Unlocking the Secrets of Terroir

There’s a kind of eerie stillness in the wine country this week--the calm before the storm. The vines themselves seem to be holding their breath as the grapes edge toward maturity.

Vintage 2002 hangs in the balance. And there are few places where the excitement is more palpable than the Stags Leap District of southeast Napa Valley, where this gentle summer promises to yield particularly expressive Cabernet Sauvignons.

There are few viticultural environments as distinctive as the Stags Leap District. Its remarkable interface of geography and climate brings grapes to a fine maturity, yielding wines that are rich and powerful yet clearly defined and often elegant.

Stags Leap District took millions of years and countless random events to form. Back in the old days--the really old days--terra firma was more like terra soupa. The coastal margin of what humans would later call California was as much liquid as solid.

Far beneath the mud, land masses crashed together in cataclysmic slow motion, opening volcanic seams that spewed melted rock and ash. Gradually the ocean waves created mountain ranges with trough-like valleys between them, and the Napa Valley was one of the troughs in the new coastal mountains.

As the two ranges defining the valley continued to rise, the atmosphere was simultaneously developing, forming a planetary envelope in which great forces gradually came into the relative balance we call climate. Rain and floods, and marine incursions, took over from the volcanoes.

The process isn’t over by any means, as Robert Louis Stevenson pointed out barely more than a century ago: “Here, indeed, all is new, nature as well as towns. The very hills of California have an unfinished look; the rains and streams have not yet carved them to their perfect shape.”

Whether it ever achieves that “perfect shape,” the Napa Valley landscape does yield singular wines--it has been mapped according to subtle but consistent characteristics of wines from different areas within the valley. The Stags Leap District viticultural area was among the first to be identified as producing a recognizable variation of Napa Valley character, particularly in Cabernet Sauvignon.

That character--a remarkable combination of power and elegance, softness and structure--became apparent in the 1970s in the Cabernet of producers such as Stag’s Leap Wine Cellars, Clos du Val and Joseph Heitz (in his Fay Vineyard bottling). It can now also be tasted in wines from Shafer, Chimney Rock, Stags’ Leap Winery and Steltzner, among others.

The appellation embraces a relatively small area about three miles long and one mile wide, east of Yountville between the Napa River and the Vaca Mountains. Unlike the west-side appellations--such as Yountville, Oakville and Rutherford, which are defined more by climate than landscape--Stags Leap has a clear physical identity. There’s a sense of entering it and leaving it, and, when inside it, of looking out at the rest of the valley.

At its southern end, the vineyards bask on open slopes inclined toward the afternoon sun. Farther north, this open bench land rises and narrows into broken, convoluted terrain. Corridors through the hills accelerate air movements, extending the southern valley’s natural air-conditioning and tempering the hot days. And the Stags Leap geological formation acts as a giant convection unit that pulls cool air from the bay to a degree not felt in the rest of the valley.

The heat and the marine influence come into extraordinary balance in a sort of craggy amphitheater at the heart of the district. It’s a valley-within-the-valley where vineyards owned by Stag’s Leap Wine Cellars, Joseph Phelps, Shafer Vineyards and Stags’ Leap Winery, among others, are set off from the main valley by broken ridges in which Steltzner Vineyards and Pine Ridge Winery also have their own little vine-filled enclaves.

“If there was no other influence than the water temperature in the bay, we’d probably be growing Merlot here,” observes Chimney Rock winemaker Doug Fletcher. “Vineyards on the other side, in Yountville and Oakville, are some of the better Merlot properties around. But it’s warm enough in Stags Leap District for good Cabernet. And the only explanation for that in my mind is the geological formations that make Stags Leap. Those big rock outcroppings get the late afternoon sun, collect the heat and radiate it out at night.”

Those outcroppings are also responsible for the second broad element of the Stags Leap terroir. The soils are primarily volcanic material that came straight down from the escarpment.

“It’s all about volcanic bedrock,” says Robert Brittan, longtime winemaker at Stags’ Leap Winery. “On the other side of the valley you’re looking at some very different bedrocks and a lot more difference in the composition of soils. You don’t see that variability in Stags Leap. And the volcanic material drives not only the soil that we grow the grapes in, but the weather, because it’s the heating of those rocks which brings cooler air up from the bay. Not only that, all our barrels are in a cave dug out of that same stuff, and that’s where the wines mature. So everything about our wine goes back to that volcanic bedrock.”

Volcanic soils typically yield bright, structured wines with firm tannins and vibrant, often spicy fruit character. A sympathetic climate can amplify those qualities to a majestic level, and the summer of ’02 has been sympathetic to the point of fawning.

Ultimately, of course, it is human intervention that turns a landscape into a vinescape. Selection of plant material, methods of cultivation and, perhaps most important, timing of the harvest have everything to do with how the land is expressed in wines.

Yet the essence of that luscious Cabernet in your glass is essentially water filtered through volcanic soil and transferred into fruit that ripened slowly and fully in the stony place called Stags Leap. And something else, too. Aside from the miraculous phenomenon of ripe fruit from bare rock, there’s an ethereal savor of time, millions of years in every sip.