Geologic History of Washington State and Current Growing Conditions in the Yakima Valley 

Tremendous natural forces have created the conditions that allow us to make wine in Washington State today.  Fire, ice, and water all played an important part in the state’s geologic history.   

15 million years ago, oceanic and continental plates ground against each other, uplifted mountains, and uncovered geologic hotspots which spewed fresh molten lava.  These outflows, known today as “basalt”, covered large tracts of land east of the Cascade Mountains.  The heavy lava depressed the land, cooling more quickly at the edges than in the middle, much like a cake or pie that settles in the center as it cools.  This gives the Columbia Plateau the “bowl” shape that we see today.  The basin’s rim is as high as 2,700 feet above sea level, while the lowest point, at Wallula Gap, is only about 200 feet.   

Long after the lava had solidified into basalt, ice lobes pushed south from Canada and flowed down from the peaks of the Rockies and the Cascades.  The coast of Washington, as far south as present-day Olympia, was buried under an ice sheet more than 3,500 feet thick.  East of the Cascades, the ice reached the edge of the Columbia Plateau.   

The ice sheets blocked Montana’s Clark’s Fork, where the city of Missoula is today, creating a vast lake which geologists call Lake Missoula.  About 12,000 years ago, the ice dam broke and released a huge flood, known as the Spokane or Missoula Floods.  The flood waters charged over the rim of the Columbia Plateau near Spokane and toward the ocean, but were slowed by the narrow Wallula Gap.  Water backed up the Yakima River Valley as far as the site of the current day city of Yakima.  Water also backed up through the Walla Walla Valley to the Blue Mountains, and along the Snake River to it’s junction with the Salmon River.  This temporary lake, “Lake Lewis”, was about 800 feet deep at its deepest point.  As huge as it was, the lake only lasted a few hours as the dammed up floodwater drained through the gap and rushed on down the Columbia River Gorge.  The flood waters left behind vast alluvial deposits which make up the soil of the Columbia, Walla Walla, and Yakima valleys.  

Another important feature of Washington’s climate and growing conditions is the barrier formed by the Cascade mountain range.  As weather systems move in from the west, clouds drop their rain on the west side of the mountains, creating a “rain shadow” to the east.  The climate of the eastern half of the state is very different from the west, receiving less than 8 inches of rain a year in many areas.  Irrigation is made possible in Eastern Washington by three large rivers: the Columbia, the Snake, and the Yakima.   

The western part of the state has a maritime climate – cool summers and mild winters – and cool-climate grapes thrive here.  The eastern half of the state has a continental climate, with hot summers and cold winters.  This area would be too warm for growing high quality wine grapes if the hot days weren’t tempered by cool nights.   

Washington’s grape growing regions are on the same latitude as the Bordeaux and Burgundy regions in France (46^th/47^th parallels).  Because of their more northerly location, Washington vineyards have up to two more hours of daylight during the peak growing season than California’s grape growing regions do.  Grapes can also be left on the vine longer during the longer growing season in Washington.  Warm days and cool nights help to preserve acids in the grapes.  All of these factors give Washington’s wine grapes distinctive flavor and qualities.   

Washington is also susceptible to harsher freezes in the winter, which can damage or kill some grape varieties.  However, the cold winters also afford winemakers in Washington some advantages.  Short daylight hours and cold winters cause the vines to go into deep dormancy, which benefits the crop the following year.  Cold winters also reduce pests and diseases, particularly phylloxera, a tiny aphid which is native to North America.  It feeds on vine roots and kills the vine.  The only remedy for this disease is to graft vinifera vines onto native American rootstock.  Washington is the only major US wine region where vineyards have never been planted using grafted rootstock.  Individual cases of phylloxera have been seen in Washington, but no vineyards have had to be destroyed.  The cold winters and sandy soils seem to naturally prevent this pest.