what I like to call crispy red fruits," said Browne. "Cranberry, rhubarb, pomegranate, tart cherry, they're crisp in aromatics with a luxurious mouthfeel, precise and clean, beautifully textured."

He added that there is often a tension and a firmness to the wines and a touch of anise spice.

Warren Dutton was among the first to plant in Green Valley, and Dutton-Goldfield as well as Hartford Court remain significant pinot producers here. Iron Horse is another important estate in the heart of the neighborhood.

The Russian River Valley Winegrowers Association kicked off the Neighborhood Initiative earlier this year with the goal of showcasing the diversity and uniqueness of the Russian River AVA. A special committee led by Guy Davis of Davis Family Wines continues to explore and discuss what distinguishes each area.

<i>Virginie Boone is a freelance wine writer based in Sonoma County. She can be reached at virginieboone@yahoo.com and followed on Twitter @vboone.</i>