Fire and Ice ~ Geology of the Yakima Valley AVA
The federal government designated the Yakima Valley AVA in early 1983, but the story of thisappellation began much earlier … fifteen million years earlier. Imagine molten lava flowing from huge fissures in the Earth’s crust around what is now eastern Washington State and northern Oregon. Hundreds of these outflows eventually covered the area under thousands of feet of basalt. The massive weight of this blanket of rock actually depressed the Earth’s crust, forming the region now called the Columbia Basin.
At the western edge of this basin, the volcanoes of the ancient Cascade Mountains spewed out their own lava. Ash and volcanic sediments rained down into rivers and lakes to the east of the mountains, and these deposits became intermingled with those old Columbia Basin basalts. The combined material is called the Ellensburg Formation, and this special alluvial-volcanic mix can be seen across the Yakima Valley today. Meanwhile, the ancestral Columbia River that flowed through this region brought in pebbles and stones from outside the Columbia Basin, including granite and quartzite. These smooth, rounded rocks still lace the soils along the old channel of the river.
Volcanoes are only part of the story shaping this region. There’s also the astounding power of tectonic plates that meet along America’s northern Pacific coast. The Pacific plate grinds against the North American plate, and this pushing and shoving has produced everything from small tremors to large, destructive earthquakes. These big forces have actually compressed and wrinkled the Columbia Basin region into a series of east-west running ridges called the Yakima fold belt. Two of these ridges, now called the Horse Heaven