the Missoula Floods, a series of geologic cataclysms that swept across Eastern Washington and down the Columbia Gorge at the end of the last ice age, between 12,000 and 15,000 years ago.
The massive floods, caused by periodic ruptures in the ice dam that created Montana’s Glacial Lake Missoula, inundated the Walla Walla Valley at least 35 times, experts say. At its highest point, the water elevation was about 1,200 feet—or the equivalent of 150 feet higher than the top of Walla Walla’s tallest building, the 12–story Marcus Whitman Hotel.
Each time those waters receded and the Walla Walla River rushed back into the Valley, the layers of sand and silt deposited by the floods were swept away and replaced with basalt pebbles, cobbles, and boulders washed downstream from the nearby Blue Mountains. These gravels accumulated over time, creating a 12-square mile alluvial fan of 3,770 acres where the river exits the Blue Mountains.
The chemistry of the alluvial fan soils that host the Cayuse vines is quite different than that of most other soils of the Walla Walla AVA. While sediments throughout much of the appellation are derived from Missoula Flood sediments that are rich in granite-derived silica, sodium, and potassium, Cayuse vineyard sediments are derived from Blue Mountains basalt, and loaded with iron, magnesium and calcium.
