Driving around the vineyards in the Snake River Valley makes a person wonder – how did all these weird shapes in the landscape occur? There are shining white hills of chalk, dark columns of basalt, and beds of volcanic cinder in shades of black, red, and orange. The history of the Snake River Valley is one of volcanoes and water shaping a bizarre and beautiful landscape.
The Snake River Valley is a rift, bounded on the north and south by fault zones. The continental crust is very thin here, due in part to the passing of the Yellowstone Hotspot immediately to the south. The thin crust allowed magma to well up and volcanoes to erupt periodically during the region’s geologic past. Beginning around 5 million years ago, a basin formed as the crust sagged and was filled by a series of wetlands and lakes, the largest now known as Ancient Lake Idaho. It seems appropriate, then, that the highest level reached by Lake Idaho, around 3400 feet elevation, forms the boundary of the Snake River Valley American Viticultural Area (AVA).
Volcanic activity continued during this time; the cinders that inspire our name were erupted under the waters of Lake Idaho. Over the millennia, Lake Idaho drained out though Hell’s Canyon, leaving behind a valley filled with sediments. The power of water continued to influence the region. The Snake and Boise Rivers both carved out their courses in the valley, leaving behind a series of terraces and slopes separating their channels. Towards the end of the last ice age, the Great Salt Lake was 1000 feet deep and many times its current size. Called Lake Bonneville, it broke through Red Rock Pass in southeastern Idaho close to the town of Preston (where Napoleon Dynamite was filmed), and drained in an cataclysmic flood through the Snake River Canyon, in the process both deepening the canyon of the Snake River and covering a large portion of the Snake River Valley in sediment.
The lakes, streams, and rivers of the region’s geologic past left behind thick deposits of sediment covering the floor of the valley, mingled in places with volcanic cinder and lava flows. These sediments and rocks have been eroded by more recent rivers and the Bonneville flood, helping create the terroir that is now home to the region’s vineyards.