Dating back some 17,000 years ago to the end of the last Ice Age, a series of violent geologic events affected the creation of the Columbia Valley's soils. As glaciers in the area were receding, an enormous ice dam formed in the valley between mountains in what is now Montana.
Melting waters were captured and held back behind the natural dam, creating a massive lake: the ancient Lake Missoula.
When the pressure behind the ice dam grew to be too much, the dam gave way, causing a torrent (some 500 cubic miles of water) to come blasting forth into the Columbia Valley in search of an outlet to the sea. The enormous wall of water tore through the valley, scouring everything in its path.
Finally, when the water reached a narrow, funneling gap along the Columbia River, the water backed up, creating a giant lake in the Yakima and Walla Walla Valleys, which then slowly drained, depositing rocks and fine-grained sediments on top of the basalt that was left behind 15 million years ago by enormous lava flows.
Scientists suspect that this scenario of dam creation, water build-up and dam bursting recurred over and over again during a half-dozen glacial advances and retreats.
Combine cataclysmic geologic activity with thousands of years of subsequent erosion and the shifting of loess caught up in countless windstorms and the result is a tremendous variation in soils throughout the Columbia Valley AVA.