Decades ago, Hoxsey's Napa Valley Wine Company did plant vines on the hill, in some cases jackhammering holes in the rock and importing soil to get them started. They ended up producing less than a ton per acre. Of gewürztraminer. He pulled the vines out.
By Luke Sykora
But while the hills themselves don't grow grapes, those who work in this part of the valley are finding that they do have a significant role to play in shaping Napa Valley terroir. Hoxsey references the Venturi principle, which, loosely, states that a fluid will necessarily speed up as it passes through a constriction in a tube. As summer's inland heat draws cool air from San Pablo Bay up the valley, the marine air reaches a choke point between the Yountville Hills and the Mayacamas Range just to the west: the wind speeds up at the choke point, but cooler air and sometimes fog is trapped to the south of the hills. According to data from Hoxsey’s weather stations, between May and September 2012 his Rock Cairn Vineyard, tucked into a small notch in the Yountville Hills at the southern end of Oakville, accumulated 200 fewer degree days than his Lincoln Creek Vineyard less than a mile north, and on the leeward side of the knoll.
Christian Moueix's Dominus Estate lies just south of Rock Cairn, on the Yountville side of the choke point. In 2008, Dominus purchased a second piece of land just north of the Yountville-Oakville line and right across from Rock Cairn. Their weather data, too, indicates that the choke point does have an impact on growing conditions. Though the two vineyards are only a mile apart, during the hot summer months, the wind at the new Schmidt Ranch property, right near the choke point, is consistently higher, but that vineyard tends to be one or even two degrees warmer than Dominus to the south—where fog hangs a bit longer in the mornings in late summer.
Tod Mostero, Dominus's director of viticulture and winemaking, has already noticed some clear contrasts between the wines coming off the two vineyards—despite the fact that the soils are very similar: gravelly alluvial fan material eroded off the Mayacamas Range to the west. "The expression you get at Schmidt is really soft tannins, aromas that are more intense, sometimes floral, sometimes tropical—violet, iris, red and tropical fruits, as opposed to Dominus’s deeper chocolaty plum."
On the east side of the hill, the soil changes dramatically—instead of rocky alluvial fans, the hills’ volcanic rock gives way abruptly to the rich alluvial soil of the Napa Valley floor. This might not be ideal for cabernet, but David DeSante, who buys old-vine sauvignon blanc and semillon from Andrew Hoxsey’s vineyard just east of the hills, finds that the higher water-holding capacity of the soil helps these white grapes retain aromatic complexity and acidity.
Plus, while the wind speed on the west side of the hill tends to clear fog out earlier, here it piles up—sometimes hanging three hours later than at the vineyards on the other side of the hill. As DeSante says of Hoxsey's sauvignon planting, "If this were a catcher's mitt, he's sitting right where the ball lands." Comparing this fruit to the old-vine sauvignon blanc he gets from St. Helena, DeSante finds the two expressions completely different. Because Napa is a fairly open valley, he observes, the factor that limits sun exposure isn't usually exposition, but fog. "Here you get minerality, and it's much lower in alcohol. In St. Helena I battle to keep it under fourteen [percent alcohol]. Here it comes in at twelve, and that’s with a harvest that's three weeks later... Napa isn't all for cabernet, right?"