Loess is an important component in most Washington wines. It’s an aeolian sediment formed by the accumulation of wind-blown silt, 20 percent or less clay and the rest equal parts sand and silt that are loosely cemented by calcium carbonate.
That blend adds to the complexity of our state’s wines. Many of Washington’s vineyards are located on gentle slopes or on valley floors. Almost all of these vineyards are planted in loess derived from sediments deposited by a series of glacial floods, known as the Missoula floods.
Underneath much of these vineyards is the other reason Washington is unique in the wine world. The bedrock is basalt alluvium or just plain basalt. At higher elevations the loess lies on top of basalt bedrock.
Because basalt is dark colored and dense, it keeps the average temperatures above average. And basalt keeps the root louse away.