The Uco Valley (Valle de Uco) is a key winegrowing region of Mendoza, Argentina. An hour's drive south from the city of Mendoza, it is home to some of the region's most famous wines. Nestled against the foothills of the Andes, the Uco Valley is vast, spanning three departments and covering an area 45 miles/72 kilometers long from north to south and 15 miles/24 kilometers wide.
The valley is crossed by the Tunuyán river which gives its name to the easternmost department, along with the Tupungato department to the north and the San Carlos department to the south. Soils here vary widely, though shallow sandy loam is typical in the Tupungato department, and limestone can be found in the Gualtallary district which is highly sought after for white wine production. Tunuyán is typified by rockier ground with very thin topsoil that seems to favor bright acidity and tart fruit notes in its wines. Heavier soils are found in San Carlos, resulting in plush textures and dark fruit flavors in the wines from this department.
In terms of elevation, the Uco spans a wide zone from 900-1,500 meters (2,950-4,900 feet) in elevation, higher and cooler than any other region in Mendoza attempting to grow red grapes.
The highest slopes are in Tupungato to the northwest of the valley, and slopes gently towards the lower elevations which are found to the south in San Carlos.
While the vineyards might seem too close to the equator for quality viticulture, altitude is key to increasing the intensity of sunlight while cooling the average daytime temperature of the vineyards so that grapes can properly ripen between seasonal threats of frost. Consequently, red grapes grown at high altitudes tend to have thicker skins and deeper levels of pigmentation, which generally translate into greater concentrations of tannins, aromas and flavors in the finished wine.
Malbec accounts for only one-third of vineyards in the Uco Valley, mainly because of recent attempts to diversify plantings of grapes in Argentina's coolest vineyard sites. International varietals such as Cabernet Franc, Cabernet Sauvignon, Syrah, Merlot and Pinot Noir bring the red grape total up to 80%, while delicate white grapes like Chardonnay and Sauvignon Blanc, unusual in the more historic regions of Mendoza, have found a natural home in the highest and coolest sites.