Fire and Ice ~ Geology of the Yakima Valley AVA

The federal government designated the Yakima Valley AVA in early 1983; but the story of this appellation began much earlier … fifteen million years earlier. Imagine molten lava flowing from huge fissures in the Earth’s crust around what is now eastern Washington State and northern Oregon. Hundreds of these outflows eventually covered the area under thousands of feet of basalt. The massive weight of this blanket of rock actually depressed the Earth’s crust, forming the region now called the Columbia Basin.

At the western edge of this basin, the volcanoes of the ancient Cascade Mountains spewed out their own lava. Ash and volcanic sediments rained down into rivers and lakes to the east of the mountains, and these deposits became intermingled with those old Columbia Basin basalts. The combined material is called the Ellensburg Formation, and this special alluvial-volcanic mix can be seen across the Yakima Valley today. Meanwhile, the ancestral Columbia River that flowed through this region brought in pebbles and stones from outside the Columbia Basin, including granite and quartzite. These smooth, rounded rocks still lace the soils along the old channel of the river.

Volcanoes are only part of the story shaping this region. There’s also the astounding power of tectonic plates that meet along America’s northern Pacific coast. The Pacific plate grinds against the North American plate, and this pushing and shoving has produced everything from small tremors to large, destructive earthquakes. These big forces have actually compressed and wrinkled the Columbia Basin region into a series of east-west running ridges called the Yakima fold belt. Two of these ridges, now called the Horse Heaven Hills and the Rattlesnake Hills, form the boundaries of today’s Yakima Valley. The uplifting of those folds even re-routed the mighty Columbia River to its present ‘S’-shaped course through south-central Washington’s TriCities and down to a spot called the Wallula Gap, along the Oregon border, where it cuts back westward and flows to the sea.

All of this heat and commotion finally ended about 18,000 years ago, when sheets of polar ice advanced south to cover much of North America. The freeze was temporary (thank goodness), and when the climate warmed, the glaciers receded. But their retreat along what is now the Idaho-Montana border created an ice dam on the Clark Fork River. With its flow blocked, the river flooded a giant valley to create what geoscientists call Glacial Lake Missoula. Holding back that lake eventually proved too much for the ice dam. It broke and a huge wall of water roared across northern Idaho and eastern Washington. The surging flood soon constricted at the Wallula Gap, and its waters backed up into the Yakima River basin, depositing the sediment that it carried from Idaho and Montana. But the inundation didn’t end there. It seems these cataclysmic floods occurred dozens of times over the course of two millennia. You can still see what are called slackwater sediments across the Yakima Valley (up to 1,200 feet in elevation), and they still constitute the deeper layers of soil in the AVA.

Since the end of that last ice age, the flood sediments of the Yakima Valley have been topped by layers of a wind-deposited soil called loess, which varies in depth according to the orientation and steepness of the slopes. It can be very fine stuff, too—almost like talcum powder. Finally, these loess-based soils have been coated in places by ash deposits from the 1980 eruption of Mt. St. Helens, rising just to the west. It seems those volcanoes had the first and final say on the landscape.

So what does all this mean to the wines of the Yakima Valley? In a word: purity. The terrain of this region remains as open and clean as when cataclysmic floods swept through at the end of the ice age. The soil components are uniformly silt and sand with quartz and micas—and nearly devoid of organic matter or pests common to the rest of the wine world. Water drains through these soils with remarkable ease, and this forces vines to send their root systems deep. Such an unalloyed foundation also allows Yakima Valley to grow ungrafted vines. It’s a very traditional, but now very unusual, technique—and possible only because of our special geology. The end result is grapes and then wines that are completely true to their varietal character.

(Lesson content reference: “Folds, Floods, and Fine Wine,” by Kevin Pogue, pp.1-17 in The Geological Society of America’s Field Guide 15, 2009)

LESSON ONE TASTING – VARIETAL PURITY IN YAKIMA VALLEY WINES
The following Yakima Valley wines* showcase the varietal purity of wines produced by Yakima Valley grapes. 2009 Doyenne Signature Syrah, 2009 Chinook Cabernet Franc, 2011 Efeste “Sauvage” Sauvignon blanc, 2008 Wineglass Cellars Cabernet Sauvignon, 2010 Rolling Bay Cabernet Sauvignon, 2010 Smasne Viognier, and 2011 Thurston Wolfe Lemberger.

*Each of these wines is made with a minimum of 85% Yakima Valley fruit.