During the last 30 years, Washington wineries have established the state as one of the world’s premier winemaking areas. Except for the Puget Sound area to the west of the Cascade Mountains, Washington has a high desert climate, and almost all Washington vineyards are irrigated. The desert environment, in combination with sandy soils and cold winters that tend to kill grapevines every six to 10 years, has proven largely resistant to phylloxera; Washington’s vines do not need to be grafted onto phylloxera-resistant rootstock. Ninety-nine percent of Washington’s winegrapes are grown on the east side of the Cascade Mountains, and eastern Washington contains seven of eight of Washington’s AVAs. All of eastern Washington’s AVAs, except for the Columbia Gorge AVA, are located within the Columbia Valley mega-AVA. There are more than 700 Washington wineries specializing in a wide number of varieties including Syrah, Cabernet Sauvignon, Merlot and Chardonnay.