The Columbia Valley in eastern Washington gets less rainfall per year than Phoenix, Arizona.
True, but not by much. On average, the Columbia Valley in eastern Washington receives 7 inches of rain per year, Phoenix averages 8.03 inches. Western Washington, near Seattle and the Pacific Coast, receive 40 to 140 inches. Were it not for the Columbia, the Yakima, the Snake, and the Walla Walla rivers, eastern Washington would be extremely dry. The irrigation from those river valleys has transformed the vast expanse into hauntingly beautiful rangeland, wheat fields, orchards, and of course— vineyards.